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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/2298-0.txt b/2298-0.txt new file mode 100644 index 0000000..23377fb --- /dev/null +++ b/2298-0.txt @@ -0,0 +1,9256 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 2298 *** + + + + +GREAT ASTRONOMERS + +by + +SIR ROBERT S. BALL D.Sc. LL.D. F.R.S. + +Lowndean Professor of Astronomy and Geometry in the +University of Cambridge + +Author of "In Starry Realms" "In the High Heavens" etc. + +WITH NUMEROUS ILLUSTRATIONS + + +[PLATE: GREENWICH OBSERVATORY.] + + + + +PREFACE. + + +It has been my object in these pages to present the life of each +astronomer in such detail as to enable the reader to realise in +some degree the man's character and surroundings; and I have +endeavoured to indicate as clearly as circumstances would permit +the main features of the discoveries by which he has become known. + +There are many types of astronomers--from the stargazer who merely +watches the heavens, to the abstract mathematician who merely +works at his desk; it has, consequently, been necessary in the +case of some lives to adopt a very different treatment from that +which seemed suitable for others. + +While the work was in progress, some of the sketches appeared in +"Good Words." The chapter on Brinkley has been chiefly derived from +an article on the "History of Dunsink Observatory," which was +published on the occasion of the tercentenary celebration of the +University of Dublin in 1892, and the life of Sir William Rowan +Hamilton is taken, with a few alterations and omissions, from an +article contributed to the "Quarterly Review" on Graves' life of +the great mathematician. The remaining chapters now appear for +the first time. For many of the facts contained in the sketch of +the late Professor Adams, I am indebted to the obituary notice +written by my friend Dr. J. W. L. Glaisher, for the Royal Astronomical +Society; while with regard to the late Sir George Airy, I have a +similar acknowledgment to make to Professor H. H. Turner. To my +friend Dr. Arthur A. Rambaut I owe my hearty thanks for his +kindness in aiding me in the revision of the work. + +R.S.B. +The Observatory, Cambridge. +October, 1895 + + + + +CONTENTS. + + +INTRODUCTION. + +PTOLEMY. + +COPERNICUS. + +TYCHO BRAHE. + +GALILEO. + +KEPLER. + +ISAAC NEWTON. + +FLAMSTEED. + +HALLEY. + +BRADLEY. + +WILLIAM HERSCHEL. + +LAPLACE. + +BRINKLEY. + +JOHN HERSCHEL. + +THE EARL OF ROSSE. + +AIRY. + +HAMILTON. + +LE VERRIER. + +ADAMS. + + + + +LIST OF ILLUSTRATIONS. + +THE OBSERVATORY, GREENWICH. + +PTOLEMY. + +PTOLEMY'S PLANETARY SCHEME. + +PTOLEMY'S THEORY OF THE MOVEMENT OF MARS. + +THORN, FROM AN OLD PRINT. + +COPERNICUS. + +FRAUENBURG, FROM AN OLD PRINT. + +EXPLANATION OF PLANETARY MOVEMENTS. + +TYCHO BRAHE. + +TYCHO'S CROSS STAFF. + +TYCHO'S "NEW STAR" SEXTANT OF 1572. + +TYCHO'S TRIGONIC SEXTANT. + +TYCHO'S ASTRONOMIC SEXTANT. + +TYCHO'S EQUATORIAL ARMILLARY. + +THE GREAT AUGSBURG QUADRANT. + +TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577. + +URANIBORG AND ITS GROUNDS. + +GROUND-PLAN OF THE OBSERVATORY. + +THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN. + +EFFIGY ON TYCHO'S TOMB AT PRAGUE. + By Permission of Messrs. A. & C. Black. + +TYCHO'S MURAL QUADRANT, URANIBORG. + +GALILEO'S PENDULUM. + +GALILEO. + +THE VILLA ARCETRI. + +FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO. + +CREST OF GALILEO'S FAMILY. + +KEPLER'S SYSTEM OF REGULAR SOLIDS. + +KEPLER. + +SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM. + +THE COMMEMORATION OF THE RUDOLPHINE TABLES. + +WOOLSTHORPE MANOR. + +TRINITY COLLEGE, CAMBRIDGE. + +DIAGRAM OF A SUNBEAM. + +ISAAC NEWTON. + +SIR ISAAC NEWTON'S LITTLE REFLECTOR. + +SIR ISAAC NEWTON'S SUN-DIAL. + +SIR ISAAC NEWTON'S TELESCOPE. + +SIR ISAAC NEWTON'S ASTROLABE. + +SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY. + +FLAMSTEED'S HOUSE. + +FLAMSTEED. + +HALLEY. + +GREENWICH OBSERVATORY IN HALLEY'S TIME. + +7, NEW KING STREET, BATH. + From a Photograph by John Poole, Bath. + +WILLIAM HERSCHEL. + +CAROLINE HERSCHEL. + +STREET VIEW, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +GARDEN VIEW, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +OBSERVATORY, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +LAPLACE. + +THE OBSERVATORY, DUNSINK. + From a Photograph by W. Lawrence, Dublin. + +ASTRONOMETER MADE BY SIR JOHN HERSCHEL. + +SIR JOHN HERSCHEL. + +NEBULA IN SOUTHERN HEMISPHERE. + +THE CLUSTER IN THE CENTAUR. + +OBSERVATORY AT FELDHAUSEN. + +GRANITE COLUMN AT FELDHAUSEN. + +THE EARL OF ROSSE. + +BIRR CASTLE. + From a Photograph by W. Lawrence, Dublin. + +THE MALL, PARSONSTOWN. + From a Photograph by W. Lawrence, Dublin. + +LORD ROSSE'S TELESCOPE. + From a Photograph by W. Lawrence, Dublin. + +ROMAN CATHOLIC CHURCH, PARSONSTOWN. + From a Photograph by W. Lawrence, Dublin. + +AIRY. + From a Photograph by E.P. Adams, Greenwich. + +HAMILTON. + +ADAMS. + +THE OBSERVATORY, CAMBRIDGE. + + + + +INTRODUCTION. + + +Of all the natural sciences there is not one which offers such +sublime objects to the attention of the inquirer as does the science +of astronomy. From the earliest ages the study of the stars has +exercised the same fascination as it possesses at the present day. +Among the most primitive peoples, the movements of the sun, the moon, +and the stars commanded attention from their supposed influence on +human affairs. + +The practical utilities of astronomy were also obvious in primeval +times. Maxims of extreme antiquity show how the avocations of the +husbandman are to be guided by the movements of the heavenly bodies. +The positions of the stars indicated the time to plough, and the time +to sow. To the mariner who was seeking a way across the trackless +ocean, the heavenly bodies offered the only reliable marks by which +his path could be guided. There was, accordingly, a stimulus both +from intellectual curiosity and from practical necessity to follow +the movements of the stars. Thus began a search for the causes of +the ever-varying phenomena which the heavens display. + +Many of the earliest discoveries are indeed prehistoric. The great +diurnal movement of the heavens, and the annual revolution of the +sun, seem to have been known in times far more ancient than those to +which any human monuments can be referred. The acuteness of the +early observers enabled them to single out the more important of the +wanderers which we now call planets. They saw that the star-like +objects, Jupiter, Saturn, and Mars, with the more conspicuous Venus, +constituted a class of bodies wholly distinct from the fixed stars +among which their movements lay, and to which they bear such a +superficial resemblance. But the penetration of the early +astronomers went even further, for they recognized that Mercury also +belongs to the same group, though this particular object is seen so +rarely. It would seem that eclipses and other phenomena were +observed at Babylon from a very remote period, while the most ancient +records of celestial observations that we possess are to be found in +the Chinese annals. + +The study of astronomy, in the sense in which we understand the word, +may be said to have commenced under the reign of the Ptolemies at +Alexandria. The most famous name in the science of this period is +that of Hipparchus who lived and worked at Rhodes about the year +160BC. It was his splendid investigations that first wrought the +observed facts into a coherent branch of knowledge. He recognized +the primary obligation which lies on the student of the heavens to +compile as complete an inventory as possible of the objects which are +there to be found. Hipparchus accordingly commenced by undertaking, +on a small scale, a task exactly similar to that on which modern +astronomers, with all available appliances of meridian circles, and +photographic telescopes, are constantly engaged at the present day. +He compiled a catalogue of the principal fixed stars, which is of +special value to astronomers, as being the earliest work of its kind +which has been handed down. He also studied the movements of the sun +and the moon, and framed theories to account for the incessant +changes which he saw in progress. He found a much more difficult +problem in his attempt to interpret satisfactorily the complicated +movements of the planets. With the view of constructing a theory +which should give some coherent account of the subject, he made many +observations of the places of these wandering stars. How great were +the advances which Hipparchus accomplished may be appreciated if we +reflect that, as a preliminary task to his more purely astronomical +labours, he had to invent that branch of mathematical science by +which alone the problems he proposed could be solved. It was for +this purpose that he devised the indispensable method of calculation +which we now know so well as trigonometry. Without the aid rendered +by this beautiful art it would have been impossible for any really +important advance in astronomical calculation to have been effected. + +But the discovery which shows, beyond all others, that Hipparchus +possessed one of the master-minds of all time was the detection of +that remarkable celestial movement known as the precession of the +equinoxes. The inquiry which conducted to this discovery involved a +most profound investigation, especially when it is remembered that in +the days of Hipparchus the means of observation of the heavenly +bodies were only of the rudest description, and the available +observations of earlier dates were extremely scanty. We can but look +with astonishment on the genius of the man who, in spite of such +difficulties, was able to detect such a phenomenon as the precession, +and to exhibit its actual magnitude. I shall endeavour to explain +the nature of this singular celestial movement, for it may be said to +offer the first instance in the history of science in which we find +that combination of accurate observation with skilful interpretation, +of which, in the subsequent development of astronomy, we have so many +splendid examples. + +The word equinox implies the condition that the night is equal to the +day. To a resident on the equator the night is no doubt equal to the +day at all times in the year, but to one who lives on any other part +of the earth, in either hemisphere, the night and the day are not +generally equal. There is, however, one occasion in spring, and +another in autumn, on which the day and the night are each twelve +hours at all places on the earth. When the night and day are equal +in spring, the point which the sun occupies on the heavens is termed +the vernal equinox. There is similarly another point in which the +sun is situated at the time of the autumnal equinox. In any +investigation of the celestial movements the positions of these two +equinoxes on the heavens are of primary importance, and Hipparchus, +with the instinct of genius, perceived their significance, and +commenced to study them. It will be understood that we can always +define the position of a point on the sky with reference to the +surrounding stars. No doubt we do not see the stars near the sun +when the sun is shining, but they are there nevertheless. The +ingenuity of Hipparchus enabled him to determine the positions of +each of the two equinoxes relatively to the stars which lie in its +immediate vicinity. After examination of the celestial places of +these points at different periods, he was led to the conclusion that +each equinox was moving relatively to the stars, though that movement +was so slow that twenty five thousand years would necessarily elapse +before a complete circuit of the heavens was accomplished. Hipparchus +traced out this phenomenon, and established it on an impregnable +basis, so that all astronomers have ever since recognised the +precession of the equinoxes as one of the fundamental facts of +astronomy. Not until nearly two thousand years after Hipparchus had +made this splendid discovery was the explanation of its cause given +by Newton. + +From the days of Hipparchus down to the present hour the science of +astronomy has steadily grown. One great observer after another has +appeared from time to time, to reveal some new phenomenon with regard +to the celestial bodies or their movements, while from time to time +one commanding intellect after another has arisen to explain the true +import of the facts of observations. The history of astronomy thus +becomes inseparable from the history of the great men to whose +labours its development is due. + +In the ensuing chapters we have endeavoured to sketch the lives and +the work of the great philosophers, by whose labours the science of +astronomy has been created. We shall commence with Ptolemy, who, +after the foundations of the science had been laid by Hipparchus, +gave to astronomy the form in which it was taught throughout the +Middle Ages. We shall next see the mighty revolution in our +conceptions of the universe which are associated with the name of +Copernicus. We then pass to those periods illumined by the genius of +Galileo and Newton, and afterwards we shall trace the careers of +other more recent discoverers, by whose industry and genius the +boundaries of human knowledge have been so greatly extended. Our +history will be brought down late enough to include some of the +illustrious astronomers who laboured in the generation which has just +passed away. + + + + +PTOLEMY. + + +[PLATE: PTOLEMY.] + +The career of the famous man whose name stands at the head of this +chapter is one of the most remarkable in the history of human +learning. There may have been other discoverers who have done more +for science than ever Ptolemy accomplished, but there never has been +any other discoverer whose authority on the subject of the movements +of the heavenly bodies has held sway over the minds of men for so +long a period as the fourteen centuries during which his opinions +reigned supreme. The doctrines he laid down in his famous book, "The +Almagest," prevailed throughout those ages. No substantial addition +was made in all that time to the undoubted truths which this work +contained. No important correction was made of the serious errors +with which Ptolemy's theories were contaminated. The authority of +Ptolemy as to all things in the heavens, and as to a good many things +on the earth (for the same illustrious man was also a diligent +geographer), was invariably final. + +Though every child may now know more of the actual truths of the +celestial motions than ever Ptolemy knew, yet the fact that his work +exercised such an astonishing effect on the human intellect for some +sixty generations, shows that it must have been an extraordinary +production. We must look into the career of this wonderful man to +discover wherein lay the secret of that marvellous success which made +him the unchallenged instructor of the human race for such a +protracted period. + +Unfortunately, we know very little as to the personal history of +Ptolemy. He was a native of Egypt, and though it has been sometimes +conjectured that he belonged to the royal families of the same name, +yet there is nothing to support such a belief. The name, Ptolemy, +appears to have been a common one in Egypt in those days. The time +at which he lived is fixed by the fact that his first recorded +observation was made in 127 AD, and his last in 151 AD. When we add +that he seems to have lived in or near Alexandria, or to use his own +words, "on the parallel of Alexandria," we have said everything that +can be said so far as his individuality is concerned. + +Ptolemy is, without doubt, the greatest figure in ancient astronomy. +He gathered up the wisdom of the philosophers who had preceded him. +He incorporated this with the results of his own observations, and +illumined it with his theories. His speculations, even when they +were, as we now know, quite erroneous, had such an astonishing +verisimilitude to the actual facts of nature that they commanded +universal assent. Even in these modern days we not unfrequently find +lovers of paradox who maintain that Ptolemy's doctrines not only seem +true, but actually are true. + +In the absence of any accurate knowledge of the science of mechanics, +philosophers in early times were forced to fall back on certain +principles of more or less validity, which they derived from their +imagination as to what the natural fitness of things ought to be. +There was no geometrical figure so simple and so symmetrical as a +circle, and as it was apparent that the heavenly bodies pursued +tracks which were not straight lines, the conclusion obviously +followed that their movements ought to be circular. There was no +argument in favour of this notion, other than the merely imaginary +reflection that circular movement, and circular movement alone, was +"perfect," whatever "perfect" may have meant. It was further +believed to be impossible that the heavenly bodies could have any +other movements save those which were perfect. Assuming this, it +followed, in Ptolemy's opinion, and in that of those who came after +him for fourteen centuries, that all the tracks of the heavenly +bodies were in some way or other to be reduced to circles. + +Ptolemy succeeded in devising a scheme by which the apparent changes +that take place in the heavens could, so far as he knew them, be +explained by certain combinations of circular movement. This seemed +to reconcile so completely the scheme of things celestial with the +geometrical instincts which pointed to the circle as the type of +perfect movement, that we can hardly wonder Ptolemy's theory met with +the astonishing success that attended it. We shall, therefore, set +forth with sufficient detail the various steps of this famous +doctrine. + +Ptolemy commences with laying down the undoubted truth that the shape +of the earth is globular. The proofs which he gives of this +fundamental fact are quite satisfactory; they are indeed the same +proofs as we give today. There is, first of all, the well-known +circumstance of which our books on geography remind us, that when an +object is viewed at a distance across the sea, the lower part of the +object appears cut off by the interposing curved mass of water. + +The sagacity of Ptolemy enabled him to adduce another argument, +which, though not quite so obvious as that just mentioned, +demonstrates the curvature of the earth in a very impressive manner +to anyone who will take the trouble to understand it. Ptolemy +mentions that travellers who went to the south reported, that, as +they did so, the appearance of the heavens at night underwent a +gradual change. Stars that they were familiar with in the northern +skies gradually sank lower in the heavens. The constellation of the +Great Bear, which in our skies never sets during its revolution round +the pole, did set and rise when a sufficient southern latitude had +been attained. On the other hand, constellations new to the +inhabitants of northern climes were seen to rise above the southern +horizon. These circumstances would be quite incompatible with the +supposition that the earth was a flat surface. Had this been so, a +little reflection will show that no such changes in the apparent +movements of the stars would be the consequence of a voyage to the +south. Ptolemy set forth with much insight the significance of this +reasoning, and even now, with the resources of modern discoveries to +help us, we can hardly improve upon his arguments. + +Ptolemy, like a true philosopher disclosing a new truth to the world, +illustrated and enforced his subject by a variety of happy +demonstrations. I must add one of them, not only on account of its +striking nature, but also because it exemplifies Ptolemy's +acuteness. If the earth were flat, said this ingenious reasoner, +sunset must necessarily take place at the same instant, no matter in +what country the observer may happen to be placed. Ptolemy, however, +proved that the time of sunset did vary greatly as the observer's +longitude was altered. To us, of course, this is quite obvious; +everybody knows that the hour of sunset may have been reached in +Great Britain while it is still noon on the western coast of +America. Ptolemy had, however, few of those sources of knowledge +which are now accessible. How was he to show that the sun actually +did set earlier at Alexandria than it would in a city which lay a +hundred miles to the west? There was no telegraph wire by which +astronomers at the two Places could communicate. There was no +chronometer or watch which could be transported from place to place; +there was not any other reliable contrivance for the keeping of +time. Ptolemy's ingenuity, however, pointed out a thoroughly +satisfactory method by which the times of sunset at two places could +be compared. He was acquainted with the fact, which must indeed have +been known from the very earliest times, that the illumination of the +moon is derived entirely from the sun. He knew that an eclipse of +the moon was due to the interposition of the earth which cuts off the +light of the sun. It was, therefore, plain that an eclipse of the +moon must be a phenomenon which would begin at the same instant from +whatever part of the earth the moon could be seen at the time. +Ptolemy, therefore, brought together from various quarters the local +times at which different observers had recorded the beginning of a +lunar eclipse. He found that the observers to the west made the time +earlier and earlier the further away their stations were from +Alexandria. On the other hand, the eastern observers set down the +hour as later than that at which the phenomenon appeared at +Alexandria. As these observers all recorded something which indeed +appeared to them simultaneously, the only interpretation was, that +the more easterly a place the later its time. Suppose there were a +number of observers along a parallel of latitude, and each noted the +hour of sunset to be six o'clock, then, since the eastern times are +earlier than western times, 6 p.m. at one station A will correspond +to 5 p.m. at a station B sufficiently to the west. If, therefore, +it is sunset to the observer at A, the hour of sunset will not yet be +reached for the observer at B. This proves conclusively that the +time of sunset is not the same all over the earth. We have, however, +already seen that the apparent time of sunset would be the same from +all stations if the earth were flat. When Ptolemy, therefore, +demonstrated that the time of sunset was not the same at various +places, he showed conclusively that the earth was not flat. + +As the same arguments applied to all parts of the earth where Ptolemy +had either been himself, or from which he could gain the necessary +information, it followed that the earth, instead of being the flat +plain, girdled with an illimitable ocean, as was generally supposed, +must be in reality globular. This led at once to a startling +consequence. It was obvious that there could be no supports of any +kind by which this globe was sustained; it therefore followed that +the mighty object must be simply poised in space. This is indeed an +astonishing doctrine to anyone who relies on what merely seems the +evidence of the senses, without giving to that evidence its due +intellectual interpretation. According to our ordinary experience, +the very idea of an object poised without support in space, appears +preposterous. Would it not fall? we are immediately asked. Yes, +doubtless it could not remain poised in any way in which we try the +experiment. We must, however, observe that there are no such ideas +as upwards or downwards in relation to open space. To say that a +body falls downwards, merely means that it tries to fall as nearly as +possible towards the centre of the earth. There is no one direction +along which a body will tend to move in space, in preference to any +other. This may be illustrated by the fact that a stone let fall at +New Zealand will, in its approach towards the earth's centre, be +actually moving upwards as far as any locality in our hemisphere is +concerned. Why, then, argued Ptolemy, may not the earth remain +poised in space, for as all directions are equally upward or equally +downward, there seems no reason why the earth should require any +support? By this reasoning he arrives at the fundamental conclusion +that the earth is a globular body freely lying in space, and +surrounded above, below, and on all sides by the glittering stars of +heaven. + +The perception of this sublime truth marks a notable epoch in the +history of the gradual development of the human intellect. No doubt, +other philosophers, in groping after knowledge, may have set forth +certain assertions that are more or less equivalent to this +fundamental truth. It is to Ptolemy we must give credit, however, +not only for announcing this doctrine, but for demonstrating it by +clear and logical argument. We cannot easily project our minds back +to the conception of an intellectual state in which this truth was +unfamiliar. It may, however, be well imagined that, to one who +thought the earth was a flat plain of indefinite extent, it would be +nothing less than an intellectual convulsion for him to be forced to +believe that he stood upon a spherical earth, forming merely a +particle relatively to the immense sphere of the heavens. + +What Ptolemy saw in the movements of the stars led him to the +conclusion that they were bright points attached to the inside of a +tremendous globe. The movements of this globe which carried the +stars were only compatible with the supposition that the earth +occupied its centre. The imperceptible effect produced by a change +in the locality of the observer on the apparent brightness of the +stars made it plain that the dimensions of the terrestrial globe must +be quite insignificant in comparison with those of the celestial +sphere. The earth might, in fact, be regarded as a grain of sand +while the stars lay upon a globe many yards in diameter. + +So tremendous was the revolution in human knowledge implied by this +discovery, that we can well imagine how Ptolemy, dazzled as it were +by the fame which had so justly accrued to him, failed to make one +further step. Had he made that step, it would have emancipated the +human intellect from the bondage of fourteen centuries of servitude +to a wholly monstrous notion of this earth's importance in the scheme +of the heavens. The obvious fact that the sun, the moon, and the +stars rose day by day, moved across the sky in a glorious +never-ending procession, and duly set when their appointed courses +had been run, demanded some explanation. The circumstance that the +fixed stars preserved their mutual distances from year to year, and +from age to age, appeared to Ptolemy to prove that the sphere which +contained those stars, and on whose surface they were believed by him +to be fixed, revolved completely around the earth once every day. He +would thus account for all the phenomena of rising and setting +consistently with the supposition that our globe was stationary. +Probably this supposition must have appeared monstrous, even to +Ptolemy. He knew that the earth was a gigantic object, but, large as +it may have been, he knew that it was only a particle in comparison +with the celestial sphere, yet he apparently believed, and certainly +succeeded in persuading other men to believe, that the celestial +sphere did actually perform these movements. + +Ptolemy was an excellent geometer. He knew that the rising and the +setting of the sun, the moon, and the myriad stars, could have been +accounted for in a different way. If the earth turned round +uniformly once a day while poised at the centre of the sphere of the +heavens, all the phenomena of rising and setting could be completely +explained. This is, indeed, obvious after a moment's reflection. +Consider yourself to be standing on the earth at the centre of the +heavens. There are stars over your head, and half the contents of +the heavens are visible, while the other half are below your +horizon. As the earth turns round, the stars over your head will +change, and unless it should happen that you have taken up your +position at either of the poles, new stars will pass into your view, +and others will disappear, for at no time can you have more than half +of the whole sphere visible. The observer on the earth would, +therefore, say that some stars were rising, and that some stars were +setting. We have, therefore, two totally distinct methods, each of +which would completely explain all the observed facts of the diurnal +movement. One of these suppositions requires that the celestial +sphere, bearing with it the stars and other celestial bodies, turns +uniformly around an invisible axis, while the earth remains +stationary at the centre. The other supposition would be, that it is +the stupendous celestial sphere which remains stationary, while the +earth at the centre rotates about the same axis as the celestial +sphere did before, but in an opposite direction, and with a uniform +velocity which would enable it to complete one turn in twenty-four +hours. Ptolemy was mathematician enough to know that either of these +suppositions would suffice for the explanation of the observed +facts. Indeed, the phenomena of the movements of the stars, so far +as he could observe them, could not be called upon to pronounce which +of these views was true, and which was false. + +Ptolemy had, therefore, to resort for guidance to indirect lines of +reasoning. One of these suppositions must be true, and yet it +appeared that the adoption of either was accompanied by a great +difficulty. It is one of his chief merits to have demonstrated that +the celestial sphere was so stupendous that the earth itself was +absolutely insignificant in comparison therewith. If, then, this +stupendous sphere rotated once in twenty-four hours, the speed with +which the movement of some of the stars must be executed would be so +portentous as to seem well-nigh impossible. It would, therefore, +seem much simpler on this ground to adopt the other alternative, and +to suppose the diurnal movements were due to the rotation of the +earth. Here Ptolemy saw, or at all events fancied he saw, objections +of the weightiest description. The evidence of the senses appeared +directly to controvert the supposition that this earth is anything +but stationary. Ptolemy might, perhaps, have dismissed this +objection on the ground that the testimony of the senses on such a +matter should be entirely subordinated to the interpretation which +our intelligence would place upon the facts to which the senses +deposed. Another objection, however, appeared to him to possess the +gravest moment. It was argued that if the earth were rotating, there +is nothing to make the air participate in this motion, mankind would +therefore be swept from the earth by the furious blasts which would +arise from the movement of the earth through an atmosphere at rest. +Even if we could imagine that the air were carried round with the +earth, the same would not apply, so thought Ptolemy, to any object +suspended in the air. So long as a bird was perched on a tree, he +might very well be carried onward by the moving earth, but the moment +he took wing, the ground would slip from under him at a frightful +pace, so that when he dropped down again he would find himself at a +distance perhaps ten times as great as that which a carrier-pigeon or +a swallow could have traversed in the same time. Some vague delusion +of this description seems even still to crop up occasionally. I +remember hearing of a proposition for balloon travelling of a very +remarkable kind. The voyager who wanted to reach any other place in +the same latitude was simply to ascend in a balloon, and wait there +till the rotation of the earth conveyed the locality which happened +to be his destination directly beneath him, whereupon he was to let +out the gas and drop down! Ptolemy knew quite enough natural +philosophy to be aware that such a proposal for locomotion would be +an utter absurdity; he knew that there was no such relative shift +between the air and the earth as this motion would imply. It +appeared to him to be necessary that the air should lag behind, if +the earth had been animated by a movement of rotation. In this he +was, as we know, entirely wrong. There were, however, in his days no +accurate notions on the subject of the laws of motion. + +Assiduous as Ptolemy may have been in the study of the heavenly +bodies, it seems evident that he cannot have devoted much thought to +the phenomena of motion of terrestrial objects. Simple, indeed, are +the experiments which might have convinced a philosopher much less +acute than Ptolemy, that, if the earth did revolve, the air must +necessarily accompany it. If a rider galloping on horseback tosses a +ball into the air, it drops again into his hand, just as it would +have done had he been remaining at rest during the ball's flight; the +ball in fact participates in the horizontal motion, so that though it +really describes a curve as any passer-by would observe, yet it +appears to the rider himself merely to move up and down in a straight +line. This fact, and many others similar to it, demonstrate clearly +that if the earth were endowed with a movement of rotation, the +atmosphere surrounding it must participate in that movement. Ptolemy +did not know this, and consequently he came to the conclusion that +the earth did not rotate, and that, therefore, notwithstanding the +tremendous improbability of so mighty an object as the celestial +sphere spinning round once in every twenty-four hours, there was no +course open except to believe that this very improbable thing did +really happen. Thus it came to pass that Ptolemy adopted as the +cardinal doctrine of his system a stationary earth poised at the +centre of the celestial sphere, which stretched around on all sides +at a distance so vast that the diameter of the earth was an +inappreciable point in comparison therewith. + +Ptolemy having thus deliberately rejected the doctrine of the earth's +rotation, had to make certain other entirely erroneous suppositions. +It was easily seen that each star required exactly the same period +for the performance of a complete revolution of the heavens. Ptolemy +knew that the stars were at enormous distances from the earth, though +no doubt his notions on this point came very far short of what we +know to be the reality. If the stars had been at very varied +distances, then it would be so wildly improbable that they should all +accomplish their revolutions in the same time, that Ptolemy came to +the conclusion that they must be all at the same distance, that is, +that they must be all on the surface of a sphere. This view, however +erroneous, was corroborated by the obvious fact that the stars in the +constellations preserved their relative places unaltered for +centuries. Thus it was that Ptolemy came to the conclusion that they +were all fixed on one spherical surface, though we are not informed +as to the material of this marvellous setting which sustained the +stars like jewels. + +Nor should we hastily pronounce this doctrine to be absurd. The +stars do appear to lie on the surface of a sphere, of which the +observer is at the centre; not only is this the aspect which the +skies present to the untechnical observer, but it is the aspect in +which the skies are presented to the most experienced astronomer of +modern days. No doubt he knows well that the stars are at the most +varied distances from him; he knows that certain stars are ten times, +or a hundred times, or a thousand times, as far as other stars. +Nevertheless, to his eye the stars appear on the surface of the +sphere, it is on that surface that his measurements of the relative +places of the stars are made; indeed, it may be said that almost all +the accurate observations in the observatory relate to the places of +the stars, not as they really are, but as they appear to be projected +on that celestial sphere whose conception we owe to the genius of +Ptolemy. + +This great philosopher shows very ingeniously that the earth must be +at the centre of the sphere. He proves that, unless this were the +case, each star would not appear to move with the absolute uniformity +which does, as a matter of fact, characterise it. In all these +reasonings we cannot but have the most profound admiration for the +genius of Ptolemy, even though he had made an error so enormous in +the fundamental point of the stability of the earth. Another error +of a somewhat similar kind seemed to Ptolemy to be demonstrated. He +had shown that the earth was an isolated object in space, and being +such was, of course, capable of movement. It could either be turned +round, or it could be moved from one place to another. We know that +Ptolemy deliberately adopted the view that the earth did not turn +round; he had then to investigate the other question, as to whether +the earth was animated by any movement of translation. He came to +the conclusion that to attribute any motion to the earth would be +incompatible with the truths at which he had already arrived. The +earth, argued Ptolemy, lies at the centre of the celestial sphere. +If the earth were to be endowed with movement, it would not lie +always at this point, it must, therefore, shift to some other part of +the sphere. The movements of the stars, however, preclude the +possibility of this; and, therefore, the earth must be as devoid of +any movement of translation as it is devoid of rotation. Thus it was +that Ptolemy convinced himself that the stability of the earth, as it +appeared to the ordinary senses, had a rational philosophical +foundation. + +Not unfrequently it is the lot of the philosophers to contend against +the doctrines of the vulgar, but when it happens, as in the case of +Ptolemy's researches, that the doctrines of the vulgar are +corroborated by philosophical investigation which bear the stamp of +the highest authority, it is not to be wondered at that such +doctrines should be deemed well-nigh impregnable. In this way we +may, perhaps, account for the remarkable fact that the theories of +Ptolemy held unchallenged sway over the human intellect for the vast +period already mentioned. + +Up to the present we have been speaking only of those primary motions +of the heavens, by which the whole sphere appeared to revolve once +every twenty-four hours. We have now to discuss the remarkable +theories by which Ptolemy endeavoured to account for the monthly +movement of the moon, for the annual movement of the sun, and for the +periodic movements of the planets which had gained for them the +titles of the wandering stars. + +Possessed with the idea that these movements must be circular, or +must be capable, directly or indirectly, of being explained by +circular movements, it seemed obvious to Ptolemy, as indeed it had +done to previous astronomers, that the track of the moon through the +stars was a circle of which the earth is the centre. A similar +movement with a yearly period must also be attributed to the sun, for +the changes in the positions of the constellations in accordance with +the progress of the seasons, placed it beyond doubt that the sun made +a circuit of the celestial sphere, even though the bright light of +the sun prevented the stars in its vicinity, from being seen in +daylight. Thus the movements both of the sun and the moon, as well +as the diurnal rotation of the celestial sphere, seemed to justify +the notion that all celestial movements must be "perfect," that is to +say, described uniformly in those circles which were the only perfect +curves. + +The simplest observations, however, show that the movements of the +planets cannot be explained in this simple fashion. Here the +geometrical genius of Ptolemy shone forth, and he devised a scheme by +which the apparent wanderings of the planets could be accounted for +without the introduction of aught save "perfect" movements. + +To understand his reasoning, let us first set forth clearly those +facts of observation which require to be explained. I shall take, in +particular, two planets, Venus and Mars, as these illustrate, in the +most striking manner, the peculiarities of the inner and the outer +planets respectively. The simplest observations would show that +Venus did not move round the heavens in the same fashion as the sun +or the moon. Look at the evening star when brightest, as it appears +in the west after sunset. Instead of moving towards the east among +the stars, like the sun or the moon, we find, week after week, that +Venus is drawing in towards the sun, until it is lost in the +sunbeams. Then the planet emerges on the other side, not to be seen +as an evening star, but as a morning star. In fact, it was plain +that in some ways Venus accompanied the sun in its annual movement. +Now it is found advancing in front of the sun to a certain limited +distance, and now it is lagging to an equal extent behind the sun. + +[FIG. 1. PTOLEMY'S PLANETARY SCHEME.] + +These movements were wholly incompatible with the supposition that +the journeys of Venus were described by a single motion of the kind +regarded as perfect. It was obvious that the movement was connected +in some strange manner with the revolution of the sun, and here was +the ingenious method by which Ptolemy sought to render account of +it. Imagine a fixed arm to extend from the earth to the sun, as +shown in the accompanying figure (Fig. 1), then this arm will move +round uniformly, in consequence of the sun's movement. At a point P +on this arm let a small circle be described. Venus is supposed to +revolve uniformly in this small circle, while the circle itself is +carried round continuously by the movement of the sun. In this way +it was possible to account for the chief peculiarities in the +movement of Venus. It will be seen that, in consequence of the +revolution around P, the spectator on the earth will sometimes see +Venus on one side of the sun, and sometimes on the other side, so +that the planet always remains in the sun's vicinity. By properly +proportioning the movements, this little contrivance simulated the +transitions from the morning star to the evening star. Thus the +changes of Venus could be accounted for by a Combination of the +"perfect" movement of P in the circle which it described uniformly +round the earth, combined with the "perfect" motion of Venus in the +circle which it described uniformly around the moving centre. + +In a precisely similar manner Ptolemy rendered an explanation of the +fitful apparitions of Mercury. Now just on one side of the sun, and +now just on the other, this rarely-seen planet moved like Venus on a +circle whereof the centre was also carried by the line joining the +sun and the earth. The circle, however, in which Mercury actually +revolved had to be smaller than that of Venus, in order to account +for the fact that Mercury lies always much closer to the sun than the +better-known planet. + +[FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.] + +The explanation of the movement of an outer planet like Mars could +also be deduced from the joint effect of two perfect motions. The +changes through which Mars goes are, however, so different from the +movements of Venus that quite a different disposition of the circles +is necessary. For consider the facts which characterise the +movements of an outer planet such as Mars. In the first place, Mars +accomplishes an entire circuit of the heaven. In this respect, no +doubt, it may be said to resemble the sun or the moon. A little +attention will, however, show that there are extraordinary +irregularities in the movement of the planet. Generally speaking, it +speeds its way from west to east among the stars, but sometimes the +attentive observer will note that the speed with which the planet +advances is slackening, and then it will seem to become stationary. +Some days later the direction of the planet's movement will be +reversed, and it will be found moving from the east towards the +west. At first it proceeds slowly and then quickens its pace, until +a certain speed is attained, which afterwards declines until a second +stationary position is reached. After a due pause the original +motion from west to east is resumed, and is continued until a similar +cycle of changes again commences. Such movements as these were +obviously quite at variance with any perfect movement in a single +circle round the earth. Here, again, the geometrical sagacity of +Ptolemy provided him with the means of representing the apparent +movements of Mars, and, at the same time, restricting the explanation +to those perfect movements which he deemed so essential. In Fig. 2 +we exhibit Ptolemy's theory as to the movement of Mars. We have, as +before, the earth at the centre, and the sun describing its circular +orbit around that centre. The path of Mars is to be taken as +exterior to that of the sun. We are to suppose that at a point +marked M there is a fictitious planet, which revolves around the +earth uniformly, in a circle called the DEFERENT. This point M, +which is thus animated by a perfect movement, is the centre of a +circle which is carried onwards with M, and around the circumference +of which Mars revolves uniformly. It is easy to show that the +combined effect of these two perfect movements is to produce exactly +that displacement of Mars in the heavens which observation +discloses. In the position represented in the figure, Mars is +obviously pursuing a course which will appear to the observer as a +movement from west to east. When, however, the planet gets round to +such a position as R, it is then moving from east to west in +consequence of its revolution in the moving circle, as indicated by +the arrow-head. On the other hand, the whole circle is carried +forward in the opposite direction. If the latter movement be less +rapid than the former, then we shall have the backward movement of +Mars on the heavens which it was desired to explain. By a proper +adjustment of the relative lengths of these arms the movements of the +planet as actually observed could be completely accounted for. + +The other outer planets with which Ptolemy was acquainted, namely, +Jupiter and Saturn, had movements of the same general character as +those of Mars. Ptolemy was equally successful in explaining the +movements they performed by the supposition that each planet had +perfect rotation in a circle of its own, which circle itself had +perfect movement around the earth in the centre. + +It is somewhat strange that Ptolemy did not advance one step further, +as by so doing he would have given great simplicity to his system. He +might, for instance, have represented the movements of Venus equally +well by putting the centre of the moving circle at the sun itself, +and correspondingly enlarging the circle in which Venus revolved. He +might, too, have arranged that the several circles which the outer +planets traversed should also have had their centres at the sun. The +planetary system would then have consisted of an earth fixed at the +centre, of a sun revolving uniformly around it, and of a system of +planets each describing its own circle around a moving centre placed +in the sun. Perhaps Ptolemy had not thought of this, or perhaps he +may have seen arguments against it. This important step was, +however, taken by Tycho. He considered that all the planets revolved +around the sun in circles, and that the sun itself, bearing all these +orbits, described a mighty circle around the earth. This point +having been reached, only one more step would have been necessary to +reach the glorious truths that revealed the structure of the solar +system. That last step was taken by Copernicus. + + + + +COPERNICUS + + +[PLATE: THORN, FROM AN OLD PRINT.] + +The quaint town of Thorn, on the Vistula, was more than two centuries +old when Copernicus was born there on the 19th of February, 1473. The +situation of this town on the frontier between Prussia and Poland, +with the commodious waterway offered by the river, made it a place of +considerable trade. A view of the town, as it was at the time of the +birth of Copernicus, is here given. The walls, with their +watch-towers, will be noted, and the strategic importance which the +situation of Thorn gave to it in the fifteenth century still belongs +thereto, so much so that the German Government recently constituted +the town a fortress of the first class. + +Copernicus, the astronomer, whose discoveries make him the great +predecessor of Kepler and Newton, did not come from a noble family, +as certain other early astronomers have done, for his father was a +tradesman. Chroniclers are, however, careful to tell us that one of +his uncles was a bishop. We are not acquainted with any of those +details of his childhood or youth which are often of such interest in +other cases where men have risen to exalted fame. It would appear +that the young Nicolaus, for such was his Christian name, received +his education at home until such time as he was deemed sufficiently +advanced to be sent to the University at Cracow. The education that +he there obtained must have been in those days of a very primitive +description, but Copernicus seems to have availed himself of it to +the utmost. He devoted himself more particularly to the study of +medicine, with the view of adopting its practice as the profession of +his life. The tendencies of the future astronomer were, however, +revealed in the fact that he worked hard at mathematics, and, like +one of his illustrious successors, Galileo, the practice of the art +of painting had for him a very great interest, and in it he obtained +some measure of success. + +By the time he was twenty-seven years old, it would seem that +Copernicus had given up the notion of becoming a medical +practitioner, and had resolved to devote himself to science. He was +engaged in teaching mathematics, and appears to have acquired some +reputation. His growing fame attracted the notice of his uncle the +bishop, at whose suggestion Copernicus took holy orders, and he was +presently appointed to a canonry in the cathedral of Frauenburg, near +the mouth of the Vistula. + +To Frauenburg, accordingly, this man of varied gifts retired. +Possessing somewhat of the ascetic spirit, he resolved to devote his +life to work of the most serious description. He eschewed all +ordinary society, restricting his intimacies to very grave and +learned companions, and refusing to engage in conversation of any +useless kind. It would seem as if his gifts for painting were +condemned as frivolous; at all events, we do not learn that he +continued to practise them. In addition to the discharge of his +theological duties, his life was occupied partly in ministering +medically to the wants of the poor, and partly with his researches in +astronomy and mathematics. His equipment in the matter of +instruments for the study of the heavens seems to have been of a very +meagre description. He arranged apertures in the walls of his house +at Allenstein, so that he could observe in some fashion the passage +of the stars across the meridian. That he possessed some talent for +practical mechanics is proved by his construction of a contrivance +for raising water from a stream, for the use of the inhabitants of +Frauenburg. Relics of this machine are still to be seen. + +[PLATE: COPERNICUS.] + +The intellectual slumber of the Middle Ages was destined to be +awakened by the revolutionary doctrines of Copernicus. It may be +noted, as an interesting circumstance, that the time at which he +discovered the scheme of the solar system has coincided with a +remarkable epoch in the world's history. The great astronomer had +just reached manhood at the time when Columbus discovered the new +world. + +Before the publication of the researches of Copernicus, the orthodox +scientific creed averred that the earth was stationary, and that the +apparent movements of the heavenly bodies were indeed real +movements. Ptolemy had laid down this doctrine 1,400 years before. +In his theory this huge error was associated with so much important +truth, and the whole presented such a coherent scheme for the +explanation of the heavenly movements, that the Ptolemaic theory was +not seriously questioned until the great work of Copernicus +appeared. No doubt others, before Copernicus, had from time to time +in some vague fashion surmised, with more or less plausibility, that +the sun, and not the earth, was the centre about which the system +really revolved. It is, however, one thing to state a scientific +fact; it is quite another thing to be in possession of the train of +reasoning, founded on observation or experiment, by which that fact +may be established. Pythagoras, it appears, had indeed told his +disciples that it was the sun, and not the earth, which was the +centre of movement, but it does not seem at all certain that +Pythagoras had any grounds which science could recognise for the +belief which is attributed to him. So far as information is +available to us, it would seem that Pythagoras associated his scheme +of things celestial with a number of preposterous notions in natural +philosophy. He may certainly have made a correct statement as to +which was the most important body in the solar system, but he +certainly did not provide any rational demonstration of the fact. +Copernicus, by a strict train of reasoning, convinced those who would +listen to him that the sun was the centre of the system. It is +useful for us to consider the arguments which he urged, and by which +he effected that intellectual revolution which is always connected +with his name. + +The first of the great discoveries which Copernicus made relates to +the rotation of the earth on its axis. That general diurnal +movement, by which the stars and all other celestial bodies appear to +be carried completely round the heavens once every twenty-four hours, +had been accounted for by Ptolemy on the supposition that the +apparent movements were the real movements. As we have already seen, +Ptolemy himself felt the extraordinary difficulty involved in the +supposition that so stupendous a fabric as the celestial sphere +should spin in the way supposed. Such movements required that many +of the stars should travel with almost inconceivable velocity. +Copernicus also saw that the daily rising and setting of the heavenly +bodies could be accounted for either by the supposition that the +celestial sphere moved round and that the earth remained at rest, or +by the supposition that the celestial sphere was at rest while the +earth turned round in the opposite direction. He weighed the +arguments on both sides as Ptolemy had done, and, as the result of +his deliberations, Copernicus came to an opposite conclusion from +Ptolemy. To Copernicus it appeared that the difficulties attending +the supposition that the celestial sphere revolved, were vastly +greater than those which appeared so weighty to Ptolemy as to force +him to deny the earth's rotation. + +Copernicus shows clearly how the observed phenomena could be +accounted for just as completely by a rotation of the earth as by a +rotation of the heavens. He alludes to the fact that, to those on +board a vessel which is moving through smooth water, the vessel +itself appears to be at rest, while the objects on shore seem to be +moving past. If, therefore, the earth were rotating uniformly, we +dwellers upon the earth, oblivious of our own movement, would wrongly +attribute to the stars the displacement which was actually the +consequence of our own motion. + +Copernicus saw the futility of the arguments by which Ptolemy had +endeavoured to demonstrate that a revolution of the earth was +impossible. It was plain to him that there was nothing whatever to +warrant refusal to believe in the rotation of the earth. In his +clear-sightedness on this matter we have specially to admire the +sagacity of Copernicus as a natural philosopher. It had been urged +that, if the earth moved round, its motion would not be imparted to +the air, and that therefore the earth would be uninhabitable by the +terrific winds which would be the result of our being carried through +the air. Copernicus convinced himself that this deduction was +preposterous. He proved that the air must accompany the earth, just +as his coat remains round him, notwithstanding the fact that he is +walking down the street. In this way he was able to show that all a +priori objections to the earth's movements were absurd, and therefore +he was able to compare together the plausibilities of the two rival +schemes for explaining the diurnal movement. + +[PLATE: FRAUENBURG, FROM AN OLD PRINT.] + +Once the issue had been placed in this form, the result could not be +long in doubt. Here is the question: Which is it more likely--that +the earth, like a grain of sand at the centre of a mighty globe, +should turn round once in twenty-four hours, or that the whole of +that vast globe should complete a rotation in the opposite direction +in the same time? Obviously, the former is far the more simple +supposition. But the case is really much stronger than this. Ptolemy +had supposed that all the stars were attached to the surface of a +sphere. He had no ground whatever for this supposition, except that +otherwise it would have been well-nigh impossible to have devised a +scheme by which the rotation of the heavens around a fixed earth +could have been arranged. Copernicus, however, with the just +instinct of a philosopher, considered that the celestial sphere, +however convenient from a geometrical point of view, as a means of +representing apparent phenomena, could not actually have a material +existence. In the first place, the existence of a material celestial +sphere would require that all the myriad stars should be at exactly +the same distances from the earth. Of course, no one will say that +this or any other arbitrary disposition of the stars is actually +impossible, but as there was no conceivable physical reason why the +distances of all the stars from the earth should be identical, it +seemed in the very highest degree improbable that the stars should be +so placed. + +Doubtless, also, Copernicus felt a considerable difficulty as to the +nature of the materials from which Ptolemy's wonderful sphere was to +be constructed. Nor could a philosopher of his penetration have +failed to observe that, unless that sphere were infinitely large, +there must have been space outside it, a consideration which would +open up other difficult questions. Whether infinite or not, it was +obvious that the celestial sphere must have a diameter at least many +thousands of times as great as that of the earth. From these +considerations Copernicus deduced the important fact that the stars +and the other celestial bodies must all be vast objects. He was thus +enabled to put the question in such a form that it could hardly +receive any answer but the correct one. Which is it more rational to +suppose, that the earth should turn round on its axis once in +twenty-four hours, or that thousands of mighty stars should circle +round the earth in the same time, many of them having to describe +circles many thousands of times greater in circumference than the +circuit of the earth at the equator? The obvious answer pressed upon +Copernicus with so much force that he was compelled to reject +Ptolemy's theory of the stationary earth, and to attribute the +diurnal rotation of the heavens to the revolution of the earth on its +axis. + +Once this tremendous step had been taken, the great difficulties +which beset the monstrous conception of the celestial sphere +vanished, for the stars need no longer be regarded as situated at +equal distances from the earth. Copernicus saw that they might lie +at the most varied degrees of remoteness, some being hundreds or +thousands of times farther away than others. The complicated +structure of the celestial sphere as a material object disappeared +altogether; it remained only as a geometrical conception, whereon we +find it convenient to indicate the places of the stars. Once the +Copernican doctrine had been fully set forth, it was impossible for +anyone, who had both the inclination and the capacity to understand +it, to withhold acceptance of its truth. The doctrine of a +stationary earth had gone for ever. + +Copernicus having established a theory of the celestial movements +which deliberately set aside the stability of the earth, it seemed +natural that he should inquire whether the doctrine of a moving earth +might not remove the difficulties presented in other celestial +phenomena. It had been universally admitted that the earth lay +unsupported in space. Copernicus had further shown that it possessed +a movement of rotation. Its want of stability being thus recognised, +it seemed reasonable to suppose that the earth might also have some +other kinds of movements as well. In this, Copernicus essayed to +solve a problem far more difficult than that which had hitherto +occupied his attention. It was a comparatively easy task to show how +the diurnal rising and setting could be accounted for by the rotation +of the earth. It was a much more difficult undertaking to +demonstrate that the planetary movements, which Ptolemy had +represented with so much success, could be completely explained by +the supposition that each of those planets revolved uniformly round +the sun, and that the earth was also a planet, accomplishing a +complete circuit of the sun once in the course of a year. + +[PLATE: EXPLANATION OF PLANETARY MOVEMENTS.] + +It would be impossible in a sketch like the present to enter into any +detail as to the geometrical propositions on which this beautiful +investigation of Copernicus depended. We can only mention a few of +the leading principles. It may be laid down in general that, if an +observer is in movement, he will, if unconscious of the fact, +attribute to the fixed objects around him a movement equal and +opposite to that which he actually possesses. A passenger on a +canal-boat sees the objects on the banks apparently moving backward +with a speed equal to that by which he is himself advancing +forwards. By an application of this principle, we can account for +all the phenomena of the movements of the planets, which Ptolemy had +so ingeniously represented by his circles. Let us take, for +instance, the most characteristic feature in the irregularities of +the outer planets. We have already remarked that Mars, though +generally advancing from west to east among the stars, occasionally +pauses, retraces his steps for awhile, again pauses, and then resumes +his ordinary onward progress. Copernicus showed clearly how this +effect was produced by the real motion of the earth, combined with +the real motion of Mars. In the adjoining figure we represent a +portion of the circular tracks in which the earth and Mars move in +accordance with the Copernican doctrine. I show particularly the +case where the earth comes directly between the planet and the sun, +because it is on such occasions that the retrograde movement (for so +this backward movement of Mars is termed) is at its highest. Mars is +then advancing in the direction shown by the arrow-head, and the +earth is also advancing in the same direction. We, on the earth, +however, being unconscious of our own motion, attribute, by the +principle I have already explained, an equal and opposite motion to +Mars. The visible effect upon the planet is, that Mars has two +movements, a real onward movement in one direction, and an apparent +movement in the opposite direction. If it so happened that the earth +was moving with the same speed as Mars, then the apparent movement +would exactly neutralise the real movement, and Mars would seem to be +at rest relatively to the surrounding stars. Under the actual +circumstances represented, however, the earth is moving faster than +Mars, and the consequence is, that the apparent movement of the +planet backwards exceeds the real movement forwards, the net result +being an apparent retrograde movement. + +With consummate skill, Copernicus showed how the applications of the +same principles could account for the characteristic movements of the +planets. His reasoning in due time bore down all opposition. The +supreme importance of the earth in the system vanished. It had now +merely to take rank as one of the planets. + +The same great astronomer now, for the first time, rendered something +like a rational account of the changes of the seasons. Nor did +certain of the more obscure astronomical phenomena escape his +attention. + +He delayed publishing his wonderful discoveries to the world until he +was quite an old man. He had a well-founded apprehension of the +storm of opposition which they would arouse. However, he yielded at +last to the entreaties of his friends, and his book was sent to the +press. But ere it made its appearance to the world, Copernicus was +seized by mortal illness. A copy of the book was brought to him on +May 23, 1543. We are told that he was able to see it and to touch +it, but no more, and he died a few hours afterwards. He was buried +in that Cathedral of Frauenburg, with which his life had been so +closely associated. + + + + +TYCHO BRAHE. + + +The most picturesque figure in the history of astronomy is +undoubtedly that of the famous old Danish astronomer whose name +stands at the head of this chapter. Tycho Brahe was alike notable +for his astronomical genius and for the extraordinary vehemence of a +character which was by no means perfect. His romantic career as a +philosopher, and his taste for splendour as a Danish noble, his +ardent friendships and his furious quarrels, make him an ideal +subject for a biographer, while the magnificent astronomical work +which he accomplished, has given him imperishable fame. + +The history of Tycho Brahe has been admirably told by Dr. Dreyer, the +accomplished astronomer who now directs the observatory at Armagh, +though himself a countryman of Tycho. Every student of the career of +the great Dane must necessarily look on Dr. Dreyer's work as the +chief authority on the subject. Tycho sprang from an illustrious +stock. His family had flourished for centuries, both in Sweden and +in Denmark, where his descendants are to be met with at the present +day. The astronomer's father was a privy councillor, and having +filled important positions in the Danish government, he was +ultimately promoted to be governor of Helsingborg Castle, where he +spent the last years of his life. His illustrious son Tycho was born +in 1546, and was the second child and eldest boy in a family of ten. + +It appears that Otto, the father of Tycho, had a brother named +George, who was childless. George, however, desired to adopt a boy +on whom he could lavish his affection and to whom he could bequeath +his wealth. A somewhat singular arrangement was accordingly entered +into by the brothers at the time when Otto was married. It was +agreed that the first son who might be born to Otto should be +forthwith handed over by the parents to George to be reared and +adopted by him. In due time little Tycho appeared, and was +immediately claimed by George in pursuance of the compact. But it +was not unnatural that the parental instinct, which had been dormant +when the agreement was made, should here interpose. Tycho's father +and mother receded from the bargain, and refused to part with their +son. George thought he was badly treated. However, he took no +violent steps until a year later, when a brother was born to Tycho. +The uncle then felt no scruple in asserting what he believed to be +his rights by the simple process of stealing the first-born nephew, +which the original bargain had promised him. After a little time it +would seem that the parents acquiesced in the loss, and thus it was +in Uncle George's home that the future astronomer passed his +childhood. + +When we read that Tycho was no more than thirteen years old at the +time he entered the University of Copenhagen, it might be at first +supposed that even in his boyish years he must have exhibited some of +those remarkable talents with which he was afterwards to astonish the +world. Such an inference should not, however, be drawn. The fact is +that in those days it was customary for students to enter the +universities at a much earlier age than is now the case. Not, +indeed, that the boys of thirteen knew more then than the boys of +thirteen know now. But the education imparted in the universities at +that time was of a much more rudimentary kind than that which we +understand by university education at present. In illustration of +this Dr. Dreyer tells us how, in the University of Wittenberg, one of +the professors, in his opening address, was accustomed to point out +that even the processes of multiplication and division in arithmetic +might be learned by any student who possessed the necessary +diligence. + +It was the wish and the intention of his uncle that Tycho's education +should be specially directed to those branches of rhetoric and +philosophy which were then supposed to be a necessary preparation for +the career of a statesman. Tycho, however, speedily made it plain to +his teachers that though he was an ardent student, yet the things +which interested him were the movements of the heavenly bodies and +not the subtleties of metaphysics. + +[PLATE: TYCHO BRAHE.] + +On the 21st October, 1560, an eclipse of the sun occurred, which was +partially visible at Copenhagen. Tycho, boy though he was, took the +utmost interest in this event. His ardour and astonishment in +connection with the circumstance were chiefly excited by the fact +that the time of the occurrence of the phenomenon could be predicted +with so much accuracy. Urged by his desire to understand the matter +thoroughly, Tycho sought to procure some book which might explain +what he so greatly wanted to know. In those days books of any kind +were but few and scarce, and scientific books were especially +unattainable. It so happened, however, that a Latin version of +Ptolemy's astronomical works had appeared a few years before the +eclipse took place, and Tycho managed to buy a copy of this book, +which was then the chief authority on celestial matters. Young as +the boy astronomer was, he studied hard, although perhaps not always +successfully, to understand Ptolemy, and to this day his copy of the +great work, copiously annotated and marked by the schoolboy hand, is +preserved as one of the chief treasures in the library of the +University at Prague. + +After Tycho had studied for about three years at the University of +Copenhagen, his uncle thought it would be better to send him, as was +usual in those days, to complete his education by a course of study +in some foreign university. The uncle cherished the hope that in +this way the attention of the young astronomer might be withdrawn +from the study of the stars and directed in what appeared to him a +more useful way. Indeed, to the wise heads of those days, the +pursuit of natural science seemed so much waste of good time which +might otherwise be devoted to logic or rhetoric or some other branch +of study more in vogue at that time. To assist in this attempt to +wean Tycho from his scientific tastes, his uncle chose as a tutor to +accompany him an intelligent and upright young man named Vedel, who +was four years senior to his pupil, and accordingly, in 1562, we find +the pair taking up their abode at the University of Leipzig. + +The tutor, however, soon found that he had undertaken a most hopeless +task. He could not succeed in imbuing Tycho with the slightest taste +for the study of the law or the other branches of knowledge which +were then thought so desirable. The stars, and nothing but the +stars, engrossed the attention of his pupil. We are told that all +the money he could obtain was spent secretly in buying astronomical +books and instruments. He learned the name of the stars from a +little globe, which he kept hidden from Vedel, and only ventured to +use during the latter's absence. No little friction was at first +caused by all this, but in after years a fast and enduring friendship +grew up between Tycho and his tutor, each of whom learned to respect +and to love the other. + +Before Tycho was seventeen he had commenced the difficult task of +calculating the movements of the planets and the places which they +occupied on the sky from time to time. He was not a little surprised +to find that the actual positions of the planets differed very widely +from those which were assigned to them by calculations from the best +existing works of astronomers. With the insight of genius he saw +that the only true method of investigating the movements of the +heavenly bodies would be to carry on a protracted series of +measurements of their places. This, which now seems to us so +obvious, was then entirely new doctrine. Tycho at once commenced +regular observations in such fashion as he could. His first +instrument was, indeed, a very primitive one, consisting of a simple +pair of compasses, which he used in this way. He placed his eye at +the hinge, and then opened the legs of the compass so that one leg +pointed to one star and the other leg to the other star. The compass +was then brought down to a divided circle, by which means the number +of degrees in the apparent angular distance of the two stars was +determined. + +His next advance in instrumental equipment was to provide himself +with the contrivance known as the "cross-staff," which he used to +observe the stars whenever opportunity offered. It must, of course, +be remembered that in those days there were no telescopes. In the +absence of optical aid, such as lenses afford the modern observers, +astronomers had to rely on mechanical appliances alone to measure the +places of the stars. Of such appliances, perhaps the most ingenious +was one known before Tycho's time, which we have represented in the +adjoining figure. + +[PLATE: TYCHO'S CROSS STAFF.] + +Let us suppose that it be desired to measure the angle between two +stars, then if the angle be not too large it can be determined in the +following manner. Let the rod AB be divided into inches and parts of +an inch, and let another rod, CD, slide up and down along AB in such +a way that the two always remain perpendicular to each other. +"Sights," like those on a rifle, are placed at A and C, and there is +a pin at D. It will easily be seen that, by sliding the movable bar +along the fixed one, it must always be possible when the stars are +not too far apart to bring the sights into such positions that one +star can be seen along DC and the other along DA. This having been +accomplished, the length from A to the cross-bar is read off on the +scale, and then, by means of a table previously prepared, the value +of the required angular distance is obtained. If the angle between +the two stars were greater than it would be possible to measure in +the way already described, then there was a provision by which the +pin at D might be moved along CD into some other position, so as to +bring the angular distance of the stars within the range of the +instrument. + +[PLATE: TYCHO'S "NEW STAR" SEXTANT OF 1572. +(The arms, of walnut wood, are about 5 1/2 ft. long.)] + +No doubt the cross-staff is a very primitive contrivance, but when +handled by one so skilful as Tycho it afforded results of +considerable accuracy. I would recommend any reader who may have a +taste for such pursuits to construct a cross-staff for himself, and +see what measurements he can accomplish with its aid. + +To employ this little instrument Tycho had to evade the vigilance of +his conscientious tutor, who felt it his duty to interdict all such +occupations as being a frivolous waste of time. It was when Vedel +was asleep that Tycho managed to escape with his cross staff and +measure the places of the heavenly bodies. Even at this early age +Tycho used to conduct his observations on those thoroughly sound +principles which lie at the foundation of all accurate modern +astronomy. Recognising the inevitable errors of workmanship in his +little instrument, he ascertained their amount and allowed for their +influence on the results which he deduced. This principle, employed +by the boy with his cross-staff in 1564, is employed at the present +day by the Astronomer Royal at Greenwich with the most superb +instruments that the skill of modern opticians has been able to +construct. + +[PLATE: TYCHO'S TRIGONIC SEXTANT. +(The arms, AB and AC, are about 5 1/2 ft. long.)] + +After the death of his uncle, when Tycho was nineteen years of age, +it appears that the young philosopher was no longer interfered with +in so far as the line which his studies were to take was concerned. +Always of a somewhat restless temperament, we now find that he +shifted his abode to the University of Rostock, where he speedily +made himself notable in connection with an eclipse of the moon on +28th October, 1566. Like every other astronomer of those days, Tycho +had always associated astronomy with astrology. He considered that +the phenomena of the heavenly bodies always had some significance in +connection with human affairs. Tycho was also a poet, and in the +united capacity of poet, astrologer, and astronomer, he posted up +some verses in the college at Rostock announcing that the lunar +eclipse was a prognostication of the death of the great Turkish +Sultan, whose mighty deeds at that time filled men's minds. Presently +news did arrive of the death of the Sultan, and Tycho was accordingly +triumphant; but a little later it appeared that the decease had taken +place BEFORE the eclipse, a circumstance which caused many a laugh at +Tycho's expense. + +[PLATE: TYCHO'S ASTRONOMIC SEXTANT. +(Made of steel: the arms, AB, AC, measure 4 ft.) + +PLATE: TYCHO'S EQUATORIAL ARMILLARY. +(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)] + +Tycho being of a somewhat turbulent disposition, it appears that, +while at the University of Rostock, he had a serious quarrel with +another Danish nobleman. We are not told for certain what was the +cause of the dispute. It does not, however, seem to have had any +more romantic origin than a difference of opinion as to which of them +knew the more mathematics. They fought, as perhaps it was becoming +for two astronomers to fight, under the canopy of heaven in utter +darkness at the dead of night, and the duel was honourably terminated +when a slice was taken off Tycho's nose by the insinuating sword of +his antagonist. For the repair of this injury the ingenuity of the +great instrument-maker was here again useful, and he made a +substitute for his nose "with a composition of gold and silver." The +imitation was so good that it is declared to have been quite equal to +the original. Dr. Lodge, however, pointedly observes that it does +not appear whether this remark was made by a friend or an enemy. + +[PLATE: THE GREAT AUGSBURG QUADRANT. +(Built of heart of oak; the radii about 19 ft.) + +PLATE: TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.] + +The next few years Tycho spent in various places ardently pursuing +somewhat varied branches of scientific study. At one time we hear of +him assisting an astronomical alderman, in the ancient city of +Augsburg, to erect a tremendous wooden machine--a quadrant of 19-feet +radius--to be used in observing the heavens. At another time we +learn that the King of Denmark had recognised the talents of his +illustrious subject, and promised to confer on him a pleasant +sinecure in the shape of a canonry, which would assist him with the +means for indulging his scientific pursuits. Again we are told that +Tycho is pursuing experiments in chemistry with the greatest energy, +nor is this so incompatible as might at first be thought with his +devotion to astronomy. In those early days of knowledge the +different sciences seemed bound together by mysterious bonds. +Alchemists and astrologers taught that the several planets were +correlated in some mysterious manner with the several metals. It +was, therefore hardly surprising that Tycho should have included a +study of the properties of the metals in the programme of his +astronomical work. + +[PLATE: URANIBORG AND ITS GROUNDS. + +PLATE: GROUND-PLAN OF THE OBSERVATORY.] + +An event, however, occurred in 1572 which stimulated Tycho's +astronomical labours, and started him on his life's work. On the +11th of November in that year, he was returning home to supper after +a day's work in his laboratory, when he happened to lift his face to +the sky, and there he beheld a brilliant new star. It was in the +constellation of Cassiopeia, and occupied a position in which there +had certainly been no bright star visible when his attention had last +been directed to that part of the heavens. Such a phenomenon was so +startling that he found it hard to trust the evidence of his senses. +He thought he must be the subject of some hallucination. He +therefore called to the servants who were accompanying him, and asked +them whether they, too, could see a brilliant object in the direction +in which he pointed. They certainly could, and thus he became +convinced that this marvellous object was no mere creation of the +fancy, but a veritable celestial body--a new star of surpassing +splendour which had suddenly burst forth. In these days of careful +scrutiny of the heavens, we are accustomed to the occasional outbreak +of new stars. It is not, however, believed that any new star which +has ever appeared has displayed the same phenomenal brilliance as was +exhibited by the star of 1572. + +This object has a value in astronomy far greater than it might at +first appear. It is true, in one sense, that Tycho discovered the +new star, but it is equally true, in a different sense, that it was +the new star which discovered Tycho. Had it not been for this +opportune apparition, it is quite possible that Tycho might have +found a career in some direction less beneficial to science than that +which he ultimately pursued. + +[PLATE: THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.] + +When he reached his home on this memorable evening, Tycho immediately +applied his great quadrant to the measurement of the place of the new +star. His observations were specially directed to the determination +of the distance of the object. He rightly conjectured that if it +were very much nearer to us than the stars in its vicinity, the +distance of the brilliant body might be determined in a short time by +the apparent changes in its distance from the surrounding points. It +was speedily demonstrated that the new star could not be as near as +the moon, by the simple fact that its apparent place, as compared +with the stars in its neighbourhood, was not appreciably altered when +it was observed below the pole, and again above the pole at an +interval of twelve hours. Such observations were possible, inasmuch +as the star was bright enough to be seen in full daylight. Tycho +thus showed conclusively that the body was so remote that the +diameter of the earth bore an insignificant ratio to the star's +distance. His success in this respect is the more noteworthy when we +find that many other observers, who studied the same object, came to +the erroneous conclusion that the new star was quite as near as the +moon, or even much nearer. In fact, it may be said, that with regard +to this object Tycho discovered everything which could possibly have +been discovered in the days before telescopes were invented. He not +only proved that the star's distance was too great for measurement, +but he showed that it had no proper motion on the heavens. He +recorded the successive changes in its brightness from week to week, +as well as the fluctuations in hue with which the alterations in +lustre were accompanied. + +It seems, nowadays, strange to find that such thoroughly scientific +observations of the new star as those which Tycho made, possessed, +even in the eyes of the great astronomer himself, a profound +astrological significance. We learn from Dr. Dreyer that, in Tycho's +opinion, "the star was at first like Venus and Jupiter, and its +effects will therefore, first, be pleasant; but as it then became +like Mars, there will next come a period of wars, seditions, +captivity, and death of princes, and destruction of cities, together +with dryness and fiery meteors in the air, pestilence, and venomous +snakes. Lastly, the star became like Saturn, and thus will finally +come a time of want, death, imprisonment, and all kinds of sad +things!" Ideas of this kind were, however, universally entertained. +It seemed, indeed, obvious to learned men of that period that such an +apparition must forebode startling events. One of the chief theories +then held was, that just as the Star of Bethlehem announced the first +coming of Christ, so the second coming, and the end of the world, was +heralded by the new star of 1572. + +The researches of Tycho on this object were the occasion of his first +appearance as an author. The publication of his book was however, +for some time delayed by the urgent remonstrances of his friends, who +thought it was beneath the dignity of a nobleman to condescend to +write a book. Happily, Tycho determined to brave the opinion of his +order; the book appeared, and was the first of a series of great +astronomical productions from the same pen. + +[PLATE: EFFIGY ON TYCHO'S TOMB AT PRAGUE.] + +The fame of the noble Dane being now widespread, the King of Denmark +entreated him to return to his native country, and to deliver a +course of lectures on astronomy in the University of Copenhagen. With +some reluctance he consented, and his introductory oration has been +preserved. He dwells, in fervent language, upon the beauty and the +interest of the celestial phenomena. He points out the imperative +necessity of continuous and systematic observation of the heavenly +bodies in order to extend our knowledge. He appeals to the practical +utility of the science, for what civilised nation could exist without +having the means of measuring time? He sets forth how the study of +these beautiful objects "exalts the mind from earthly and trivial +things to heavenly ones;" and then he winds up by assuring them that +"a special use of astronomy is that it enables us to draw conclusions +from the movements in the celestial regions as to human fate." + +An interesting event, which occurred in 1572, distracted Tycho's +attention from astronomical matters. He fell in love. The young +girl on whom his affections were set appears to have sprung from +humble origin. Here again his august family friends sought to +dissuade him from a match they thought unsuitable for a nobleman. +But Tycho never gave way in anything. It is suggested that he did +not seek a wife among the highborn dames of his own rank from the +dread that the demands of a fashionable lady would make too great an +inroad on the time that he wished to devote to science. At all +events, Tycho's union seems to have been a happy one, and he had a +large family of children; none of whom, however, inherited their +father's talents. + +[PLATE: TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.] + +Tycho had many scientific friends in Germany, among whom his work was +held in high esteem. The treatment that he there met with seemed to +him so much more encouraging than that which he received in Denmark +that he formed the notion of emigrating to Basle and making it his +permanent abode. A whisper of this intention was conveyed to the +large-hearted King of Denmark, Frederick II. He wisely realised how +great would be the fame which would accrue to his realm if he could +induce Tycho to remain within Danish territory and carry on there the +great work of his life. A resolution to make a splendid proposal to +Tycho was immediately formed. A noble youth was forthwith despatched +as a messenger, and ordered to travel day and night until he reached +Tycho, whom he was to summon to the king. The astronomer was in bed +on the morning of 11th February, 1576, when the message was +delivered. Tycho, of course, set off at once and had an audience of +the king at Copenhagen. The astronomer explained that what he wanted +was the means to pursue his studies unmolested, whereupon the king +offered him the Island of Hven, in the Sound near Elsinore. There he +would enjoy all the seclusion that he could desire. The king further +promised that he would provide the funds necessary for building a +house and for founding the greatest observatory that had ever yet +been reared for the study of the heavens. After due deliberation and +consultation with his friends, Tycho accepted the king's offer. He +was forthwith granted a pension, and a deed was drawn up formally +assigning the Island of Hven to his use all the days of his life. + +The foundation of the famous castle of Uraniborg was laid on 30th +August, 1576. The ceremony was a formal and imposing one, in +accordance with Tycho's ideas of splendour. A party of scientific +friends had assembled, and the time had been chosen so that the +heavenly bodies were auspiciously placed. Libations of costly wines +were poured forth, and the stone was placed with due solemnity. The +picturesque character of this wonderful temple for the study of the +stars may be seen in the figures with which this chapter is +illustrated. + +One of the most remarkable instruments that has ever been employed in +studying the heavens was the mural quadrant which Tycho erected in +one of the apartments of Uraniborg. By its means the altitudes of +the celestial bodies could be observed with much greater accuracy +than had been previously attainable. This wonderful contrivance is +represented on the preceding page. It will be observed that the +walls of the room are adorned by pictures with a lavishness of +decoration not usually to be found in scientific establishments. + +A few years later, when the fame of the observatory at Hven became +more widely spread, a number of young men flocked to Tycho to study +under his direction. He therefore built another observatory for +their use in which the instruments were placed in subterranean rooms +of which only the roofs appeared above the ground. There was a +wonderful poetical inscription over the entrance to this underground +observatory, expressing the astonishment of Urania at finding, even +in the interior of the earth, a cavern devoted to the study of the +heavens. Tycho was indeed always fond of versifying, and he lost no +opportunity of indulging this taste whenever an occasion presented +itself. + +Around the walls of the subterranean observatory were the pictures of +eight astronomers, each with a suitable inscription--one of these of +course represented Tycho himself, and beneath were written words to +the effect that posterity should judge of his work. The eighth +picture depicted an astronomer who has not yet come into existence. +Tychonides was his name, and the inscription presses the modest hope +that when he does appear he will be worthy of his great predecessor. +The vast expenses incurred in the erection and the maintenance of +this strange establishment were defrayed by a succession of grants +from the royal purse. + +For twenty years Tycho laboured hard at Uraniborg in the pursuit of +science. His work mainly consisted in the determination of the +places of the moon, the planets, and the stars on the celestial +sphere. The extraordinary pains taken by Tycho to have his +observations as accurate as his instruments would permit, have justly +entitled him to the admiration of all succeeding astronomers. His +island home provided the means of recreation as well as a place for +work. He was surrounded by his family, troops of friends were not +wanting, and a pet dwarf seems to have been an inmate of his curious +residence. By way of change from his astronomical labours he used +frequently to work with his students in his chemical laboratory. It +is not indeed known what particular problems in chemistry occupied +his attention. We are told, however, that he engaged largely in the +production of medicines, and as these appear to have been dispensed +gratuitously there was no lack of patients. + +Tycho's imperious and grasping character frequently brought him into +difficulties, which seem to have increased with his advancing years. +He had ill-treated one of his tenants on Hven, and an adverse +decision by the courts seems to have greatly exasperated the +astronomer. Serious changes also took place in his relations to the +court at Copenhagen. When the young king was crowned in 1596, he +reversed the policy of his predecessor with reference to Hven. The +liberal allowances to Tycho were one after another withdrawn, and +finally even his pension was stopped. Tycho accordingly abandoned +Hven in a tumult of rage and mortification. A few years later we +find him in Bohemia a prematurely aged man, and he died on the 24th +October, 1601. + + + + +GALILEO. + + +Among the ranks of the great astronomers it would be difficult to +find one whose life presents more interesting features and remarkable +vicissitudes than does that of Galileo. We may consider him as the +patient investigator and brilliant discoverer. We may consider him +in his private relations, especially to his daughter, Sister Maria +Celeste, a woman of very remarkable character; and we have also the +pathetic drama at the close of Galileo's life, when the philosopher +drew down upon himself the thunders of the Inquisition. + +The materials for the sketch of this astonishing man are sufficiently +abundant. We make special use in this place of those charming +letters which his daughter wrote to him from her convent home. More +than a hundred of these have been preserved, and it may well be +doubted whether any more beautiful and touching series of letters +addressed to a parent by a dearly loved child have ever been +written. An admirable account of this correspondence is contained in +a little book entitled "The Private Life of Galileo," published +anonymously by Messrs. Macmillan in 1870, and I have been much +indebted to the author of that volume for many of the facts contained +in this chapter. + +Galileo was born at Pisa, on 18th February, 1564. He was the eldest +son of Vincenzo de' Bonajuti de' Galilei, a Florentine noble. +Notwithstanding his illustrious birth and descent, it would seem that +the home in which the great philosopher's childhood was spent was an +impoverished one. It was obvious at least that the young Galileo +would have to be provided with some profession by which he might earn +a livelihood. From his father he derived both by inheritance and by +precept a keen taste for music, and it appears that he became an +excellent performer on the lute. He was also endowed with +considerable artistic power, which he cultivated diligently. Indeed, +it would seem that for some time the future astronomer entertained +the idea of devoting himself to painting as a profession. His +father, however, decided that he should study medicine. Accordingly, +we find that when Galileo was seventeen years of age, and had added a +knowledge of Greek and Latin to his acquaintance with the fine arts, +he was duly entered at the University of Pisa. + +Here the young philosopher obtained some inkling of mathematics, +whereupon he became so much interested in this branch of science, +that he begged to be allowed to study geometry. In compliance with +his request, his father permitted a tutor to be engaged for this +purpose; but he did so with reluctance, fearing that the attention of +the young student might thus be withdrawn from that medical work +which was regarded as his primary occupation. The event speedily +proved that these anxieties were not without some justification. The +propositions of Euclid proved so engrossing to Galileo that it was +thought wise to avoid further distraction by terminating the +mathematical tutor's engagement. But it was too late for the desired +end to be attained. Galileo had now made such progress that he was +able to continue his geometrical studies by himself. Presently he +advanced to that famous 47th proposition which won his lively +admiration, and on he went until he had mastered the six books of +Euclid, which was a considerable achievement for those days. + +The diligence and brilliance of the young student at Pisa did not, +however, bring him much credit with the University authorities. In +those days the doctrines of Aristotle were regarded as the embodiment +of all human wisdom in natural science as well as in everything +else. It was regarded as the duty of every student to learn +Aristotle off by heart, and any disposition to doubt or even to +question the doctrines of the venerated teacher was regarded as +intolerable presumption. But young Galileo had the audacity to think +for himself about the laws of nature. He would not take any +assertion of fact on the authority of Aristotle when he had the means +of questioning nature directly as to its truth or falsehood. His +teachers thus came to regard him as a somewhat misguided youth, +though they could not but respect the unflagging industry with which +he amassed all the knowledge he could acquire. + +[PLATE: GALILEO'S PENDULUM.] + +We are so accustomed to the use of pendulums in our clocks that +perhaps we do not often realise that the introduction of this method +of regulating time-pieces was really a notable invention worthy the +fame of the great astronomer to whom it was due. It appears that +sitting one day in the Cathedral of Pisa, Galileo's attention became +concentrated on the swinging of a chandelier which hung from the +ceiling. It struck him as a significant point, that whether the arc +through which the pendulum oscillated was a long one or a short one, +the time occupied in each vibration was sensibly the same. This +suggested to the thoughtful observer that a pendulum would afford the +means by which a time-keeper might be controlled, and accordingly +Galileo constructed for the first time a clock on this principle. The +immediate object sought in this apparatus was to provide a means of +aiding physicians in counting the pulses of their patients. + +The talents of Galileo having at length extorted due recognition from +the authorities, he was appointed, at the age of twenty-five, +Professor of Mathematics at the University of Pisa. Then came the +time when he felt himself strong enough to throw down the gauntlet to +the adherents of the old philosophy. As a necessary part of his +doctrine on the movement of bodies Aristotle had asserted that the +time occupied by a stone in falling depends upon its weight, so that +the heavier the stone the less time would it require to fall from a +certain height to the earth. It might have been thought that a +statement so easily confuted by the simplest experiments could never +have maintained its position in any accepted scheme of philosophy. +But Aristotle had said it, and to anyone who ventured to express a +doubt the ready sneer was forthcoming, "Do you think yourself a +cleverer man than Aristotle?" Galileo determined to demonstrate in +the most emphatic manner the absurdity of a doctrine which had for +centuries received the sanction of the learned. The summit of the +Leaning Tower of Pisa offered a highly dramatic site for the great +experiment. The youthful professor let fall from the overhanging top +a large heavy body and a small light body simultaneously. According +to Aristotle the large body ought to have reached the ground much +sooner than the small one, but such was found not to be the case. In +the sight of a large concourse of people the simple fact was +demonstrated that the two bodies fell side by side, and reached the +ground at the same time. Thus the first great step was taken in the +overthrow of that preposterous system of unquestioning adhesion to +dogma, which had impeded the development of the knowledge of nature +for nearly two thousand years. + +This revolutionary attitude towards the ancient beliefs was not +calculated to render Galileo's relations with the University +authorities harmonious. He had also the misfortune to make enemies +in other quarters. Don Giovanni de Medici, who was then the Governor +of the Port of Leghorn, had designed some contrivance by which he +proposed to pump out a dock. But Galileo showed up the absurdity of +this enterprise in such an aggressive manner that Don Giovanni took +mortal offence, nor was he mollified when the truths of Galileo's +criticisms were abundantly verified by the total failure of his +ridiculous invention. In various ways Galileo was made to feel his +position at Pisa so unpleasant that he was at length compelled to +abandon his chair in the University. The active exertions of his +friends, of whom Galileo was so fortunate as to have had throughout +his life an abundant supply, then secured his election to the +Professorship of Mathematics at Padua, whither he went in 1592. + +[PLATE: PORTRAIT OF GALILEO.] + +It was in this new position that Galileo entered on that marvellous +career of investigation which was destined to revolutionize science. +The zeal with which he discharged his professorial duties was indeed +of the most unremitting character. He speedily drew such crowds to +listen to his discourses on Natural Philosophy that his lecture-room +was filled to overflowing. He also received many private pupils in +his house for special instruction. Every moment that could be spared +from these labours was devoted to his private study and to his +incessant experiments. + +Like many another philosopher who has greatly extended our knowledge +of nature, Galileo had a remarkable aptitude for the invention of +instruments designed for philosophical research. To facilitate his +practical work, we find that in 1599 he had engaged a skilled workman +who was to live in his house, and thus be constantly at hand to try +the devices for ever springing from Galileo's fertile brain. Among +the earliest of his inventions appears to have been the thermometer, +which he constructed in 1602. No doubt this apparatus in its +primitive form differed in some respects from the contrivance we call +by the same name. Galileo at first employed water as the agent, by +the expansion of which the temperature was to be measured. He +afterwards saw the advantage of using spirits for the same purpose. +It was not until about half a century later that mercury came to be +recognised as the liquid most generally suitable for the thermometer. + +The time was now approaching when Galileo was to make that mighty +step in the advancement of human knowledge which followed on the +application of the telescope to astronomy. As to how his idea of +such an instrument originated, we had best let him tell us in his own +words. The passage is given in a letter which he writes to his +brother-in-law, Landucci. + +"I write now because I have a piece of news for you, though whether +you will be glad or sorry to hear it I cannot say; for I have now no +hope of returning to my own country, though the occurrence which has +destroyed that hope has had results both useful and honourable. You +must know, then, that two months ago there was a report spread here +that in Flanders some one had presented to Count Maurice of Nassau a +glass manufactured in such a way as to make distant objects appear +very near, so that a man at the distance of two miles could be +clearly seen. This seemed to me so marvellous that I began to think +about it. As it appeared to me to have a foundation in the Theory of +Perspective, I set about contriving how to make it, and at length I +found out, and have succeeded so well that the one I have made is far +superior to the Dutch telescope. It was reported in Venice that I +had made one, and a week since I was commanded to show it to his +Serenity and to all the members of the senate, to their infinite +amazement. Many gentlemen and senators, even the oldest, have +ascended at various times the highest bell-towers in Venice to spy +out ships at sea making sail for the mouth of the harbour, and have +seen them clearly, though without my telescope they would have been +invisible for more than two hours. The effect of this instrument is +to show an object at a distance of say fifty miles, as if it were but +five miles." + +The remarkable properties of the telescope at once commanded +universal attention among intellectual men. Galileo received +applications from several quarters for his new instrument, of which +it would seem that he manufactured a large number to be distributed +as gifts to various illustrious personages. + +But it was reserved for Galileo himself to make that application of +the instrument to the celestial bodies by which its peculiar powers +were to inaugurate the new era in astronomy. The first discovery +that was made in this direction appears to have been connected with +the number of the stars. Galileo saw to his amazement that through +his little tube he could count ten times as many stars in the sky as +his unaided eye could detect. Here was, indeed, a surprise. We are +now so familiar with the elementary facts of astronomy that it is not +always easy to realise how the heavens were interpreted by the +observers in those ages prior to the invention of the telescope. We +can hardly, indeed, suppose that Galileo, like the majority of those +who ever thought of such matters, entertained the erroneous belief +that the stars were on the surface of a sphere at equal distances +from the observer. No one would be likely to have retained his +belief in such a doctrine when he saw how the number of visible stars +could be increased tenfold by means of Galileo's telescope. It would +have been almost impossible to refuse to draw the inference that the +stars thus brought into view were still more remote objects which the +telescope was able to reveal, just in the same way as it showed +certain ships to the astonished Venetians, when at the time these +ships were beyond the reach of unaided vision. + +Galileo's celestial discoveries now succeeded each other rapidly. +That beautiful Milky Way, which has for ages been the object of +admiration to all lovers of nature, never disclosed its true nature +to the eye of man till the astronomer of Padua turned on it his magic +tube. The splendid zone of silvery light was then displayed as +star-dust scattered over the black background of the sky. It was +observed that though the individual stars were too small to be seen +severally without optical aid, yet such was their incredible number +that the celestial radiance produced that luminosity with which every +stargazer was so familiar. + +But the greatest discovery made by the telescope in these early days, +perhaps, indeed, the greatest discovery that the telescope has ever +accomplished, was the detection of the system of four satellites +revolving around the great planet Jupiter. This phenomenon was so +wholly unexpected by Galileo that, at first, he could hardly believe +his eyes. However, the reality of the existence of a system of four +moons attending the great planet was soon established beyond all +question. Numbers of great personages crowded to Galileo to see for +themselves this beautiful miniature representing the sun with its +system of revolving planets. + +Of course there were, as usual, a few incredulous people who refused +to believe the assertion that four more moving bodies had to be added +to the planetary system. They scoffed at the notion; they said the +satellites may have been in the telescope, but that they were not in +the sky. One sceptical philosopher is reported to have affirmed, +that even if he saw the moons of Jupiter himself he would not believe +in them, as their existence was contrary to the principles of +common-sense! + +There can be no doubt that a special significance attached to the new +discovery at this particular epoch in the history of science. It +must be remembered that in those days the doctrine of Copernicus, +declaring that the sun, and not the earth, was the centre of the +system, that the earth revolved on its axis once a day, and that it +described a mighty circle round the sun once a year, had only +recently been promulgated. This new view of the scheme of nature had +been encountered with the most furious opposition. It may possibly +have been that Galileo himself had not felt quite confident in the +soundness of the Copernican theory, prior to the discovery of the +satellites of Jupiter. But when a picture was there exhibited in +which a number of relatively small globes were shown to be revolving +around a single large globe in the centre, it seemed impossible not +to feel that the beautiful spectacle so displayed was an emblem of +the relations of the planets to the sun. It was thus made manifest +to Galileo that the Copernican theory of the planetary system must be +the true one. The momentous import of this opinion upon the future +welfare of the great philosopher will presently appear. + +It would seem that Galileo regarded his residence at Padua as a state +of undesirable exile from his beloved Tuscany. He had always a +yearning to go back to his own country and at last the desired +opportunity presented itself. For now that Galileo's fame had become +so great, the Grand Duke of Tuscany desired to have the philosopher +resident at Florence, in the belief that he would shed lustre on the +Duke's dominions. Overtures were accordingly made to Galileo, and +the consequence was that in 1616 we find him residing at Florence, +bearing the title of Mathematician and Philosopher to the Grand Duke. + +Two daughters, Polissena and Virginia, and one son, Vincenzo, had +been born to Galileo in Padua. It was the custom in those days that +as soon as the daughter of an Italian gentleman had grown up, her +future career was somewhat summarily decided. Either a husband was +to be forthwith sought out, or she was to enter the convent with the +object of taking the veil as a professed nun. It was arranged that +the two daughters of Galileo, while still scarcely more than +children, should both enter the Franciscan convent of St. Matthew, at +Arcetri. The elder daughter Polissena, took the name of Sister Maria +Celeste, while Virginia became Sister Arcangela. The latter seems to +have been always delicate and subject to prolonged melancholy, and +she is of but little account in the narrative of the life of +Galileo. But Sister Maria Celeste, though never leaving the convent, +managed to preserve a close intimacy with her beloved father. This +was maintained only partly by Galileo's visits, which were very +irregular and were, indeed, often suspended for long intervals. But +his letters to this daughter were evidently frequent and +affectionate, especially in the latter part of his life. Most +unfortunately, however, all his letters have been lost. There are +grounds for believing that they were deliberately destroyed when +Galileo was seized by the Inquisition, lest they should have been +used as evidence against him, or lest they should have compromised +the convent where they were received. But Sister Maria Celeste's +letters to her father have happily been preserved, and most touching +these letters are. We can hardly read them without thinking how the +sweet and gentle nun would have shrunk from the idea of their +publication. + +Her loving little notes to her "dearest lord and father," as she used +affectionately to call Galileo, were almost invariably accompanied by +some gift, trifling it may be, but always the best the poor nun had +to bestow. The tender grace of these endearing communications was +all the more precious to him from the fact that the rest of Galileo's +relatives were of quite a worthless description. He always +acknowledged the ties of his kindred in the most generous way, but +their follies and their vices, their selfishness and their +importunities, were an incessant source of annoyance to him, almost +to the last day of his life. + +On 19th December, 1625, Sister Maria Celeste writes:-- + +"I send two baked pears for these days of vigil. But as the greatest +treat of all, I send you a rose, which ought to please you extremely, +seeing what a rarity it is at this season; and with the rose you must +accept its thorns, which represent the bitter passion of our Lord, +whilst the green leaves represent the hope we may entertain that +through the same sacred passion we, having passed through the +darkness of the short winter of our mortal life, may attain to the +brightness and felicity of an eternal spring in heaven." + +When the wife and children of Galileo's shiftless brother came to +take up their abode in the philosopher's home, Sister Maria Celeste +feels glad to think that her father has now some one who, however +imperfectly, may fulfil the duty of looking after him. A graceful +note on Christmas Eve accompanies her little gifts. She hopes that-- + +"In these holy days the peace of God may rest on him and all the +house. The largest collar and sleeves I mean for Albertino, the +other two for the two younger boys, the little dog for baby, and the +cakes for everybody, except the spice-cakes, which are for you. +Accept the good-will which would readily do much more." + +The extraordinary forbearance with which Galileo continually placed +his time, his purse, and his influence at the service of those who +had repeatedly proved themselves utterly unworthy of his countenance, +is thus commented on by the good nun.-- + +"Now it seems to me, dearest lord and father, that your lordship is +walking in the right path, since you take hold of every occasion that +presents itself to shower continual benefits on those who only repay +you with ingratitude. This is an action which is all the more +virtuous and perfect as it is the more difficult." + +When the plague was raging in the neighbourhood, the loving +daughter's solicitude is thus shown:-- + +"I send you two pots of electuary as a preventive against the +plague. The one without the label consists of dried figs, walnuts, +rue, and salt, mixed together with honey. A piece of the size of a +walnut to be taken in the morning, fasting, with a little Greek +wine." + +The plague increasing still more, Sister Maria Celeste obtained with +much difficulty, a small quantity of a renowned liqueur, made by +Abbess Ursula, an exceptionally saintly nun. This she sends to her +father with the words:-- + +"I pray your lordship to have faith in this remedy. For if you have +so much faith in my poor miserable prayers, much more may you have in +those of such a holy person; indeed, through her merits you may feel +sure of escaping all danger from the plague." + +Whether Galileo took the remedy we do not know, but at all events +he escaped the plague. + +[PLATE: THE VILLA ARCETRI. +Galileo's residence, where Milton visited him.] + +From Galileo's new home in Florence the telescope was again directed +to the skies, and again did astounding discoveries reward the +astronomer's labours. The great success which he had met with in +studying Jupiter naturally led Galileo to look at Saturn. Here he +saw a spectacle which was sufficiently amazing, though he failed to +interpret it accurately. It was quite manifest that Saturn did not +exhibit a simple circular disc like Jupiter, or like Mars. It seemed +to Galileo as if the planet consisted of three bodies, a large globe +in the centre, and a smaller one on each side. The enigmatical +nature of the discovery led Galileo to announce it in an enigmatical +manner. He published a string of letters which, when duly +transposed, made up a sentence which affirmed that the planet Saturn +was threefold. Of course we now know that this remarkable appearance +of the planet was due to the two projecting portions of the ring. +With the feeble power of Galileo's telescope, these seemed merely +like small globes or appendages to the large central body. + +The last of Galileo's great astronomical discoveries related to the +libration of the moon. I think that the detection of this phenomenon +shows his acuteness of observation more remarkably than does any one +of his other achievements with the telescope. It is well known that +the moon constantly keeps the same face turned towards the earth. +When, however, careful measurements have been made with regard to the +spots and marks on the lunar surface, it is found that there is a +slight periodic variation which permits us to see now a little to the +east or to the west, now a little to the north or to the south of +the average lunar disc. + +But the circumstances which make the career of Galileo so especially +interesting from the biographer's point of view, are hardly so much +the triumphs that he won as the sufferings that he endured. The +sufferings and the triumphs were, however, closely connected, and it +is fitting that we should give due consideration to what was perhaps +the greatest drama in the history of science. + +On the appearance of the immortal work of Copernicus, in which it was +taught that the earth rotated on its axis, and that the earth, like +the other planets, revolved round the sun, orthodoxy stood aghast. +The Holy Roman Church submitted this treatise, which bore the name +"De Revolutionibus Orbium Coelestium," to the Congregation of the +Index. After due examination it was condemned as heretical in 1615. +Galileo was suspected, on no doubt excellent grounds, of entertaining +the objectionable views of Copernicus. He was accordingly privately +summoned before Cardinal Bellarmine on 26th February 1616, and duly +admonished that he was on no account to teach or to defend the +obnoxious doctrines. Galileo was much distressed by this +intimation. He felt it a serious matter to be deprived of the +privilege of discoursing with his friends about the Copernican +system, and of instructing his disciples in the principles of the +great theory of whose truth he was perfectly convinced. It pained +him, however, still more to think, devout Catholic as he was, that +such suspicions of his fervent allegiance to his Church should ever +have existed, as were implied by the words and monitions of Cardinal +Bellarmine. + +In 1616, Galileo had an interview with Pope Paul V., who received the +great astronomer very graciously, and walked up and down with him in +conversation for three-quarters of an hour. Galileo complained to +his Holiness of the attempts made by his enemies to embarrass him +with the authorities of the Church, but the Pope bade him be +comforted. His Holiness had himself no doubts of Galileo's +orthodoxy, and he assured him that the Congregation of the Index +should give Galileo no further trouble so long as Paul V. was in the +chair of St. Peter. + +On the death of Paul V. in 1623, Maffeo Barberini was elected Pope, +as Urban VIII. This new Pope, while a cardinal, had been an intimate +friend of Galileo's, and had indeed written Latin verses in praise of +the great astronomer and his discoveries. It was therefore not +unnatural for Galileo to think that the time had arrived when, with +the use of due circumspection, he might continue his studies and his +writings, without fear of incurring the displeasure of the Church. +Indeed, in 1624, one of Galileo's friends writing from Rome, urges +Galileo to visit the city again, and added that-- + +"Under the auspices of this most excellent, learned, and benignant +Pontiff, science must flourish. Your arrival will be welcome to his +Holiness. He asked me if you were coming, and when, and in short, he +seems to love and esteem you more than ever." + +The visit was duly paid, and when Galileo returned to Florence, the +Pope wrote a letter from which the following is an extract, +commanding the philosopher to the good offices of the young +Ferdinand, who had shortly before succeeded his father in the Grand +Duchy of Tuscany. + +"We find in Galileo not only literary distinction, but also the love +of piety, and he is also strong in those qualities by which the +pontifical good-will is easily obtained. And now, when he has been +brought to this city to congratulate us on our elevation, we have +very lovingly embraced him; nor can we suffer him to return to the +country whither your liberality calls him, without an ample provision +of pontifical love. And that you may know how dear he is to us, we +have willed to give him this honourable testimonial of virtue and +piety. And we further signify that every benefit which you shall +confer upon him, imitating or even surpassing your father's +liberality, will conduce to our gratification." + +The favourable reception which had been accorded to him by Pope Urban +VIII. seems to have led Galileo to expect that there might be some +corresponding change in the attitude of the Papal authorities on the +great question of the stability of the earth. He accordingly +proceeded with the preparation of the chief work of his life, "The +Dialogue of the two Systems." It was submitted for inspection by the +constituted authorities. The Pope himself thought that, if a few +conditions which he laid down were duly complied with, there could be +no objection to the publication of the work. In the first place, the +title of the book was to be so carefully worded as to show plainly +that the Copernican doctrine was merely to be regarded as an +hypothesis, and not as a scientific fact. Galileo was also +instructed to conclude the book with special arguments which had been +supplied by the Pope himself, and which appeared to his Holiness to +be quite conclusive against the new doctrine of Copernicus. + +Formal leave for the publication of the Dialogue was then given to +Galileo by the Inquisitor General, and it was accordingly sent to the +press. It might be thought that the anxieties of the astronomer +about his book would then have terminated. As a matter of fact, they +had not yet seriously begun. Riccardi, the Master of the Sacred +Palace, having suddenly had some further misgivings, sent to Galileo +for the manuscript while the work was at the printer's, in order that +the doctrine it implied might be once again examined. Apparently, +Riccardi had come to the conclusion that he had not given the matter +sufficient attention, when the authority to go to press had been +first and, perhaps, hastily given. Considerable delay in the issue +of the book was the result of these further deliberations. At last, +however, in June, 1632, Galileo's great work, "The Dialogue of the +two Systems," was produced for the instruction of the world, though +the occasion was fraught with ruin to the immortal author. + +[PLATE: FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.] + +The book, on its publication, was received and read with the greatest +avidity. But presently the Master of The Sacred Palace found reason +to regret that he had given his consent to its appearance. He +accordingly issued a peremptory order to sequestrate every copy in +Italy. This sudden change in the Papal attitude towards Galileo +formed the subject of a strong remonstrance addressed to the Roman +authorities by the Grand Duke of Tuscany. The Pope himself seemed to +have become impressed all at once with the belief that the work +contained matter of an heretical description. The general +interpretation put upon the book seems to have shown the authorities +that they had mistaken its true tendency, notwithstanding the fact +that it had been examined again and again by theologians deputed for +the duty. To the communication from the Grand Duke the Pope returned +answer, that he had decided to submit the book to a congregation of +"learned, grave, and saintly men," who would weigh every word in it. +The views of his Holiness personally on the subject were expressed in +his belief that the Dialogue contained the most perverse matter that +could come into a reader's hands. + +The Master of the Sacred Palace was greatly blamed by the authorities +for having given his sanction to its issue. He pleaded that the book +had not been printed in the precise terms of the original manuscript +which had been submitted to him. It was also alleged that Galileo +had not adhered to his promise of inserting properly the arguments +which the Pope himself had given in support of the old and orthodox +view. One of these had, no doubt, been introduced, but, so far from +mending Galileo's case, it had made matters really look worse for the +poor philosopher. The Pope's argument had been put into the mouth of +one of the characters in the Dialogue named "Simplicio." Galileo's +enemies maintained that by adopting such a method for the expression +of his Holiness's opinion, Galileo had intended to hold the Pope +himself up to ridicule. Galileo's friends maintained that nothing +could have been farther from his intention. It seems, however, +highly probable that the suspicions thus aroused had something to say +to the sudden change of front on the part of the Papal authorities. + +On 1st October, 1632, Galileo received an order to appear before the +Inquisition at Rome on the grave charge of heresy. Galileo, of +course, expressed his submission, but pleaded for a respite from +compliance with the summons, on the ground of his advanced age and +his failing health. The Pope was, however, inexorable; he said that +he had warned Galileo of his danger while he was still his friend. +The command could not be disobeyed. Galileo might perform the +journey as slowly as he pleased, but it was imperatively necessary +for him to set forth and at once. + +On 20th January, 1633, Galileo started on his weary journey to Rome, +in compliance with this peremptory summons. On 13th February he was +received as the guest of Niccolini, the Tuscan ambassador, who had +acted as his wise and ever-kind friend throughout the whole affair. +It seemed plain that the Holy Office were inclined to treat Galileo +with as much clemency and consideration as was consistent with the +determination that the case against him should be proceeded with to +the end. The Pope intimated that in consequence of his respect for +the Grand Duke of Tuscany he should permit Galileo to enjoy the +privilege, quite unprecedented for a prisoner charged with heresy, of +remaining as an inmate in the ambassador's house. He ought, +strictly, to have been placed in the dungeons of the Inquisition. +When the examination of the accused had actually commenced, Galileo +was confined, not, indeed, in the dungeons, but in comfortable rooms +at the Holy Office. + +By the judicious and conciliatory language of submission which +Niccolini had urged Galileo to use before the Inquisitors, they were +so far satisfied that they interceded with the Pope for his release. +During the remainder of the trial Galileo was accordingly permitted +to go back to the ambassador's, where he was most heartily welcomed. +Sister Maria Celeste, evidently thinking this meant that the whole +case was at an end, thus expresses herself:-- + +"The joy that your last dear letter brought me, and the having to +read it over and over to the nuns, who made quite a jubilee on +hearing its contents, put me into such an excited state that at last +I got a severe attack of headache." + +In his defence Galileo urged that he had already been acquitted in +1616 by Cardinal Bellarmine, when a charge of heresy was brought +against him, and he contended that anything he might now have done, +was no more than he had done on the preceding occasion, when the +orthodoxy of his doctrines received solemn confirmation. The +Inquisition seemed certainly inclined to clemency, but the Pope was +not satisfied. Galileo was accordingly summoned again on the 21st +June. He was to be threatened with torture if he did not forthwith +give satisfactory explanations as to the reasons which led him to +write the Dialogue. In this proceeding the Pope assured the Tuscan +ambassador that he was treating Galileo with the utmost consideration +possible in consequence of his esteem and regard for the Grand Duke, +whose servant Galileo was. It was, however, necessary that some +exemplary punishment be meted out to the astronomer, inasmuch as by +the publication of the Dialogue he had distinctly disobeyed the +injunction of silence laid upon him by the decree of 1616. Nor was +it admissible for Galileo to plead that his book had been sanctioned +by the Master of the Sacred College, to whose inspection it had been +again and again submitted. It was held, that if the Master of the +Sacred College had been unaware of the solemn warning the philosopher +had already received sixteen years previously, it was the duty of +Galileo to have drawn his attention to that fact. + +On the 22nd June, 1633, Galileo was led to the great hall of the +Inquisition, and compelled to kneel before the cardinals there +assembled and hear his sentence. In a long document, most +elaborately drawn up, it is definitely charged against Galileo that, +in publishing the Dialogue, he committed the essentially grave error +of treating the doctrine of the earth's motion as open to +discussion. Galileo knew, so the document affirmed, that the Church +had emphatically pronounced this notion to be contrary to Holy Writ, +and that for him to consider a doctrine so stigmatized as having any +shadow of probability in its favour was an act of disrespect to the +authority of the Church which could not be overlooked. It was also +charged against Galileo that in his Dialogue he has put the strongest +arguments into the mouth, not of those who supported the orthodox +doctrine, but of those who held the theory as to the earth's motion +which the Church had so deliberately condemned. + +After due consideration of the defence made by the prisoner, it was +thereupon decreed that he had rendered himself vehemently suspected +of heresy by the Holy Office, and in consequence had incurred all the +censures and penalties of the sacred canons, and other decrees +promulgated against such persons. The graver portion of these +punishments would be remitted, if Galileo would solemnly repudiate +the heresies referred to by an abjuration to be pronounced by him in +the terms laid down. + +At the same time it was necessary to mark, in some emphatic manner, +the serious offence which had been committed, so that it might serve +both as a punishment to Galileo and as a warning to others. It was +accordingly decreed that he should be condemned to imprisonment in +the Holy Office during the pleasure of the Papal authorities, and +that he should recite once a week for three years the seven +Penitential Psalms. + +Then followed that ever-memorable scene in the great hall of the +Inquisition, in which the aged and infirm Galileo, the inventor of +the telescope and the famous astronomer, knelt down to abjure before +the most eminent and reverend Lords Cardinal, Inquisitors General +throughout the Christian Republic against heretical depravity. With +his hands on the Gospels, Galileo was made to curse and detest the +false opinion that the sun was the centre of the universe and +immovable, and that the earth was not the centre of the same, and +that it moved. He swore that for the future he will never say nor +write such things as may bring him under suspicion, and that if he +does so he submits to all the pains and penalties of the sacred +canons. This abjuration was subsequently read in Florence before +Galileo's disciples, who had been specially summoned to attend. + +It has been noted that neither on the first occasion, in 1616, nor on +the second in 1633, did the reigning Pope sign the decrees concerning +Galileo. The contention has accordingly been made that Paul V. and +Urban VIII. are both alike vindicated from any technical +responsibility for the attitude of the Romish Church towards the +Copernican doctrines. The significance of this circumstance has been +commented on in connection with the doctrine of the infallibility of +the Pope. + +We can judge of the anxiety felt by Sister Maria Celeste about her +beloved father during these terrible trials. The wife of the +ambassador Niccolini, Galileo's steadfast friend, most kindly wrote +to give the nun whatever quieting assurances the case would permit. +There is a renewed flow of these touching epistles from the daughter +to her father. Thus she sends word-- + +"The news of your fresh trouble has pierced my soul with grief all +the more that it came quite unexpectedly." + +And again, on hearing that he had been permitted to leave Rome, +she writes-- + +"I wish I could describe the rejoicing of all the mothers and sisters +on hearing of your happy arrival at Siena. It was indeed most +extraordinary. On hearing the news the Mother Abbess and many of the +nuns ran to me, embracing me and weeping for joy and tenderness." + +The sentence of imprisonment was at first interpreted leniently by +the Pope. Galileo was allowed to reside in qualified durance in the +archbishop's house at Siena. Evidently the greatest pain that he +endured arose from the forced separation from that daughter, whom he +had at last learned to love with an affection almost comparable with +that she bore to him. She had often told him that she never had any +pleasure equal to that with which she rendered any service to her +father. To her joy, she discovers that she can relieve him from the +task of reciting the seven Penitential Psalms which had been imposed +as a Penance:-- + +"I began to do this a while ago," she writes, "and it gives me much +pleasure. First, because I am persuaded that prayer in obedience to +Holy Church must be efficacious; secondly, in order to save you the +trouble of remembering it. If I had been able to do more, most +willingly would I have entered a straiter prison than the one I live +in now, if by so doing I could have set you at liberty." + +[PLATE: CREST OF GALILEO'S FAMILY.] + +Sister Maria Celeste was gradually failing in health, but the great +privilege was accorded to her of being able once again to embrace her +beloved lord and master. Galileo had, in fact, been permitted to +return to his old home; but on the very day when he heard of his +daughter's death came the final decree directing him to remain in his +own house in perpetual solitude. + +Amid the advancing infirmities of age, the isolation from friends, +and the loss of his daughter, Galileo once again sought consolation +in hard work. He commenced his famous dialogue on Motion. Gradually, +however, his sight began to fail, and blindness was at last added to +his other troubles. On January 2nd, 1638, he writes to Diodati:-- + +"Alas, your dear friend and servant, Galileo, has been for the last +month perfectly blind, so that this heaven, this earth, this universe +which I by my marvellous discoveries and clear demonstrations have +enlarged a hundred thousand times beyond the belief of the wise men +of bygone ages, henceforward is for me shrunk into such a small space +as is filled by my own bodily sensations." + +But the end was approaching--the great philosopher, was attacked by +low fever, from which he died on the 8th January, 1643. + + + + +KEPLER. + + +While the illustrious astronomer, Tycho Brahe, lay on his death-bed, +he had an interview which must ever rank as one of the important +incidents in the history of science. The life of Tycho had been +passed, as we have seen, in the accumulation of vast stores of +careful observations of the positions of the heavenly bodies. It was +not given to him to deduce from his splendid work the results to +which they were destined to lead. It was reserved for another +astronomer to distil, so to speak, from the volumes in which Tycho's +figures were recorded, the great truths of the universe which those +figures contained. Tycho felt that his work required an interpreter, +and he recognised in the genius of a young man with whom he was +acquainted the agent by whom the world was to be taught some of the +great truths of nature. To the bedside of the great Danish +astronomer the youthful philosopher was summoned, and with his last +breath Tycho besought of him to spare no labour in the performance of +those calculations, by which alone the secrets of the movements of +the heavens could be revealed. The solemn trust thus imposed was +duly accepted, and the man who accepted it bore the immortal name of +Kepler. + +Kepler was born on the 27th December, 1571, at Weil, in the Duchy of +Wurtemberg. It would seem that the circumstances of his childhood +must have been singularly unhappy. His father, sprung from a +well-connected family, was but a shiftless and idle adventurer; nor +was the great astronomer much more fortunate in his other parent. His +mother was an ignorant and ill-tempered woman; indeed, the +ill-assorted union came to an abrupt end through the desertion of the +wife by her husband when their eldest son John, the hero of our +present sketch, was eighteen years old. The childhood of this lad, +destined for such fame, was still further embittered by the +circumstance that when he was four years old he had a severe attack +of small-pox. Not only was his eyesight permanently injured, but +even his constitution appears to have been much weakened by this +terrible malady. + +It seems, however, that the bodily infirmities of young John Kepler +were the immediate cause of his attention being directed to the +pursuit of knowledge. Had the boy been fitted like other boys for +ordinary manual work, there can be hardly any doubt that to manual +work his life must have been devoted. But, though his body was +feeble, he soon gave indications of the possession of considerable +mental power. It was accordingly thought that a suitable sphere for +his talents might be found in the Church which, in those days, was +almost the only profession that afforded an opening for an +intellectual career. We thus find that by the time John Kepler was +seventeen years old he had attained a sufficient standard of +knowledge to entitle him to admission on the foundation of the +University at Tubingen. + +In the course of his studies at this institution he seems to have +divided his attention equally between astronomy and divinity. It not +unfrequently happens that when a man has attained considerable +proficiency in two branches of knowledge he is not able to see very +clearly in which of the two pursuits his true vocation lies. His +friends and onlookers are often able to judge more wisely than he +himself can do as to which of the two lines it would be better for +him to pursue. This incapacity for perceiving the path in which +greatness awaited him, existed in the case of Kepler. Personally, he +inclined to enter the ministry, in which a promising career seemed +open to him. He yielded, however, to friends, who evidently knew him +better than he knew himself, and accepted in 1594, the important +Professorship of astronomy which had been offered to him in the +University of Gratz. + +It is difficult for us in these modern days to realise the somewhat +extraordinary duties which were expected from an astronomical +professor in the sixteenth century. He was, of course, required to +employ his knowledge of the heavens in the prediction of eclipses, +and of the movements of the heavenly bodies generally. This seems +reasonable enough; but what we are not prepared to accept is the +obligation which lay on the astronomers to predict the fates of +nations and the destinies of individuals. + +It must be remembered that it was the almost universal belief in +those days, that all the celestial spheres revolved in some +mysterious fashion around the earth, which appeared by far the most +important body in the universe. It was imagined that the sun, the +moon, and the stars indicated, in the vicissitudes of their +movements, the careers of nations and of individuals. Such being the +generally accepted notion, it seemed to follow that a professor who +was charged with the duty of expounding the movements of the heavenly +bodies must necessarily be looked to for the purpose of deciphering +the celestial decrees regarding the fate of man which the heavenly +luminaries were designed to announce. + +Kepler threw himself with characteristic ardour into even this +fantastic phase of the labours of the astronomical professor; he +diligently studied the rules of astrology, which the fancies of +antiquity had compiled. Believing sincerely as he did in the +connection between the aspect of the stars and the state of human +affairs, he even thought that he perceived, in the events of his own +life, a corroboration of the doctrine which affirmed the influence of +the planets upon the fate of individuals. + +[PLATE: KEPLER'S SYSTEM OF REGULAR SOLIDS.] + +But quite independently of astrology there seem to have been many +other delusions current among the philosophers of Kepler's time. It +is now almost incomprehensible how the ablest men of a few centuries +ago should have entertained such preposterous notions, as they did, +with respect to the system of the universe. As an instance of what +is here referred to, we may cite the extraordinary notion which, +under the designation of a discovery, first brought Kepler into +fame. Geometers had long known that there were five, but no more +than five, regular solid figures. There is, for instance, the cube +with six sides, which is, of course, the most familiar of these +solids. Besides the cube there are other figures of four, eight, +twelve, and twenty sides respectively. It also happened that there +were five planets, but no more than five, known to the ancients, +namely, Mercury, Venus, Mars, Jupiter, and Saturn. To Kepler's +lively imaginations this coincidence suggested the idea that the five +regular solids corresponded to the five planets, and a number of +fancied numerical relations were adduced on the subject. The +absurdity of this doctrine is obvious enough, especially when we +observe that, as is now well known, there are two large planets, and +a host of small planets, over and above the magical number of the +regular solids. In Kepler's time, however, this doctrine was so far +from being regarded as absurd, that its announcement was hailed as a +great intellectual triumph. Kepler was at once regarded with +favour. It seems, indeed, to have been the circumstance which +brought him into correspondence with Tycho Brahe. By its means also +he became known to Galileo. + +The career of a scientific professor in those early days appears +generally to have been marked by rather more striking vicissitudes +than usually befall a professor in a modern university. Kepler was a +Protestant, and as such he had been appointed to his professorship at +Gratz. A change, however, having taken place in the religious belief +entertained by the ruling powers of the University, the Protestant +professors were expelled. It seems that special influence having +been exerted in Kepler's case on account of his exceptional eminence, +he was recalled to Gratz and reinstated in the tenure of his chair. +But his pupils had vanished, so that the great astronomer was glad to +accept a post offered him by Tycho Brahe in the observatory which the +latter had recently established near Prague. + +On Tycho's death, which occurred soon after, an opening presented +itself which gave Kepler the opportunity his genius demanded. He was +appointed to succeed Tycho in the position of imperial mathematician. +But a far more important point, both for Kepler and for science, +was that to him was confided the use of Tycho's observations. It was, +indeed, by the discussion of Tycho's results that Kepler was enabled +to make the discoveries which form such an important part of +astronomical history. + +Kepler must also be remembered as one of the first great astronomers +who ever had the privilege of viewing celestial bodies through a +telescope. It was in 1610 that he first held in his hands one of +those little instruments which had been so recently applied to the +heavens by Galileo. It should, however, be borne in mind that the +epoch-making achievements of Kepler did not arise from any telescopic +observations that he made, or, indeed, that any one else made. They +were all elaborately deduced from Tycho's measurements of the +positions of the planets, obtained with his great instruments, which +were unprovided with telescopic assistance. + +To realise the tremendous advance which science received from +Kepler's great work, it is to be understood that all the astronomers +who laboured before him at the difficult subject of the celestial +motions, took it for granted that the planets must revolve in +circles. If it did not appear that a planet moved in a fixed circle, +then the ready answer was provided by Ptolemy's theory that the +circle in which the planet did move was itself in motion, so that its +centre described another circle. + +When Kepler had before him that wonderful series of observations of +the planet, Mars, which had been accumulated by the extraordinary +skill of Tycho, he proved, after much labour, that the movements of +the planet refused to be represented in a circular form. Nor would +it do to suppose that Mars revolved in one circle, the centre of +which revolved in another circle. On no such supposition could the +movements of the planets be made to tally with those which Tycho had +actually observed. This led to the astonishing discovery of the true +form of a planet's orbit. For the first time in the history of +astronomy the principle was laid down that the movement of a planet +could not be represented by a circle, nor even by combinations of +circles, but that it could be represented by an elliptic path. In +this path the sun is situated at one of those two points in the +ellipse which are known as its foci. + +[PLATE: KEPLER.] + +Very simple apparatus is needed for the drawing of one of those +ellipses which Kepler has shown to possess such astonishing +astronomical significance. Two pins are stuck through a sheet of +paper on a board, the point of a pencil is inserted in a loop of +string which passes over the pins, and as the pencil is moved round +in such a way as to keep the string stretched, that beautiful curve +known as the ellipse is delineated, while the positions of the pins +indicate the two foci of the curve. If the length of the loop of +string is unchanged then the nearer the pins are together, the +greater will be the resemblance between the ellipse and the circle, +whereas the more the pins are separated the more elongated does the +ellipse become. The orbit of a great planet is, in general, one of +those ellipses which approaches a nearly circular form. It +fortunately happens, however, that the orbit of Mars makes a wider +departure from the circular form than any of the other important +planets. It is, doubtless, to this circumstance that we must +attribute the astonishing success of Kepler in detecting the true +shape of a planetary orbit. Tycho's observations would not have been +sufficiently accurate to have exhibited the elliptic nature of a +planetary orbit which, like that of Venus, differed very little from +a circle. + +The more we ponder on this memorable achievement the more striking +will it appear. It must be remembered that in these days we know of +the physical necessity which requires that a planet shall revolve in +an ellipse and not in any other curve. But Kepler had no such +knowledge. Even to the last hour of his life he remained in +ignorance of the existence of any natural cause which ordained that +planets should follow those particular curves which geometers know so +well. Kepler's assignment of the ellipse as the true form of the +planetary orbit is to be regarded as a brilliant guess, the truth of +which Tycho's observations enabled him to verify. Kepler also +succeeded in pointing out the law according to which the velocity of +a planet at different points of its path could be accurately +specified. Here, again, we have to admire the sagacity with which +this marvellously acute astronomer guessed the deep truth of nature. +In this case also he was quite unprovided with any reason for +expecting from physical principles that such a law as he discovered +must be obeyed. It is quite true that Kepler had some slight +knowledge of the existence of what we now know as gravitation. He +had even enunciated the remarkable doctrine that the ebb and flow of +the tide must be attributed to the attraction of the moon on the +waters of the earth. He does not, however, appear to have had any +anticipation of those wonderful discoveries which Newton was destined +to make a little later, in which he demonstrated that the laws +detected by Kepler's marvellous acumen were necessary consequences of +the principle of universal gravitation. + +[PLATE: SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.] + +To appreciate the relations of Kepler and Tycho it is necessary to +note the very different way in which these illustrious astronomers +viewed the system of the heavens. It should be observed that +Copernicus had already expounded the true system, which located the +sun at the centre of the planetary system. But in the days of Tycho +Brahe this doctrine had not as yet commanded universal assent. In +fact, the great observer himself did not accept the new views of +Copernicus. It appeared to Tycho that the earth not only appeared to +be the centre of things celestial, but that it actually was the +centre. It is, indeed, not a little remarkable that a student of the +heavens so accurate as Tycho should have deliberately rejected the +Copernican doctrine in favour of the system which now seems so +preposterous. Throughout his great career, Tycho steadily observed +the places of the sun, the moon, and the planets, and as steadily +maintained that all those bodies revolved around the earth fixed in +the centre. Kepler, however, had the advantage of belonging to the +new school. He utilised the observations of Tycho in developing the +great Copernican theory whose teaching Tycho stoutly resisted. + +Perhaps a chapter in modern science may illustrate the intellectual +relation of these great men. The revolution produced by Copernicus +in the doctrine of the heavens has often been likened to the +revolution which the Darwinian theory produced in the views held by +biologists as to life on this earth. The Darwinian theory did not at +first command universal assent even among those naturalists whose +lives had been devoted with the greatest success to the study of +organisms. Take, for instance, that great naturalist, Professor +Owen, by whose labours vast extension has been given to our knowledge +of the fossil animals which dwelt on the earth in past ages. Now, +though Owens researches were intimately connected with the great +labours of Darwin, and afforded the latter material for his +epoch-making generalization, yet Owen deliberately refused to accept +the new doctrines. Like Tycho, he kept on rigidly accumulating his +facts under the influence of a set of ideas as to the origin of +living forms which are now universally admitted to be erroneous. If, +therefore, we liken Darwin to Copernicus, and Owen to Tycho, we may +liken the biologists of the present day to Kepler, who interpreted +the results of accurate observation upon sound theoretical +principles. + +In reading the works of Kepler in the light of our modern knowledge +we are often struck by the extent to which his perception of the +sublimest truths in nature was associated with the most extravagant +errors and absurdities. But, of course, it must be remembered that +he wrote in an age in which even the rudiments of science, as we now +understand it, were almost entirely unknown. + +It may well be doubted whether any joy experienced by mortals is more +genuine than that which rewards the successful searcher after natural +truths. Every science-worker, be his efforts ever so humble, will be +able to sympathise with the enthusiastic delight of Kepler when at +last, after years of toil, the glorious light broke forth, and that +which he considered to be the greatest of his astonishing laws first +dawned upon him. Kepler rightly judged that the number of days which +a planet required to perform its voyage round the sun must be +connected in some manner with the distance from the planet to the +sun; that is to say, with the radius of the planet's orbit, inasmuch +as we may for our present object regard the planet's orbit as +circular. + +Here, again, in his search for the unknown law, Kepler had no +accurate dynamical principles to guide his steps. Of course, we now +know not only what the connection between the planet's distance and +the planet's periodic time actually is, but we also know that it is a +necessary consequence of the law of universal gravitation. Kepler, +it is true, was not without certain surmises on the subject, but they +were of the most fanciful description. His notions of the planets, +accurate as they were in certain important respects, were mixed up +with vague ideas as to the properties of metals and the geometrical +relations of the regular solids. Above all, his reasoning was +penetrated by the supposed astrological influences of the stars and +their significant relation to human fate. Under the influence of +such a farrago of notions, Kepler resolved to make all sorts of +trials in his search for the connection between the distance of a +planet from the sun and the time in which the revolution of that +planet was accomplished. + +It was quite easily demonstrated that the greater the distance of the +planet from the sun the longer was the time required for its +journey. It might have been thought that the time would be directly +proportional to the distance. It was, however, easy to show that +this supposition did not agree with the fact. Finding that this +simple relation would not do, Kepler undertook a vast series of +calculations to find out the true method of expressing the +connection. At last, after many vain attempts, he found, to his +indescribable joy, that the square of the time in which a planet +revolves around the sun was proportional to the cube of the average +distance of the planet from that body. + +The extraordinary way in which Kepler's views on celestial matters +were associated with the wildest speculations, is well illustrated in +the work in which he propounded his splendid discovery just referred +to. The announcement of the law connecting the distances of the +planets from the sun with their periodic times, was then mixed up +with a preposterous conception about the properties of the different +planets. They were supposed to be associated with some profound +music of the spheres inaudible to human ears, and performed only for +the benefit of that being whose soul formed the animating spirit of +the sun. + +Kepler was also the first astronomer who ever ventured to predict the +occurrence of that remarkable phenomenon, the transit of a planet in +front of the sun's disc. He published, in 1629, a notice to the +curious in things celestial, in which he announced that both of the +planets, Mercury and Venus, were to make a transit across the sun on +specified days in the winter of 1631. The transit of Mercury was +duly observed by Gassendi, and the transit of Venus also took place, +though, as we now know, the circumstances were such that it was not +possible for the phenomenon to be witnessed by any European +astronomer. + +In addition to Kepler's discoveries already mentioned, with which his +name will be for ever associated, his claim on the gratitude of +astronomers chiefly depends on the publication of his famous +Rudolphine tables. In this remarkable work means are provided for +finding the places of the planets with far greater accuracy than had +previously been attainable. + +Kepler, it must be always remembered, was not an astronomical +observer. It was his function to deal with the observations made by +Tycho, and, from close study and comparison of the results, to work +out the movements of the heavenly bodies. It was, in fact, Tycho who +provided as it were the raw material, while it was the genius of +Kepler which wrought that material into a beautiful and serviceable +form. For more than a century the Rudolphine tables were regarded as +a standard astronomical work. In these days we are accustomed to +find the movements of the heavenly bodies set forth with all +desirable exactitude in the NAUTICAL ALMANACK, and the similar +publication issued by foreign Governments. Let it be remembered that +it was Kepler who first imparted the proper impulse in this +direction. + +[PLATE: THE COMMEMORATION OF THE RUDOLPHINE TABLES.] + +When Kepler was twenty-six he married an heiress from Styria, who, +though only twenty-three years old, had already had some experience +in matrimony. Her first husband had died; and it was after her +second husband had divorced her that she received the addresses of +Kepler. It will not be surprising to hear that his domestic affairs +do not appear to have been particularly happy, and his wife died in +1611. Two years later, undeterred by the want of success in his +first venture, he sought a second partner, and he evidently +determined not to make a mistake this time. Indeed, the methodical +manner in which he made his choice of the lady to whom he should +propose has been duly set forth by him and preserved for our +edification. With some self-assurance he asserts that there were no +fewer than eleven spinsters desirous of sharing his joys and +sorrows. He has carefully estimated and recorded the merits and +demerits of each of these would-be brides. The result of his +deliberations was that he awarded himself to an orphan girl, +destitute even of a portion. Success attended his choice, and his +second marriage seems to have proved a much more suitable union than +his first. He had five children by the first wife and seven by the +second. + +The years of Kepler's middle life were sorely distracted by a trouble +which, though not uncommon in those days, is one which we find it +difficult to realise at the present time. His mother, Catherine +Kepler, had attained undesirable notoriety by the suspicion that she +was guilty of witchcraft. Years were spent in legal investigations, +and it was only after unceasing exertions on the part of the +astronomer for upwards of a twelve-month that he was finally able to +procure her acquittal and release from prison. + +It is interesting for us to note that at one time there was a +proposal that Kepler should forsake his native country and adopt +England as a home. It arose in this wise. The great man was +distressed throughout the greater part of his life by pecuniary +anxieties. Finding him in a strait of this description, the English +ambassador in Venice, Sir Henry Wotton, in the year 1620, besought +Kepler to come over to England, where he assured him that he would +obtain a favourable reception, and where, he was able to add, +Kepler's great scientific work was already highly esteemed. But his +efforts were unavailing; Kepler would not leave his own country. He +was then forty-nine years of age, and doubtless a home in a foreign +land, where people spoke a strange tongue, had not sufficient +attraction for him, even when accompanied with the substantial +inducements which the ambassador was able to offer. Had Kepler +accepted this invitation, he would, in transferring his home to +England, have anticipated the similar change which took place in the +career of another great astronomer two centuries later. It will be +remembered that Herschel, in his younger days, did transfer himself +to England, and thus gave to England the imperishable fame of +association with his triumphs. + +The publication of the Rudolphine tables of the celestial movements +entailed much expense. A considerable part of this was defrayed by +the Government at Venice but the balance occasioned no little trouble +and anxiety to Kepler. No doubt the authorities of those days were +even less willing to spend money on scientific matters than are the +Governments of more recent times. For several years the imperial +Treasury was importuned to relieve him from his anxieties. The +effects of so much worry, and of the long journeys which were +involved, at last broke down Kepler's health completely. As we have +already mentioned, he had never been strong from infancy, and he +finally succumbed to a fever in November, 1630, at the age of +fifty-nine. He was interred at St. Peter's Church at Ratisbon. + +Though Kepler had not those personal characteristics which have made +his great predecessor, Tycho Brahe, such a romantic figure, yet a +picturesque element in Kepler's character is not wanting. It was, +however, of an intellectual kind. His imagination, as well as his +reasoning faculties, always worked together. He was incessantly +prompted by the most extraordinary speculations. The great majority +of them were in a high degree wild and chimerical, but every now and +then one of his fancies struck right to the heart of nature, and an +immortal truth was brought to light. + +I remember visiting the observatory of one of our greatest modern +astronomers, and in a large desk he showed me a multitude of +photographs which he had attempted but which had not been successful, +and then he showed me the few and rare pictures which had succeeded, +and by which important truths had been revealed. With a felicity of +expression which I have often since thought of, he alluded to the +contents of the desk as the "chips." They were useless, but they +were necessary incidents in the truly successful work. So it is in +all great and good work. Even the most skilful man of science +pursues many a wrong scent. Time after time he goes off on some +track that plays him false. The greater the man's genius and +intellectual resource, the more numerous will be the ventures which +he makes, and the great majority of those ventures are certain to be +fruitless. They are in fact, the "chips." In Kepler's case the +chips were numerous enough. They were of the most extraordinary +variety and structure. But every now and then a sublime discovery +was made of such a character as to make us regard even the most +fantastic of Kepler's chips with the greatest veneration and respect. + + + +ISAAC NEWTON. + + +It was just a year after the death of Galileo, that an infant came +into the world who was christened Isaac Newton. Even the great fame +of Galileo himself must be relegated to a second place in comparison +with that of the philosopher who first expounded the true theory of +the universe. + +Isaac Newton was born on the 25th of December (old style), 1642, at +Woolsthorpe, in Lincolnshire, about a half-mile from Colsterworth, +and eight miles south of Grantham. His father, Mr. Isaac Newton, had +died a few months after his marriage to Harriet Ayscough, the +daughter of Mr. James Ayscough, of Market Overton, in Rutlandshire. +The little Isaac was at first so excessively frail and weakly that +his life was despaired of. The watchful mother, however, tended her +delicate child with such success that he seems to have thriven better +than might have been expected from the circumstances of his infancy, +and he ultimately acquired a frame strong enough to outlast the +ordinary span of human life. + +For three years they continued to live at Woolsthorpe, the widow's +means of livelihood being supplemented by the income from another +small estate at Sewstern, in a neighbouring part of Leicestershire. + +[PLATE: WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy.] + +In 1645, Mrs. Newton took as a second husband the Rev. Barnabas +Smith, and on moving to her new home, about a mile from Woolsthorpe, +she entrusted little Isaac to her mother, Mrs. Ayscough. In due +time we find that the boy was sent to the public school at Grantham, +the name of the master being Stokes. For the purpose of being near +his work, the embryo philosopher was boarded at the house of Mr. +Clark, an apothecary at Grantham. We learn from Newton himself that +at first he had a very low place in the class lists of the school, +and was by no means one of those model school-boys who find favour in +the eyes of the school-master by attention to Latin grammar. Isaac's +first incentive to diligent study seems to have been derived from the +circumstance that he was severely kicked by one of the boys who was +above him in the class. This indignity had the effect of stimulating +young Newton's activity to such an extent that he not only attained +the desired object of passing over the head of the boy who had +maltreated him, but continued to rise until he became the head of the +school. + +The play-hours of the great philosopher were devoted to pursuits very +different from those of most school-boys. His chief amusement was +found in making mechanical toys and various ingenious contrivances. +He watched day by day with great interest the workmen engaged in +constructing a windmill in the neighbourhood of the school, the +result of which was that the boy made a working model of the windmill +and of its machinery, which seems to have been much admired, as +indicating his aptitude for mechanics. We are told that Isaac also +indulged in somewhat higher flights of mechanical enterprise. He +constructed a carriage, the wheels of which were to be driven by the +hands of the occupant, while the first philosophical instrument he +made was a clock, which was actuated by water. He also devoted much +attention to the construction of paper kites, and his skill in this +respect was highly appreciated by his school-fellows. Like a true +philosopher, even at this stage he experimented on the best methods +of attaching the string, and on the proportions which the tail ought +to have. He also made lanthorns of paper to provide himself with +light as he walked to school in the dark winter mornings. + +The only love affair in Newton's life appears to have commenced while +he was still of tender years. The incidents are thus described in +Brewster's "Life of Newton," a work to which I am much indebted in +this chapter. + +"In the house where he lodged there were some female inmates, in +whose company he appears to have taken much pleasure. One of these, +a Miss Storey, sister to Dr. Storey, a physician at Buckminster, near +Colsterworth, was two or three years younger than Newton and to great +personal attractions she seems to have added more than the usual +allotment of female talent. The society of this young lady and her +companions was always preferred to that of his own school-fellows, +and it was one of his most agreeable occupations to construct for +them little tables and cupboards, and other utensils for holding +their dolls and their trinkets. He had lived nearly six years in the +same house with Miss Storey, and there is reason to believe that +their youthful friendship gradually rose to a higher passion; but the +smallness of her portion, and the inadequacy of his own fortune, +appear to have prevented the consummation of their happiness. Miss +Storey was afterwards twice married, and under the name of Mrs. +Vincent, Dr. Stukeley visited her at Grantham in 1727, at the age of +eighty-two, and obtained from her many particulars respecting the +early history of our author. Newton's esteem for her continued +unabated during his life. He regularly visited her when he went to +Lincolnshire, and never failed to relieve her from little pecuniary +difficulties which seem to have beset her family." + +The schoolboy at Grantham was only fourteen years of age when his +mother became a widow for the second time. She then returned to the +old family home at Woolsthorpe, bringing with her the three children +of her second marriage. Her means appear to have been somewhat +scanty, and it was consequently thought necessary to recall Isaac +from the school. His recently-born industry had been such that he +had already made good progress in his studies, and his mother hoped +that he would now lay aside his books, and those silent meditations +to which, even at this early age, he had become addicted. It was +expected that, instead of such pursuits, which were deemed quite +useless, the boy would enter busily into the duties of the farm and +the details of a country life. But before long it became manifest +that the study of nature and the pursuit of knowledge had such a +fascination for the youth that he could give little attention to +aught else. It was plain that he would make but an indifferent +farmer. He greatly preferred experimenting on his water-wheels to +looking after labourers, while he found that working at mathematics +behind a hedge was much more interesting than chaffering about the +price of bullocks in the market place. Fortunately for humanity his +mother, like a wise woman, determined to let her boy's genius have +the scope which it required. He was accordingly sent back to +Grantham school, with the object of being trained in the knowledge +which would fit him for entering the University of Cambridge. + +[PLATE: TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope.] + +It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen, +was enrolled as an undergraduate of Trinity College, Cambridge. +Little did those who sent him there dream that this boy was destined +to be the most illustrious student who ever entered the portals of +that great seat of learning. Little could the youth himself have +foreseen that the rooms near the gateway which he occupied would +acquire a celebrity from the fact that he dwelt in them, or that the +ante-chapel of his college was in good time to be adorned by that +noble statue, which is regarded as one of the chief art treasures of +Cambridge University, both on account of its intrinsic beauty and the +fact that it commemorates the fame of her most distinguished alumnus, +Isaac Newton, the immortal astronomer. Indeed, his advent at the +University seemed to have been by no means auspicious or brilliant. +His birth was, as we have seen, comparatively obscure, and though he +had already given indication of his capacity for reflecting on +philosophical matters, yet he seems to have been but ill-equipped +with the routine knowledge which youths are generally expected to +take with them to the Universities. + +From the outset of his college career, Newton's attention seems to +have been mainly directed to mathematics. Here he began to give +evidence of that marvellous insight into the deep secrets of nature +which more than a century later led so dispassionate a judge as +Laplace to pronounce Newton's immortal work as pre-eminent above all +the productions of the human intellect. But though Newton was one of +the very greatest mathematicians that ever lived, he was never a +mathematician for the mere sake of mathematics. He employed his +mathematics as an instrument for discovering the laws of nature. His +industry and genius soon brought him under the notice of the +University authorities. It is stated in the University records that +he obtained a Scholarship in 1664. Two years later we find that +Newton, as well as many residents in the University, had to leave +Cambridge temporarily on account of the breaking out of the plague. +The philosopher retired for a season to his old home at Woolsthorpe, +and there he remained until he was appointed a Fellow of Trinity +College, Cambridge, in 1667. From this time onwards, Newton's +reputation as a mathematician and as a natural philosopher steadily +advanced, so that in 1669, while still but twenty-seven years of age, +he was appointed to the distinguished position of Lucasian Professor +of Mathematics at Cambridge. Here he found the opportunity to +continue and develop that marvellous career of discovery which formed +his life's work. + +The earliest of Newton's great achievements in natural philosophy was +his detection of the composite character of light. That a beam of +ordinary sunlight is, in fact, a mixture of a very great number of +different-coloured lights, is a doctrine now familiar to every one +who has the slightest education in physical science. We must, +however, remember that this discovery was really a tremendous advance +in knowledge at the time when Newton announced it. + +[PLATE: DIAGRAM OF A SUNBEAM.] + +We here give the little diagram originally drawn by Newton, to +explain the experiment by which he first learned the composition of +light. A sunbeam is admitted into a darkened room through an +opening, H, in a shutter. This beam when not interfered with will +travel in a straight line to the screen, and there reproduce a bright +spot of the same shape as the hole in the shutter. If, however, a +prism of glass, A B C, be introduced so that the beam traverse it, +then it will be seen at once that the light is deflected from its +original track. There is, however, a further and most important +change which takes place. The spot of light is not alone removed to +another part of the screen, but it becomes spread out into a long +band beautifully coloured, and exhibiting the hues of the rainbow. At +the top are the violet rays, and then in descending order we have the +indigo, blue, green, yellow, orange, and red. + +The circumstance in this phenomenon which appears to have +particularly arrested Newton's attention, was the elongation which +the luminous spot underwent in consequence of its passage through the +prism. When the prism was absent the spot was nearly circular, but +when the prism was introduced the spot was about five times as long +as it was broad. To ascertain the explanation of this was the first +problem to be solved. It seemed natural to suppose that it might be +due to the thickness of the glass in the prism which the light +traversed, or to the angle of incidence at which the light fell upon +the prism. He found, however, upon careful trial, that the phenomenon +could not be thus accounted for. It was not until after much patient +labour that the true explanation dawned upon him. He discovered that +though the beam of white light looks so pure and so simple, yet in +reality it is composed of differently coloured lights blended +together. These are, of course, indistinguishable in the compound +beam, but they are separated or disentangled, so to speak, by the +action of the prism. The rays at the blue end of the spectrum are +more powerfully deflected by the action of the glass than are the +rays at the red end. Thus, the rays variously coloured red, orange, +yellow, green, blue, indigo, violet, are each conducted to a +different part of the screen. In this way the prism has the effect +of exhibiting the constitution of the composite beam of light. + +To us this now seems quite obvious, but Newton did not adopt it +hastily. With characteristic caution he verified the explanation by +many different experiments, all of which confirmed his discovery. One +of these may be mentioned. He made a hole in the screen at that part +on which the violet rays fell. Thus a violet ray was allowed to pass +through, all the rest of the light being intercepted, and on this +beam so isolated he was able to try further experiments. For +instance, when he interposed another prism in its path, he found, as +he expected, that it was again deflected, and he measured the amount +of the deflection. Again he tried the same experiment with one of +the red rays from the opposite end of the coloured band. He allowed +it to pass through the same aperture in the screen, and he tested the +amount by which the second prism was capable of producing deflection. +He thus found, as he had expected to find, that the second prism was +more efficacious in bending the violet rays than in bending the red +rays. Thus he confirmed the fact that the various hues of the +rainbow were each bent by a prism to a different extent, violet being +acted upon the most, and red the least. + +[PLATE: ISAAC NEWTON.] + +Not only did Newton decompose a white beam into its constituent +colours, but conversely by interposing a second prism with its angle +turned upwards, he reunited the different colours, and thus +reproduced the original beam of white light. In several other ways +also he illustrated his famous proposition, which then seemed so +startling, that white light was the result of a mixture of all hues +of the rainbow. By combining painters' colours in the right +proportion he did not indeed succeed in producing a mixture which +would ordinarily be called white, but he obtained a grey pigment. +Some of this he put on the floor of his room for comparison with a +piece of white paper. He allowed a beam of bright sunlight to fall +upon the paper and the mixed colours side by side, and a friend he +called in for his opinion pronounced that under these circumstances +the mixed colours looked the whiter of the two. + +By repeated demonstrations Newton thus established his great +discovery of the composite character of light. He at once perceived +that his researches had an important bearing upon the principles +involved in the construction of a telescope. Those who employed the +telescope for looking at the stars, had been long aware of the +imperfections which prevented all the various rays from being +conducted to the same focus. But this imperfection had hitherto been +erroneously accounted for. It had been supposed that the reason why +success had not been attained in the construction of a refracting +telescope was due to the fact that the object glass, made as it then +was of a single piece, had not been properly shaped. Mathematicians +had abundantly demonstrated that a single lens, if properly figured, +must conduct all rays of light to the same focus, provided all rays +experienced equal refraction in passing through the glass. Until +Newton's discovery of the composition of white light, it had been +taken for granted that the several rays in a white beam were equally +refrangible. No doubt if this had been the case, a perfect telescope +could have been produced by properly shaping the object glass. But +when Newton had demonstrated that light was by no means so simple as +had been supposed, it became obvious that a satisfactory refracting +telescope was an impossibility when only a single object lens was +employed, however carefully that lens might have been wrought. Such +an objective might, no doubt, be made to conduct any one group of +rays of a particular shade to the same focus, but the rays of other +colours in the beam of white light must necessarily travel somewhat +astray. In this way Newton accounted for a great part of the +difficulties which had hitherto beset the attempts to construct a +perfect refracting telescope. + +We now know how these difficulties can be, to a great extent, +overcome, by employing for the objective a composite lens made of two +pieces of glass possessing different qualities. To these achromatic +object glasses, as they are called, the great development of +astronomical knowledge, since Newton's time, is due. But it must be +remarked that, although the theoretical possibility of constructing +an achromatic lens was investigated by Newton, he certainly came to +the conclusion that the difficulty could not be removed by employing +a composite objective, with two different kinds of glass. In this +his marvellous sagacity in the interpretation of nature seems for +once to have deserted him. We can, however, hardly regret that +Newton failed to discover the achromatic objective, when we observe +that it was in consequence of his deeming an achromatic objective to +be impossible that he was led to the invention of the reflecting +telescope. Finding, as he believed, that the defects of the +telescope could not be remedied by any application of the principle +of refraction he was led to look in quite a different direction for +the improvement of the tool on which the advancement of astronomy +depended. The REFRACTION of light depended as he had found, upon the +colour of the light. The laws of REFLECTION were, however, quite +independent of the colour. Whether rays be red or green, blue or +yellow, they are all reflected in precisely the same manner from a +mirror. Accordingly, Newton perceived that if he could construct a +telescope the action of which depended upon reflection, instead of +upon refraction, the difficulty which had hitherto proved an +insuperable obstacle to the improvement of the instrument would be +evaded. + +[PLATE: SIR ISAAC NEWTON'S LITTLE REFLECTOR.] + +For this purpose Newton fashioned a concave mirror from a mixture of +copper and tin, a combination which gives a surface with almost the +lustre of silver. When the light of a star fell upon the surface, an +image of the star was produced in the focus of this mirror, and then +this image was examined by a magnifying eye-piece. Such is the +principle of the famous reflecting telescope which bears the name of +Newton. The little reflector which he constructed, represented in +the adjoining figure, is still preserved as one of the treasures of +the Royal Society. The telescope tube had the very modest dimension +of one inch in diameter. It was, however, the precursor of a whole +series of magnificent instruments, each outstripping the other in +magnitude, until at last the culminating point was attained in 1845, +by the construction of Lord Rosse's mammoth reflector of six feet in +aperture. + +Newton's discovery of the composition of light led to an embittered +controversy, which caused no little worry to the great Philosopher. +Some of those who attacked him enjoyed considerable and, it must be +admitted, even well-merited repute in the ranks of science. They +alleged, however, that the elongation of the coloured band which +Newton had noticed was due to this, to that, or to the other--to +anything, in fact, rather than to the true cause which Newton +assigned. With characteristic patience and love of truth, Newton +steadily replied to each such attack. He showed most completely how +utterly his adversaries had misunderstood the subject, and how slight +indeed was their acquaintance with the natural phenomenon in +question. In reply to each point raised, he was ever able to cite +fresh experiments and adduce fresh illustrations, until at last his +opponents retired worsted from the combat. + +It has been often a matter for surprise that Newton, throughout his +whole career, should have taken so much trouble to expose the errors +of those who attacked his views. He used even to do this when it +plainly appeared that his adversaries did not understand the subject +they were discussing. A philosopher might have said, "I know I am +right, and whether others think I am right or not may be a matter of +concern to them, but it is certainly not a matter about which I need +trouble. If after having been told the truth they elect to remain in +error, so much the worse for them; my time can be better employed +than in seeking to put such people right." This, however, was not +Newton's method. He spent much valuable time in overthrowing +objections which were often of a very futile description. Indeed, he +suffered a great deal of annoyance from the persistency, and in some +cases one might almost say from the rancour, of the attacks which +were made upon him. Unfortunately for himself, he did not possess +that capacity for sublime indifference to what men may say, which is +often the happy possession of intellects greatly inferior to his. + +The subject of optics still continuing to engross Newton's attention, +he followed up his researches into the structure of the sunbeam by +many other valuable investigations in connection with light. Every +one has noticed the beautiful colours manifested in a soap-bubble. +Here was a subject which not unnaturally attracted the attention of +one who had expounded the colours of the spectrum with such success. +He perceived that similar hues were produced by other thin plates of +transparent material besides soap-bubbles, and his ingenuity was +sufficient to devise a method by which the thicknesses of the +different films could be measured. We can hardly, indeed, say that a +like success attended his interpretation of these phenomena to that +which had been so conspicuous in his explanation of the spectrum. It +implies no disparagement to the sublime genius of Newton to admit +that the doctrines he put forth as to the causes of the colours in +the soap-bubbles can be no longer accepted. We must remember that +Newton was a pioneer in accounting for the physical properties of +light. The facts that he established are indeed unquestionable, but +the explanations which he was led to offer of some of them are seen +to be untenable in the fuller light of our present knowledge. + +[PLATE: SIR ISAAC NEWTON'S SUN-DIAL.] + +Had Newton done nothing beyond making his wonderful discoveries in +light, his fame would have gone down to posterity as one of the +greatest of Nature's interpreters. But it was reserved for him to +accomplish other discoveries, which have pushed even his analysis of +the sunbeam into the background; it is he who has expounded the +system of the universe by the discovery of the law of universal +gravitation. + +The age had indeed become ripe for the advent of the genius of +Newton. Kepler had discovered with marvellous penetration the laws +which govern the movements of the planets around the sun, and in +various directions it had been more or less vaguely felt that the +explanation of Kepler's laws, as well as of many other phenomena, +must be sought for in connection with the attractive power of +matter. But the mathematical analysis which alone could deal with +this subject was wanting; it had to be created by Newton. + +At Woolsthorpe, in the year 1666, Newton's attention appears to have +been concentrated upon the subject of gravitation. Whatever may be +the extent to which we accept the more or less mythical story as to +how the fall of an apple first directed the attention of the +philosopher to the fact that gravitation must extend through space, +it seems, at all events, certain that this is an excellent +illustration of the line of reasoning which he followed. He argued +in this way. The earth attracts the apple; it would do so, no matter +how high might be the tree from which that apple fell. It would then +seem to follow that this power which resides in the earth by which it +can draw all external bodies towards it, extends far beyond the +altitude of the loftiest tree. Indeed, we seem to find no limit to +it. At the greatest elevation that has ever been attained, the +attractive power of the earth is still exerted, and though we cannot +by any actual experiment reach an altitude more than a few miles +above the earth, yet it is certain that gravitation would extend to +elevations far greater. It is plain, thought Newton, that an apple +let fall from a point a hundred miles above this earth's surface, +would be drawn down by the attraction, and would continually gather +fresh velocity until it reached the ground. From a hundred miles it +was natural to think of what would happen at a thousand miles, or at +hundreds of thousands of miles. No doubt the intensity of the +attraction becomes weaker with every increase in the altitude, but +that action would still exist to some extent, however lofty might be +the elevation which had been attained. + +It then occurred to Newton, that though the moon is at a distance of +two hundred and forty thousand miles from the earth, yet the +attractive power of the earth must extend to the moon. He was +particularly led to think of the moon in this connection, not only +because the moon is so much closer to the earth than are any other +celestial bodies, but also because the moon is an appendage to the +earth, always revolving around it. The moon is certainly attracted +to the earth, and yet the moon does not fall down; how is this to be +accounted for? The explanation was to be found in the character of +the moon's present motion. If the moon were left for a moment at +rest, there can be no doubt that the attraction of the earth would +begin to draw the lunar globe in towards our globe. In the course of +a few days our satellite would come down on the earth with a most +fearful crash. This catastrophe is averted by the circumstance that +the moon has a movement of revolution around the earth. Newton was +able to calculate from the known laws of mechanics, which he had +himself been mainly instrumental in discovering, what the attractive +power of the earth must be, so that the moon shall move precisely as +we find it to move. It then appeared that the very power which makes +an apple fall at the earth's surface is the power which guides the +moon in its orbit. + +[PLATE: SIR ISAAC NEWTON'S TELESCOPE.] + +Once this step had been taken, the whole scheme of the universe might +almost be said to have become unrolled before the eye of the +philosopher. It was natural to suppose that just as the moon was +guided and controlled by the attraction of the earth, so the earth +itself, in the course of its great annual progress, should be guided +and controlled by the supreme attractive power of the sun. If this +were so with regard to the earth, then it would be impossible to +doubt that in the same way the movements of the planets could be +explained to be consequences of solar attraction. + +It was at this point that the great laws of Kepler became especially +significant. Kepler had shown how each of the planets revolves in an +ellipse around the sun, which is situated on one of the foci. This +discovery had been arrived at from the interpretation of +observations. Kepler had himself assigned no reason why the orbit of +a planet should be an ellipse rather than any other of the infinite +number of closed curves which might be traced around the sun. Kepler +had also shown, and here again he was merely deducing the results +from observation, that when the movements of two planets were +compared together, the squares of the periodic times in which each +planet revolved were proportional to the cubes of their mean +distances from the sun. This also Kepler merely knew to be true as a +fact, he gave no demonstration of the reason why nature should have +adopted this particular relation between the distance and the +periodic time rather than any other. Then, too, there was the law by +which Kepler with unparalleled ingenuity, explained the way in which +the velocity of a planet varies at the different points of its track, +when he showed how the line drawn from the sun to the planet +described equal areas around the sun in equal times. These were the +materials with which Newton set to work. He proposed to infer from +these the actual laws regulating the force by which the sun guides +the planets. Here it was that his sublime mathematical genius came +into play. Step by step Newton advanced until he had completely +accounted for all the phenomena. + +In the first place, he showed that as the planet describes equal +areas in equal times about the sun, the attractive force which the +sun exerts upon it must necessarily be directed in a straight line +towards the sun itself. He also demonstrated the converse truth, +that whatever be the nature of the force which emanated from a sun, +yet so long as that force was directed through the sun's centre, any +body which revolved around it must describe equal areas in equal +times, and this it must do, whatever be the actual character of the +law according to which the intensity of the force varies at different +parts of the planet's journey. Thus the first advance was taken in +the exposition of the scheme of the universe. + +The next step was to determine the law according to which the force +thus proved to reside in the sun varied with the distance of the +planet. Newton presently showed by a most superb effort of +mathematical reasoning, that if the orbit of a planet were an ellipse +and if the sun were at one of the foci of that ellipse, the intensity +of the attractive force must vary inversely as the square of the +planet's distance. If the law had any other expression than the +inverse square of the distance, then the orbit which the planet must +follow would not be an ellipse; or if an ellipse, it would, at all +events, not have the sun in the focus. Hence he was able to show +from Kepler's laws alone that the force which guided the planets was +an attractive power emanating from the sun, and that the intensity of +this attractive power varied with the inverse square of the distance +between the two bodies. + +These circumstances being known, it was then easy to show that the +last of Kepler's three laws must necessarily follow. If a number of +planets were revolving around the sun, then supposing the materials +of all these bodies were equally affected by gravitation, it can be +demonstrated that the square of the periodic time in which each +planet completes its orbit is proportional to the cube of the +greatest diameter in that orbit. + +[PLATE: SIR ISAAC NEWTON'S ASTROLABE.] + +These superb discoveries were, however, but the starting point from +which Newton entered on a series of researches, which disclosed many +of the profoundest secrets in the scheme of celestial mechanics. His +natural insight showed that not only large masses like the sun and +the earth, and the moon, attract each other, but that every particle +in the universe must attract every other particle with a force which +varies inversely as the square of the distance between them. If, for +example, the two particles were placed twice as far apart, then the +intensity of the force which sought to bring them together would be +reduced to one-fourth. If two particles, originally ten miles +asunder, attracted each other with a certain force, then, when the +distance was reduced to one mile, the intensity of the attraction +between the two particles would be increased one-hundred-fold. This +fertile principle extends throughout the whole of nature. In some +cases, however, the calculation of its effect upon the actual +problems of nature would be hardly possible, were it not for another +discovery which Newton's genius enabled him to accomplish. In the +case of two globes like the earth and the moon, we must remember that +we are dealing not with particles, but with two mighty masses of +matter, each composed of innumerable myriads of particles. Every +particle in the earth does attract every particle in the moon with a +force which varies inversely as the square of their distance. The +calculation of such attractions is rendered feasible by the following +principle. Assuming that the earth consists of materials +symmetrically arranged in shells of varying densities, we may then, +in calculating its attraction, regard the whole mass of the globe as +concentrated at its centre. Similarly we may regard the moon as +concentrated at the centre of its mass. In this way the earth and +the moon can both be regarded as particles in point of size, each +particle having, however, the entire mass of the corresponding +globe. The attraction of one particle for another is a much more +simple matter to investigate than the attraction of the myriad +different points of the earth upon the myriad different points of the +moon. + +Many great discoveries now crowded in upon Newton. He first of all +gave the explanation of the tides that ebb and flow around our +shores. Even in the earliest times the tides had been shown to be +related to the moon. It was noticed that the tides were specially +high during full moon or during new moon, and this circumstance +obviously pointed to the existence of some connection between the +moon and these movements of the water, though as to what that +connection was no one had any accurate conception until Newton +announced the law of gravitation. Newton then made it plain that the +rise and fall of the water was simply a consequence of the attractive +power which the moon exerted upon the oceans lying upon our globe. He +showed also that to a certain extent the sun produces tides, and he +was able to explain how it was that when the sun and the moon both +conspire, the joint result was to produce especially high tides, +which we call "spring tides"; whereas if the solar tide was low, +while the lunar tide was high, then we had the phenomenon of "neap" +tides. + +But perhaps the most signal of Newton's applications of the law of +gravitation was connected with certain irregularities in the +movements of the moon. In its orbit round the earth our satellite +is, of course, mainly guided by the great attraction of our globe. If +there were no other body in the universe, then the centre of the moon +must necessarily perform an ellipse, and the centre of the earth +would lie in the focus of that ellipse. Nature, however, does not +allow the movements to possess the simplicity which this arrangement +would imply, for the sun is present as a source of disturbance. The +sun attracts the moon, and the sun attracts the earth, but in +different degrees, and the consequence is that the moon's movement +with regard to the earth is seriously affected by the influence of +the sun. It is not allowed to move exactly in an ellipse, nor is the +earth exactly in the focus. How great was Newton's achievement in +the solution of this problem will be appreciated if we realise that +he not only had to determine from the law of gravitation the nature +of the disturbance of the moon, but he had actually to construct the +mathematical tools by which alone such calculations could be +effected. + +The resources of Newton's genius seemed, however, to prove equal to +almost any demand that could be made upon it. He saw that each +planet must disturb the other, and in that way he was able to render +a satisfactory account of certain phenomena which had perplexed all +preceding investigators. That mysterious movement by which the pole +of the earth sways about among the stars had been long an unsolved +enigma, but Newton showed that the moon grasped with its attraction +the protuberant mass at the equatorial regions of the earth, and thus +tilted the earth's axis in a way that accounted for the phenomenon +which had been known but had never been explained for two thousand +years. All these discoveries were brought together in that immortal +work, Newton's "Principia." + +Down to the year 1687, when the "Principia" was published, Newton had +lived the life of a recluse at Cambridge, being entirely occupied +with those transcendent researches to which we have referred. But in +that year he issued from his seclusion under circumstances of +considerable historical interest. King James the Second attempted an +invasion of the rights and privileges of the University of Cambridge +by issuing a command that Father Francis, a Benedictine monk, should +be received as a Master of Arts in the University, without having taken +the oaths of allegiance and supremacy. With this arbitrary command +the University sternly refused to comply. The Vice-Chancellor was +accordingly summoned to answer for an act of contempt to the authority +of the Crown. Newton was one of nine delegates who were chosen to +defend the independence of the University before the High Court. +They were able to show that Charles the Second, who had issued a +MANDAMUS under somewhat similar circumstances, had been induced after +due consideration to withdraw it. This argument appeared satisfactory, +and the University gained their case. Newton's next step in public +life was his election, by a narrow majority, as member for the +University, and during the years 1688 and 1689, he seems to have +attended to his parliamentary duties with considerable regularity. + +An incident which happened in 1692 was apparently the cause of +considerable disturbance in Newton's equanimity, if not in his +health. He had gone to early morning chapel, leaving a lighted +candle among his papers on his desk. Tradition asserts that his +little dog "Diamond" upset the candle; at all events, when Newton +came back he found that many valuable papers had perished in a +conflagration. The loss of these manuscripts seems to have had a +serious effect. Indeed, it has been asserted that the distress +reduced Newton to a state of mental aberration for a considerable +time. This has, apparently, not been confirmed, but there is no +doubt that he experienced considerable disquiet, for in writing on +September 13th, 1693, to Mr. Pepys, he says: + +"I am extremely troubled at the embroilment I am in, and have +neither ate nor slept well this twelve-month, nor have my former +consistency of mind." + +Notwithstanding the fame which Newton had achieved, by the +publication of his, "Principia," and by all his researches, the State +had not as yet taken any notice whatever of the most illustrious man +of science that this or any other country has ever produced. Many of +his friends had exerted themselves to procure him some permanent +appointment, but without success. It happened, however, that Mr. +Montagu, who had sat with Newton in Parliament, was appointed +Chancellor of the Exchequer in 1694. Ambitious of distinction in his +new office, Mr. Montagu addressed himself to the improvement of the +current coin, which was then in a very debased condition. It +fortunately happened that an opportunity occurred of appointing a new +official in the Mint; and Mr. Montagu on the 19th of March, 1695, +wrote to offer Mr. Newton the position of warden. The salary was to +be five or six hundred a year, and the business would not require +more attendance than Newton could spare. The Lucasian professor +accepted this post, and forthwith entered upon his new duties. + +The knowledge of physics which Newton had acquired by his experiments +was of much use in connection with his duties at the Mint. He +carried out the re-coinage with great skill in the course of two +years, and as a reward for his exertions, he was appointed, in 1697, +to the Mastership of the Mint, with a salary between 1,200 Pounds and +1,500 Pounds per annum. In 1701, his duties at the Mint being so +engrossing, he resigned his Lucasian professorship at Cambridge, and +at the same time he had to surrender his fellowship at Trinity +College. This closed his connection with the University of +Cambridge. It should, however, be remarked that at a somewhat +earlier stage in his career he was very nearly being appointed to an +office which might have enabled the University to retain the great +philosopher within its precincts. Some of his friends had almost +succeeded in securing his nomination to the Provostship of King's +College, Cambridge; the appointment, however, fell through, inasmuch +as the statute could not be evaded, which required that the Provost +of King's College should be in holy orders. + +In those days it was often the custom for illustrious mathematicians, +when they had discovered a solution for some new and striking +problem, to publish that problem as a challenge to the world, while +withholding their own solution. A famous instance of this is found +in what is known as the Brachistochrone problem, which was solved by +John Bernouilli. The nature of this problem may be mentioned. It +was to find the shape of the curve along which a body would slide +down from one point (A) to another point (B) in the shortest time. It +might at first be thought that the straight line from A to B, as it +is undoubtedly the shortest distance between the points, would also +be the path of quickest descent; but this is not so. There is a +curved line, down which a bead, let us say, would run on a smooth +wire from A to B in a shorter time than the same bead would require +to run down the straight wire. Bernouilli's problem was to find out +what that curve must be. Newton solved it correctly; he showed that +the curve was a part of what is termed a cycloid--that is to say, a +curve like that which is described by a point on the rim of a +carriage-wheel as the wheel runs along the ground. Such was Newton's +geometrical insight that he was able to transmit a solution of the +problem on the day after he had received it, to the President of the +Royal Society. + +In 1703 Newton, whose world wide fame was now established, was +elected President of the Royal Society. Year after year he was +re-elected to this distinguished position, and his tenure, which +lasted twenty-five years, only terminated with his life. It was in +discharge of his duties as President of the Royal Society that Newton +was brought into contact with Prince George of Denmark. In April, +1705, the Queen paid a visit to Cambridge as the guest of Dr. +Bentley, the then Master of Trinity, and in a court held at Trinity +Lodge on April 15th, 1705, the honour of knighthood was conferred +upon the discoverer of gravitation. + +Urged by illustrious friends, who sought the promotion of knowledge, +Newton gave his attention to the publication of a new edition of the +"Principia." His duties at the Mint, however, added to the supreme +duty of carrying on his original investigations, left him but little +time for the more ordinary task of the revision. He was accordingly +induced to associate with himself for this purpose a distinguished +young mathematician, Roger Coates, a Fellow of Trinity College, +Cambridge, who had recently been appointed Plumian Professor of +Astronomy. On July 27th, 1713, Newton, by this time a favourite at +Court, waited on the Queen, and presented her with a copy of the new +edition of the "Principia." + +Throughout his life Newton appears to have been greatly interested in +theological studies, and he specially devoted his attention to the +subject of prophecy. He left behind him a manuscript on the +prophecies of Daniel and the Apocalypse of St. John, and he also +wrote various theological papers. Many other subjects had from time +to time engaged his attention. He studied the laws of heat; he +experimented in pursuit of the dreams of the Alchymist; while the +philosopher who had revealed the mechanism of the heavens found +occasional relaxation in trying to interpret hieroglyphics. In the +last few years of his life he bore with fortitude a painful ailment, +and on Monday, March 20th, 1727, he died in the eighty-fifth year of +his age. On Tuesday, March 28th, he was buried in Westminster Abbey. + +Though Newton lived long enough to receive the honour that his +astonishing discoveries so justly merited, and though for many years +of his life his renown was much greater than that of any of his +contemporaries, yet it is not too much to say that, in the years +which have since elapsed, Newton's fame has been ever steadily +advancing, so that it never stood higher than it does at this moment. + +We hardly know whether to admire more the sublime discoveries at +which he arrived, or the extraordinary character of the intellectual +processes by which those discoveries were reached. Viewed from +either standpoint, Newton's "Principia" is incomparably the greatest +work on science that has ever yet been produced. + +[PLATE: SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.] + + + + +FLAMSTEED. + + +Among the manuscripts preserved at Greenwich Observatory are certain +documents in which Flamsteed gives an account of his own life. We +may commence our sketch by quoting the following passage from this +autobiography:--"To keep myself from idleness, and to recreate +myself, I have intended here to give some account of my life, in my +youth, before the actions thereof, and the providences of God +therein, be too far passed out of my memory; and to observe the +accidents of all my years, and inclinations of my mind, that +whosoever may light upon these papers may see I was not so wholly +taken up, either with my father's business or my mathematics, but +that I both admitted and found time for other as weighty +considerations." + +The chief interest which attaches to the name of Flamsteed arises +from the fact that he was the first of the illustrious series of +Astronomers Royal who have presided over Greenwich Observatory. In +that capacity Flamsteed was able to render material assistance to +Newton by providing him with the observations which his lunar theory +required. + +John Flamsteed was born at Denby, in Derbyshire, on the 19th of +August, 1646. His mother died when he was three years old, and the +second wife, whom his father took three years later, only lived until +Flamsteed was eight, there being also two younger sisters. In his +boyhood the future astronomer tells us that he was very fond of those +romances which affect boy's imagination, but as he writes, "At twelve +years of age I left all the wild ones and betook myself to read the +better sort of them, which, though they were not probable, yet +carried no seeming impossibility in the picturing." By the time +Flamsteed was fifteen years old he had embarked in still more serious +work, for he had read Plutarch's "Lives," Tacitus' "Roman History," +and many other books of a similar description. In 1661 he became ill +with some serious rheumatic affection, which obliged him to be +withdrawn from school. It was then for the first time that he +received the rudiments of a scientific education. He had, however, +attained his sixteenth year before he made any progress in +arithmetic. He tells us how his father taught him "the doctrine of +fractions," and "the golden rule of three"--lessons which he seemed +to have learned easily and quickly. One of the books which he read +at this time directed his attention to astronomical instruments, and +he was thus led to construct for himself a quadrant, by which he +could take some simple astronomical observations. He further +calculated a table to give the sun's altitudes at different hours, +and thus displayed those tastes for practical astronomy which he +lived to develop so greatly. It appears that these scientific +studies were discountenanced by his father, who designed that his son +should follow a business career. Flamsteed's natural inclination, +however, forced him to prosecute astronomical work, notwithstanding +the impediments that lay in his path. Unfortunately, his +constitutional delicacy seems to have increased, and he had just +completed his eighteenth year, "when," to use his own words, "the +winter came on and thrust me again into the chimney, whence the heat +and the dryness of the preceding summer had happily once before +withdrawn me. But, it not being a fit season for physic, it was +thought fit to let me alone this winter, and try the skill of another +physician on me in the spring." + +It appears that at this time a quack named Valentine Greatrackes, was +reputed to have effected most astonishing cures in Ireland merely by +the stroke of his hands, without the application of any medicine +whatever. Flamsteed's father, despairing of any remedy for his son +from the legitimate branch of the profession, despatched him to +Ireland on August 26th, 1665, he being then, as recorded with +astronomical accuracy, "nineteen years, six days, and eleven hours +old." The young astronomer, accompanied by a friend, arrived on a +Tuesday at Liverpool but the wind not being favourable, they remained +there till the following Friday, when a shift of the wind to the east +took place. They embarked accordingly on a vessel called the SUPPLY +at noon, and on Saturday night came in sight of Dublin. Ere they +could land, however, they were nearly being wrecked on Lambay +Island. This peril safely passed, there was a long delay for +quarantine before they were at last allowed on shore. On Thursday, +September 6th, they set out from Dublin, where they had been +sojourning at the "Ship" Hotel, in Dame Street, towards Assaune, +where Greatrackes received his patients. + +[PLATE: FLAMSTEED'S HOUSE.] + +Flamsteed gives an interesting account of his travels in Ireland. +They dined at Naas on the first day, and on September 8th they +reached Carlow, a town which is described as one of the fairest they +saw on their journey. By Sunday morning, September 10th, having lost +their way several times, they reached Castleton, called commonly Four +Mile Waters. Flamsteed inquired of the host in the inn where they +might find a church, but was told that the minister lived twelve +miles away, and that they had no sermon except when he came to +receive his tithes once a year, and a woman added that "they had +plenty enough of everything necessary except the word of God." The +travellers accordingly went on to Cappoquin, which lies up the river +Blackwater, on the road to Lismore, eight miles from Youghal. Thence +they immediately started on foot to Assaune. About a mile from +Cappoquin, and entering into the house of Mr. Greatrackes, they saw +him touch several patients, "whereof some were nearly cured, others +were on the mending hand, and some on whom his strokes had no +effect." Flamsteed was touched by the famous quack on the afternoon +of September 11th, but we are hardly surprised to hear his remark +that "he found not his disease to stir." Next morning the astronomer +came again to see Mr. Greatrackes, who had "a kind of majestical yet +affable presence, and a composed carriage." Even after the third +touching had been submitted to, no benefit seems to have been +derived. We must, however record, to the credit of Mr. Greatrackes, +that he refused to accept any payment from Flamsteed, because he was +a stranger. + +Finding it useless to protract his stay any longer, Flamsteed and his +friend set out on their return to Dublin. In the course of his +journey he seems to have been much impressed with Clonmel, which he +describes as an "exceedingly pleasantly seated town." But in those +days a journey to Ireland was so serious an enterprise that when +Flamsteed did arrive safely back at Derby after an absence of a +month, he adds, "For God's providence in this journey, His name be +praised, Amen." + +As to the expected benefits to his health from the expedition we may +quote his own words: "In the winter following I was indifferent +hearty, and my disease was not so violent as it used to be at that +time formerly. But whether through God's mercy I received this +through Mr. Greatrackes' touch, or my journey and vomiting at sea, I +am uncertain; but, by some circumstances, I guess that I received a +benefit from both." + +It is evident that by this time Flamsteed's interest in all +astronomical matters had greatly increased. He studied the +construction of sun-dials, he formed a catalogue of seventy of the +fixed stars, with their places on the heavens, and he computed the +circumstances of the solar eclipse which was to happen on June 22nd, +1666. It is interesting to note that even in those days the +doctrines of the astrologers still found a considerable degree of +credence, and Flamsteed spent a good deal of his time in astrological +studies and computations. He investigated the methods of casting a +nativity, but a suspicion, or, indeed, rather more than a suspicion, +seems to have crossed his mind as to the value of these astrological +predictions, for he says in fine, "I found astrology to give +generally strong conjectural hints, not perfect declarations." + +All this time, however, the future Astronomer Royal was steadily +advancing in astronomical inquiries of a recondite nature. He had +investigated the obliquity of the ecliptic with extreme care, so far +as the circumstances of astronomical observation would at that time +permit. He had also sought to discover the sun's distance from the +earth in so far as it could be obtained by determining when the moon +was exactly half illuminated, and he had measured, with much +accuracy, the length of the tropical year. It will thus be seen +that, even at the age of twenty, Flamsteed had made marked progress, +considering how much his time had been interfered with by ill-health. + +Other branches of astronomy began also to claim his attention. We +learn that in 1669 and 1670 he compared the planets Jupiter and Mars +with certain fixed stars near which they passed. His instrumental +means, though very imperfect, were still sufficient to enable him to +measure the intervals on the celestial sphere between the planets and +the stars. As the places of the stars were known, Flamsteed was thus +able to obtain the places of the planets. This is substantially the +way in which astronomers of the present day still proceed when they +desire to determine the places of the planets, inasmuch as, directly +or indirectly those places are always obtained relatively to the +fixed stars. By his observations at this early period, Flamsteed +was, it is true, not able to obtain any great degree of accuracy; he +succeeded, however, in proving that the tables by which the places of +the planets were ordinarily given were not to be relied upon. + +[PLATE: FLAMSTEED.] + +Flamsteed's labours in astronomy and in the allied branches of +science were now becoming generally known, and he gradually came to +correspond with many distinguished men of learning. One of the first +occasions which brought the talents of the young astronomer into fame +was the publication of some calculations concerning certain +astronomical phenomena which were to happen in the year 1670. In the +monthly revolution of the moon its disc passes over those stars which +lie along its track. The disappearance of a star by the +interposition of the moon is called an "occultation." Owing to the +fact that our satellite is comparatively near us, the position which +the moon appears to occupy on the heavens varies from different parts +of the earth, it consequently happens that a star which would be +occulted to an observer in one locality, would often not be occulted +to an observer who was situated elsewhere. Even when an occultation +is visible from both places, the times at which the star disappears +from view will, generally speaking, be different. Much calculation +is therefore necessary to decide the circumstances under which the +occultations of stars may be visible from any particular station. +Having a taste for such computations, Flamsteed calculated the +occultations which were to happen in the year 1670, it being the case +that several remarkable stars would be passed over by the moon during +this year. Of course at the present time, we find such information +duly set forth in the NAUTICAL ALMANAC, but a couple of centuries ago +there was no such source of astronomical knowledge as is now to be +found in that invaluable publication, which astronomers and +navigators know so well. Flamsteed accordingly sent the results of +his work to the President of the Royal Society. The paper which +contained them was received very favourably, and at once brought +Flamsteed into notice among the most eminent members of that +illustrious body, one of whom, Mr. Collins, became through life his +faithful friend and constant correspondent. Flamsteed's father was +naturally gratified with the remarkable notice which his son was +receiving from the great and learned; accordingly he desired him to +go to London, that he might make the personal acquaintance of those +scientific friends whom he had only known by correspondence +previously. Flamsteed was indeed glad to avail himself of this +opportunity. Thus he became acquainted with Dr. Barrow, and +especially with Newton, who was then Lucasian Professor of +Mathematics at Cambridge. It seems to have been in consequence of +this visit to London that Flamsteed entered himself as a member of +Jesus College, Cambridge. We have but little information as to his +University career, but at all events he took his degree of M.A. on +June 5th, 1674. + +Up to this time it would seem that Flamsteed had been engaged, to a +certain extent, in the business carried on by his father. It is true +that he does not give any explicit details, yet there are frequent +references to journeys which he had to take on business matters. But +the time now approached when Flamsteed was to start on an independent +career, and it appears that he took his degree in Cambridge with the +object of entering into holy orders, so that he might settle in a +small living near Derby, which was in the gift of a friend of his +father, and would be at the disposal of the young astronomer. This +scheme was, however, not carried out, but Flamsteed does not tell us +why it failed, his only remark being, that "the good providence of +God that had designed me for another station ordered it otherwise." + +Sir Jonas Moore, one of the influential friends whom Flamsteed's +talents had attracted, seems to have procured for him the position of +king's astronomer, with a salary of 100 pounds per annum. A larger +salary appears to have been designed at first for this office, which +was now being newly created, but as Flamsteed was resolved on taking +holy orders, a lesser salary was in his case deemed sufficient. The +building of the observatory, in which the first Astronomer Royal was +to be installed, seems to have been brought about, or, at all events, +its progress was accelerated, in a somewhat curious manner. + +A Frenchman, named Le Sieur de S. Pierre, came over to London to +promulgate a scheme for discovering longitudes, then a question of +much importance. He brought with him introductions to distinguished +people, and his mission attracted a great deal of attention. The +proposals which he made came under Flamsteed's notice, who pointed +out that the Frenchman's projects were quite inapplicable in the +present state of astronomical science, inasmuch as the places of the +stars were not known with the degree of accuracy which would be +necessary if such methods were to be rendered available. Flamsteed +then goes on to say:--"I heard no more of the Frenchman after this; +but was told that my letters had been shown King Charles. He was +startled at the assertion of the fixed stars' places being false in +the catalogue, and said, with some vehemence, he must have them anew +observed, examined, and corrected, for the use of his seamen." + +The first question to be settled was the site for the new +observatory. Hyde Park and Chelsea College were both mentioned as +suitable localities, but, at Sir Christopher Wren's suggestion, +Greenwich Hill was finally resolved upon. The king made a grant of +five hundred pounds of money. He gave bricks from Tilbury Fort, +while materials, in the shape of wood, iron, and lead, were available +from a gatehouse demolished in the Tower. The king also promised +whatever further material aid might be shown to be necessary. The +first stone of the Royal Observatory was laid on August 10th, 1675, +and within a few years a building was erected in which the art of +modern practical astronomy was to be created. Flamsteed strove with +extraordinary diligence, and in spite of many difficulties, to obtain +a due provision of astronomical instruments, and to arrange for the +carrying on of his observations. Notwithstanding the king's +promises, the astronomer was, however, but scantily provided with +means, and he had no assistants to help him in his work. It follows +that all the observations, as well as the reductions, and, indeed, +all the incidental work of the observatory, had to be carried on by +himself alone. Flamsteed, as we have seen, had, however, many +staunch friends. Sir Jonas Moore in particular at all times rendered +him most valuable assistance, and encouraged him by the warm sympathy +and keen interest which he showed in astronomy. The work of the +first Astronomer Royal was frequently interrupted by recurrent +attacks of the complaints to which we have already referred. He says +himself that "his distempers stick so close that that he cannot +remove them," and he lost much time by prostration from headaches, as +well as from more serious affections. + +The year 1678 found him in the full tide of work in his observatory. +He was specially engaged on the problem of the earth's motion, which +he sought to derive from observations of the sun and of Venus. But +this, as well as many other astronomical researches which he +undertook, were only subsidiary to that which he made the main task +of his life, namely, the formation of a catalogue of fixed stars. At +the time when Flamsteed commenced his career, the only available +catalogue of fixed stars was that of Tycho Brahe. This work had been +published at the commencement of the seventeenth century, and it +contained about a thousand stars. The positions assigned to these +stars, though obtained with wonderful skill, considering the many +difficulties under which Tycho laboured, were quite inaccurate when +judged by our modern standards. Tycho's instruments were necessarily +most rudely divided, and he had, of course, no telescopes to aid him. +Consequently it was merely by a process of sighting that he could +obtain the places of the stars. It must further be remembered that +Tycho had no clocks, and no micrometers. He had, indeed, but little +correct knowledge of the motions of the heavenly bodies to guide +him. To determine the longitudes of a few principal stars he +conceived the ingenious idea of measuring by day the position of +Venus with respect to the sun, an observation which the exceptional +brightness of this planet rendered possible without telescopic aid, +and then by night he observed the position of Venus with regard to +the stars. + +It has been well remarked by Mr. Baily, in his introduction to the +"British Catalogue of Stars," that "Flamsteed's observations, by a +fortunate combination of circumstances, commenced a new and a +brilliant era. It happened that, at that period, the powerful mind +of Newton was directed to this subject; a friendly intercourse then +existed between these two distinguished characters; and thus the +first observations that could lay any claim to accuracy were at once +brought in aid of those deep researches in which our illustrious +geometer was then engaged. The first edition of the 'Principia' +bears testimony to the assistance afforded by Flamsteed to Newton in +these inquiries; although the former considers that the +acknowledgment is not so ample as it ought to have been." + +Although Flamsteed's observations can hardly be said to possess the +accuracy of those made in more recent times, when instruments so much +superior to his have been available, yet they possess an interest of +a special kind from their very antiquity. This circumstance renders +them of particular importance to the astronomer, inasmuch as they are +calculated to throw light on the proper motions of the stars. +Flamsteed's work may, indeed, be regarded as the origin of all +subsequent catalogues, and the nomenclature which he adopted, though +in some respects it can hardly be said to be very defensible, is, +nevertheless, that which has been adopted by all subsequent +astronomers. There were also a great many errors, as might be +expected in a work of such extent, composed almost entirely of +numerical detail. Many of these errors have been corrected by Baily +himself, the assiduous editor of "Flamsteed's Life and Works," for +Flamsteed was so harassed from various causes in the latter part of +his life, and was so subject to infirmities all through his career, +that he was unable to revise his computations with the care that +would have been necessary. Indeed, he observed many additional stars +which he never included in the British Catalogue. It is, as Baily +well remarks, "rather a matter of astonishment that he accomplished +so much, considering his slender means, his weak frame, and the +vexations which he constantly experienced." + +Flamsteed had the misfortune, in the latter part of his life, to +become estranged from his most eminent scientific contemporaries. He +had supplied Newton with places of the moon, at the urgent +solicitation of the author of the "Principia," in order that the +lunar theory should be carefully compared with observation. But +Flamsteed appears to have thought that in Newton's further request +for similar information, he appeared to be demanding as a right that +which Flamsteed considered he was only called upon to render as a +favour. A considerable dispute grew out of this matter, and there +are many letters and documents, bearing on the difficulties which +subsequently arose, that are not, perhaps, very creditable to either +party. + +Notwithstanding his feeble constitution, Flamsteed lived to the age +of seventy-three, his death occurring on the last day of the year +1719. + + + + +HALLEY. + + +Isaac Newton was just fourteen years of age when the birth of Edmund +Halley, who was destined in after years to become Newton's warmly +attached friend, and one of his most illustrious scientific +contemporaries, took place. There can be little doubt that the fame +as an astronomer which Halley ultimately acquired, great as it +certainly was, would have been even greater still had it not been +somewhat impaired by the misfortune that he had to shine in the same +sky as that which was illumined by the unparalleled genius of Newton. + +Edmund Halley was born at Haggerston, in the Parish of St. Leonard's, +Shoreditch, on October 29th, 1656. His father, who bore the same +name as his famous son, was a soap-boiler in Winchester Street, +London, and he had conducted his business with such success that he +accumulated an ample fortune. I have been unable to obtain more than +a very few particulars with respect to the early life of the future +astronomer. It would, however, appear that from boyhood he showed +considerable aptitude for the acquisition of various kinds of +learning, and he also had some capacity for mechanical invention. +Halley seems to have received a sound education at St. Paul's School, +then under the care of Dr. Thomas Gale. + +Here, the young philosopher rapidly distanced his competitors in the +various branches of ordinary school instruction. His superiority +was, however, most conspicuous in mathematical studies, and, as a +natural development of such tastes, we learn that by the time he had +left school he had already made good progress in astronomy. At the +age of seventeen he was entered as a commoner at Queen's College, +Oxford, and the reputation that he brought with him to the University +may be inferred from the remark of the writer of "Athenae +Oxonienses," that Halley came to Oxford "with skill in Latin, Greek, +and Hebrew, and such a knowledge of geometry as to make a complete +dial." Though his studies were thus of a somewhat multifarious +nature, yet it is plain that from the first his most favourite +pursuit was astronomy. His earliest efforts in practical observation +were connected with an eclipse which he observed from his father's +house in Winchester Street. It also appears that he had studied +theoretical branches of astronomy so far as to be conversant with the +application of mathematics to somewhat abstruse problems. + +Up to the time of Kepler, philosophers had assumed almost as an axiom +that the heavenly bodies must revolve in circles and that the motion +of the planet around the orbit which it described must be uniform. We +have already seen how that great philosopher, after very persevering +labour, succeeded in proving that the orbits of the planets were not +circles, but that they were ellipses of small eccentricity. Kepler +was, however, unable to shake himself free from the prevailing notion +that the angular motion of the planet ought to be of a uniform +character around some point. He had indeed proved that the motion +round the focus of the ellipse in which the sun lies is not of this +description. One of his most important discoveries even related to +the fact that at some parts of its orbit a planet swings around the +sun with greater angular velocity than at others. But it so happens +that in elliptic tracks which differ but little from circles, as is +the case with all the more important planetary orbits, the motion +round the empty focus of the ellipse is very nearly uniform. It +seemed natural to assume, that this was exactly the case, in which +event each of the two foci of the ellipse would have had a special +significance in relation to the movement of the planet. The youthful +Halley, however, demonstrated that so far as the empty focus was +concerned, the movement of the planet around it, though so nearly +uniform, was still not exactly so, and at the age of nineteen, he +published a treatise on the subject which at once placed him in the +foremost rank amongst theoretical astronomers. + +But Halley had no intention of being merely an astronomer with his +pen. He longed to engage in the practical work of observing. He saw +that the progress of exact astronomy must depend largely on the +determination of the positions of the stars with all attainable +accuracy. He accordingly determined to take up this branch of work, +which had been so successfully initiated by Tycho Brahe. + +At the present day, astronomers of the great national observatories +are assiduously engaged in the determination of the places of the +stars. A knowledge of the exact positions of these bodies is indeed +of the most fundamental importance, not alone for the purposes of +scientific astronomy, but also for navigation and for extensive +operations of surveying in which accuracy is desired. The fact that +Halley determined to concentrate himself on this work shows clearly +the scientific acumen of the young astronomer. + +Halley, however, found that Hevelius, at Dantzig, and Flamsteed, the +Astronomer Royal at Greenwich, were both engaged on work of this +character. He accordingly determined to direct his energies in a way +that he thought would be more useful to science. He resigned to the +two astronomers whom I have named the investigation of the stars in +the northern hemisphere, and he sought for himself a field hitherto +almost entirely unworked. He determined to go to the southern +hemisphere, there to measure and survey those stars which were +invisible in Europe, so that his work should supplement the labours +of the northern astronomers, and that the joint result of his labours +and of theirs might be a complete survey of the most important stars +on the surface of the heavens. + +In these days, after so many ardent students everywhere have devoted +themselves to the study of Nature, it seems difficult for a beginner +to find a virgin territory in which to commence his explorations. +Halley may, however, be said to have enjoyed the privilege of +commencing to work in a magnificent region, the contents of which +were previously almost entirely unknown. Indeed none of the stars +which were so situated as to have been invisible from Tycho Brahe's +observatory at Uraniborg, in Denmark, could be said to have been +properly observed. There was, no doubt, a rumour that a Dutchman had +observed southern stars from the island of Sumatra, and certain stars +were indicated in the southern heavens on a celestial globe. On +examination, however, Halley found that no reliance could be placed +on the results which had been obtained, so that practically the field +before him may be said to have been unworked. + +At the age of twenty, without having even waited to take that degree +at the university which the authorities would have been glad to +confer on so promising an undergraduate, this ardent student of +Nature sought his father's permission to go to the southern +hemisphere for the purpose of studying the stars which lie around the +southern pole. His father possessed the necessary means, and he had +likewise the sagacity to encourage the young astronomer. He was +indeed most anxious to make everything as easy as possible for so +hopeful a son. He provided him with an allowance of 300 pounds a +year, which was regarded as a very munificent provision in those +days. Halley was also furnished with letters of recommendation from +King Charles II., as well as from the directors of the East India +Company. He accordingly set sail with his instruments in the year +1676, in one of the East India Company's ships, for the island of St. +Helena, which he had selected as the scene of his labours. + +[PLATE: HALLEY.] + +After an uneventful voyage of three months, the astronomer landed on +St. Helena, with his sextant of five and a half feet radius, and a +telescope 24 feet long, and forthwith plunged with ardour into his +investigation of the southern skies. He met, however, with one very +considerable disappointment. The climate of this island had been +represented to him as most favourable for astronomical observation; +but instead of the pure blue skies he had been led to expect, he +found that they were almost always more or less clouded, and that +rain was frequent, so that his observations were very much +interrupted. On this account he only remained at St. Helena for a +single year, having, during that time, and in spite of many +difficulties, accomplished a piece of work which earned for him the +title of "our southern Tycho." Thus did Halley establish his fame as +an astronomer on the same lonely rock in mid-Atlantic, which nearly a +century and a-half later became the scene of Napoleon's imprisonment, +when his star, in which he believed so firmly, had irretrievably set. + +On his return to England, Halley prepared a map which showed the +result of his labours, and he presented it to the king, in 1677. +Like his great predecessor Tycho, Halley did not altogether disdain +the arts of the courtier, for he endeavoured to squeeze a new +constellation into the group around the southern pole which he styled +"The Royal Oak," adding a description to the effect that the +incidents of which "The Royal Oak" was a symbol were of sufficient +importance to be inscribed on the surface of the heavens. + +There is reason to think that Charles II. duly appreciated the +scientific renown which one of his subjects had achieved, and it was +probably through the influence of the king that Halley was made a +Master of Arts at Oxford on November 18th, 1678. Special reference +was made on the occasion to his observations at St. Helena, as +evidence of unusual attainments in mathematics and astronomy. This +degree was no small honour to such a young man, who, as we have seen, +quitted his university before he had the opportunity of graduating in +the ordinary manner. + +On November 30th, in the same year, the astronomer received a further +distinction in being elected a Fellow of the Royal Society. From +this time forward he took a most active part in the affairs of the +Society, and the numerous papers which he read before it form a very +valuable part of that notable series of volumes known as the +"Philosophical Transactions." He was subsequently elected to the +important office of secretary to the Royal Society, and he discharged +the duties of his post until his appointment to Greenwich +necessitated his resignation. + +Within a year of Halley's election as a Fellow of the Royal Society, +he was chosen by the Society to represent them in a discussion which +had arisen with Hevelius. The nature of this discussion, or rather +the fact that any discussion should have been necessary, may seem +strange to modern astronomers, for the point is one on which it would +now seem impossible for there to be any difference of opinion. We +must, however, remember that the days of Halley were, comparatively +speaking, the days of infancy as regards the art of astronomical +observation, and issues that now seem obvious were often, in those +early times, the occasions of grave and anxious consideration. The +particular question on which Halley had to represent the Royal +Society may be simply stated. When Tycho Brahe made his memorable +investigations into the places of the stars, he had no telescopes to +help him. The famous instruments at Uraniborg were merely provided +with sights, by which the telescope was pointed to a star on the same +principle as a rifle is sighted for a target. Shortly after Tycho's +time, Galileo invented the telescope. Of course every one admitted +at once the extraordinary advantages which the telescope had to +offer, so far as the mere question of the visibility of objects was +concerned. But the bearing of Galileo's invention upon what we may +describe as the measuring part of astronomy was not so immediately +obvious. If a star be visible to the unaided eye, we can determine +its place by such instruments as those which Tycho used, in which no +telescope is employed. We can, however, also avail ourselves of an +instrument in which we view the star not directly but through the +intervention of the telescope. Can the place of the star be +determined more accurately by the latter method than it can when the +telescope is dispensed with? With our present knowledge, of course, +there is no doubt about the answer; every one conversant with +instruments knows that we can determine the place of a star far more +accurately with the telescope than is possible by any mere sighting +apparatus. In fact an observer would be as likely to make an error +of a minute with the sighting apparatus in Tycho's instrument, as he +would be to make an error of a second with the modern telescope, or, +to express the matter somewhat differently, we may say, speaking +quite generally, that the telescopic method of determining the places +of the stars does not lead to errors more than one-sixtieth part as +great as which are unavoidable when we make use of Tycho's method. + +But though this is so apparent to the modern astronomer, it was not +at all apparent in the days of Halley, and accordingly he was sent +off to discuss the question with the Continental astronomers. +Hevelius, as the representative of the older method, which Tycho had +employed with such success, maintained that an instrument could be +pointed more accurately at a star by the use of sights than by the +use of a telescope, and vigorously disputed the claims put forward by +those who believed that the latter method was the more suitable. On +May 14th, 1679, Halley started for Dantzig, and the energetic +character of the man may be judged from the fact that on the very +night of his arrival he commenced to make the necessary +observations. In those days astronomical telescopes had only +obtained a fractional part of the perfection possessed by the +instruments in our modern observatories, and therefore it may not be +surprising that the results of the trial were not immediately +conclusive. Halley appears to have devoted much time to the +investigation; indeed, he remained at Dantzig for more than a +twelve-month. On his return to England, he spoke highly of the skill +which Hevelius exhibited in the use of his antiquated methods, but +Halley was nevertheless too sagacious an observer to be shaken in his +preference for the telescopic method of observation. + +The next year we find our young astronomer starting for a Continental +tour, and we, who complain if the Channel passage lasts more than an +hour or two, may note Halley's remark in writing to Hooke on June +15th, 1680: "Having fallen in with bad weather we took forty hours in +the journey from Dover to Calais." The scientific distinction which +he had already attained was such that he was received in Paris with +marked attention. A great deal of his time seems to have been passed +in the Paris observatory, where Cassini, the presiding genius, +himself an astronomer of well-deserved repute, had extended a hearty +welcome to his English visitor. They made observations together of +the place of the splendid comet which was then attracting universal +attention, and Halley found the work thus done of much use when he +subsequently came to investigate the path pursued by this body. +Halley was wise enough to spare no pains to derive all possible +advantages from his intercourse with the distinguished savants of the +French capital. In the further progress of his tour he visited the +principal cities of the Continent, leaving behind him everywhere the +memory of an amiable disposition and of a rare intelligence. + +After Halley's return to England, in 1682, he married a young lady +named Mary Tooke, with whom he lived happily, till her death +fifty-five years later. On his marriage, he took up his abode in +Islington, where he erected his instruments and recommenced his +observations. + +It has often been the good fortune of astronomers to render practical +services to humanity by their investigations, and Halley's +achievements in this respect deserve to be noted. A few years after +he had settled in England, he published an important paper on the +variation of the magnetic compass, for so the departure of the needle +from the true north is termed. This subject had indeed early engaged +his attention, and he continued to feel much interest in it up to the +end of his life. With respect to his labours in this direction, Sir +John Herschel says: "To Halley we owe the first appreciation of the +real complexity of the subject of magnetism. It is wonderful indeed, +and a striking proof of the penetration and sagacity of this +extraordinary man, that with his means of information he should have +been able to draw such conclusions, and to take so large and +comprehensive a view of the subject as he appears to have done." In +1692, Halley explained his theory of terrestrial magnetism, and +begged captains of ships to take observations of the variations of +the compass in all parts of the world, and to communicate them to the +Royal Society, "in order that all the facts may be readily available +to those who are hereafter to complete this difficult and complicated +subject." + +The extent to which Halley was in advance of his contemporaries, in +the study of terrestrial magnetism, may be judged from the fact that +the subject was scarcely touched after his time till the year 1811. +The interest which he felt in it was not of a merely theoretical +kind, nor was it one which could be cultivated in an easy-chair. Like +all true investigators, he longed to submit his theory to the test of +experiment, and for that purpose Halley determined to observe the +magnetic variation for himself. He procured from King William III. +the command of a vessel called the "Paramour Pink," with which he +started for the South Seas in 1694. This particular enterprise was +not, however, successful; for, on crossing the line, some of his men +fell sick and one of his lieutenants mutinied, so that he was obliged +to return the following year with his mission unaccomplished. The +government cashiered the lieutenant, and Halley having procured a +second smaller vessel to accompany the "Paramour Pink," started once +more in September, 1699. He traversed the Atlantic to the 52nd +degree of southern latitude, beyond which his further advance was +stopped. "In these latitudes," he writes to say, "we fell in with +great islands of ice of so incredible height and magnitude, that I +scarce dare write my thoughts of it." + +On his return in 1700, Halley published a general chart, showing the +variation of the compass at the different places which he had +visited. On these charts he set down lines connecting those +localities at which the magnetic variation was identical. He thus +set an example of the graphic representation of large masses of +complex facts, in such a manner as to appeal at once to the eye, a +method of which we make many applications in the present day. + +But probably the greatest service which Halley ever rendered to human +knowledge was the share in which he took in bringing Newton's +"Principia" before the world. In fact, as Dr. Glaisher, writing in +1888, has truly remarked, "but for Halley the 'Principia' would not +have existed." + +It was a visit from Halley in the year 1684 which seems to have first +suggested to Newton the idea of publishing the results of his +investigations on gravitation. Halley, and other scientific +contemporaries, had no doubt some faint glimmering of the great truth +which only Newton's genius was able fully to reveal. Halley had +indeed shown how, on the assumptions that the planets move in +circular orbits round the sun, and that the squares of their periodic +times are proportional to the cubes of their mean distances, it may +be proved that the force acting on each planet must vary inversely as +the square of its distance from the sun. Since, however, each of the +planets actually moves in an ellipse, and therefore, at continually +varying distances from the sun, it becomes a much more difficult +matter to account mathematically for the body's motions on the +supposition that the attractive force varies inversely as the square +of the distance. This was the question with which Halley found +himself confronted, but which his mathematical abilities were not +adequate to solve. It would seem that both Hooke and Sir Christopher +Wren were interested in the same problem; in fact, the former claimed +to have arrived at a solution, but declined to make known his +results, giving as an excuse his desire that others having tried and +failed might learn to value his achievements all the more. Halley, +however, confessed that his attempts at the solution were +unsuccessful, and Wren, in order to encourage the other two +philosophers to pursue the inquiry, offered to present a book of +forty shillings value to either of them who should in the space of +two months bring him a convincing proof of it. Such was the value +which Sir Christopher set on the Law of Gravitation, upon which the +whole fabric of modern astronomy may be said to stand. + +Finding himself unequal to the task, Halley went down to Cambridge to +see Newton on the subject, and was delighted to learn that the great +mathematician had already completed the investigation. He showed +Halley that the motions of all the planets could be completely +accounted for on the hypothesis of a force of attraction directed +towards the sun, which varies inversely as the square of the distance +from that body. + +Halley had the genius to perceive the tremendous importance of +Newton's researches, and he ceased not to urge upon the recluse man +of science the necessity for giving his new discoveries publication. +He paid another visit to Cambridge with the object of learning more +with regard to the mathematical methods which had already conducted +Newton to such sublime truths, and he again encouraged the latter +both to pursue his investigations, and to give some account of them +to the world. In December of the same year Halley had the +gratification of announcing to the Royal Society that Newton had +promised to send that body a paper containing his researches on +Gravitation. + +It seems that at this epoch the finances of the Royal Society were at +a very low ebb. This impecuniosity was due to the fact that a book +by Willoughby, entitled "De Historia Piscium," had been recently +printed by the society at great expense. In fact, the coffers were +so low that they had some difficulty in paying the salaries of their +permanent officials. It appears that the public did not care about +the history of fishes, or at all events the volume did not meet with +the ready demand which was expected for it. Indeed, it has been +recorded that when Halley had undertaken to measure the length of a +degree of the earth's surface, at the request of the Royal Society, +it was ordered that his expenses be defrayed either in 50 pounds +sterling, or in fifty books of fishes. Thus it happened that on June +2nd, the Council, after due consideration of ways and means in +connection with the issue of the Principia, "ordered that Halley +should undertake the business of looking after the book and printing +it at his own charge," which he engaged to do. + +It was, as we have elsewhere mentioned, characteristic of Newton that +he detested controversies, and he was, in fact, inclined to suppress +the third book of the "Principia" altogether rather than have any +conflict with Hooke with respect to the discoveries there +enunciated. He also thought of changing the name of the work to De +Motu Corporum Libri Duo, but upon second thoughts, he retained the +original title, remarking, as he wrote to Halley, "It will help the +sale of the book, which I ought not to diminish, now it is yours," a +sentence which shows conclusively, if further proof were necessary, +that Halley had assumed the responsibility of its publication. + +Halley spared no pains in pushing forward the publication of his +illustrious friend's great work, so that in the same year he was in a +position to present a complete copy to King James II., with a proper +discourse of his own. Halley also wrote a set of Latin hexameters in +praise of Newton's genius, which he printed at the beginning of the +work. The last line of this specimen of Halley's poetic muse may be +thus rendered: "Nor mortals nearer may approach the gods." + +The intimate friendship between the two greatest astronomers of the +time continued without interruption till the death of Newton. It +has, indeed, been alleged that some serious cause of estrangement +arose between them. There is, however, no satisfactory ground for +this statement; indeed, it may be regarded as effectually disposed of +by the fact that, in the year 1727, Halley took up the defence of his +friend, and wrote two learned papers in support of Newton's "System +of Chronology," which had been seriously attacked by a certain +ecclesiastic. It is quite evident to any one who has studied these +papers that Halley's friendship for Newton was as ardent as ever. + +The generous zeal with which Halley adopted and defended the +doctrines of Newton with regard to the movements of the celestial +bodies was presently rewarded by a brilliant discovery, which has +more than any of his other researches rendered his name a familiar +one to astronomers. Newton, having explained the movement of the +planets, was naturally led to turn his attention to comets. He +perceived that their journeyings could be completely accounted for as +consequences of the attraction of the sun, and he laid down the +principles by which the orbit of a comet could be determined, +provided that observations of its positions were obtained at three +different dates. The importance of these principles was by no one +more quickly recognised than by Halley, who saw at once that it +provided the means of detecting something like order in the movements +of these strange wanderers. The doctrine of Gravitation seemed to +show that just as the planets revolved around the sun in ellipses, so +also must the comets. The orbit, however, in the case of the comet, +is so extremely elongated that the very small part of the elliptic +path within which the comet is both near enough and bright enough to +be seen from the earth, is indistinguishable from a parabola. +Applying these principles, Halley thought it would be instructive to +study the movements of certain bright comets, concerning which +reliable observations could be obtained. At the expense of much +labour, he laid down the paths pursued by twenty-four of these +bodies, which had appeared between the years 1337 and 1698. Amongst +them he noticed three, which followed tracks so closely resembling +each other, that he was led to conclude the so called three comets +could only have been three different appearances of the same body. +The first of these occurred in 1531, the second was seen by Kepler in +1607, and the third by Halley himself in 1682. These dates suggested +that the observed phenomena might be due to the successive returns of +one and the same comet after intervals of seventy-five or seventy-six +years. On the further examination of ancient records, Halley found +that a comet had been seen in the year 1456, a date, it will be +observed, seventy-five years before 1531. Another had been observed +seventy-six years earlier than 1456, viz., in 1380, and another +seventy-five years before that, in 1305. + +As Halley thus found that a comet had been recorded on several +occasions at intervals of seventy-five or seventy-six years, he was +led to the conclusion that these several apparitions related to one +and the same object, which was an obedient vassal of the sun, +performing an eccentric journey round that luminary in a period of +seventy-five or seventy-six years. To realise the importance of this +discovery, it should be remembered that before Halley's time a comet, +if not regarded merely as a sign of divine displeasure, or as an omen +of intending disaster, had at least been regarded as a chance visitor +to the solar system, arriving no one knew whence, and going no one +knew whither. + +A supreme test remained to be applied to Halley's theory. The +question arose as to the date at which this comet would be seen +again. We must observe that the question was complicated by the fact +that the body, in the course of its voyage around the sun, was +exposed to the incessant disturbing action produced by the attraction +of the several planets. The comet therefore, does not describe a +simple ellipse as it would do if the attraction of the sun were the +only force by which its movement were controlled. Each of the +planets solicits the comet to depart from its track, and though the +amount of these attractions may be insignificant in comparison with +the supreme controlling force of the sun, yet the departure from the +ellipse is quite sufficient to produce appreciable irregularities in +the comet's movement. At the time when Halley lived, no means +existed of calculating with precision the effect of the disturbance a +comet might experience from the action of the different planets. +Halley exhibited his usual astronomical sagacity in deciding that +Jupiter would retard the return of the comet to some extent. Had it +not been for this disturbance the comet would apparently have been +due in 1757 or early in 1758. But the attraction of the great planet +would cause delay, so that Halley assigned, for the date of its +re-appearance, either the end of 1758 or the beginning of 1759. +Halley knew that he could not himself live to witness the fulfilment +of his prediction, but he says: "If it should return, according to +our predictions, about the year 1758, impartial posterity will not +refuse to acknowledge that this was first discovered by an +Englishman." This was, indeed, a remarkable prediction of an event +to occur fifty-three years after it had been uttered. The way in +which it was fulfilled forms one of the most striking episodes in the +history of astronomy. The comet was first seen on Christmas Day, +1758, and passed through its nearest point to the sun on March 13th, +1759. Halley had then been lying in his grave for seventeen years, +yet the verification of his prophecy reflects a glory on his name +which will cause it to live for ever in the annals of astronomy. The +comet paid a subsequent visit in 1835, and its next appearance is due +about 1910. + +Halley next entered upon a labour which, if less striking to the +imagination than his discoveries with regard to comets, is still of +inestimable value in astronomy. He undertook a series of +investigations with the object of improving our knowledge of the +movements of the planets. This task was practically finished in +1719, though the results of it were not published until after his +death in 1749. In the course of it he was led to investigate closely +the motion of Venus, and thus he came to recognise for the first time +the peculiar importance which attaches to the phenomenon of the +transit of this planet across the sun. Halley saw that the transit, +which was to take place in the year 1761, would afford a favourable +opportunity for determining the distance of the sun, and thus +learning the scale of the solar system. He predicted the +circumstances of the phenomenon with an astonishing degree of +accuracy, considering his means of information, and it is +unquestionably to the exertions of Halley in urging the importance of +the matter upon astronomers that we owe the unexampled degree of +interest taken in the event, and the energy which scientific men +exhibited in observing it. The illustrious astronomer had no hope of +being himself a witness of the event, for it could not happen till +many years after his death. This did not, however, diminish his +anxiety to impress upon those who would then be alive, the importance +of the occurrence, nor did it lead him to neglect anything which +might contribute to the success of the observations. As we now know, +Halley rather over-estimated the value of the transit of Venus, as a +means of determining the solar distance. The fact is that the +circumstances are such that the observation of the time of contact +between the edge of the planet and the edge of the sun cannot be made +with the accuracy which he had expected. + +In 1691, Halley became a candidate for the Savilian Professorship of +Astronomy at Oxford. He was not, however, successful, for his +candidature was opposed by Flamsteed, the Astronomer Royal of the +time, and another was appointed. He received some consolation for +this particular disappointment by the fact that, in 1696, owing to +Newton's friendly influence, he was appointed deputy Controller of +the Mint at Chester, an office which he did not retain for long, as +it was abolished two years later. At last, in 1703, he received what +he had before vainly sought, and he was appointed to the Savilian +chair. + +His observations of the eclipse of the sun, which occurred in 1715, +added greatly to Halley's reputation. This phenomenon excited +special attention, inasmuch as it was the first total eclipse of the +sun which had been visible in London since the year 1140. Halley +undertook the necessary calculations, and predicted the various +circumstances with a far higher degree of precision than the official +announcement. He himself observed the phenomenon from the Royal +Society's rooms, and he minutely describes the outer atmosphere of +the sun, now known as the corona; without, however, offering an +opinion as to whether it was a solar or a lunar appendage. + +At last Halley was called to the dignified office which he of all men +was most competent to fill. On February 9th, 1720, he was appointed +Astronomer Royal in succession to Flamsteed. He found things at the +Royal Observatory in a most unsatisfactory state. Indeed, there were +no instruments, nor anything else that was movable; for such things, +being the property of Flamsteed, had been removed by his widow, and +though Halley attempted to purchase from that lady some of the +instruments which his predecessor had employed, the unhappy personal +differences which had existed between him and Flamsteed, and which, +as we have already seen, prevented his election as Savilian Professor +of Astronomy, proved a bar to the negotiation. Greenwich Observatory +wore a very different appearance in those days, from that which the +modern visitor, who is fortunate enough to gain admission, may now +behold. Not only did Halley find it bereft of instruments, we learn +besides that he had no assistants, and was obliged to transact the +whole business of the establishment single-handed. + +In 1721, however, he obtained a grant of 500 pounds from the Board of +Ordnance, and accordingly a transit instrument was erected in the +same year. Some time afterwards he procured an eight-foot quadrant, +and with these instruments, at the age of sixty-four, he commenced a +series of observations on the moon. He intended, if his life was +spared, to continue his observations for a period of eighteen years, +this being, as astronomers know, a very important cycle in connection +with lunar movements. The special object of this vast undertaking +was to improve the theory of the moon's motion, so that it might +serve more accurately to determine longitudes at sea. This +self-imposed task Halley lived to carry to a successful termination, +and the tables deduced from his observations, and published after his +death, were adopted almost universally by astronomers, those of the +French nation being the only exception. + +Throughout his life Halley had been singularly free from illness of +every kind, but in 1737 he had a stroke of paralysis. Notwithstanding +this, however, he worked diligently at his telescope till 1739, after +which his health began rapidly to give way. He died on January 14th, +1742, in the eighty-sixth year of his age, retaining his mental +faculties to the end. He was buried in the cemetery of the church of +Lee in Kent, in the same grave as his wife, who had died five years +previously. We are informed by Admiral Smyth that Pond, a later +Astronomer Royal, was afterwards laid in the same tomb. + +Halley's disposition seems to have been generous and candid, and +wholly free from anything like jealousy or rancour. In person he was +rather above the middle height, and slight in build; his complexion +was fair, and he is said to have always spoken, as well as acted, +with uncommon sprightliness. In the eloge pronounced upon him at the +Paris Academie Des Sciences, of which Halley had been made a member +in 1719 it was said, "he possessed all the qualifications which were +necessary to please princes who were desirous of instruction, with a +great extent of knowledge and a constant presence of mind; his +answers were ready, and at the same time pertinent, judicious, polite +and sincere." + +[PLATE: GREENWICH OBSERVATORY IN HALLEY'S TIME.] + +Thus we find that Peter the Great was one of his most ardent +admirers. He consulted the astronomer on matters connected with +shipbuilding, and invited him to his own table. But Halley possessed +nobler qualifications than the capacity of pleasing Princes. He was +able to excite and to retain the love and admiration of his equals. +This was due to the warmth of his attachments, the unselfishness of +his devotion to his friends, and to a vein of gaiety and good-humour +which pervaded all his conversation. + + + + +BRADLEY. + + +James Bradley was descended from an ancient family in the county of +Durham. He was born in 1692 or 1693, at Sherbourne, in +Gloucestershire, and was educated in the Grammar School at +Northleach. From thence he proceeded in due course to Oxford, where +he was admitted a commoner at Balliol College, on March 15th, 1711. +Much of his time, while an undergraduate, was passed in Essex with +his maternal uncle, the Rev. James Pound, who was a well-known man of +science and a diligent observer of the stars. It was doubtless by +intercourse with his uncle that young Bradley became so expert in the +use of astronomical instruments, but the immortal discoveries he +subsequently made show him to have been a born astronomer. + +The first exhibition of Bradley's practical skill seems to be +contained in two observations which he made in 1717 and 1718. They +have been published by Halley, whose acuteness had led him to +perceive the extraordinary scientific talents of the young +astronomer. Another illustration of the sagacity which Bradley +manifested, even at the very commencement of his astronomical career, +is contained in a remark of Halley's, who says: "Dr. Pound and his +nephew, Mr. Bradley, did, myself being present, in the last +opposition of the sun and Mars this way demonstrate the extreme +minuteness of the sun's parallax, and that it was not more than +twelve seconds nor less than nine seconds." To make the significance +of this plain, it should be observed that the determination of the +sun's parallax is equivalent to the determination of the distance +from the earth to the sun. At the time of which we are now writing, +this very important unit of celestial measurement was only very +imperfectly known, and the observations of Pound and Bradley may be +interpreted to mean that, from their observations, they had come to +the conclusion that the distance from the earth to the sun must be +more than 94 millions of miles, and less than 125 millions. We now, +of course, know that they were not exactly right, for the true +distance of the sun is about 93 millions of miles. We cannot, +however, but think that it was a very remarkable approach for the +veteran astronomer and his brilliant nephew to make towards the +determination of a magnitude which did not become accurately known +till fifty years later. + +Among the earliest parts of astronomical work to which Bradley's +attention was directed, were the eclipses of Jupiter's satellites. +These phenomena are specially attractive inasmuch as they can be so +readily observed, and Bradley found it extremely interesting to +calculate the times at which the eclipses should take place, and then +to compare his observations with the predicted times. From the +success that he met with in this work, and from his other labours, +Bradley's reputation as an astronomer increased so greatly that on +November the 6th, 1718, he was elected a Fellow of the Royal Society. + +Up to this time the astronomical investigations of Bradley had been +more those of an amateur than of a professional astronomer, and as it +did not at first seem likely that scientific work would lead to any +permanent provision, it became necessary for the youthful astronomer +to choose a profession. It had been all along intended that he +should enter the Church, though for some reason which is not told us, +he did not take orders as soon as his age would have entitled him to +do so. In 1719, however, the Bishop of Hereford offered Bradley the +Vicarage of Bridstow, near Ross, in Monmouthshire, and on July 25th, +1720, he having then taken priest's orders, was duly instituted in +his vicarage. In the beginning of the next year, Bradley had some +addition to his income from the proceeds of a Welsh living, which, +being a sinecure, he was able to hold with his appointment at +Bridstow. It appears, however, that his clerical occupations were +not very exacting in their demands upon his time, for he was still +able to pay long and often-repeated visits to his uncle at +Wandsworth, who, being himself a clergyman, seems to have received +occasional assistance in his ministerial duties from his astronomical +nephew. + +The time, however, soon arrived when Bradley was able to make a +choice between continuing to exercise his profession as a divine, or +devoting himself to a scientific career. The Savilian Professorship +of Astronomy in the University of Oxford became vacant by the death +of Dr. John Keill. The statutes forbade that the Savilian Professor +should also hold a clerical appointment, and Mr. Pound would +certainly have been elected to the professorship had he consented to +surrender his preferments in the Church. But Pound was unwilling to +sacrifice his clerical position, and though two or three other +candidates appeared in the field, yet the talents of Bradley were so +conspicuous that he was duly elected, his willingness to resign the +clerical profession having been first ascertained. + +There can be no doubt that, with such influential friends as Bradley +possessed, he would have made great advances had he adhered to his +profession as a divine. Bishop Hoadly, indeed, with other marks of +favour, had already made the astronomer his chaplain. The engrossing +nature of Bradley's interest in astronomy decided him, however, to +sacrifice all other prospects in comparison with the opening afforded +by the Savilian Professorship. It was not that Bradley found himself +devoid of interest in clerical matters, but he felt that the true +scope for such abilities as he possessed would be better found in the +discharge of the scientific duties of the Oxford chair than in the +spiritual charge of a parish. On April the 26th, 1722, Bradley read +his inaugural lecture in that new position on which he was destined +to confer such lustre. + +It must, of course, be remembered that in those early days the art of +constructing the astronomical telescope was very imperfectly +understood. The only known method for getting over the peculiar +difficulties presented in the construction of the refracting +telescope, was to have it of the most portentous length. In fact, +Bradley made several of his observations with an instrument of two +hundred and twelve feet focus. In such a case, no tube could be +used, and the object glass was merely fixed at the top of a high +pole. Notwithstanding the inconvenience and awkwardness of such an +instrument, Bradley by its means succeeded in making many careful +measurements. He observed, for example, the transit of Mercury over +the sun's disc, on October 9th, 1723; he also observed the dimensions +of the planet Venus, while a comet which Halley discovered on October +the 9th, 1723, was assiduously observed at Wanstead up to the middle +of the ensuing month. The first of Bradley's remarkable +contributions to the "Philosophical Transactions" relates to this +comet, and the extraordinary amount of work that he went through in +connection therewith may be seen from an examination of his book of +Calculations which is still extant. + +The time was now approaching when Bradley was to make the first of +those two great discoveries by which his name has acquired a lustre +that has placed him in the very foremost rank of astronomical +discoverers. As has been often the case in the history of science, +the first of these great successes was attained while he was pursuing +a research intended for a wholly different purpose. It had long been +recognised that as the earth describes a vast orbit, nearly two +hundred million miles in diameter, in its annual journey round the +sun, the apparent places of the stars should alter, to some extent, +in correspondence with the changes in the earth's position. The +nearer the star the greater the shift in its apparent place on the +heavens, which must arise from the fact that it was seen from +different positions in the earth's orbit. It had been pointed out +that these apparent changes in the places of the stars, due to the +movement of the earth, would provide the means of measuring the +distances of the stars. As, however, these distances are enormously +great in comparison with the orbit which the earth describes around +the sun, the attempt to determine the distances of the stars by the +shift in their positions had hitherto proved ineffectual. Bradley +determined to enter on this research once again; he thought that by +using instruments of greater power, and by making measurements of +increased delicacy, he would be able to perceive and to measure +displacements which had proved so small as to elude the skill of the +other astronomers who had previously made efforts in the same +direction. In order to simplify the investigation as much as +possible, Bradley devoted his attention to one particular star, Beta +Draconis, which happened to pass near his zenith. The object of +choosing a star in this position was to avoid the difficulties which +would be introduced by refraction had the star occupied any other +place in the heavens than that directly overhead. + +We are still able to identify the very spot on which the telescope +stood which was used in this memorable research. It was erected at +the house then occupied by Molyneux, on the western extremity of Kew +Green. The focal length was 24 feet 3 inches, and the eye-glass was +3 and a half feet above the ground floor. The instrument was first +set up on November 26th, 1725. If there had been any appreciable +disturbance in the place of Beta Draconis in consequence of the +movement of the earth around the sun, the star must appear to have +the smallest latitude when in conjunction with the sun, and the +greatest when in opposition. The star passed the meridian at noon in +December, and its position was particularly noticed by Molyneux on +the third of that month. Any perceptible displacement by +parallax--for so the apparent change in position, due to the earth's +motion, is called--would would have made the star shift towards the +north. Bradley, however, when observing it on the 17th, was +surprised to find that the apparent place of the star, so far from +shifting towards the north, as they had perhaps hoped it would, was +found to lie a little more to the south than when it was observed +before. He took extreme care to be sure that there was no mistake in +his observation, and, true astronomer as he was, he scrutinized with +the utmost minuteness all the circumstances of the adjustment of his +instruments. Still the star went to the south, and it continued so +advancing in the same direction until the following March, by which +time it had moved no less than twenty seconds south from the place +which it occupied when the first observation was made. After a brief +pause, in which no apparent movement was perceptible, the star by the +middle of April appeared to be returning to the north. Early in June +it reached the same distance from the zenith which it had in +December. By September the star was as much as thirty-nine seconds +more to the north than it had been in March, then it returned towards +the south, regaining in December the same situation which it had +occupied twelve months before. + +This movement of the star being directly opposite to the movements +which would have been the consequence of parallax, seemed to show +that even if the star had any parallax its effects upon the apparent +place were entirely masked by a much larger motion of a totally +different description. Various attempts were made to account for the +phenomenon, but they were not successful. Bradley accordingly +determined to investigate the whole subject in a more thorough +manner. One of his objects was to try whether the same movements +which he had observed in one star were in any similar degree +possessed by other stars. For this purpose he set up a new +instrument at Wanstead, and there he commenced a most diligent +scrutiny of the apparent places of several stars which passed at +different distances from the zenith. He found in the course of this +research that other stars exhibited movements of a similar +description to those which had already proved so perplexing. For a +long time the cause of these apparent movements seemed a mystery. At +last, however, the explanation of these remarkable phenomena dawned +upon him, and his great discovery was made. + +One day when Bradley was out sailing he happened to remark that every +time the boat was laid on a different tack the vane at the top of the +boat's mast shifted a little, as if there had been a slight change in +the direction of the wind. After he had noticed this three or four +times he made a remark to the sailors to the effect that it was very +strange the wind should always happen to change just at the moment +when the boat was going about. The sailors, however, said there had +been no change in the wind, but that the alteration in the vane was +due to the fact that the boat's course had been altered. In fact, +the position of the vane was determined both by the course of the +boat and the direction of the wind, and if either of these were +altered there would be a corresponding change in the direction of the +vane. This meant, of course, that the observer in the boat which was +moving along would feel the wind coming from a point different from +that in which the wind appeared to be blowing when the boat was at +rest, or when it was sailing in some different direction. Bradley's +sagacity saw in this observation the clue to the Difficulty which had +so long troubled him. + +It had been discovered before the time of Bradley that the passage of +light through space is not an instantaneous phenomenon. Light +requires time for its journey. Galileo surmised that the sun may +have reached the horizon before we see it there, and it was indeed +sufficiently obvious that a physical action, like the transmission of +light, could hardly take place without requiring some lapse of time. +The speed with which light actually travelled was, however, so rapid +that its determination eluded all the means of experimenting which +were available in those days. The penetration of Roemer had +previously detected irregularities in the observed times of the +eclipses of Jupiter's satellites, which were undoubtedly due to the +interval which light required for stretching across the +interplanetary spaces. Bradley argued that as light can only travel +with a certain speed, it may in a measure be regarded like the wind, +which he noticed in the boat. If the observer were at rest, that is +to say, if the earth were a stationary object, the direction in which +the light actually does come would be different from that in which it +appears to come when the earth is in motion. It is true that the +earth travels but eighteen miles a second, while the velocity with +which light is borne along attains to as much as 180,000 miles a +second. The velocity of light is thus ten thousand times greater +than the speed of the earth. But even though the wind blew ten +thousand times faster than the speed with which the boat was sailing +there would still be some change, though no doubt a very small +change, in the position of the vane when the boat was in progress +from the position it would have if the boat were at rest. It +therefore occurred to this most acute of astronomers that when the +telescope was pointed towards a star so as to place it apparently in +the centre of the field of view, yet it was not generally the true +position of the star. It was not, in fact, the position in which the +star would have been observed had the earth been at rest. Provided +with this suggestion, he explained the apparent movements of the +stars by the principle known as the "aberration of light." Every +circumstance was accounted for as a consequence of the relative +movements of the earth and of the light from the star. This +beautiful discovery not only established in the most forcible manner +the nature of the movement of light; not only did it illustrate the +truth of the Copernican theory which asserted that the earth revolved +around the sun, but it was also of the utmost importance in the +improvement of practical astronomy. Every observer now knows that, +generally speaking, the position which the star appears to have is +not exactly the position in which the star does actually lie. The +observer is, however, able, by the application of the principles +which Bradley so clearly laid down, to apply to an observation the +correction which is necessary to obtain from it the true place in +which the object is actually situated. This memorable achievement at +once conferred on Bradley the highest astronomical fame. He tested +his discovery in every way, but only to confirm its truth in the most +complete manner. + +Halley, the Astronomer Royal, died on the 14th, January, 1742, and +Bradley was immediately pointed out as his successor. He was +accordingly appointed Astronomer Royal in February, 1742. On first +taking up his abode at Greenwich he was unable to conduct his +observations owing to the wretched condition in which he found the +instruments. He devoted himself, however, assiduously to their +repair, and his first transit observation is recorded on the 25th +July, 1742. He worked with such energy that on one day it appears +that 255 transit observations were taken by himself alone, and in +September, 1747, he had completed the series of observations which +established his second great discovery, the nutation of the earth's +axis. The way in which he was led to the detection of the nutation +is strikingly illustrative of the extreme care with which Bradley +conducted his observations. He found that in the course of a +twelve-month, when the star had completed the movement which was due +to aberration, it did not return exactly to the same position which +it had previously occupied. At first he thought this must be due to +some instrumental error, but after closer examination and repeated +study of the effect as manifested by many different stars, he came to +the conclusion that its origin must be sought in some quite different +source. The fact is that a certain change takes place in the +apparent position of the stars which is not due to the movement of +the star itself, but is rather to be attributed to changes in the +points from which the star's positions are measured. + +We may explain the matter in this way. As the earth is not a sphere, +but has protuberant parts at the equator, the attraction of the moon +exercises on those protuberant parts a pulling effect which +continually changes the direction of the earth's axis, and +consequently the position of the pole must be in a state of incessant +fluctuation. The pole to which the earth's axis points on the sky +is, therefore, slowly changing. At present it happens to lie near +the Pole Star, but it will not always remain there. It describes a +circle around the pole of the Ecliptic, requiring about 25,000 years +for a complete circuit. In the course of its progress the pole will +gradually pass now near one star and now near another, so that many +stars will in the lapse of ages discharge the various functions which +the present Pole Star does for us. In about 12,000 years, for +instance, the pole will have come near the bright star, Vega. This +movement of the pole had been known for ages. But what Bradley +discovered was that the pole, instead of describing an uniform +movement as had been previously supposed, followed a sinuous course +now on one side and now on the other of its mean place. This he +traced to the fluctuations of the moon's orbit, which undergoes a +continuous change in a period of nineteen years. Thus the efficiency +with which the moon acts on the protuberant mass of the earth varies, +and thus the pole is caused to oscillate. + +This subtle discovery, if perhaps in some ways less impressive than +Bradley's earlier achievements of the detection of the aberration of +light, is regarded by astronomers as testifying even in a higher +degree to his astonishing care and skill as an observer, and justly +entitles him to a unique place among the astronomers whose +discoveries have been effected by consummate practical skill in the +use of astronomical instruments. + +Of Bradley's private or domestic life there is but little to tell. In +1744, soon after he became Astronomer Royal, he married a daughter of +Samuel Peach, of Chalford, in Gloucestershire. There was but one +child, a daughter, who became the wife of her cousin, Rev. Samuel +Peach, rector of Compton, Beauchamp, in Berkshire. + +Bradley's last two years of life were clouded by a melancholy +depression of spirits, due to an apprehension that he should survive +his rational faculties. It seems, however, that the ill he dreaded +never came upon him, for he retained his mental powers to the close. +He died on 13th July, 1762, aged seventy, and was buried at +Michinghamton. + + + + +WILLIAM HERSCHEL. + + +William Herschel, one of the greatest astronomers that has ever +lived, was born at Hanover, on the 15th November, 1738. His father, +Isaac Herschel, was a man evidently of considerable ability, whose +life was devoted to the study and practice of music, by which he +earned a somewhat precarious maintenance. He had but few worldly +goods to leave to his children, but he more than compensated for this +by bequeathing to them a splendid inheritance of genius. Touches of +genius were, indeed, liberally scattered among the members of Isaac's +large family, and in the case of his forth child, William, and of a +sister several years younger, it was united with that determined +perseverance and rigid adherence to principle which enabled genius to +fulfil its perfect work. + +A faithful chronicler has given us an interesting account of the way +in which Isaac Herschel educated his sons; the narrative is taken +from the recollections of one who, at the time we are speaking of, +was an unnoticed little girl five or six years old. She writes:-- + +"My brothers were often introduced as solo performers and assistants +in the orchestra at the Court, and I remember that I was frequently +prevented from going to sleep by the lively criticisms on music on +coming from a concert. Often I would keep myself awake that I might +listen to their animating remarks, for it made me so happy to see +them so happy. But generally their conversation would branch out on +philosophical subjects, when my brother William and my father often +argued with such warmth that my mother's interference became +necessary, when the names--Euler, Leibnitz, and Newton--sounded +rather too loud for the repose of her little ones, who had to be at +school by seven in the morning." The child whose reminiscences are +here given became afterwards the famous Caroline Herschel. The +narrative of her life, by Mrs. John Herschel, is a most interesting +book, not only for the account it contains of the remarkable woman +herself, but also because it provides the best picture we have of the +great astronomer to whom Caroline devoted her life. + +This modest family circle was, in a measure, dispersed at the +outbreak of the Seven Years' War in 1756. The French proceeded to +invade Hanover, which, it will be remembered, belonged at this time +to the British dominions. Young William Herschel had already +obtained the position of a regular performer in the regimental band +of the Hanoverian Guards, and it was his fortune to obtain some +experience of actual warfare in the disastrous battle of Hastenbeck. +He was not wounded, but he had to spend the night after the battle in +a ditch, and his meditations on the occasion convinced him that +soldiering was not the profession exactly adapted to his tastes. We +need not attempt to conceal the fact that he left his regiment by the +very simple but somewhat risky process of desertion. He had, it +would seem, to adopt disguises to effect his escape. At all events, +by some means he succeeded in eluding detection and reached England +in safety. It is interesting to have learned on good authority that +many years after this offence was committed it was solemnly +forgiven. When Herschel had become the famous astronomer, and as +such visited King George at Windsor, the King at their first meeting +handed to him his pardon for deserting from the army, written out in +due form by his Majesty himself. + +It seems that the young musician must have had some difficulty in +providing for his maintenance during the first few years of his abode +in England. It was not until he had reached the age of twenty-two +that he succeeded in obtaining any regular appointment. He was then +made Instructor of Music to the Durham Militia. Shortly afterwards, +his talents being more widely recognised, he was appointed as +organist at the parish church at Halifax, and his prospects in life +now being fairly favourable, and the Seven Years' War being over, he +ventured to pay a visit to Hanover to see his father. We can imagine +the delight with which old Isaac Herschel welcomed his promising son, +as well as his parental pride when a concert was given at which some +of William's compositions were performed. If the father was so +intensely gratified on this occasion, what would his feelings have +been could he have lived to witness his son's future career? But +this pleasure was not to be his, for he died many years before +William became an astronomer. + +In 1766, about a couple of years after his return to England from +This visit to his old home, we find that Herschel had received a +further promotion to be organist in the Octagon Chapel, at Bath. +Bath was then, as now, a highly fashionable resort, and many notable +personages patronised the rising musician. Herschel had other points +in his favour besides his professional skill; his appearance was +good, his address was prepossessing, and even his nationality was a +distinct advantage, inasmuch as he was a Hanoverian in the reign of +King George the Third. On Sundays he played the organ, to the great +delight of the congregation, and on week-days he was occupied by +giving lessons to private pupils, and in preparation for public +performances. He thus came to be busily employed, and seems to have +been in the enjoyment of comfortable means. + +[PLATE: 7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.] + +From his earliest youth Herschel had been endowed with that +invaluable characteristic, an eager curiosity for knowledge. He was +naturally desirous of perfecting himself in the theory of music, and +thus he was led to study mathematics. When he had once tasted the +charms of mathematics, he saw vast regions of knowledge unfolded +before him, and in this way he was induced to direct his attention to +astronomy. More and more this pursuit seems to have engrossed his +attention, until at last it had become an absorbing passion. Herschel +was, however, still obliged, by the exigency of procuring a +livelihood, to give up the best part of his time to his profession as +a musician; but his heart was eagerly fixed on another science, and +every spare moment was steadily devoted to astronomy. For many +years, however, he continued to labour at his original calling, nor +was it until he had attained middle age and become the most +celebrated astronomer of the time, that he was enabled to concentrate +his attention exclusively on his favourite pursuit. + +It was with quite a small telescope which had been lent him by a +friend that Herschel commenced his career as an observer. However, +he speedily discovered that to see all he wanted to see, a telescope +of far greater power would be necessary, and he determined to obtain +this more powerful instrument by actually making it with his own +hands. At first it may seem scarcely likely that one whose +occupation had previously been the study and practice of music should +meet with success in so technical an operation as the construction of +a telescope. It may, however, be mentioned that the kind of +instrument which Herschel designed to construct was formed on a very +different principle from the refracting telescopes with which we are +ordinarily familiar. His telescope was to be what is termed a +reflector. In this type of instrument the optical power is obtained +by the use of a mirror at the bottom of the tube, and the astronomer +looks down through the tube TOWARDS HIS MIRROR and views the +reflection of the stars with its aid. Its efficiency as a telescope +depends entirely on the accuracy with which the requisite form has +been imparted to the mirror. The surface has to be hollowed out a +little, and this has to be done so truly that the slightest deviation +from good workmanship in this essential particular would be fatal to +efficient performance of the telescope. + +[PLATE: WILLIAM HERSCHEL.] + +The mirror that Herschel employed was composed of a mixture of two +parts of copper to one of tin; the alloy thus obtained is an +intensely hard material, very difficult to cast into the proper +shape, and very difficult to work afterwards. It possesses, however, +when polished, a lustre hardly inferior to that of silver itself. +Herschel has recorded hardly any particulars as to the actual process +by which he cast and figured his reflectors. We are however, told +that in later years, after his telescopes had become famous, he made +a considerable sum of money by the manufacture and sale of great +instruments. Perhaps this may be the reason why he never found it +expedient to publish any very explicit details as to the means by +which his remarkable successes were obtained. + +[PLATE: CAROLINE HERSCHEL.] + +Since Herschel's time many other astronomers, notably the late Earl +of Rosse, have experimented in the same direction, and succeeded in +making telescopes certainly far greater, and probably more perfect, +than any which Herschel appears to have constructed. The details of +these later methods are now well known, and have been extensively +practised. Many amateurs have thus been able to make telescopes by +following the instructions so clearly laid down by Lord Rosse and the +other authorities. Indeed, it would seem that any one who has a +little mechanical skill and a good deal of patience ought now to +experience no great difficulty in constructing a telescope quite as +powerful as that which first brought Herschel into fame. I should, +however, mention that in these modern days the material generally +used for the mirror is of a more tractable description than the +metallic substance which was employed by Herschel and by Lord Rosse. +A reflecting telescope of the present day would not be fitted with a +mirror composed of that alloy known as speculum metal, whose +composition I have already mentioned. It has been found more +advantageous to employ a glass mirror carefully figured and polished, +just as a metallic mirror would have been, and then to impart to the +polished glass surface a fine coating of silver laid down by a +chemical process. The silver-on-glass mirrors are so much lighter +and so much easier to construct that the more old-fashioned metallic +mirrors may be said to have fallen into almost total disuse. In one +respect however, the metallic mirror may still claim the advantage +that, with reasonable care, its surface will last bright and +untarnished for a much longer period than can the silver film on the +glass. However, the operation of re-silvering a glass has now become +such a simple one that the advantage this indicates is not relatively +so great as might at first be supposed. + +[PLATE: STREET VIEW, HERSCHEL HOUSE, SLOUGH.] + +Some years elapsed after Herschel's attention had been first directed +to astronomy, before he reaped the reward of his exertions in the +possession of a telescope which would adequately reveal some of the +glories of the heavens. It was in 1774, when the astronomer was +thirty-six years old, that he obtained his first glimpse of the stars +with an instrument of his own construction. Night after night, as +soon as his musical labours were ended, his telescopes were brought +out, sometimes into the small back garden of his house at Bath, and +sometimes into the street in front of his hall-door. It was +characteristic of him that he was always endeavouring to improve his +apparatus. He was incessantly making fresh mirrors, or trying new +lenses, or combinations of lenses to act as eye-pieces, or projecting +alterations in the mounting by which the telescope was supported. +Such was his enthusiasm that his house, we are told, was incessantly +littered with the usual indications of the workman's presence, +greatly to the distress of his sister, who, at this time, had come to +take up her abode with him and look after his housekeeping. Indeed, +she complained that in his astronomical ardour he sometimes omitted +to take off, before going into his workshop, the beautiful lace +ruffles which he wore while conducting a concert, and that +consequently they became soiled with the pitch employed in the +polishing of his mirrors. + +This sister, who occupies such a distinct place in scientific history +is the same little girl to whom we have already referred. From her +earliest days she seems to have cherished a passionate admiration for +her brilliant brother William. It was the proudest delight of her +childhood as well as of her mature years to render him whatever +service she could; no man of science was ever provided with a more +capable or energetic helper than William Herschel found in this +remarkable woman. Whatever work had to be done she was willing to +bear her share in it, or even to toil at it unassisted if she could +be allowed to do so. She not only managed all his domestic affairs, +but in the grinding of the lenses and in the polishing of the mirrors +she rendered every assistance that was possible. At one stage of the +very delicate operation of fashioning a reflector, it is necessary +for the workman to remain with his hand on the mirror for many hours +in succession. When such labours were in progress, Caroline used to +sit by her brother, and enliven the time by reading stories aloud, +sometimes pausing to feed him with a spoon while his hands were +engaged on the task from which he could not desist for a moment. + +When mathematical work had to be done Caroline was ready for it; she +had taught herself sufficient to enable her to perform the kind of +calculations, not, perhaps, very difficult ones, that Herschel's work +required; indeed, it is not too much to say that the mighty life-work +which this man was enabled to perform could never have been accomplished +had it not been for the self-sacrifice of this ever-loving and faithful +sister. When Herschel was at the telescope at night, Caroline sat by +him at her desk, pen in hand, ready to write down the notes of the +observations as they fell from her brother's lips. This was no +insignificant toil. The telescope was, of course, in the open air, +and as Herschel not unfrequently continued his observations throughout +the whole of a long winter's night, there were but few women who could +have accomplished the task which Caroline so cheerfully executed. +From dusk till dawn, when the sky was clear, were Herschel's observing +hours, and what this sometimes implied we can realise from the fact +that Caroline assures us she had sometimes to desist because the ink +had actually frozen in her pen. The night's work over, a brief rest +was taken, and while William had his labours for the day to attend to, +Caroline carefully transcribed the observations made during the night +before, reduced all the figures and prepared everything in readiness +for the observations that were to follow on the ensuing evening. + +But we have here been anticipating a little of the future which lay +before the great astronomer; we must now revert to the history of his +early work, at Bath, in 1774, when Herschel's scrutiny of the skies +first commenced with an instrument of his own manufacture. For some +few years he did not attain any result of importance; no doubt he +made a few interesting observations, but the value of the work during +those years is to be found, not in any actual discoveries which were +accomplished, but in the practice which Herschel obtained in the use +of his instruments. It was not until 1782 that the great achievement +took place by which he at once sprang into fame. + +[PLATE: GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.] + +It is sometimes said that discoveries are made by accident, and, no +doubt, to a certain extent, but only, I fancy to a very small extent, +this statement may be true. It is, at all events, certain that such +lucky accidents do not often fall to the lot of people unless those +people have done much to deserve them. This was certainly the case +with Herschel. He appears to have formed a project for making a +close examination of all the stars above a certain magnitude. Perhaps +he intended to confine this research to a limited region of the sky, +but, at all events, he seems to have undertaken the work +energetically and systematically. Star after star was brought to the +centre of the field of view of his telescope, and after being +carefully examined was then displaced, while another star was brought +forward to be submitted to the same process. In the great majority +of cases such observations yield really nothing of importance; no +doubt even the smallest star in the heavens would, if we could find +out all about it, reveal far more than all the astronomers that were +ever on the earth have even conjectured. What we actually learn +about the great majority of stars is only information of the most +meagre description. We see that the star is a little point of light, +and we see nothing more. + +In the great review which Herschel undertook he doubtless examined +hundreds, or perhaps thousands of stars, allowing them to pass away +without note or comment. But on an ever-memorable night in March, +1782, it happened that he was pursuing his task among the stars in +the Constellation of Gemini. Doubtless, on that night, as on so many +other nights, one star after another was looked at only to be +dismissed, as not requiring further attention. On the evening in +question, however, one star was noticed which, to Herschel's acute +vision seemed different from the stars which in so many thousands are +strewn over the sky. A star properly so called appears merely as a +little point of light, which no increase of magnifying power will +ever exhibit with a true disc. But there was something in the +star-like object which Herschel saw that immediately arrested his +attention and made him apply to it a higher magnifying power. This +at once disclosed the fact that the object possessed a disc, that is, +a definite, measurable size, and that it was thus totally different +from any one of the hundreds and thousands of stars which exist +elsewhere in space. Indeed, we may say at once that this little +object was not a star at all; it was a planet. That such was its +true nature was confirmed, after a little further observation, by +perceiving that the body was shifting its place on the heavens +relatively to the stars. The organist at the Octagon Chapel at Bath +had, therefore, discovered a new planet with his home-made telescope. + +I can imagine some one will say, "Oh, there was nothing so wonderful +in that; are not planets always being discovered? Has not M. Palisa, +for instance, discovered about eighty of such objects, and are there +not hundreds of them known nowadays?" This is, to a certain extent, +quite true. I have not the least desire to detract from the credit +of those industrious and sharp-sighted astronomers who have in modern +days brought so many of these little objects within our cognisance. I +think, however, it must be admitted that such discoveries have a +totally different importance in the history of science from that +which belongs to the peerless achievement of Herschel. In the first +place, it must be observed that the minor planets now brought to +light are so minute that if a score of them were rolled to together +into one lump it would not be one-thousandth part of the size of the +grand planet discovered by Herschel. This is, nevertheless, not the +most important point. What marks Herschel's achievement as one of +the great epochs in the history of astronomy is the fact that the +detection of Uranus was the very first recorded occasion of the +discovery of any planet whatever. + +For uncounted ages those who watched the skies had been aware of the +existence of the five old planets--Jupiter, Mercury, Saturn, Venus, +and Mars. It never seems to have occurred to any of the ancient +philosophers that there could be other similar objects as yet +undetected over and above the well-known five. Great then was the +astonishment of the scientific world when the Bath organist announced +his discovery that the five planets which had been known from all +antiquity must now admit the company of a sixth. And this sixth +planet was, indeed, worthy on every ground to be received into the +ranks of the five glorious bodies of antiquity. It was, no doubt, +not so large as Saturn, it was certainly very much less than Jupiter; +on the other hand, the new body was very much larger than Mercury, +than Venus, or than Mars, and the earth itself seemed quite an +insignificant object in comparison with this newly added member of +the Solar System. In one respect, too, Herschel's new planet was a +much more imposing object than any one of the older bodies; it swept +around the sun in a majestic orbit, far outside that of Saturn, which +had previously been regarded as the boundary of the Solar System, and +its stately progress required a period of not less than eighty-one +years. + +King George the Third, hearing of the achievements of the Hanoverian +musician, felt much interest in his discovery, and accordingly +Herschel was bidden to come to Windsor, and to bring with him the +famous telescope, in order to exhibit the new planet to the King, and +to tell his Majesty all about it. The result of the interview was to +give Herschel the opportunity for which he had so long wished, of +being able to devote himself exclusively to science for the rest of +his life. + +[PLATE: VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.] + +The King took so great a fancy to the astronomer that he first, as I +have already mentioned, duly pardoned his desertion from the army, +some twenty-five years previously. As a further mark of his favour +the King proposed to confer on Herschel the title of his Majesty's +own astronomer, to assign to him a residence near Windsor, to provide +him with a salary, and to furnish such funds as might be required for +the erection of great telescopes, and for the conduct of that mighty +scheme of celestial observation on which Herschel was so eager to +enter. Herschel's capacity for work would have been much impaired if +he had been deprived of the aid of his admirable sister, and to her, +therefore, the King also assigned a salary, and she was installed as +Herschel's assistant in his new post. + +With his usually impulsive determination, Herschel immediately cut +himself free from all his musical avocations at Bath, and at once +entered on the task of making and erecting the great telescopes at +Windsor. There, for more than thirty years, he and his faithful +sister prosecuted with unremitting ardour their nightly scrutiny of +the sky. Paper after paper was sent to the Royal Society, describing +the hundreds, indeed the thousands, of objects such as double stars; +nebulae and clusters, which were first revealed to human gaze during +those midnight vigils. To the end of his life he still continued at +every possible opportunity to devote himself to that beloved pursuit +in which he had such unparalleled success. No single discovery of +Herschel's later years was, however, of the same momentous +description as that which first brought him to fame. + +[PLATE: THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH.] + +Herschel married when considerably advanced in life and he lived to +enjoy the indescribable pleasure of finding that his only son, +afterwards Sir John Herschel, was treading worthily in his footsteps, +and attaining renown as an astronomical observer, second only to that +of his father. The elder Herschel died in 1822, and his illustrious +sister Caroline then returned to Hanover, where she lived for many +years to receive the respect and attention which were so justly +hers. She died at a very advanced age in 1848. + + + + +LAPLACE. + + +The author of the "Mecanique Celeste" was born at Beaumont-en-Auge, +near Honfleur, in 1749, just thirteen years later than his renowned +friend Lagrange. His father was a farmer, but appears to have been +in a position to provide a good education for a son who seemed +promising. Considering the unorthodoxy in religious matters which is +generally said to have characterized Laplace in later years, it is +interesting to note that when he was a boy the subject which first +claimed his attention was theology. He was, however, soon introduced +to the study of mathematics, in which he presently became so +proficient, that while he was still no more than eighteen years old, +he obtained employment as a mathematical teacher in his native town. + +Desiring wider opportunities for study and for the acquisition of +fame than could be obtained in the narrow associations of provincial +life, young Laplace started for Paris, being provided with letters of +introduction to D'Alembert, who then occupied the most prominent +position as a mathematician in France, if not in the whole of +Europe. D'Alembert's fame was indeed so brilliant that Catherine the +Great wrote to ask him to undertake the education of her Son, and +promised the splendid income of a hundred thousand francs. He +preferred, however, a quiet life of research in Paris, although there +was but a modest salary attached to his office. The philosopher +accordingly declined the alluring offer to go to Russia, even though +Catherine wrote again to say: "I know that your refusal arises from +your desire to cultivate your studies and your friendships in quiet. +But this is of no consequence: bring all your friends with you, and I +promise you that both you and they shall have every accommodation in +my power." With equal firmness the illustrious mathematician +resisted the manifold attractions with which Frederick the Great +sought to induce him, to take up his residence at Berlin. In reading +of these invitations we cannot but be struck at the extraordinary +respect which was then paid to scientific distinction. It must be +remembered that the discoveries of such a man as D'Alembert were +utterly incapable of being appreciated except by those who possessed +a high degree of mathematical culture. We nevertheless find the +potentates of Russia and Prussia entreating and, as it happens, +vainly entreating, the most distinguished mathematician in France to +accept the positions that they were proud to offer him. + +It was to D'Alembert, the profound mathematician, that young Laplace, +the son of the country farmer, presented his letters of +introduction. But those letters seem to have elicited no reply, +whereupon Laplace wrote to D'Alembert submitting a discussion on some +point in Dynamics. This letter instantly produced the desired +effect. D'Alembert thought that such mathematical talent as the +young man displayed was in itself the best of introductions to his +favour. It could not be overlooked, and accordingly he invited +Laplace to come and see him. Laplace, of course, presented himself, +and ere long D'Alembert obtained for the rising philosopher a +professorship of mathematics in the Military School in Paris. This +gave the brilliant young mathematician the opening for which he +sought, and he quickly availed himself of it. + +Laplace was twenty-three years old when his first memoir on a +profound mathematical subject appeared in the Memoirs of the Academy +at Turin. From this time onwards we find him publishing one memoir +after another in which he attacks, and in many cases successfully +vanquishes, profound difficulties in the application of the Newtonian +theory of gravitation to the explanation of the solar system. Like +his great contemporary Lagrange, he loftily attempted problems which +demanded consummate analytical skill for their solution. The +attention of the scientific world thus became riveted on the splendid +discoveries which emanated from these two men, each gifted with +extraordinary genius. + +Laplace's most famous work is, of course, the "Mecanique Celeste," in +which he essayed a comprehensive attempt to carry out the principles +which Newton had laid down, into much greater detail than Newton had +found practicable. The fact was that Newton had not only to +construct the theory of gravitation, but he had to invent the +mathematical tools, so to speak, by which his theory could be applied +to the explanation of the movements of the heavenly bodies. In the +course of the century which had elapsed between the time of Newton +and the time of Laplace, mathematics had been extensively developed. +In particular, that potent instrument called the infinitesimal +calculus, which Newton had invented for the investigation of nature, +had become so far perfected that Laplace, when he attempted to +unravel the movements of the heavenly bodies, found himself provided +with a calculus far more efficient than that which had been available +to Newton. The purely geometrical methods which Newton employed, +though they are admirably adapted for demonstrating in a general way +the tendencies of forces and for explaining the more obvious +phenomena by which the movements of the heavenly bodies are +disturbed, are yet quite inadequate for dealing with the more subtle +effects of the Law of Gravitation. The disturbances which one planet +exercises upon the rest can only be fully ascertained by the aid of +long calculation, and for these calculations analytical methods are +required. + +With an armament of mathematical methods which had been perfected +since the days of Newton by the labours of two or three generations +of consummate mathematical inventors, Laplace essayed in the +"Mecanique Celeste" to unravel the mysteries of the heavens. It will +hardly be disputed that the book which he has produced is one of the +most difficult books to understand that has ever been written. In +great part, of course, this difficulty arises from the very nature of +the subject, and is so far unavoidable. No one need attempt to read +the "Mecanique Celeste" who has not been naturally endowed with +considerable mathematical aptitude which he has cultivated by years +of assiduous study. The critic will also note that there are grave +defects in Laplace's method of treatment. The style is often +extremely obscure, and the author frequently leaves great gaps in his +argument, to the sad discomfiture of his reader. Nor does it mend +matters to say, as Laplace often does say, that it is "easy to see" +how one step follows from another. Such inferences often present +great difficulties even to excellent mathematicians. Tradition +indeed tells us that when Laplace had occasion to refer to his own +book, it sometimes happened that an argument which he had dismissed +with his usual formula, "Il est facile a voir," cost the illustrious +author himself an hour or two of hard thinking before he could +recover the train of reasoning which had been omitted. But there are +certain parts of this great work which have always received the +enthusiastic admiration of mathematicians. Laplace has, in fact, +created whole tracts of science, some of which have been subsequently +developed with much advantage in the prosecution of the study of +Nature. + +Judged by a modern code the gravest defect of Laplace's great work is +rather of a moral than of a mathematical nature. Lagrange and he +advanced together in their study of the mechanics of the heavens, at +one time perhaps along parallel lines, while at other times they +pursued the same problem by almost identical methods. Sometimes the +important result was first reached by Lagrange, sometimes it was +Laplace who had the good fortune to make the discovery. It would +doubtless be a difficult matter to draw the line which should exactly +separate the contributions to astronomy made by one of these +illustrious mathematicians, and the contributions made by the other. +But in his great work Laplace in the loftiest manner disdained to +accord more than the very barest recognition to Lagrange, or to any +of the other mathematicians, Newton alone excepted, who had advanced +our knowledge of the mechanism of the heavens. It would be quite +impossible for a student who confined his reading to the "Mecanique +Celeste" to gather from any indications that it contains whether the +discoveries about which he was reading had been really made by +Laplace himself or whether they had not been made by Lagrange, or by +Euler, or by Clairaut. With our present standard of morality in such +matters, any scientific man who now brought forth a work in which he +presumed to ignore in this wholesale fashion the contributions of +others to the subject on which he was writing, would be justly +censured and bitter controversies would undoubtedly arise. Perhaps +we ought not to judge Laplace by the standard of our own time, and in +any case I do not doubt that Laplace might have made a plausible +defence. It is well known that when two investigators are working at +the same subjects, and constantly publishing their results, it +sometimes becomes difficult for each investigator himself to +distinguish exactly between what he has accomplished and that which +must be credited to his rival. Laplace may probably have said to +himself that he was going to devote his energies to a great work on +the interpretation of Nature, that it would take all his time and all +his faculties, and all the resources of knowledge that he could +command, to deal justly with the mighty problems before him. He +would not allow himself to be distracted by any side issue. He could +not tolerate that pages should be wasted in merely discussing to whom +we owe each formula, and to whom each deduction from such formula is +due. He would rather endeavour to produce as complete a picture as +he possibly could of the celestial mechanics, and whether it were by +means of his mathematics alone, or whether the discoveries of others +may have contributed in any degree to the result, is a matter so +infinitesimally insignificant in comparison with the grandeur of his +subject that he would altogether neglect it. "If Lagrange should +think," Laplace might say, "that his discoveries had been unduly +appropriated, the proper course would be for him to do exactly what I +have done. Let him also write a "Mecanique Celeste," let him employ +those consummate talents which he possesses in developing his noble +subject to the utmost. Let him utilise every result that I or any +other mathematician have arrived at, but not trouble himself unduly +with unimportant historical details as to who discovered this, and +who discovered that; let him produce such a work as he could write, +and I shall heartily welcome it as a splendid contribution to our +science." Certain it is that Laplace and Lagrange continued the best +of friends, and on the death of the latter it was Laplace who was +summoned to deliver the funeral oration at the grave of his great +rival. + +The investigations of Laplace are, generally speaking, of too +technical a character to make it possible to set forth any account of +them in such a work as the present. He did publish, however, one +treatise, called the "Systeme du Monde," in which, without +introducing mathematical symbols, he was able to give a general +account of the theories of the celestial movements, and of the +discoveries to which he and others had been led. In this work the +great French astronomer sketched for the first time that remarkable +doctrine by which his name is probably most generally known to those +readers of astronomical books who are not specially mathematicians. +It is in the "Systeme du Monde" that Laplace laid down the principles +of the Nebular Theory which, in modern days, has been generally +accepted by those philosophers who are competent to judge, as +substantially a correct expression of a great historical fact. + +[PLATE: LAPLACE.] + +The Nebular Theory gives a physical account of the origin of the +solar system, consisting of the sun in the centre, with the planets +and their attendant satellites. Laplace perceived the significance +of the fact that all the planets revolved in the same direction +around the sun; he noticed also that the movements of rotation of the +planets on their axes were performed in the same direction as that in +which a planet revolves around the sun; he saw that the orbits of the +satellites, so far at least as he knew them, revolved around their +primaries also in the same direction. Nor did it escape his +attention that the sun itself rotated on its axis in the same sense. +His philosophical mind was led to reflect that such a remarkable +unanimity in the direction of the movements in the solar system +demanded some special explanation. It would have been in the highest +degree improbable that there should have been this unanimity unless +there had been some physical reason to account for it. To appreciate +the argument let us first concentrate our attention on three +particular bodies, namely the earth, the sun, and the moon. First +the earth revolves around the sun in a certain direction, and the +earth also rotates on its axis. The direction in which the earth +turns in accordance with this latter movement might have been that in +which it revolves around the sun, or it might of course have been +opposite thereto. As a matter of fact the two agree. The moon in +its monthly revolution around the earth follows also the same +direction, and our satellite rotates on its axis in the same period +as its monthly revolution, but in doing so is again observing this +same law. We have therefore in the earth and moon four movements, +all taking place in the same direction, and this is also identical +with that in which the sun rotates once every twenty-five days. Such +a coincidence would be very unlikely unless there were some physical +reason for it. Just as unlikely would it be that in tossing a coin +five heads or five tails should follow each other consecutively. If +we toss a coin five times the chances that it will turn up all heads +or all tails is but a small one. The probability of such an event is +only one-sixteenth. + +There are, however, in the solar system many other bodies besides the +three just mentioned which are animated by this common movement. +Among them are, of course, the great planets, Jupiter, Saturn, Mars, +Venus, and Mercury, and the satellites which attend on these +planets. All these planets rotate on their axes in the same +direction as they revolve around the sun, and all their satellites +revolve also in the same way. Confining our attention merely to the +earth, the sun, and the five great planets with which Laplace was +acquainted, we have no fewer than six motions of revolution and seven +motions of rotation, for in the latter we include the rotation of the +sun. We have also sixteen satellites of the planets mentioned whose +revolutions round their primaries are in the same direction. The +rotation of the moon on its axis may also be reckoned, but as to the +rotations of the satellites of the other planets we cannot speak with +any confidence, as they are too far off to be observed with the +necessary accuracy. We have thus thirty circular movements in the +solar system connected with the sun and moon and those great planets +than which no others were known in the days of Laplace. The +significant fact is that all these thirty movements take place in the +same direction. That this should be the case without some physical +reason would be just as unlikely as that in tossing a coin thirty +times it should turn up all heads or all tails every time without +exception. + +We can express the argument numerically. Calculation proves that +such an event would not generally happen oftener than once out of +five hundred millions of trials. To a philosopher of Laplace's +penetration, who had made a special study of the theory of +probabilities, it seemed well-nigh inconceivable that there should +have been such unanimity in the celestial movements, unless there had +been some adequate reason to account for it. We might, indeed, add +that if we were to include all the objects which are now known to +belong to the solar system, the argument from probability might be +enormously increased in strength. To Laplace the argument appeared +so conclusive that he sought for some physical cause of the +remarkable phenomenon which the solar system presented. Thus it was +that the famous Nebular Hypothesis took its rise. Laplace devised a +scheme for the origin of the sun and the planetary system, in which +it would be a necessary consequence that all the movements should +take place in the same direction as they are actually observed to do. + +Let us suppose that in the beginning there was a gigantic mass of +nebulous material, so highly heated that the iron and other +substances which now enter into the composition of the earth and +planets were then suspended in a state of vapour. There is nothing +unreasonable in such a supposition indeed, we know as a matter of +fact that there are thousands of such nebulae to be discerned at +present through our telescopes. It would be extremely unlikely that +any object could exist without possessing some motion of rotation; we +may in fact assert that for rotation to be entirety absent from the +great primeval nebula would be almost infinitely improbable. As ages +rolled on, the nebula gradually dispersed away by radiation its +original stores of heat, and, in accordance with well-known physical +principles, the materials of which it was formed would tend to +coalesce. The greater part of those materials would become +concentrated in a mighty mass surrounded by outlying uncondensed +vapours. There would, however, also be regions throughout the extent +of the nebula, in which subsidiary centres of condensation would be +found. In its long course of cooling, the nebula would, therefore, +tend ultimately to form a mighty central body with a number of +smaller bodies disposed around it. As the nebula was initially +endowed with a movement of rotation, the central mass into which it +had chiefly condensed would also revolve, and the subsidiary bodies +would be animated by movements of revolution around the central +body. These movements would be all pursued in one common direction, +and it follows, from well-known mechanical principles, that each of +the subsidiary masses, besides participating in the general +revolution around the central body, would also possess a rotation +around its axis, which must likewise be performed in the same +direction. Around the subsidiary bodies other objects still smaller +would be formed, just as they themselves were formed relatively to +the great central mass. + +As the ages sped by, and the heat of these bodies became gradually +dissipated, the various objects would coalesce, first into molten +liquid masses, and thence, at a further stage of cooling, they would +assume the appearance of solid masses, thus producing the planetary +bodies such as we now know them. The great central mass, on account +of its preponderating dimensions, would still retain, for further +uncounted ages, a large quantity of its primeval heat, and would thus +display the splendours of a glowing sun. In this way Laplace was +able to account for the remarkable phenomena presented in the +movements of the bodies of the solar system. There are many other +points also in which the nebular theory is known to tally with the +facts of observation. In fact, each advance in science only seems to +make it more certain that the Nebular Hypothesis substantially +represents the way in which our solar system has grown to its present +form. + +Not satisfied with a career which should be merely scientific, +Laplace sought to connect himself with public affairs. Napoleon +appreciated his genius, and desired to enlist him in the service of +the State. Accordingly he appointed Laplace to be Minister of the +Interior. The experiment was not successful, for he was not by +nature a statesman. Napoleon was much disappointed at the ineptitude +which the great mathematician showed for official life, and, in +despair of Laplace's capacity as an administrator, declared that he +carried the spirit of his infinitesimal calculus into the management +of business. Indeed, Laplace's political conduct hardly admits of +much defence. While he accepted the honours which Napoleon showered +on him in the time of his prosperity, he seems to have forgotten all +this when Napoleon could no longer render him service. Laplace was +made a Marquis by Louis XVIII., a rank which he transmitted to his +son, who was born in 1789. During the latter part of his life the +philosopher lived in a retired country place at Arcueile. Here he +pursued his studies, and by strict abstemiousness, preserved himself +from many of the infirmities of old age. He died on March the 5th, +1827, in his seventy-eighth year, his last words being, "What we know +is but little, what we do not know is immense." + + + + +BRINKLEY. + + +Provost Baldwin held absolute sway in the University of Dublin for +forty-one years. His memory is well preserved there. The Bursar +still dispenses the satisfactory revenues which Baldwin left to the +College. None of us ever can forget the marble angels round the +figure of the dying Provost on which we used to gaze during the pangs +of the Examination Hall. + +Baldwin died in 1785, and was succeeded by Francis Andrews, a Fellow +of seventeen years' standing. As to the scholastic acquirements of +Andrews, all I can find is a statement that he was complimented by +the polite Professors of Padua on the elegance and purity with which +he discoursed to them in Latin. Andrews was also reputed to be a +skilful lawyer. He was certainly a Privy Councillor and a prominent +member of the Irish House of Commons, and his social qualities were +excellent. Perhaps it was Baldwin's example that stimulated a desire +in Andrews to become a benefactor to his college. He accordingly +bequeathed a sum of 3,000 pounds and an annual income of 250 pounds +wherewith to build and endow an astronomical Observatory in the +University. The figures just stated ought to be qualified by the +words of cautious Ussher (afterwards the first Professor of +Astronomy), that "this money was to arise from an accumulation of a +part of his property, to commence upon a particular contingency +happening to his family." The astronomical endowment was soon in +jeopardy by litigation. Andrews thought he had provided for his +relations by leaving to them certain leasehold interests connected +with the Provost's estate. The law courts, however, held that these +interests were not at the disposal of the testator, and handed them +over to Hely Hutchinson, the next Provost. The disappointed +relations then petitioned the Irish Parliament to redress this +grievance by transferring to them the moneys designed by Andrews for +the Observatory. It would not be right, they contended, that the +kindly intentions of the late Provost towards his kindred should be +frustrated for the sake of maintaining what they described as "a +purely ornamental institution." The authorities of the College +protested against this claim. Counsel were heard, and a Committee of +the House made a report declaring the situation of the relations to +be a hard one. Accordingly, a compromise was made, and the dispute +terminated. + +The selection of a site for the new astronomical Observatory was made +by the Board of Trinity College. The beautiful neighbourhood of +Dublin offered a choice of excellent localities. On the north side +of the Liffey an Observatory could have been admirably placed, either +on the remarkable promontory of Howth or on the elevation of which +Dunsink is the summit. On the south side of Dublin there are several +eminences that would have been suitable: the breezy heaths at +Foxrock combine all necessary conditions; the obelisk hill at +Killiney would have given one of the most picturesque sites for an +Observatory in the world; while near Delgany two or three other good +situations could be mentioned. But the Board of those pre-railway +days was naturally guided by the question of proximity. Dunsink was +accordingly chosen as the most suitable site within the distance of a +reasonable walk from Trinity College. + +The northern boundary of the Phoenix Park approaches the little river +Tolka, which winds through a succession of delightful bits of sylvan +scenery, such as may be found in the wide demesne of Abbotstown and +the classic shades of Glasnevin. From the banks of the Tolka, on the +opposite side of the park, the pastures ascend in a gentle slope to +culminate at Dunsink, where at a distance of half a mile from the +stream, of four miles from Dublin, and at a height of 300 feet above +the sea, now stands the Observatory. From the commanding position of +Dunsink a magnificent view is obtained. To the east the sea is +visible, while the southern prospect over the valley of the Liffey is +bounded by a range of hills and mountains extending from Killiney to +Bray Head, thence to the little Sugar Loaf, the Two Rock and the +Three Rock Mountains, over the flank of which the summit of the Great +Sugar Loaf is just perceptible. Directly in front opens the fine +valley of Glenasmole, with Kippure Mountain, while the range can be +followed to its western extremity at Lyons. The climate of Dunsink +is well suited for astronomical observation. No doubt here, as +elsewhere in Ireland, clouds are abundant, but mists or haze are +comparatively unusual, and fogs are almost unknown. + +The legal formalities to be observed in assuming occupation exacted a +delay of many months; accordingly, it was not until the 10th +December, 1782, that a contract could be made with Mr. Graham Moyers +for the erection of a meridian-room and a dome for an equatorial, in +conjunction with a becoming residence for the astronomer. Before the +work was commenced at Dunsink, the Board thought it expedient to +appoint the first Professor of Astronomy. They met for this purpose +on the 22nd January, 1783, and chose the Rev. Henry Ussher, a Senior +Fellow of Trinity College, Dublin. The wisdom of the appointment was +immediately shown by the assiduity with which Ussher engaged in +founding the observatory. In three years he had erected the +buildings and equipped them with instruments, several of which were +of his own invention. On the 19th of February, 1785, a special grant +of 200 pounds was made by the Board to Dr. Ussher as some recompense +for his labours. It happened that the observatory was not the only +scientific institution which came into being in Ireland at this +period; the newly-kindled ardour for the pursuit of knowledge led, at +the same time, to the foundation of the Royal Irish Academy. By a +fitting coincidence, the first memoir published in the "Transactions +Of The Royal Irish Academy," was by the first Andrews, Professor of +Astronomy. It was read on the 13th of June, 1785, and bore the +title, "Account of the Observatory belonging to Trinity College," by +the Rev. H. Ussher, D.D., M.R.I.A., F.R.S. This communication shows +the extensive design that had been originally intended for Dunsink, +only a part of which was, however, carried out. For instance, two +long corridors, running north and south from the central edifice, +which are figured in the paper, never developed into bricks and +mortar. We are not told why the original scheme had to be +contracted; but perhaps the reason may be not unconnected with a +remark of Ussher's, that the College had already advanced from its +own funds a sum considerably exceeding the original bequest. The +picture of the building shows also the dome for the South equatorial, +which was erected many years later. + +Ussher died in 1790. During his brief career at the observatory, he +observed eclipses, and is stated to have done other scientific work. +The minutes of the Board declare that the infant institution had +already obtained celebrity by his labours, and they urge the claims +of his widow to a pension, on the ground that the disease from which +he died had been contracted by his nightly vigils. The Board also +promised a grant of fifty guineas as a help to bring out Dr. Ussher's +sermons. They advanced twenty guineas to his widow towards the +publication of his astronomical papers. They ordered his bust to be +executed for the observatory, and offered "The Death of Ussher" as +the subject of a prize essay; but, so far as I can find, neither the +sermons nor the papers, neither the bust nor the prize essay, ever +came into being. + +There was keen competition for the chair of Astronomy which the death +of Ussher vacated. The two candidates were Rev. John Brinkley, of +Caius College, Cambridge, a Senior Wrangler (born at Woodbridge, +Suffolk, in 1763), and Mr. Stack, Fellow of Trinity College, Dublin, +and author of a book on Optics. A majority of the Board at first +supported Stack, while Provost Hely Hutchinson and one or two others +supported Brinkley. In those days the Provost had a veto at +elections, so that ultimately Stack was withdrawn and Brinkley was +elected. This took place on the 11th December, 1790. The national +press of the day commented on the preference shown to the young +Englishman, Brinkley, over his Irish rival. An animated controversy +ensued. The Provost himself condescended to enter the lists and to +vindicate his policy by a long letter in the "Public Register" or +"Freeman's Journal," of 21st December, 1790. This letter was +anonymous, but its authorship is obvious. It gives the +correspondence with Maskelyne and other eminent astronomers, whose +advice and guidance had been sought by the Provost. It also contends +that "the transactions of the Board ought not to be canvassed in the +newspapers." For this reference, as well as for much other +information, I am indebted to my friend, the Rev. John Stubbs, D.D. + +[PLATE: THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin.] + +The next event in the history of the Observatory was the issue of +Letters Patent (32 Geo. III., A.D. 1792), in which it is recited that +"We grant and ordain that there shall be forever hereafter a +Professor of Astronomy, on the foundation of Dr. Andrews, to be +called and known by the name of the Royal Astronomer of Ireland." The +letters prescribe the various duties of the astronomer and the mode +of his election. They lay down regulations as to the conduct of the +astronomical work, and as to the choice of an assistant. They direct +that the Provost and the Senior Fellows shall make a thorough +inspection of the observatory once every year in June or July; and +this duty was first undertaken on the 5th of July, 1792. It may be +noted that the date on which the celebration of the tercentenary of +the University was held happens to coincide with the centenary of the +first visitation of the observatory. The visitors on the first +occasion were A. Murray, Matthew Young, George Hall, and John +Barrett. They record that they find the buildings, books and +instruments in good condition; but the chief feature in this report, +as well as in many which followed it, related to a circumstance to +which we have not yet referred. + +In the original equipment of the observatory, Ussher, with the +natural ambition of a founder, desired to place in it a telescope of +more magnificent proportions than could be found anywhere else. The +Board gave a spirited support to this enterprise, and negotiations +were entered into with the most eminent instrument-maker of those +days. This was Jesse Ramsden (1735-1800), famous as the improver of +the sextant, as the constructor of the great theodolite used by +General Roy in the English Survey, and as the inventor of the +dividing engine for graduating astronomical instruments. Ramsden had +built for Sir George Schuckburgh the largest and most perfect +equatorial ever attempted. He had constructed mural quadrants for +Padua and Verona, which elicited the wonder of astronomers when Dr. +Maskelyne declared he could detect no error in their graduation so +large as two seconds and a half. But Ramsden maintained that even +better results would be obtained by superseding the entire quadrant +by the circle. He obtained the means of testing this prediction when +he completed a superb circle for Palermo of five feet diameter. +Finding his anticipations were realised, he desired to apply the same +principles on a still grander scale. Ramsden was in this mood when +he met with Dr. Ussher. The enthusiasm of the astronomer and the +instrument-maker communicated itself to the Board, and a tremendous +circle, to be ten feet in diameter, was forthwith projected. + +Projected, but never carried out. After Ramsden had to some extent +completed a 10-foot circle, he found such difficulties that he tried +a 9-foot, and this again he discarded for an 8-foot, which was +ultimately accomplished, though not entirely by himself. +Notwithstanding the contraction from the vast proportions originally +designed, the completed instrument must still be regarded as a +colossal piece of astronomical workmanship. Even at this day I do +not know that any other observatory can show a circle eight feet in +diameter graduated all round. + +I think it is Professor Piazzi Smith who tells us how grateful he was +to find a large telescope he had ordered finished by the opticians on +the very day they had promised it. The day was perfectly correct; it +was only the year that was wrong. A somewhat remarkable experience +in this direction is chronicled by the early reports of the visitors +to Dunsink Observatory. I cannot find the date on which the great +circle was ordered from Ramsden, but it is fixed with sufficient +precision by an allusion in Ussher's paper to the Royal Irish +Academy, which shows that by the 13th June, 1785, the order had been +given, but that the abandonment of the 10-foot scale had not then +been contemplated. It was reasonable that the board should allow +Ramsden ample time for the completion of a work at once so elaborate +and so novel. It could not have been finished in a year, nor would +there have been much reason for complaint if the maker had found he +required two or even three years more. + +Seven years gone, and still no telescope, was the condition in which +the Board found matters at their first visitation in 1792. They had, +however, assurances from Ramsden that the instrument would be +completed within the year; but, alas for such promises, another seven +years rolled on, and in 1799 the place for the great circle was still +vacant at Dunsink. Ramsden had fallen into bad health, and the Board +considerately directed that "inquiries should be made." Next year +there was still no progress, so the Board were roused to threaten +Ramsden with a suit at law; but the menace was never executed, for +the malady of the great optician grew worse, and he died that year. + +Affairs had now assumed a critical aspect, for the college had +advanced much money to Ramsden during these fifteen years, and the +instrument was still unfinished. An appeal was made by the Provost +to Dr. Maskelyne, the Astronomer Royal of England, for his advice and +kindly offices in this emergency. Maskelyne responds--in terms +calculated to allay the anxiety of the Bursar--"Mr. Ramsden has left +property behind him, and the College can be in no danger of losing +both their money and the instrument." The business of Ramsden was +then undertaken by Berge, who proceeded to finish the circle quite as +deliberately as his predecessor. After four years Berge promised the +instrument in the following August, but it did not come. Two years +later (1806) the professor complains that he can get no answer from +Berge. In 1807, it is stated that Berge will send the telescope in a +month. He did not; but in the next year (1808), about twenty-three +years after the great circle was ordered, it was erected at Dunsink, +where it is still to be seen. + +The following circumstances have been authenticated by the signatures +of Provosts, Proctors, Bursars, and other College dignitaries:--In +1793 the Board ordered two of the clocks at the observatory to be +sent to Mr. Crosthwaite for repairs. Seven years later, in 1800, Mr. +Crosthwaite was asked if the clocks were ready. This impatience was +clearly unreasonable, for even in four more years, 1804, we find the +two clocks were still in hand. Two years later, in 1806, the Board +determined to take vigorous action by asking the Bursar to call upon +Crosthwaite. This evidently produced some effect, for in the +following year, 1807, the Professor had no doubt that the clocks +would be speedily returned. After eight years more, in 1815, one of +the clocks was still being repaired, and so it was in 1816, which is +the last record we have of these interesting time-pieces. Astronomers +are, however, accustomed to deal with such stupendous periods in +their calculations, that even the time taken to repair a clock seems +but small in comparison. + +The long tenure of the chair of Astronomy by Brinkley is divided into +two nearly equal periods by the year in which the great circle was +erected. Brinkley was eighteen years waiting for his telescope, and +he had eighteen years more in which to use it. During the first of +these periods Brinkley devoted himself to mathematical research; +during the latter he became a celebrated astronomer. Brinkley's +mathematical labours procured for their author some reputation as a +mathematician. They appear to be works of considerable mathematical +elegance, but not indicating any great power of original thought. +Perhaps it has been prejudicial to Brinkley's fame in this direction, +that he was immediately followed in his chair by so mighty a genius +as William Rowan Hamilton. + +After the great circle had been at last erected, Brinkley was able to +begin his astronomical work in earnest. Nor was there much time to +lose. He was already forty-five years old, a year older than was +Herschel when he commenced his immortal career at Slough. Stimulated +by the consciousness of having the command of an instrument of unique +perfection, Brinkley loftily attempted the very highest class of +astronomical research. He resolved to measure anew with his own eye +and with his own hand the constants of aberration and of nutation. He +also strove to solve that great problem of the universe, the +discovery of the distance of a fixed star. + +These were noble problems, and they were nobly attacked. But to +appraise with justice this work of Brinkley, done seventy years ago, +we must not apply to it the same criterion as we would think right to +apply to similar work were it done now. We do not any longer use +Brinkley's constant of aberration, nor do we now think that +Brinkley's determinations of the star distances were reliable. But, +nevertheless, his investigations exercised a marked influence on the +progress of science; they stimulated the study of the principles on +which exact measurements were to be conducted. + +Brinkley had another profession in addition to that of an +astronomer. He was a divine. When a man endeavours to pursue two +distinct occupations concurrently, it will be equally easy to explain +why his career should be successful, or why it should be the +reverse. If he succeeds, he will, of course, exemplify the wisdom of +having two strings to his bow. Should he fail, it is, of course, +because he has attempted to sit on two stools at once. In Brinkley's +case, his two professions must be likened to the two strings rather +than to the two stools. It is true that his practical experience of +his clerical life was very slender. He had made no attempt to +combine the routine of a parish with his labours in the observatory. +Nor do we associate a special eminence in any department of religious +work with his name. If, however, we are to measure Brinkley's merits +as a divine by the ecclesiastical preferment which he received, his +services to theology must have rivalled his services to astronomy. +Having been raised step by step in the Church, he was at last +appointed to the See of Cloyne, in 1826, as the successor of Bishop +Berkeley. + +Now, though it was permissible for the Archdeacon to be also the +Andrews Professor, yet when the Archdeacon became a Bishop, it was +understood that he should transfer his residence from the observatory +to the palace. The chair of Astronomy accordingly became vacant. +Brinkley's subsequent career seems to have been devoted entirely to +ecclesiastical matters, and for the last ten years of his life he did +not contribute a paper to any scientific society. Arago, after a +characteristic lament that Brinkley should have forsaken the pursuit +of science for the temporal and spiritual attractions of a bishopric, +pays a tribute to the conscientiousness of the quondam astronomer, +who would not even allow a telescope to be brought into the palace +lest his mind should be distracted from his sacred duties. + +The good bishop died on the 13th September, 1835. He was buried in +the chapel of Trinity College, and a fine monument to his memory is a +familiar object at the foot of the noble old staircase of the library. +The best memorial of Brinkley is his admirable book on the "Elements +of Plane Astronomy." It passed through many editions in his lifetime, +and even at the present day the same work, revised first by Dr. Luby, +and more recently by the Rev. Dr. Stubbs and Dr. Brunnow, has a large +and well-merited circulation. + + + + +JOHN HERSCHEL. + + +This illustrious son of an illustrious father was born at Slough, +near Windsor, on the 7th March, 1792. He was the only child of Sir +William Herschel, who had married somewhat late in life, as we have +already mentioned. + +[PLATE: ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon.] + +The surroundings among which the young astronomer was reared afforded +him an excellent training for that career on which he was to enter, +and in which he was destined to attain a fame only less brilliant +than that of his father. The circumstances of his youth permitted +him to enjoy one great advantage which was denied to the elder +Herschel. He was able, from his childhood, to devote himself almost +exclusively to intellectual pursuits. William Herschel, in the early +part of his career, had only been able to snatch occasional hours for +study from his busy life as a professional musician. But the son, +having been born with a taste for the student's life, was fortunate +enough to have been endowed with the leisure and the means to enjoy +it from the commencement. His early years have been so well +described by the late Professor Pritchard in the "Report of the +Council of the Royal Astronomical Society for 1872," that I venture +to make an extract here:-- + +"A few traits of John Herschel's boyhood, mentioned by himself in his +maturer life, have been treasured up by those who were dear to him, +and the record of some of them may satisfy a curiosity as pardonable +as inevitable, which craves to learn through what early steps great +men or great nations become illustrious. His home was singular, and +singularly calculated to nurture into greatness any child born as +John Herschel was with natural gifts, capable of wide development. At +the head of the house there was the aged, observant, reticent +philosopher, and rarely far away his devoted sister, Caroline +Herschel, whose labours and whose fame are still cognisable as a +beneficent satellite to the brighter light of her illustrious +brother. It was in the companionship of these remarkable persons, +and under the shadow of his father's wonderful telescope, that John +Herschel passed his boyish years. He saw them, in silent but +ceaseless industry, busied about things which had no apparent concern +with the world outside the walls of that well-known house, but which, +at a later period of his life, he, with an unrivalled eloquence, +taught his countrymen to appreciate as foremost among those living +influences which but satisfy and elevate the noblest instincts of our +nature. What sort of intercourse passed between the father and the +boy may be gathered from an incident or two which he narrated as +having impressed themselves permanently on the memory of his youth. +He once asked his father what he thought was the oldest of all +things. The father replied, after the Socratic method, by putting +another question: 'And what do you yourself suppose is the oldest of +all things?' The boy was not successful in his answers, thereon the +old astronomer took up a small stone from the garden walk: 'There, my +child, there is the oldest of all the things that I certainly know.' +On another occasion his father is said to have asked the boy, 'What +sort of things, do you think, are most alike?' The delicate, +blue-eyed boy, after a short pause, replied, 'The leaves of the same +tree are most like each other.' 'Gather, then, a handful of leaves of +that tree,' rejoined the philosopher, 'and choose two that are +alike.' The boy failed; but he hid the lesson in his heart, and his +thoughts were revealed after many days. These incidents may be +trifles; nor should we record them here had not John Herschel +himself, though singularly reticent about his personal emotions, +recorded them as having made a strong impression on his mind. Beyond +all doubt we can trace therein, first, that grasp and grouping of +many things in one, implied in the stone as the oldest of things; +and, secondly, that fine and subtle discrimination of each thing out +of many like things as forming the main features which characterized +the habit of our venerated friend's philosophy." + +John Herschel entered St. John's College, Cambridge, when he was +seventeen years of age. His university career abundantly fulfilled +his father's eager desire, that his only son should develop a +capacity for the pursuit of science. After obtaining many lesser +distinctions, he finally came out as Senior Wrangler in 1813. It +was, indeed, a notable year in the mathematical annals of the +University. Second on that list, in which Herschel's name was first, +appeared that of the illustrious Peacock, afterwards Dean of Ely, who +remained throughout life one of Herschel's most intimate friends. + +Almost immediately after taking his degree, Herschel gave evidence of +possessing a special aptitude for original scientific investigation. +He sent to the Royal Society a mathematical paper which was published +in the PHILOSOPHICAL TRANSACTIONS. Doubtless the splendour that +attached to the name he bore assisted him in procuring early +recognition of his own great powers. Certain it is that he was made +a Fellow of the Royal Society at the unprecedentedly early age of +twenty-one. Even after this remarkable encouragement to adopt a +scientific career as the business of his life, it does not seem that +John Herschel at first contemplated devoting himself exclusively to +science. He commenced to prepare for the profession of the Law by +entering as a student at the Middle Temple, and reading with a +practising barrister. + +But a lawyer John Herschel was not destined to become. Circumstances +brought him into association with some leading scientific men. He +presently discovered that his inclinations tended more and more in +the direction of purely scientific pursuits. Thus it came to pass +that the original intention as to the calling which he should follow +was gradually abandoned. Fortunately for science Herschel found its +pursuit so attractive that he was led, as his father had been before +him, to give up his whole life to the advancement of knowledge. Nor +was it unnatural that a Senior Wrangler, who had once tasted the +delights of mathematical research, should have been tempted to devote +much time to this fascinating pursuit. By the time John Herschel was +twenty-nine he had published so much mathematical work, and his +researches were considered to possess so much merit, that the Royal +Society awarded him the Copley Medal, which was the highest +distinction it was capable of conferring. + +At the death of his father in 1822, John Herschel, with his tastes +already formed for a scientific career, found himself in the +possession of ample means. To him also passed all his father's great +telescopes and apparatus. These material aids, together with a +dutiful sense of filial obligation, decided him to make practical +astronomy the main work of his life. He decided to continue to its +completion that great survey of the heavens which had already been +inaugurated, and, indeed, to a large extent accomplished, by his +father. + +The first systematic piece of practical astronomical work which John +Herschel undertook was connected with the measurement of what are +known as "Double Stars." It should be observed, that there are in +the heavens a number of instances in which two stars are seen in very +close association. In the case of those objects to which the +expression "Double Stars" is generally applied, the two luminous +points are so close together that even though they might each be +quite bright enough to be visible to the unaided eye, yet their +proximity is such that they cannot be distinguished as two separate +objects without optical aid. The two stars seem fused together into +one. In the telescope, however, the bodies may be discerned +separately, though they are frequently so close together that it +taxes the utmost power of the instrument to indicate the division +between them. + +The appearance presented by a double star might arise from the +circumstance that the two stars, though really separated from each +other by prodigious distances, happened to lie nearly in the same +line of vision, as seen from our point of view. No doubt, many of +the so-called double stars could be accounted for on this +supposition. Indeed, in the early days when but few double stars +were known, and when telescopes were not powerful enough to exhibit +the numerous close doubles which have since been brought to light, +there seems to have been a tendency to regard all double stars as +merely such perspective effects. It was not at first suggested that +there could be any physical connection between the components of each +pair. The appearance presented was regarded as merely due to the +circumstance that the line joining the two bodies happened to pass +near the earth. + +[PLATE: SIR JOHN HERSCHEL.] + +In the early part of his career, Sir William Herschel seems to have +entertained the view then generally held by other astronomers with +regard to the nature of these stellar pairs. The great observer +thought that the double stars could therefore be made to afford a +means of solving that problem in which so many of the observers of +the skies had been engaged, namely, the determination of the +distances of the stars from the earth. Herschel saw that the +displacement of the earth in its annual movement round the sun would +produce an apparent shift in the place of the nearer of the two stars +relatively to the other, supposed to be much more remote. If this +shift could be measured, then the distance of the nearer of the stars +could be estimated with some degree of precision. + +As has not unfrequently happened in the history of science, an effect +was perceived of a very different nature from that which had been +anticipated. If the relative places of the two stars had been +apparently deranged merely in consequence of the motion of the earth, +then the phenomenon would be an annual one. After the lapse of a +year the two stars would have regained their original relative +positions. This was the effect for which William Herschel was +looking. In certain of the so called double stars, he, no doubt, did +find a movement. He detected the remarkable fact that both the +apparent distance and the relative positions of the two bodies were +changing. But what was his surprise to observe that these +alterations were not of an annually periodic character. It became +evident then that in some cases one of the component stars was +actually revolving around the other, in an orbit which required many +years for its completion. Here was indeed a remarkable discovery. It +was clearly impossible to suppose that movements of this kind could +be mere apparent displacements, arising from the annual shift in our +point of view, in consequence of the revolution of the earth. +Herschel's discovery established the interesting fact that, in +certain of these double stars, or binary stars, as these particular +objects are more expressively designated, there is an actual orbital +revolution of a character similar to that which the earth performs +around the sun. Thus it was demonstrated that in these particular +double stars the nearness of the two components was not merely +apparent. The objects must actually lie close together at a distance +which is small in comparison with the distance at which either of +them is separated from the earth. The fact that the heavens contain +pairs of twin suns in mutual revolution was thus brought to light. + +In consequence of this beautiful discovery, the attention of +astronomers was directed to the subject of double stars with a degree +of interest which these objects had never before excited. It was +therefore not unnatural that John Herschel should have been attracted +to this branch of astronomical work. Admiration for his father's +discovery alone might have suggested that the son should strive to +develop this territory newly opened up to research. But it also +happened that the mathematical talents of the younger Herschel +inclined his inquiries in the same direction. He saw clearly that, +when sufficient observations of any particular binary star had been +accumulated, it would then be within the power of the mathematician +to elicit from those observations the shape and the position in space +of the path which each of the revolving stars described around the +other. Indeed, in some cases he would be able to perform the +astonishing feat of determining from his calculations the weight of +these distant suns, and thus be enabled to compare them with the mass +of our own sun. + +[PLATE: NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel.] + +But this work must follow the observations, it could not precede +them. The first step was therefore to observe and to measure with +the utmost care the positions and distances of those particular +double stars which appear to offer the greatest promise in this +particular research. In 1821, Herschel and a friend of his, Mr. +James South, agreed to work together with this object. South was a +medical man with an ardent devotion to science, and possessed of +considerable wealth. He procured the best astronomical instruments +that money could obtain, and became a most enthusiastic astronomer +and a practical observer of tremendous energy. + +South and John Herschel worked together for two years in the +observation and measurement of the double stars discovered by Sir +William Herschel. In the course of this time their assiduity was +rewarded by the accumulation of so great a mass of careful +measurements that when published, they formed quite a volume in the +"Philosophical Transactions." The value and accuracy of the work, +when estimated by standards which form proper criteria for that +period, is universally recognised. It greatly promoted the progress +of sidereal astronomy, and the authors were in consequence awarded +medals from the Royal Society, and the Royal Astronomical Society, +as well as similar testimonials from various foreign institutions. + +This work must, however, be regarded as merely introductory to the +main labours of John Herschel's life. His father devoted the greater +part of his years as an observer to what he called his "sweeps" of +the heavens. The great reflecting telescope, twenty feet long, was +moved slowly up and down through an arc of about two degrees towards +and from the pole, while the celestial panorama passed slowly in the +course of the diurnal motion before the keenly watching eye of the +astronomer. Whenever a double star traversed the field Herschel +described it to his sister Caroline, who, as we have already +mentioned, was his invariable assistant in his midnight watches. When +a nebula appeared, then he estimated its size and its brightness, he +noticed whether it had a nucleus, or whether it had stars disposed in +any significant manner with regard to it. He also dictated any other +circumstance which he deemed worthy of record. These observations +were duly committed to writing by the same faithful and indefatigable +scribe, whose business it also was to take a memorandum of the exact +position of the object as indicated by a dial placed in front of her +desk, and connected with the telescope. + +John Herschel undertook the important task of re-observing the +various double stars and nebulae which had been discovered during +these memorable vigils. The son, however, lacked one inestimable +advantage which had been possessed by the father. John Herschel had +no assistant to discharge all those duties which Caroline had so +efficiently accomplished. He had, therefore, to modify the system of +sweeping previously adopted in order to enable all the work both of +observing and of recording to be done by himself. This, in many +ways, was a great drawback to the work of the younger astronomer. The +division of labour between the observer and the scribe enables a +greatly increased quantity of work to be got through. It is also +distinctly disadvantageous to an observer to have to use his eye at +the telescope directly after he has been employing it for reading the +graduations on a circle, by the light of a lamp, or for entering +memoranda in a note book. Nebulae, especially, are often so +excessively faint that they can only be properly observed by an eye +which is in that highly sensitive condition which is obtained by long +continuance in darkness. The frequent withdrawal of the eye from the +dark field of the telescope, and the application of it to reading by +artificial light, is very prejudicial to its use for the more +delicate purpose. John Herschel, no doubt, availed himself of every +precaution to mitigate the ill effects of this inconvenience as much +as possible, but it must have told upon his labours as compared with +those of his father. + +But nevertheless John Herschel did great work during his "sweeps." He +was specially particular to note all the double stars which presented +themselves to his observation. Of course some little discretion must +be allowed in deciding as to what degree of proximity in adjacent +stars does actually bring them within the category of "double +stars." Sir John set down all such objects as seemed to him likely +to be of interest, and the results of his discoveries in this branch +of astronomy amount to some thousands. Six or seven great memoirs in +the TRANSACTIONS of the Royal Astronomical Society have been devoted +to giving an account of his labours in this department of astronomy. + +[PLATE: THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.] + +One of the achievements by which Sir John Herschel is best known is +his invention of a method by which the orbits of binary stars could +be determined. It will be observed that when one star revolves +around another in consequence of the law of gravitation, the orbit +described must be an ellipse. This ellipse, however, generally +speaking, appears to us more or less foreshortened, for it is easily +seen that only under highly exceptional circumstances would the plane +in which the stars move happen to be directly square to the line of +view. It therefore follows that what we observe is not exactly the +track of one star around the other; it is rather the projection of +that track as seen on the surface of the sky. Now it is remarkable +that this apparent path is still an ellipse. Herschel contrived a +very ingenious and simple method by which he could discover from the +observations the size and position of the ellipse in which the +revolution actually takes place. He showed how, from the study of +the apparent orbit of the star, and from certain measurements which +could easily be effected upon it, the determination of the true +ellipse in which the movement is performed could be arrived at. In +other words, Herschel solved in a beautiful manner the problem of +finding the true orbits of double stars. The importance of this work +may be inferred from the fact that it has served as the basis on +which scores of other investigators have studied the fascinating +subject of the movement of binary stars. + +The labours, both in the discovery and measurement of the double +stars, and in the discussion of the observations with the object of +finding the orbits of such stars as are in actual revolution, +received due recognition in yet another gold medal awarded by the +Royal Society. An address was delivered on the occasion by the Duke +of Sussex (30th November, 1833), in the course of which, after +stating that the medal had been conferred on Sir John Herschel, he +remarks:-- + +"It has been said that distance of place confers the same privilege +as distance of time, and I should gladly avail myself of the +privilege which is thus afforded me by Sir John Herschel's separation +from his country and friends, to express my admiration of his +character in stronger terms than I should otherwise venture to use; +for the language of panegyric, however sincerely it may flow from the +heart, might be mistaken for that of flattery, if it could not thus +claim somewhat of an historical character; but his great attainments +in almost every department of human knowledge, his fine powers as a +philosophical writer, his great services and his distinguished +devotion to science, the high principles which have regulated his +conduct in every relation of life, and, above all, his engaging +modesty, which is the crown of all his other virtues, presenting such +a model of an accomplished philosopher as can rarely be found beyond +the regions of fiction, demand abler pens than mine to describe them +in adequate terms, however much inclined I might feel to undertake +the task." + +The first few lines of the eulogium just quoted allude to Herschel's +absence from England. This was not merely an episode of interest in +the career of Herschel, it was the occasion of one of the greatest +scientific expeditions in the whole history of astronomy. + +Herschel had, as we have seen, undertaken a revision of his father's +"sweeps" for new objects, in those skies which are visible from our +latitudes in the northern hemisphere. He had well-nigh completed +this task. Zone by zone the whole of the heavens which could be +observed from Windsor had passed under his review. He had added +hundreds to the list of nebulae discovered by his father. He had +announced thousands of double stars. At last, however, the great +survey was accomplished. The contents of the northern hemisphere, so +far at least as they could be disclosed by his telescope of twenty +feet focal length, had been revealed. + +[PLATE: SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope.] + +But Herschel felt that this mighty task had to be supplemented by +another of almost equal proportions, before it could be said that the +twenty-foot telescope had done its work. It was only the northern +half of the celestial sphere which had been fully explored. The +southern half was almost virgin territory, for no other astronomer +was possessed of a telescope of such power as those which the +Herschels had used. It is true, of course, that as a certain margin +of the southern hemisphere was visible from these latitudes, it had +been more or less scrutinized by observers in northern skies. And +the glimpses which had thus been obtained of the celestial objects in +the southern sky, were such as to make an eager astronomer long for a +closer acquaintance with the celestial wonders of the south. The +most glorious object in the sidereal heavens, the Great Nebula in +Orion, lies indeed in that southern hemisphere to which the younger +Herschel's attention now became directed. It fortunately happens, +however, for votaries of astronomy all the world over, that Nature +has kindly placed her most astounding object, the great Nebula in +Orion, in such a favoured position, near the equator, that from a +considerable range of latitudes, both north and south, the wonders of +the Nebula can be explored. There are grounds for thinking that the +southern heavens contain noteworthy objects which, on the whole, are +nearer to the solar system than are the noteworthy objects in the +northern skies. The nearest star whose distance is known, Alpha +Centauri, lies in the southern hemisphere, and so also does the most +splendid cluster of stars. + +Influenced by the desire to examine these objects, Sir John Herschel +determined to take his great telescope to a station in the southern +hemisphere, and thus complete his survey of the sidereal heavens. The +latitude of the Cape of Good Hope is such that a suitable site could +be there found for his purpose. The purity of the skies in South +Africa promised to provide for the astronomer those clear nights +which his delicate task of surveying the nebulae would require. + +On November 13, 1833, Sir John Herschel, who had by this time +received the honour of knighthood from William IV., sailed from +Portsmouth for the Cape of Good Hope, taking with him his gigantic +instruments. After a voyage of two months, which was considered to +be a fair passage in those days, he landed in Table Bay, and having +duly reconnoitred various localities, he decided to place his +observatory at a place called Feldhausen, about six miles from Cape +Town, near the base of the Table Mountain. A commodious residence +was there available, and in it he settled with his family. A +temporary building was erected to contain the equatorial, but the +great twenty-foot telescope was accommodated with no more shelter +than is provided by the open canopy of heaven. + +As in his earlier researches at home, the attention of the great +astronomer at the Cape of Good Hope was chiefly directed to the +measurement of the relative positions and distances apart of the +double stars, and to the close examination of the nebulae. In the +delineation of the form of these latter objects Herschel found ample +employment for his skilful pencil. Many of the drawings he has made +of the celestial wonders in the southern sky are admirable examples +of celestial portraiture. + +The number of the nebulae and of those kindred objects, the star +clusters, which Herschel studied in the southern heavens, during four +years of delightful labour, amount in all to one thousand seven +hundred and seven. His notes on their appearance, and the +determinations of their positions, as well as his measurements of +double stars, and much other valuable astronomical research, were +published in a splendid volume, brought out at the cost of the Duke +of Northumberland. This is, indeed, a monumental work, full of +interesting and instructive reading for any one who has a taste for +astronomy. + +Herschel had the good fortune to be at the Cape on the occasion of +the periodical return of Halley's great comet in 1833. To the study +of this body he gave assiduous attention, and the records of his +observations form one of the most interesting chapters in that +remarkable volume to which we have just referred. + +[PLATE: COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens.] + +Early in 1838 Sir John Herschel returned to England. He had made +many friends at the Cape, who deeply sympathised with his self- +imposed labours while he was resident among them. They desired to +preserve the recollection of this visit, which would always, they +considered, be a source of gratification in the colony. Accordingly, +a number of scientific friends in that part of the world raised a +monument with a suitable inscription, on the spot which had been +occupied by the great twenty-foot reflector at Feldhausen. + +His return to England after five years of absence was naturally an +occasion for much rejoicing among the lovers of astronomy. He was +entertained at a memorable banquet, and the Queen, at her coronation, +made him a baronet. His famous aunt Caroline, at that time aged +eighty, was still in the enjoyment of her faculties, and was able to +estimate at its true value the further lustre which was added to the +name she bore. But there is reason to believe that her satisfaction +was not quite unmixed with other feelings. With whatever favour she +might regard her nephew, he was still not the brother to whom her +life had been devoted. So jealous was this vigorous old lady of the +fame of the great brother William, that she could hardly hear with +patience of the achievements of any other astronomer, and this +failing existed in some degree even when that other astronomer +happened to be her illustrious nephew. + +With Sir John Herschel's survey of the Southern Hemisphere it may be +said that his career as an observing astronomer came to a close. He +did not again engage in any systematic telescopic research. But it +must not be inferred from this statement that he desisted from active +astronomical work. It has been well observed that Sir John Herschel +was perhaps the only astronomer who has studied with success, and +advanced by original research, every department of the great science +with which his name is associated. It was to some other branches of +astronomy besides those concerned with looking through telescopes, +that the rest of the astronomer's life was to be devoted. + +To the general student Sir John Herschel is best known by the volume +which he published under the title of "Outlines of Astronomy." This +is, indeed, a masterly work, in which the characteristic difficulties +of the subject are resolutely faced and expounded with as much +simplicity as their nature will admit. As a literary effort this +work is admirable, both on account of its picturesque language and +the ennobling conceptions of the universe which it unfolds. The +student who desires to become acquainted with those recondite +departments of astronomy, in which the effects of the disturbing +action of one planet upon the motions of another planet are +considered, will turn to the chapters in Herschel's famous work on +the subject. There he will find this complex matter elucidated, +without resort to difficult mathematics. Edition after edition of +this valuable work has appeared, and though the advances of modern +astronomy have left it somewhat out of date in certain departments, +yet the expositions it contains of the fundamental parts of the +science still remain unrivalled. + +Another great work which Sir John undertook after his return from the +Cape, was a natural climax to those labours on which his father and +he had been occupied for so many years. We have already explained +how the work of both these observers had been mainly devoted to the +study of the nebulae and the star clusters. The results of their +discoveries had been announced to the world in numerous isolated +memoirs. The disjointed nature of these publications made their use +very inconvenient. But still it was necessary for those who desired +to study the marvellous objects discovered by the Herschels, to have +frequent recourse to the original works. To incorporate all the +several observations of nebular into one great systematic catalogue, +seemed, therefore, to be an indispensable condition of progress in +this branch of knowledge. No one could have been so fitted for this +task as Sir John Herschel. He, therefore, attacked and carried +through the great undertaking. Thus at last a grand catalogue of +nebulae and clusters was produced. Never before was there so +majestic an inventory. If we remember that each of the nebulae is an +object so vast, that the whole of the solar system would form an +inconsiderable speck by comparison, what are we to think of a +collection in which these objects are enumerated in thousands? In +this great catalogue we find arranged in systematic order all the +nebulae and all the clusters which had been revealed by the diligence +of the Herschels, father and son, in the Northern Hemisphere, and of +the son alone in the Southern Hemisphere. Nor should we omit to +mention that the labours of other astronomers were likewise +incorporated. It was unavoidable that the descriptions given to each +of the objects should be very slight. Abbreviations are used, which +indicate that a nebula is bright, or very bright, or extremely +bright, or faint, or very faint, or extremely faint. Such phrases +have certainly but a relative and technical meaning in such a +catalogue. The nebulae entered as extremely bright by the +experienced astronomer are only so described by way of contrast to +the great majority of these delicate telescopic objects. Most of the +nebulae, indeed, are so difficult to see, that they admit of but very +slight description. It should be observed that Herschel's catalogue +augmented the number of known nebulous objects to more than ten times +that collected into any catalogue which had ever been compiled before +the days of William Herschel's observing began. But the study of +these objects still advances, and the great telescopes now in use +could probably show at least twice as many of these objects as are +contained in the list of Herschel, of which a new and enlarged +edition has since been brought out by Dr. Dreyer. + +One of the best illustrations of Sir John Herschel's literary powers +is to be found in the address which he delivered at the Royal +Astronomical Society, on the occasion of presenting a medal to Mr. +Francis Baily, in recognition of his catalogue of stars. The passage +I shall here cite places in its proper aspect the true merit of the +laborious duty involved in such a task as that which Mr. Baily had +carried through with such success:-- + +"If we ask to what end magnificent establishments are maintained by +states and sovereigns, furnished with masterpieces of art, and placed +under the direction of men of first-rate talent and high-minded +enthusiasm, sought out for those qualities among the foremost in the +ranks of science, if we demand QUI BONO? for what good a Bradley has +toiled, or a Maskelyne or a Piazzi has worn out his venerable age in +watching, the answer is--not to settle mere speculative points in the +doctrine of the universe; not to cater for the pride of man by +refined inquiries into the remoter mysteries of nature; not to trace +the path of our system through space, or its history through past and +future eternities. These, indeed, are noble ends and which I am far +from any thought of depreciating; the mind swells in their +contemplation, and attains in their pursuit an expansion and a +hardihood which fit it for the boldest enterprise. But the direct +practical utility of such labours is fully worthy of their +speculative grandeur. The stars are the landmarks of the universe; +and, amidst the endless and complicated fluctuations of our system, +seem placed by its Creator as guides and records, not merely to +elevate our minds by the contemplation of what is vast, but to teach +us to direct our actions by reference to what is immutable in His +works. It is, indeed, hardly possible to over-appreciate their value +in this point of view. Every well-determined star, from the moment +its place is registered, becomes to the astronomer, the geographer, +the navigator, the surveyor, a point of departure which can never +deceive or fail him, the same for ever and in all places, of a +delicacy so extreme as to be a test for every instrument yet invented +by man, yet equally adapted for the most ordinary purposes; as +available for regulating a town clock as for conducting a navy to the +Indies; as effective for mapping down the intricacies of a petty +barony as for adjusting the boundaries of Transatlantic empires. When +once its place has been thoroughly ascertained and carefully +recorded, the brazen circle with which that useful work was done may +moulder, the marble pillar may totter on its base, and the astronomer +himself survive only in the gratitude of posterity; but the record +remains, and transfuses all its own exactness into every +determination which takes it for a groundwork, giving to inferior +instruments--nay, even to temporary contrivances, and to the +observations of a few weeks or days--all the precision attained +originally at the cost of so much time, labour, and expense." + +Sir John Herschel wrote many other works besides those we have +mentioned. His "Treatise on Meteorology" is, indeed, a standard work +on this subject, and numerous articles from the same pen on +miscellaneous subjects, which have been collected and reprinted, +seemed as a relaxation from his severe scientific studies. Like +certain other great mathematicians Herschel was also a poet, and he +published a translation of the Iliad into blank verse. + +In his later years Sir John Herschel lived a retired life. For a +brief period he had, indeed, been induced to accept the office of +Master of the Mint. It was, however, evident that the routine of +such an occupation was not in accordance with his tastes, and he +gladly resigned it, to return to the seclusion of his study in his +beautiful home at Collingwood, in Kent. + +His health having gradually failed, he died on the 11th May, 1871, in +the seventy-ninth year of his age. + + + + +THE EARL OF ROSSE. + + +The subject of our present sketch occupies quite a distinct position +in scientific history. Unlike many others who have risen by their +scientific discoveries from obscurity to fame, the great Earl of +Rosse was himself born in the purple. His father, who, under the +title of Sir Lawrence Parsons, had occupied a distinguished position +in the Irish Parliament, succeeded on the death of his father to the +Earldom which had been recently created. The subject of our present +memoir was, therefore, the third of the Earls of Rosse, and he was +born in York on June 17, 1800. Prior to his father's death in 1841, +he was known as Lord Oxmantown. + +The University education of the illustrious astronomer was begun in +Dublin and completed at Oxford. We do not hear in his case of any +very remarkable University career. Lord Rosse was, however, a +diligent student, and obtained a first-class in mathematics. He +always took a great deal of interest in social questions, and was a +profound student of political economy. He had a seat in the House of +Commons, as member for King's County, from 1821 to 1834, his +ancestral estate being situated in this part of Ireland. + +[PLATE: THE EARL OF ROSSE.] + +Lord Rosse was endowed by nature with a special taste for mechanical +pursuits. Not only had he the qualifications of a scientific +engineer, but he had the manual dexterity which qualified him +personally to carry out many practical arts. Lord Rosse was, in +fact, a skilful mechanic, an experienced founder, and an ingenious +optician. His acquaintances were largely among those who were +interested in mechanical pursuits, and it was his delight to visit +the works or engineering establishments where refined processes in +the arts were being carried on. It has often been stated--and as I +have been told by members of his family, truly stated--that on one +occasion, after he had been shown over some large works in the north +of England, the proprietor bluntly said that he was greatly in want +of a foreman, and would indeed be pleased if his visitor, who had +evinced such extraordinary capacity for mechanical operations, would +accept the post. Lord Rosse produced his card, and gently explained +that he was not exactly the right man, but he appreciated the +compliment, and this led to a pleasant dinner, and was the basis of a +long friendship. + +I remember on one occasion hearing Lord Rosse explain how it was that +he came to devote his attention to astronomy. It appears that when +he found himself in the possession of leisure and of means, he +deliberately cast around to think how that means and that leisure +could be most usefully employed. Nor was it surprising that he +should search for a direction which would offer special scope for his +mechanical tastes. He came to the conclusion that the building of +great telescopes was an art which had received no substantial advance +since the great days of William Herschel. He saw that to construct +mighty instruments for studying the heavens required at once the +command of time and the command of wealth, while he also felt that +this was a subject the inherent difficulties of which would tax to +the uttermost whatever mechanical skill he might possess. Thus it +was he decided that the construction of great telescopes should +become the business of his life. + +[PLATE: BIRR CASTLE. + +PLATE: THE MALL, PARSONSTOWN.] + +In the centre of Ireland, seventy miles from Dublin, on the border +between King's County and Tipperary, is a little town whereof we must +be cautious before writing the name. The inhabitants of that town +frequently insist that its name is Birr, * while the official +designation is Parsonstown, and to this day for every six people who +apply one name to the town, there will be half a dozen who use the +other. But whichever it may be, Birr or Parsonstown--and I shall +generally call it by the latter name--it is a favourable specimen of +an Irish county town. The widest street is called the Oxmantown +Mall. It is bordered by the dwelling-houses of the chief residents, +and adorned with rows of stately trees. At one end of this +distinctly good feature in the town is the Parish Church, while at +the opposite end are the gates leading into Birr Castle, the +ancestral home of the house of Parsons. Passing through the gates +the visitor enters a spacious demesne, possessing much beauty of wood +and water, one of the most pleasing features being the junction of +the two rivers, which unite at a spot ornamented by beautiful +timber. At various points illustrations of the engineering skill of +the great Earl will be observed. The beauty of the park has been +greatly enhanced by the construction of an ample lake, designed with +the consummate art by which art is concealed. Even in mid-summer it +is enlivened by troops of wild ducks preening themselves in that +confidence which they enjoy in those happy localities where the sound +of a gun is seldom heard. The water is led into the lake by a tube +which passes under one of the two rivers just mentioned, while the +overflow from the lake turns a water-wheel, which works a pair of +elevators ingeniously constructed for draining the low-lying parts of +the estate. + + * Considering the fame acquired by Parsonstown from Lord Rosse's + mirrors, it may be interesting to note the following extract from + "The Natural History of Ireland," by Dr. Gerard Boate, Thomas + Molyneux M.D., F.R.S., and others, which shows that 150 years ago + Parsonstown was famous for its glass:-- + + "We shall conclude this chapter with the glass, there having been + several glasshouses set up by the English in Ireland, none in Dublin + or other cities, but all of them in the country; amongst which the + principal was that of Birre, a market town, otherwise called + Parsonstown, after one Sir Lawrence Parsons, who, having purchased + that lordship, built a goodly house upon it; his son William Parsons + having succeeded him in the possession of it; which town is situate + in Queen's County, about fifty miles (Irish) to the southwest of + Dublin, upon the borders of the two provinces of Leinster and Munster; + from this place Dublin was furnished with all sorts of window and + drinking glasses, and such other as commonly are in use. One part of + the materials, viz., the sand, they had out of England; the other, + to wit the ashes, they made in the place of ash-tree, and used no + other. The chiefest difficulty was to get the clay for the pots to + melt the materials in; this they had out of the north."--Chap. XXI., + Sect. VIII. "Of the Glass made in Ireland." + +Birr Castle itself is a noble mansion with reminiscences from the +time of Cromwell. It is surrounded by a moat and a drawbridge of +modern construction, and from its windows beautiful views can be had +over the varied features of the park. But while the visitors to +Parsonstown will look with great interest on this residence of an +Irish landlord, whose delight it was to dwell in his own country, and +among his own people, yet the feature which they have specially come +to observe is not to be found in the castle itself. On an extensive +lawn, sweeping down from the moat towards the lake, stand two noble +masonry walls. They are turreted and clad with ivy, and considerably +loftier than any ordinary house. As the visitor approaches, he will +see between those walls what may at first sight appear to him to be +the funnel of a steamer lying down horizontally. On closer approach +he will find that it is an immense wooden tube, sixty feet long, and +upwards of six feet in diameter. It is in fact large enough to admit +of a tall man entering into it and walking erect right through from +one end to the other. This is indeed the most gigantic instrument +which has ever been constructed for the purpose of exploring the +heavens. Closely adjoining the walls between which the great tube +swings, is a little building called "The Observatory." In this the +smaller instruments are contained, and there are kept the books which +are necessary for reference. The observatory also offers shelter to +the observers, and provides the bright fire and the cup of warm tea, +which are so acceptable in the occasional intervals of a night's +observation passed on the top of the walls with no canopy but the +winter sky. + +Almost the first point which would strike the visitor to Lord Rosse's +telescope is that the instrument at which he is looking is not only +enormously greater than anything of the kind that he has ever seen +before, but also that it is something of a totally different nature. +In an ordinary telescope he is accustomed to find a tube with lenses +of glass at either end, while the large telescopes that we see in our +observatories are also in general constructed on the same principle. +At one end there is the object-glass, and at the other end the +eye-piece, and of course it is obvious that with an instrument of +this construction it is to the lower end of the tube that the eye of +the observer must be placed when the telescope is pointed to the +skies. But in Lord Rosse's telescope you would look in vain for +these glasses, and it is not at the lower end of the instrument that +you are to take your station when you are going to make your +observations. The astronomer at Parsonstown has rather to avail +himself of the ingenious system of staircases and galleries, by which +he is enabled to obtain access to the mouth of the great tube. The +colossal telescope which swings between the great walls, like +Herschel's great telescope already mentioned, is a reflector, the +original invention of which is due of course to Newton. The optical +work which is accomplished by the lenses in the ordinary telescope is +effected in the type of instrument constructed by Lord Rosse by a +reflecting mirror which is placed at the lower end of the vast tube. +The mirror in this instrument is made of a metal consisting of two +parts of copper to one of tin. As we have already seen, this mixture +forms an alloy of a very peculiar nature. The copper and the tin +both surrender their distinctive qualities, and unite to form a +material of a very different physical character. The copper is tough +and brown, the tin is no doubt silvery in hue, but soft and almost +fibrous in texture. When the two metals are mixed together in the +proportions I have stated, the alloy obtained is intensely hard and +quite brittle being in both these respects utterly unlike either of +the two ingredients of which it is composed. It does, however, +resemble the tin in its whiteness, but it acquires a lustre far +brighter than tin; in fact, this alloy hardly falls short of silver +itself in its brilliance when polished. + +[PLATE: LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin.] + +The first duty that Lord Rosse had to undertake was the construction +of this tremendous mirror, six feet across, and about four or five +inches thick. The dimensions were far in excess of those which had +been contemplated in any previous attempt of the same kind. Herschel +had no doubt fashioned one mirror of four feet in diameter, and many +others of smaller dimensions, but the processes which he employed had +never been fully published, and it was obvious that, with a large +increase in dimensions, great additional difficulties had to be +encountered. Difficulties began at the very commencement of the +process, and were experienced in one form or another at every +subsequent stage. In the first place, the mere casting of a great +disc of this mixture of tin and copper, weighing something like three +or four tons, involved very troublesome problems. No doubt a casting +of this size, if the material had been, for example, iron, would have +offered no difficulties beyond those with which every practical +founder is well acquainted, and which he has to encounter daily in +the course of his ordinary work. But speculum metal is a material of +a very intractable description. There is, of course, no practical +difficulty in melting the copper, nor in adding the proper proportion +of tin when the copper has been melted. There may be no great +difficulty in arranging an organization by which several crucibles, +filled with the molten material, shall be poured simultaneously so as +to obtain the requisite mass of metal, but from this point the +difficulties begin. For speculum metal when cold is excessively +brittle, and were the casting permitted to cool like an ordinary +copper or iron casting, the mirror would inevitably fly into pieces. +Lord Rosse, therefore, found it necessary to anneal the casting with +extreme care by allowing it to cool very slowly. This was +accomplished by drawing the disc of metal as soon as it had entered +into the solid state, though still glowing red, into an annealing +oven. There the temperature was allowed to subside so gradually, +that six weeks elapsed before the mirror had reached the temperature +of the external air. The necessity for extreme precaution in the +operation of annealing will be manifest if we reflect on one of the +accidents which happened. On a certain occasion, after the cooling +of a great casting had been completed, it was found, on withdrawing +the speculum, that it was cracked into two pieces. This mishap was +eventually traced to the fact that one of the walls of the oven had +only a single brick in its thickness, and that therefore the heat had +escaped more easily through that side than through the other sides +which were built of double thickness. The speculum had, +consequently, not cooled uniformly, and hence the fracture had +resulted. Undeterred, however, by this failure, as well as by not a +few other difficulties, into a description of which we cannot now +enter, Lord Rosse steadily adhered to his self-imposed task, and at +last succeeded in casting two perfect discs on which to commence the +tedious processes of grinding and polishing. The magnitude of the +operations involved may perhaps be appreciated if I mention that the +value of the mere copper and tin entering into the composition of +each of the mirrors was about 500 pounds. + +In no part of his undertaking was Lord Rosse's mechanical ingenuity +more taxed than in the devising of the mechanism for carrying out the +delicate operations of grinding and polishing the mirrors, whose +casting we have just mentioned. In the ordinary operations of the +telescope-maker, such processes had hitherto been generally effected +by hand, but, of course, such methods became impossible when dealing +with mirrors which were as large as a good-sized dinner table, and +whose weight was measured by tons. The rough grinding was effected +by means of a tool of cast iron about the same size as the mirror, +which was moved by suitable machinery both backwards and forwards, +and round and round, plenty of sand and water being supplied between +the mirror and the tool to produce the necessary attrition. As the +process proceeded and as the surface became smooth, emery was used +instead of sand; and when this stage was complete, the grinding tool +was removed and the polishing tool was substituted. The essential +part of this was a surface of pitch, which, having been temporarily +softened by heat, was then placed on the mirror, and accepted from +the mirror the proper form. Rouge was then introduced as the +polishing powder, and the operation was continued about nine hours, +by which time the great mirror had acquired the appearance of highly +polished silver. When completed, the disc of speculum metal was +about six feet across and four inches thick. The depression in the +centre was about half an inch. Mounted on a little truck, the great +speculum was then conveyed to the instrument, to be placed in its +receptacle at the bottom of the tube, the length of which was sixty +feet, this being the focal distance of the mirror. Another small +reflector was inserted in the great tube sideways, so as to direct +the gaze of the observer down upon the great reflector. Thus was +completed the most colossal instrument for the exploration of the +heavens which the art of man has ever constructed. + +[PLATE: ROMAN CATHOLIC CHURCH AT PARSONSTOWN.] + +It was once my privilege to be one of those to whom the illustrious +builder of the great telescope entrusted its use. For two seasons in +1865 and 1866 I had the honour of being Lord Rosse's astronomer. +During that time I passed many a fine night in the observer's +gallery, examining different objects in the heavens with the aid of +this remarkable instrument. At the time I was there, the objects +principally studied were the nebulae, those faint stains of light +which lie on the background of the sky. Lord Rosse's telescope was +specially suited for the scrutiny of these objects, inasmuch as their +delicacy required all the light-grasping power which could be +provided. + +One of the greatest discoveries made by Lord Rosse, when his huge +instrument was first turned towards the heavens, consisted in the +detection of the spiral character of some of the nebulous forms. +When the extraordinary structure of these objects was first +announced, the discovery was received with some degree of +incredulity. Other astronomers looked at the same objects, and when +they failed to discern--and they frequently did fail to discern--the +spiral structure which Lord Rosse had indicated, they drew the +conclusion that this spiral structure did not exist. They thought it +must be due possibly to some instrumental defect or to the +imagination of the observer. It was, however, hardly possible for +any one who was both willing and competent to examine into the +evidence, to doubt the reality of Lord Rosse's discoveries. It +happens, however, that they have been recently placed beyond all +doubt by testimony which it is impossible to gainsay. A witness +never influenced by imagination has now come forward, and the +infallible photographic plate has justified Lord Rosse. Among the +remarkable discoveries which Dr. Isaac Roberts has recently made in +the application of his photographic apparatus to the heavens, there +is none more striking than that which declares, not only that the +nebulae which Lord Rosse described as spirals, actually do possess +the character so indicated, but that there are many others of the +same description. He has even brought to light the astonishingly +interesting fact that there are invisible objects of this class which +have never been seen by human eye, but whose spiral character is +visible to the peculiar delicacy of the photographic telescope. + +In his earlier years, Lord Rosse himself used to be a diligent +observer of the heavenly bodies with the great telescope which was +completed in the year 1845. But I think that those who knew Lord +Rosse well, will agree that it was more the mechanical processes +incidental to the making of the telescope which engaged his interest +than the actual observations with the telescope when it was +completed. Indeed one who was well acquainted with him believed Lord +Rosse's special interest in the great telescope ceased when the last +nail had been driven into it. But the telescope was never allowed to +lie idle, for Lord Rosse always had associated with him some ardent +young astronomer, whose delight it was to employ to the uttermost the +advantages of his position in exploring the wonders of the sky. Among +those who were in this capacity in the early days of the great +telescope, I may mention my esteemed friend Dr. Johnston Stoney. + +Such was the renown of Lord Rosse himself, brought about by his +consummate mechanical genius and his astronomical discoveries, and +such the interest which gathered around the marvellous workshops at +Birr castle, wherein his monumental exhibitions of optical skill were +constructed, that visitors thronged to see him from all parts of the +world. His home at Parsonstown became one of the most remarkable +scientific centres in Great Britain; thither assembled from time to +time all the leading men of science in the country, as well as many +illustrious foreigners. For many years Lord Rosse filled with marked +distinction the exalted position of President of the Royal Society, +and his advice and experience in practical mechanical matters were +always at the disposal of those who sought his assistance. Personally +and socially Lord Rosse endeared himself to all with whom he came in +contact. I remember one of the attendants telling me that on one +occasion he had the misfortune to let fall and break one of the small +mirrors on which Lord Rosse had himself expended many hours of hard +personal labour. The only remark of his lordship was that "accidents +will happen." + +The latter years of his life Lord Rosse passed in comparative +seclusion; he occasionally went to London for a brief sojourn during +the season, and he occasionally went for a cruise in his yacht; but +the greater part of the year he spent at Birr Castle, devoting +himself largely to the study of political and social questions, and +rarely going outside the walls of his demesne, except to church on +Sunday mornings. He died on October 31, 1867. + +He was succeeded by his eldest son, the present Earl of Rosse, who +has inherited his father's scientific abilities, and done much +notable work with the great telescope. + + + + +AIRY. + + +In our sketch of the life of Flamsteed, we have referred to the +circumstances under which the famous Observatory that crowns +Greenwich Hill was founded. We have also had occasion to mention +that among the illustrious successors of Flamsteed both Halley and +Bradley are to be included. But a remarkable development of +Greenwich Observatory from the modest establishment of early days +took place under the direction of the distinguished astronomer whose +name is at the head of this chapter. By his labours this temple of +science was organised to such a degree of perfection that it has +served in many respects as a model for other astronomical +establishments in various parts of the world. An excellent account +of Airy's career has been given by Professor H. H. Turner, in the +obituary notice published by the Royal Astronomical Society. To this +I am indebted for many of the particulars here to be set down +concerning the life of the illustrious Astronomer Royal. + +The family from which Airy took his origin came from Kentmere, in +Westmoreland. His father, William Airy, belonged to a Lincolnshire +branch of the same stock. His mother's maiden name was Ann Biddell, +and her family resided at Playford, near Ipswich. William Airy held +some small government post which necessitated an occasional change of +residence to different parts of the country, and thus it was that his +son, George Biddell, came to be born at Alnwick, on 27th July, 1801. +The boy's education, so far as his school life was concerned was +partly conducted at Hereford and partly at Colchester. He does not, +however, seem to have derived much benefit from the hours which he +passed in the schoolroom. But it was delightful to him to spend his +holidays on the farm at Playford, where his uncle, Arthur Biddell, +showed him much kindness. The scenes of his early youth remained +dear to Airy throughout his life, and in subsequent years he himself +owned a house at Playford, to which it was his special delight to +resort for relaxation during the course of his arduous career. In +spite of the defects of his school training he seems to have +manifested such remarkable abilities that his uncle decided to enter +him in Cambridge University. He accordingly joined Trinity College +as a sizar in 1819, and after a brilliant career in mathematical and +physical science he graduated as Senior Wrangler in 1823. It may be +noted as an exceptional circumstance that, notwithstanding the +demands on his time in studying for his tripos, he was able, after +his second term of residence, to support himself entirely by taking +private pupils. In the year after he had taken his degree he was +elected to a Fellowship at Trinity College. + +Having thus gained an independent position, Airy immediately entered +upon that career of scientific work which he prosecuted without +intermission almost to the very close of his life. One of his most +interesting researches in these early days is on the subject of +Astigmatism, which defect he had discovered in his own eyes. His +investigations led him to suggest a means of correcting this defect +by using a pair of spectacles with lenses so shaped as to counteract +the derangement which the astigmatic eye impressed upon the rays of +light. His researches on this subject were of a very complete +character, and the principles he laid down are to the present day +practically employed by oculists in the treatment of this +malformation. + +On the 7th of December, 1826, Airy was elected to the Lucasian +Professorship of Mathematics in the University of Cambridge, the +chair which Newton's occupancy had rendered so illustrious. His +tenure of this office only lasted for two years, when he exchanged it +for the Plumian Professorship. The attraction which led him to +desire this change is doubtless to be found in the circumstance that +the Plumian Professorship of Astronomy carried with it at that time +the appointment of director of the new astronomical observatory, the +origin of which must now be described. + +Those most interested in the scientific side of University life +decided in 1820 that it would be proper to found an astronomical +observatory at Cambridge. Donations were accordingly sought for this +purpose, and upwards of 6,000 pounds were contributed by members of +the University and the public. To this sum 5,000 pounds were added +by a grant from the University chest, and in 1824 further sums +amounting altogether to 7,115 pounds were given by the University for +the same object. The regulations as to the administration of the new +observatory placed it under the management of the Plumian Professor, +who was to be provided with two assistants. Their duties were to +consist in making meridian observations of the sun, moon, and the +stars, and the observations made each year were to be printed and +published. The observatory was also to be used in the educational +work of the University, for it was arranged that smaller instruments +were to be provided by which students could be instructed in the +practical art of making astronomical observations. + +The building of the Cambridge Astronomical Observatory was completed +in 1824, but in 1828, when Airy entered on the discharge of his +duties as Director, the establishment was still far from completion, +in so far as its organisation was concerned. Airy commenced his work +so energetically that in the next year after his appointment he was +able to publish the first volume of "Cambridge Astronomical +Observations," notwithstanding that every part of the work, from the +making of observations to the revising of the proof-sheets, had to be +done by himself. + +It may here be remarked that these early volumes of the publications +of the Cambridge Observatory contained the first exposition of those +systematic methods of astronomical work which Airy afterwards +developed to such a great extent at Greenwich, and which have been +subsequently adopted in many other places. No more profitable +instruction for the astronomical beginner can be found than that +which can be had by the study of these volumes, in which the Plumian +Professor has laid down with admirable clearness the true principles +on which meridian work should be conducted. + +[PLATE: SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich.] + +Airy gradually added to the instruments with which the observatory +was originally equipped. A mural circle was mounted in 1832, and in +the same year a small equatorial was erected by Jones. This was made +use of by Airy in a well-known series of observations of Jupiter's +fourth satellite for the determination of the mass of the great +planet. His memoir on this subject fully expounds the method of +finding the weight of a planet from observations of the movements of +a satellite by which the planet is attended. This is, indeed, a +valuable investigation which no student of astronomy can afford to +neglect. The ardour with which Airy devoted himself to astronomical +studies may be gathered from a remarkable report on the progress of +astronomy during the present century, which he communicated to the +British Association at its second meeting in 1832. In the early +years of his life at Cambridge his most famous achievement was +connected with a research in theoretical astronomy for which +consummate mathematical power was required. We can only give a brief +account of the Subject, for to enter into any full detail with regard +to it would be quite out of the question. + +Venus is a planet of about the same size and the same weight as the +earth, revolving in an orbit which lies within that described by our +globe. Venus, consequently, takes less time than the earth to +accomplish one revolution round the sun, and it happens that the +relative movements of Venus and the earth are so proportioned that in +the time in which our earth accomplishes eight of her revolutions the +other planet will have accomplished almost exactly thirteen. It, +therefore, follows that if the earth and Venus are in line with the +sun at one date, then in eight years later both planets will again be +found at the same points in their orbits. In those eight years the +earth has gone round eight times, and has, therefore, regained its +original position, while in the same period Venus has accomplished +thirteen complete revolutions, and, therefore, this planet also has +reached the same spot where it was at first. Venus and the earth, of +course, attract each other, and in consequence of these mutual +attractions the earth is swayed from the elliptic track which it +would otherwise pursue. In like manner Venus is also forced by the +attraction of the earth to revolve in a track which deviates from +that which it would otherwise follow. Owing to the fact that the sun +is of such preponderating magnitude (being, in fact, upwards of +300,000 times as heavy as either Venus or the earth), the +disturbances induced in the motion of either planet, in consequence +of the attraction of the other, are relatively insignificant to the +main controlling agency by which each of the movements is governed. +It is, however, possible under certain circumstances that the +disturbing effects produced upon one planet by the other can become +so multiplied as to produce peculiar effects which attain measurable +dimensions. Suppose that the periodic times in which the earth and +Venus revolved had no simple relation to each other, then the points +of their tracks in which the two planets came into line with the sun +would be found at different parts of the orbits, and consequently the +disturbances would to a great extent neutralise each other, and +produce but little appreciable effect. As, however, Venus and the +earth come back every eight years to nearly the same positions at the +same points of their track, an accumulative effect is produced. For +the disturbance of one planet upon the other will, of course, be +greatest when those two planets are nearest, that is, when they lie +in line with the sun and on the same side of it. Every eight years a +certain part of the orbit of the earth is, therefore, disturbed by +the attraction of Venus with peculiar vigour. The consequence is +that, owing to the numerical relation between the movements of the +planets to which I have referred, disturbing effects become +appreciable which would otherwise be too small to permit of +recognition. Airy proposed to himself to compute the effects which +Venus would have on the movement of the earth in consequence of the +circumstance that eight revolutions of the one planet required almost +the same time as thirteen revolutions of the other. This is a +mathematical inquiry of the most arduous description, but the Plumian +Professor succeeded in working it out, and he had, accordingly, the +gratification of announcing to the Royal Society that he had detected +the influence which Venus was thus able to assert on the movement of +our earth around the sun. This remarkable investigation gained for +its author the gold medal of the Royal Astronomical Society in the +year 1832. + +In consequence of his numerous discoveries, Airy's scientific fame +had become so well recognised that the Government awarded him a +special pension, and in 1835, when Pond, who was then Astronomer +Royal, resigned, Airy was offered the post at Greenwich. There was +in truth, no scientific inducement to the Plumian Professor to leave +the comparatively easy post he held at Cambridge, in which he had +ample leisure to devote himself to those researches which specially +interested him, and accept that of the much more arduous observatory +at Greenwich. There were not even pecuniary inducements to make the +change; however, he felt it to be his duty to accede to the request +which the Government had made that he would take up the position +which Pond had vacated, and accordingly Airy went to Greenwich as +Astronomer Royal on October 1st, 1835. + +He immediately began with his usual energy to organise the systematic +conduct of the business of the National Observatory. To realise one +of the main characteristics of Airy's great work at Greenwich, it is +necessary to explain a point that might not perhaps be understood +without a little explanation by those who have no practical +experience in an observatory. In the work of an establishment such +as Greenwich, an observation almost always consists of a measurement +of some kind. The observer may, for instance, be making a +measurement of the time at which a star passes across a spider line +stretched through the field of view; on another occasion his object +may be the measurement of an angle which is read off by examining +through a microscope the lines of division on a graduated circle when +the telescope is so pointed that the star is placed on a certain mark +in the field of view. In either case the immediate result of the +astronomical observation is a purely numerical one, but it rarely +happens, indeed we may say it never happens, that the immediate +numerical result which the observation gives expresses directly the +quantity which we are really seeking for. No doubt the observation +has been so designed that the quantity we want to find can be +obtained from the figures which the measurement gives, but the object +sought is not those figures, for there are always a multitude of +other influences by which those figures are affected. For example, +if an observation were to be perfect, then the telescope with which +the observation is made should be perfectly placed in the exact +position which it ought to occupy; this is, however, never the case, +for no mechanic can ever construct or adjust a telescope so perfectly +as the wants of the astronomer demand. The clock also by which we +determine the time of the observation should be correct, but this is +rarely if ever the case. We have to correct our observations for +such errors, that is to say, we have to determine the errors in the +positions of our telescopes and the errors in the going of our +clocks, and then we have to determine what the observations would +have been had our telescopes been absolutely perfect, and had our +clocks been absolutely correct. There are also many other matters +which have to be attended to in order to reduce our observations so +as to obtain from the figures as yielded to the observer at the +telescope the actual quantities which it is his object to determine. + +The work of effecting these reductions is generally a very intricate +and laborious matter, so that it has not unfrequently happened that +while observations have accumulated in an observatory, yet the +tedious duty of reducing these observations has been allowed to fall +into arrear. When Airy entered on his duties at Greenwich he found +there an enormous mass of observations which, though implicitly +containing materials of the greatest value to astronomers, were, in +their unreduced form, entirely unavailable for any useful purpose. +He, therefore, devoted himself to coping with the reduction of the +observations of his predecessors. He framed systematic methods by +which the reductions were to be effected, and he so arranged the work +that little more than careful attention to numerical accuracy would +be required for the conduct of the operations. Encouraged by the +Admiralty, for it is under this department that Greenwich Observatory +is placed, the Astronomer Royal employed a large force of computers +to deal with the work. BY his energy and admirable organisation he +managed to reduce an extremely valuable series of planetary +observations, and to publish the results, which have been of the +greatest importance to astronomical investigation. + +The Astronomer Royal was a capable, practical engineer as well as an +optician, and he presently occupied himself by designing astronomical +instruments of improved pattern, which should replace the antiquated +instruments he found in the observatory. In the course of years the +entire equipment underwent a total transformation. He ordered a +great meridian circle, every part of which may be said to have been +formed from his own designs. He also designed the mounting for a +fine equatorial telescope worked by a driving clock, which he had +himself invented. Gradually the establishment at Greenwich waxed +great under his incessant care. It was the custom for the +observatory to be inspected every year by a board of visitors, whose +chairman was the President of the Royal Society. At each annual +visitation, held on the first Saturday in June, the visitors received +a report from the Astronomer Royal, in which he set forth the +business which had been accomplished during the past year. It was on +these occasions that applications were made to the Admiralty, either +for new instruments or for developing the work of the observatory in +some other way. After the more official business of the inspection +was over, the observatory was thrown open to visitors, and hundreds +of people enjoyed on that day the privilege of seeing the national +observatory. These annual gatherings are happily still continued, +and the first Saturday in June is known to be the occasion of one of +the most interesting reunions of scientific men which takes place in +the course of the year. + +Airy's scientific work was, however, by no means confined to the +observatory. He interested himself largely in expeditions for the +observation of eclipses and in projects for the measurement of arcs +on the earth. He devoted much attention to the collection of magnetic +observations from various parts of the world. Especially will it be +remembered that the circumstances of the transits of Venus, which +occurred in 1874 and in 1882, were investigated by him, and under his +guidance expeditions were sent forth to observe the transits from +those localities in remote parts of the earth where observations most +suitable for the determination of the sun's distance from the earth +could be obtained. The Astronomer Royal also studied tidal +phenomena, and he rendered great service to the country in the +restoration of the standards of length and weight which had been +destroyed in the great fire at the House of Parliament in October, +1834. In the most practical scientific matters his advice was often +sought, and was as cheerfully rendered. Now we find him engaged in +an investigation of the irregularities of the compass in iron ships, +with a view to remedying its defects; now we find him reporting on +the best gauge for railways. Among the most generally useful +developments of the observatory must be mentioned the telegraphic +method for the distribution of exact time. By arrangement with the +Post Office, the astronomers at Greenwich despatch each morning a +signal from the observatory to London at ten o'clock precisely. By +special apparatus, this signal is thence distributed automatically +over the country, so as to enable the time to be known everywhere +accurately to a single second. It was part of the same system that a +time ball should be dropped daily at one o'clock at Deal, as well as +at other places, for the purpose of enabling ship's chronometers to +be regulated. + +Airy's writings were most voluminous, and no fewer than forty-eight +memoirs by him are mentioned in the "Catalogue of Scientific +Memoirs," published by the Royal Society up to the year 1873, and +this only included ten years out of an entire life of most +extraordinary activity. Many other subjects besides those of a +purely scientific character from time to time engaged his attention. +He wrote, for instance, a very interesting treatise on the Roman +invasion of Britain, especially with a view of determining the port +from which Caesar set forth from Gaul, and the point at which he +landed on the British coast. Airy was doubtless led to this +investigation by his study of the tidal phenomena in the Straits of +Dover. Perhaps the Astronomer Royal is best known to the general +reading public by his excellent lectures on astronomy, delivered at +the Ipswich Museum in 1848. This book has passed through many +editions, and it gives a most admirable account of the manner in +which the fundamental problems in astronomy have to be attacked. + +As years rolled by almost every honour and distinction that could be +conferred upon a scientific man was awarded to Sir George Airy. He +was, indeed, the recipient of other honours not often awarded for +scientific distinction. Among these we may mention that in 1875 he +received the freedom of the City of London, "as a recognition of his +indefatigable labours in astronomy, and of his eminent services in +the advancement of practical science, whereby he has so materially +benefited the cause of commerce and civilisation." + +Until his eightieth year Airy continued to discharge his labours at +Greenwich with unflagging energy. At last, on August 15th, 1881, he +resigned the office which he had held so long with such distinction +to himself and such benefit to his country. He had married in 1830 +the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died +in 1875, and three sons and three daughters survived him. One +daughter is the wife of Dr. Routh, of Cambridge, and his other +daughters were the constant companions of their father during the +declining years of his life. Up to the age of ninety he enjoyed +perfect physical health, but an accidental fall which then occurred +was attended with serious results. He died on Saturday, January 2nd, +1892, and was buried in the churchyard at Playford. + + + + +HAMILTON. + + +William Rowan Hamilton was born at midnight between the 3rd and 4th +of August, 1805, at Dublin, in the house which was then 29, but +subsequently 36, Dominick Street. His father, Archibald Hamilton, +was a solicitor, and William was the fourth of a family of nine. With +reference to his descent, it may be sufficient to notice that his +ancestors appear to have been chiefly of gentle Irish families, but +that his maternal grandmother was of Scottish birth. When he was +about a year old, his father and mother decided to hand over the +education of the child to his uncle, James Hamilton, a clergyman of +Trim, in County Meath. James Hamilton's sister, Sydney, resided with +him, and it was in their home that the days of William's childhood +were passed. + +In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of +letters will be found, in which Aunt Sydney details the progress of +the boy to his mother in Dublin. Probably there is no record of an +infant prodigy more extraordinary than that which these letters +contain. At three years old his aunt assured the mother that William +is "a hopeful blade," but at that time it was his physical vigour to +which she apparently referred; for the proofs of his capacity, which +she adduces, related to his prowess in making boys older than himself +fly before him. In the second letter, a month later, we hear that +William is brought in to read the Bible for the purpose of putting to +shame other boys double his age who could not read nearly so well. +Uncle James appears to have taken much pains with William's +schooling, but his aunt said that "how he picks up everything is +astonishing, for he never stops playing and jumping about." When he +was four years and three months old, we hear that he went out to dine +at the vicar's, and amused the company by reading for them equally +well whether the book was turned upside down or held in any other +fashion. His aunt assures the mother that "Willie is a most sensible +little creature, but at the same time has a great deal of roguery." +At four years and five months old he came up to pay his mother a +visit in town, and she writes to her sister a description of the +boy;-- + +"His reciting is astonishing, and his clear and accurate knowledge of +geography is beyond belief; he even draws the countries with a pencil +on paper, and will cut them out, though not perfectly accurate, yet +so well that a anybody knowing the countries could not mistake them; +but, you will think this nothing when I tell you that he reads Latin, +Greek, and Hebrew." + +Aunt Sydney recorded that the moment Willie got back to Trim he was +desirous of at once resuming his former pursuits. He would not eat +his breakfast till his uncle had heard him his Hebrew, and he +comments on the importance of proper pronunciation. At five he was +taken to see a friend, to whom he repeated long passages from +Dryden. A gentleman present, who was not unnaturally sceptical about +Willie's attainments, desired to test him in Greek, and took down a +copy of Homer which happened to have the contracted type, and to his +amazement Willie went on with the greatest ease. At six years and +nine months he was translating Homer and Virgil; a year later his +uncle tells us that William finds so little difficulty in learning +French and Italian, that he wishes to read Homer in French. He is +enraptured with the Iliad, and carries it about with him, repeating +from it whatever particularly pleases him. At eight years and one +month the boy was one of a party who visited the Scalp in the Dublin +mountains, and he was so delighted with the scenery that he forthwith +delivered an oration in Latin. At nine years and six months he is +not satisfied until he learns Sanscrit; three months later his thirst +for the Oriental languages is unabated, and at ten years and four +months he is studying Arabic and Persian. When nearly twelve he +prepared a manuscript ready for publication. It was a "Syriac +Grammar," in Syriac letters and characters compiled from that of +Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was +fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a +visit to Dublin, and, as a practical exercise in his Oriental +languages, the young scholar addressed to his Excellency a letter in +Persian; a translation of which production is given by Mr. Graves. +When William was fourteen he had the misfortune to lose his father; +and he had lost his mother two years previously. The boy and his +three sisters were kindly provided for by different members of the +family on both sides. + +It was when William was about fifteen that his attention began to be +turned towards scientific subjects. These were at first regarded +rather as a relaxation from the linguistic studies with which he had +been so largely occupied. On November 22nd, 1820, he notes in his +journal that he had begun Newton's "Principia": he commenced also the +study of astronomy by observing eclipses, occultations, and similar +phenomena. When he was sixteen we learn that he had read conic +sections, and that he was engaged in the study of pendulums. After +an attack of illness, he was moved for change to Dublin, and in May, +1822, we find him reading the differential calculus and Laplace's +"Mecanique Celeste." He criticises an important part of Laplace's +work relative to the demonstration of the parallelogram of forces. In +this same year appeared the first gushes of those poems which +afterwards flowed in torrents. + +His somewhat discursive studies had, however, now to give place to a +more definite course of reading in preparation for entrance to the +University of Dublin. The tutor under whom he entered, Charles +Boyton, was himself a distinguished man, but he frankly told the +young William that he could be of little use to him as a tutor, for +his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom +this is recorded, adds, "But there is one thing which Boyton would +promise to be to him, and that was a FRIEND; and that one proof he +would give of this should be that, if ever he saw William beginning +to be UPSET by the sensation he would excite, and the notice he would +attract, he would tell him of it." At the beginning of his college +career he distanced all his competitors in every intellectual +pursuit. At his first term examination in the University he was +first in Classics and first in Mathematics, while he received the +Chancellor's prize for a poem on the Ionian Islands, and another for +his poem on Eustace de St. Pierre. + +There is abundant testimony that Hamilton had "a heart for friendship +formed." Among the warmest of the friends whom he made in these +early days was the gifted Maria Edgeworth, who writes to her sister +about "young Mr. Hamilton, an admirable Crichton of eighteen, a real +prodigy of talents, who Dr. Brinkley says may be a second Newton, +quiet, gentle, and simple." His sister Eliza, to whom he was +affectionately attached, writes to him in 1824:-- + +"I had been drawing pictures of you in my mind in your study at +Cumberland Street with 'Xenophon,' &c., on the table, and you, with +your most awfully sublime face of thought, now sitting down, and now +walking about, at times rubbing your hands with an air of +satisfaction, and at times bursting forth into some very heroical +strain of poetry in an unknown language, and in your own internal +solemn ventriloquist-like voice, when you address yourself to the +silence and solitude of your own room, and indeed, at times, even +when your mysterious poetical addresses are not quite unheard." + +This letter is quoted because it refers to a circumstance which all +who ever met with Hamilton, even in his latest years, will remember. +He was endowed with two distinct voices, one a high treble, the other +a deep bass, and he alternately employed these voices not only in +ordinary conversation, but when he was delivering an address on the +profundities of Quaternions to the Royal Irish Academy, or on +similar occasions. His friends had long grown so familiar with this +peculiarity that they were sometimes rather surprised to find how +ludicrous it appeared to strangers. + +Hamilton was fortunate in finding, while still at a very early age, a +career open before him which was worthy of his talents. He had not +ceased to be an undergraduate before he was called to fill an +illustrious chair in his university. The circumstances are briefly +as follows. + +We have already mentioned that, in 1826, Brinkley was appointed +Bishop of Cloyne, and the professorship of astronomy thereupon became +vacant. Such was Hamilton's conspicuous eminence that, +notwithstanding he was still an undergraduate, and had only just +completed his twenty-first year, he was immediately thought of as a +suitable successor to the chair. Indeed, so remarkable were his +talents in almost every direction that had the vacancy been in the +professorship of classics or of mathematics, of English literature or +of metaphysics, of modern or of Oriental languages, it seems +difficult to suppose that he would not have occurred to every one as +a possible successor. The chief ground, however, on which the +friends of Hamilton urged his appointment was the earnest of original +power which he had already shown in a research on the theory of +Systems of Rays. This profound work created a new branch of optics, +and led a few years later to a superb discovery, by which the fame of +its author became world-wide. + +At first Hamilton thought it would be presumption for him to apply +for so exalted a position; he accordingly retired to the country, and +resumed his studies for his degree. Other eminent candidates came +forward, among them some from Cambridge, and a few of the Fellows +from Trinity College, Dublin, also sent in their claims. It was not +until Hamilton received an urgent letter from his tutor Boyton, in +which he was assured of the favourable disposition of the Board +towards his candidature, that he consented to come forward, and on +June 16th, 1827, he was unanimously chosen to succeed the Bishop of +Cloyne as Professor of Astronomy in the University. The appointment +met with almost universal approval. It should, however, be noted +that Brinkley, whom Hamilton succeeded, did not concur in the general +sentiment. No one could have formed a higher opinion than he had +done of Hamilton's transcendent powers; indeed, it was on that very +ground that he seemed to view the appointment with disapprobation. +He considered that it would have been wiser for Hamilton to have +obtained a Fellowship, in which capacity he would have been able to +exercise a greater freedom in his choice of intellectual pursuits. +The bishop seems to have thought, and not without reason, that +Hamilton's genius would rather recoil from much of the routine work +of an astronomical establishment. Now that Hamilton's whole life is +before us, it is easy to see that the bishop was entirely wrong. It +is quite true that Hamilton never became a skilled astronomical +observer; but the seclusion of the observatory was eminently +favourable to those gigantic labours to which his life was devoted, +and which have shed so much lustre, not only on Hamilton himself, but +also on his University and his country. + +In his early years at Dunsink, Hamilton did make some attempts at a +practical use of the telescopes, but he possessed no natural aptitude +for such work, while exposure which it involved seems to have acted +injuriously on his health. He, therefore, gradually allowed his +attention to be devoted to those mathematical researches in which he +had already given such promise of distinction. Although it was in +pure mathematics that he ultimately won his greatest fame, yet he +always maintained and maintained with justice, that he had ample +claims to the title of an astronomer. In his later years he set +forth this position himself in a rather striking manner. De Morgan +had written commending to Hamilton's notice Grant's "History of +Physical Astronomy." After becoming acquainted with the book, +Hamilton writes to his friend as follows:-- + +"The book is very valuable, and very creditable to its composer. But +your humble servant may be pardoned if he finds himself somewhat +amused at the title, 'History of Physical Astronomy from the Earliest +Ages to the Middle of the Nineteenth Century,' when he fails to +observe any notice of the discoveries of Sir W. R. Hamilton in the +theory of the 'Dynamics of the Heavens.'" + +The intimacy between the two correspondents will account for the tone +of this letter; and, indeed, Hamilton supplies in the lines which +follow ample grounds for his complaint. He tells how Jacobi spoke of +him in Manchester in 1842 as "le Lagrange de votre pays," and how +Donkin had said that, "The Analytical Theory of Dynamics as it exists +at present is due mainly to the labours of La Grange Poisson, +Sir W. R. Hamilton, and Jacobi, whose researches on this subject +present a series of discoveries hardly paralleled for their elegance +and importance in any other branch of mathematics." In the same +letter Hamilton also alludes to the success which had attended the +applications of his methods in other hands than his own to the +elucidation of the difficult subject of Planetary Perturbations. +Even had his contributions to science amounted to no more than these +discoveries, his tenure of the chair would have been an illustrious +one. It happens, however, that in the gigantic mass of his +intellectual work these researches, though intrinsically of such +importance, assume what might almost be described as a relative +insignificance. + +The most famous achievement of Hamilton's earlier years at the +observatory was the discovery of conical refraction. This was one of +those rare events in the history of science, in which a sagacious +calculation has predicted a result of an almost startling character, +subsequently confirmed by observation. At once this conferred on the +young professor a world-wide renown. Indeed, though he was still +only twenty-seven, he had already lived through an amount of +intellectual activity which would have been remarkable for a man of +threescore and ten. + +Simultaneously with his growth in fame came the growth of his several +friendships. There were, in the first place, his scientific +friendships with Herschel, Robinson, and many others with whom he had +copious correspondence. In the excellent biography to which I have +referred, Hamilton's correspondence with Coleridge may be read, as +can also the letters to his lady correspondents, among them being +Maria Edgeworth, Lady Dunraven, and Lady Campbell. Many of these +sheets relate to literary matters, but they are largely intermingled +With genial pleasantry, and serve at all events to show the affection +and esteem with which he was regarded by all who had the privilege of +knowing him. There are also the letters to the sisters whom he +adored, letters brimming over with such exalted sentiment, that most +ordinary sisters would be tempted to receive them with a smile in the +excessively improbable event of their still more ordinary brothers +attempting to pen such effusions. There are also indications of +letters to and from other young ladies who from time to time were the +objects of Hamilton's tender admiration. We use the plural +advisedly, for, as Mr. Graves has set forth, Hamilton's love affairs +pursued a rather troubled course. The attention which he lavished on +one or two fair ones was not reciprocated, and even the intense +charms of mathematical discovery could not assuage the pangs which +the disappointed lover experienced. At last he reached the haven of +matrimony in 1833, when he was married to Miss Bayly. Of his married +life Hamilton said, many years later to De Morgan, that it was as +happy as he expected, and happier than he deserved. He had two sons, +William and Archibald, and one daughter, Helen, who became the wife +of Archdeacon O'Regan. + +[PLATE: SIR W. ROWAN HAMILTON.] + +The most remarkable of Hamilton's friendships in his early years was +unquestionably that with Wordsworth. It commenced with Hamilton's +visit to Keswick; and on the first evening, when the poet met the +young mathematician, an incident occurred which showed the mutual +interest that was aroused. Hamilton thus describes it in a letter to +his sister Eliza:-- + +"He (Wordsworth) walked back with our party as far as their lodge, +and then, on our bidding Mrs. Harrison good-night, I offered to walk +back with him while my party proceeded to the hotel. This offer he +accepted, and our conversation had become so interesting that when we +had arrived at his home, a distance of about a mile, he proposed to +walk back with me on my way to Ambleside, a proposal which you may be +sure I did not reject; so far from it that when he came to turn once +more towards his home I also turned once more along with him. It was +very late when I reached the hotel after all this walking." + +Hamilton also submitted to Wordsworth an original poem, entitled +"It Haunts me Yet." The reply of Wordsworth is worth repeating:-- + +"With a safe conscience I can assure you that, in my judgment, your +verses are animated with the poetic spirit, as they are evidently the +product of strong feeling. The sixth and seventh stanzas affected me +much, even to the dimming of my eyes and faltering of my voice while +I was reading them aloud. Having said this, I have said enough. Now +for the per contra. You will not, I am sure, be hurt when I tell you +that the workmanship (what else could be expected from so young a +writer?) is not what it ought to be. . . + +"My household desire to be remembered to you in no formal way. +Seldom have I parted--never, I was going to say--with one whom after +so short an acquaintance I lost sight of with more regret. I trust +we shall meet again." + +The further affectionate intercourse between Hamilton and Wordsworth +is fully set forth, and to Hamilton's latest years a recollection of +his "Rydal hours" was carefully treasured and frequently referred +to. Wordsworth visited Hamilton at the observatory, where a +beautiful shady path in the garden is to the present day spoken of as +"Wordsworth's Walk." + +It was the practice of Hamilton to produce a sonnet on almost every +occasion which admitted of poetical treatment, and it was his delight +to communicate his verses to his friends all round. When Whewell was +producing his "Bridgewater Treatises," he writes to Hamilton in +1833:-- + +"Your sonnet which you showed me expressed much better than I could +express it the feeling with which I tried to write this book, and I +once intended to ask your permission to prefix the sonnet to my book, +but my friends persuaded me that I ought to tell my story in my own +prose, however much better your verse might be." + +The first epoch-marking contribution to Theoretical Dynamics after +the time of Newton was undoubtedly made by Lagrange, in his discovery +of the general equations of Motion. The next great step in the same +direction was that taken by Hamilton in his discovery of a still more +comprehensive method. Of this contribution Hamilton writes to +Whewell, March 31st, 1834:-- + +"As to my late paper, a day or two ago sent off to London, it is +merely mathematical and deductive. I ventured, indeed, to call it +the 'Mecanique Analytique' of Lagrange, 'a scientific poem'; and +spoke of Dynamics, or the Science of Force, as treating of 'Power +acting by Law in Space and Time.' In other respects it is as +unpoetical and unmetaphysical as my gravest friends could desire." + +It may well be doubted whether there is a more beautiful chapter in +the whole of mathematical philosophy than that which contains +Hamilton's dynamical theory. It is disfigured by no tedious +complexity of symbols; it condescends not to any particular problems; +it is an all embracing theory, which gives an intellectual grasp of +the most appropriate method for discovering the result of the +application of force to matter. It is the very generality of this +doctrine which has somewhat impeded the applications of which it is +susceptible. The exigencies of examinations are partly responsible +for the fact that the method has not become more familiar to students +of the higher mathematics. An eminent professor has complained that +Hamilton's essay on dynamics was of such an extremely abstract +character, that he found himself unable to extract from it problems +suitable for his examination papers. + +The following extract is from a letter of Professor Sylvester to +Hamilton, dated 20th of September, 1841. It will show how his works +were appreciated by so consummate a mathematician as the writer:-- + +"Believe me, sir, it is not the least of my regrets in quitting this +empire to feel that I forego the casual occasion of meeting those +masters of my art, yourself chief amongst the number, whose +acquaintance, whose conversation, or even notice, have in themselves +the power to inspire, and almost to impart fresh vigour to the +understanding, and the courage and faith without which the efforts of +invention are in vain. The golden moments I enjoyed under your +hospitable roof at Dunsink, or moments such as they were, may +probably never again fall to my lot. + +"At a vast distance, and in an humble eminence, I still promise myself +the calm satisfaction of observing your blazing course in the +elevated regions of discovery. Such national honour as you are able +to confer on your country is, perhaps, the only species of that +luxury for the rich (I mean what is termed one's glory) which is not +bought at the expense of the comforts of the million." + +The study of metaphysics was always a favourite recreation when +Hamilton sought for a change from the pursuit of mathematics. In the +year 1834 we find him a diligent student of Kant; and, to show the +views of the author of Quaternions and of Algebra as the Science of +Pure Time on the "Critique of the Pure Reason," we quote the +following letter, dated 18th of July, 1834, from Hamilton to Viscount +Adare:-- + +"I have read a large part of the 'Critique of the Pure Reason,' and +find it wonderfully clear, and generally quite convincing. +Notwithstanding some previous preparation from Berkeley, and from my +own thoughts, I seem to have learned much from Kant's own statement +of his views of 'Space and Time.' Yet, on the whole, a large part of +my pleasure consists in recognising through Kant's works, opinions, +or rather views, which have been long familiar to myself, although +far more clearly and systematically expressed and combined by him. +. . . Kant is, I think, much more indebted than he owns, or, perhaps +knows, to Berkeley, whom he calls by a sneer, 'GUTEM Berkeley'. . . +as it were, 'good soul, well meaning man,' who was able for all that +to shake to its centre the world of human thought, and to effect a +revolution among the early consequences of which was the growth of +Kant himself." + +At several meetings of the British Association Hamilton was a very +conspicuous figure. Especially was this the case in 1835, when the +Association met in Dublin, and when Hamilton, though then but thirty +years old, had attained such celebrity that even among a very +brilliant gathering his name was perhaps the most renowned. A +banquet was given at Trinity College in honour of the meeting. The +distinguished visitors assembled in the Library of the University. +The Earl of Mulgrave, then Lord Lieutenant of Ireland, made this the +opportunity of conferring on Hamilton the honour of knighthood, +gracefully adding, as he did so: "I but set the royal, and therefore +the national mark, on a distinction already acquired by your genius +and labours." + +The banquet followed, writes Mr. Graves. "It was no little addition +to the honour Hamilton had already received that, when Professor +Whewell returned thanks for the toast of the University of Cambridge, +he thought it appropriate to add the words, 'There was one point +which strongly pressed upon him at that moment: it was now one +hundred and thirty years since a great man in another Trinity College +knelt down before his sovereign, and rose up Sir Isaac Newton.' The +compliment was welcomed by immense applause." + +A more substantial recognition of the labours of Hamilton took place +subsequently. He thus describes it in a letter to Mr. Graves of 14th +of November, 1843:-- + +"The Queen has been pleased--and you will not doubt that it was +entirely unsolicited, and even unexpected, on my part--'to express +her entire approbation of the grant of a pension of two hundred +pounds per annum from the Civil List' to me for scientific services. +The letters from Sir Robert Peel and from the Lord Lieutenant of +Ireland in which this grant has been communicated or referred to have +been really more gratifying to my feelings than the addition to my +income, however useful, and almost necessary, that may have been." + +The circumstances we have mentioned might lead to the supposition +that Hamilton was then at the zenith of his fame but this was not +so. It might more truly be said, that his achievements up to this +point were rather the preliminary exercises which fitted him for the +gigantic task of his life. The name of Hamilton is now chiefly +associated with his memorable invention of the calculus of +Quaternions. It was to the creation of this branch of mathematics +that the maturer powers of his life were devoted; in fact he gives us +himself an illustration of how completely habituated he became to the +new modes of thought which Quaternions originated. In one of his +later years he happened to take up a copy of his famous paper on +Dynamics, a paper which at the time created such a sensation among +mathematicians, and which is at this moment regarded as one of the +classics of dynamical literature. He read, he tells us, his paper +with considerable interest, and expressed his feelings of +gratification that he found himself still able to follow its +reasoning without undue effort. But it seemed to him all the time as +a work belonging to an age of analysis now entirely superseded. + +In order to realise the magnitude of the revolution which Hamilton +has wrought in the application of symbols to mathematical +investigation, it is necessary to think of what Hamilton did beside +the mighty advance made by Descartes. To describe the character of +the quaternion calculus would be unsuited to the pages of this work, +but we may quote an interesting letter, written by Hamilton from his +death-bed, twenty-two years later, to his son Archibald, in which he +has recorded the circumstances of the discovery:-- + +"Indeed, I happen to be able to put the finger of memory upon the year +and month--October, 1843--when having recently returned from visits +to Cork and Parsonstown, connected with a meeting of the British +Association, the desire to discover the laws of multiplication +referred to, regained with me a certain strength and earnestness +which had for years been dormant, but was then on the point of being +gratified, and was occasionally talked of with you. Every morning in +the early part of the above-cited month, on my coming down to +breakfast, your (then) little brother William Edwin, and yourself, +used to ask me, 'Well papa, can you multiply triplets?' Whereto I +was always obliged to reply, with a sad shake of the head: 'No, I +can only ADD and subtract them,' + +"But on the 16th day of the same month--which happened to be Monday, +and a Council day of the Royal Irish Academy--I was walking in to +attend and preside, and your mother was walking with me along the +Royal Canal, to which she had perhaps driven; and although she talked +with me now and then, yet an UNDERCURRENT of thought was going on in +my mind which gave at last a RESULT, whereof it is not too much to +say that I felt AT ONCE the importance. An ELECTRIC circuit seemed +to CLOSE; and a spark flashed forth the herald (as I FORESAW +IMMEDIATELY) of many long years to come of definitely directed +thought and work by MYSELF, if spared, and, at all events, on the +part of OTHERS if I should even be allowed to live long enough +distinctly to communicate the discovery. Nor could I resist the +impulse--unphilosophical as it may have been--to cut with a knife on +a stone of Brougham Bridge as we passed it, the fundamental formula +which contains the SOLUTION of the PROBLEM, but, of course, the +inscription has long since mouldered away. A more durable notice +remains, however, on the Council Books of the Academy for that day +(October 16, 1843), which records the fact that I then asked for and +obtained leave to read a Paper on 'Quaternions,' at the First General +Meeting of the Session; which reading took place accordingly, on +Monday, the 13th of November following." + +Writing to Professor Tait, Hamilton gives further particulars of the +same event. And again in a letter to the Rev. J. W. Stubbs:-- + +"To-morrow will be the fifteenth birthday of the Quaternions. They +started into life full-grown on the 16th October, 1843, as I was +walking with Lady Hamilton to Dublin, and came up to Brougham +Bridge--which my boys have since called Quaternion Bridge. I pulled +out a pocketbook which still exists, and made entry, on which at the +very moment I felt that it might be worth my while to expend the +labour of at least ten or fifteen years to come. But then it is fair +to say that this was because I felt a problem to have been at that +moment solved, an intellectual want relieved which had haunted me for +at least fifteen years before. + +"But did the thought of establishing such a system, in which +geometrically opposite facts--namely, two lines (or areas) which are +opposite IN SPACE give ALWAYS a positive product--ever come into +anybody's head till I was led to it in October, 1843, by trying to +extend my old theory of algebraic couples, and of algebra as the +science of pure time? As to my regarding geometrical addition of +lines as equivalent to composition of motions (and as performed by +the same rules), that is indeed essential in my theory but not +peculiar to it; on the contrary, I am only one of many who have been +led to this view of addition." + +Pilgrims in future ages will doubtless visit the spot commemorated by +the invention of Quaternions. Perhaps as they look at that by no +means graceful structure Quaternion Bridge, they will regret that the +hand of some Old Mortality had not been occasionally employed in +cutting the memorable inscription afresh. It is now irrecoverably +lost. + +It was ten years after the discovery that the great volume appeared +under the title of "Lectures on Quaternions," Dublin, 1853. The +reception of this work by the scientific world was such as might have +been expected from the extraordinary reputation of its author, and +the novelty and importance of the new calculus. His valued friend, +Sir John Herschel, writes to him in that style of which he was a +master:-- + +"Now, most heartily let me congratulate you on getting out your +book--on having found utterance, ore rotundo, for all that labouring +and seething mass of thought which has been from time to time sending +out sparks, and gleams, and smokes, and shaking the soil about you; +but now breaks into a good honest eruption, with a lava stream and a +shower of fertilizing ashes. + +"Metaphor and simile apart, there is work for a twelve-month to any +man to read such a book, and for half a lifetime to digest it, and I +am glad to see it brought to a conclusion." + +We may also record Hamilton's own opinion expressed to Humphrey +Lloyd:-- + +"In general, although in one sense I hope that I am actually growing +modest about the quaternions, from my seeing so many peeps and vistas +into future expansions of their principles, I still must assert that +this discovery appears to me to be as important for the middle of the +nineteenth century as the discovery of fluxions was for the close of +the seventeenth." + +Bartholomew Lloyd died in 1837. He had been the Provost of Trinity +College, and the President of the Royal Irish Academy. Three +candidates were put forward by their respective friends for the +vacant Presidency. One was Humphrey Lloyd, the son of the late +Provost, and the two others were Hamilton and Archbishop Whately. +Lloyd from the first urged strongly the claims of Hamilton, and +deprecated the putting forward of his own name. Hamilton in like +manner desired to withdraw in favour of Lloyd. The wish was strongly +felt by many of the Fellows of the College that Lloyd should be +elected, in consequence of his having a more intimate association +with collegiate life than Hamilton; while his scientific eminence was +world-wide. The election ultimately gave Hamilton a considerable +majority over Lloyd, behind whom the Archbishop followed at a +considerable distance. All concluded happily, for both Lloyd and the +Archbishop expressed, and no doubt felt, the pre-eminent claims of +Hamilton, and both of them cordially accepted the office of a +Vice-President, to which, according to the constitution of the +Academy, it is the privilege of the incoming President to nominate. + +In another chapter I have mentioned as a memorable episode in +astronomical history, that Sir J. Herschel went for a prolonged +sojourn to the Cape of Good Hope, for the purpose of submitting the +southern skies to the same scrutiny with the great telescope that his +father had given to the northern skies. The occasion of Herschel's +return after the brilliant success of his enterprise, was celebrated +by a banquet. On June 15th, 1838, Hamilton was assigned the high +honour of proposing the health of Herschel. This banquet is +otherwise memorable in Hamilton's career as being one of the two +occasions in which he was in the company of his intimate friend De +Morgan. + +In the year 1838 a scheme was adopted by the Royal Irish Academy for +the award of medals to the authors of papers which appeared to +possess exceptionally high merit. At the institution of the medal +two papers were named in competition for the prize. One was +Hamilton's "Memoir on Algebra, as the Science of Pure Time." The +other was Macullagh's paper on the "Laws of Crystalline Reflection +and Refraction." Hamilton expresses his gratification that, mainly +in consequence of his own exertions, he succeeded in having the medal +awarded to Macullagh rather than to himself. Indeed, it would almost +appear as if Hamilton had procured a letter from Sir J. Herschel, +which indicated the importance of Macullagh's memoir in such a way as +to decide the issue. It then became Hamilton's duty to award the +medal from the chair, and to deliver an address in which he expressed +his own sense of the excellence of Macullagh's scientific work. It +is the more necessary to allude to these points, because in the whole +of his scientific career it would seem that Macullagh was the only +man with whom Hamilton had ever even an approach to a dispute about +priority. The incident referred to took place in connection with the +discovery of conical refraction, the fame of which Macullagh made a +preposterous attempt to wrest from Hamilton. This is evidently +alluded to in Hamilton's letter to the Marquis of Northampton, dated +June 28th, 1838, in which we read:-- + +"And though some former circumstances prevented me from applying to +the person thus distinguished the sacred name of FRIEND, I had the +pleasure of doing justice...to his high intellectual merits... I +believe he was not only gratified but touched, and may, perhaps, +regard me in future with feelings more like those which I long to +entertain towards him." + +Hamilton was in the habit, from time to time, of commencing the +keeping of a journal, but it does not appear to have been +systematically conducted. Whatever difficulties the biographer may +have experienced from its imperfections and irregularities, seem to +be amply compensated for by the practice which Hamilton had of +preserving copies of his letters, and even of comparatively +insignificant memoranda. In fact, the minuteness with which +apparently trivial matters were often noted down appears almost +whimsical. He frequently made a memorandum of the name of the person +who carried a letter to the post, and of the hour in which it was +despatched. On the other hand, the letters which he received were +also carefully preserved in a mighty mass of manuscripts, with which +his study was encumbered, and with which many other parts of the +house were not unfrequently invaded. If a letter was laid aside for +a few hours, it would become lost to view amid the seething mass of +papers, though occasionally, to use his own expression, it might be +seen "eddying" to the surface in some later disturbance. + +The great volume of "Lectures on Quaternions" had been issued, and +the author had received the honours which the completion of such a +task would rightfully bring him. The publication of an immortal work +does not, however, necessarily provide the means for paying the +printer's bill. The printing of so robust a volume was necessarily +costly; and even if all the copies could be sold, which at the time +did not seem very likely, they would hardly have met the inevitable +expenses. The provision of the necessary funds was, therefore, a +matter for consideration. The Board of Trinity College had already +contributed 200 pounds to the printing, but yet another hundred was +required. Even the discoverer of Quaternions found this a source of +much anxiety. However, the board, urged by the representation of +Humphrey Lloyd, now one of its members, and, as we have already seen, +one of Hamilton's staunchest friends, relieved him of all liability. +We may here note that, notwithstanding the pension which Hamilton +enjoyed in addition to the salary of his chair, he seems always to +have been in some what straitened circumstances, or, to use his own +words in one of his letters to De Morgan, "Though not an embarrassed +man, I am anything rather than a rich one." It appears that, +notwithstanding the world-wide fame of Hamilton's discoveries, the +only profit in a pecuniary sense that he ever obtained from any of +his works was by the sale of what he called his Icosian Game. Some +enterprising publisher, on the urgent representations of one of +Hamilton's friends in London, bought the copyright of the Icosian +Game for 25 pounds. Even this little speculation proved unfortunate +for the purchaser, as the public could not be induced to take the +necessary interest in the matter. + +After the completion of his great book, Hamilton appeared for awhile +to permit himself a greater indulgence than usual in literary +relaxations. He had copious correspondence with his intimate friend, +Aubrey de Vere, and there were multitudes of letters from those +troops of friends whom it was Hamilton's privilege to possess. He +had been greatly affected by the death of his beloved sister Eliza, a +poetess of much taste and feeling. She left to him her many papers +to preserve or to destroy, but he said it was only after the +expiration of four years of mourning that he took courage to open her +pet box of letters. + +The religious side of Hamilton's character is frequently illustrated +in these letters; especially is this brought out in the +correspondence with De Vere, who had seceded to the Church of Rome. +Hamilton writes, August 4, 1855:-- + +"If, then, it be painfully evident to both, that under such +circumstances there CANNOT (whatever we may both DESIRE) be NOW in +the nature of things, or of minds, the same degree of INTIMACY +between us as of old; since we could no longer TALK with the same +degree of unreserve on every subject which happened to present +itself, but MUST, from the simplest instincts of courtesy, be each on +his guard not to say what might be offensive, or, at least, painful +to the other; yet WE were ONCE so intimate, and retain still, and, as +I trust, shall always retain, so much of regard and esteem and +appreciation for each other, made tender by so many associations of +my early youth and your boyhood, which can never be forgotten by +either of us, that (as times go) TWO OR THREE VERY RESPECTABLE +FRIENDSHIPS might easily be carved out from the fragments of our +former and ever-to-be-remembered INTIMACY. It would be no +exaggeration to quote the words: 'Heu! quanto minus est cum reliquis +versari, quam tui meminisse!'" + +In 1858 a correspondence on the subject of Quaternions commenced +between Professor Tait and Sir William Hamilton. It was particularly +gratifying to the discoverer that so competent a mathematician as +Professor Tait should have made himself acquainted with the new +calculus. It is, of course, well known that Professor Tait +subsequently brought out a most valuable elementary treatise on +Quaternions, to which those who are anxious to become acquainted with +the subject will often turn in preference to the tremendous work of +Hamilton. + +In the year 1861 gratifying information came to hand of the progress +which the study of Quaternions was making abroad. Especially did the +subject attract the attention of that accomplished mathematician, +Moebius, who had already in his "Barycentrische Calculus" been led to +conceptions which bore more affinity to Quaternions than could be +found in the writings of any other mathematician. Such notices of +his work were always pleasing to Hamilton, and they served, perhaps, +as incentives to that still closer and more engrossing labour by +which he became more and more absorbed. During the last few years of +his life he was observed to be even more of a recluse than he had +hitherto been. His powers of long and continuous study seemed to +grow with advancing years, and his intervals of relaxation, such as +they were, became more brief and more infrequent. + +It was not unusual for him to work for twelve hours at a stretch. +The dawn would frequently surprise him as he looked up to snuff his +candles after a night of fascinating labour at original research. +Regularity in habits was impossible to a student who had prolonged +fits of what he called his mathematical trances. Hours for rest and +hours for meals could only be snatched in the occasional the lucid +intervals between one attack of Quaternions and the next. When +hungry, he would go to see whether anything could be found on the +sideboard; when thirsty, he would visit the locker, and the one +blemish in the man's personal character is that these latter visits +were sometimes paid too often. + +As an example of one of Hamilton's rare diversions from the all- +absorbing pursuit of Quaternions, we find that he was seized with +curiosity to calculate back to the date of the Hegira, which he found +on the 15th July, 622. He speaks of the satisfaction with which he +ascertained subsequently that Herschel had assigned precisely the +same date. Metaphysics remained also, as it had ever been, a +favourite subject of Hamilton's readings and meditations and of +correspondence with his friends. He wrote a very long letter to Dr. +Ingleby on the subject of his "Introduction to Metaphysics." In it +Hamilton alludes, as he has done also in other places, to a +peculiarity of his own vision. It was habitual to him, by some +defect in the correlation of his eyes, to see always a distinct image +with each; in fact, he speaks of the remarkable effect which the use +of a good stereoscope had on his sensations of vision. It was then, +for the first time, that he realised how the two images which he had +always seen hitherto would, under normal circumstances, be blended +into one. He cites this fact as bearing on the phenomena of +binocular vision, and he draws from it the inference that the +necessity of binocular vision for the correct appreciation of +distance is unfounded. "I am quite sure," he says, "that I SEE +DISTANCE with EACH EYE SEPARATELY." + +The commencement of 1865, the last year of his life saw Hamilton as +diligent as ever, and corresponding with Salmon and Cayley. On April +26th he writes to a friend to say, that his health has not been good +for years past, and that so much work has injured his constitution; +and he adds, that it is not conducive to good spirits to find that he +is accumulating another heavy bill with the printer for the +publication of the "Elements." This was, indeed, up to the day of +his death, a cause for serious anxiety. It may, however, be +mentioned that the whole cost, which amounted to nearly 500 pounds, +was, like that of the previous volume, ultimately borne by the +College. Contrary to anticipation, the enterprise, even in a +pecuniary sense, cannot have been a very unprofitable one. The whole +edition has long been out of print, and as much as 5 pounds has since +been paid for a single copy. + +It was on the 9th of May, 1865, that Hamilton was in Dublin for the +last time. A few days later he had a violent attack of gout, and on +the 4th of June he became alarmingly ill, and on the next day had an +attack of epileptic convulsions. However, he slightly rallied, so +that before the end of the month he was again at work at the +"Elements." A gratifying incident brightened some of the last days +of his life. The National Academy of Science in America had then +been just formed. A list of foreign Associates had to be chosen from +the whole world, and a discussion took place as to what name should +be placed first on the list. Hamilton was informed by private +communication that this great distinction was awarded to him by a +majority of two-thirds. + +In August he was still at work on the table of contents of the +"Elements," and one of his very latest efforts was his letter to Mr. +Gould, in America, communicating his acknowledgements of the honour +which had been just conferred upon him by the National Academy. On +the 2nd of September Mr. Graves went to the observatory, in response +to a summons, and the great mathematician at once admitted to his +friend that he felt the end was approaching. He mentioned that he +had found in the 145th Psalm a wonderfully suitable expression of his +thoughts and feelings, and he wished to testify his faith and +thankfulness as a Christian by partaking of the Lord's Supper. He +died at half-past two on the afternoon of the 2nd of September, 1865, +aged sixty years and one month. He was buried in Mount Jerome +Cemetery on the 7th of September. + +Many were the letters and other more public manifestations of the +feelings awakened by Hamilton's death. Sir John Herschel wrote to +the widow:-- + +"Permit me only to add that among the many scientific friends whom +time has deprived me of, there has been none whom I more deeply +lament, not only for his splendid talents, but for the excellence of +his disposition and the perfect simplicity of his manners--so great, +and yet devoid of pretensions." + +De Morgan, his old mathematical crony, as Hamilton affectionately +styled him, also wrote to Lady Hamilton:-- + +"I have called him one of my dearest friends, and most truly; for I +know not how much longer than twenty-five years we have been in +intimate correspondence, of most friendly agreement or disagreement, +of most cordial interest in each other. And yet we did not know each +other's faces. I met him about 1830 at Babbage's breakfast table, +and there for the only time in our lives we conversed. I saw him, a +long way off, at the dinner given to Herschel (about 1838) on his +return from the Cape and there we were not near enough, nor on that +crowded day could we get near enough, to exchange a word. And this +is all I ever saw, and, so it has pleased God, all I shall see in +this world of a man whose friendly communications were among my +greatest social enjoyments, and greatest intellectual treats." + +There is a very interesting memoir of Hamilton written by De Morgan, +in the "Gentleman's Magazine" for 1866, in which he produces an +excellent sketch of his friend, illustrated by personal reminiscences +and anecdotes. He alludes, among other things, to the picturesque +confusion of the papers in his study. There was some sort of order +in the mass, discernible however, by Hamilton alone, and any invasion +of the domestics, with a view to tidying up, would throw the +mathematician as we are informed, into "a good honest thundering +passion." + +Hardly any two men, who were both powerful mathematicians, could have +been more dissimilar in every other respect than were Hamilton and De +Morgan. The highly poetical temperament of Hamilton was remarkably +contrasted with the practical realism of De Morgan. Hamilton sends +sonnets to his friend, who replies by giving the poet advice about +making his will. The metaphysical subtleties, with which Hamilton +often filled his sheets, did not seem to have the same attraction for +De Morgan that he found in battles about the quantification of the +Predicate. De Morgan was exquisitely witty, and though his jokes +were always appreciated by his correspondent, yet Hamilton seldom +ventured on anything of the same kind in reply; indeed his rare +attempts at humour only produced results of the most ponderous +description. But never were two scientific correspondents more +perfectly in sympathy with each other. Hamilton's work on +Quaternions, his labours in Dynamics, his literary tastes, his +metaphysics, and his poetry, were all heartily welcomed by his +friend, whose letters in reply invariably evince the kindliest +interest in all Hamilton's concerns. In a similar way De Morgan's +letters to Hamilton always met with a heartfelt response. + +Alike for the memory of Hamilton, for the credit of his University, +and for the benefit of science, let us hope that a collected edition +of his works will ere long appear--a collection which shall show +those early achievements in splendid optical theory, those +achievements of his more mature powers which made him the Lagrange of +his country, and finally those creations of the Quaternion Calculus +by which new capabilities have been bestowed on the human intellect. + + + + +LE VERRIER. + + +The name of Le Verrier is one that goes down to fame on account of +very different discoveries from those which have given renown to +several of the other astronomers whom we have mentioned. We are +sometimes apt to identify the idea of an astronomer with that of a +man who looks through a telescope at the stars; but the word +astronomer has really much wider significance. No man who ever lived +has been more entitled to be designated an astronomer than Le +Verrier, and yet it is certain that he never made a telescopic +discovery of any kind. Indeed, so far as his scientific achievements +have been concerned, he might never have looked through a telescope +at all. + +For the full interpretation of the movements of the heavenly bodies, +mathematical knowledge of the most advanced character is demanded. +The mathematician at the outset calls upon the astronomer who uses +the instruments in the observatory, to ascertain for him at various +times the exact positions occupied by the sun, the moon, and the +planets. These observations, obtained with the greatest care, and +purified as far as possible from the errors by which they may be +affected form, as it were, the raw material on which the +mathematician exercises his skill. It is for him to elicit from the +observed places the true laws which govern the movements of the +heavenly bodies. Here is indeed a task in which the highest powers +of the human intellect may be worthily employed. + +Among those who have laboured with the greatest success in the +interpretation of the observations made with instruments of +precision, Le Verrier holds a highly honoured place. To him it has +been given to provide a superb illustration of the success with which +the mind of man can penetrate the deep things of Nature. + +The illustrious Frenchman, Urban Jean Joseph Le Verrier, was born on +the 11th March, 1811, at St. Lo, in the department of Manche. He +received his education in that famous school for education in the +higher branches of science, the Ecole Polytechnique, and acquired +there considerable fame as a mathematician. On leaving the school Le +Verrier at first purposed to devote himself to the public service, in +the department of civil engineering; and it is worthy of note that +his earliest scientific work was not in those mathematical researches +in which he was ultimately to become so famous. His duties in the +engineering department involved practical chemical research in the +laboratory. In this he seems to have become very expert, and +probably fame as a chemist would have been thus attained, had not +destiny led him into another direction. As it was, he did engage in +some original chemical research. His first contributions to science +were the fruits of his laboratory work; one of his papers was on the +combination of phosphorus and hydrogen, and another on the +combination of phosphorus and oxygen. + +His mathematical labours at the Ecole Polytechnique had, however, +revealed to Le Verrier that he was endowed with the powers requisite +for dealing with the subtlest instruments of mathematical analysis. +When he was twenty-eight years old, his first great astronomical +investigation was brought forth. It will be necessary to enter into +some explanation as to the nature of this, inasmuch as it was the +commencement of the life-work which he was to pursue. + +If but a single planet revolved around the sun, then the orbit of +that planet would be an ellipse, and the shape and size, as well as +the position of the ellipse, would never alter. One revolution after +another would be traced out, exactly in the same manner, in +compliance with the force continuously exerted by the sun. Suppose, +however, that a second planet be introduced into the system. The sun +will exert its attraction on this second planet also, and it will +likewise describe an orbit round the central globe. We can, however, +no longer assert that the orbit in which either of the planets moves +remains exactly an ellipse. We may, indeed, assume that the mass of +the sun is enormously greater than that of either of the planets. In +this case the attraction of the sun is a force of such preponderating +magnitude, that the actual path of each planet remains nearly the +same as if the other planet were absent. But it is impossible for +the orbit of each planet not to be affected in some degree by the +attraction of the other planet. The general law of nature asserts +that every body in space attracts every other body. So long as there +is only a single planet, it is the single attraction between the sun +and that planet which is the sole controlling principle of the +movement, and in consequence of it the ellipse is described. But +when a second planet is introduced, each of the two bodies is not +only subject to the attraction of the sun, but each one of the +planets attracts the other. It is true that this mutual attraction +is but small, but, nevertheless, it produces some effect. It +"disturbs," as the astronomer says, the elliptic orbit which would +otherwise have been pursued. Hence it follows that in the actual +planetary system where there are several planets disturbing each +other, it is not true to say that the orbits are absolutely elliptic. + +At the same time in any single revolution a planet may for most +practical purposes be said to be actually moving in an ellipse. As, +however, time goes on, the ellipse gradually varies. It alters its +shape, it alters its plane, and it alters its position in that +plane. If, therefore, we want to study the movements of the planets, +when great intervals of time are concerned, it is necessary to have +the means of learning the nature of the movement of the orbit in +consequence of the disturbances it has experienced. + +We may illustrate the matter by supposing the planet to be running +like a railway engine on a track which has been laid in a long +elliptic path. We may suppose that while the planet is coursing +along, the shape of the track is gradually altering. But this +alteration may be so slow, that it does not appreciably affect the +movement of the engine in a single revolution. We can also suppose +that the plane in which the rails have been laid has a slow +oscillation in level, and that the whole orbit is with more or less +uniformity moved slowly about in the plane. + +In short periods of time the changes in the shapes and positions of +the planetary orbits, in consequence of their mutual attractions, are +of no great consequence. When, however, we bring thousands of years +into consideration, then the displacements of the planetary orbits +attain considerable dimensions, and have, in fact, produced a +profound effect on the system. + +It is of the utmost interest to investigate the extent to which one +planet can affect another in virtue of their mutual attractions. Such +investigations demand the exercise of the highest mathematical +gifts. But not alone is intellectual ability necessary for success +in such inquiries. It must be united with a patient capacity for +calculations of an arduous type, protracted, as they frequently have +to be, through many years of labour. Le Verrier soon found in these +profound inquiries adequate scope for the exercise of his peculiar +gifts. His first important astronomical publication contained an +investigation of the changes which the orbits of several of the +planets, including the earth, have undergone in times past, and which +they will undergo in times to come. + +As an illustration of these researches, we may take the case of the +planet in which we are, of course, especially interested, namely, the +earth, and we can investigate the changes which, in the lapse of +time, the earth's orbit has undergone, in consequence of the +disturbance to which it has been subjected by the other planets. In +a century, or even in a thousand years, there is but little +recognisable difference in the shape of the track pursued by the +earth. Vast periods of time are required for the development of the +large consequences of planetary perturbation. Le Verrier has, +however, given us the particulars of what the earth's journey through +space has been at intervals of 20,000 years back from the present +date. His furthest calculation throws our glance back to the state +of the earth's track 100,000 years ago, while, with a bound forward, +he shows us what the earth's orbit is to be in the future, at +successive intervals of 20,000 years, till a date is reached which is +100,000 years in advance of A.D. 1800. + +The talent which these researches displayed brought Le Verrier into +notice. At that time the Paris Observatory was presided over by +Arago, a SAVANT who occupies a distinguished position in French +scientific annals. Arago at once perceived that Le Verrier was just +the man who possessed the qualifications suitable for undertaking a +problem of great importance and difficulty that had begun to force +itself on the attention of astronomers. What this great problem was, +and how astonishing was the solution it received, must now be +considered. + +Ever since Herschel brought himself into fame by his superb discovery +of the great planet Uranus, the movements of this new addition to the +solar system were scrutinized with care and attention. The position +of Uranus was thus accurately determined from time to time. At +length, when sufficient observations of this remote planet had been +brought together, the route which the newly-discovered body pursued +through the heavens was ascertained by those calculations with which +astronomers are familiar. It happens, however, that Uranus possesses +a superficial resemblance to a star. Indeed the resemblance is so +often deceptive that long ere its detection as a planet by Herschel, +it had been observed time after time by skilful astronomers, who +little thought that the star-like point at which they looked was +anything but a star. From these early observations it was possible +to determine the track of Uranus, and it was found that the great +planet takes a period of no less than eighty-four years to accomplish +a circuit. Calculations were made of the shape of the orbit in which +it revolved before its discovery by Herschel, and these were compared +with the orbit which observations showed the same body to pursue in +those later years when its planetary character was known. It could +not, of course, be expected that the orbit should remain unaltered; +the fact that the great planets Jupiter and Saturn revolve in the +vicinity of Uranus must necessarily imply that the orbit of the +latter undergoes considerable changes. When, however, due allowance +has been made for whatever influence the attraction of Jupiter and +Saturn, and we may add of the earth and all the other Planets, could +possibly produce, the movements of Uranus were still inexplicable. It +was perfectly obvious that there must be some other influence at work +besides that which could be attributed to the planets already known. + +Astronomers could only recognise one solution of such a difficulty. +It was impossible to doubt that there must be some other planet in +addition to the bodies at that time known, and that the perturbations +of Uranus hitherto unaccounted for, were due to the disturbances +caused by the action of this unknown planet. Arago urged Le Verrier +to undertake the great problem of searching for this body, whose +theoretical existence seemed demonstrated. But the conditions of the +search were such that it must needs be conducted on principles wholly +different from any search which had ever before been undertaken for a +celestial object. For this was not a case in which mere survey with +a telescope might be expected to lead to the discovery. + +Certain facts might be immediately presumed with reference to the +unknown object. There could be no doubt that the unknown disturber +of Uranus must be a large body with a mass far exceeding that of the +earth. It was certain, however, that it must be so distant that it +could only appear from our point of view as a very small object. +Uranus itself lay beyond the range, or almost beyond the range, of +unassisted vision. It could be shown that the planet by which the +disturbance was produced revolved in an orbit which must lie outside +that of Uranus. It seemed thus certain that the planet could not be +a body visible to the unaided eye. Indeed, had it been at all +conspicuous its planetary character would doubtless have been +detected ages ago. The unknown body must therefore be a planet which +would have to be sought for by telescopic aid. + +There is, of course, a profound physical difference between a planet +and a star, for the star is a luminous sun, and the planet is merely +a dark body, rendered visible by the sunlight which falls upon it. +Notwithstanding that a star is a sun thousands of times larger than +the planet and millions of times more remote, yet it is a singular +fact that telescopic planets possess an illusory resemblance to the +stars among which their course happens to lie. So far as actual +appearance goes, there is indeed only one criterion by which a planet +of this kind can be discriminated from a star. If the planet be +large enough the telescope will show that it possesses a disc, and +has a visible and measurable circular outline. This feature a star +does not exhibit. The stars are indeed so remote that no matter how +large they may be intrinsically, they only exhibit radiant points of +light, which the utmost powers of the telescope fail to magnify into +objects with an appreciable diameter. The older and well-known +planets, such as Jupiter and Mars, possess discs, which, though not +visible to the unaided eye, were clearly enough discernible with the +slightest telescopic power. But a very remote planet like Uranus, +though it possessed a disc large enough to be quickly appreciated by +the consummate observing skill of Herschel, was nevertheless so +stellar in its appearance, that it had been observed no fewer than +seventeen times by experienced astronomers prior to Herschel. In +each case the planetary nature of the object had been overlooked, and +it had been taken for granted that it was a star. It presented no +difference which was sufficient to arrest attention. + +As the unknown body by which Uranus was disturbed was certainly much +more remote than Uranus, it seemed to be certain that though it might +show a disc perceptible to very close inspection, yet that the disc +must be so minute as not to be detected except with extreme care. In +other words, it seemed probable that the body which was to be sought +for could not readily be discriminated from a small star, to which +class of object it bore a superficial resemblance, though, as a +matter of fact, there was the profoundest difference between the two +bodies. + +There are on the heavens many hundreds of thousands of stars, and the +problem of identifying the planet, if indeed it should lie among +these stars, seemed a very complex matter. Of course it is the +abundant presence of the stars which causes the difficulty. If the +stars could have been got rid of, a sweep over the heavens would at +once disclose all the planets which are bright enough to be visible +with the telescopic power employed. It is the fortuitous resemblance +of the planet to the stars which enables it to escape detection. To +discriminate the planet among stars everywhere in the sky would be +almost impossible. If, however, some method could be devised for +localizing that precise region in which the planet's existence might +be presumed, then the search could be undertaken with some prospect +of success. + +To a certain extent the problem of localizing the region on the sky +in which the planet might be expected admitted of an immediate +limitation. It is known that all the planets, or perhaps I ought +rather to say, all the great planets, confine their movements to a +certain zone around the heavens. This zone extends some way on +either side of that line called the ecliptic in which the earth +pursues its journey around the sun. It was therefore to be inferred +that the new planet need not be sought for outside this zone. It is +obvious that this consideration at once reduces the area to be +scrutinized to a small fraction of the entire heavens. But even +within the zone thus defined there are many thousands of stars. It +would seem a hopeless task to detect the new planet unless some +further limitation to its position could be assigned. + +It was accordingly suggested to Le Verrier that he should endeavour +to discover in what particular part of the strip of the celestial +sphere which we have indicated the search for the unknown planet +should be instituted. The materials available to the mathematician +for the solution of this problem were to be derived solely from the +discrepancies between the calculated places in which Uranus should be +found, taking into account the known causes of disturbance, and the +actual places in which observation had shown the planet to exist. +Here was indeed an unprecedented problem, and one of extraordinary +difficulty. Le Verrier, however, faced it, and, to the astonishment +of the world, succeeded in carrying it through to a brilliant +solution. We cannot here attempt to enter into any account of the +mathematical investigations that were necessary. All that we can do +is to give a general indication of the method which had to be +adopted. + +Let us suppose that a planet is revolving outside Uranus, at a +distance which is suggested by the several distances at which the +other planets are dispersed around the sun. Let us assume that this +outer planet has started on its course, in a prescribed path, and +that it has a certain mass. It will, of course, disturb the motion +of Uranus, and in consequence of that disturbance Uranus will follow +a path the nature of which can be determined by calculation. It +will, however, generally be found that the path so ascertained does +not tally with the actual path which observations have indicated for +Uranus. This demonstrates that the assumed circumstances of the +unknown planet must be in some respects erroneous, and the astronomer +commences afresh with an amended orbit. At last after many trials, +Le Verrier ascertained that, by assuming a certain size, shape, and +position for the unknown Planet's orbit, and a certain value for the +mass of the hypothetical body, it would be possible to account for +the observed disturbances of Uranus. Gradually it became clear to +the perception of this consummate mathematician, not only that the +difficulties in the movements of Uranus could be thus explained, but +that no other explanation need be sought for. It accordingly +appeared that a planet possessing the mass which he had assigned, and +moving in the orbit which his calculations had indicated, must indeed +exist, though no eye had ever beheld any such body. Here was, +indeed, an astonishing result. The mathematician sitting at his +desk, by studying the observations which had been supplied to him of +one planet, is able to discover the existence of another planet, and +even to assign the very position which it must occupy, ere ever the +telescope is invoked for its discovery. + +Thus it was that the calculations of Le Verrier narrowed greatly the +area to be scrutinised in the telescopic search which was presently +to be instituted. It was already known, as we have just pointed out, +that the planet must lie somewhere on the ecliptic. The French +mathematician had now further indicated the spot on the ecliptic at +which, according to his calculations, the planet must actually be +found. And now for an episode in this history which will be +celebrated so long as science shall endure. It is nothing less than +the telescopic confirmation of the existence of this new planet, +which had previously been indicated only by mathematical +calculation. Le Verrier had not himself the instruments necessary +for studying the heavens, nor did he possess the skill of the +practical astronomer. He, therefore, wrote to Dr. Galle, of the +Observatory at Berlin, requesting him to undertake a telescopic +search for the new planet in the vicinity which the mathematical +calculation had indicated for the whereabouts of the planet at that +particular time. Le Verrier added that he thought the planet ought +to admit of being recognised by the possession of a disc sufficiently +definite to mark the distinction between it and the surrounding +stars. + +It was the 23rd September, 1846, when the request from Le Verrier +reached the Berlin Observatory, and the night was clear, so that the +memorable search was made on the same evening. The investigation was +facilitated by the circumstance that a diligent observer had recently +compiled elaborate star maps for certain tracts of the heavens lying +in a sufficiently wide zone on both sides of the equator. These maps +were as yet only partially complete, but it happened that Hora. XXI., +which included the very spot which Le Verrier's results referred to, +had been just issued. Dr. Galle had thus before his eyes a chart of +all the stars which were visible in that part of the heavens at the +time when the map was made. The advantage of such an assistance to +the search could hardly be over-estimated. It at once gave the +astronomer another method of recognising the planet besides that +afforded by its possible possession of a disc. For as the planet was +a moving body, it would not have been in the same place relatively to +the stars at the time when the map was constructed, as it occupied +some years later when the search was being made. If the body should +be situated in the spot which Le Verrier's calculations indicated in +the autumn of 1846, then it might be regarded as certain that it +would not be found in that same place on a map drawn some years +previously. + +The search to be undertaken consisted in a comparison made point by +point between the bodies shown on the map, and those stars in the sky +which Dr. Galle's telescope revealed. In the course of this +comparison it presently appeared that a star-like object of the +eighth magnitude, which was quite a conspicuous body in the +telescope, was not represented in the map. This at once attracted +the earnest attention of the astronomer, and raised his hopes that +here was indeed the planet. Nor were these hopes destined to be +disappointed. It could not be supposed that a star of the eighth +magnitude would have been overlooked in the preparation of a chart +whereon stars of many lower degrees of brightness were set down. One +other supposition was of course conceivable. It might have been that +this suspicious object belonged to the class of variables, for there +are many such stars whose brightness fluctuates, and if it had +happened that the map was constructed at a time when the star in +question had but feeble brilliance, it might have escaped notice. It +is also well known that sometimes new stars suddenly develop, so that +the possibility that what Dr. Galle saw should have been a variable +star or should have been a totally new star had to be provided +against. + +Fortunately a test was immediately available to decide whether the +new object was indeed the long sought for planet, or whether it was a +star of one of the two classes to which I have just referred. A star +remains fixed, but a planet is in motion. No doubt when a planet +lies at the distance at which this new planet was believed to be +situated, its apparent motion would be so slow that it would not be +easy to detect any change in the course of a single night's +observation. Dr. Galle, however, addressed himself with much skill +to the examination of the place of the new body. Even in the course +of the night he thought he detected slight movements, and he awaited +with much anxiety the renewal of his observations on the subsequent +evenings. His suspicions as to the movement of the body were then +amply confirmed, and the planetary nature of the new object was thus +unmistakably detected. + +Great indeed was the admiration of the scientific world at this +superb triumph. Here was a mighty planet whose very existence was +revealed by the indications afforded by refined mathematical +calculation. At once the name of Le Verrier, already known to those +conversant with the more profound branches of astronomy, became +everywhere celebrated. It soon, however, appeared, that the fame +belonging to this great achievement had to be shared between Le +Verrier and another astronomer, J. C. Adams, of Cambridge. In our +chapter on this great English mathematician we shall describe the +manner in which he was independently led to the same discovery. + +Directly the planetary nature of the newly-discovered body had been +established, the great observatories naturally included this +additional member of the solar system in their working lists, so that +day after day its place was carefully determined. When sufficient +time had elapsed the shape and position of the orbit of the body +became known. Of course, it need hardly be said that observations +applied to the planet itself must necessarily provide a far more +accurate method of determining the path which it follows, than would +be possible to Le Verrier, when all he had to base his calculations +upon was the influence of the planet reflected, so to speak, from +Uranus. It may be noted that the true elements of the planet, when +revealed by direct observation, showed that there was a considerable +discrepancy between the track of the planet which Le Verrier had +announced, and that which the planet was actually found to pursue. + +The name of the newly-discovered body had next to be considered. As +the older members of the system were already known by the same names +as great heathen divinities, it was obvious that some similar source +should be invoked for a suggestion as to a name for the most recent +planet. The fact that this body was so remote in the depths of +space, not unnaturally suggested the name "Neptune." Such is +accordingly the accepted designation of that mighty globe which +revolves in the track that at present seems to trace out the +frontiers of our system. + +Le Verrier attained so much fame by this discovery, that when, in +1854, Arago's place had to be filled at the head of the great Paris +Observatory, it was universally felt that the discoverer of Neptune +was the suitable man to assume the office which corresponds in France +to that of the Astronomer Royal in England. It was true that the +work of the astronomical mathematician had hitherto been of an +abstract character. His discoveries had been made at his desk and +not in the observatory, and he had no practical acquaintance with the +use of astronomical instruments. However, he threw himself into the +technical duties of the observatory with vigour and determination. He +endeavoured to inspire the officers of the establishment with +enthusiasm for that systematic work which is so necessary for the +accomplishment of useful astronomical research. It must, however, be +admitted that Le Verrier was not gifted with those natural qualities +which would make him adapted for the successful administration of +such an establishment. Unfortunately disputes arose between the +Director and his staff. At last the difficulties of the situation +became so great that the only possible solution was to supersede Le +Verrier, and he was accordingly obliged to retire. He was succeeded +in his high office by another eminent mathematician, M. Delaunay, +only less distinguished than Le Verrier himself. + +Relieved of his official duties, Le Verrier returned to the +mathematics he loved. In his non-official capacity he continued to +work with the greatest ardour at his researches on the movements of +the planets. After the death of M. Delaunay, who was accidentally +drowned in 1873, Le Verrier was restored to the directorship of the +observatory, and he continued to hold the office until his death. + +The nature of the researches to which the life of Le Verrier was +subsequently devoted are not such as admit of description in a +general sketch like this, where the language, and still less the +symbols, of mathematics could not be suitably introduced. It may, +however, be said in general that he was particularly engaged with the +study of the effects produced on the movements of the planets by +their mutual attractions. The importance of this work to astronomy +consists, to a considerable extent, in the fact that by such +calculations we are enabled to prepare tables by which the places of +the different heavenly bodies can be predicted for our almanacs. To +this task Le Verrier devoted himself, and the amount of work he has +accomplished would perhaps have been deemed impossible had it not +been actually done. + +The superb success which had attended Le Verrier's efforts to explain +the cause of the perturbations of Uranus, naturally led this +wonderful computer to look for a similar explanation of certain other +irregularities in planetary movements. To a large extent he +succeeded in showing how the movements of each of the great planets +could be satisfactorily accounted for by the influence of the +attractions of the other bodies of the same class. One circumstance +in connection with these investigations is sufficiently noteworthy to +require a few words here. Just as at the opening of his career, Le +Verrier had discovered that Uranus, the outermost planet of the then +known system, exhibited the influence of an unknown external body, so +now it appeared to him that Mercury, the innermost body of our +system, was also subjected to some disturbances, which could not be +satisfactorily accounted for as consequences of any known agents of +attraction. The ellipse in which Mercury revolved was animated by a +slow movement, which caused it to revolve in its plane. It appeared +to Le Verrier that this displacement was incapable of explanation by +the action of any of the known bodies of our system. He was, +therefore, induced to try whether he could not determine from the +disturbances of Mercury the existence of some other planet, at +present unknown, which revolved inside the orbit of the known +planet. Theory seemed to indicate that the observed alteration in +the track of the planet could be thus accounted for. He naturally +desired to obtain telescopic confirmation which might verify the +existence of such a body in the same way as Dr. Galle verified the +existence of Neptune. If there were, indeed, an intramercurial +planet, then it must occasionally cross between the earth and the +sun, and might now and then be expected to be witnessed in the actual +act of transit. So confident did Le Verrier feel in the existence of +such a body that an observation of a dark object in transit, by +Lescarbault on 26th March, 1859, was believed by the mathematician to +be the object which his theory indicated. Le Verrier also thought it +likely that another transit of the same object would be seen in +March, 1877. Nothing of the kind was, however, witnessed, +notwithstanding that an assiduous watch was kept, and the explanation +of the change in Mercury's orbit must, therefore, be regarded as +still to be sought for. + +Le Verrier naturally received every honour that could be bestowed +upon a man of science. The latter part of his life was passed during +the most troubled period of modern French history. He was a +supporter of the Imperial Dynasty, and during the Commune he +experienced much anxiety; indeed, at one time grave fears were +entertained for his personal safety. + +Early in 1877 his health, which had been gradually failing for some +years, began to give way. He appeared to rally somewhat in the +summer, but in September he sank rapidly, and died on Sunday, the +23rd of that month. + +His remains were borne to the cemetery on Mont Parnasse in a public +funeral. Among his pallbearers were leading men of science, from +other countries as well as France, and the memorial discourses +pronounced at the grave expressed their admiration of his talents and +of the greatness of the services he had rendered to science. + + + + +ADAMS. + + +The illustrious mathematician who, among Englishmen, at all events, +was second only to Newton by his discoveries in theoretical +astronomy, was born on June the 5th, 1819, at the farmhouse of +Lidcot, seven miles from Launceston, in Cornwall. His early +education was imparted under the guidance of the Rev. John Couch +Grylls, a first cousin of his mother. He appears to have received an +education of the ordinary school type in classics and mathematics, +but his leisure hours were largely devoted to studying what +astronomical books he could find in the library of the Mechanics' +Institute at Devonport. He was twenty years old when he entered St. +John's College, Cambridge. His career in the University was one of +almost unparalleled distinction, and it is recorded that his +answering at the Wranglership examination, where he came out at the +head of the list in 1843, was so high that he received more than +double the marks awarded to the Second Wrangler. + +Among the papers found after his death was the following memorandum, +dated July the 3rd, 1841: "Formed a design at the beginning of this +week of investigating, as soon as possible after taking my degree, +the irregularities in the motion of Uranus, which are as yet +unaccounted for, in order to find whether they may be attributed to +the action of an undiscovered planet beyond it; and, if possible, +thence to determine the elements of its orbit approximately, which +would lead probably to its discovery." + +After he had taken his degree, and had thus obtained a little +relaxation from the lines within which his studies had previously +been necessarily confined, Adams devoted himself to the study of the +perturbations of Uranus, in accordance with the resolve which we have +just seen that he formed while he was still an undergraduate. As a +first attempt he made the supposition that there might be a planet +exterior to Uranus, at a distance which was double that of Uranus +from the sun. Having completed his calculation as to the effect +which such a hypothetical planet might exercise upon the movement of +Uranus, he came to the conclusion that it would be quite possible to +account completely for the unexplained difficulties by the action of +an exterior planet, if only that planet were of adequate size and had +its orbit properly placed. It was necessary, however, to follow up +the problem more precisely, and accordingly an application was made +through Professor Challis, the Director of the Cambridge Observatory, +to the Astronomer Royal, with the object of obtaining from the +observations made at Greenwich Observatory more accurate values for +the disturbances suffered by Uranus. Basing his work on the more +precise materials thus available, Adams undertook his calculations +anew, and at last, with his completed results, he called at Greenwich +Observatory on October the 21st, 1845. He there left for the +Astronomer Royal a paper which contained the results at which he had +arrived for the mass and the mean distance of the hypothetical planet +as well as the other elements necessary for calculating its exact +position. + +[PLATE: JOHN COUCH ADAMS.] + +As we have seen in the preceding chapter, Le Verrier had been also +investigating the same problem. The place which Le Verrier assigned +to the hypothetical disturbing planet for the beginning of the year +1847, was within a degree of that to which Adams's computations +pointed, and which he had communicated to the Astronomer Royal seven +months before Le Verrier's work appeared. On July the 29th, 1846, +Professor Challis commenced to search for the unknown object with the +Northumberland telescope belonging to the Cambridge Observatory. He +confined his attention to a limited region in the heavens, extending +around that point to which Mr. Adams' calculations pointed. The +relative places of all the stars, or rather star-like objects within +this area, were to be carefully measured. When the same observations +were repeated a week or two later, then the distances of the several +pairs of stars from each other would be found unaltered, but any +planet which happened to lie among the objects measured would +disclose its existence by the alterations in distance due to its +motion in the interval. This method of search, though no doubt it +must ultimately have proved successful, was necessarily a very +tedious one, but to Professor Challis, unfortunately, no other method +was available. Thus it happened that, though Challis commenced his +search at Cambridge two months earlier than Galle at Berlin, yet, as +we have already explained, the possession of accurate star-maps by +Dr. Galle enabled him to discover the planet on the very first night +that he looked for it. + +The rival claims of Adams and Le Verrier to the discovery of Neptune, +or rather, we should say, the claims put forward by their respective +champions, for neither of the illustrious investigators themselves +condescended to enter into the personal aspect of the question, need +not be further discussed here. The main points of the controversy +have been long since settled, and we cannot do better than quote the +words of Sir John Herschel when he addressed the Royal Astronomical +Society in 1848:-- + +"As genius and destiny have joined the names of Le Verrier and Adams, +I shall by no means put them asunder; nor will they ever be +pronounced apart so long as language shall celebrate the triumphs of +science in her sublimest walks. On the great discovery of Neptune, +which may be said to have surpassed, by intelligible and legitimate +means, the wildest pretensions of clairvoyance, it Would now be quite +superfluous for me to dilate. That glorious event and the steps +which led to it, and the various lights in which it has been placed, +are already familiar to every one having the least tincture of +science. I will only add that as there is not, nor henceforth ever +can be, the slightest rivalry on the subject between these two +illustrious men--as they have met as brothers, and as such will, I +trust, ever regard each other--we have made, we could make, no +distinction between then, on this occasion. May they both long adorn +and augment our science, and add to their own fame already so high +and pure, by fresh achievements." + +Adams was elected a Fellow of St. John's College, Cambridge, in 1843; +but as he did not take holy orders, his Fellowship, in accordance +with the rules then existing came to an end in 1852. In the +following year he was, however, elected to a Fellowship at Pembroke +College, which he retained until the end of his life. In 1858 he was +appointed Professor of Mathematics in the University of St. Andrews, +but his residence in the north was only a brief one, for in the same +year he was recalled to Cambridge as Lowndean Professor of Astronomy +and Geometry, in succession to Peacock. In 1861 Challis retired from +the Directorship of the Cambridge Observatory, and Adams was +appointed to succeed him. + +The discovery of Neptune was a brilliant inauguration of the +astronomical career of Adams. He worked at, and wrote upon, the +theory of the motions of Biela's comet; he made important corrections +to the theory of Saturn; he investigated the mass of Uranus, a +subject in which he was naturally interested from its importance in +the theory of Neptune; he also improved the methods of computing the +orbits of double stars. But all these must be regarded as his minor +labours, for next to the discovery of Neptune the fame of Adams +mainly rests on his researches upon certain movements of the moon, +and upon the November meteors. + +The periodic time of the moon is the interval required for one +circuit of its orbit. This interval is known with accuracy at the +present day, and by means of the ancient eclipses the period of the +moon's revolution two thousand years ago can be also ascertained. It +had been discovered by Halley that the period which the moon requires +to accomplish each of its revolutions around the earth has been +steadily, though no doubt slowly, diminishing. The change thus +produced is not appreciable when only small intervals of time are +considered, but it becomes appreciable when we have to deal with +intervals of thousands of years. The actual effect which is produced +by the lunar acceleration, for so this phenomenon is called, may be +thus estimated. If we suppose that the moon had, throughout the +ages, revolved around the earth in precisely the same periodic time +which it has at present, and if from this assumption we calculate +back to find where the moon must have been about two thousand years +ago, we obtain a position which the ancient eclipses show to be +different from that in which the moon was actually situated. The +interval between the position in which the moon would have been found +two thousand years ago if there had been no acceleration, and the +position in which the moon was actually placed, amounts to about a +degree, that is to say, to an arc on the heavens which is twice the +moon's apparent diameter. + +If no other bodies save the earth and the moon were present in the +universe, it seems certain that the motion of the moon would never +have exhibited this acceleration. In such a simple case as that +which I have supposed the orbit of the moon would have remained for +ever absolutely unchanged. It is, however, well known that the +presence of the sun exerts a disturbing influence upon the movements +of the moon. In each revolution our satellite is continually drawn +aside by the action of the sun from the place which it would +otherwise have occupied. These irregularities are known as the +perturbations of the lunar orbit, they have long been studied, and +the majority of them have been satisfactorily accounted for. It +seems, however, to those who first investigated the question that the +phenomenon of the lunar acceleration could not be explained as a +consequence of solar perturbation, and, as no other agent competent +to produce such effects was recognised by astronomers, the lunar +acceleration presented an unsolved enigma. + +At the end of the last century the illustrious French mathematician +Laplace undertook a new investigation of the famous problem, and was +rewarded with a success which for a long time appeared to be quite +complete. Let us suppose that the moon lies directly between the +earth and the sun, then both earth and moon are pulled towards the +sun by the solar attraction; as, however, the moon is the nearer of +the two bodies to the attracting centre it is pulled the more +energetically, and consequently there is an increase in the distance +between the earth and the moon. Similarly when the moon happens to +lie on the other side of the earth, so that the earth is interposed +directly between the moon and the sun, the solar attraction exerted +upon the earth is more powerful than the same influence upon the +moon. Consequently in this case, also, the distance of the moon from +the earth is increased by the solar disturbance. These instances +will illustrate the general truth, that, as one of the consequences +of the disturbing influence exerted by the sun upon the earth-moon +system, there is an increase in the dimensions of the average orbit +which the moon describes around the earth. As the time required by +the moon to accomplish a journey round the earth depends upon its +distance from the earth, it follows that among the influences of the +sun upon the moon there must be an enlargement of the periodic time, +from what it would have been had there been no solar disturbing +action. + +This was known long before the time of Laplace, but it did not +directly convey any explanation of the lunar acceleration. It no +doubt amounted to the assertion that the moon's periodic time was +slightly augmented by the disturbance, but it did not give any +grounds for suspecting that there was a continuous change in +progress. It was, however, apparent that the periodic time was +connected with the solar disturbance, so that, if there were any +alteration in the amount of the sun's disturbing effect, there must +be a corresponding alteration in the moon's periodic time. Laplace, +therefore, perceived that, if he could discover any continuous change +in the ability of the sun for disturbing the moon, he would then have +accounted for a continuous change in the moon's periodic time, and +that thus an explanation of the long-vexed question of the lunar +acceleration might be forthcoming. + +The capability of the sun for disturbing the earth-moon system is +obviously connected with the distance of the earth from the sun. If +the earth moved in an orbit which underwent no change whatever, then +the efficiency of the sun as a disturbing agent would not undergo any +change of the kind which was sought for. But if there were any +alteration in the shape or size of the earth's orbit, then that might +involve such changes in the distance between the earth and the sun as +would possibly afford the desired agent for producing the observed +lunar effect. It is known that the earth revolves in an orbit which, +though nearly circular, is strictly an ellipse. If the earth were +the only planet revolving around the sun then that ellipse would +remain unaltered from age to age. The earth is, however, only one of +a large number of planets which circulate around the great luminary, +and are guided and controlled by his supreme attracting power. These +planets mutually attract each other, and in consequence of their +mutual attractions the orbits of the planets are disturbed from the +simple elliptic form which they would otherwise possess. The +movement of the earth, for instance, is not, strictly speaking, +performed in an elliptical orbit. We may, however, regard it as +revolving in an ellipse provided we admit that the ellipse is itself +in slow motion. + +It is a remarkable characteristic of the disturbing effects of the +planets that the ellipse in which the earth is at any moment moving +always retains the same length; that is to say, its longest diameter +is invariable. In all other respects the ellipse is continually +changing. It alters its position, it changes its plane, and, most +important of all, it changes its eccentricity. Thus, from age to age +the shape of the track which the earth describes may at one time be +growing more nearly a circle, or at another time may be departing +more widely from a circle. These alterations are very small in +amount, and they take place with extreme slowness, but they are in +incessant progress, and their amount admits of being accurately +calculated. At the present time, and for thousands of years past, as +well as for thousands of years to come, the eccentricity of the +earth's orbit is diminishing, and consequently the orbit described by +the earth each year is becoming more nearly circular. We must, +however, remember that under all circumstances the length of the +longest axis of the ellipse is unaltered, and consequently the size +of the track which the earth describes around the sun is gradually +increasing. In other words, it may be said that during the present +ages the average distance between the earth and the sun is waxing +greater in consequence of the perturbations which the earth +experiences from the attraction of the other planets. We have, +however, already seen that the efficiency of the solar attraction for +disturbing the moon's movement depends on the distance between the +earth and the sun. As therefore the average distance between the +earth and the sun is increasing, at all events during the thousands +of years over which our observations extend, it follows that the +ability of the sun for disturbing the moon must be gradually +diminishing. + +[PLATE: CAMBRIDGE OBSERVATORY.] + +It has been pointed out that, in consequence of the solar +disturbance, the orbit of the moon must be some what enlarged. As it +now appears that the solar disturbance is on the whole declining, it +follows that the orbit of the moon, which has to be adjusted +relatively to the average value of the solar disturbance, must also +be gradually declining. In other words, the moon must be approaching +nearer to the earth in consequence of the alterations in the +eccentricity of the earth's orbit produced by the attraction of the +other planets. It is true that the change in the moon's position +thus arising is an extremely small one, and the consequent effect in +accelerating the moon's motion is but very slight. It is in fact +almost imperceptible, except when great periods of time are +involved. Laplace undertook a calculation on this subject. He knew +what the efficiency of the planets in altering the dimensions of the +earth's orbit amounted to; from this he was able to determine the +changes that would be propagated into the motion of the moon. Thus +he ascertained, or at all events thought he had ascertained, that the +acceleration of the moon's motion, as it had been inferred from the +observations of the ancient eclipses which have been handed down to +us, could be completely accounted for as a consequence of planetary +perturbation. This was regarded as a great scientific triumph. Our +belief in the universality of the law of gravitation would, in fact, +have been seriously challenged unless some explanation of the lunar +acceleration had been forthcoming. For about fifty years no one +questioned the truth of Laplace's investigation. When a +mathematician of his eminence had rendered an explanation of the +remarkable facts of observation which seemed so complete, it is not +surprising that there should have been but little temptation to doubt +it. On undertaking a new calculation of the same question, Professor +Adams found that Laplace had not pursued this approximation +sufficiently far, and that consequently there was a considerable +error in the result of his analysis. Adams, it must be observed, did +not impugn the value of the lunar acceleration which Halley had +deduced from the observations, but what he did show was, that the +calculation by which Laplace thought he had provided an explanation +of this acceleration was erroneous. Adams, in fact, proved that the +planetary influence which Laplace had detected only possessed about +half the efficiency which the great French mathematician had +attributed to it. There were not wanting illustrious mathematicians +who came forward to defend the calculations of Laplace. They +computed the question anew and arrived at results practically +coincident with those he had given. On the other hand certain +distinguished mathematicians at home and abroad verified the results +of Adams. The issue was merely a mathematical one. It had only one +correct solution. Gradually it appeared that those who opposed Adams +presented a number of different solutions, all of them discordant +with his, and, usually, discordant with each other. Adams showed +distinctly where each of these investigators had fallen into error, +and at last it became universally admitted that the Cambridge +Professor had corrected Laplace in a very fundamental point of +astronomical theory. + +Though it was desirable to have learned the truth, yet the breach +between observation and calculation which Laplace was believed to +have closed thus became reopened. Laplace's investigation, had it +been correct, would have exactly explained the observed facts. It +was, however, now shown that his solution was not correct, and that +the lunar acceleration, when strictly calculated as a consequence of +solar perturbations, only produced about half the effect which was +wanted to explain the ancient eclipses completely. It now seems +certain that there is no means of accounting for the lunar +acceleration as a direct consequence of the laws of gravitation, if +we suppose, as we have been in the habit of supposing, that the +members of the solar system concerned may be regarded as rigid +particles. It has, however, been suggested that another explanation +of a very interesting kind may be forthcoming, and this we must +endeavour to set forth. + +It will be remembered that we have to explain why the period of +revolution of the moon is now shorter than it used to be. If we +imagine the length of the period to be expressed in terms of days and +fractions of a day, that is to say, in terms of the rotations of the +earth around its axis, then the difficulty encountered is, that the +moon now requires for each of its revolutions around the earth rather +a smaller number of rotations of the earth around its axis than used +formerly to be the case. Of course this may be explained by the fact +that the moon is now moving more swiftly than of yore, but it is +obvious that an explanation of quite a different kind might be +conceivable. The moon may be moving just at the same pace as ever, +but the length of the day may be increasing. If the length of the +day is increasing, then, of course, a smaller number of days will be +required for the moon to perform each revolution even though the +moon's period was itself really unchanged. It would, therefore, seem +as if the phenomenon known as the lunar acceleration is the result of +the two causes. The first of these is that discovered by Laplace, +though its value was over-estimated by him, in which the perturbations +of the earth by the planets indirectly affect the motion of the +moon. The remaining part of the acceleration of our satellite is +apparent rather than real, it is not that the moon is moving more +quickly, but that our time-piece, the earth, is revolving more +slowly, and is thus actually losing time. It is interesting to note +that we can detect a physical explanation for the apparent checking +of the earth's motion which is thus manifested. The tides which ebb +and flow on the earth exert a brake-like action on the revolving +globe, and there can be no doubt that they are gradually reducing its +speed, and thus lengthening the day. It has accordingly been +suggested that it is this action of the tides which produces the +supplementary effect necessary to complete the physical explanation +of the lunar acceleration, though it would perhaps be a little +premature to assert that this has been fully demonstrated. + +The third of Professor Adams' most notable achievements was connected +with the great shower of November meteors which astonished the world +in 1866. This splendid display concentrated the attention of +astronomers on the theory of the movements of the little objects by +which the display was produced. For the definite discovery of the +track in which these bodies revolve, we are indebted to the labours +of Professor Adams, who, by a brilliant piece of mathematical work, +completed the edifice whose foundations had been laid by Professor +Newton, of Yale, and other astronomers. + +Meteors revolve around the sun in a vast swarm, every individual +member of which pursues an orbit in accordance with the well-known +laws of Kepler. In order to understand the movements of these +objects, to account satisfactorily for their periodic recurrence, and +to predict the times of their appearance, it became necessary to +learn the size and the shape of the track which the swarm followed, +as well as the position which it occupied. Certain features of the +track could no doubt be readily assigned. The fact that the shower +recurs on one particular day of the year, viz., November 13th, +defines one point through which the orbit must pass. The position on +the heavens of the radiant point from which the meteors appear to +diverge, gives another element in the track. The sun must of course +be situated at the focus, so that only one further piece of +information, namely, the periodic time, will be necessary to complete +our knowledge of the movements of the system. Professor H. Newton, +of Yale, had shown that the choice of possible orbits for the +meteoric swarm is limited to five. There is, first, the great +ellipse in which we now know the meteors revolve once every thirty +three and one quarter years. There is next an orbit of a nearly +circular kind in which the periodic time would be a little more than +a year. There is a similar track in which the periodic time would be +a few days short of a year, while two other smaller orbits would also +be conceivable. Professor Newton had pointed out a test by which it +would be possible to select the true orbit, which we know must be one +or other of these five. The mathematical difficulties which attended +the application of this test were no doubt great, but they did not +baffle Professor Adams. + +There is a continuous advance in the date of this meteoric shower. +The meteors now cross our track at the point occupied by the earth on +November 13th, but this point is gradually altering. The only +influence known to us which could account for the continuous change +in the plane of the meteor's orbit arises from the attraction of the +various planets. The problem to be solved may therefore be attacked +in this manner. A specified amount of change in the plane of the +orbit of the meteors is known to arise, and the changes which ought +to result from the attraction of the planets can be computed for each +of the five possible orbits, in one of which it is certain that the +meteors must revolve. Professor Adams undertook the work. Its +difficulty principally arises from the high eccentricity of the +largest of the orbits, which renders the more ordinary methods of +calculation inapplicable. After some months of arduous labour the +work was completed, and in April, 1867, Adams announced his solution +of the problem. He showed that if the meteors revolved in the +largest of the five orbits, with the periodic time of thirty three +and one quarter years, the perturbations of Jupiter would account for +a change to the extent of twenty minutes of arc in the point in which +the orbit crosses the earth's track. The attraction of Saturn would +augment this by seven minutes, and Uranus would add one minute more, +while the influence of the Earth and of the other planets would be +inappreciable. The accumulated effect is thus twenty-eight minutes, +which is practically coincident with the observed value as determined +by Professor Newton from an examination of all the showers of which +there is any historical record. Having thus showed that the great +orbit was a possible path for the meteors, Adams next proved that no +one of the other four orbits would be disturbed in the same manner. +Indeed, it appeared that not half the observed amount of change could +arise in any orbit except in that one with the long period. Thus was +brought to completion the interesting research which demonstrated the +true relation of the meteor swarm to the solar system. + +Besides those memorable scientific labours with which his attention +was so largely engaged, Professor Adams found time for much other +study. He occasionally allowed himself to undertake as a relaxation +some pieces of numerical calculation, so tremendously long that we +can only look on them with astonishment. He has calculated certain +important mathematical constants accurately to more than two hundred +places of decimals. He was a diligent reader of works on history, +geology, and botany, and his arduous labours were often beguiled by +novels, of which, like many other great men, he was very fond. He +had also the taste of a collector, and he brought together about +eight hundred volumes of early printed works, many of considerable +rarity and value. As to his personal character, I may quote the +words of Dr. Glaisher when he says, "Strangers who first met him were +invariably struck by his simple and unaffected manner. He was a +delightful companion, always cheerful and genial, showing in society +but few traces of his really shy and retiring disposition. His +nature was sympathetic and generous, and in few men have the moral +and intellectual qualities been more perfectly balanced." + +In 1863 he married the daughter of Haliday Bruce, Esq., of Dublin and +up to the close of his life he lived at the Cambridge Observatory, +pursuing his mathematical work and enjoying the society of his +friends. + +He died, after a long illness, on 21st January, 1892, and was +interred in St. Giles's Cemetery, on the Huntingdon Road, Cambridge. + + +*** END OF THE PROJECT GUTENBERG EBOOK 2298 *** diff --git a/2298-h/2298-h.htm b/2298-h/2298-h.htm new file mode 100644 index 0000000..b3213ff --- /dev/null +++ b/2298-h/2298-h.htm @@ -0,0 +1,9603 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" +"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"> + <head> +<meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> +<title>Great Astronomers | Project Gutenberg</title> +<style type="text/css"> + p {margin-top:.75em;text-align:justify;margin-bottom:.75em;text-indent:2%;} + +.c {text-align:center;text-indent:0%;} + +.nind {text-indent:0%;} + +div.footnote {margin:5% 10% 5% 10%;font-size:80%;} + + h1,h3 {margin-top:15%;text-align:center;clear:both;} + +.r {text-align:right;margin-right;5%;} + + table {margin-left:auto;margin-right:auto;border:none;text-align:left;} + + body{margin-left:10%;margin-right:10%;background:#F8F8F8;color:black;font-family:"Times New Roman", serif;font-size:medium;} + + ul {list-style-type:none;text-indent:-1em;font-size:80%;} + +li {padding:.25%;} + +a:link {background-color:#F8F8F8;color:blue;text-decoration:none;} + + link {background-color:#F8F8F8;color:blue;text-decoration:none;} + +a:visited {background-color:#F8F8F8;color:purple;text-decoration:none;} + +a:hover {background-color:##F8F8F8;color:#FF0000;text-decoration:underline;} + +.smcap {font-variant:small-caps;font-size:95%;} + + img {border:none;} + +.caption {font-weight:bold;font-size:small;} + +.figcenter {margin:auto;text-align:center;} + +.figleft {float:left;clear:left;margin-left:0;margin-bottom:1em;margin-top:1em;margin-right:1em;padding:0;text-align:center;} + +.figright {float:right;clear:right;margin-left:1em;margin-bottom:1em;margin-top:1em;margin-right:0;padding:0;text-align:center;} +</style> + </head> +<body> +<div>*** START OF THE PROJECT GUTENBERG EBOOK 2298 ***</div> + +<div class="figcenter" style="width: 550px;"> +<a href="images/ill_front.jpg"> +<img src="images/ill_front_sml.jpg" width="550" height="338" alt="GREENWICH OBSERVATORY." title="" /></a> +<span class="caption">GREENWICH OBSERVATORY.</span> +</div> + +<h1>GREAT ASTRONOMERS</h1> + +<p class="c"><b>by</b></p> + +<p class="c"><b><big>SIR ROBERT S. BALL D.Sc. LL.D. F.R.S.</big></b></p> + +<p class="c"><b><small>Lowndean Professor of Astronomy and Geometry in the +University of Cambridge<br /> +Author of "In Starry Realms" "In the High Heavens" etc.</small></b></p> + +<p class="c"><b>WITH NUMEROUS ILLUSTRATIONS</b></p> + +<p><a name="greenwich" id="greenwich"></a></p> + +<h3><a name="PREFACE" id="PREFACE"></a>PREFACE.</h3> +<p>It has been my object in these pages to present the life of each +astronomer in such detail as to enable the reader to realise in +some degree the man's character and surroundings; and I have +endeavoured to indicate as clearly as circumstances would permit +the main features of the discoveries by which he has become known.</p> + +<p>There are many types of astronomers—from the stargazer who merely +watches the heavens, to the abstract mathematician who merely +works at his desk; it has, consequently, been necessary in the +case of some lives to adopt a very different treatment from that +which seemed suitable for others.</p> + +<p>While the work was in progress, some of the sketches appeared in +"Good Words." The chapter on Brinkley has been chiefly derived from +an article on the "History of Dunsink Observatory," which was +published on the occasion of the tercentenary celebration of the +University of Dublin in 1892, and the life of Sir William Rowan +Hamilton is taken, with a few alterations and omissions, from an +article contributed to the "Quarterly Review" on Graves' life of +the great mathematician. The remaining chapters now appear for +the first time. For many of the facts contained in the sketch of +the late Professor Adams, I am indebted to the obituary notice +written by my friend Dr. J. W. L. Glaisher, for the Royal Astronomical +Society; while with regard to the late Sir George Airy, I have a +similar acknowledgment to make to Professor H. H. Turner. To my +friend Dr. Arthur A. Rambaut I owe my hearty thanks for his +kindness in aiding me in the revision of the work.</p> + +<p class="r">R.S.B.</p> +<p class="nind"><small>The Observatory, Cambridge.<br /> +October, 1895</small></p> + +<h3><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h3> +<table border="0" cellpadding="0" cellspacing="0" summary=""> +<tr><td align="left"><a href="#PREFACE">P<small>REFACE</small>.</a></td></tr> +<tr><td align="left"><a href="#INTRODUCTION">I<small>NTRODUCTION</small>.</a></td></tr> +<tr><td align="left"><a href="#PTOLEMY">P<small>TOLEMY</small>.</a></td></tr> +<tr><td align="left"><a href="#COPERNICUS">C<small>OPERNICUS</small>.</a></td></tr> +<tr><td align="left"><a href="#TYCHO_BRAHE">T<small>YCHO</small> B<small>RAHE</small>.</a></td></tr> +<tr><td align="left"><a href="#GALILEO">G<small>ALILEO</small>.</a></td></tr> +<tr><td align="left"><a href="#KEPLER">K<small>EPLER</small>.</a></td></tr> +<tr><td align="left"><a href="#ISAAC_NEWTON">I<small>SAAC</small> N<small>EWTON</small>.</a></td></tr> +<tr><td align="left"><a href="#FLAMSTEED">F<small>LAMSTEED</small>.</a></td></tr> +<tr><td align="left"><a href="#HALLEY">H<small>ALLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#BRADLEY">B<small>RADLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#WILLIAM_HERSCHEL">W<small>ILLIAM</small> H<small>ERSCHEL</small>.</a></td></tr> +<tr><td align="left"><a href="#LAPLACE">L<small>APLACE</small>.</a></td></tr> +<tr><td align="left"><a href="#BRINKLEY">B<small>RINKLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#JOHN_HERSCHEL">J<small>OHN</small> H<small>ERSCHEL</small>.</a></td></tr> +<tr><td align="left"><a href="#THE_EARL_OF_ROSSE">T<small>HE</small> E<small>ARL OF</small> R<small>OSSE</small>.</a></td></tr> +<tr><td align="left"><a href="#AIRY">A<small>IRY</small>.</a></td></tr> +<tr><td align="left"><a href="#HAMILTON">H<small>AMILTON</small>.</a></td></tr> +<tr><td align="left"><a href="#LE_VERRIER">L<small>E</small> V<small>ERRIER</small>.</a></td></tr> +<tr><td align="left"><a href="#ADAMS">A<small>DAMS</small>.</a></td></tr> +</table> + +<h3><a name="LIST_OF_ILLUSTRATIONS" id="LIST_OF_ILLUSTRATIONS"></a>LIST OF ILLUSTRATIONS.</h3> + +<p class="c"><small>[Note of etext transcriber: The illustrations by be seen enlarged by clicking on them.]</small></p> + +<ul> +<li><a href="#greenwich">THE OBSERVATORY, GREENWICH.</a></li> + +<li><a href="#PTOLEMY">PTOLEMY.</a></li> + +<li><a href="#fig_1">PTOLEMY'S PLANETARY SCHEME.</a></li> + +<li><a href="#fig_2">PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.</a></li> + +<li><a href="#thorn">THORN, FROM AN OLD PRINT.</a></li> + +<li><a href="#copernicus_ill">COPERNICUS.</a></li> + +<li><a href="#frauenburg">FRAUENBURG, FROM AN OLD PRINT.</a></li> + +<li><a href="#explanation">EXPLANATION OF PLANETARY MOVEMENTS.</a></li> + +<li><a href="#tycho">TYCHO BRAHE.</a></li> + +<li><a href="#tycho_ill">TYCHO'S CROSS STAFF.</a></li> + +<li><a href="#new_star">TYCHO'S "NEW STAR" SEXTANT OF 1572.</a></li> + +<li><a href="#trigonic_sextant">TYCHO'S TRIGONIC SEXTANT.</a></li> + +<li><a href="#astronomic_sextant">TYCHO'S ASTRONOMIC SEXTANT.</a></li> + +<li><a href="#equatorial_armillary">TYCHO'S EQUATORIAL ARMILLARY.</a></li> + +<li><a href="#augsburg_quadrant">THE GREAT AUGSBURG QUADRANT.</a></li> + +<li><a href="#new_scheme">TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.</a></li> + +<li><a href="#uraniborg">URANIBORG AND ITS GROUNDS.</a></li> + +<li><a href="#grnd_pln_uraniborg">GROUND-PLAN OF THE OBSERVATORY.</a></li> + +<li><a href="#uraniborg_hven">THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.</a></li> + +<li><a href="#effigy">EFFIGY ON TYCHO'S TOMB AT PRAGUE.</a> +<ul><li>By Permission of Messrs. A. & C. Black.</li></ul></li> +<li><a href="#quadrant">TYCHO'S MURAL QUADRANT, URANIBORG.</a></li> + +<li><a href="#galileo_pendulum">GALILEO'S PENDULUM.</a></li> + +<li><a href="#portrait">GALILEO.</a></li> + +<li><a href="#arcetri">THE VILLA ARCETRI.</a></li> + +<li><a href="#facsimile">FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.</a></li> + +<li><a href="#crest">CREST OF GALILEO'S FAMILY.</a></li> + +<li><a href="#solids">KEPLER'S SYSTEM OF REGULAR SOLIDS.</a></li> + +<li><a href="#kepler_ill">KEPLER.</a></li> + +<li><a href="#symbolical">SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.</a></li> + +<li><a href="#commemoration">THE COMMEMORATION OF THE RUDOLPHINE TABLES.</a></li> + +<li><a href="#woolsthorpe">WOOLSTHORPE MANOR.</a></li> + +<li><a href="#trinity">TRINITY COLLEGE, CAMBRIDGE.</a></li> + +<li><a href="#diagram">DIAGRAM OF A SUNBEAM.</a></li> + +<li><a href="#isaac">ISAAC NEWTON.</a></li> + +<li><a href="#newton_reflector">SIR ISAAC NEWTON'S LITTLE REFLECTOR.</a></li> + +<li><a href="#sun-dial">SIR ISAAC NEWTON'S SUN-DIAL.</a></li> + +<li><a href="#newton_telescope">SIR ISAAC NEWTON'S TELESCOPE.</a></li> + +<li><a href="#newton_astrolabe">SIR ISAAC NEWTON'S ASTROLABE.</a></li> + +<li><a href="#royal_society">SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.</a></li> + +<li><a href="#flamsteed_house">FLAMSTEED'S HOUSE.</a></li> + +<li><a href="#flamsteed_ill">FLAMSTEED.</a></li> + +<li><a href="#halley_ill">HALLEY.</a></li> + +<li><a href="#greenwich_observatory">GREENWICH OBSERVATORY IN HALLEY'S TIME.</a></li> + +<li><a href="#new_king">7, NEW KING STREET, BATH.</a><ul> +<li>From a Photograph by John Poole, Bath.</li></ul></li> + +<li><a href="#william">WILLIAM HERSCHEL.</a></li> + +<li><a href="#caroline">CAROLINE HERSCHEL.</a></li> + +<li><a href="#street">STREET VIEW, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#garden">GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#view_herschel_house">OBSERVATORY, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#telescope_slough">THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#laplace_ill">LAPLACE.</a></li> + +<li><a href="#dunsink">THE OBSERVATORY, DUNSINK.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#astronometer">ASTRONOMETER MADE BY SIR JOHN HERSCHEL.</a></li> + +<li><a href="#john_herschel_ill">SIR JOHN HERSCHEL.</a></li> + +<li><a href="#nebula">NEBULA IN SOUTHERN HEMISPHERE.</a></li> + +<li><a href="#centaur">THE CLUSTER IN THE CENTAUR.</a></li> + +<li><a href="#herschel_observatory_feldhausen">OBSERVATORY AT FELDHAUSEN.</a></li> + +<li><a href="#column">GRANITE COLUMN AT FELDHAUSEN.</a></li> + +<li><a href="#rosse_ill">THE EARL OF ROSSE.</a></li> + +<li><a href="#birr">BIRR CASTLE.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#mall">THE MALL, PARSONSTOWN.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#lord_rosse_telescope">LORD ROSSE'S TELESCOPE.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#roman">ROMAN CATHOLIC CHURCH, PARSONSTOWN.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#sir_airy">AIRY.</a><ul> +<li>From a Photograph by E.P. Adams, Greenwich.</li></ul></li> + +<li><a href="#rowan_hamilton">HAMILTON.</a></li> + +<li><a href="#john">ADAMS.</a></li> + +<li><a href="#cambridge">THE OBSERVATORY, CAMBRIDGE.</a></li> +</ul> +<h3><a name="INTRODUCTION" id="INTRODUCTION"></a>INTRODUCTION.</h3> +<p>Of all the natural sciences there is not one which offers such +sublime objects to the attention of the inquirer as does the science +of astronomy. From the earliest ages the study of the stars has +exercised the same fascination as it possesses at the present day. +Among the most primitive peoples, the movements of the sun, the moon, +and the stars commanded attention from their supposed influence on +human affairs.</p> + +<p>The practical utilities of astronomy were also obvious in primeval +times. Maxims of extreme antiquity show how the avocations of the +husbandman are to be guided by the movements of the heavenly bodies. +The positions of the stars indicated the time to plough, and the time +to sow. To the mariner who was seeking a way across the trackless +ocean, the heavenly bodies offered the only reliable marks by which +his path could be guided. There was, accordingly, a stimulus both +from intellectual curiosity and from practical necessity to follow +the movements of the stars. Thus began a search for the causes of +the ever-varying phenomena which the heavens display.</p> + +<p>Many of the earliest discoveries are indeed prehistoric. The great +diurnal movement of the heavens, and the annual revolution of the +sun, seem to have been known in times far more ancient than those to +which any human monuments can be referred. The acuteness of the +early observers enabled them to single out the more important of the +wanderers which we now call planets. They saw that the star-like +objects, Jupiter, Saturn, and Mars, with the more conspicuous Venus, +constituted a class of bodies wholly distinct from the fixed stars +among which their movements lay, and to which they bear such a +superficial resemblance. But the penetration of the early +astronomers went even further, for they recognized that Mercury also +belongs to the same group, though this particular object is seen so +rarely. It would seem that eclipses and other phenomena were +observed at Babylon from a very remote period, while the most ancient +records of celestial observations that we possess are to be found in +the Chinese annals.</p> + +<p>The study of astronomy, in the sense in which we understand the word, +may be said to have commenced under the reign of the Ptolemies at +Alexandria. The most famous name in the science of this period is +that of Hipparchus who lived and worked at Rhodes about the year +160BC. It was his splendid investigations that first wrought the +observed facts into a coherent branch of knowledge. He recognized +the primary obligation which lies on the student of the heavens to +compile as complete an inventory as possible of the objects which are +there to be found. Hipparchus accordingly commenced by undertaking, +on a small scale, a task exactly similar to that on which modern +astronomers, with all available appliances of meridian circles, and +photographic telescopes, are constantly engaged at the present day. +He compiled a catalogue of the principal fixed stars, which is of +special value to astronomers, as being the earliest work of its kind +which has been handed down. He also studied the movements of the sun +and the moon, and framed theories to account for the incessant +changes which he saw in progress. He found a much more difficult +problem in his attempt to interpret satisfactorily the complicated +movements of the planets. With the view of constructing a theory +which should give some coherent account of the subject, he made many +observations of the places of these wandering stars. How great were +the advances which Hipparchus accomplished may be appreciated if we +reflect that, as a preliminary task to his more purely astronomical +labours, he had to invent that branch of mathematical science by +which alone the problems he proposed could be solved. It was for +this purpose that he devised the indispensable method of calculation +which we now know so well as trigonometry. Without the aid rendered +by this beautiful art it would have been impossible for any really +important advance in astronomical calculation to have been effected.</p> + +<p>But the discovery which shows, beyond all others, that Hipparchus +possessed one of the master-minds of all time was the detection of +that remarkable celestial movement known as the precession of the +equinoxes. The inquiry which conducted to this discovery involved a +most profound investigation, especially when it is remembered that in +the days of Hipparchus the means of observation of the heavenly +bodies were only of the rudest description, and the available +observations of earlier dates were extremely scanty. We can but look +with astonishment on the genius of the man who, in spite of such +difficulties, was able to detect such a phenomenon as the precession, +and to exhibit its actual magnitude. I shall endeavour to explain +the nature of this singular celestial movement, for it may be said to +offer the first instance in the history of science in which we find +that combination of accurate observation with skilful interpretation, +of which, in the subsequent development of astronomy, we have so many +splendid examples.</p> + +<p>The word equinox implies the condition that the night is equal to the +day. To a resident on the equator the night is no doubt equal to the +day at all times in the year, but to one who lives on any other part +of the earth, in either hemisphere, the night and the day are not +generally equal. There is, however, one occasion in spring, and +another in autumn, on which the day and the night are each twelve +hours at all places on the earth. When the night and day are equal +in spring, the point which the sun occupies on the heavens is termed +the vernal equinox. There is similarly another point in which the +sun is situated at the time of the autumnal equinox. In any +investigation of the celestial movements the positions of these two +equinoxes on the heavens are of primary importance, and Hipparchus, +with the instinct of genius, perceived their significance, and +commenced to study them. It will be understood that we can always +define the position of a point on the sky with reference to the +surrounding stars. No doubt we do not see the stars near the sun +when the sun is shining, but they are there nevertheless. The +ingenuity of Hipparchus enabled him to determine the positions of +each of the two equinoxes relatively to the stars which lie in its +immediate vicinity. After examination of the celestial places of +these points at different periods, he was led to the conclusion that +each equinox was moving relatively to the stars, though that movement +was so slow that twenty five thousand years would necessarily elapse +before a complete circuit of the heavens was accomplished. Hipparchus +traced out this phenomenon, and established it on an impregnable +basis, so that all astronomers have ever since recognised the +precession of the equinoxes as one of the fundamental facts of +astronomy. Not until nearly two thousand years after Hipparchus had +made this splendid discovery was the explanation of its cause given +by Newton.</p> + +<p>From the days of Hipparchus down to the present hour the science of +astronomy has steadily grown. One great observer after another has +appeared from time to time, to reveal some new phenomenon with regard +to the celestial bodies or their movements, while from time to time +one commanding intellect after another has arisen to explain the true +import of the facts of observations. The history of astronomy thus +becomes inseparable from the history of the great men to whose +labours its development is due.</p> + +<p>In the ensuing chapters we have endeavoured to sketch the lives and +the work of the great philosophers, by whose labours the science of +astronomy has been created. We shall commence with Ptolemy, who, +after the foundations of the science had been laid by Hipparchus, +gave to astronomy the form in which it was taught throughout the +Middle Ages. We shall next see the mighty revolution in our +conceptions of the universe which are associated with the name of +Copernicus. We then pass to those periods illumined by the genius of +Galileo and Newton, and afterwards we shall trace the careers of +other more recent discoverers, by whose industry and genius the +boundaries of human knowledge have been so greatly extended. Our +history will be brought down late enough to include some of the +illustrious astronomers who laboured in the generation which has just +passed away.</p> + +<h3><a name="PTOLEMY" id="PTOLEMY"></a>PTOLEMY.</h3> + +<div class="figcenter" style="width: 410px;"> +<a href="images/ill_ptolemy.jpg"> +<img src="images/ill_ptolemy_sml.jpg" width="410" height="486" alt="PTOLEMY." title="" /></a> +<span class="caption">PTOLEMY.</span> +</div> + +<p>The career of the famous man whose name stands at the head of this +chapter is one of the most remarkable in the history of human +learning. There may have been other discoverers who have done more +for science than ever Ptolemy accomplished, but there never has been +any other discoverer whose authority on the subject of the movements +of the heavenly bodies has held sway over the minds of men for so +long a period as the fourteen centuries during which his opinions +reigned supreme. The doctrines he laid down in his famous book, "The +Almagest," prevailed throughout those ages. No substantial addition +was made in all that time to the undoubted truths which this work +contained. No important correction was made of the serious errors +with which Ptolemy's theories were contaminated. The authority of +Ptolemy as to all things in the heavens, and as to a good many things +on the earth (for the same illustrious man was also a diligent +geographer), was invariably final.</p> + +<p>Though every child may now know more of the actual truths of the +celestial motions than ever Ptolemy knew, yet the fact that his work +exercised such an astonishing effect on the human intellect for some +sixty generations, shows that it must have been an extraordinary +production. We must look into the career of this wonderful man to +discover wherein lay the secret of that marvellous success which made +him the unchallenged instructor of the human race for such a +protracted period.</p> + +<p>Unfortunately, we know very little as to the personal history of +Ptolemy. He was a native of Egypt, and though it has been sometimes +conjectured that he belonged to the royal families of the same name, +yet there is nothing to support such a belief. The name, Ptolemy, +appears to have been a common one in Egypt in those days. The time +at which he lived is fixed by the fact that his first recorded +observation was made in 127 AD, and his last in 151 AD. When we add +that he seems to have lived in or near Alexandria, or to use his own +words, "on the parallel of Alexandria," we have said everything that +can be said so far as his individuality is concerned.</p> + +<p>Ptolemy is, without doubt, the greatest figure in ancient astronomy. +He gathered up the wisdom of the philosophers who had preceded him. +He incorporated this with the results of his own observations, and +illumined it with his theories. His speculations, even when they +were, as we now know, quite erroneous, had such an astonishing +verisimilitude to the actual facts of nature that they commanded +universal assent. Even in these modern days we not unfrequently find +lovers of paradox who maintain that Ptolemy's doctrines not only seem +true, but actually are true.</p> + +<p>In the absence of any accurate knowledge of the science of mechanics, +philosophers in early times were forced to fall back on certain +principles of more or less validity, which they derived from their +imagination as to what the natural fitness of things ought to be. +There was no geometrical figure so simple and so symmetrical as a +circle, and as it was apparent that the heavenly bodies pursued +tracks which were not straight lines, the conclusion obviously +followed that their movements ought to be circular. There was no +argument in favour of this notion, other than the merely imaginary +reflection that circular movement, and circular movement alone, was +"perfect," whatever "perfect" may have meant. It was further +believed to be impossible that the heavenly bodies could have any +other movements save those which were perfect. Assuming this, it +followed, in Ptolemy's opinion, and in that of those who came after +him for fourteen centuries, that all the tracks of the heavenly +bodies were in some way or other to be reduced to circles.</p> + +<p>Ptolemy succeeded in devising a scheme by which the apparent changes +that take place in the heavens could, so far as he knew them, be +explained by certain combinations of circular movement. This seemed +to reconcile so completely the scheme of things celestial with the +geometrical instincts which pointed to the circle as the type of +perfect movement, that we can hardly wonder Ptolemy's theory met with +the astonishing success that attended it. We shall, therefore, set +forth with sufficient detail the various steps of this famous +doctrine.</p> + +<p>Ptolemy commences with laying down the undoubted truth that the shape +of the earth is globular. The proofs which he gives of this +fundamental fact are quite satisfactory; they are indeed the same +proofs as we give today. There is, first of all, the well-known +circumstance of which our books on geography remind us, that when an +object is viewed at a distance across the sea, the lower part of the +object appears cut off by the interposing curved mass of water.</p> + +<p>The sagacity of Ptolemy enabled him to adduce another argument, +which, though not quite so obvious as that just mentioned, +demonstrates the curvature of the earth in a very impressive manner +to anyone who will take the trouble to understand it. Ptolemy +mentions that travellers who went to the south reported, that, as +they did so, the appearance of the heavens at night underwent a +gradual change. Stars that they were familiar with in the northern +skies gradually sank lower in the heavens. The constellation of the +Great Bear, which in our skies never sets during its revolution round +the pole, did set and rise when a sufficient southern latitude had +been attained. On the other hand, constellations new to the +inhabitants of northern climes were seen to rise above the southern +horizon. These circumstances would be quite incompatible with the +supposition that the earth was a flat surface. Had this been so, a +little reflection will show that no such changes in the apparent +movements of the stars would be the consequence of a voyage to the +south. Ptolemy set forth with much insight the significance of this +reasoning, and even now, with the resources of modern discoveries to +help us, we can hardly improve upon his arguments.</p> + +<p>Ptolemy, like a true philosopher disclosing a new truth to the world, +illustrated and enforced his subject by a variety of happy +demonstrations. I must add one of them, not only on account of its +striking nature, but also because it exemplifies Ptolemy's +acuteness. If the earth were flat, said this ingenious reasoner, +sunset must necessarily take place at the same instant, no matter in +what country the observer may happen to be placed. Ptolemy, however, +proved that the time of sunset did vary greatly as the observer's +longitude was altered. To us, of course, this is quite obvious; +everybody knows that the hour of sunset may have been reached in +Great Britain while it is still noon on the western coast of +America. Ptolemy had, however, few of those sources of knowledge +which are now accessible. How was he to show that the sun actually +did set earlier at Alexandria than it would in a city which lay a +hundred miles to the west? There was no telegraph wire by which +astronomers at the two Places could communicate. There was no +chronometer or watch which could be transported from place to place; +there was not any other reliable contrivance for the keeping of +time. Ptolemy's ingenuity, however, pointed out a thoroughly +satisfactory method by which the times of sunset at two places could +be compared. He was acquainted with the fact, which must indeed have +been known from the very earliest times, that the illumination of the +moon is derived entirely from the sun. He knew that an eclipse of +the moon was due to the interposition of the earth which cuts off the +light of the sun. It was, therefore, plain that an eclipse of the +moon must be a phenomenon which would begin at the same instant from +whatever part of the earth the moon could be seen at the time. +Ptolemy, therefore, brought together from various quarters the local +times at which different observers had recorded the beginning of a +lunar eclipse. He found that the observers to the west made the time +earlier and earlier the further away their stations were from +Alexandria. On the other hand, the eastern observers set down the +hour as later than that at which the phenomenon appeared at +Alexandria. As these observers all recorded something which indeed +appeared to them simultaneously, the only interpretation was, that +the more easterly a place the later its time. Suppose there were a +number of observers along a parallel of latitude, and each noted the +hour of sunset to be six o'clock, then, since the eastern times are +earlier than western times, 6 p.m. at one station A will correspond +to 5 p.m. at a station B sufficiently to the west. If, therefore, +it is sunset to the observer at A, the hour of sunset will not yet be +reached for the observer at B. This proves conclusively that the +time of sunset is not the same all over the earth. We have, however, +already seen that the apparent time of sunset would be the same from +all stations if the earth were flat. When Ptolemy, therefore, +demonstrated that the time of sunset was not the same at various +places, he showed conclusively that the earth was not flat.</p> + +<p>As the same arguments applied to all parts of the earth where Ptolemy +had either been himself, or from which he could gain the necessary +information, it followed that the earth, instead of being the flat +plain, girdled with an illimitable ocean, as was generally supposed, +must be in reality globular. This led at once to a startling +consequence. It was obvious that there could be no supports of any +kind by which this globe was sustained; it therefore followed that +the mighty object must be simply poised in space. This is indeed an +astonishing doctrine to anyone who relies on what merely seems the +evidence of the senses, without giving to that evidence its due +intellectual interpretation. According to our ordinary experience, +the very idea of an object poised without support in space, appears +preposterous. Would it not fall? we are immediately asked. Yes, +doubtless it could not remain poised in any way in which we try the +experiment. We must, however, observe that there are no such ideas +as upwards or downwards in relation to open space. To say that a +body falls downwards, merely means that it tries to fall as nearly as +possible towards the centre of the earth. There is no one direction +along which a body will tend to move in space, in preference to any +other. This may be illustrated by the fact that a stone let fall at +New Zealand will, in its approach towards the earth's centre, be +actually moving upwards as far as any locality in our hemisphere is +concerned. Why, then, argued Ptolemy, may not the earth remain +poised in space, for as all directions are equally upward or equally +downward, there seems no reason why the earth should require any +support? By this reasoning he arrives at the fundamental conclusion +that the earth is a globular body freely lying in space, and +surrounded above, below, and on all sides by the glittering stars of +heaven.</p> + +<p>The perception of this sublime truth marks a notable epoch in the +history of the gradual development of the human intellect. No doubt, +other philosophers, in groping after knowledge, may have set forth +certain assertions that are more or less equivalent to this +fundamental truth. It is to Ptolemy we must give credit, however, +not only for announcing this doctrine, but for demonstrating it by +clear and logical argument. We cannot easily project our minds back +to the conception of an intellectual state in which this truth was +unfamiliar. It may, however, be well imagined that, to one who +thought the earth was a flat plain of indefinite extent, it would be +nothing less than an intellectual convulsion for him to be forced to +believe that he stood upon a spherical earth, forming merely a +particle relatively to the immense sphere of the heavens.</p> + +<p>What Ptolemy saw in the movements of the stars led him to the +conclusion that they were bright points attached to the inside of a +tremendous globe. The movements of this globe which carried the +stars were only compatible with the supposition that the earth +occupied its centre. The imperceptible effect produced by a change +in the locality of the observer on the apparent brightness of the +stars made it plain that the dimensions of the terrestrial globe must +be quite insignificant in comparison with those of the celestial +sphere. The earth might, in fact, be regarded as a grain of sand +while the stars lay upon a globe many yards in diameter.</p> + +<p>So tremendous was the revolution in human knowledge implied by this +discovery, that we can well imagine how Ptolemy, dazzled as it were +by the fame which had so justly accrued to him, failed to make one +further step. Had he made that step, it would have emancipated the +human intellect from the bondage of fourteen centuries of servitude +to a wholly monstrous notion of this earth's importance in the scheme +of the heavens. The obvious fact that the sun, the moon, and the +stars rose day by day, moved across the sky in a glorious +never-ending procession, and duly set when their appointed courses +had been run, demanded some explanation. The circumstance that the +fixed stars preserved their mutual distances from year to year, and +from age to age, appeared to Ptolemy to prove that the sphere which +contained those stars, and on whose surface they were believed by him +to be fixed, revolved completely around the earth once every day. He +would thus account for all the phenomena of rising and setting +consistently with the supposition that our globe was stationary. +Probably this supposition must have appeared monstrous, even to +Ptolemy. He knew that the earth was a gigantic object, but, large as +it may have been, he knew that it was only a particle in comparison +with the celestial sphere, yet he apparently believed, and certainly +succeeded in persuading other men to believe, that the celestial +sphere did actually perform these movements.</p> + +<p>Ptolemy was an excellent geometer. He knew that the rising and the +setting of the sun, the moon, and the myriad stars, could have been +accounted for in a different way. If the earth turned round +uniformly once a day while poised at the centre of the sphere of the +heavens, all the phenomena of rising and setting could be completely +explained. This is, indeed, obvious after a moment's reflection. +Consider yourself to be standing on the earth at the centre of the +heavens. There are stars over your head, and half the contents of +the heavens are visible, while the other half are below your +horizon. As the earth turns round, the stars over your head will +change, and unless it should happen that you have taken up your +position at either of the poles, new stars will pass into your view, +and others will disappear, for at no time can you have more than half +of the whole sphere visible. The observer on the earth would, +therefore, say that some stars were rising, and that some stars were +setting. We have, therefore, two totally distinct methods, each of +which would completely explain all the observed facts of the diurnal +movement. One of these suppositions requires that the celestial +sphere, bearing with it the stars and other celestial bodies, turns +uniformly around an invisible axis, while the earth remains +stationary at the centre. The other supposition would be, that it is +the stupendous celestial sphere which remains stationary, while the +earth at the centre rotates about the same axis as the celestial +sphere did before, but in an opposite direction, and with a uniform +velocity which would enable it to complete one turn in twenty-four +hours. Ptolemy was mathematician enough to know that either of these +suppositions would suffice for the explanation of the observed +facts. Indeed, the phenomena of the movements of the stars, so far +as he could observe them, could not be called upon to pronounce which +of these views was true, and which was false.</p> + +<p>Ptolemy had, therefore, to resort for guidance to indirect lines of +reasoning. One of these suppositions must be true, and yet it +appeared that the adoption of either was accompanied by a great +difficulty. It is one of his chief merits to have demonstrated that +the celestial sphere was so stupendous that the earth itself was +absolutely insignificant in comparison therewith. If, then, this +stupendous sphere rotated once in twenty-four hours, the speed with +which the movement of some of the stars must be executed would be so +portentous as to seem well-nigh impossible. It would, therefore, +seem much simpler on this ground to adopt the other alternative, and +to suppose the diurnal movements were due to the rotation of the +earth. Here Ptolemy saw, or at all events fancied he saw, objections +of the weightiest description. The evidence of the senses appeared +directly to controvert the supposition that this earth is anything +but stationary. Ptolemy might, perhaps, have dismissed this +objection on the ground that the testimony of the senses on such a +matter should be entirely subordinated to the interpretation which +our intelligence would place upon the facts to which the senses +deposed. Another objection, however, appeared to him to possess the +gravest moment. It was argued that if the earth were rotating, there +is nothing to make the air participate in this motion, mankind would +therefore be swept from the earth by the furious blasts which would +arise from the movement of the earth through an atmosphere at rest. +Even if we could imagine that the air were carried round with the +earth, the same would not apply, so thought Ptolemy, to any object +suspended in the air. So long as a bird was perched on a tree, he +might very well be carried onward by the moving earth, but the moment +he took wing, the ground would slip from under him at a frightful +pace, so that when he dropped down again he would find himself at a +distance perhaps ten times as great as that which a carrier-pigeon or +a swallow could have traversed in the same time. Some vague delusion +of this description seems even still to crop up occasionally. I +remember hearing of a proposition for balloon travelling of a very +remarkable kind. The voyager who wanted to reach any other place in +the same latitude was simply to ascend in a balloon, and wait there +till the rotation of the earth conveyed the locality which happened +to be his destination directly beneath him, whereupon he was to let +out the gas and drop down! Ptolemy knew quite enough natural +philosophy to be aware that such a proposal for locomotion would be +an utter absurdity; he knew that there was no such relative shift +between the air and the earth as this motion would imply. It +appeared to him to be necessary that the air should lag behind, if +the earth had been animated by a movement of rotation. In this he +was, as we know, entirely wrong. There were, however, in his days no +accurate notions on the subject of the laws of motion.</p> + +<p>Assiduous as Ptolemy may have been in the study of the heavenly +bodies, it seems evident that he cannot have devoted much thought to +the phenomena of motion of terrestrial objects. Simple, indeed, are +the experiments which might have convinced a philosopher much less +acute than Ptolemy, that, if the earth did revolve, the air must +necessarily accompany it. If a rider galloping on horseback tosses a +ball into the air, it drops again into his hand, just as it would +have done had he been remaining at rest during the ball's flight; the +ball in fact participates in the horizontal motion, so that though it +really describes a curve as any passer-by would observe, yet it +appears to the rider himself merely to move up and down in a straight +line. This fact, and many others similar to it, demonstrate clearly +that if the earth were endowed with a movement of rotation, the +atmosphere surrounding it must participate in that movement. Ptolemy +did not know this, and consequently he came to the conclusion that +the earth did not rotate, and that, therefore, notwithstanding the +tremendous improbability of so mighty an object as the celestial +sphere spinning round once in every twenty-four hours, there was no +course open except to believe that this very improbable thing did +really happen. Thus it came to pass that Ptolemy adopted as the +cardinal doctrine of his system a stationary earth poised at the +centre of the celestial sphere, which stretched around on all sides +at a distance so vast that the diameter of the earth was an +inappreciable point in comparison therewith.</p> + +<p>Ptolemy having thus deliberately rejected the doctrine of the earth's +rotation, had to make certain other entirely erroneous suppositions. +It was easily seen that each star required exactly the same period +for the performance of a complete revolution of the heavens. Ptolemy +knew that the stars were at enormous distances from the earth, though +no doubt his notions on this point came very far short of what we +know to be the reality. If the stars had been at very varied +distances, then it would be so wildly improbable that they should all +accomplish their revolutions in the same time, that Ptolemy came to +the conclusion that they must be all at the same distance, that is, +that they must be all on the surface of a sphere. This view, however +erroneous, was corroborated by the obvious fact that the stars in the +constellations preserved their relative places unaltered for +centuries. Thus it was that Ptolemy came to the conclusion that they +were all fixed on one spherical surface, though we are not informed +as to the material of this marvellous setting which sustained the +stars like jewels.</p> + +<p>Nor should we hastily pronounce this doctrine to be absurd. The +stars do appear to lie on the surface of a sphere, of which the +observer is at the centre; not only is this the aspect which the +skies present to the untechnical observer, but it is the aspect in +which the skies are presented to the most experienced astronomer of +modern days. No doubt he knows well that the stars are at the most +varied distances from him; he knows that certain stars are ten times, +or a hundred times, or a thousand times, as far as other stars. +Nevertheless, to his eye the stars appear on the surface of the +sphere, it is on that surface that his measurements of the relative +places of the stars are made; indeed, it may be said that almost all +the accurate observations in the observatory relate to the places of +the stars, not as they really are, but as they appear to be projected +on that celestial sphere whose conception we owe to the genius of +Ptolemy.</p> + +<p>This great philosopher shows very ingeniously that the earth must be +at the centre of the sphere. He proves that, unless this were the +case, each star would not appear to move with the absolute uniformity +which does, as a matter of fact, characterise it. In all these +reasonings we cannot but have the most profound admiration for the +genius of Ptolemy, even though he had made an error so enormous in +the fundamental point of the stability of the earth. Another error +of a somewhat similar kind seemed to Ptolemy to be demonstrated. He +had shown that the earth was an isolated object in space, and being +such was, of course, capable of movement. It could either be turned +round, or it could be moved from one place to another. We know that +Ptolemy deliberately adopted the view that the earth did not turn +round; he had then to investigate the other question, as to whether +the earth was animated by any movement of translation. He came to +the conclusion that to attribute any motion to the earth would be +incompatible with the truths at which he had already arrived. The +earth, argued Ptolemy, lies at the centre of the celestial sphere. +If the earth were to be endowed with movement, it would not lie +always at this point, it must, therefore, shift to some other part of +the sphere. The movements of the stars, however, preclude the +possibility of this; and, therefore, the earth must be as devoid of +any movement of translation as it is devoid of rotation. Thus it was +that Ptolemy convinced himself that the stability of the earth, as it +appeared to the ordinary senses, had a rational philosophical +foundation.</p> + +<p>Not unfrequently it is the lot of the philosophers to contend against +the doctrines of the vulgar, but when it happens, as in the case of +Ptolemy's researches, that the doctrines of the vulgar are +corroborated by philosophical investigation which bear the stamp of +the highest authority, it is not to be wondered at that such +doctrines should be deemed well-nigh impregnable. In this way we +may, perhaps, account for the remarkable fact that the theories of +Ptolemy held unchallenged sway over the human intellect for the vast +period already mentioned.</p> + +<p>Up to the present we have been speaking only of those primary motions +of the heavens, by which the whole sphere appeared to revolve once +every twenty-four hours. We have now to discuss the remarkable +theories by which Ptolemy endeavoured to account for the monthly +movement of the moon, for the annual movement of the sun, and for the +periodic movements of the planets which had gained for them the +titles of the wandering stars.</p> + +<p>Possessed with the idea that these movements must be circular, or +must be capable, directly or indirectly, of being explained by +circular movements, it seemed obvious to Ptolemy, as indeed it had +done to previous astronomers, that the track of the moon through the +stars was a circle of which the earth is the centre. A similar +movement with a yearly period must also be attributed to the sun, for +the changes in the positions of the constellations in accordance with +the progress of the seasons, placed it beyond doubt that the sun made +a circuit of the celestial sphere, even though the bright light of +the sun prevented the stars in its vicinity, from being seen in +daylight. Thus the movements both of the sun and the moon, as well +as the diurnal rotation of the celestial sphere, seemed to justify +the notion that all celestial movements must be "perfect," that is to +say, described uniformly in those circles which were the only perfect +curves.</p> + +<p>The simplest observations, however, show that the movements of the +planets cannot be explained in this simple fashion. Here the +geometrical genius of Ptolemy shone forth, and he devised a scheme by +which the apparent wanderings of the planets could be accounted for +without the introduction of aught save "perfect" movements.</p> + +<p>To understand his reasoning, let us first set forth clearly those +facts of observation which require to be explained. I shall take, in +particular, two planets, Venus and Mars, as these illustrate, in the +most striking manner, the peculiarities of the inner and the outer +planets respectively. The simplest observations would show that +Venus did not move round the heavens in the same fashion as the sun +or the moon. Look at the evening star when brightest, as it appears +in the west after sunset. Instead of moving towards the east among +the stars, like the sun or the moon, we find, week after week, that +Venus is drawing in towards the sun, until it is lost in the +sunbeams. Then the planet emerges on the other side, not to be seen +as an evening star, but as a morning star. In fact, it was plain +that in some ways Venus accompanied the sun in its annual movement. +Now it is found advancing in front of the sun to a certain limited +distance, and now it is lagging to an equal extent behind the sun.</p> + +<p><a name="fig_1" id="fig_1"></a></p> + +<div class="figcenter" style="width: 303px;"> +<a href="images/ill_fig1.jpg"> +<img src="images/ill_fig1_sml.jpg" width="303" height="286" alt="FIG. 1. PTOLEMY'S PLANETARY SCHEME." title="" /></a> +<span class="caption">FIG. 1. PTOLEMY'S PLANETARY SCHEME.</span> +</div> + +<p>These movements were wholly incompatible with the supposition that +the journeys of Venus were described by a single motion of the kind +regarded as perfect. It was obvious that the movement was connected +in some strange manner with the revolution of the sun, and here was +the ingenious method by which Ptolemy sought to render account of +it. Imagine a fixed arm to extend from the earth to the sun, as +shown in the accompanying figure (Fig. 1), then this arm will move +round uniformly, in consequence of the sun's movement. At a point P +on this arm let a small circle be described. Venus is supposed to +revolve uniformly in this small circle, while the circle itself is +carried round continuously by the movement of the sun. In this way +it was possible to account for the chief peculiarities in the +movement of Venus. It will be seen that, in consequence of the +revolution around P, the spectator on the earth will sometimes see +Venus on one side of the sun, and sometimes on the other side, so +that the planet always remains in the sun's vicinity. By properly +proportioning the movements, this little contrivance simulated the +transitions from the morning star to the evening star. Thus the +changes of Venus could be accounted for by a Combination of the +"perfect" movement of P in the circle which it described uniformly +round the earth, combined with the "perfect" motion of Venus in the +circle which it described uniformly around the moving centre.</p> + +<p>In a precisely similar manner Ptolemy rendered an explanation of the +fitful apparitions of Mercury. Now just on one side of the sun, and +now just on the other, this rarely-seen planet moved like Venus on a +circle whereof the centre was also carried by the line joining the +sun and the earth. The circle, however, in which Mercury actually +revolved had to be smaller than that of Venus, in order to account +for the fact that Mercury lies always much closer to the sun than the +better-known planet.</p> + +<p><a name="fig_2" id="fig_2"></a></p> + +<div class="figcenter" style="width: 356px;"> +<a href="images/ill_fig2.jpg"> +<img src="images/ill_fig2_sml.jpg" width="356" height="327" alt="FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS." title="" /></a> +<span class="caption">FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.</span> +</div> + +<p>The explanation of the movement of an outer planet like Mars could +also be deduced from the joint effect of two perfect motions. The +changes through which Mars goes are, however, so different from the +movements of Venus that quite a different disposition of the circles +is necessary. For consider the facts which characterise the +movements of an outer planet such as Mars. In the first place, Mars +accomplishes an entire circuit of the heaven. In this respect, no +doubt, it may be said to resemble the sun or the moon. A little +attention will, however, show that there are extraordinary +irregularities in the movement of the planet. Generally speaking, it +speeds its way from west to east among the stars, but sometimes the +attentive observer will note that the speed with which the planet +advances is slackening, and then it will seem to become stationary. +Some days later the direction of the planet's movement will be +reversed, and it will be found moving from the east towards the +west. At first it proceeds slowly and then quickens its pace, until +a certain speed is attained, which afterwards declines until a second +stationary position is reached. After a due pause the original +motion from west to east is resumed, and is continued until a similar +cycle of changes again commences. Such movements as these were +obviously quite at variance with any perfect movement in a single +circle round the earth. Here, again, the geometrical sagacity of +Ptolemy provided him with the means of representing the apparent +movements of Mars, and, at the same time, restricting the explanation +to those perfect movements which he deemed so essential. In Fig. 2 +we exhibit Ptolemy's theory as to the movement of Mars. We have, as +before, the earth at the centre, and the sun describing its circular +orbit around that centre. The path of Mars is to be taken as +exterior to that of the sun. We are to suppose that at a point +marked M there is a fictitious planet, which revolves around the +earth uniformly, in a circle called the DEFERENT. This point M, +which is thus animated by a perfect movement, is the centre of a +circle which is carried onwards with M, and around the circumference +of which Mars revolves uniformly. It is easy to show that the +combined effect of these two perfect movements is to produce exactly +that displacement of Mars in the heavens which observation +discloses. In the position represented in the figure, Mars is +obviously pursuing a course which will appear to the observer as a +movement from west to east. When, however, the planet gets round to +such a position as R, it is then moving from east to west in +consequence of its revolution in the moving circle, as indicated by +the arrow-head. On the other hand, the whole circle is carried +forward in the opposite direction. If the latter movement be less +rapid than the former, then we shall have the backward movement of +Mars on the heavens which it was desired to explain. By a proper +adjustment of the relative lengths of these arms the movements of the +planet as actually observed could be completely accounted for.</p> + +<p>The other outer planets with which Ptolemy was acquainted, namely, +Jupiter and Saturn, had movements of the same general character as +those of Mars. Ptolemy was equally successful in explaining the +movements they performed by the supposition that each planet had +perfect rotation in a circle of its own, which circle itself had +perfect movement around the earth in the centre.</p> + +<p>It is somewhat strange that Ptolemy did not advance one step further, +as by so doing he would have given great simplicity to his system. He +might, for instance, have represented the movements of Venus equally +well by putting the centre of the moving circle at the sun itself, +and correspondingly enlarging the circle in which Venus revolved. He +might, too, have arranged that the several circles which the outer +planets traversed should also have had their centres at the sun. The +planetary system would then have consisted of an earth fixed at the +centre, of a sun revolving uniformly around it, and of a system of +planets each describing its own circle around a moving centre placed +in the sun. Perhaps Ptolemy had not thought of this, or perhaps he +may have seen arguments against it. This important step was, +however, taken by Tycho. He considered that all the planets revolved +around the sun in circles, and that the sun itself, bearing all these +orbits, described a mighty circle around the earth. This point +having been reached, only one more step would have been necessary to +reach the glorious truths that revealed the structure of the solar +system. That last step was taken by Copernicus.</p> + +<h3><a name="COPERNICUS" id="COPERNICUS"></a>COPERNICUS.</h3> +<p><a name="thorn" id="thorn"></a></p> + +<div class="figcenter" style="width: 585px;"> +<a href="images/ill_thorn.jpg"> +<img src="images/ill_thorn_sml.jpg" width="585" height="242" alt="THORN, FROM AN OLD PRINT." title="" /></a> +<span class="caption">THORN, FROM AN OLD PRINT.</span> +</div> + +<p>The quaint town of Thorn, on the Vistula, was more than two centuries +old when Copernicus was born there on the 19th of February, 1473. The +situation of this town on the frontier between Prussia and Poland, +with the commodious waterway offered by the river, made it a place of +considerable trade. A view of the town, as it was at the time of the +birth of Copernicus, is here given. The walls, with their +watch-towers, will be noted, and the strategic importance which the +situation of Thorn gave to it in the fifteenth century still belongs +thereto, so much so that the German Government recently constituted +the town a fortress of the first class.</p> + +<p>Copernicus, the astronomer, whose discoveries make him the great +predecessor of Kepler and Newton, did not come from a noble family, +as certain other early astronomers have done, for his father was a +tradesman. Chroniclers are, however, careful to tell us that one of +his uncles was a bishop. We are not acquainted with any of those +details of his childhood or youth which are often of such interest in +other cases where men have risen to exalted fame. It would appear +that the young Nicolaus, for such was his Christian name, received +his education at home until such time as he was deemed sufficiently +advanced to be sent to the University at Cracow. The education that +he there obtained must have been in those days of a very primitive +description, but Copernicus seems to have availed himself of it to +the utmost. He devoted himself more particularly to the study of +medicine, with the view of adopting its practice as the profession of +his life. The tendencies of the future astronomer were, however, +revealed in the fact that he worked hard at mathematics, and, like +one of his illustrious successors, Galileo, the practice of the art +of painting had for him a very great interest, and in it he obtained +some measure of success.</p> + +<p>By the time he was twenty-seven years old, it would seem that +Copernicus had given up the notion of becoming a medical +practitioner, and had resolved to devote himself to science. He was +engaged in teaching mathematics, and appears to have acquired some +reputation. His growing fame attracted the notice of his uncle the +bishop, at whose suggestion Copernicus took holy orders, and he was +presently appointed to a canonry in the cathedral of Frauenburg, near +the mouth of the Vistula.</p> + +<p>To Frauenburg, accordingly, this man of varied gifts retired. +Possessing somewhat of the ascetic spirit, he resolved to devote his +life to work of the most serious description. He eschewed all +ordinary society, restricting his intimacies to very grave and +learned companions, and refusing to engage in conversation of any +useless kind. It would seem as if his gifts for painting were +condemned as frivolous; at all events, we do not learn that he +continued to practise them. In addition to the discharge of his +theological duties, his life was occupied partly in ministering +medically to the wants of the poor, and partly with his researches in +astronomy and mathematics. His equipment in the matter of +instruments for the study of the heavens seems to have been of a very +meagre description. He arranged apertures in the walls of his house +at Allenstein, so that he could observe in some fashion the passage +of the stars across the meridian. That he possessed some talent for +practical mechanics is proved by his construction of a contrivance +for raising water from a stream, for the use of the inhabitants of +Frauenburg. Relics of this machine are still to be seen.</p> + +<p><a name="copernicus_ill" id="copernicus_ill"></a></p> + +<div class="figcenter" style="width: 395px;"> +<a href="images/ill_copernicus.jpg"> +<img src="images/ill_copernicus_sml.jpg" width="395" height="469" alt="COPERNICUS." title="" /></a> +<span class="caption">COPERNICUS.</span> +</div> + +<p>The intellectual slumber of the Middle Ages was destined to be +awakened by the revolutionary doctrines of Copernicus. It may be +noted, as an interesting circumstance, that the time at which he +discovered the scheme of the solar system has coincided with a +remarkable epoch in the world's history. The great astronomer had +just reached manhood at the time when Columbus discovered the new +world.</p> + +<p>Before the publication of the researches of Copernicus, the orthodox +scientific creed averred that the earth was stationary, and that the +apparent movements of the heavenly bodies were indeed real +movements. Ptolemy had laid down this doctrine 1,400 years before. +In his theory this huge error was associated with so much important +truth, and the whole presented such a coherent scheme for the +explanation of the heavenly movements, that the Ptolemaic theory was +not seriously questioned until the great work of Copernicus +appeared. No doubt others, before Copernicus, had from time to time +in some vague fashion surmised, with more or less plausibility, that +the sun, and not the earth, was the centre about which the system +really revolved. It is, however, one thing to state a scientific +fact; it is quite another thing to be in possession of the train of +reasoning, founded on observation or experiment, by which that fact +may be established. Pythagoras, it appears, had indeed told his +disciples that it was the sun, and not the earth, which was the +centre of movement, but it does not seem at all certain that +Pythagoras had any grounds which science could recognise for the +belief which is attributed to him. So far as information is +available to us, it would seem that Pythagoras associated his scheme +of things celestial with a number of preposterous notions in natural +philosophy. He may certainly have made a correct statement as to +which was the most important body in the solar system, but he +certainly did not provide any rational demonstration of the fact. +Copernicus, by a strict train of reasoning, convinced those who would +listen to him that the sun was the centre of the system. It is +useful for us to consider the arguments which he urged, and by which +he effected that intellectual revolution which is always connected +with his name.</p> + +<p>The first of the great discoveries which Copernicus made relates to +the rotation of the earth on its axis. That general diurnal +movement, by which the stars and all other celestial bodies appear to +be carried completely round the heavens once every twenty-four hours, +had been accounted for by Ptolemy on the supposition that the +apparent movements were the real movements. As we have already seen, +Ptolemy himself felt the extraordinary difficulty involved in the +supposition that so stupendous a fabric as the celestial sphere +should spin in the way supposed. Such movements required that many +of the stars should travel with almost inconceivable velocity. +Copernicus also saw that the daily rising and setting of the heavenly +bodies could be accounted for either by the supposition that the +celestial sphere moved round and that the earth remained at rest, or +by the supposition that the celestial sphere was at rest while the +earth turned round in the opposite direction. He weighed the +arguments on both sides as Ptolemy had done, and, as the result of +his deliberations, Copernicus came to an opposite conclusion from +Ptolemy. To Copernicus it appeared that the difficulties attending +the supposition that the celestial sphere revolved, were vastly +greater than those which appeared so weighty to Ptolemy as to force +him to deny the earth's rotation.</p> + +<p>Copernicus shows clearly how the observed phenomena could be +accounted for just as completely by a rotation of the earth as by a +rotation of the heavens. He alludes to the fact that, to those on +board a vessel which is moving through smooth water, the vessel +itself appears to be at rest, while the objects on shore seem to be +moving past. If, therefore, the earth were rotating uniformly, we +dwellers upon the earth, oblivious of our own movement, would wrongly +attribute to the stars the displacement which was actually the +consequence of our own motion.</p> + +<p>Copernicus saw the futility of the arguments by which Ptolemy had +endeavoured to demonstrate that a revolution of the earth was +impossible. It was plain to him that there was nothing whatever to +warrant refusal to believe in the rotation of the earth. In his +clear-sightedness on this matter we have specially to admire the +sagacity of Copernicus as a natural philosopher. It had been urged +that, if the earth moved round, its motion would not be imparted to +the air, and that therefore the earth would be uninhabitable by the +terrific winds which would be the result of our being carried through +the air. Copernicus convinced himself that this deduction was +preposterous. He proved that the air must accompany the earth, just +as his coat remains round him, notwithstanding the fact that he is +walking down the street. In this way he was able to show that all a +priori objections to the earth's movements were absurd, and therefore +he was able to compare together the plausibilities of the two rival +schemes for explaining the diurnal movement.</p> + +<p><a name="frauenburg" id="frauenburg"></a></p> + +<div class="figcenter" style="width: 571px;"> +<a href="images/ill_frauenburg.jpg"> +<img src="images/ill_frauenburg_sml.jpg" width="571" height="392" alt="FRAUENBURG, FROM AN OLD PRINT." title="" /></a> +<span class="caption">FRAUENBURG, FROM AN OLD PRINT.</span> +</div> + +<p>Once the issue had been placed in this form, the result could not be +long in doubt. Here is the question: Which is it more likely—that +the earth, like a grain of sand at the centre of a mighty globe, +should turn round once in twenty-four hours, or that the whole of +that vast globe should complete a rotation in the opposite direction +in the same time? Obviously, the former is far the more simple +supposition. But the case is really much stronger than this. Ptolemy +had supposed that all the stars were attached to the surface of a +sphere. He had no ground whatever for this supposition, except that +otherwise it would have been well-nigh impossible to have devised a +scheme by which the rotation of the heavens around a fixed earth +could have been arranged. Copernicus, however, with the just +instinct of a philosopher, considered that the celestial sphere, +however convenient from a geometrical point of view, as a means of +representing apparent phenomena, could not actually have a material +existence. In the first place, the existence of a material celestial +sphere would require that all the myriad stars should be at exactly +the same distances from the earth. Of course, no one will say that +this or any other arbitrary disposition of the stars is actually +impossible, but as there was no conceivable physical reason why the +distances of all the stars from the earth should be identical, it +seemed in the very highest degree improbable that the stars should be +so placed.</p> + +<p>Doubtless, also, Copernicus felt a considerable difficulty as to the +nature of the materials from which Ptolemy's wonderful sphere was to +be constructed. Nor could a philosopher of his penetration have +failed to observe that, unless that sphere were infinitely large, +there must have been space outside it, a consideration which would +open up other difficult questions. Whether infinite or not, it was +obvious that the celestial sphere must have a diameter at least many +thousands of times as great as that of the earth. From these +considerations Copernicus deduced the important fact that the stars +and the other celestial bodies must all be vast objects. He was thus +enabled to put the question in such a form that it could hardly +receive any answer but the correct one. Which is it more rational to +suppose, that the earth should turn round on its axis once in +twenty-four hours, or that thousands of mighty stars should circle +round the earth in the same time, many of them having to describe +circles many thousands of times greater in circumference than the +circuit of the earth at the equator? The obvious answer pressed upon +Copernicus with so much force that he was compelled to reject +Ptolemy's theory of the stationary earth, and to attribute the +diurnal rotation of the heavens to the revolution of the earth on its +axis.</p> + +<p>Once this tremendous step had been taken, the great difficulties +which beset the monstrous conception of the celestial sphere +vanished, for the stars need no longer be regarded as situated at +equal distances from the earth. Copernicus saw that they might lie +at the most varied degrees of remoteness, some being hundreds or +thousands of times farther away than others. The complicated +structure of the celestial sphere as a material object disappeared +altogether; it remained only as a geometrical conception, whereon we +find it convenient to indicate the places of the stars. Once the +Copernican doctrine had been fully set forth, it was impossible for +anyone, who had both the inclination and the capacity to understand +it, to withhold acceptance of its truth. The doctrine of a +stationary earth had gone for ever.</p> + +<p>Copernicus having established a theory of the celestial movements +which deliberately set aside the stability of the earth, it seemed +natural that he should inquire whether the doctrine of a moving earth +might not remove the difficulties presented in other celestial +phenomena. It had been universally admitted that the earth lay +unsupported in space. Copernicus had further shown that it possessed +a movement of rotation. Its want of stability being thus recognised, +it seemed reasonable to suppose that the earth might also have some +other kinds of movements as well. In this, Copernicus essayed to +solve a problem far more difficult than that which had hitherto +occupied his attention. It was a comparatively easy task to show how +the diurnal rising and setting could be accounted for by the rotation +of the earth. It was a much more difficult undertaking to +demonstrate that the planetary movements, which Ptolemy had +represented with so much success, could be completely explained by +the supposition that each of those planets revolved uniformly round +the sun, and that the earth was also a planet, accomplishing a +complete circuit of the sun once in the course of a year.</p> + +<p><a name="explanation" id="explanation"></a></p> + +<div class="figcenter" style="width: 291px;"> +<a href="images/ill_041.jpg"> +<img src="images/ill_041_sml.jpg" width="291" height="325" alt="EXPLANATION OF PLANETARY MOVEMENTS." title="" /></a> +<span class="caption">EXPLANATION OF PLANETARY MOVEMENTS.</span> +</div> + +<p>It would be impossible in a sketch like the present to enter into any +detail as to the geometrical propositions on which this beautiful +investigation of Copernicus depended. We can only mention a few of +the leading principles. It may be laid down in general that, if an +observer is in movement, he will, if unconscious of the fact, +attribute to the fixed objects around him a movement equal and +opposite to that which he actually possesses. A passenger on a +canal-boat sees the objects on the banks apparently moving backward +with a speed equal to that by which he is himself advancing +forwards. By an application of this principle, we can account for +all the phenomena of the movements of the planets, which Ptolemy had +so ingeniously represented by his circles. Let us take, for +instance, the most characteristic feature in the irregularities of +the outer planets. We have already remarked that Mars, though +generally advancing from west to east among the stars, occasionally +pauses, retraces his steps for awhile, again pauses, and then resumes +his ordinary onward progress. Copernicus showed clearly how this +effect was produced by the real motion of the earth, combined with +the real motion of Mars. In the adjoining figure we represent a +portion of the circular tracks in which the earth and Mars move in +accordance with the Copernican doctrine. I show particularly the +case where the earth comes directly between the planet and the sun, +because it is on such occasions that the retrograde movement (for so +this backward movement of Mars is termed) is at its highest. Mars is +then advancing in the direction shown by the arrow-head, and the +earth is also advancing in the same direction. We, on the earth, +however, being unconscious of our own motion, attribute, by the +principle I have already explained, an equal and opposite motion to +Mars. The visible effect upon the planet is, that Mars has two +movements, a real onward movement in one direction, and an apparent +movement in the opposite direction. If it so happened that the earth +was moving with the same speed as Mars, then the apparent movement +would exactly neutralise the real movement, and Mars would seem to be +at rest relatively to the surrounding stars. Under the actual +circumstances represented, however, the earth is moving faster than +Mars, and the consequence is, that the apparent movement of the +planet backwards exceeds the real movement forwards, the net result +being an apparent retrograde movement.</p> + +<p>With consummate skill, Copernicus showed how the applications of the +same principles could account for the characteristic movements of the +planets. His reasoning in due time bore down all opposition. The +supreme importance of the earth in the system vanished. It had now +merely to take rank as one of the planets.</p> + +<p>The same great astronomer now, for the first time, rendered something +like a rational account of the changes of the seasons. Nor did +certain of the more obscure astronomical phenomena escape his +attention.</p> + +<p>He delayed publishing his wonderful discoveries to the world until he +was quite an old man. He had a well-founded apprehension of the +storm of opposition which they would arouse. However, he yielded at +last to the entreaties of his friends, and his book was sent to the +press. But ere it made its appearance to the world, Copernicus was +seized by mortal illness. A copy of the book was brought to him on +May 23, 1543. We are told that he was able to see it and to touch +it, but no more, and he died a few hours afterwards. He was buried +in that Cathedral of Frauenburg, with which his life had been so +closely associated.</p> + +<h3><a name="TYCHO_BRAHE" id="TYCHO_BRAHE"></a>TYCHO BRAHE.</h3> +<p>The most picturesque figure in the history of astronomy is +undoubtedly that of the famous old Danish astronomer whose name +stands at the head of this chapter. Tycho Brahe was alike notable +for his astronomical genius and for the extraordinary vehemence of a +character which was by no means perfect. His romantic career as a +philosopher, and his taste for splendour as a Danish noble, his +ardent friendships and his furious quarrels, make him an ideal +subject for a biographer, while the magnificent astronomical work +which he accomplished, has given him imperishable fame.</p> + +<p>The history of Tycho Brahe has been admirably told by Dr. Dreyer, the +accomplished astronomer who now directs the observatory at Armagh, +though himself a countryman of Tycho. Every student of the career of +the great Dane must necessarily look on Dr. Dreyer's work as the +chief authority on the subject. Tycho sprang from an illustrious +stock. His family had flourished for centuries, both in Sweden and +in Denmark, where his descendants are to be met with at the present +day. The astronomer's father was a privy councillor, and having +filled important positions in the Danish government, he was +ultimately promoted to be governor of Helsingborg Castle, where he +spent the last years of his life. His illustrious son Tycho was born +in 1546, and was the second child and eldest boy in a family of ten.</p> + +<p>It appears that Otto, the father of Tycho, had a brother named +George, who was childless. George, however, desired to adopt a boy +on whom he could lavish his affection and to whom he could bequeath +his wealth. A somewhat singular arrangement was accordingly entered +into by the brothers at the time when Otto was married. It was +agreed that the first son who might be born to Otto should be +forthwith handed over by the parents to George to be reared and +adopted by him. In due time little Tycho appeared, and was +immediately claimed by George in pursuance of the compact. But it +was not unnatural that the parental instinct, which had been dormant +when the agreement was made, should here interpose. Tycho's father +and mother receded from the bargain, and refused to part with their +son. George thought he was badly treated. However, he took no +violent steps until a year later, when a brother was born to Tycho. +The uncle then felt no scruple in asserting what he believed to be +his rights by the simple process of stealing the first-born nephew, +which the original bargain had promised him. After a little time it +would seem that the parents acquiesced in the loss, and thus it was +in Uncle George's home that the future astronomer passed his +childhood.</p> + +<p>When we read that Tycho was no more than thirteen years old at the +time he entered the University of Copenhagen, it might be at first +supposed that even in his boyish years he must have exhibited some of +those remarkable talents with which he was afterwards to astonish the +world. Such an inference should not, however, be drawn. The fact is +that in those days it was customary for students to enter the +universities at a much earlier age than is now the case. Not, +indeed, that the boys of thirteen knew more then than the boys of +thirteen know now. But the education imparted in the universities at +that time was of a much more rudimentary kind than that which we +understand by university education at present. In illustration of +this Dr. Dreyer tells us how, in the University of Wittenberg, one of +the professors, in his opening address, was accustomed to point out +that even the processes of multiplication and division in arithmetic +might be learned by any student who possessed the necessary +diligence.</p> + +<p>It was the wish and the intention of his uncle that Tycho's education +should be specially directed to those branches of rhetoric and +philosophy which were then supposed to be a necessary preparation for +the career of a statesman. Tycho, however, speedily made it plain to +his teachers that though he was an ardent student, yet the things +which interested him were the movements of the heavenly bodies and +not the subtleties of metaphysics.</p> + +<p><a name="tycho" id="tycho"></a></p> + +<div class="figcenter" style="width: 451px;"> +<a href="images/ill_brahe.jpg"> +<img src="images/ill_brahe_sml.jpg" width="451" height="572" alt="TYCHO BRAHE." title="" /></a> +<span class="caption">TYCHO BRAHE.</span> +</div> + +<p>On the 21st October, 1560, an eclipse of the sun occurred, which was +partially visible at Copenhagen. Tycho, boy though he was, took the +utmost interest in this event. His ardour and astonishment in +connection with the circumstance were chiefly excited by the fact +that the time of the occurrence of the phenomenon could be predicted +with so much accuracy. Urged by his desire to understand the matter +thoroughly, Tycho sought to procure some book which might explain +what he so greatly wanted to know. In those days books of any kind +were but few and scarce, and scientific books were especially +unattainable. It so happened, however, that a Latin version of +Ptolemy's astronomical works had appeared a few years before the +eclipse took place, and Tycho managed to buy a copy of this book, +which was then the chief authority on celestial matters. Young as +the boy astronomer was, he studied hard, although perhaps not always +successfully, to understand Ptolemy, and to this day his copy of the +great work, copiously annotated and marked by the schoolboy hand, is +preserved as one of the chief treasures in the library of the +University at Prague.</p> + +<p>After Tycho had studied for about three years at the University of +Copenhagen, his uncle thought it would be better to send him, as was +usual in those days, to complete his education by a course of study +in some foreign university. The uncle cherished the hope that in +this way the attention of the young astronomer might be withdrawn +from the study of the stars and directed in what appeared to him a +more useful way. Indeed, to the wise heads of those days, the +pursuit of natural science seemed so much waste of good time which +might otherwise be devoted to logic or rhetoric or some other branch +of study more in vogue at that time. To assist in this attempt to +wean Tycho from his scientific tastes, his uncle chose as a tutor to +accompany him an intelligent and upright young man named Vedel, who +was four years senior to his pupil, and accordingly, in 1562, we find +the pair taking up their abode at the University of Leipzig.</p> + +<p>The tutor, however, soon found that he had undertaken a most hopeless +task. He could not succeed in imbuing Tycho with the slightest taste +for the study of the law or the other branches of knowledge which +were then thought so desirable. The stars, and nothing but the +stars, engrossed the attention of his pupil. We are told that all +the money he could obtain was spent secretly in buying astronomical +books and instruments. He learned the name of the stars from a +little globe, which he kept hidden from Vedel, and only ventured to +use during the latter's absence. No little friction was at first +caused by all this, but in after years a fast and enduring friendship +grew up between Tycho and his tutor, each of whom learned to respect +and to love the other.</p> + +<p>Before Tycho was seventeen he had commenced the difficult task of +calculating the movements of the planets and the places which they +occupied on the sky from time to time. He was not a little surprised +to find that the actual positions of the planets differed very widely +from those which were assigned to them by calculations from the best +existing works of astronomers. With the insight of genius he saw +that the only true method of investigating the movements of the +heavenly bodies would be to carry on a protracted series of +measurements of their places. This, which now seems to us so +obvious, was then entirely new doctrine. Tycho at once commenced +regular observations in such fashion as he could. His first +instrument was, indeed, a very primitive one, consisting of a simple +pair of compasses, which he used in this way. He placed his eye at +the hinge, and then opened the legs of the compass so that one leg +pointed to one star and the other leg to the other star. The compass +was then brought down to a divided circle, by which means the number +of degrees in the apparent angular distance of the two stars was +determined.</p> + +<p>His next advance in instrumental equipment was to provide himself +with the contrivance known as the "cross-staff," which he used to +observe the stars whenever opportunity offered. It must, of course, +be remembered that in those days there were no telescopes. In the +absence of optical aid, such as lenses afford the modern observers, +astronomers had to rely on mechanical appliances alone to measure the +places of the stars. Of such appliances, perhaps the most ingenious +was one known before Tycho's time, which we have represented in the +adjoining figure.</p> + +<p><a name="tycho_ill" id="tycho_ill"></a></p> + +<div class="figcenter" style="width: 279px;"> +<a href="images/ill_cross_staff.jpg"> +<img src="images/ill_cross_staff_sml.jpg" width="279" height="290" alt="TYCHO'S CROSS STAFF." title="" /></a> +</div> + +<p>Let us suppose that it be desired to measure the angle between two +stars, then if the angle be not too large it can be determined in the +following manner. Let the rod AB be divided into inches and parts of +an inch, and let another rod, CD, slide up and down along AB in such +a way that the two always remain perpendicular to each other. +"Sights," like those on a rifle, are placed at A and C, and there is +a pin at D. It will easily be seen that, by sliding the movable bar +along the fixed one, it must always be possible when the stars are +not too far apart to bring the sights into such positions that one +star can be seen along DC and the other along DA. This having been +accomplished, the length from A to the cross-bar is read off on the +scale, and then, by means of a table previously prepared, the value +of the required angular distance is obtained. If the angle between +the two stars were greater than it would be possible to measure in +the way already described, then there was a provision by which the +pin at D might be moved along CD into some other position, so as to +bring the angular distance of the stars within the range of the +instrument.</p> + +<p><a name="new_star" id="new_star"></a></p> + +<div class="figright" style="width: 257px;"> +<a href="images/ill_new_star.jpg"> +<img src="images/ill_new_star_sml.jpg" width="257" height="410" alt="TYCHO'S "NEW STAR" SEXTANT OF 1572. +(The arms, of walnut wood, are about 5 1/2 ft. long.)" title="" /></a> +<span class="caption">TYCHO'S "NEW STAR" SEXTANT OF 1572. +<br />(The arms, of walnut wood, are about 5 1/2 ft. long.)</span> +</div> + +<p>No doubt the cross-staff is a very primitive contrivance, but when +handled by one so skilful as Tycho it afforded results of +considerable accuracy. I would recommend any reader who may have a +taste for such pursuits to construct a cross-staff for himself, and +see what measurements he can accomplish with its aid.</p> + +<p>To employ this little instrument Tycho had to evade the vigilance of +his conscientious tutor, who felt it his duty to interdict all such +occupations as being a frivolous waste of time. It was when Vedel +was asleep that Tycho managed to escape with his cross staff and +measure the places of the heavenly bodies. Even at this early age +Tycho used to conduct his observations on those thoroughly sound +principles which lie at the foundation of all accurate modern +astronomy. Recognising the inevitable errors of workmanship in his +little instrument, he ascertained their amount and allowed for their +influence on the results which he deduced. This principle, employed +by the boy with his cross-staff in 1564, is employed at the present +day by the Astronomer Royal at Greenwich with the most superb +instruments that the skill of modern opticians has been able to +construct.</p> + +<p><a name="trigonic_sextant" id="trigonic_sextant"></a></p> + +<div class="figleft" style="width: 260px;"> +<a href="images/ill_trigonic_sextant.jpg"> +<img src="images/ill_trigonic_sextant_sml.jpg" width="260" height="411" alt="TYCHO'S TRIGONIC SEXTANT. +(The arms, AB and AC, are about 5 1/2 ft. long.)" title="" /></a> +<span class="caption">TYCHO'S TRIGONIC SEXTANT. +<br />(The arms, AB and AC, are about 5 1/2 ft. long.)</span> +</div> + +<p>After the death of his uncle, when Tycho was nineteen years of age, +it appears that the young philosopher was no longer interfered with +in so far as the line which his studies were to take was concerned. +Always of a somewhat restless temperament, we now find that he +shifted his abode to the University of Rostock, where he speedily +made himself notable in connection with an eclipse of the moon on +28th October, 1566. Like every other astronomer of those days, Tycho +had always associated astronomy with astrology. He considered that +the phenomena of the heavenly bodies always had some significance in +connection with human affairs. Tycho was also a poet, and in the +united capacity of poet, astrologer, and astronomer, he posted up +some verses in the college at Rostock announcing that the lunar +eclipse was a prognostication of the death of the great Turkish +Sultan, whose mighty deeds at that time filled men's minds. Presently +news did arrive of the death of the Sultan, and Tycho was accordingly +triumphant; but a little later it appeared that the decease had taken +place BEFORE the eclipse, a circumstance which caused many a laugh at +Tycho's expense.</p> + +<p><a name="astronomic_sextant" id="astronomic_sextant"></a></p> + +<div class="figright" style="width: 274px;"> +<a href="images/ill_astronomic_sextant.jpg"> +<img src="images/ill_astronomic_sextant_sml.jpg" width="274" height="433" alt="TYCHO'S ASTRONOMIC SEXTANT. +(Made of steel; the arms, A B, A C, measure 4ft.)" title="" /></a> +<span class="caption">TYCHO'S ASTRONOMIC SEXTANT.<br /> +(Made of steel; the arms, A B, A C, measure 4ft.)</span> +</div> + +<p><a name="equatorial_armillary" id="equatorial_armillary"></a></p> + +<div class="figleft" style="width: 257px;"> +<a href="images/ill_equatorial_armillary.jpg"> +<img src="images/ill_equatorial_armillary_sml.jpg" width="257" height="414" alt="TYCHO'S EQUATORIAL ARMILLARY. +(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)" title="" /></a> +<span class="caption">TYCHO'S EQUATORIAL ARMILLARY. +<br />(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)</span> +</div> + +<p>Tycho being of a somewhat turbulent disposition, it appears that, +while at the University of Rostock, he had a serious quarrel with +another Danish nobleman. We are not told for certain what was the +cause of the dispute. It does not, however, seem to have had any +more romantic origin than a difference of opinion as to which of them +knew the more mathematics. They fought, as perhaps it was becoming +for two astronomers to fight, under the canopy of heaven in utter +darkness at the dead of night, and the duel was honourably terminated +when a slice was taken off Tycho's nose by the insinuating sword of +his antagonist. For the repair of this injury the ingenuity of the +great instrument-maker was here again useful, and he made a +substitute for his nose "with a composition of gold and silver." The +imitation was so good that it is declared to have been quite equal to +the original. Dr. Lodge, however, pointedly observes that it does +not appear whether this remark was made by a friend or an enemy.</p> + +<p><a name="augsburg_quadrant" id="augsburg_quadrant"></a></p> + +<div class="figright" style="width: 268px;clear:both;"> +<a href="images/ill_augsburg_quadrant.jpg"> +<img src="images/ill_augsburg_quadrant_sml.jpg" +width="268" height="409" alt="THE GREAT AUGSBURG QUADRANT" +title="" /></a> +<span class="caption">THE GREAT AUGSBURG QUADRANT.</span> +</div> +<p><a name="new_scheme" id="new_scheme"></a></p> + +<div class="figcenter" style="width: 446px;clear:both;"> +<a href="images/ill_new_scheme.jpg"> +<img src="images/ill_new_scheme_sml.jpg" width="446" height="446" alt="TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577." title="" /></a> +<span class="caption">TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.</span> +</div> + +<p>The next few years Tycho spent in various places ardently pursuing +somewhat varied branches of scientific study. At one time we hear of +him assisting an astronomical alderman, in the ancient city of +Augsburg, to erect a tremendous wooden machine—a quadrant of 19-feet +radius—to be used in observing the heavens. At another time we +learn that the King of Denmark had recognised the talents of his +illustrious subject, and promised to confer on him a pleasant +sinecure in the shape of a canonry, which would assist him with the +means for indulging his scientific pursuits. Again we are told that +Tycho is pursuing experiments in chemistry with the greatest energy, +nor is this so incompatible as might at first be thought with his +devotion to astronomy. In those early days of knowledge the +different sciences seemed bound together by mysterious bonds. +Alchemists and astrologers taught that the several planets were +correlated in some mysterious manner with the several metals. It +was, therefore hardly surprising that Tycho should have included a +study of the properties of the metals in the programme of his +astronomical work.</p> + +<p><a name="uraniborg" id="uraniborg"></a></p> + +<div class="figcenter" style="width: 449px;"> +<a href="images/ill_uraniborg.jpg"> +<img src="images/ill_uraniborg_sml.jpg" width="449" height="444" alt="URANIBORG AND ITS GROUNDS. + +PLATE: GROUND-PLAN OF THE OBSERVATORY." title="" /></a> +<span class="caption">URANIBORG AND ITS GROUNDS.</span> +</div> +<p><a name="grnd_pln_uraniborg" id="grnd_pln_uraniborg"></a></p> + +<div class="figcenter" style="width: 401px;"> +<a href="images/ill_grnd_pln_observatory.jpg"> +<img src="images/ill_grnd_pln_observatory_sml.jpg" width="401" height="279" alt="GROUND-PLAN OF THE OBSERVATORY." title="" /></a> +<span class="caption">GROUND-PLAN OF THE OBSERVATORY.</span> +</div> + +<p>An event, however, occurred in 1572 which stimulated Tycho's +astronomical labours, and started him on his life's work. On the +11th of November in that year, he was returning home to supper after +a day's work in his laboratory, when he happened to lift his face to +the sky, and there he beheld a brilliant new star. It was in the +constellation of Cassiopeia, and occupied a position in which there +had certainly been no bright star visible when his attention had last +been directed to that part of the heavens. Such a phenomenon was so +startling that he found it hard to trust the evidence of his senses. +He thought he must be the subject of some hallucination. He +therefore called to the servants who were accompanying him, and asked +them whether they, too, could see a brilliant object in the direction +in which he pointed. They certainly could, and thus he became +convinced that this marvellous object was no mere creation of the +fancy, but a veritable celestial body—a new star of surpassing +splendour which had suddenly burst forth. In these days of careful +scrutiny of the heavens, we are accustomed to the occasional outbreak +of new stars. It is not, however, believed that any new star which +has ever appeared has displayed the same phenomenal brilliance as was +exhibited by the star of 1572.</p> + +<p>This object has a value in astronomy far greater than it might at +first appear. It is true, in one sense, that Tycho discovered the +new star, but it is equally true, in a different sense, that it was +the new star which discovered Tycho. Had it not been for this +opportune apparition, it is quite possible that Tycho might have +found a career in some direction less beneficial to science than that +which he ultimately pursued.</p> + +<p><a name="uraniborg_hven" id="uraniborg_hven"></a></p> + +<div class="figcenter" style="width: 433px;"> +<a href="images/ill_observatory_hven.jpg"> +<img src="images/ill_observatory_hven_sml.jpg" width="433" height="321" alt="THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN." title="" /></a> +<span class="caption">THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.</span> +</div> + +<p>When he reached his home on this memorable evening, Tycho immediately +applied his great quadrant to the measurement of the place of the new +star. His observations were specially directed to the determination +of the distance of the object. He rightly conjectured that if it +were very much nearer to us than the stars in its vicinity, the +distance of the brilliant body might be determined in a short time by +the apparent changes in its distance from the surrounding points. It +was speedily demonstrated that the new star could not be as near as +the moon, by the simple fact that its apparent place, as compared +with the stars in its neighbourhood, was not appreciably altered when +it was observed below the pole, and again above the pole at an +interval of twelve hours. Such observations were possible, inasmuch +as the star was bright enough to be seen in full daylight. Tycho +thus showed conclusively that the body was so remote that the +diameter of the earth bore an insignificant ratio to the star's +distance. His success in this respect is the more noteworthy when we +find that many other observers, who studied the same object, came to +the erroneous conclusion that the new star was quite as near as the +moon, or even much nearer. In fact, it may be said, that with regard +to this object Tycho discovered everything which could possibly have +been discovered in the days before telescopes were invented. He not +only proved that the star's distance was too great for measurement, +but he showed that it had no proper motion on the heavens. He +recorded the successive changes in its brightness from week to week, +as well as the fluctuations in hue with which the alterations in +lustre were accompanied.</p> + +<p>It seems, nowadays, strange to find that such thoroughly scientific +observations of the new star as those which Tycho made, possessed, +even in the eyes of the great astronomer himself, a profound +astrological significance. We learn from Dr. Dreyer that, in Tycho's +opinion, "the star was at first like Venus and Jupiter, and its +effects will therefore, first, be pleasant; but as it then became +like Mars, there will next come a period of wars, seditions, +captivity, and death of princes, and destruction of cities, together +with dryness and fiery meteors in the air, pestilence, and venomous +snakes. Lastly, the star became like Saturn, and thus will finally +come a time of want, death, imprisonment, and all kinds of sad +things!" Ideas of this kind were, however, universally entertained. +It seemed, indeed, obvious to learned men of that period that such an +apparition must forebode startling events. One of the chief theories +then held was, that just as the Star of Bethlehem announced the first +coming of Christ, so the second coming, and the end of the world, was +heralded by the new star of 1572.</p> + +<p>The researches of Tycho on this object were the occasion of his first +appearance as an author. The publication of his book was however, +for some time delayed by the urgent remonstrances of his friends, who +thought it was beneath the dignity of a nobleman to condescend to +write a book. Happily, Tycho determined to brave the opinion of his +order; the book appeared, and was the first of a series of great +astronomical productions from the same pen.</p> + +<p><a name="effigy" id="effigy"></a></p> + +<div class="figright" style="width: 221px;"> +<a href="images/ill_tomb_effigy.jpg"> +<img src="images/ill_tomb_effigy_sml.jpg" width="221" height="384" alt="EFFIGY ON TYCHO'S TOMB AT PRAGUE." title="" /></a> +<span class="caption">EFFIGY ON TYCHO'S TOMB AT PRAGUE.</span> +</div> + +<p>The fame of the noble Dane being now widespread, the King of Denmark +entreated him to return to his native country, and to deliver a +course of lectures on astronomy in the University of Copenhagen. With +some reluctance he consented, and his introductory oration has been +preserved. He dwells, in fervent language, upon the beauty and the +interest of the celestial phenomena. He points out the imperative +necessity of continuous and systematic observation of the heavenly +bodies in order to extend our knowledge. He appeals to the practical +utility of the science, for what civilised nation could exist without +having the means of measuring time? He sets forth how the study of +these beautiful objects "exalts the mind from earthly and trivial +things to heavenly ones;" and then he winds up by assuring them that +"a special use of astronomy is that it enables us to draw conclusions +from the movements in the celestial regions as to human fate."</p> + +<p>An interesting event, which occurred in 1572, distracted Tycho's +attention from astronomical matters. He fell in love. The young +girl on whom his affections were set appears to have sprung from +humble origin. Here again his august family friends sought to +dissuade him from a match they thought unsuitable for a nobleman. +But Tycho never gave way in anything. It is suggested that he did +not seek a wife among the highborn dames of his own rank from the +dread that the demands of a fashionable lady would make too great an +inroad on the time that he wished to devote to science. At all +events, Tycho's union seems to have been a happy one, and he had a +large family of children; none of whom, however, inherited their +father's talents.</p> + +<p><a name="quadrant" id="quadrant"></a></p> + +<div class="figcenter" style="width: 419px;"> +<a href="images/ill_mural_quadrant.jpg"> +<img src="images/ill_mural_quadrant_sml.jpg" width="419" height="570" alt="TYCHO'S MURAL QUADRANT PICTURE, URANIBORG." title="" /></a> +<span class="caption">TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.</span> +</div> + +<p>Tycho had many scientific friends in Germany, among whom his work was +held in high esteem. The treatment that he there met with seemed to +him so much more encouraging than that which he received in Denmark +that he formed the notion of emigrating to Basle and making it his +permanent abode. A whisper of this intention was conveyed to the +large-hearted King of Denmark, Frederick II. He wisely realised how +great would be the fame which would accrue to his realm if he could +induce Tycho to remain within Danish territory and carry on there the +great work of his life. A resolution to make a splendid proposal to +Tycho was immediately formed. A noble youth was forthwith despatched +as a messenger, and ordered to travel day and night until he reached +Tycho, whom he was to summon to the king. The astronomer was in bed +on the morning of 11th February, 1576, when the message was +delivered. Tycho, of course, set off at once and had an audience of +the king at Copenhagen. The astronomer explained that what he wanted +was the means to pursue his studies unmolested, whereupon the king +offered him the Island of Hven, in the Sound near Elsinore. There he +would enjoy all the seclusion that he could desire. The king further +promised that he would provide the funds necessary for building a +house and for founding the greatest observatory that had ever yet +been reared for the study of the heavens. After due deliberation and +consultation with his friends, Tycho accepted the king's offer. He +was forthwith granted a pension, and a deed was drawn up formally +assigning the Island of Hven to his use all the days of his life.</p> + +<p>The foundation of the famous castle of Uraniborg was laid on 30th +August, 1576. The ceremony was a formal and imposing one, in +accordance with Tycho's ideas of splendour. A party of scientific +friends had assembled, and the time had been chosen so that the +heavenly bodies were auspiciously placed. Libations of costly wines +were poured forth, and the stone was placed with due solemnity. The +picturesque character of this wonderful temple for the study of the +stars may be seen in the figures with which this chapter is +illustrated.</p> + +<p>One of the most remarkable instruments that has ever been employed in +studying the heavens was the mural quadrant which Tycho erected in +one of the apartments of Uraniborg. By its means the altitudes of +the celestial bodies could be observed with much greater accuracy +than had been previously attainable. This wonderful contrivance is +represented on the preceding page. It will be observed that the +walls of the room are adorned by pictures with a lavishness of +decoration not usually to be found in scientific establishments.</p> + +<p>A few years later, when the fame of the observatory at Hven became +more widely spread, a number of young men flocked to Tycho to study +under his direction. He therefore built another observatory for +their use in which the instruments were placed in subterranean rooms +of which only the roofs appeared above the ground. There was a +wonderful poetical inscription over the entrance to this underground +observatory, expressing the astonishment of Urania at finding, even +in the interior of the earth, a cavern devoted to the study of the +heavens. Tycho was indeed always fond of versifying, and he lost no +opportunity of indulging this taste whenever an occasion presented +itself.</p> + +<p>Around the walls of the subterranean observatory were the pictures of +eight astronomers, each with a suitable inscription—one of these of +course represented Tycho himself, and beneath were written words to +the effect that posterity should judge of his work. The eighth +picture depicted an astronomer who has not yet come into existence. +Tychonides was his name, and the inscription presses the modest hope +that when he does appear he will be worthy of his great predecessor. +The vast expenses incurred in the erection and the maintenance of +this strange establishment were defrayed by a succession of grants +from the royal purse.</p> + +<p>For twenty years Tycho laboured hard at Uraniborg in the pursuit of +science. His work mainly consisted in the determination of the +places of the moon, the planets, and the stars on the celestial +sphere. The extraordinary pains taken by Tycho to have his +observations as accurate as his instruments would permit, have justly +entitled him to the admiration of all succeeding astronomers. His +island home provided the means of recreation as well as a place for +work. He was surrounded by his family, troops of friends were not +wanting, and a pet dwarf seems to have been an inmate of his curious +residence. By way of change from his astronomical labours he used +frequently to work with his students in his chemical laboratory. It +is not indeed known what particular problems in chemistry occupied +his attention. We are told, however, that he engaged largely in the +production of medicines, and as these appear to have been dispensed +gratuitously there was no lack of patients.</p> + +<p>Tycho's imperious and grasping character frequently brought him into +difficulties, which seem to have increased with his advancing years. +He had ill-treated one of his tenants on Hven, and an adverse +decision by the courts seems to have greatly exasperated the +astronomer. Serious changes also took place in his relations to the +court at Copenhagen. When the young king was crowned in 1596, he +reversed the policy of his predecessor with reference to Hven. The +liberal allowances to Tycho were one after another withdrawn, and +finally even his pension was stopped. Tycho accordingly abandoned +Hven in a tumult of rage and mortification. A few years later we +find him in Bohemia a prematurely aged man, and he died on the 24th +October, 1601.</p> + +<h3><a name="GALILEO" id="GALILEO"></a>GALILEO.</h3> +<p>Among the ranks of the great astronomers it would be difficult to +find one whose life presents more interesting features and remarkable +vicissitudes than does that of Galileo. We may consider him as the +patient investigator and brilliant discoverer. We may consider him +in his private relations, especially to his daughter, Sister Maria +Celeste, a woman of very remarkable character; and we have also the +pathetic drama at the close of Galileo's life, when the philosopher +drew down upon himself the thunders of the Inquisition.</p> + +<p>The materials for the sketch of this astonishing man are sufficiently +abundant. We make special use in this place of those charming +letters which his daughter wrote to him from her convent home. More +than a hundred of these have been preserved, and it may well be +doubted whether any more beautiful and touching series of letters +addressed to a parent by a dearly loved child have ever been +written. An admirable account of this correspondence is contained in +a little book entitled "The Private Life of Galileo," published +anonymously by Messrs. Macmillan in 1870, and I have been much +indebted to the author of that volume for many of the facts contained +in this chapter.</p> + +<p>Galileo was born at Pisa, on 18th February, 1564. He was the eldest +son of Vincenzo de' Bonajuti de' Galilei, a Florentine noble. +Notwithstanding his illustrious birth and descent, it would seem that +the home in which the great philosopher's childhood was spent was an +impoverished one. It was obvious at least that the young Galileo +would have to be provided with some profession by which he might earn +a livelihood. From his father he derived both by inheritance and by +precept a keen taste for music, and it appears that he became an +excellent performer on the lute. He was also endowed with +considerable artistic power, which he cultivated diligently. Indeed, +it would seem that for some time the future astronomer entertained +the idea of devoting himself to painting as a profession. His +father, however, decided that he should study medicine. Accordingly, +we find that when Galileo was seventeen years of age, and had added a +knowledge of Greek and Latin to his acquaintance with the fine arts, +he was duly entered at the University of Pisa.</p> + +<p>Here the young philosopher obtained some inkling of mathematics, +whereupon he became so much interested in this branch of science, +that he begged to be allowed to study geometry. In compliance with +his request, his father permitted a tutor to be engaged for this +purpose; but he did so with reluctance, fearing that the attention of +the young student might thus be withdrawn from that medical work +which was regarded as his primary occupation. The event speedily +proved that these anxieties were not without some justification. The +propositions of Euclid proved so engrossing to Galileo that it was +thought wise to avoid further distraction by terminating the +mathematical tutor's engagement. But it was too late for the desired +end to be attained. Galileo had now made such progress that he was +able to continue his geometrical studies by himself. Presently he +advanced to that famous 47th proposition which won his lively +admiration, and on he went until he had mastered the six books of +Euclid, which was a considerable achievement for those days.</p> + +<p>The diligence and brilliance of the young student at Pisa did not, +however, bring him much credit with the University authorities. In +those days the doctrines of Aristotle were regarded as the embodiment +of all human wisdom in natural science as well as in everything +else. It was regarded as the duty of every student to learn +Aristotle off by heart, and any disposition to doubt or even to +question the doctrines of the venerated teacher was regarded as +intolerable presumption. But young Galileo had the audacity to think +for himself about the laws of nature. He would not take any +assertion of fact on the authority of Aristotle when he had the means +of questioning nature directly as to its truth or falsehood. His +teachers thus came to regard him as a somewhat misguided youth, +though they could not but respect the unflagging industry with which +he amassed all the knowledge he could acquire.</p> + +<p><a name="galileo_pendulum" id="galileo_pendulum"></a></p> + +<div class="figcenter" style="width: 313px;"> +<a href="images/ill_galileo_pendulum.jpg"> +<img src="images/ill_galileo_pendulum_sml.jpg" width="313" height="448" alt="GALILEO'S PENDULUM." title="" /></a> +<span class="caption">GALILEO'S PENDULUM.</span> +</div> + +<p>We are so accustomed to the use of pendulums in our clocks that +perhaps we do not often realise that the introduction of this method +of regulating time-pieces was really a notable invention worthy the +fame of the great astronomer to whom it was due. It appears that +sitting one day in the Cathedral of Pisa, Galileo's attention became +concentrated on the swinging of a chandelier which hung from the +ceiling. It struck him as a significant point, that whether the arc +through which the pendulum oscillated was a long one or a short one, +the time occupied in each vibration was sensibly the same. This +suggested to the thoughtful observer that a pendulum would afford the +means by which a time-keeper might be controlled, and accordingly +Galileo constructed for the first time a clock on this principle. The +immediate object sought in this apparatus was to provide a means of +aiding physicians in counting the pulses of their patients.</p> + +<p>The talents of Galileo having at length extorted due recognition from +the authorities, he was appointed, at the age of twenty-five, +Professor of Mathematics at the University of Pisa. Then came the +time when he felt himself strong enough to throw down the gauntlet to +the adherents of the old philosophy. As a necessary part of his +doctrine on the movement of bodies Aristotle had asserted that the +time occupied by a stone in falling depends upon its weight, so that +the heavier the stone the less time would it require to fall from a +certain height to the earth. It might have been thought that a +statement so easily confuted by the simplest experiments could never +have maintained its position in any accepted scheme of philosophy. +But Aristotle had said it, and to anyone who ventured to express a +doubt the ready sneer was forthcoming, "Do you think yourself a +cleverer man than Aristotle?" Galileo determined to demonstrate in +the most emphatic manner the absurdity of a doctrine which had for +centuries received the sanction of the learned. The summit of the +Leaning Tower of Pisa offered a highly dramatic site for the great +experiment. The youthful professor let fall from the overhanging top +a large heavy body and a small light body simultaneously. According +to Aristotle the large body ought to have reached the ground much +sooner than the small one, but such was found not to be the case. In +the sight of a large concourse of people the simple fact was +demonstrated that the two bodies fell side by side, and reached the +ground at the same time. Thus the first great step was taken in the +overthrow of that preposterous system of unquestioning adhesion to +dogma, which had impeded the development of the knowledge of nature +for nearly two thousand years.</p> + +<p>This revolutionary attitude towards the ancient beliefs was not +calculated to render Galileo's relations with the University +authorities harmonious. He had also the misfortune to make enemies +in other quarters. Don Giovanni de Medici, who was then the Governor +of the Port of Leghorn, had designed some contrivance by which he +proposed to pump out a dock. But Galileo showed up the absurdity of +this enterprise in such an aggressive manner that Don Giovanni took +mortal offence, nor was he mollified when the truths of Galileo's +criticisms were abundantly verified by the total failure of his +ridiculous invention. In various ways Galileo was made to feel his +position at Pisa so unpleasant that he was at length compelled to +abandon his chair in the University. The active exertions of his +friends, of whom Galileo was so fortunate as to have had throughout +his life an abundant supply, then secured his election to the +Professorship of Mathematics at Padua, whither he went in 1592.</p> + +<p><a name="portrait" id="portrait"></a></p> + +<div class="figcenter" style="width: 427px;"> +<a href="images/ill_portrait_galileo.jpg"> +<img src="images/ill_portrait_galileo_sml.jpg" width="427" height="533" alt="PORTRAIT OF GALILEO." title="" /></a> +<span class="caption">PORTRAIT OF GALILEO.</span> +</div> + +<p>It was in this new position that Galileo entered on that marvellous +career of investigation which was destined to revolutionize science. +The zeal with which he discharged his professorial duties was indeed +of the most unremitting character. He speedily drew such crowds to +listen to his discourses on Natural Philosophy that his lecture-room +was filled to overflowing. He also received many private pupils in +his house for special instruction. Every moment that could be spared +from these labours was devoted to his private study and to his +incessant experiments.</p> + +<p>Like many another philosopher who has greatly extended our knowledge +of nature, Galileo had a remarkable aptitude for the invention of +instruments designed for philosophical research. To facilitate his +practical work, we find that in 1599 he had engaged a skilled workman +who was to live in his house, and thus be constantly at hand to try +the devices for ever springing from Galileo's fertile brain. Among +the earliest of his inventions appears to have been the thermometer, +which he constructed in 1602. No doubt this apparatus in its +primitive form differed in some respects from the contrivance we call +by the same name. Galileo at first employed water as the agent, by +the expansion of which the temperature was to be measured. He +afterwards saw the advantage of using spirits for the same purpose. +It was not until about half a century later that mercury came to be +recognised as the liquid most generally suitable for the thermometer.</p> + +<p>The time was now approaching when Galileo was to make that mighty +step in the advancement of human knowledge which followed on the +application of the telescope to astronomy. As to how his idea of +such an instrument originated, we had best let him tell us in his own +words. The passage is given in a letter which he writes to his +brother-in-law, Landucci.</p> + +<p>"I write now because I have a piece of news for you, though whether +you will be glad or sorry to hear it I cannot say; for I have now no +hope of returning to my own country, though the occurrence which has +destroyed that hope has had results both useful and honourable. You +must know, then, that two months ago there was a report spread here +that in Flanders some one had presented to Count Maurice of Nassau a +glass manufactured in such a way as to make distant objects appear +very near, so that a man at the distance of two miles could be +clearly seen. This seemed to me so marvellous that I began to think +about it. As it appeared to me to have a foundation in the Theory of +Perspective, I set about contriving how to make it, and at length I +found out, and have succeeded so well that the one I have made is far +superior to the Dutch telescope. It was reported in Venice that I +had made one, and a week since I was commanded to show it to his +Serenity and to all the members of the senate, to their infinite +amazement. Many gentlemen and senators, even the oldest, have +ascended at various times the highest bell-towers in Venice to spy +out ships at sea making sail for the mouth of the harbour, and have +seen them clearly, though without my telescope they would have been +invisible for more than two hours. The effect of this instrument is +to show an object at a distance of say fifty miles, as if it were but +five miles."</p> + +<p>The remarkable properties of the telescope at once commanded +universal attention among intellectual men. Galileo received +applications from several quarters for his new instrument, of which +it would seem that he manufactured a large number to be distributed +as gifts to various illustrious personages.</p> + +<p>But it was reserved for Galileo himself to make that application of +the instrument to the celestial bodies by which its peculiar powers +were to inaugurate the new era in astronomy. The first discovery +that was made in this direction appears to have been connected with +the number of the stars. Galileo saw to his amazement that through +his little tube he could count ten times as many stars in the sky as +his unaided eye could detect. Here was, indeed, a surprise. We are +now so familiar with the elementary facts of astronomy that it is not +always easy to realise how the heavens were interpreted by the +observers in those ages prior to the invention of the telescope. We +can hardly, indeed, suppose that Galileo, like the majority of those +who ever thought of such matters, entertained the erroneous belief +that the stars were on the surface of a sphere at equal distances +from the observer. No one would be likely to have retained his +belief in such a doctrine when he saw how the number of visible stars +could be increased tenfold by means of Galileo's telescope. It would +have been almost impossible to refuse to draw the inference that the +stars thus brought into view were still more remote objects which the +telescope was able to reveal, just in the same way as it showed +certain ships to the astonished Venetians, when at the time these +ships were beyond the reach of unaided vision.</p> + +<p>Galileo's celestial discoveries now succeeded each other rapidly. +That beautiful Milky Way, which has for ages been the object of +admiration to all lovers of nature, never disclosed its true nature +to the eye of man till the astronomer of Padua turned on it his magic +tube. The splendid zone of silvery light was then displayed as +star-dust scattered over the black background of the sky. It was +observed that though the individual stars were too small to be seen +severally without optical aid, yet such was their incredible number +that the celestial radiance produced that luminosity with which every +stargazer was so familiar.</p> + +<p>But the greatest discovery made by the telescope in these early days, +perhaps, indeed, the greatest discovery that the telescope has ever +accomplished, was the detection of the system of four satellites +revolving around the great planet Jupiter. This phenomenon was so +wholly unexpected by Galileo that, at first, he could hardly believe +his eyes. However, the reality of the existence of a system of four +moons attending the great planet was soon established beyond all +question. Numbers of great personages crowded to Galileo to see for +themselves this beautiful miniature representing the sun with its +system of revolving planets.</p> + +<p>Of course there were, as usual, a few incredulous people who refused +to believe the assertion that four more moving bodies had to be added +to the planetary system. They scoffed at the notion; they said the +satellites may have been in the telescope, but that they were not in +the sky. One sceptical philosopher is reported to have affirmed, +that even if he saw the moons of Jupiter himself he would not believe +in them, as their existence was contrary to the principles of +common-sense!</p> + +<p>There can be no doubt that a special significance attached to the new +discovery at this particular epoch in the history of science. It +must be remembered that in those days the doctrine of Copernicus, +declaring that the sun, and not the earth, was the centre of the +system, that the earth revolved on its axis once a day, and that it +described a mighty circle round the sun once a year, had only +recently been promulgated. This new view of the scheme of nature had +been encountered with the most furious opposition. It may possibly +have been that Galileo himself had not felt quite confident in the +soundness of the Copernican theory, prior to the discovery of the +satellites of Jupiter. But when a picture was there exhibited in +which a number of relatively small globes were shown to be revolving +around a single large globe in the centre, it seemed impossible not +to feel that the beautiful spectacle so displayed was an emblem of +the relations of the planets to the sun. It was thus made manifest +to Galileo that the Copernican theory of the planetary system must be +the true one. The momentous import of this opinion upon the future +welfare of the great philosopher will presently appear.</p> + +<p>It would seem that Galileo regarded his residence at Padua as a state +of undesirable exile from his beloved Tuscany. He had always a +yearning to go back to his own country and at last the desired +opportunity presented itself. For now that Galileo's fame had become +so great, the Grand Duke of Tuscany desired to have the philosopher +resident at Florence, in the belief that he would shed lustre on the +Duke's dominions. Overtures were accordingly made to Galileo, and +the consequence was that in 1616 we find him residing at Florence, +bearing the title of Mathematician and Philosopher to the Grand Duke.</p> + +<p>Two daughters, Polissena and Virginia, and one son, Vincenzo, had +been born to Galileo in Padua. It was the custom in those days that +as soon as the daughter of an Italian gentleman had grown up, her +future career was somewhat summarily decided. Either a husband was +to be forthwith sought out, or she was to enter the convent with the +object of taking the veil as a professed nun. It was arranged that +the two daughters of Galileo, while still scarcely more than +children, should both enter the Franciscan convent of St. Matthew, at +Arcetri. The elder daughter Polissena, took the name of Sister Maria +Celeste, while Virginia became Sister Arcangela. The latter seems to +have been always delicate and subject to prolonged melancholy, and +she is of but little account in the narrative of the life of +Galileo. But Sister Maria Celeste, though never leaving the convent, +managed to preserve a close intimacy with her beloved father. This +was maintained only partly by Galileo's visits, which were very +irregular and were, indeed, often suspended for long intervals. But +his letters to this daughter were evidently frequent and +affectionate, especially in the latter part of his life. Most +unfortunately, however, all his letters have been lost. There are +grounds for believing that they were deliberately destroyed when +Galileo was seized by the Inquisition, lest they should have been +used as evidence against him, or lest they should have compromised +the convent where they were received. But Sister Maria Celeste's +letters to her father have happily been preserved, and most touching +these letters are. We can hardly read them without thinking how the +sweet and gentle nun would have shrunk from the idea of their +publication.</p> + +<p>Her loving little notes to her "dearest lord and father," as she used +affectionately to call Galileo, were almost invariably accompanied by +some gift, trifling it may be, but always the best the poor nun had +to bestow. The tender grace of these endearing communications was +all the more precious to him from the fact that the rest of Galileo's +relatives were of quite a worthless description. He always +acknowledged the ties of his kindred in the most generous way, but +their follies and their vices, their selfishness and their +importunities, were an incessant source of annoyance to him, almost +to the last day of his life.</p> + +<p>On 19th December, 1625, Sister Maria Celeste writes:—</p> + +<p>"I send two baked pears for these days of vigil. But as the greatest +treat of all, I send you a rose, which ought to please you extremely, +seeing what a rarity it is at this season; and with the rose you must +accept its thorns, which represent the bitter passion of our Lord, +whilst the green leaves represent the hope we may entertain that +through the same sacred passion we, having passed through the +darkness of the short winter of our mortal life, may attain to the +brightness and felicity of an eternal spring in heaven."</p> + +<p>When the wife and children of Galileo's shiftless brother came to +take up their abode in the philosopher's home, Sister Maria Celeste +feels glad to think that her father has now some one who, however +imperfectly, may fulfil the duty of looking after him. A graceful +note on Christmas Eve accompanies her little gifts. She hopes that—</p> + +<p>"In these holy days the peace of God may rest on him and all the +house. The largest collar and sleeves I mean for Albertino, the +other two for the two younger boys, the little dog for baby, and the +cakes for everybody, except the spice-cakes, which are for you. +Accept the good-will which would readily do much more."</p> + +<p>The extraordinary forbearance with which Galileo continually placed +his time, his purse, and his influence at the service of those who +had repeatedly proved themselves utterly unworthy of his countenance, +is thus commented on by the good nun.—</p> + +<p>"Now it seems to me, dearest lord and father, that your lordship is +walking in the right path, since you take hold of every occasion that +presents itself to shower continual benefits on those who only repay +you with ingratitude. This is an action which is all the more +virtuous and perfect as it is the more difficult."</p> + +<p>When the plague was raging in the neighbourhood, the loving +daughter's solicitude is thus shown:—</p> + +<p>"I send you two pots of electuary as a preventive against the +plague. The one without the label consists of dried figs, walnuts, +rue, and salt, mixed together with honey. A piece of the size of a +walnut to be taken in the morning, fasting, with a little Greek +wine."</p> + +<p>The plague increasing still more, Sister Maria Celeste obtained with +much difficulty, a small quantity of a renowned liqueur, made by +Abbess Ursula, an exceptionally saintly nun. This she sends to her +father with the words:—</p> + +<p>"I pray your lordship to have faith in this remedy. For if you have +so much faith in my poor miserable prayers, much more may you have in +those of such a holy person; indeed, through her merits you may feel +sure of escaping all danger from the plague."</p> + +<p>Whether Galileo took the remedy we do not know, but at all events +he escaped the plague.</p> + +<p><a name="arcetri" id="arcetri"></a></p> + +<div class="figcenter" style="width: 406px;"> +<a href="images/ill_villa_arcetri.jpg"> +<img src="images/ill_villa_arcetri_sml.jpg" width="406" height="312" alt="THE VILLA ARCETRI. +Galileo's residence, where Milton visited him." title="" /></a> +<span class="caption">THE VILLA ARCETRI. +Galileo's residence, where Milton visited him.</span> +</div> + +<p>From Galileo's new home in Florence the telescope was again directed +to the skies, and again did astounding discoveries reward the +astronomer's labours. The great success which he had met with in +studying Jupiter naturally led Galileo to look at Saturn. Here he +saw a spectacle which was sufficiently amazing, though he failed to +interpret it accurately. It was quite manifest that Saturn did not +exhibit a simple circular disc like Jupiter, or like Mars. It seemed +to Galileo as if the planet consisted of three bodies, a large globe +in the centre, and a smaller one on each side. The enigmatical +nature of the discovery led Galileo to announce it in an enigmatical +manner. He published a string of letters which, when duly +transposed, made up a sentence which affirmed that the planet Saturn +was threefold. Of course we now know that this remarkable appearance +of the planet was due to the two projecting portions of the ring. +With the feeble power of Galileo's telescope, these seemed merely +like small globes or appendages to the large central body.</p> + +<p>The last of Galileo's great astronomical discoveries related to the +libration of the moon. I think that the detection of this phenomenon +shows his acuteness of observation more remarkably than does any one +of his other achievements with the telescope. It is well known that +the moon constantly keeps the same face turned towards the earth. +When, however, careful measurements have been made with regard to the +spots and marks on the lunar surface, it is found that there is a +slight periodic variation which permits us to see now a little to the +east or to the west, now a little to the north or to the south of +the average lunar disc.</p> + +<p>But the circumstances which make the career of Galileo so especially +interesting from the biographer's point of view, are hardly so much +the triumphs that he won as the sufferings that he endured. The +sufferings and the triumphs were, however, closely connected, and it +is fitting that we should give due consideration to what was perhaps +the greatest drama in the history of science.</p> + +<p>On the appearance of the immortal work of Copernicus, in which it was +taught that the earth rotated on its axis, and that the earth, like +the other planets, revolved round the sun, orthodoxy stood aghast. +The Holy Roman Church submitted this treatise, which bore the name +"De Revolutionibus Orbium Coelestium," to the Congregation of the +Index. After due examination it was condemned as heretical in 1615. +Galileo was suspected, on no doubt excellent grounds, of entertaining +the objectionable views of Copernicus. He was accordingly privately +summoned before Cardinal Bellarmine on 26th February 1616, and duly +admonished that he was on no account to teach or to defend the +obnoxious doctrines. Galileo was much distressed by this +intimation. He felt it a serious matter to be deprived of the +privilege of discoursing with his friends about the Copernican +system, and of instructing his disciples in the principles of the +great theory of whose truth he was perfectly convinced. It pained +him, however, still more to think, devout Catholic as he was, that +such suspicions of his fervent allegiance to his Church should ever +have existed, as were implied by the words and monitions of Cardinal +Bellarmine.</p> + +<p>In 1616, Galileo had an interview with Pope Paul V., who received the +great astronomer very graciously, and walked up and down with him in +conversation for three-quarters of an hour. Galileo complained to +his Holiness of the attempts made by his enemies to embarrass him +with the authorities of the Church, but the Pope bade him be +comforted. His Holiness had himself no doubts of Galileo's +orthodoxy, and he assured him that the Congregation of the Index +should give Galileo no further trouble so long as Paul V. was in the +chair of St. Peter.</p> + +<p>On the death of Paul V. in 1623, Maffeo Barberini was elected Pope, +as Urban VIII. This new Pope, while a cardinal, had been an intimate +friend of Galileo's, and had indeed written Latin verses in praise of +the great astronomer and his discoveries. It was therefore not +unnatural for Galileo to think that the time had arrived when, with +the use of due circumspection, he might continue his studies and his +writings, without fear of incurring the displeasure of the Church. +Indeed, in 1624, one of Galileo's friends writing from Rome, urges +Galileo to visit the city again, and added that—</p> + +<p>"Under the auspices of this most excellent, learned, and benignant +Pontiff, science must flourish. Your arrival will be welcome to his +Holiness. He asked me if you were coming, and when, and in short, he +seems to love and esteem you more than ever."</p> + +<p>The visit was duly paid, and when Galileo returned to Florence, the +Pope wrote a letter from which the following is an extract, +commanding the philosopher to the good offices of the young +Ferdinand, who had shortly before succeeded his father in the Grand +Duchy of Tuscany.</p> + +<p>"We find in Galileo not only literary distinction, but also the love +of piety, and he is also strong in those qualities by which the +pontifical good-will is easily obtained. And now, when he has been +brought to this city to congratulate us on our elevation, we have +very lovingly embraced him; nor can we suffer him to return to the +country whither your liberality calls him, without an ample provision +of pontifical love. And that you may know how dear he is to us, we +have willed to give him this honourable testimonial of virtue and +piety. And we further signify that every benefit which you shall +confer upon him, imitating or even surpassing your father's +liberality, will conduce to our gratification."</p> + +<p>The favourable reception which had been accorded to him by Pope Urban +VIII. seems to have led Galileo to expect that there might be some +corresponding change in the attitude of the Papal authorities on the +great question of the stability of the earth. He accordingly +proceeded with the preparation of the chief work of his life, "The +Dialogue of the two Systems." It was submitted for inspection by the +constituted authorities. The Pope himself thought that, if a few +conditions which he laid down were duly complied with, there could be +no objection to the publication of the work. In the first place, the +title of the book was to be so carefully worded as to show plainly +that the Copernican doctrine was merely to be regarded as an +hypothesis, and not as a scientific fact. Galileo was also +instructed to conclude the book with special arguments which had been +supplied by the Pope himself, and which appeared to his Holiness to +be quite conclusive against the new doctrine of Copernicus.</p> + +<p>Formal leave for the publication of the Dialogue was then given to +Galileo by the Inquisitor General, and it was accordingly sent to the +press. It might be thought that the anxieties of the astronomer +about his book would then have terminated. As a matter of fact, they +had not yet seriously begun. Riccardi, the Master of the Sacred +Palace, having suddenly had some further misgivings, sent to Galileo +for the manuscript while the work was at the printer's, in order that +the doctrine it implied might be once again examined. Apparently, +Riccardi had come to the conclusion that he had not given the matter +sufficient attention, when the authority to go to press had been +first and, perhaps, hastily given. Considerable delay in the issue +of the book was the result of these further deliberations. At last, +however, in June, 1632, Galileo's great work, "The Dialogue of the +two Systems," was produced for the instruction of the world, though +the occasion was fraught with ruin to the immortal author.</p> + +<p><a name="facsimile" id="facsimile"></a></p> + +<div class="figcenter" style="width: 297px;"> +<a href="images/ill_sketch_lunar_sfc.jpg"> +<img src="images/ill_sketch_lunar_sfc_sml.jpg" width="297" height="294" alt="FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO." title="" /></a> +<span class="caption">FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.</span> +</div> + +<p>The book, on its publication, was received and read with the greatest +avidity. But presently the Master of The Sacred Palace found reason +to regret that he had given his consent to its appearance. He +accordingly issued a peremptory order to sequestrate every copy in +Italy. This sudden change in the Papal attitude towards Galileo +formed the subject of a strong remonstrance addressed to the Roman +authorities by the Grand Duke of Tuscany. The Pope himself seemed to +have become impressed all at once with the belief that the work +contained matter of an heretical description. The general +interpretation put upon the book seems to have shown the authorities +that they had mistaken its true tendency, notwithstanding the fact +that it had been examined again and again by theologians deputed for +the duty. To the communication from the Grand Duke the Pope returned +answer, that he had decided to submit the book to a congregation of +"learned, grave, and saintly men," who would weigh every word in it. +The views of his Holiness personally on the subject were expressed in +his belief that the Dialogue contained the most perverse matter that +could come into a reader's hands.</p> + +<p>The Master of the Sacred Palace was greatly blamed by the authorities +for having given his sanction to its issue. He pleaded that the book +had not been printed in the precise terms of the original manuscript +which had been submitted to him. It was also alleged that Galileo +had not adhered to his promise of inserting properly the arguments +which the Pope himself had given in support of the old and orthodox +view. One of these had, no doubt, been introduced, but, so far from +mending Galileo's case, it had made matters really look worse for the +poor philosopher. The Pope's argument had been put into the mouth of +one of the characters in the Dialogue named "Simplicio." Galileo's +enemies maintained that by adopting such a method for the expression +of his Holiness's opinion, Galileo had intended to hold the Pope +himself up to ridicule. Galileo's friends maintained that nothing +could have been farther from his intention. It seems, however, +highly probable that the suspicions thus aroused had something to say +to the sudden change of front on the part of the Papal authorities.</p> + +<p>On 1st October, 1632, Galileo received an order to appear before the +Inquisition at Rome on the grave charge of heresy. Galileo, of +course, expressed his submission, but pleaded for a respite from +compliance with the summons, on the ground of his advanced age and +his failing health. The Pope was, however, inexorable; he said that +he had warned Galileo of his danger while he was still his friend. +The command could not be disobeyed. Galileo might perform the +journey as slowly as he pleased, but it was imperatively necessary +for him to set forth and at once.</p> + +<p>On 20th January, 1633, Galileo started on his weary journey to Rome, +in compliance with this peremptory summons. On 13th February he was +received as the guest of Niccolini, the Tuscan ambassador, who had +acted as his wise and ever-kind friend throughout the whole affair. +It seemed plain that the Holy Office were inclined to treat Galileo +with as much clemency and consideration as was consistent with the +determination that the case against him should be proceeded with to +the end. The Pope intimated that in consequence of his respect for +the Grand Duke of Tuscany he should permit Galileo to enjoy the +privilege, quite unprecedented for a prisoner charged with heresy, of +remaining as an inmate in the ambassador's house. He ought, +strictly, to have been placed in the dungeons of the Inquisition. +When the examination of the accused had actually commenced, Galileo +was confined, not, indeed, in the dungeons, but in comfortable rooms +at the Holy Office.</p> + +<p>By the judicious and conciliatory language of submission which +Niccolini had urged Galileo to use before the Inquisitors, they were +so far satisfied that they interceded with the Pope for his release. +During the remainder of the trial Galileo was accordingly permitted +to go back to the ambassador's, where he was most heartily welcomed. +Sister Maria Celeste, evidently thinking this meant that the whole +case was at an end, thus expresses herself:—</p> + +<p>"The joy that your last dear letter brought me, and the having to +read it over and over to the nuns, who made quite a jubilee on +hearing its contents, put me into such an excited state that at last +I got a severe attack of headache."</p> + +<p>In his defence Galileo urged that he had already been acquitted in +1616 by Cardinal Bellarmine, when a charge of heresy was brought +against him, and he contended that anything he might now have done, +was no more than he had done on the preceding occasion, when the +orthodoxy of his doctrines received solemn confirmation. The +Inquisition seemed certainly inclined to clemency, but the Pope was +not satisfied. Galileo was accordingly summoned again on the 21st +June. He was to be threatened with torture if he did not forthwith +give satisfactory explanations as to the reasons which led him to +write the Dialogue. In this proceeding the Pope assured the Tuscan +ambassador that he was treating Galileo with the utmost consideration +possible in consequence of his esteem and regard for the Grand Duke, +whose servant Galileo was. It was, however, necessary that some +exemplary punishment be meted out to the astronomer, inasmuch as by +the publication of the Dialogue he had distinctly disobeyed the +injunction of silence laid upon him by the decree of 1616. Nor was +it admissible for Galileo to plead that his book had been sanctioned +by the Master of the Sacred College, to whose inspection it had been +again and again submitted. It was held, that if the Master of the +Sacred College had been unaware of the solemn warning the philosopher +had already received sixteen years previously, it was the duty of +Galileo to have drawn his attention to that fact.</p> + +<p>On the 22nd June, 1633, Galileo was led to the great hall of the +Inquisition, and compelled to kneel before the cardinals there +assembled and hear his sentence. In a long document, most +elaborately drawn up, it is definitely charged against Galileo that, +in publishing the Dialogue, he committed the essentially grave error +of treating the doctrine of the earth's motion as open to +discussion. Galileo knew, so the document affirmed, that the Church +had emphatically pronounced this notion to be contrary to Holy Writ, +and that for him to consider a doctrine so stigmatized as having any +shadow of probability in its favour was an act of disrespect to the +authority of the Church which could not be overlooked. It was also +charged against Galileo that in his Dialogue he has put the strongest +arguments into the mouth, not of those who supported the orthodox +doctrine, but of those who held the theory as to the earth's motion +which the Church had so deliberately condemned.</p> + +<p>After due consideration of the defence made by the prisoner, it was +thereupon decreed that he had rendered himself vehemently suspected +of heresy by the Holy Office, and in consequence had incurred all the +censures and penalties of the sacred canons, and other decrees +promulgated against such persons. The graver portion of these +punishments would be remitted, if Galileo would solemnly repudiate +the heresies referred to by an abjuration to be pronounced by him in +the terms laid down.</p> + +<p>At the same time it was necessary to mark, in some emphatic manner, +the serious offence which had been committed, so that it might serve +both as a punishment to Galileo and as a warning to others. It was +accordingly decreed that he should be condemned to imprisonment in +the Holy Office during the pleasure of the Papal authorities, and +that he should recite once a week for three years the seven +Penitential Psalms.</p> + +<p>Then followed that ever-memorable scene in the great hall of the +Inquisition, in which the aged and infirm Galileo, the inventor of +the telescope and the famous astronomer, knelt down to abjure before +the most eminent and reverend Lords Cardinal, Inquisitors General +throughout the Christian Republic against heretical depravity. With +his hands on the Gospels, Galileo was made to curse and detest the +false opinion that the sun was the centre of the universe and +immovable, and that the earth was not the centre of the same, and +that it moved. He swore that for the future he will never say nor +write such things as may bring him under suspicion, and that if he +does so he submits to all the pains and penalties of the sacred +canons. This abjuration was subsequently read in Florence before +Galileo's disciples, who had been specially summoned to attend.</p> + +<p>It has been noted that neither on the first occasion, in 1616, nor on +the second in 1633, did the reigning Pope sign the decrees concerning +Galileo. The contention has accordingly been made that Paul V. and +Urban VIII. are both alike vindicated from any technical +responsibility for the attitude of the Romish Church towards the +Copernican doctrines. The significance of this circumstance has been +commented on in connection with the doctrine of the infallibility of +the Pope.</p> + +<p>We can judge of the anxiety felt by Sister Maria Celeste about her +beloved father during these terrible trials. The wife of the +ambassador Niccolini, Galileo's steadfast friend, most kindly wrote +to give the nun whatever quieting assurances the case would permit. +There is a renewed flow of these touching epistles from the daughter +to her father. Thus she sends word—</p> + +<p>"The news of your fresh trouble has pierced my soul with grief all +the more that it came quite unexpectedly."</p> + +<p>And again, on hearing that he had been permitted to leave Rome, +she writes—</p> + +<p>"I wish I could describe the rejoicing of all the mothers and sisters +on hearing of your happy arrival at Siena. It was indeed most +extraordinary. On hearing the news the Mother Abbess and many of the +nuns ran to me, embracing me and weeping for joy and tenderness."</p> + +<p>The sentence of imprisonment was at first interpreted leniently by +the Pope. Galileo was allowed to reside in qualified durance in the +archbishop's house at Siena. Evidently the greatest pain that he +endured arose from the forced separation from that daughter, whom he +had at last learned to love with an affection almost comparable with +that she bore to him. She had often told him that she never had any +pleasure equal to that with which she rendered any service to her +father. To her joy, she discovers that she can relieve him from the +task of reciting the seven Penitential Psalms which had been imposed +as a Penance:—</p> + +<p>"I began to do this a while ago," she writes, "and it gives me much +pleasure. First, because I am persuaded that prayer in obedience to +Holy Church must be efficacious; secondly, in order to save you the +trouble of remembering it. If I had been able to do more, most +willingly would I have entered a straiter prison than the one I live +in now, if by so doing I could have set you at liberty."</p> + +<p><a name="crest" id="crest"></a></p> + +<div class="figcenter" style="width: 281px;"> +<a href="images/ill_fm_crest_galileo.jpg"> +<img src="images/ill_fm_crest_galileo_sml.jpg" width="281" height="258" alt="CREST OF GALILEO'S FAMILY." title="" /></a> +<span class="caption">CREST OF GALILEO'S FAMILY.</span> +</div> + +<p>Sister Maria Celeste was gradually failing in health, but the great +privilege was accorded to her of being able once again to embrace her +beloved lord and master. Galileo had, in fact, been permitted to +return to his old home; but on the very day when he heard of his +daughter's death came the final decree directing him to remain in his +own house in perpetual solitude.</p> + +<p>Amid the advancing infirmities of age, the isolation from friends, +and the loss of his daughter, Galileo once again sought consolation +in hard work. He commenced his famous dialogue on Motion. Gradually, +however, his sight began to fail, and blindness was at last added to +his other troubles. On January 2nd, 1638, he writes to Diodati:—</p> + +<p>"Alas, your dear friend and servant, Galileo, has been for the last +month perfectly blind, so that this heaven, this earth, this universe +which I by my marvellous discoveries and clear demonstrations have +enlarged a hundred thousand times beyond the belief of the wise men +of bygone ages, henceforward is for me shrunk into such a small space +as is filled by my own bodily sensations."</p> + +<p>But the end was approaching—the great philosopher, was attacked by +low fever, from which he died on the 8th January, 1643.</p> + +<h3><a name="KEPLER" id="KEPLER"></a>KEPLER.</h3> +<p>While the illustrious astronomer, Tycho Brahe, lay on his death-bed, +he had an interview which must ever rank as one of the important +incidents in the history of science. The life of Tycho had been +passed, as we have seen, in the accumulation of vast stores of +careful observations of the positions of the heavenly bodies. It was +not given to him to deduce from his splendid work the results to +which they were destined to lead. It was reserved for another +astronomer to distil, so to speak, from the volumes in which Tycho's +figures were recorded, the great truths of the universe which those +figures contained. Tycho felt that his work required an interpreter, +and he recognised in the genius of a young man with whom he was +acquainted the agent by whom the world was to be taught some of the +great truths of nature. To the bedside of the great Danish +astronomer the youthful philosopher was summoned, and with his last +breath Tycho besought of him to spare no labour in the performance of +those calculations, by which alone the secrets of the movements of +the heavens could be revealed. The solemn trust thus imposed was +duly accepted, and the man who accepted it bore the immortal name of +Kepler.</p> + +<p>Kepler was born on the 27th December, 1571, at Weil, in the Duchy of +Wurtemberg. It would seem that the circumstances of his childhood +must have been singularly unhappy. His father, sprung from a +well-connected family, was but a shiftless and idle adventurer; nor +was the great astronomer much more fortunate in his other parent. His +mother was an ignorant and ill-tempered woman; indeed, the +ill-assorted union came to an abrupt end through the desertion of the +wife by her husband when their eldest son John, the hero of our +present sketch, was eighteen years old. The childhood of this lad, +destined for such fame, was still further embittered by the +circumstance that when he was four years old he had a severe attack +of small-pox. Not only was his eyesight permanently injured, but +even his constitution appears to have been much weakened by this +terrible malady.</p> + +<p>It seems, however, that the bodily infirmities of young John Kepler +were the immediate cause of his attention being directed to the +pursuit of knowledge. Had the boy been fitted like other boys for +ordinary manual work, there can be hardly any doubt that to manual +work his life must have been devoted. But, though his body was +feeble, he soon gave indications of the possession of considerable +mental power. It was accordingly thought that a suitable sphere for +his talents might be found in the Church which, in those days, was +almost the only profession that afforded an opening for an +intellectual career. We thus find that by the time John Kepler was +seventeen years old he had attained a sufficient standard of +knowledge to entitle him to admission on the foundation of the +University at Tubingen.</p> + +<p>In the course of his studies at this institution he seems to have +divided his attention equally between astronomy and divinity. It not +unfrequently happens that when a man has attained considerable +proficiency in two branches of knowledge he is not able to see very +clearly in which of the two pursuits his true vocation lies. His +friends and onlookers are often able to judge more wisely than he +himself can do as to which of the two lines it would be better for +him to pursue. This incapacity for perceiving the path in which +greatness awaited him, existed in the case of Kepler. Personally, he +inclined to enter the ministry, in which a promising career seemed +open to him. He yielded, however, to friends, who evidently knew him +better than he knew himself, and accepted in 1594, the important +Professorship of astronomy which had been offered to him in the +University of Gratz.</p> + +<p>It is difficult for us in these modern days to realise the somewhat +extraordinary duties which were expected from an astronomical +professor in the sixteenth century. He was, of course, required to +employ his knowledge of the heavens in the prediction of eclipses, +and of the movements of the heavenly bodies generally. This seems +reasonable enough; but what we are not prepared to accept is the +obligation which lay on the astronomers to predict the fates of +nations and the destinies of individuals.</p> + +<p>It must be remembered that it was the almost universal belief in +those days, that all the celestial spheres revolved in some +mysterious fashion around the earth, which appeared by far the most +important body in the universe. It was imagined that the sun, the +moon, and the stars indicated, in the vicissitudes of their +movements, the careers of nations and of individuals. Such being the +generally accepted notion, it seemed to follow that a professor who +was charged with the duty of expounding the movements of the heavenly +bodies must necessarily be looked to for the purpose of deciphering +the celestial decrees regarding the fate of man which the heavenly +luminaries were designed to announce.</p> + +<p>Kepler threw himself with characteristic ardour into even this +fantastic phase of the labours of the astronomical professor; he +diligently studied the rules of astrology, which the fancies of +antiquity had compiled. Believing sincerely as he did in the +connection between the aspect of the stars and the state of human +affairs, he even thought that he perceived, in the events of his own +life, a corroboration of the doctrine which affirmed the influence of +the planets upon the fate of individuals.</p> + +<p><a name="solids" id="solids"></a></p> + +<div class="figcenter" style="width: 276px;"> +<a href="images/ill_kepler_solids.jpg"> +<img src="images/ill_kepler_solids_sml.jpg" width="276" height="257" alt="KEPLER'S SYSTEM OF REGULAR SOLIDS." title="" /></a> +<span class="caption">KEPLER'S SYSTEM OF REGULAR SOLIDS.</span> +</div> + +<p>But quite independently of astrology there seem to have been many +other delusions current among the philosophers of Kepler's time. It +is now almost incomprehensible how the ablest men of a few centuries +ago should have entertained such preposterous notions, as they did, +with respect to the system of the universe. As an instance of what +is here referred to, we may cite the extraordinary notion which, +under the designation of a discovery, first brought Kepler into +fame. Geometers had long known that there were five, but no more +than five, regular solid figures. There is, for instance, the cube +with six sides, which is, of course, the most familiar of these +solids. Besides the cube there are other figures of four, eight, +twelve, and twenty sides respectively. It also happened that there +were five planets, but no more than five, known to the ancients, +namely, Mercury, Venus, Mars, Jupiter, and Saturn. To Kepler's +lively imaginations this coincidence suggested the idea that the five +regular solids corresponded to the five planets, and a number of +fancied numerical relations were adduced on the subject. The +absurdity of this doctrine is obvious enough, especially when we +observe that, as is now well known, there are two large planets, and +a host of small planets, over and above the magical number of the +regular solids. In Kepler's time, however, this doctrine was so far +from being regarded as absurd, that its announcement was hailed as a +great intellectual triumph. Kepler was at once regarded with +favour. It seems, indeed, to have been the circumstance which +brought him into correspondence with Tycho Brahe. By its means also +he became known to Galileo.</p> + +<p>The career of a scientific professor in those early days appears +generally to have been marked by rather more striking vicissitudes +than usually befall a professor in a modern university. Kepler was a +Protestant, and as such he had been appointed to his professorship at +Gratz. A change, however, having taken place in the religious belief +entertained by the ruling powers of the University, the Protestant +professors were expelled. It seems that special influence having +been exerted in Kepler's case on account of his exceptional eminence, +he was recalled to Gratz and reinstated in the tenure of his chair. +But his pupils had vanished, so that the great astronomer was glad to +accept a post offered him by Tycho Brahe in the observatory which the +latter had recently established near Prague.</p> + +<p>On Tycho's death, which occurred soon after, an opening presented +itself which gave Kepler the opportunity his genius demanded. He was +appointed to succeed Tycho in the position of imperial mathematician. +But a far more important point, both for Kepler and for science, +was that to him was confided the use of Tycho's observations. It was, +indeed, by the discussion of Tycho's results that Kepler was enabled +to make the discoveries which form such an important part of +astronomical history.</p> + +<p>Kepler must also be remembered as one of the first great astronomers +who ever had the privilege of viewing celestial bodies through a +telescope. It was in 1610 that he first held in his hands one of +those little instruments which had been so recently applied to the +heavens by Galileo. It should, however, be borne in mind that the +epoch-making achievements of Kepler did not arise from any telescopic +observations that he made, or, indeed, that any one else made. They +were all elaborately deduced from Tycho's measurements of the +positions of the planets, obtained with his great instruments, which +were unprovided with telescopic assistance.</p> + +<p>To realise the tremendous advance which science received from +Kepler's great work, it is to be understood that all the astronomers +who laboured before him at the difficult subject of the celestial +motions, took it for granted that the planets must revolve in +circles. If it did not appear that a planet moved in a fixed circle, +then the ready answer was provided by Ptolemy's theory that the +circle in which the planet did move was itself in motion, so that its +centre described another circle.</p> + +<p>When Kepler had before him that wonderful series of observations of +the planet, Mars, which had been accumulated by the extraordinary +skill of Tycho, he proved, after much labour, that the movements of +the planet refused to be represented in a circular form. Nor would +it do to suppose that Mars revolved in one circle, the centre of +which revolved in another circle. On no such supposition could the +movements of the planets be made to tally with those which Tycho had +actually observed. This led to the astonishing discovery of the true +form of a planet's orbit. For the first time in the history of +astronomy the principle was laid down that the movement of a planet +could not be represented by a circle, nor even by combinations of +circles, but that it could be represented by an elliptic path. In +this path the sun is situated at one of those two points in the +ellipse which are known as its foci.</p> + +<p><a name="kepler_ill" id="kepler_ill"></a></p> + +<div class="figcenter" style="width: 425px;"> +<a href="images/ill_kepler.jpg"> +<img src="images/ill_kepler_sml.jpg" width="425" height="526" alt="KEPLER." title="" /></a> +<span class="caption">KEPLER.</span> +</div> + +<p>Very simple apparatus is needed for the drawing of one of those +ellipses which Kepler has shown to possess such astonishing +astronomical significance. Two pins are stuck through a sheet of +paper on a board, the point of a pencil is inserted in a loop of +string which passes over the pins, and as the pencil is moved round +in such a way as to keep the string stretched, that beautiful curve +known as the ellipse is delineated, while the positions of the pins +indicate the two foci of the curve. If the length of the loop of +string is unchanged then the nearer the pins are together, the +greater will be the resemblance between the ellipse and the circle, +whereas the more the pins are separated the more elongated does the +ellipse become. The orbit of a great planet is, in general, one of +those ellipses which approaches a nearly circular form. It +fortunately happens, however, that the orbit of Mars makes a wider +departure from the circular form than any of the other important +planets. It is, doubtless, to this circumstance that we must +attribute the astonishing success of Kepler in detecting the true +shape of a planetary orbit. Tycho's observations would not have been +sufficiently accurate to have exhibited the elliptic nature of a +planetary orbit which, like that of Venus, differed very little from +a circle.</p> + +<p>The more we ponder on this memorable achievement the more striking +will it appear. It must be remembered that in these days we know of +the physical necessity which requires that a planet shall revolve in +an ellipse and not in any other curve. But Kepler had no such +knowledge. Even to the last hour of his life he remained in +ignorance of the existence of any natural cause which ordained that +planets should follow those particular curves which geometers know so +well. Kepler's assignment of the ellipse as the true form of the +planetary orbit is to be regarded as a brilliant guess, the truth of +which Tycho's observations enabled him to verify. Kepler also +succeeded in pointing out the law according to which the velocity of +a planet at different points of its path could be accurately +specified. Here, again, we have to admire the sagacity with which +this marvellously acute astronomer guessed the deep truth of nature. +In this case also he was quite unprovided with any reason for +expecting from physical principles that such a law as he discovered +must be obeyed. It is quite true that Kepler had some slight +knowledge of the existence of what we now know as gravitation. He +had even enunciated the remarkable doctrine that the ebb and flow of +the tide must be attributed to the attraction of the moon on the +waters of the earth. He does not, however, appear to have had any +anticipation of those wonderful discoveries which Newton was destined +to make a little later, in which he demonstrated that the laws +detected by Kepler's marvellous acumen were necessary consequences of +the principle of universal gravitation.</p> + +<p><a name="symbolical" id="symbolical"></a></p> + +<div class="figcenter" style="width: 320px;"> +<a href="images/ill_symbolic_planetary_system.jpg"> +<img src="images/ill_symbolic_planetary_system_sml.jpg" width="320" height="362" alt="SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM." title="" /></a> +<span class="caption">SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.</span> +</div> + +<p>To appreciate the relations of Kepler and Tycho it is necessary to +note the very different way in which these illustrious astronomers +viewed the system of the heavens. It should be observed that +Copernicus had already expounded the true system, which located the +sun at the centre of the planetary system. But in the days of Tycho +Brahe this doctrine had not as yet commanded universal assent. In +fact, the great observer himself did not accept the new views of +Copernicus. It appeared to Tycho that the earth not only appeared to +be the centre of things celestial, but that it actually was the +centre. It is, indeed, not a little remarkable that a student of the +heavens so accurate as Tycho should have deliberately rejected the +Copernican doctrine in favour of the system which now seems so +preposterous. Throughout his great career, Tycho steadily observed +the places of the sun, the moon, and the planets, and as steadily +maintained that all those bodies revolved around the earth fixed in +the centre. Kepler, however, had the advantage of belonging to the +new school. He utilised the observations of Tycho in developing the +great Copernican theory whose teaching Tycho stoutly resisted.</p> + +<p>Perhaps a chapter in modern science may illustrate the intellectual +relation of these great men. The revolution produced by Copernicus +in the doctrine of the heavens has often been likened to the +revolution which the Darwinian theory produced in the views held by +biologists as to life on this earth. The Darwinian theory did not at +first command universal assent even among those naturalists whose +lives had been devoted with the greatest success to the study of +organisms. Take, for instance, that great naturalist, Professor +Owen, by whose labours vast extension has been given to our knowledge +of the fossil animals which dwelt on the earth in past ages. Now, +though Owens researches were intimately connected with the great +labours of Darwin, and afforded the latter material for his +epoch-making generalization, yet Owen deliberately refused to accept +the new doctrines. Like Tycho, he kept on rigidly accumulating his +facts under the influence of a set of ideas as to the origin of +living forms which are now universally admitted to be erroneous. If, +therefore, we liken Darwin to Copernicus, and Owen to Tycho, we may +liken the biologists of the present day to Kepler, who interpreted +the results of accurate observation upon sound theoretical +principles.</p> + +<p>In reading the works of Kepler in the light of our modern knowledge +we are often struck by the extent to which his perception of the +sublimest truths in nature was associated with the most extravagant +errors and absurdities. But, of course, it must be remembered that +he wrote in an age in which even the rudiments of science, as we now +understand it, were almost entirely unknown.</p> + +<p>It may well be doubted whether any joy experienced by mortals is more +genuine than that which rewards the successful searcher after natural +truths. Every science-worker, be his efforts ever so humble, will be +able to sympathise with the enthusiastic delight of Kepler when at +last, after years of toil, the glorious light broke forth, and that +which he considered to be the greatest of his astonishing laws first +dawned upon him. Kepler rightly judged that the number of days which +a planet required to perform its voyage round the sun must be +connected in some manner with the distance from the planet to the +sun; that is to say, with the radius of the planet's orbit, inasmuch +as we may for our present object regard the planet's orbit as +circular.</p> + +<p>Here, again, in his search for the unknown law, Kepler had no +accurate dynamical principles to guide his steps. Of course, we now +know not only what the connection between the planet's distance and +the planet's periodic time actually is, but we also know that it is a +necessary consequence of the law of universal gravitation. Kepler, +it is true, was not without certain surmises on the subject, but they +were of the most fanciful description. His notions of the planets, +accurate as they were in certain important respects, were mixed up +with vague ideas as to the properties of metals and the geometrical +relations of the regular solids. Above all, his reasoning was +penetrated by the supposed astrological influences of the stars and +their significant relation to human fate. Under the influence of +such a farrago of notions, Kepler resolved to make all sorts of +trials in his search for the connection between the distance of a +planet from the sun and the time in which the revolution of that +planet was accomplished.</p> + +<p>It was quite easily demonstrated that the greater the distance of the +planet from the sun the longer was the time required for its +journey. It might have been thought that the time would be directly +proportional to the distance. It was, however, easy to show that +this supposition did not agree with the fact. Finding that this +simple relation would not do, Kepler undertook a vast series of +calculations to find out the true method of expressing the +connection. At last, after many vain attempts, he found, to his +indescribable joy, that the square of the time in which a planet +revolves around the sun was proportional to the cube of the average +distance of the planet from that body.</p> + +<p>The extraordinary way in which Kepler's views on celestial matters +were associated with the wildest speculations, is well illustrated in +the work in which he propounded his splendid discovery just referred +to. The announcement of the law connecting the distances of the +planets from the sun with their periodic times, was then mixed up +with a preposterous conception about the properties of the different +planets. They were supposed to be associated with some profound +music of the spheres inaudible to human ears, and performed only for +the benefit of that being whose soul formed the animating spirit of +the sun.</p> + +<p>Kepler was also the first astronomer who ever ventured to predict the +occurrence of that remarkable phenomenon, the transit of a planet in +front of the sun's disc. He published, in 1629, a notice to the +curious in things celestial, in which he announced that both of the +planets, Mercury and Venus, were to make a transit across the sun on +specified days in the winter of 1631. The transit of Mercury was +duly observed by Gassendi, and the transit of Venus also took place, +though, as we now know, the circumstances were such that it was not +possible for the phenomenon to be witnessed by any European +astronomer.</p> + +<p>In addition to Kepler's discoveries already mentioned, with which his +name will be for ever associated, his claim on the gratitude of +astronomers chiefly depends on the publication of his famous +Rudolphine tables. In this remarkable work means are provided for +finding the places of the planets with far greater accuracy than had +previously been attainable.</p> + +<p>Kepler, it must be always remembered, was not an astronomical +observer. It was his function to deal with the observations made by +Tycho, and, from close study and comparison of the results, to work +out the movements of the heavenly bodies. It was, in fact, Tycho who +provided as it were the raw material, while it was the genius of +Kepler which wrought that material into a beautiful and serviceable +form. For more than a century the Rudolphine tables were regarded as +a standard astronomical work. In these days we are accustomed to +find the movements of the heavenly bodies set forth with all +desirable exactitude in the NAUTICAL ALMANACK, and the similar +publication issued by foreign Governments. Let it be remembered that +it was Kepler who first imparted the proper impulse in this +direction.</p> + +<p><a name="commemoration" id="commemoration"></a></p> + +<div class="figcenter" style="width: 447px;"> +<a href="images/ill_commemoration_rudolphine_tables.jpg"> +<img src="images/ill_commemoration_rudolphine_tables_sml.jpg" width="447" height="692" alt="THE COMMEMORATION OF THE RUDOLPHINE TABLES." title="" /></a> +<span class="caption">THE COMMEMORATION OF THE RUDOLPHINE TABLES.</span> +</div> + +<p>When Kepler was twenty-six he married an heiress from Styria, who, +though only twenty-three years old, had already had some experience +in matrimony. Her first husband had died; and it was after her +second husband had divorced her that she received the addresses of +Kepler. It will not be surprising to hear that his domestic affairs +do not appear to have been particularly happy, and his wife died in +1611. Two years later, undeterred by the want of success in his +first venture, he sought a second partner, and he evidently +determined not to make a mistake this time. Indeed, the methodical +manner in which he made his choice of the lady to whom he should +propose has been duly set forth by him and preserved for our +edification. With some self-assurance he asserts that there were no +fewer than eleven spinsters desirous of sharing his joys and +sorrows. He has carefully estimated and recorded the merits and +demerits of each of these would-be brides. The result of his +deliberations was that he awarded himself to an orphan girl, +destitute even of a portion. Success attended his choice, and his +second marriage seems to have proved a much more suitable union than +his first. He had five children by the first wife and seven by the +second.</p> + +<p>The years of Kepler's middle life were sorely distracted by a trouble +which, though not uncommon in those days, is one which we find it +difficult to realise at the present time. His mother, Catherine +Kepler, had attained undesirable notoriety by the suspicion that she +was guilty of witchcraft. Years were spent in legal investigations, +and it was only after unceasing exertions on the part of the +astronomer for upwards of a twelve-month that he was finally able to +procure her acquittal and release from prison.</p> + +<p>It is interesting for us to note that at one time there was a +proposal that Kepler should forsake his native country and adopt +England as a home. It arose in this wise. The great man was +distressed throughout the greater part of his life by pecuniary +anxieties. Finding him in a strait of this description, the English +ambassador in Venice, Sir Henry Wotton, in the year 1620, besought +Kepler to come over to England, where he assured him that he would +obtain a favourable reception, and where, he was able to add, +Kepler's great scientific work was already highly esteemed. But his +efforts were unavailing; Kepler would not leave his own country. He +was then forty-nine years of age, and doubtless a home in a foreign +land, where people spoke a strange tongue, had not sufficient +attraction for him, even when accompanied with the substantial +inducements which the ambassador was able to offer. Had Kepler +accepted this invitation, he would, in transferring his home to +England, have anticipated the similar change which took place in the +career of another great astronomer two centuries later. It will be +remembered that Herschel, in his younger days, did transfer himself +to England, and thus gave to England the imperishable fame of +association with his triumphs.</p> + +<p>The publication of the Rudolphine tables of the celestial movements +entailed much expense. A considerable part of this was defrayed by +the Government at Venice but the balance occasioned no little trouble +and anxiety to Kepler. No doubt the authorities of those days were +even less willing to spend money on scientific matters than are the +Governments of more recent times. For several years the imperial +Treasury was importuned to relieve him from his anxieties. The +effects of so much worry, and of the long journeys which were +involved, at last broke down Kepler's health completely. As we have +already mentioned, he had never been strong from infancy, and he +finally succumbed to a fever in November, 1630, at the age of +fifty-nine. He was interred at St. Peter's Church at Ratisbon.</p> + +<p>Though Kepler had not those personal characteristics which have made +his great predecessor, Tycho Brahe, such a romantic figure, yet a +picturesque element in Kepler's character is not wanting. It was, +however, of an intellectual kind. His imagination, as well as his +reasoning faculties, always worked together. He was incessantly +prompted by the most extraordinary speculations. The great majority +of them were in a high degree wild and chimerical, but every now and +then one of his fancies struck right to the heart of nature, and an +immortal truth was brought to light.</p> + +<p>I remember visiting the observatory of one of our greatest modern +astronomers, and in a large desk he showed me a multitude of +photographs which he had attempted but which had not been successful, +and then he showed me the few and rare pictures which had succeeded, +and by which important truths had been revealed. With a felicity of +expression which I have often since thought of, he alluded to the +contents of the desk as the "chips." They were useless, but they +were necessary incidents in the truly successful work. So it is in +all great and good work. Even the most skilful man of science +pursues many a wrong scent. Time after time he goes off on some +track that plays him false. The greater the man's genius and +intellectual resource, the more numerous will be the ventures which +he makes, and the great majority of those ventures are certain to be +fruitless. They are in fact, the "chips." In Kepler's case the +chips were numerous enough. They were of the most extraordinary +variety and structure. But every now and then a sublime discovery +was made of such a character as to make us regard even the most +fantastic of Kepler's chips with the greatest veneration and respect.</p> + +<h3><a name="ISAAC_NEWTON" id="ISAAC_NEWTON"></a>ISAAC NEWTON.</h3> +<p>It was just a year after the death of Galileo, that an infant came +into the world who was christened Isaac Newton. Even the great fame +of Galileo himself must be relegated to a second place in comparison +with that of the philosopher who first expounded the true theory of +the universe.</p> + +<p>Isaac Newton was born on the 25th of December (old style), 1642, at +Woolsthorpe, in Lincolnshire, about a half-mile from Colsterworth, +and eight miles south of Grantham. His father, Mr. Isaac Newton, had +died a few months after his marriage to Harriet Ayscough, the +daughter of Mr. James Ayscough, of Market Overton, in Rutlandshire. +The little Isaac was at first so excessively frail and weakly that +his life was despaired of. The watchful mother, however, tended her +delicate child with such success that he seems to have thriven better +than might have been expected from the circumstances of his infancy, +and he ultimately acquired a frame strong enough to outlast the +ordinary span of human life.</p> + +<p>For three years they continued to live at Woolsthorpe, the widow's +means of livelihood being supplemented by the income from another +small estate at Sewstern, in a neighbouring part of Leicestershire.</p> + +<p><a name="woolsthorpe" id="woolsthorpe"></a></p> + +<div class="figcenter" style="width: 312px;"> +<a href="images/ill_woolsthorpe_manor.jpg"> +<img src="images/ill_woolsthorpe_manor_sml.jpg" width="312" height="185" alt="WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy." title="" /></a> +<span class="caption">WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy.</span> +</div> + +<p>In 1645, Mrs. Newton took as a second husband the Rev. Barnabas +Smith, and on moving to her new home, about a mile from Woolsthorpe, +she entrusted little Isaac to her mother, Mrs. Ayscough. In due +time we find that the boy was sent to the public school at Grantham, +the name of the master being Stokes. For the purpose of being near +his work, the embryo philosopher was boarded at the house of Mr. +Clark, an apothecary at Grantham. We learn from Newton himself that +at first he had a very low place in the class lists of the school, +and was by no means one of those model school-boys who find favour in +the eyes of the school-master by attention to Latin grammar. Isaac's +first incentive to diligent study seems to have been derived from the +circumstance that he was severely kicked by one of the boys who was +above him in the class. This indignity had the effect of stimulating +young Newton's activity to such an extent that he not only attained +the desired object of passing over the head of the boy who had +maltreated him, but continued to rise until he became the head of the +school.</p> + +<p>The play-hours of the great philosopher were devoted to pursuits very +different from those of most school-boys. His chief amusement was +found in making mechanical toys and various ingenious contrivances. +He watched day by day with great interest the workmen engaged in +constructing a windmill in the neighbourhood of the school, the +result of which was that the boy made a working model of the windmill +and of its machinery, which seems to have been much admired, as +indicating his aptitude for mechanics. We are told that Isaac also +indulged in somewhat higher flights of mechanical enterprise. He +constructed a carriage, the wheels of which were to be driven by the +hands of the occupant, while the first philosophical instrument he +made was a clock, which was actuated by water. He also devoted much +attention to the construction of paper kites, and his skill in this +respect was highly appreciated by his school-fellows. Like a true +philosopher, even at this stage he experimented on the best methods +of attaching the string, and on the proportions which the tail ought +to have. He also made lanthorns of paper to provide himself with +light as he walked to school in the dark winter mornings.</p> + +<p>The only love affair in Newton's life appears to have commenced while +he was still of tender years. The incidents are thus described in +Brewster's "Life of Newton," a work to which I am much indebted in +this chapter.</p> + +<p>"In the house where he lodged there were some female inmates, in +whose company he appears to have taken much pleasure. One of these, +a Miss Storey, sister to Dr. Storey, a physician at Buckminster, near +Colsterworth, was two or three years younger than Newton and to great +personal attractions she seems to have added more than the usual +allotment of female talent. The society of this young lady and her +companions was always preferred to that of his own school-fellows, +and it was one of his most agreeable occupations to construct for +them little tables and cupboards, and other utensils for holding +their dolls and their trinkets. He had lived nearly six years in the +same house with Miss Storey, and there is reason to believe that +their youthful friendship gradually rose to a higher passion; but the +smallness of her portion, and the inadequacy of his own fortune, +appear to have prevented the consummation of their happiness. Miss +Storey was afterwards twice married, and under the name of Mrs. +Vincent, Dr. Stukeley visited her at Grantham in 1727, at the age of +eighty-two, and obtained from her many particulars respecting the +early history of our author. Newton's esteem for her continued +unabated during his life. He regularly visited her when he went to +Lincolnshire, and never failed to relieve her from little pecuniary +difficulties which seem to have beset her family."</p> + +<p>The schoolboy at Grantham was only fourteen years of age when his +mother became a widow for the second time. She then returned to the +old family home at Woolsthorpe, bringing with her the three children +of her second marriage. Her means appear to have been somewhat +scanty, and it was consequently thought necessary to recall Isaac +from the school. His recently-born industry had been such that he +had already made good progress in his studies, and his mother hoped +that he would now lay aside his books, and those silent meditations +to which, even at this early age, he had become addicted. It was +expected that, instead of such pursuits, which were deemed quite +useless, the boy would enter busily into the duties of the farm and +the details of a country life. But before long it became manifest +that the study of nature and the pursuit of knowledge had such a +fascination for the youth that he could give little attention to +aught else. It was plain that he would make but an indifferent +farmer. He greatly preferred experimenting on his water-wheels to +looking after labourers, while he found that working at mathematics +behind a hedge was much more interesting than chaffering about the +price of bullocks in the market place. Fortunately for humanity his +mother, like a wise woman, determined to let her boy's genius have +the scope which it required. He was accordingly sent back to +Grantham school, with the object of being trained in the knowledge +which would fit him for entering the University of Cambridge.</p> + +<p><a name="trinity" id="trinity"></a></p> + +<div class="figcenter" style="width: 325px;"> +<a href="images/ill_trinity_college.jpg"> +<img src="images/ill_trinity_college_sml.jpg" width="325" height="410" alt="TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope." title="" /></a> +<span class="caption">TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope.</span> +</div> + +<p>It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen, +was enrolled as an undergraduate of Trinity College, Cambridge. +Little did those who sent him there dream that this boy was destined +to be the most illustrious student who ever entered the portals of +that great seat of learning. Little could the youth himself have +foreseen that the rooms near the gateway which he occupied would +acquire a celebrity from the fact that he dwelt in them, or that the +ante-chapel of his college was in good time to be adorned by that +noble statue, which is regarded as one of the chief art treasures of +Cambridge University, both on account of its intrinsic beauty and the +fact that it commemorates the fame of her most distinguished alumnus, +Isaac Newton, the immortal astronomer. Indeed, his advent at the +University seemed to have been by no means auspicious or brilliant. +His birth was, as we have seen, comparatively obscure, and though he +had already given indication of his capacity for reflecting on +philosophical matters, yet he seems to have been but ill-equipped +with the routine knowledge which youths are generally expected to +take with them to the Universities.</p> + +<p>From the outset of his college career, Newton's attention seems to +have been mainly directed to mathematics. Here he began to give +evidence of that marvellous insight into the deep secrets of nature +which more than a century later led so dispassionate a judge as +Laplace to pronounce Newton's immortal work as pre-eminent above all +the productions of the human intellect. But though Newton was one of +the very greatest mathematicians that ever lived, he was never a +mathematician for the mere sake of mathematics. He employed his +mathematics as an instrument for discovering the laws of nature. His +industry and genius soon brought him under the notice of the +University authorities. It is stated in the University records that +he obtained a Scholarship in 1664. Two years later we find that +Newton, as well as many residents in the University, had to leave +Cambridge temporarily on account of the breaking out of the plague. +The philosopher retired for a season to his old home at Woolsthorpe, +and there he remained until he was appointed a Fellow of Trinity +College, Cambridge, in 1667. From this time onwards, Newton's +reputation as a mathematician and as a natural philosopher steadily +advanced, so that in 1669, while still but twenty-seven years of age, +he was appointed to the distinguished position of Lucasian Professor +of Mathematics at Cambridge. Here he found the opportunity to +continue and develop that marvellous career of discovery which formed +his life's work.</p> + +<p>The earliest of Newton's great achievements in natural philosophy was +his detection of the composite character of light. That a beam of +ordinary sunlight is, in fact, a mixture of a very great number of +different-coloured lights, is a doctrine now familiar to every one +who has the slightest education in physical science. We must, +however, remember that this discovery was really a tremendous advance +in knowledge at the time when Newton announced it.</p> + +<p><a name="diagram" id="diagram"></a></p> + +<div class="figcenter" style="width: 390px;"> +<a href="images/ill_diagram_sunbeam.jpg"> +<img src="images/ill_diagram_sunbeam_sml.jpg" width="390" height="163" alt="DIAGRAM OF A SUNBEAM." title="" /></a> +<span class="caption">DIAGRAM OF A SUNBEAM.</span> +</div> + +<p>We here give the little diagram originally drawn by Newton, to +explain the experiment by which he first learned the composition of +light. A sunbeam is admitted into a darkened room through an +opening, H, in a shutter. This beam when not interfered with will +travel in a straight line to the screen, and there reproduce a bright +spot of the same shape as the hole in the shutter. If, however, a +prism of glass, A B C, be introduced so that the beam traverse it, +then it will be seen at once that the light is deflected from its +original track. There is, however, a further and most important +change which takes place. The spot of light is not alone removed to +another part of the screen, but it becomes spread out into a long +band beautifully coloured, and exhibiting the hues of the rainbow. At +the top are the violet rays, and then in descending order we have the +indigo, blue, green, yellow, orange, and red.</p> + +<p>The circumstance in this phenomenon which appears to have +particularly arrested Newton's attention, was the elongation which +the luminous spot underwent in consequence of its passage through the +prism. When the prism was absent the spot was nearly circular, but +when the prism was introduced the spot was about five times as long +as it was broad. To ascertain the explanation of this was the first +problem to be solved. It seemed natural to suppose that it might be +due to the thickness of the glass in the prism which the light +traversed, or to the angle of incidence at which the light fell upon +the prism. He found, however, upon careful trial, that the phenomenon +could not be thus accounted for. It was not until after much patient +labour that the true explanation dawned upon him. He discovered that +though the beam of white light looks so pure and so simple, yet in +reality it is composed of differently coloured lights blended +together. These are, of course, indistinguishable in the compound +beam, but they are separated or disentangled, so to speak, by the +action of the prism. The rays at the blue end of the spectrum are +more powerfully deflected by the action of the glass than are the +rays at the red end. Thus, the rays variously coloured red, orange, +yellow, green, blue, indigo, violet, are each conducted to a +different part of the screen. In this way the prism has the effect +of exhibiting the constitution of the composite beam of light.</p> + +<p>To us this now seems quite obvious, but Newton did not adopt it +hastily. With characteristic caution he verified the explanation by +many different experiments, all of which confirmed his discovery. One +of these may be mentioned. He made a hole in the screen at that part +on which the violet rays fell. Thus a violet ray was allowed to pass +through, all the rest of the light being intercepted, and on this +beam so isolated he was able to try further experiments. For +instance, when he interposed another prism in its path, he found, as +he expected, that it was again deflected, and he measured the amount +of the deflection. Again he tried the same experiment with one of +the red rays from the opposite end of the coloured band. He allowed +it to pass through the same aperture in the screen, and he tested the +amount by which the second prism was capable of producing deflection. +He thus found, as he had expected to find, that the second prism was +more efficacious in bending the violet rays than in bending the red +rays. Thus he confirmed the fact that the various hues of the +rainbow were each bent by a prism to a different extent, violet being +acted upon the most, and red the least.</p> + +<p><a name="isaac" id="isaac"></a></p> + +<div class="figcenter" style="width: 390px;"> +<a href="images/ill_newton.jpg"> +<img src="images/ill_newton_sml.jpg" width="390" height="469" alt="ISAAC NEWTON." title="" /></a> +<span class="caption">ISAAC NEWTON.</span> +</div> + +<p>Not only did Newton decompose a white beam into its constituent +colours, but conversely by interposing a second prism with its angle +turned upwards, he reunited the different colours, and thus +reproduced the original beam of white light. In several other ways +also he illustrated his famous proposition, which then seemed so +startling, that white light was the result of a mixture of all hues +of the rainbow. By combining painters' colours in the right +proportion he did not indeed succeed in producing a mixture which +would ordinarily be called white, but he obtained a grey pigment. +Some of this he put on the floor of his room for comparison with a +piece of white paper. He allowed a beam of bright sunlight to fall +upon the paper and the mixed colours side by side, and a friend he +called in for his opinion pronounced that under these circumstances +the mixed colours looked the whiter of the two.</p> + +<p>By repeated demonstrations Newton thus established his great +discovery of the composite character of light. He at once perceived +that his researches had an important bearing upon the principles +involved in the construction of a telescope. Those who employed the +telescope for looking at the stars, had been long aware of the +imperfections which prevented all the various rays from being +conducted to the same focus. But this imperfection had hitherto been +erroneously accounted for. It had been supposed that the reason why +success had not been attained in the construction of a refracting +telescope was due to the fact that the object glass, made as it then +was of a single piece, had not been properly shaped. Mathematicians +had abundantly demonstrated that a single lens, if properly figured, +must conduct all rays of light to the same focus, provided all rays +experienced equal refraction in passing through the glass. Until +Newton's discovery of the composition of white light, it had been +taken for granted that the several rays in a white beam were equally +refrangible. No doubt if this had been the case, a perfect telescope +could have been produced by properly shaping the object glass. But +when Newton had demonstrated that light was by no means so simple as +had been supposed, it became obvious that a satisfactory refracting +telescope was an impossibility when only a single object lens was +employed, however carefully that lens might have been wrought. Such +an objective might, no doubt, be made to conduct any one group of +rays of a particular shade to the same focus, but the rays of other +colours in the beam of white light must necessarily travel somewhat +astray. In this way Newton accounted for a great part of the +difficulties which had hitherto beset the attempts to construct a +perfect refracting telescope.</p> + +<p>We now know how these difficulties can be, to a great extent, +overcome, by employing for the objective a composite lens made of two +pieces of glass possessing different qualities. To these achromatic +object glasses, as they are called, the great development of +astronomical knowledge, since Newton's time, is due. But it must be +remarked that, although the theoretical possibility of constructing +an achromatic lens was investigated by Newton, he certainly came to +the conclusion that the difficulty could not be removed by employing +a composite objective, with two different kinds of glass. In this +his marvellous sagacity in the interpretation of nature seems for +once to have deserted him. We can, however, hardly regret that +Newton failed to discover the achromatic objective, when we observe +that it was in consequence of his deeming an achromatic objective to +be impossible that he was led to the invention of the reflecting +telescope. Finding, as he believed, that the defects of the +telescope could not be remedied by any application of the principle +of refraction he was led to look in quite a different direction for +the improvement of the tool on which the advancement of astronomy +depended. The REFRACTION of light depended as he had found, upon the +colour of the light. The laws of REFLECTION were, however, quite +independent of the colour. Whether rays be red or green, blue or +yellow, they are all reflected in precisely the same manner from a +mirror. Accordingly, Newton perceived that if he could construct a +telescope the action of which depended upon reflection, instead of +upon refraction, the difficulty which had hitherto proved an +insuperable obstacle to the improvement of the instrument would be +evaded.</p> + +<p><a name="newton_reflector" id="newton_reflector"></a></p> + +<div class="figcenter" style="width: 278px;"> +<a href="images/ill_little_reflector.jpg"> +<img src="images/ill_little_reflector_sml.jpg" width="278" height="284" alt="SIR ISAAC NEWTON'S LITTLE REFLECTOR." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S LITTLE REFLECTOR.</span> +</div> + +<p>For this purpose Newton fashioned a concave mirror from a mixture of +copper and tin, a combination which gives a surface with almost the +lustre of silver. When the light of a star fell upon the surface, an +image of the star was produced in the focus of this mirror, and then +this image was examined by a magnifying eye-piece. Such is the +principle of the famous reflecting telescope which bears the name of +Newton. The little reflector which he constructed, represented in +the adjoining figure, is still preserved as one of the treasures of +the Royal Society. The telescope tube had the very modest dimension +of one inch in diameter. It was, however, the precursor of a whole +series of magnificent instruments, each outstripping the other in +magnitude, until at last the culminating point was attained in 1845, +by the construction of Lord Rosse's mammoth reflector of six feet in +aperture.</p> + +<p>Newton's discovery of the composition of light led to an embittered +controversy, which caused no little worry to the great Philosopher. +Some of those who attacked him enjoyed considerable and, it must be +admitted, even well-merited repute in the ranks of science. They +alleged, however, that the elongation of the coloured band which +Newton had noticed was due to this, to that, or to the other—to +anything, in fact, rather than to the true cause which Newton +assigned. With characteristic patience and love of truth, Newton +steadily replied to each such attack. He showed most completely how +utterly his adversaries had misunderstood the subject, and how slight +indeed was their acquaintance with the natural phenomenon in +question. In reply to each point raised, he was ever able to cite +fresh experiments and adduce fresh illustrations, until at last his +opponents retired worsted from the combat.</p> + +<p>It has been often a matter for surprise that Newton, throughout his +whole career, should have taken so much trouble to expose the errors +of those who attacked his views. He used even to do this when it +plainly appeared that his adversaries did not understand the subject +they were discussing. A philosopher might have said, "I know I am +right, and whether others think I am right or not may be a matter of +concern to them, but it is certainly not a matter about which I need +trouble. If after having been told the truth they elect to remain in +error, so much the worse for them; my time can be better employed +than in seeking to put such people right." This, however, was not +Newton's method. He spent much valuable time in overthrowing +objections which were often of a very futile description. Indeed, he +suffered a great deal of annoyance from the persistency, and in some +cases one might almost say from the rancour, of the attacks which +were made upon him. Unfortunately for himself, he did not possess +that capacity for sublime indifference to what men may say, which is +often the happy possession of intellects greatly inferior to his.</p> + +<p>The subject of optics still continuing to engross Newton's attention, +he followed up his researches into the structure of the sunbeam by +many other valuable investigations in connection with light. Every +one has noticed the beautiful colours manifested in a soap-bubble. +Here was a subject which not unnaturally attracted the attention of +one who had expounded the colours of the spectrum with such success. +He perceived that similar hues were produced by other thin plates of +transparent material besides soap-bubbles, and his ingenuity was +sufficient to devise a method by which the thicknesses of the +different films could be measured. We can hardly, indeed, say that a +like success attended his interpretation of these phenomena to that +which had been so conspicuous in his explanation of the spectrum. It +implies no disparagement to the sublime genius of Newton to admit +that the doctrines he put forth as to the causes of the colours in +the soap-bubbles can be no longer accepted. We must remember that +Newton was a pioneer in accounting for the physical properties of +light. The facts that he established are indeed unquestionable, but +the explanations which he was led to offer of some of them are seen +to be untenable in the fuller light of our present knowledge.</p> + +<p><a name="sun-dial" id="sun-dial"></a></p> + +<div class="figcenter" style="width: 402px;"> +<a href="images/ill_newton_sundial.jpg"> +<img src="images/ill_newton_sundial_sml.jpg" width="402" height="485" alt="SIR ISAAC NEWTON'S SUN-DIAL." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S SUN-DIAL.</span> +</div> + +<p>Had Newton done nothing beyond making his wonderful discoveries in +light, his fame would have gone down to posterity as one of the +greatest of Nature's interpreters. But it was reserved for him to +accomplish other discoveries, which have pushed even his analysis of +the sunbeam into the background; it is he who has expounded the +system of the universe by the discovery of the law of universal +gravitation.</p> + +<p>The age had indeed become ripe for the advent of the genius of +Newton. Kepler had discovered with marvellous penetration the laws +which govern the movements of the planets around the sun, and in +various directions it had been more or less vaguely felt that the +explanation of Kepler's laws, as well as of many other phenomena, +must be sought for in connection with the attractive power of +matter. But the mathematical analysis which alone could deal with +this subject was wanting; it had to be created by Newton.</p> + +<p>At Woolsthorpe, in the year 1666, Newton's attention appears to have +been concentrated upon the subject of gravitation. Whatever may be +the extent to which we accept the more or less mythical story as to +how the fall of an apple first directed the attention of the +philosopher to the fact that gravitation must extend through space, +it seems, at all events, certain that this is an excellent +illustration of the line of reasoning which he followed. He argued +in this way. The earth attracts the apple; it would do so, no matter +how high might be the tree from which that apple fell. It would then +seem to follow that this power which resides in the earth by which it +can draw all external bodies towards it, extends far beyond the +altitude of the loftiest tree. Indeed, we seem to find no limit to +it. At the greatest elevation that has ever been attained, the +attractive power of the earth is still exerted, and though we cannot +by any actual experiment reach an altitude more than a few miles +above the earth, yet it is certain that gravitation would extend to +elevations far greater. It is plain, thought Newton, that an apple +let fall from a point a hundred miles above this earth's surface, +would be drawn down by the attraction, and would continually gather +fresh velocity until it reached the ground. From a hundred miles it +was natural to think of what would happen at a thousand miles, or at +hundreds of thousands of miles. No doubt the intensity of the +attraction becomes weaker with every increase in the altitude, but +that action would still exist to some extent, however lofty might be +the elevation which had been attained.</p> + +<p>It then occurred to Newton, that though the moon is at a distance of +two hundred and forty thousand miles from the earth, yet the +attractive power of the earth must extend to the moon. He was +particularly led to think of the moon in this connection, not only +because the moon is so much closer to the earth than are any other +celestial bodies, but also because the moon is an appendage to the +earth, always revolving around it. The moon is certainly attracted +to the earth, and yet the moon does not fall down; how is this to be +accounted for? The explanation was to be found in the character of +the moon's present motion. If the moon were left for a moment at +rest, there can be no doubt that the attraction of the earth would +begin to draw the lunar globe in towards our globe. In the course of +a few days our satellite would come down on the earth with a most +fearful crash. This catastrophe is averted by the circumstance that +the moon has a movement of revolution around the earth. Newton was +able to calculate from the known laws of mechanics, which he had +himself been mainly instrumental in discovering, what the attractive +power of the earth must be, so that the moon shall move precisely as +we find it to move. It then appeared that the very power which makes +an apple fall at the earth's surface is the power which guides the +moon in its orbit.</p> + +<p><a name="newton_telescope" id="newton_telescope"></a></p> + +<div class="figcenter" style="width: 378px;"> +<a href="images/ill_newton_telescope.jpg"> +<img src="images/ill_newton_telescope_sml.jpg" width="378" height="202" alt="SIR ISAAC NEWTON'S TELESCOPE." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S TELESCOPE.</span> +</div> + +<p>Once this step had been taken, the whole scheme of the universe might +almost be said to have become unrolled before the eye of the +philosopher. It was natural to suppose that just as the moon was +guided and controlled by the attraction of the earth, so the earth +itself, in the course of its great annual progress, should be guided +and controlled by the supreme attractive power of the sun. If this +were so with regard to the earth, then it would be impossible to +doubt that in the same way the movements of the planets could be +explained to be consequences of solar attraction.</p> + +<p>It was at this point that the great laws of Kepler became especially +significant. Kepler had shown how each of the planets revolves in an +ellipse around the sun, which is situated on one of the foci. This +discovery had been arrived at from the interpretation of +observations. Kepler had himself assigned no reason why the orbit of +a planet should be an ellipse rather than any other of the infinite +number of closed curves which might be traced around the sun. Kepler +had also shown, and here again he was merely deducing the results +from observation, that when the movements of two planets were +compared together, the squares of the periodic times in which each +planet revolved were proportional to the cubes of their mean +distances from the sun. This also Kepler merely knew to be true as a +fact, he gave no demonstration of the reason why nature should have +adopted this particular relation between the distance and the +periodic time rather than any other. Then, too, there was the law by +which Kepler with unparalleled ingenuity, explained the way in which +the velocity of a planet varies at the different points of its track, +when he showed how the line drawn from the sun to the planet +described equal areas around the sun in equal times. These were the +materials with which Newton set to work. He proposed to infer from +these the actual laws regulating the force by which the sun guides +the planets. Here it was that his sublime mathematical genius came +into play. Step by step Newton advanced until he had completely +accounted for all the phenomena.</p> + +<p>In the first place, he showed that as the planet describes equal +areas in equal times about the sun, the attractive force which the +sun exerts upon it must necessarily be directed in a straight line +towards the sun itself. He also demonstrated the converse truth, +that whatever be the nature of the force which emanated from a sun, +yet so long as that force was directed through the sun's centre, any +body which revolved around it must describe equal areas in equal +times, and this it must do, whatever be the actual character of the +law according to which the intensity of the force varies at different +parts of the planet's journey. Thus the first advance was taken in +the exposition of the scheme of the universe.</p> + +<p>The next step was to determine the law according to which the force +thus proved to reside in the sun varied with the distance of the +planet. Newton presently showed by a most superb effort of +mathematical reasoning, that if the orbit of a planet were an ellipse +and if the sun were at one of the foci of that ellipse, the intensity +of the attractive force must vary inversely as the square of the +planet's distance. If the law had any other expression than the +inverse square of the distance, then the orbit which the planet must +follow would not be an ellipse; or if an ellipse, it would, at all +events, not have the sun in the focus. Hence he was able to show +from Kepler's laws alone that the force which guided the planets was +an attractive power emanating from the sun, and that the intensity of +this attractive power varied with the inverse square of the distance +between the two bodies.</p> + +<p>These circumstances being known, it was then easy to show that the +last of Kepler's three laws must necessarily follow. If a number of +planets were revolving around the sun, then supposing the materials +of all these bodies were equally affected by gravitation, it can be +demonstrated that the square of the periodic time in which each +planet completes its orbit is proportional to the cube of the +greatest diameter in that orbit.</p> + +<p><a name="newton_astrolabe" id="newton_astrolabe"></a></p> + +<div class="figcenter" style="width: 419px;"> +<a href="images/ill_newton_astrolabe.jpg"> +<img src="images/ill_newton_astrolabe_sml.jpg" width="419" height="511" alt="SIR ISAAC NEWTON'S ASTROLABE." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S ASTROLABE.</span> +</div> + +<p>These superb discoveries were, however, but the starting point from +which Newton entered on a series of researches, which disclosed many +of the profoundest secrets in the scheme of celestial mechanics. His +natural insight showed that not only large masses like the sun and +the earth, and the moon, attract each other, but that every particle +in the universe must attract every other particle with a force which +varies inversely as the square of the distance between them. If, for +example, the two particles were placed twice as far apart, then the +intensity of the force which sought to bring them together would be +reduced to one-fourth. If two particles, originally ten miles +asunder, attracted each other with a certain force, then, when the +distance was reduced to one mile, the intensity of the attraction +between the two particles would be increased one-hundred-fold. This +fertile principle extends throughout the whole of nature. In some +cases, however, the calculation of its effect upon the actual +problems of nature would be hardly possible, were it not for another +discovery which Newton's genius enabled him to accomplish. In the +case of two globes like the earth and the moon, we must remember that +we are dealing not with particles, but with two mighty masses of +matter, each composed of innumerable myriads of particles. Every +particle in the earth does attract every particle in the moon with a +force which varies inversely as the square of their distance. The +calculation of such attractions is rendered feasible by the following +principle. Assuming that the earth consists of materials +symmetrically arranged in shells of varying densities, we may then, +in calculating its attraction, regard the whole mass of the globe as +concentrated at its centre. Similarly we may regard the moon as +concentrated at the centre of its mass. In this way the earth and +the moon can both be regarded as particles in point of size, each +particle having, however, the entire mass of the corresponding +globe. The attraction of one particle for another is a much more +simple matter to investigate than the attraction of the myriad +different points of the earth upon the myriad different points of the +moon.</p> + +<p>Many great discoveries now crowded in upon Newton. He first of all +gave the explanation of the tides that ebb and flow around our +shores. Even in the earliest times the tides had been shown to be +related to the moon. It was noticed that the tides were specially +high during full moon or during new moon, and this circumstance +obviously pointed to the existence of some connection between the +moon and these movements of the water, though as to what that +connection was no one had any accurate conception until Newton +announced the law of gravitation. Newton then made it plain that the +rise and fall of the water was simply a consequence of the attractive +power which the moon exerted upon the oceans lying upon our globe. He +showed also that to a certain extent the sun produces tides, and he +was able to explain how it was that when the sun and the moon both +conspire, the joint result was to produce especially high tides, +which we call "spring tides"; whereas if the solar tide was low, +while the lunar tide was high, then we had the phenomenon of "neap" +tides.</p> + +<p>But perhaps the most signal of Newton's applications of the law of +gravitation was connected with certain irregularities in the +movements of the moon. In its orbit round the earth our satellite +is, of course, mainly guided by the great attraction of our globe. If +there were no other body in the universe, then the centre of the moon +must necessarily perform an ellipse, and the centre of the earth +would lie in the focus of that ellipse. Nature, however, does not +allow the movements to possess the simplicity which this arrangement +would imply, for the sun is present as a source of disturbance. The +sun attracts the moon, and the sun attracts the earth, but in +different degrees, and the consequence is that the moon's movement +with regard to the earth is seriously affected by the influence of +the sun. It is not allowed to move exactly in an ellipse, nor is the +earth exactly in the focus. How great was Newton's achievement in +the solution of this problem will be appreciated if we realise that +he not only had to determine from the law of gravitation the nature +of the disturbance of the moon, but he had actually to construct the +mathematical tools by which alone such calculations could be +effected.</p> + +<p>The resources of Newton's genius seemed, however, to prove equal to +almost any demand that could be made upon it. He saw that each +planet must disturb the other, and in that way he was able to render +a satisfactory account of certain phenomena which had perplexed all +preceding investigators. That mysterious movement by which the pole +of the earth sways about among the stars had been long an unsolved +enigma, but Newton showed that the moon grasped with its attraction +the protuberant mass at the equatorial regions of the earth, and thus +tilted the earth's axis in a way that accounted for the phenomenon +which had been known but had never been explained for two thousand +years. All these discoveries were brought together in that immortal +work, Newton's "Principia."</p> + +<p>Down to the year 1687, when the "Principia" was published, Newton had +lived the life of a recluse at Cambridge, being entirely occupied +with those transcendent researches to which we have referred. But in +that year he issued from his seclusion under circumstances of +considerable historical interest. King James the Second attempted an +invasion of the rights and privileges of the University of Cambridge +by issuing a command that Father Francis, a Benedictine monk, should +be received as a Master of Arts in the University, without having taken +the oaths of allegiance and supremacy. With this arbitrary command +the University sternly refused to comply. The Vice-Chancellor was +accordingly summoned to answer for an act of contempt to the authority +of the Crown. Newton was one of nine delegates who were chosen to +defend the independence of the University before the High Court. +They were able to show that Charles the Second, who had issued a +MANDAMUS under somewhat similar circumstances, had been induced after +due consideration to withdraw it. This argument appeared satisfactory, +and the University gained their case. Newton's next step in public +life was his election, by a narrow majority, as member for the +University, and during the years 1688 and 1689, he seems to have +attended to his parliamentary duties with considerable regularity.</p> + +<p>An incident which happened in 1692 was apparently the cause of +considerable disturbance in Newton's equanimity, if not in his +health. He had gone to early morning chapel, leaving a lighted +candle among his papers on his desk. Tradition asserts that his +little dog "Diamond" upset the candle; at all events, when Newton +came back he found that many valuable papers had perished in a +conflagration. The loss of these manuscripts seems to have had a +serious effect. Indeed, it has been asserted that the distress +reduced Newton to a state of mental aberration for a considerable +time. This has, apparently, not been confirmed, but there is no +doubt that he experienced considerable disquiet, for in writing on +September 13th, 1693, to Mr. Pepys, he says:</p> + +<p>"I am extremely troubled at the embroilment I am in, and have +neither ate nor slept well this twelve-month, nor have my former +consistency of mind."</p> + +<p>Notwithstanding the fame which Newton had achieved, by the +publication of his, "Principia," and by all his researches, the State +had not as yet taken any notice whatever of the most illustrious man +of science that this or any other country has ever produced. Many of +his friends had exerted themselves to procure him some permanent +appointment, but without success. It happened, however, that Mr. +Montagu, who had sat with Newton in Parliament, was appointed +Chancellor of the Exchequer in 1694. Ambitious of distinction in his +new office, Mr. Montagu addressed himself to the improvement of the +current coin, which was then in a very debased condition. It +fortunately happened that an opportunity occurred of appointing a new +official in the Mint; and Mr. Montagu on the 19th of March, 1695, +wrote to offer Mr. Newton the position of warden. The salary was to +be five or six hundred a year, and the business would not require +more attendance than Newton could spare. The Lucasian professor +accepted this post, and forthwith entered upon his new duties.</p> + +<p>The knowledge of physics which Newton had acquired by his experiments +was of much use in connection with his duties at the Mint. He +carried out the re-coinage with great skill in the course of two +years, and as a reward for his exertions, he was appointed, in 1697, +to the Mastership of the Mint, with a salary between 1,200 Pounds and +1,500 Pounds per annum. In 1701, his duties at the Mint being so +engrossing, he resigned his Lucasian professorship at Cambridge, and +at the same time he had to surrender his fellowship at Trinity +College. This closed his connection with the University of +Cambridge. It should, however, be remarked that at a somewhat +earlier stage in his career he was very nearly being appointed to an +office which might have enabled the University to retain the great +philosopher within its precincts. Some of his friends had almost +succeeded in securing his nomination to the Provostship of King's +College, Cambridge; the appointment, however, fell through, inasmuch +as the statute could not be evaded, which required that the Provost +of King's College should be in holy orders.</p> + +<p>In those days it was often the custom for illustrious mathematicians, +when they had discovered a solution for some new and striking +problem, to publish that problem as a challenge to the world, while +withholding their own solution. A famous instance of this is found +in what is known as the Brachistochrone problem, which was solved by +John Bernouilli. The nature of this problem may be mentioned. It +was to find the shape of the curve along which a body would slide +down from one point (A) to another point (B) in the shortest time. It +might at first be thought that the straight line from A to B, as it +is undoubtedly the shortest distance between the points, would also +be the path of quickest descent; but this is not so. There is a +curved line, down which a bead, let us say, would run on a smooth +wire from A to B in a shorter time than the same bead would require +to run down the straight wire. Bernouilli's problem was to find out +what that curve must be. Newton solved it correctly; he showed that +the curve was a part of what is termed a cycloid—that is to say, a +curve like that which is described by a point on the rim of a +carriage-wheel as the wheel runs along the ground. Such was Newton's +geometrical insight that he was able to transmit a solution of the +problem on the day after he had received it, to the President of the +Royal Society.</p> + +<p>In 1703 Newton, whose world wide fame was now established, was +elected President of the Royal Society. Year after year he was +re-elected to this distinguished position, and his tenure, which +lasted twenty-five years, only terminated with his life. It was in +discharge of his duties as President of the Royal Society that Newton +was brought into contact with Prince George of Denmark. In April, +1705, the Queen paid a visit to Cambridge as the guest of Dr. +Bentley, the then Master of Trinity, and in a court held at Trinity +Lodge on April 15th, 1705, the honour of knighthood was conferred +upon the discoverer of gravitation.</p> + +<p>Urged by illustrious friends, who sought the promotion of knowledge, +Newton gave his attention to the publication of a new edition of the +"Principia." His duties at the Mint, however, added to the supreme +duty of carrying on his original investigations, left him but little +time for the more ordinary task of the revision. He was accordingly +induced to associate with himself for this purpose a distinguished +young mathematician, Roger Coates, a Fellow of Trinity College, +Cambridge, who had recently been appointed Plumian Professor of +Astronomy. On July 27th, 1713, Newton, by this time a favourite at +Court, waited on the Queen, and presented her with a copy of the new +edition of the "Principia."</p> + +<p>Throughout his life Newton appears to have been greatly interested in +theological studies, and he specially devoted his attention to the +subject of prophecy. He left behind him a manuscript on the +prophecies of Daniel and the Apocalypse of St. John, and he also +wrote various theological papers. Many other subjects had from time +to time engaged his attention. He studied the laws of heat; he +experimented in pursuit of the dreams of the Alchymist; while the +philosopher who had revealed the mechanism of the heavens found +occasional relaxation in trying to interpret hieroglyphics. In the +last few years of his life he bore with fortitude a painful ailment, +and on Monday, March 20th, 1727, he died in the eighty-fifth year of +his age. On Tuesday, March 28th, he was buried in Westminster Abbey.</p> + +<p>Though Newton lived long enough to receive the honour that his +astonishing discoveries so justly merited, and though for many years +of his life his renown was much greater than that of any of his +contemporaries, yet it is not too much to say that, in the years +which have since elapsed, Newton's fame has been ever steadily +advancing, so that it never stood higher than it does at this moment.</p> + +<p>We hardly know whether to admire more the sublime discoveries at +which he arrived, or the extraordinary character of the intellectual +processes by which those discoveries were reached. Viewed from +either standpoint, Newton's "Principia" is incomparably the greatest +work on science that has ever yet been produced.</p> + +<p><a name="royal_society" id="royal_society"></a></p> + +<div class="figcenter" style="width: 327px;"> +<a href="images/ill_newtons_sundial_royal_society.jpg"> +<img src="images/ill_newtons_sundial_royal_society_sml.jpg" width="327" height="192" alt="SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.</span> +</div> + +<h3><a name="FLAMSTEED" id="FLAMSTEED"></a>FLAMSTEED.</h3> +<p>Among the manuscripts preserved at Greenwich Observatory are certain +documents in which Flamsteed gives an account of his own life. We +may commence our sketch by quoting the following passage from this +autobiography:—"To keep myself from idleness, and to recreate +myself, I have intended here to give some account of my life, in my +youth, before the actions thereof, and the providences of God +therein, be too far passed out of my memory; and to observe the +accidents of all my years, and inclinations of my mind, that +whosoever may light upon these papers may see I was not so wholly +taken up, either with my father's business or my mathematics, but +that I both admitted and found time for other as weighty +considerations."</p> + +<p>The chief interest which attaches to the name of Flamsteed arises +from the fact that he was the first of the illustrious series of +Astronomers Royal who have presided over Greenwich Observatory. In +that capacity Flamsteed was able to render material assistance to +Newton by providing him with the observations which his lunar theory +required.</p> + +<p>John Flamsteed was born at Denby, in Derbyshire, on the 19th of +August, 1646. His mother died when he was three years old, and the +second wife, whom his father took three years later, only lived until +Flamsteed was eight, there being also two younger sisters. In his +boyhood the future astronomer tells us that he was very fond of those +romances which affect boy's imagination, but as he writes, "At twelve +years of age I left all the wild ones and betook myself to read the +better sort of them, which, though they were not probable, yet +carried no seeming impossibility in the picturing." By the time +Flamsteed was fifteen years old he had embarked in still more serious +work, for he had read Plutarch's "Lives," Tacitus' "Roman History," +and many other books of a similar description. In 1661 he became ill +with some serious rheumatic affection, which obliged him to be +withdrawn from school. It was then for the first time that he +received the rudiments of a scientific education. He had, however, +attained his sixteenth year before he made any progress in +arithmetic. He tells us how his father taught him "the doctrine of +fractions," and "the golden rule of three"—lessons which he seemed +to have learned easily and quickly. One of the books which he read +at this time directed his attention to astronomical instruments, and +he was thus led to construct for himself a quadrant, by which he +could take some simple astronomical observations. He further +calculated a table to give the sun's altitudes at different hours, +and thus displayed those tastes for practical astronomy which he +lived to develop so greatly. It appears that these scientific +studies were discountenanced by his father, who designed that his son +should follow a business career. Flamsteed's natural inclination, +however, forced him to prosecute astronomical work, notwithstanding +the impediments that lay in his path. Unfortunately, his +constitutional delicacy seems to have increased, and he had just +completed his eighteenth year, "when," to use his own words, "the +winter came on and thrust me again into the chimney, whence the heat +and the dryness of the preceding summer had happily once before +withdrawn me. But, it not being a fit season for physic, it was +thought fit to let me alone this winter, and try the skill of another +physician on me in the spring."</p> + +<p>It appears that at this time a quack named Valentine Greatrackes, was +reputed to have effected most astonishing cures in Ireland merely by +the stroke of his hands, without the application of any medicine +whatever. Flamsteed's father, despairing of any remedy for his son +from the legitimate branch of the profession, despatched him to +Ireland on August 26th, 1665, he being then, as recorded with +astronomical accuracy, "nineteen years, six days, and eleven hours +old." The young astronomer, accompanied by a friend, arrived on a +Tuesday at Liverpool but the wind not being favourable, they remained +there till the following Friday, when a shift of the wind to the east +took place. They embarked accordingly on a vessel called the SUPPLY +at noon, and on Saturday night came in sight of Dublin. Ere they +could land, however, they were nearly being wrecked on Lambay +Island. This peril safely passed, there was a long delay for +quarantine before they were at last allowed on shore. On Thursday, +September 6th, they set out from Dublin, where they had been +sojourning at the "Ship" Hotel, in Dame Street, towards Assaune, +where Greatrackes received his patients.</p> + +<p><a name="flamsteed_house" id="flamsteed_house"></a></p> + +<div class="figcenter" style="width: 420px;"> +<a href="images/ill_flamsteeds_house.jpg"> +<img src="images/ill_flamsteeds_house_sml.jpg" width="420" height="313" alt="FLAMSTEED'S HOUSE." title="" /></a> +<span class="caption">FLAMSTEED'S HOUSE.</span> +</div> + +<p>Flamsteed gives an interesting account of his travels in Ireland. +They dined at Naas on the first day, and on September 8th they +reached Carlow, a town which is described as one of the fairest they +saw on their journey. By Sunday morning, September 10th, having lost +their way several times, they reached Castleton, called commonly Four +Mile Waters. Flamsteed inquired of the host in the inn where they +might find a church, but was told that the minister lived twelve +miles away, and that they had no sermon except when he came to +receive his tithes once a year, and a woman added that "they had +plenty enough of everything necessary except the word of God." The +travellers accordingly went on to Cappoquin, which lies up the river +Blackwater, on the road to Lismore, eight miles from Youghal. Thence +they immediately started on foot to Assaune. About a mile from +Cappoquin, and entering into the house of Mr. Greatrackes, they saw +him touch several patients, "whereof some were nearly cured, others +were on the mending hand, and some on whom his strokes had no +effect." Flamsteed was touched by the famous quack on the afternoon +of September 11th, but we are hardly surprised to hear his remark +that "he found not his disease to stir." Next morning the astronomer +came again to see Mr. Greatrackes, who had "a kind of majestical yet +affable presence, and a composed carriage." Even after the third +touching had been submitted to, no benefit seems to have been +derived. We must, however record, to the credit of Mr. Greatrackes, +that he refused to accept any payment from Flamsteed, because he was +a stranger.</p> + +<p>Finding it useless to protract his stay any longer, Flamsteed and his +friend set out on their return to Dublin. In the course of his +journey he seems to have been much impressed with Clonmel, which he +describes as an "exceedingly pleasantly seated town." But in those +days a journey to Ireland was so serious an enterprise that when +Flamsteed did arrive safely back at Derby after an absence of a +month, he adds, "For God's providence in this journey, His name be +praised, Amen."</p> + +<p>As to the expected benefits to his health from the expedition we may +quote his own words: "In the winter following I was indifferent +hearty, and my disease was not so violent as it used to be at that +time formerly. But whether through God's mercy I received this +through Mr. Greatrackes' touch, or my journey and vomiting at sea, I +am uncertain; but, by some circumstances, I guess that I received a +benefit from both."</p> + +<p>It is evident that by this time Flamsteed's interest in all +astronomical matters had greatly increased. He studied the +construction of sun-dials, he formed a catalogue of seventy of the +fixed stars, with their places on the heavens, and he computed the +circumstances of the solar eclipse which was to happen on June 22nd, +1666. It is interesting to note that even in those days the +doctrines of the astrologers still found a considerable degree of +credence, and Flamsteed spent a good deal of his time in astrological +studies and computations. He investigated the methods of casting a +nativity, but a suspicion, or, indeed, rather more than a suspicion, +seems to have crossed his mind as to the value of these astrological +predictions, for he says in fine, "I found astrology to give +generally strong conjectural hints, not perfect declarations."</p> + +<p>All this time, however, the future Astronomer Royal was steadily +advancing in astronomical inquiries of a recondite nature. He had +investigated the obliquity of the ecliptic with extreme care, so far +as the circumstances of astronomical observation would at that time +permit. He had also sought to discover the sun's distance from the +earth in so far as it could be obtained by determining when the moon +was exactly half illuminated, and he had measured, with much +accuracy, the length of the tropical year. It will thus be seen +that, even at the age of twenty, Flamsteed had made marked progress, +considering how much his time had been interfered with by ill-health.</p> + +<p>Other branches of astronomy began also to claim his attention. We +learn that in 1669 and 1670 he compared the planets Jupiter and Mars +with certain fixed stars near which they passed. His instrumental +means, though very imperfect, were still sufficient to enable him to +measure the intervals on the celestial sphere between the planets and +the stars. As the places of the stars were known, Flamsteed was thus +able to obtain the places of the planets. This is substantially the +way in which astronomers of the present day still proceed when they +desire to determine the places of the planets, inasmuch as, directly +or indirectly those places are always obtained relatively to the +fixed stars. By his observations at this early period, Flamsteed +was, it is true, not able to obtain any great degree of accuracy; he +succeeded, however, in proving that the tables by which the places of +the planets were ordinarily given were not to be relied upon.</p> + +<p><a name="flamsteed_ill" id="flamsteed_ill"></a></p> + +<div class="figcenter" style="width: 382px;"> +<a href="images/ill_flamsteed.jpg"> +<img src="images/ill_flamsteed_sml.jpg" width="382" height="478" alt="FLAMSTEED." title="" /></a> +<span class="caption">FLAMSTEED.</span> +</div> + +<p>Flamsteed's labours in astronomy and in the allied branches of +science were now becoming generally known, and he gradually came to +correspond with many distinguished men of learning. One of the first +occasions which brought the talents of the young astronomer into fame +was the publication of some calculations concerning certain +astronomical phenomena which were to happen in the year 1670. In the +monthly revolution of the moon its disc passes over those stars which +lie along its track. The disappearance of a star by the +interposition of the moon is called an "occultation." Owing to the +fact that our satellite is comparatively near us, the position which +the moon appears to occupy on the heavens varies from different parts +of the earth, it consequently happens that a star which would be +occulted to an observer in one locality, would often not be occulted +to an observer who was situated elsewhere. Even when an occultation +is visible from both places, the times at which the star disappears +from view will, generally speaking, be different. Much calculation +is therefore necessary to decide the circumstances under which the +occultations of stars may be visible from any particular station. +Having a taste for such computations, Flamsteed calculated the +occultations which were to happen in the year 1670, it being the case +that several remarkable stars would be passed over by the moon during +this year. Of course at the present time, we find such information +duly set forth in the NAUTICAL ALMANAC, but a couple of centuries ago +there was no such source of astronomical knowledge as is now to be +found in that invaluable publication, which astronomers and +navigators know so well. Flamsteed accordingly sent the results of +his work to the President of the Royal Society. The paper which +contained them was received very favourably, and at once brought +Flamsteed into notice among the most eminent members of that +illustrious body, one of whom, Mr. Collins, became through life his +faithful friend and constant correspondent. Flamsteed's father was +naturally gratified with the remarkable notice which his son was +receiving from the great and learned; accordingly he desired him to +go to London, that he might make the personal acquaintance of those +scientific friends whom he had only known by correspondence +previously. Flamsteed was indeed glad to avail himself of this +opportunity. Thus he became acquainted with Dr. Barrow, and +especially with Newton, who was then Lucasian Professor of +Mathematics at Cambridge. It seems to have been in consequence of +this visit to London that Flamsteed entered himself as a member of +Jesus College, Cambridge. We have but little information as to his +University career, but at all events he took his degree of M.A. on +June 5th, 1674.</p> + +<p>Up to this time it would seem that Flamsteed had been engaged, to a +certain extent, in the business carried on by his father. It is true +that he does not give any explicit details, yet there are frequent +references to journeys which he had to take on business matters. But +the time now approached when Flamsteed was to start on an independent +career, and it appears that he took his degree in Cambridge with the +object of entering into holy orders, so that he might settle in a +small living near Derby, which was in the gift of a friend of his +father, and would be at the disposal of the young astronomer. This +scheme was, however, not carried out, but Flamsteed does not tell us +why it failed, his only remark being, that "the good providence of +God that had designed me for another station ordered it otherwise."</p> + +<p>Sir Jonas Moore, one of the influential friends whom Flamsteed's +talents had attracted, seems to have procured for him the position of +king's astronomer, with a salary of 100 pounds per annum. A larger +salary appears to have been designed at first for this office, which +was now being newly created, but as Flamsteed was resolved on taking +holy orders, a lesser salary was in his case deemed sufficient. The +building of the observatory, in which the first Astronomer Royal was +to be installed, seems to have been brought about, or, at all events, +its progress was accelerated, in a somewhat curious manner.</p> + +<p>A Frenchman, named Le Sieur de S. Pierre, came over to London to +promulgate a scheme for discovering longitudes, then a question of +much importance. He brought with him introductions to distinguished +people, and his mission attracted a great deal of attention. The +proposals which he made came under Flamsteed's notice, who pointed +out that the Frenchman's projects were quite inapplicable in the +present state of astronomical science, inasmuch as the places of the +stars were not known with the degree of accuracy which would be +necessary if such methods were to be rendered available. Flamsteed +then goes on to say:—"I heard no more of the Frenchman after this; +but was told that my letters had been shown King Charles. He was +startled at the assertion of the fixed stars' places being false in +the catalogue, and said, with some vehemence, he must have them anew +observed, examined, and corrected, for the use of his seamen."</p> + +<p>The first question to be settled was the site for the new +observatory. Hyde Park and Chelsea College were both mentioned as +suitable localities, but, at Sir Christopher Wren's suggestion, +Greenwich Hill was finally resolved upon. The king made a grant of +five hundred pounds of money. He gave bricks from Tilbury Fort, +while materials, in the shape of wood, iron, and lead, were available +from a gatehouse demolished in the Tower. The king also promised +whatever further material aid might be shown to be necessary. The +first stone of the Royal Observatory was laid on August 10th, 1675, +and within a few years a building was erected in which the art of +modern practical astronomy was to be created. Flamsteed strove with +extraordinary diligence, and in spite of many difficulties, to obtain +a due provision of astronomical instruments, and to arrange for the +carrying on of his observations. Notwithstanding the king's +promises, the astronomer was, however, but scantily provided with +means, and he had no assistants to help him in his work. It follows +that all the observations, as well as the reductions, and, indeed, +all the incidental work of the observatory, had to be carried on by +himself alone. Flamsteed, as we have seen, had, however, many +staunch friends. Sir Jonas Moore in particular at all times rendered +him most valuable assistance, and encouraged him by the warm sympathy +and keen interest which he showed in astronomy. The work of the +first Astronomer Royal was frequently interrupted by recurrent +attacks of the complaints to which we have already referred. He says +himself that "his distempers stick so close that that he cannot +remove them," and he lost much time by prostration from headaches, as +well as from more serious affections.</p> + +<p>The year 1678 found him in the full tide of work in his observatory. +He was specially engaged on the problem of the earth's motion, which +he sought to derive from observations of the sun and of Venus. But +this, as well as many other astronomical researches which he +undertook, were only subsidiary to that which he made the main task +of his life, namely, the formation of a catalogue of fixed stars. At +the time when Flamsteed commenced his career, the only available +catalogue of fixed stars was that of Tycho Brahe. This work had been +published at the commencement of the seventeenth century, and it +contained about a thousand stars. The positions assigned to these +stars, though obtained with wonderful skill, considering the many +difficulties under which Tycho laboured, were quite inaccurate when +judged by our modern standards. Tycho's instruments were necessarily +most rudely divided, and he had, of course, no telescopes to aid him. +Consequently it was merely by a process of sighting that he could +obtain the places of the stars. It must further be remembered that +Tycho had no clocks, and no micrometers. He had, indeed, but little +correct knowledge of the motions of the heavenly bodies to guide +him. To determine the longitudes of a few principal stars he +conceived the ingenious idea of measuring by day the position of +Venus with respect to the sun, an observation which the exceptional +brightness of this planet rendered possible without telescopic aid, +and then by night he observed the position of Venus with regard to +the stars.</p> + +<p>It has been well remarked by Mr. Baily, in his introduction to the +"British Catalogue of Stars," that "Flamsteed's observations, by a +fortunate combination of circumstances, commenced a new and a +brilliant era. It happened that, at that period, the powerful mind +of Newton was directed to this subject; a friendly intercourse then +existed between these two distinguished characters; and thus the +first observations that could lay any claim to accuracy were at once +brought in aid of those deep researches in which our illustrious +geometer was then engaged. The first edition of the 'Principia' +bears testimony to the assistance afforded by Flamsteed to Newton in +these inquiries; although the former considers that the +acknowledgment is not so ample as it ought to have been."</p> + +<p>Although Flamsteed's observations can hardly be said to possess the +accuracy of those made in more recent times, when instruments so much +superior to his have been available, yet they possess an interest of +a special kind from their very antiquity. This circumstance renders +them of particular importance to the astronomer, inasmuch as they are +calculated to throw light on the proper motions of the stars. +Flamsteed's work may, indeed, be regarded as the origin of all +subsequent catalogues, and the nomenclature which he adopted, though +in some respects it can hardly be said to be very defensible, is, +nevertheless, that which has been adopted by all subsequent +astronomers. There were also a great many errors, as might be +expected in a work of such extent, composed almost entirely of +numerical detail. Many of these errors have been corrected by Baily +himself, the assiduous editor of "Flamsteed's Life and Works," for +Flamsteed was so harassed from various causes in the latter part of +his life, and was so subject to infirmities all through his career, +that he was unable to revise his computations with the care that +would have been necessary. Indeed, he observed many additional stars +which he never included in the British Catalogue. It is, as Baily +well remarks, "rather a matter of astonishment that he accomplished +so much, considering his slender means, his weak frame, and the +vexations which he constantly experienced."</p> + +<p>Flamsteed had the misfortune, in the latter part of his life, to +become estranged from his most eminent scientific contemporaries. He +had supplied Newton with places of the moon, at the urgent +solicitation of the author of the "Principia," in order that the +lunar theory should be carefully compared with observation. But +Flamsteed appears to have thought that in Newton's further request +for similar information, he appeared to be demanding as a right that +which Flamsteed considered he was only called upon to render as a +favour. A considerable dispute grew out of this matter, and there +are many letters and documents, bearing on the difficulties which +subsequently arose, that are not, perhaps, very creditable to either +party.</p> + +<p>Notwithstanding his feeble constitution, Flamsteed lived to the age +of seventy-three, his death occurring on the last day of the year +1719.</p> + +<h3><a name="HALLEY" id="HALLEY"></a>HALLEY.</h3> +<p>Isaac Newton was just fourteen years of age when the birth of Edmund +Halley, who was destined in after years to become Newton's warmly +attached friend, and one of his most illustrious scientific +contemporaries, took place. There can be little doubt that the fame +as an astronomer which Halley ultimately acquired, great as it +certainly was, would have been even greater still had it not been +somewhat impaired by the misfortune that he had to shine in the same +sky as that which was illumined by the unparalleled genius of Newton.</p> + +<p>Edmund Halley was born at Haggerston, in the Parish of St. Leonard's, +Shoreditch, on October 29th, 1656. His father, who bore the same +name as his famous son, was a soap-boiler in Winchester Street, +London, and he had conducted his business with such success that he +accumulated an ample fortune. I have been unable to obtain more than +a very few particulars with respect to the early life of the future +astronomer. It would, however, appear that from boyhood he showed +considerable aptitude for the acquisition of various kinds of +learning, and he also had some capacity for mechanical invention. +Halley seems to have received a sound education at St. Paul's School, +then under the care of Dr. Thomas Gale.</p> + +<p>Here, the young philosopher rapidly distanced his competitors in the +various branches of ordinary school instruction. His superiority +was, however, most conspicuous in mathematical studies, and, as a +natural development of such tastes, we learn that by the time he had +left school he had already made good progress in astronomy. At the +age of seventeen he was entered as a commoner at Queen's College, +Oxford, and the reputation that he brought with him to the University +may be inferred from the remark of the writer of "Athenae +Oxonienses," that Halley came to Oxford "with skill in Latin, Greek, +and Hebrew, and such a knowledge of geometry as to make a complete +dial." Though his studies were thus of a somewhat multifarious +nature, yet it is plain that from the first his most favourite +pursuit was astronomy. His earliest efforts in practical observation +were connected with an eclipse which he observed from his father's +house in Winchester Street. It also appears that he had studied +theoretical branches of astronomy so far as to be conversant with the +application of mathematics to somewhat abstruse problems.</p> + +<p>Up to the time of Kepler, philosophers had assumed almost as an axiom +that the heavenly bodies must revolve in circles and that the motion +of the planet around the orbit which it described must be uniform. We +have already seen how that great philosopher, after very persevering +labour, succeeded in proving that the orbits of the planets were not +circles, but that they were ellipses of small eccentricity. Kepler +was, however, unable to shake himself free from the prevailing notion +that the angular motion of the planet ought to be of a uniform +character around some point. He had indeed proved that the motion +round the focus of the ellipse in which the sun lies is not of this +description. One of his most important discoveries even related to +the fact that at some parts of its orbit a planet swings around the +sun with greater angular velocity than at others. But it so happens +that in elliptic tracks which differ but little from circles, as is +the case with all the more important planetary orbits, the motion +round the empty focus of the ellipse is very nearly uniform. It +seemed natural to assume, that this was exactly the case, in which +event each of the two foci of the ellipse would have had a special +significance in relation to the movement of the planet. The youthful +Halley, however, demonstrated that so far as the empty focus was +concerned, the movement of the planet around it, though so nearly +uniform, was still not exactly so, and at the age of nineteen, he +published a treatise on the subject which at once placed him in the +foremost rank amongst theoretical astronomers.</p> + +<p>But Halley had no intention of being merely an astronomer with his +pen. He longed to engage in the practical work of observing. He saw +that the progress of exact astronomy must depend largely on the +determination of the positions of the stars with all attainable +accuracy. He accordingly determined to take up this branch of work, +which had been so successfully initiated by Tycho Brahe.</p> + +<p>At the present day, astronomers of the great national observatories +are assiduously engaged in the determination of the places of the +stars. A knowledge of the exact positions of these bodies is indeed +of the most fundamental importance, not alone for the purposes of +scientific astronomy, but also for navigation and for extensive +operations of surveying in which accuracy is desired. The fact that +Halley determined to concentrate himself on this work shows clearly +the scientific acumen of the young astronomer.</p> + +<p>Halley, however, found that Hevelius, at Dantzig, and Flamsteed, the +Astronomer Royal at Greenwich, were both engaged on work of this +character. He accordingly determined to direct his energies in a way +that he thought would be more useful to science. He resigned to the +two astronomers whom I have named the investigation of the stars in +the northern hemisphere, and he sought for himself a field hitherto +almost entirely unworked. He determined to go to the southern +hemisphere, there to measure and survey those stars which were +invisible in Europe, so that his work should supplement the labours +of the northern astronomers, and that the joint result of his labours +and of theirs might be a complete survey of the most important stars +on the surface of the heavens.</p> + +<p>In these days, after so many ardent students everywhere have devoted +themselves to the study of Nature, it seems difficult for a beginner +to find a virgin territory in which to commence his explorations. +Halley may, however, be said to have enjoyed the privilege of +commencing to work in a magnificent region, the contents of which +were previously almost entirely unknown. Indeed none of the stars +which were so situated as to have been invisible from Tycho Brahe's +observatory at Uraniborg, in Denmark, could be said to have been +properly observed. There was, no doubt, a rumour that a Dutchman had +observed southern stars from the island of Sumatra, and certain stars +were indicated in the southern heavens on a celestial globe. On +examination, however, Halley found that no reliance could be placed +on the results which had been obtained, so that practically the field +before him may be said to have been unworked.</p> + +<p>At the age of twenty, without having even waited to take that degree +at the university which the authorities would have been glad to +confer on so promising an undergraduate, this ardent student of +Nature sought his father's permission to go to the southern +hemisphere for the purpose of studying the stars which lie around the +southern pole. His father possessed the necessary means, and he had +likewise the sagacity to encourage the young astronomer. He was +indeed most anxious to make everything as easy as possible for so +hopeful a son. He provided him with an allowance of 300 pounds a +year, which was regarded as a very munificent provision in those +days. Halley was also furnished with letters of recommendation from +King Charles II., as well as from the directors of the East India +Company. He accordingly set sail with his instruments in the year +1676, in one of the East India Company's ships, for the island of St. +Helena, which he had selected as the scene of his labours.</p> + +<p><a name="halley_ill" id="halley_ill"></a></p> + +<div class="figcenter" style="width: 407px;"> +<a href="images/ill_haley.jpg"> +<img src="images/ill_haley_sml.jpg" width="407" height="484" alt="HALLEY." title="" /></a> +<span class="caption">HALLEY.</span> +</div> + +<p>After an uneventful voyage of three months, the astronomer landed on +St. Helena, with his sextant of five and a half feet radius, and a +telescope 24 feet long, and forthwith plunged with ardour into his +investigation of the southern skies. He met, however, with one very +considerable disappointment. The climate of this island had been +represented to him as most favourable for astronomical observation; +but instead of the pure blue skies he had been led to expect, he +found that they were almost always more or less clouded, and that +rain was frequent, so that his observations were very much +interrupted. On this account he only remained at St. Helena for a +single year, having, during that time, and in spite of many +difficulties, accomplished a piece of work which earned for him the +title of "our southern Tycho." Thus did Halley establish his fame as +an astronomer on the same lonely rock in mid-Atlantic, which nearly a +century and a-half later became the scene of Napoleon's imprisonment, +when his star, in which he believed so firmly, had irretrievably set.</p> + +<p>On his return to England, Halley prepared a map which showed the +result of his labours, and he presented it to the king, in 1677. +Like his great predecessor Tycho, Halley did not altogether disdain +the arts of the courtier, for he endeavoured to squeeze a new +constellation into the group around the southern pole which he styled +"The Royal Oak," adding a description to the effect that the +incidents of which "The Royal Oak" was a symbol were of sufficient +importance to be inscribed on the surface of the heavens.</p> + +<p>There is reason to think that Charles II. duly appreciated the +scientific renown which one of his subjects had achieved, and it was +probably through the influence of the king that Halley was made a +Master of Arts at Oxford on November 18th, 1678. Special reference +was made on the occasion to his observations at St. Helena, as +evidence of unusual attainments in mathematics and astronomy. This +degree was no small honour to such a young man, who, as we have seen, +quitted his university before he had the opportunity of graduating in +the ordinary manner.</p> + +<p>On November 30th, in the same year, the astronomer received a further +distinction in being elected a Fellow of the Royal Society. From +this time forward he took a most active part in the affairs of the +Society, and the numerous papers which he read before it form a very +valuable part of that notable series of volumes known as the +"Philosophical Transactions." He was subsequently elected to the +important office of secretary to the Royal Society, and he discharged +the duties of his post until his appointment to Greenwich +necessitated his resignation.</p> + +<p>Within a year of Halley's election as a Fellow of the Royal Society, +he was chosen by the Society to represent them in a discussion which +had arisen with Hevelius. The nature of this discussion, or rather +the fact that any discussion should have been necessary, may seem +strange to modern astronomers, for the point is one on which it would +now seem impossible for there to be any difference of opinion. We +must, however, remember that the days of Halley were, comparatively +speaking, the days of infancy as regards the art of astronomical +observation, and issues that now seem obvious were often, in those +early times, the occasions of grave and anxious consideration. The +particular question on which Halley had to represent the Royal +Society may be simply stated. When Tycho Brahe made his memorable +investigations into the places of the stars, he had no telescopes to +help him. The famous instruments at Uraniborg were merely provided +with sights, by which the telescope was pointed to a star on the same +principle as a rifle is sighted for a target. Shortly after Tycho's +time, Galileo invented the telescope. Of course every one admitted +at once the extraordinary advantages which the telescope had to +offer, so far as the mere question of the visibility of objects was +concerned. But the bearing of Galileo's invention upon what we may +describe as the measuring part of astronomy was not so immediately +obvious. If a star be visible to the unaided eye, we can determine +its place by such instruments as those which Tycho used, in which no +telescope is employed. We can, however, also avail ourselves of an +instrument in which we view the star not directly but through the +intervention of the telescope. Can the place of the star be +determined more accurately by the latter method than it can when the +telescope is dispensed with? With our present knowledge, of course, +there is no doubt about the answer; every one conversant with +instruments knows that we can determine the place of a star far more +accurately with the telescope than is possible by any mere sighting +apparatus. In fact an observer would be as likely to make an error +of a minute with the sighting apparatus in Tycho's instrument, as he +would be to make an error of a second with the modern telescope, or, +to express the matter somewhat differently, we may say, speaking +quite generally, that the telescopic method of determining the places +of the stars does not lead to errors more than one-sixtieth part as +great as which are unavoidable when we make use of Tycho's method.</p> + +<p>But though this is so apparent to the modern astronomer, it was not +at all apparent in the days of Halley, and accordingly he was sent +off to discuss the question with the Continental astronomers. +Hevelius, as the representative of the older method, which Tycho had +employed with such success, maintained that an instrument could be +pointed more accurately at a star by the use of sights than by the +use of a telescope, and vigorously disputed the claims put forward by +those who believed that the latter method was the more suitable. On +May 14th, 1679, Halley started for Dantzig, and the energetic +character of the man may be judged from the fact that on the very +night of his arrival he commenced to make the necessary +observations. In those days astronomical telescopes had only +obtained a fractional part of the perfection possessed by the +instruments in our modern observatories, and therefore it may not be +surprising that the results of the trial were not immediately +conclusive. Halley appears to have devoted much time to the +investigation; indeed, he remained at Dantzig for more than a +twelve-month. On his return to England, he spoke highly of the skill +which Hevelius exhibited in the use of his antiquated methods, but +Halley was nevertheless too sagacious an observer to be shaken in his +preference for the telescopic method of observation.</p> + +<p>The next year we find our young astronomer starting for a Continental +tour, and we, who complain if the Channel passage lasts more than an +hour or two, may note Halley's remark in writing to Hooke on June +15th, 1680: "Having fallen in with bad weather we took forty hours in +the journey from Dover to Calais." The scientific distinction which +he had already attained was such that he was received in Paris with +marked attention. A great deal of his time seems to have been passed +in the Paris observatory, where Cassini, the presiding genius, +himself an astronomer of well-deserved repute, had extended a hearty +welcome to his English visitor. They made observations together of +the place of the splendid comet which was then attracting universal +attention, and Halley found the work thus done of much use when he +subsequently came to investigate the path pursued by this body. +Halley was wise enough to spare no pains to derive all possible +advantages from his intercourse with the distinguished savants of the +French capital. In the further progress of his tour he visited the +principal cities of the Continent, leaving behind him everywhere the +memory of an amiable disposition and of a rare intelligence.</p> + +<p>After Halley's return to England, in 1682, he married a young lady +named Mary Tooke, with whom he lived happily, till her death +fifty-five years later. On his marriage, he took up his abode in +Islington, where he erected his instruments and recommenced his +observations.</p> + +<p>It has often been the good fortune of astronomers to render practical +services to humanity by their investigations, and Halley's +achievements in this respect deserve to be noted. A few years after +he had settled in England, he published an important paper on the +variation of the magnetic compass, for so the departure of the needle +from the true north is termed. This subject had indeed early engaged +his attention, and he continued to feel much interest in it up to the +end of his life. With respect to his labours in this direction, Sir +John Herschel says: "To Halley we owe the first appreciation of the +real complexity of the subject of magnetism. It is wonderful indeed, +and a striking proof of the penetration and sagacity of this +extraordinary man, that with his means of information he should have +been able to draw such conclusions, and to take so large and +comprehensive a view of the subject as he appears to have done." In +1692, Halley explained his theory of terrestrial magnetism, and +begged captains of ships to take observations of the variations of +the compass in all parts of the world, and to communicate them to the +Royal Society, "in order that all the facts may be readily available +to those who are hereafter to complete this difficult and complicated +subject."</p> + +<p>The extent to which Halley was in advance of his contemporaries, in +the study of terrestrial magnetism, may be judged from the fact that +the subject was scarcely touched after his time till the year 1811. +The interest which he felt in it was not of a merely theoretical +kind, nor was it one which could be cultivated in an easy-chair. Like +all true investigators, he longed to submit his theory to the test of +experiment, and for that purpose Halley determined to observe the +magnetic variation for himself. He procured from King William III. +the command of a vessel called the "Paramour Pink," with which he +started for the South Seas in 1694. This particular enterprise was +not, however, successful; for, on crossing the line, some of his men +fell sick and one of his lieutenants mutinied, so that he was obliged +to return the following year with his mission unaccomplished. The +government cashiered the lieutenant, and Halley having procured a +second smaller vessel to accompany the "Paramour Pink," started once +more in September, 1699. He traversed the Atlantic to the 52nd +degree of southern latitude, beyond which his further advance was +stopped. "In these latitudes," he writes to say, "we fell in with +great islands of ice of so incredible height and magnitude, that I +scarce dare write my thoughts of it."</p> + +<p>On his return in 1700, Halley published a general chart, showing the +variation of the compass at the different places which he had +visited. On these charts he set down lines connecting those +localities at which the magnetic variation was identical. He thus +set an example of the graphic representation of large masses of +complex facts, in such a manner as to appeal at once to the eye, a +method of which we make many applications in the present day.</p> + +<p>But probably the greatest service which Halley ever rendered to human +knowledge was the share in which he took in bringing Newton's +"Principia" before the world. In fact, as Dr. Glaisher, writing in +1888, has truly remarked, "but for Halley the 'Principia' would not +have existed."</p> + +<p>It was a visit from Halley in the year 1684 which seems to have first +suggested to Newton the idea of publishing the results of his +investigations on gravitation. Halley, and other scientific +contemporaries, had no doubt some faint glimmering of the great truth +which only Newton's genius was able fully to reveal. Halley had +indeed shown how, on the assumptions that the planets move in +circular orbits round the sun, and that the squares of their periodic +times are proportional to the cubes of their mean distances, it may +be proved that the force acting on each planet must vary inversely as +the square of its distance from the sun. Since, however, each of the +planets actually moves in an ellipse, and therefore, at continually +varying distances from the sun, it becomes a much more difficult +matter to account mathematically for the body's motions on the +supposition that the attractive force varies inversely as the square +of the distance. This was the question with which Halley found +himself confronted, but which his mathematical abilities were not +adequate to solve. It would seem that both Hooke and Sir Christopher +Wren were interested in the same problem; in fact, the former claimed +to have arrived at a solution, but declined to make known his +results, giving as an excuse his desire that others having tried and +failed might learn to value his achievements all the more. Halley, +however, confessed that his attempts at the solution were +unsuccessful, and Wren, in order to encourage the other two +philosophers to pursue the inquiry, offered to present a book of +forty shillings value to either of them who should in the space of +two months bring him a convincing proof of it. Such was the value +which Sir Christopher set on the Law of Gravitation, upon which the +whole fabric of modern astronomy may be said to stand.</p> + +<p>Finding himself unequal to the task, Halley went down to Cambridge to +see Newton on the subject, and was delighted to learn that the great +mathematician had already completed the investigation. He showed +Halley that the motions of all the planets could be completely +accounted for on the hypothesis of a force of attraction directed +towards the sun, which varies inversely as the square of the distance +from that body.</p> + +<p>Halley had the genius to perceive the tremendous importance of +Newton's researches, and he ceased not to urge upon the recluse man +of science the necessity for giving his new discoveries publication. +He paid another visit to Cambridge with the object of learning more +with regard to the mathematical methods which had already conducted +Newton to such sublime truths, and he again encouraged the latter +both to pursue his investigations, and to give some account of them +to the world. In December of the same year Halley had the +gratification of announcing to the Royal Society that Newton had +promised to send that body a paper containing his researches on +Gravitation.</p> + +<p>It seems that at this epoch the finances of the Royal Society were at +a very low ebb. This impecuniosity was due to the fact that a book +by Willoughby, entitled "De Historia Piscium," had been recently +printed by the society at great expense. In fact, the coffers were +so low that they had some difficulty in paying the salaries of their +permanent officials. It appears that the public did not care about +the history of fishes, or at all events the volume did not meet with +the ready demand which was expected for it. Indeed, it has been +recorded that when Halley had undertaken to measure the length of a +degree of the earth's surface, at the request of the Royal Society, +it was ordered that his expenses be defrayed either in 50 pounds +sterling, or in fifty books of fishes. Thus it happened that on June +2nd, the Council, after due consideration of ways and means in +connection with the issue of the Principia, "ordered that Halley +should undertake the business of looking after the book and printing +it at his own charge," which he engaged to do.</p> + +<p>It was, as we have elsewhere mentioned, characteristic of Newton that +he detested controversies, and he was, in fact, inclined to suppress +the third book of the "Principia" altogether rather than have any +conflict with Hooke with respect to the discoveries there +enunciated. He also thought of changing the name of the work to De +Motu Corporum Libri Duo, but upon second thoughts, he retained the +original title, remarking, as he wrote to Halley, "It will help the +sale of the book, which I ought not to diminish, now it is yours," a +sentence which shows conclusively, if further proof were necessary, +that Halley had assumed the responsibility of its publication.</p> + +<p>Halley spared no pains in pushing forward the publication of his +illustrious friend's great work, so that in the same year he was in a +position to present a complete copy to King James II., with a proper +discourse of his own. Halley also wrote a set of Latin hexameters in +praise of Newton's genius, which he printed at the beginning of the +work. The last line of this specimen of Halley's poetic muse may be +thus rendered: "Nor mortals nearer may approach the gods."</p> + +<p>The intimate friendship between the two greatest astronomers of the +time continued without interruption till the death of Newton. It +has, indeed, been alleged that some serious cause of estrangement +arose between them. There is, however, no satisfactory ground for +this statement; indeed, it may be regarded as effectually disposed of +by the fact that, in the year 1727, Halley took up the defence of his +friend, and wrote two learned papers in support of Newton's "System +of Chronology," which had been seriously attacked by a certain +ecclesiastic. It is quite evident to any one who has studied these +papers that Halley's friendship for Newton was as ardent as ever.</p> + +<p>The generous zeal with which Halley adopted and defended the +doctrines of Newton with regard to the movements of the celestial +bodies was presently rewarded by a brilliant discovery, which has +more than any of his other researches rendered his name a familiar +one to astronomers. Newton, having explained the movement of the +planets, was naturally led to turn his attention to comets. He +perceived that their journeyings could be completely accounted for as +consequences of the attraction of the sun, and he laid down the +principles by which the orbit of a comet could be determined, +provided that observations of its positions were obtained at three +different dates. The importance of these principles was by no one +more quickly recognised than by Halley, who saw at once that it +provided the means of detecting something like order in the movements +of these strange wanderers. The doctrine of Gravitation seemed to +show that just as the planets revolved around the sun in ellipses, so +also must the comets. The orbit, however, in the case of the comet, +is so extremely elongated that the very small part of the elliptic +path within which the comet is both near enough and bright enough to +be seen from the earth, is indistinguishable from a parabola. +Applying these principles, Halley thought it would be instructive to +study the movements of certain bright comets, concerning which +reliable observations could be obtained. At the expense of much +labour, he laid down the paths pursued by twenty-four of these +bodies, which had appeared between the years 1337 and 1698. Amongst +them he noticed three, which followed tracks so closely resembling +each other, that he was led to conclude the so called three comets +could only have been three different appearances of the same body. +The first of these occurred in 1531, the second was seen by Kepler in +1607, and the third by Halley himself in 1682. These dates suggested +that the observed phenomena might be due to the successive returns of +one and the same comet after intervals of seventy-five or seventy-six +years. On the further examination of ancient records, Halley found +that a comet had been seen in the year 1456, a date, it will be +observed, seventy-five years before 1531. Another had been observed +seventy-six years earlier than 1456, viz., in 1380, and another +seventy-five years before that, in 1305.</p> + +<p>As Halley thus found that a comet had been recorded on several +occasions at intervals of seventy-five or seventy-six years, he was +led to the conclusion that these several apparitions related to one +and the same object, which was an obedient vassal of the sun, +performing an eccentric journey round that luminary in a period of +seventy-five or seventy-six years. To realise the importance of this +discovery, it should be remembered that before Halley's time a comet, +if not regarded merely as a sign of divine displeasure, or as an omen +of intending disaster, had at least been regarded as a chance visitor +to the solar system, arriving no one knew whence, and going no one +knew whither.</p> + +<p>A supreme test remained to be applied to Halley's theory. The +question arose as to the date at which this comet would be seen +again. We must observe that the question was complicated by the fact +that the body, in the course of its voyage around the sun, was +exposed to the incessant disturbing action produced by the attraction +of the several planets. The comet therefore, does not describe a +simple ellipse as it would do if the attraction of the sun were the +only force by which its movement were controlled. Each of the +planets solicits the comet to depart from its track, and though the +amount of these attractions may be insignificant in comparison with +the supreme controlling force of the sun, yet the departure from the +ellipse is quite sufficient to produce appreciable irregularities in +the comet's movement. At the time when Halley lived, no means +existed of calculating with precision the effect of the disturbance a +comet might experience from the action of the different planets. +Halley exhibited his usual astronomical sagacity in deciding that +Jupiter would retard the return of the comet to some extent. Had it +not been for this disturbance the comet would apparently have been +due in 1757 or early in 1758. But the attraction of the great planet +would cause delay, so that Halley assigned, for the date of its +re-appearance, either the end of 1758 or the beginning of 1759. +Halley knew that he could not himself live to witness the fulfilment +of his prediction, but he says: "If it should return, according to +our predictions, about the year 1758, impartial posterity will not +refuse to acknowledge that this was first discovered by an +Englishman." This was, indeed, a remarkable prediction of an event +to occur fifty-three years after it had been uttered. The way in +which it was fulfilled forms one of the most striking episodes in the +history of astronomy. The comet was first seen on Christmas Day, +1758, and passed through its nearest point to the sun on March 13th, +1759. Halley had then been lying in his grave for seventeen years, +yet the verification of his prophecy reflects a glory on his name +which will cause it to live for ever in the annals of astronomy. The +comet paid a subsequent visit in 1835, and its next appearance is due +about 1910.</p> + +<p>Halley next entered upon a labour which, if less striking to the +imagination than his discoveries with regard to comets, is still of +inestimable value in astronomy. He undertook a series of +investigations with the object of improving our knowledge of the +movements of the planets. This task was practically finished in +1719, though the results of it were not published until after his +death in 1749. In the course of it he was led to investigate closely +the motion of Venus, and thus he came to recognise for the first time +the peculiar importance which attaches to the phenomenon of the +transit of this planet across the sun. Halley saw that the transit, +which was to take place in the year 1761, would afford a favourable +opportunity for determining the distance of the sun, and thus +learning the scale of the solar system. He predicted the +circumstances of the phenomenon with an astonishing degree of +accuracy, considering his means of information, and it is +unquestionably to the exertions of Halley in urging the importance of +the matter upon astronomers that we owe the unexampled degree of +interest taken in the event, and the energy which scientific men +exhibited in observing it. The illustrious astronomer had no hope of +being himself a witness of the event, for it could not happen till +many years after his death. This did not, however, diminish his +anxiety to impress upon those who would then be alive, the importance +of the occurrence, nor did it lead him to neglect anything which +might contribute to the success of the observations. As we now know, +Halley rather over-estimated the value of the transit of Venus, as a +means of determining the solar distance. The fact is that the +circumstances are such that the observation of the time of contact +between the edge of the planet and the edge of the sun cannot be made +with the accuracy which he had expected.</p> + +<p>In 1691, Halley became a candidate for the Savilian Professorship of +Astronomy at Oxford. He was not, however, successful, for his +candidature was opposed by Flamsteed, the Astronomer Royal of the +time, and another was appointed. He received some consolation for +this particular disappointment by the fact that, in 1696, owing to +Newton's friendly influence, he was appointed deputy Controller of +the Mint at Chester, an office which he did not retain for long, as +it was abolished two years later. At last, in 1703, he received what +he had before vainly sought, and he was appointed to the Savilian +chair.</p> + +<p>His observations of the eclipse of the sun, which occurred in 1715, +added greatly to Halley's reputation. This phenomenon excited +special attention, inasmuch as it was the first total eclipse of the +sun which had been visible in London since the year 1140. Halley +undertook the necessary calculations, and predicted the various +circumstances with a far higher degree of precision than the official +announcement. He himself observed the phenomenon from the Royal +Society's rooms, and he minutely describes the outer atmosphere of +the sun, now known as the corona; without, however, offering an +opinion as to whether it was a solar or a lunar appendage.</p> + +<p>At last Halley was called to the dignified office which he of all men +was most competent to fill. On February 9th, 1720, he was appointed +Astronomer Royal in succession to Flamsteed. He found things at the +Royal Observatory in a most unsatisfactory state. Indeed, there were +no instruments, nor anything else that was movable; for such things, +being the property of Flamsteed, had been removed by his widow, and +though Halley attempted to purchase from that lady some of the +instruments which his predecessor had employed, the unhappy personal +differences which had existed between him and Flamsteed, and which, +as we have already seen, prevented his election as Savilian Professor +of Astronomy, proved a bar to the negotiation. Greenwich Observatory +wore a very different appearance in those days, from that which the +modern visitor, who is fortunate enough to gain admission, may now +behold. Not only did Halley find it bereft of instruments, we learn +besides that he had no assistants, and was obliged to transact the +whole business of the establishment single-handed.</p> + +<p>In 1721, however, he obtained a grant of 500 pounds from the Board of +Ordnance, and accordingly a transit instrument was erected in the +same year. Some time afterwards he procured an eight-foot quadrant, +and with these instruments, at the age of sixty-four, he commenced a +series of observations on the moon. He intended, if his life was +spared, to continue his observations for a period of eighteen years, +this being, as astronomers know, a very important cycle in connection +with lunar movements. The special object of this vast undertaking +was to improve the theory of the moon's motion, so that it might +serve more accurately to determine longitudes at sea. This +self-imposed task Halley lived to carry to a successful termination, +and the tables deduced from his observations, and published after his +death, were adopted almost universally by astronomers, those of the +French nation being the only exception.</p> + +<p>Throughout his life Halley had been singularly free from illness of +every kind, but in 1737 he had a stroke of paralysis. Notwithstanding +this, however, he worked diligently at his telescope till 1739, after +which his health began rapidly to give way. He died on January 14th, +1742, in the eighty-sixth year of his age, retaining his mental +faculties to the end. He was buried in the cemetery of the church of +Lee in Kent, in the same grave as his wife, who had died five years +previously. We are informed by Admiral Smyth that Pond, a later +Astronomer Royal, was afterwards laid in the same tomb.</p> + +<p>Halley's disposition seems to have been generous and candid, and +wholly free from anything like jealousy or rancour. In person he was +rather above the middle height, and slight in build; his complexion +was fair, and he is said to have always spoken, as well as acted, +with uncommon sprightliness. In the eloge pronounced upon him at the +Paris Academie Des Sciences, of which Halley had been made a member +in 1719 it was said, "he possessed all the qualifications which were +necessary to please princes who were desirous of instruction, with a +great extent of knowledge and a constant presence of mind; his +answers were ready, and at the same time pertinent, judicious, polite +and sincere."</p> + +<p><a name="greenwich_observatory" id="greenwich_observatory"></a></p> + +<div class="figcenter" style="width: 705px;"> +<a href="images/ill_grnch_oberservatory_halleys_time.jpg"> +<img src="images/ill_grnch_oberservatory_halleys_time_sml.jpg" width="705" height="429" alt="GREENWICH OBSERVATORY IN HALLEY'S TIME." title="" /></a> +<span class="caption">GREENWICH OBSERVATORY IN HALLEY'S TIME.</span> +</div> + +<p>Thus we find that Peter the Great was one of his most ardent +admirers. He consulted the astronomer on matters connected with +shipbuilding, and invited him to his own table. But Halley possessed +nobler qualifications than the capacity of pleasing Princes. He was +able to excite and to retain the love and admiration of his equals. +This was due to the warmth of his attachments, the unselfishness of +his devotion to his friends, and to a vein of gaiety and good-humour +which pervaded all his conversation.</p> + +<h3><a name="BRADLEY" id="BRADLEY"></a>BRADLEY.</h3> +<p>James Bradley was descended from an ancient family in the county of +Durham. He was born in 1692 or 1693, at Sherbourne, in +Gloucestershire, and was educated in the Grammar School at +Northleach. From thence he proceeded in due course to Oxford, where +he was admitted a commoner at Balliol College, on March 15th, 1711. +Much of his time, while an undergraduate, was passed in Essex with +his maternal uncle, the Rev. James Pound, who was a well-known man of +science and a diligent observer of the stars. It was doubtless by +intercourse with his uncle that young Bradley became so expert in the +use of astronomical instruments, but the immortal discoveries he +subsequently made show him to have been a born astronomer.</p> + +<p>The first exhibition of Bradley's practical skill seems to be +contained in two observations which he made in 1717 and 1718. They +have been published by Halley, whose acuteness had led him to +perceive the extraordinary scientific talents of the young +astronomer. Another illustration of the sagacity which Bradley +manifested, even at the very commencement of his astronomical career, +is contained in a remark of Halley's, who says: "Dr. Pound and his +nephew, Mr. Bradley, did, myself being present, in the last +opposition of the sun and Mars this way demonstrate the extreme +minuteness of the sun's parallax, and that it was not more than +twelve seconds nor less than nine seconds." To make the significance +of this plain, it should be observed that the determination of the +sun's parallax is equivalent to the determination of the distance +from the earth to the sun. At the time of which we are now writing, +this very important unit of celestial measurement was only very +imperfectly known, and the observations of Pound and Bradley may be +interpreted to mean that, from their observations, they had come to +the conclusion that the distance from the earth to the sun must be +more than 94 millions of miles, and less than 125 millions. We now, +of course, know that they were not exactly right, for the true +distance of the sun is about 93 millions of miles. We cannot, +however, but think that it was a very remarkable approach for the +veteran astronomer and his brilliant nephew to make towards the +determination of a magnitude which did not become accurately known +till fifty years later.</p> + +<p>Among the earliest parts of astronomical work to which Bradley's +attention was directed, were the eclipses of Jupiter's satellites. +These phenomena are specially attractive inasmuch as they can be so +readily observed, and Bradley found it extremely interesting to +calculate the times at which the eclipses should take place, and then +to compare his observations with the predicted times. From the +success that he met with in this work, and from his other labours, +Bradley's reputation as an astronomer increased so greatly that on +November the 6th, 1718, he was elected a Fellow of the Royal Society.</p> + +<p>Up to this time the astronomical investigations of Bradley had been +more those of an amateur than of a professional astronomer, and as it +did not at first seem likely that scientific work would lead to any +permanent provision, it became necessary for the youthful astronomer +to choose a profession. It had been all along intended that he +should enter the Church, though for some reason which is not told us, +he did not take orders as soon as his age would have entitled him to +do so. In 1719, however, the Bishop of Hereford offered Bradley the +Vicarage of Bridstow, near Ross, in Monmouthshire, and on July 25th, +1720, he having then taken priest's orders, was duly instituted in +his vicarage. In the beginning of the next year, Bradley had some +addition to his income from the proceeds of a Welsh living, which, +being a sinecure, he was able to hold with his appointment at +Bridstow. It appears, however, that his clerical occupations were +not very exacting in their demands upon his time, for he was still +able to pay long and often-repeated visits to his uncle at +Wandsworth, who, being himself a clergyman, seems to have received +occasional assistance in his ministerial duties from his astronomical +nephew.</p> + +<p>The time, however, soon arrived when Bradley was able to make a +choice between continuing to exercise his profession as a divine, or +devoting himself to a scientific career. The Savilian Professorship +of Astronomy in the University of Oxford became vacant by the death +of Dr. John Keill. The statutes forbade that the Savilian Professor +should also hold a clerical appointment, and Mr. Pound would +certainly have been elected to the professorship had he consented to +surrender his preferments in the Church. But Pound was unwilling to +sacrifice his clerical position, and though two or three other +candidates appeared in the field, yet the talents of Bradley were so +conspicuous that he was duly elected, his willingness to resign the +clerical profession having been first ascertained.</p> + +<p>There can be no doubt that, with such influential friends as Bradley +possessed, he would have made great advances had he adhered to his +profession as a divine. Bishop Hoadly, indeed, with other marks of +favour, had already made the astronomer his chaplain. The engrossing +nature of Bradley's interest in astronomy decided him, however, to +sacrifice all other prospects in comparison with the opening afforded +by the Savilian Professorship. It was not that Bradley found himself +devoid of interest in clerical matters, but he felt that the true +scope for such abilities as he possessed would be better found in the +discharge of the scientific duties of the Oxford chair than in the +spiritual charge of a parish. On April the 26th, 1722, Bradley read +his inaugural lecture in that new position on which he was destined +to confer such lustre.</p> + +<p>It must, of course, be remembered that in those early days the art of +constructing the astronomical telescope was very imperfectly +understood. The only known method for getting over the peculiar +difficulties presented in the construction of the refracting +telescope, was to have it of the most portentous length. In fact, +Bradley made several of his observations with an instrument of two +hundred and twelve feet focus. In such a case, no tube could be +used, and the object glass was merely fixed at the top of a high +pole. Notwithstanding the inconvenience and awkwardness of such an +instrument, Bradley by its means succeeded in making many careful +measurements. He observed, for example, the transit of Mercury over +the sun's disc, on October 9th, 1723; he also observed the dimensions +of the planet Venus, while a comet which Halley discovered on October +the 9th, 1723, was assiduously observed at Wanstead up to the middle +of the ensuing month. The first of Bradley's remarkable +contributions to the "Philosophical Transactions" relates to this +comet, and the extraordinary amount of work that he went through in +connection therewith may be seen from an examination of his book of +Calculations which is still extant.</p> + +<p>The time was now approaching when Bradley was to make the first of +those two great discoveries by which his name has acquired a lustre +that has placed him in the very foremost rank of astronomical +discoverers. As has been often the case in the history of science, +the first of these great successes was attained while he was pursuing +a research intended for a wholly different purpose. It had long been +recognised that as the earth describes a vast orbit, nearly two +hundred million miles in diameter, in its annual journey round the +sun, the apparent places of the stars should alter, to some extent, +in correspondence with the changes in the earth's position. The +nearer the star the greater the shift in its apparent place on the +heavens, which must arise from the fact that it was seen from +different positions in the earth's orbit. It had been pointed out +that these apparent changes in the places of the stars, due to the +movement of the earth, would provide the means of measuring the +distances of the stars. As, however, these distances are enormously +great in comparison with the orbit which the earth describes around +the sun, the attempt to determine the distances of the stars by the +shift in their positions had hitherto proved ineffectual. Bradley +determined to enter on this research once again; he thought that by +using instruments of greater power, and by making measurements of +increased delicacy, he would be able to perceive and to measure +displacements which had proved so small as to elude the skill of the +other astronomers who had previously made efforts in the same +direction. In order to simplify the investigation as much as +possible, Bradley devoted his attention to one particular star, Beta +Draconis, which happened to pass near his zenith. The object of +choosing a star in this position was to avoid the difficulties which +would be introduced by refraction had the star occupied any other +place in the heavens than that directly overhead.</p> + +<p>We are still able to identify the very spot on which the telescope +stood which was used in this memorable research. It was erected at +the house then occupied by Molyneux, on the western extremity of Kew +Green. The focal length was 24 feet 3 inches, and the eye-glass was +3 and a half feet above the ground floor. The instrument was first +set up on November 26th, 1725. If there had been any appreciable +disturbance in the place of Beta Draconis in consequence of the +movement of the earth around the sun, the star must appear to have +the smallest latitude when in conjunction with the sun, and the +greatest when in opposition. The star passed the meridian at noon in +December, and its position was particularly noticed by Molyneux on +the third of that month. Any perceptible displacement by +parallax—for so the apparent change in position, due to the earth's +motion, is called—would would have made the star shift towards the +north. Bradley, however, when observing it on the 17th, was +surprised to find that the apparent place of the star, so far from +shifting towards the north, as they had perhaps hoped it would, was +found to lie a little more to the south than when it was observed +before. He took extreme care to be sure that there was no mistake in +his observation, and, true astronomer as he was, he scrutinized with +the utmost minuteness all the circumstances of the adjustment of his +instruments. Still the star went to the south, and it continued so +advancing in the same direction until the following March, by which +time it had moved no less than twenty seconds south from the place +which it occupied when the first observation was made. After a brief +pause, in which no apparent movement was perceptible, the star by the +middle of April appeared to be returning to the north. Early in June +it reached the same distance from the zenith which it had in +December. By September the star was as much as thirty-nine seconds +more to the north than it had been in March, then it returned towards +the south, regaining in December the same situation which it had +occupied twelve months before.</p> + +<p>This movement of the star being directly opposite to the movements +which would have been the consequence of parallax, seemed to show +that even if the star had any parallax its effects upon the apparent +place were entirely masked by a much larger motion of a totally +different description. Various attempts were made to account for the +phenomenon, but they were not successful. Bradley accordingly +determined to investigate the whole subject in a more thorough +manner. One of his objects was to try whether the same movements +which he had observed in one star were in any similar degree +possessed by other stars. For this purpose he set up a new +instrument at Wanstead, and there he commenced a most diligent +scrutiny of the apparent places of several stars which passed at +different distances from the zenith. He found in the course of this +research that other stars exhibited movements of a similar +description to those which had already proved so perplexing. For a +long time the cause of these apparent movements seemed a mystery. At +last, however, the explanation of these remarkable phenomena dawned +upon him, and his great discovery was made.</p> + +<p>One day when Bradley was out sailing he happened to remark that every +time the boat was laid on a different tack the vane at the top of the +boat's mast shifted a little, as if there had been a slight change in +the direction of the wind. After he had noticed this three or four +times he made a remark to the sailors to the effect that it was very +strange the wind should always happen to change just at the moment +when the boat was going about. The sailors, however, said there had +been no change in the wind, but that the alteration in the vane was +due to the fact that the boat's course had been altered. In fact, +the position of the vane was determined both by the course of the +boat and the direction of the wind, and if either of these were +altered there would be a corresponding change in the direction of the +vane. This meant, of course, that the observer in the boat which was +moving along would feel the wind coming from a point different from +that in which the wind appeared to be blowing when the boat was at +rest, or when it was sailing in some different direction. Bradley's +sagacity saw in this observation the clue to the Difficulty which had +so long troubled him.</p> + +<p>It had been discovered before the time of Bradley that the passage of +light through space is not an instantaneous phenomenon. Light +requires time for its journey. Galileo surmised that the sun may +have reached the horizon before we see it there, and it was indeed +sufficiently obvious that a physical action, like the transmission of +light, could hardly take place without requiring some lapse of time. +The speed with which light actually travelled was, however, so rapid +that its determination eluded all the means of experimenting which +were available in those days. The penetration of Roemer had +previously detected irregularities in the observed times of the +eclipses of Jupiter's satellites, which were undoubtedly due to the +interval which light required for stretching across the +interplanetary spaces. Bradley argued that as light can only travel +with a certain speed, it may in a measure be regarded like the wind, +which he noticed in the boat. If the observer were at rest, that is +to say, if the earth were a stationary object, the direction in which +the light actually does come would be different from that in which it +appears to come when the earth is in motion. It is true that the +earth travels but eighteen miles a second, while the velocity with +which light is borne along attains to as much as 180,000 miles a +second. The velocity of light is thus ten thousand times greater +than the speed of the earth. But even though the wind blew ten +thousand times faster than the speed with which the boat was sailing +there would still be some change, though no doubt a very small +change, in the position of the vane when the boat was in progress +from the position it would have if the boat were at rest. It +therefore occurred to this most acute of astronomers that when the +telescope was pointed towards a star so as to place it apparently in +the centre of the field of view, yet it was not generally the true +position of the star. It was not, in fact, the position in which the +star would have been observed had the earth been at rest. Provided +with this suggestion, he explained the apparent movements of the +stars by the principle known as the "aberration of light." Every +circumstance was accounted for as a consequence of the relative +movements of the earth and of the light from the star. This +beautiful discovery not only established in the most forcible manner +the nature of the movement of light; not only did it illustrate the +truth of the Copernican theory which asserted that the earth revolved +around the sun, but it was also of the utmost importance in the +improvement of practical astronomy. Every observer now knows that, +generally speaking, the position which the star appears to have is +not exactly the position in which the star does actually lie. The +observer is, however, able, by the application of the principles +which Bradley so clearly laid down, to apply to an observation the +correction which is necessary to obtain from it the true place in +which the object is actually situated. This memorable achievement at +once conferred on Bradley the highest astronomical fame. He tested +his discovery in every way, but only to confirm its truth in the most +complete manner.</p> + +<p>Halley, the Astronomer Royal, died on the 14th, January, 1742, and +Bradley was immediately pointed out as his successor. He was +accordingly appointed Astronomer Royal in February, 1742. On first +taking up his abode at Greenwich he was unable to conduct his +observations owing to the wretched condition in which he found the +instruments. He devoted himself, however, assiduously to their +repair, and his first transit observation is recorded on the 25th +July, 1742. He worked with such energy that on one day it appears +that 255 transit observations were taken by himself alone, and in +September, 1747, he had completed the series of observations which +established his second great discovery, the nutation of the earth's +axis. The way in which he was led to the detection of the nutation +is strikingly illustrative of the extreme care with which Bradley +conducted his observations. He found that in the course of a +twelve-month, when the star had completed the movement which was due +to aberration, it did not return exactly to the same position which +it had previously occupied. At first he thought this must be due to +some instrumental error, but after closer examination and repeated +study of the effect as manifested by many different stars, he came to +the conclusion that its origin must be sought in some quite different +source. The fact is that a certain change takes place in the +apparent position of the stars which is not due to the movement of +the star itself, but is rather to be attributed to changes in the +points from which the star's positions are measured.</p> + +<p>We may explain the matter in this way. As the earth is not a sphere, +but has protuberant parts at the equator, the attraction of the moon +exercises on those protuberant parts a pulling effect which +continually changes the direction of the earth's axis, and +consequently the position of the pole must be in a state of incessant +fluctuation. The pole to which the earth's axis points on the sky +is, therefore, slowly changing. At present it happens to lie near +the Pole Star, but it will not always remain there. It describes a +circle around the pole of the Ecliptic, requiring about 25,000 years +for a complete circuit. In the course of its progress the pole will +gradually pass now near one star and now near another, so that many +stars will in the lapse of ages discharge the various functions which +the present Pole Star does for us. In about 12,000 years, for +instance, the pole will have come near the bright star, Vega. This +movement of the pole had been known for ages. But what Bradley +discovered was that the pole, instead of describing an uniform +movement as had been previously supposed, followed a sinuous course +now on one side and now on the other of its mean place. This he +traced to the fluctuations of the moon's orbit, which undergoes a +continuous change in a period of nineteen years. Thus the efficiency +with which the moon acts on the protuberant mass of the earth varies, +and thus the pole is caused to oscillate.</p> + +<p>This subtle discovery, if perhaps in some ways less impressive than +Bradley's earlier achievements of the detection of the aberration of +light, is regarded by astronomers as testifying even in a higher +degree to his astonishing care and skill as an observer, and justly +entitles him to a unique place among the astronomers whose +discoveries have been effected by consummate practical skill in the +use of astronomical instruments.</p> + +<p>Of Bradley's private or domestic life there is but little to tell. In +1744, soon after he became Astronomer Royal, he married a daughter of +Samuel Peach, of Chalford, in Gloucestershire. There was but one +child, a daughter, who became the wife of her cousin, Rev. Samuel +Peach, rector of Compton, Beauchamp, in Berkshire.</p> + +<p>Bradley's last two years of life were clouded by a melancholy +depression of spirits, due to an apprehension that he should survive +his rational faculties. It seems, however, that the ill he dreaded +never came upon him, for he retained his mental powers to the close. +He died on 13th July, 1762, aged seventy, and was buried at +Michinghamton.</p> + +<h3><a name="WILLIAM_HERSCHEL" id="WILLIAM_HERSCHEL"></a>WILLIAM HERSCHEL.</h3> +<p>William Herschel, one of the greatest astronomers that has ever +lived, was born at Hanover, on the 15th November, 1738. His father, +Isaac Herschel, was a man evidently of considerable ability, whose +life was devoted to the study and practice of music, by which he +earned a somewhat precarious maintenance. He had but few worldly +goods to leave to his children, but he more than compensated for this +by bequeathing to them a splendid inheritance of genius. Touches of +genius were, indeed, liberally scattered among the members of Isaac's +large family, and in the case of his forth child, William, and of a +sister several years younger, it was united with that determined +perseverance and rigid adherence to principle which enabled genius to +fulfil its perfect work.</p> + +<p>A faithful chronicler has given us an interesting account of the way +in which Isaac Herschel educated his sons; the narrative is taken +from the recollections of one who, at the time we are speaking of, +was an unnoticed little girl five or six years old. She writes:—</p> + +<p>"My brothers were often introduced as solo performers and assistants +in the orchestra at the Court, and I remember that I was frequently +prevented from going to sleep by the lively criticisms on music on +coming from a concert. Often I would keep myself awake that I might +listen to their animating remarks, for it made me so happy to see +them so happy. But generally their conversation would branch out on +philosophical subjects, when my brother William and my father often +argued with such warmth that my mother's interference became +necessary, when the names—Euler, Leibnitz, and Newton—sounded +rather too loud for the repose of her little ones, who had to be at +school by seven in the morning." The child whose reminiscences are +here given became afterwards the famous Caroline Herschel. The +narrative of her life, by Mrs. John Herschel, is a most interesting +book, not only for the account it contains of the remarkable woman +herself, but also because it provides the best picture we have of the +great astronomer to whom Caroline devoted her life.</p> + +<p>This modest family circle was, in a measure, dispersed at the +outbreak of the Seven Years' War in 1756. The French proceeded to +invade Hanover, which, it will be remembered, belonged at this time +to the British dominions. Young William Herschel had already +obtained the position of a regular performer in the regimental band +of the Hanoverian Guards, and it was his fortune to obtain some +experience of actual warfare in the disastrous battle of Hastenbeck. +He was not wounded, but he had to spend the night after the battle in +a ditch, and his meditations on the occasion convinced him that +soldiering was not the profession exactly adapted to his tastes. We +need not attempt to conceal the fact that he left his regiment by the +very simple but somewhat risky process of desertion. He had, it +would seem, to adopt disguises to effect his escape. At all events, +by some means he succeeded in eluding detection and reached England +in safety. It is interesting to have learned on good authority that +many years after this offence was committed it was solemnly +forgiven. When Herschel had become the famous astronomer, and as +such visited King George at Windsor, the King at their first meeting +handed to him his pardon for deserting from the army, written out in +due form by his Majesty himself.</p> + +<p>It seems that the young musician must have had some difficulty in +providing for his maintenance during the first few years of his abode +in England. It was not until he had reached the age of twenty-two +that he succeeded in obtaining any regular appointment. He was then +made Instructor of Music to the Durham Militia. Shortly afterwards, +his talents being more widely recognised, he was appointed as +organist at the parish church at Halifax, and his prospects in life +now being fairly favourable, and the Seven Years' War being over, he +ventured to pay a visit to Hanover to see his father. We can imagine +the delight with which old Isaac Herschel welcomed his promising son, +as well as his parental pride when a concert was given at which some +of William's compositions were performed. If the father was so +intensely gratified on this occasion, what would his feelings have +been could he have lived to witness his son's future career? But +this pleasure was not to be his, for he died many years before +William became an astronomer.</p> + +<p>In 1766, about a couple of years after his return to England from +This visit to his old home, we find that Herschel had received a +further promotion to be organist in the Octagon Chapel, at Bath. +Bath was then, as now, a highly fashionable resort, and many notable +personages patronised the rising musician. Herschel had other points +in his favour besides his professional skill; his appearance was +good, his address was prepossessing, and even his nationality was a +distinct advantage, inasmuch as he was a Hanoverian in the reign of +King George the Third. On Sundays he played the organ, to the great +delight of the congregation, and on week-days he was occupied by +giving lessons to private pupils, and in preparation for public +performances. He thus came to be busily employed, and seems to have +been in the enjoyment of comfortable means.</p> + +<p><a name="new_king" id="new_king"></a></p> + +<div class="figcenter" style="width: 292px;"> +<a href="images/ill_7_new_king_st.jpg"> +<img src="images/ill_7_new_king_st_sml.jpg" width="292" height="532" alt="7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED." title="" /></a> +<span class="caption">7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.</span> +</div> + +<p>From his earliest youth Herschel had been endowed with that +invaluable characteristic, an eager curiosity for knowledge. He was +naturally desirous of perfecting himself in the theory of music, and +thus he was led to study mathematics. When he had once tasted the +charms of mathematics, he saw vast regions of knowledge unfolded +before him, and in this way he was induced to direct his attention to +astronomy. More and more this pursuit seems to have engrossed his +attention, until at last it had become an absorbing passion. Herschel +was, however, still obliged, by the exigency of procuring a +livelihood, to give up the best part of his time to his profession as +a musician; but his heart was eagerly fixed on another science, and +every spare moment was steadily devoted to astronomy. For many +years, however, he continued to labour at his original calling, nor +was it until he had attained middle age and become the most +celebrated astronomer of the time, that he was enabled to concentrate +his attention exclusively on his favourite pursuit.</p> + +<p>It was with quite a small telescope which had been lent him by a +friend that Herschel commenced his career as an observer. However, +he speedily discovered that to see all he wanted to see, a telescope +of far greater power would be necessary, and he determined to obtain +this more powerful instrument by actually making it with his own +hands. At first it may seem scarcely likely that one whose +occupation had previously been the study and practice of music should +meet with success in so technical an operation as the construction of +a telescope. It may, however, be mentioned that the kind of +instrument which Herschel designed to construct was formed on a very +different principle from the refracting telescopes with which we are +ordinarily familiar. His telescope was to be what is termed a +reflector. In this type of instrument the optical power is obtained +by the use of a mirror at the bottom of the tube, and the astronomer +looks down through the tube TOWARDS HIS MIRROR and views the +reflection of the stars with its aid. Its efficiency as a telescope +depends entirely on the accuracy with which the requisite form has +been imparted to the mirror. The surface has to be hollowed out a +little, and this has to be done so truly that the slightest deviation +from good workmanship in this essential particular would be fatal to +efficient performance of the telescope.</p> + +<p><a name="william" id="william"></a></p> + +<div class="figcenter" style="width: 411px;"> +<a href="images/ill_herschel.jpg"> +<img src="images/ill_herschel_sml.jpg" width="411" height="495" alt="WILLIAM HERSCHEL." title="" /></a> +<span class="caption">WILLIAM HERSCHEL.</span> +</div> + +<p>The mirror that Herschel employed was composed of a mixture of two +parts of copper to one of tin; the alloy thus obtained is an +intensely hard material, very difficult to cast into the proper +shape, and very difficult to work afterwards. It possesses, however, +when polished, a lustre hardly inferior to that of silver itself. +Herschel has recorded hardly any particulars as to the actual process +by which he cast and figured his reflectors. We are however, told +that in later years, after his telescopes had become famous, he made +a considerable sum of money by the manufacture and sale of great +instruments. Perhaps this may be the reason why he never found it +expedient to publish any very explicit details as to the means by +which his remarkable successes were obtained.</p> + +<p><a name="caroline" id="caroline"></a></p> + +<div class="figcenter" style="width: 406px;"> +<a href="images/ill_caroline_herschel.jpg"> +<img src="images/ill_caroline_herschel_sml.jpg" width="406" height="509" alt="CAROLINE HERSCHEL." title="" /></a> +<span class="caption">CAROLINE HERSCHEL.</span> +</div> + +<p>Since Herschel's time many other astronomers, notably the late Earl +of Rosse, have experimented in the same direction, and succeeded in +making telescopes certainly far greater, and probably more perfect, +than any which Herschel appears to have constructed. The details of +these later methods are now well known, and have been extensively +practised. Many amateurs have thus been able to make telescopes by +following the instructions so clearly laid down by Lord Rosse and the +other authorities. Indeed, it would seem that any one who has a +little mechanical skill and a good deal of patience ought now to +experience no great difficulty in constructing a telescope quite as +powerful as that which first brought Herschel into fame. I should, +however, mention that in these modern days the material generally +used for the mirror is of a more tractable description than the +metallic substance which was employed by Herschel and by Lord Rosse. +A reflecting telescope of the present day would not be fitted with a +mirror composed of that alloy known as speculum metal, whose +composition I have already mentioned. It has been found more +advantageous to employ a glass mirror carefully figured and polished, +just as a metallic mirror would have been, and then to impart to the +polished glass surface a fine coating of silver laid down by a +chemical process. The silver-on-glass mirrors are so much lighter +and so much easier to construct that the more old-fashioned metallic +mirrors may be said to have fallen into almost total disuse. In one +respect however, the metallic mirror may still claim the advantage +that, with reasonable care, its surface will last bright and +untarnished for a much longer period than can the silver film on the +glass. However, the operation of re-silvering a glass has now become +such a simple one that the advantage this indicates is not relatively +so great as might at first be supposed.</p> + +<p><a name="street" id="street"></a></p> + +<div class="figcenter" style="width: 426px;"> +<a href="images/ill_herschel_house_slough.jpg"> +<img src="images/ill_herschel_house_slough_sml.jpg" width="426" height="318" alt="STREET VIEW, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">STREET VIEW, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>Some years elapsed after Herschel's attention had been first directed +to astronomy, before he reaped the reward of his exertions in the +possession of a telescope which would adequately reveal some of the +glories of the heavens. It was in 1774, when the astronomer was +thirty-six years old, that he obtained his first glimpse of the stars +with an instrument of his own construction. Night after night, as +soon as his musical labours were ended, his telescopes were brought +out, sometimes into the small back garden of his house at Bath, and +sometimes into the street in front of his hall-door. It was +characteristic of him that he was always endeavouring to improve his +apparatus. He was incessantly making fresh mirrors, or trying new +lenses, or combinations of lenses to act as eye-pieces, or projecting +alterations in the mounting by which the telescope was supported. +Such was his enthusiasm that his house, we are told, was incessantly +littered with the usual indications of the workman's presence, +greatly to the distress of his sister, who, at this time, had come to +take up her abode with him and look after his housekeeping. Indeed, +she complained that in his astronomical ardour he sometimes omitted +to take off, before going into his workshop, the beautiful lace +ruffles which he wore while conducting a concert, and that +consequently they became soiled with the pitch employed in the +polishing of his mirrors.</p> + +<p>This sister, who occupies such a distinct place in scientific history +is the same little girl to whom we have already referred. From her +earliest days she seems to have cherished a passionate admiration for +her brilliant brother William. It was the proudest delight of her +childhood as well as of her mature years to render him whatever +service she could; no man of science was ever provided with a more +capable or energetic helper than William Herschel found in this +remarkable woman. Whatever work had to be done she was willing to +bear her share in it, or even to toil at it unassisted if she could +be allowed to do so. She not only managed all his domestic affairs, +but in the grinding of the lenses and in the polishing of the mirrors +she rendered every assistance that was possible. At one stage of the +very delicate operation of fashioning a reflector, it is necessary +for the workman to remain with his hand on the mirror for many hours +in succession. When such labours were in progress, Caroline used to +sit by her brother, and enliven the time by reading stories aloud, +sometimes pausing to feed him with a spoon while his hands were +engaged on the task from which he could not desist for a moment.</p> + +<p>When mathematical work had to be done Caroline was ready for it; she +had taught herself sufficient to enable her to perform the kind of +calculations, not, perhaps, very difficult ones, that Herschel's work +required; indeed, it is not too much to say that the mighty life-work +which this man was enabled to perform could never have been accomplished +had it not been for the self-sacrifice of this ever-loving and faithful +sister. When Herschel was at the telescope at night, Caroline sat by +him at her desk, pen in hand, ready to write down the notes of the +observations as they fell from her brother's lips. This was no +insignificant toil. The telescope was, of course, in the open air, +and as Herschel not unfrequently continued his observations throughout +the whole of a long winter's night, there were but few women who could +have accomplished the task which Caroline so cheerfully executed. +From dusk till dawn, when the sky was clear, were Herschel's observing +hours, and what this sometimes implied we can realise from the fact +that Caroline assures us she had sometimes to desist because the ink +had actually frozen in her pen. The night's work over, a brief rest +was taken, and while William had his labours for the day to attend to, +Caroline carefully transcribed the observations made during the night +before, reduced all the figures and prepared everything in readiness +for the observations that were to follow on the ensuing evening.</p> + +<p>But we have here been anticipating a little of the future which lay +before the great astronomer; we must now revert to the history of his +early work, at Bath, in 1774, when Herschel's scrutiny of the skies +first commenced with an instrument of his own manufacture. For some +few years he did not attain any result of importance; no doubt he +made a few interesting observations, but the value of the work during +those years is to be found, not in any actual discoveries which were +accomplished, but in the practice which Herschel obtained in the use +of his instruments. It was not until 1782 that the great achievement +took place by which he at once sprang into fame.</p> + +<p><a name="garden" id="garden"></a></p> + +<div class="figcenter" style="width: 421px;"> +<a href="images/ill_garden_view_herschel_house_slough.jpg"> +<img src="images/ill_garden_view_herschel_house_slough_sml.jpg" width="421" height="340" alt="GARDEN VIEW, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>It is sometimes said that discoveries are made by accident, and, no +doubt, to a certain extent, but only, I fancy to a very small extent, +this statement may be true. It is, at all events, certain that such +lucky accidents do not often fall to the lot of people unless those +people have done much to deserve them. This was certainly the case +with Herschel. He appears to have formed a project for making a +close examination of all the stars above a certain magnitude. Perhaps +he intended to confine this research to a limited region of the sky, +but, at all events, he seems to have undertaken the work +energetically and systematically. Star after star was brought to the +centre of the field of view of his telescope, and after being +carefully examined was then displaced, while another star was brought +forward to be submitted to the same process. In the great majority +of cases such observations yield really nothing of importance; no +doubt even the smallest star in the heavens would, if we could find +out all about it, reveal far more than all the astronomers that were +ever on the earth have even conjectured. What we actually learn +about the great majority of stars is only information of the most +meagre description. We see that the star is a little point of light, +and we see nothing more.</p> + +<p>In the great review which Herschel undertook he doubtless examined +hundreds, or perhaps thousands of stars, allowing them to pass away +without note or comment. But on an ever-memorable night in March, +1782, it happened that he was pursuing his task among the stars in +the Constellation of Gemini. Doubtless, on that night, as on so many +other nights, one star after another was looked at only to be +dismissed, as not requiring further attention. On the evening in +question, however, one star was noticed which, to Herschel's acute +vision seemed different from the stars which in so many thousands are +strewn over the sky. A star properly so called appears merely as a +little point of light, which no increase of magnifying power will +ever exhibit with a true disc. But there was something in the +star-like object which Herschel saw that immediately arrested his +attention and made him apply to it a higher magnifying power. This +at once disclosed the fact that the object possessed a disc, that is, +a definite, measurable size, and that it was thus totally different +from any one of the hundreds and thousands of stars which exist +elsewhere in space. Indeed, we may say at once that this little +object was not a star at all; it was a planet. That such was its +true nature was confirmed, after a little further observation, by +perceiving that the body was shifting its place on the heavens +relatively to the stars. The organist at the Octagon Chapel at Bath +had, therefore, discovered a new planet with his home-made telescope.</p> + +<p>I can imagine some one will say, "Oh, there was nothing so wonderful +in that; are not planets always being discovered? Has not M. Palisa, +for instance, discovered about eighty of such objects, and are there +not hundreds of them known nowadays?" This is, to a certain extent, +quite true. I have not the least desire to detract from the credit +of those industrious and sharp-sighted astronomers who have in modern +days brought so many of these little objects within our cognisance. I +think, however, it must be admitted that such discoveries have a +totally different importance in the history of science from that +which belongs to the peerless achievement of Herschel. In the first +place, it must be observed that the minor planets now brought to +light are so minute that if a score of them were rolled to together +into one lump it would not be one-thousandth part of the size of the +grand planet discovered by Herschel. This is, nevertheless, not the +most important point. What marks Herschel's achievement as one of +the great epochs in the history of astronomy is the fact that the +detection of Uranus was the very first recorded occasion of the +discovery of any planet whatever.</p> + +<p>For uncounted ages those who watched the skies had been aware of the +existence of the five old planets—Jupiter, Mercury, Saturn, Venus, +and Mars. It never seems to have occurred to any of the ancient +philosophers that there could be other similar objects as yet +undetected over and above the well-known five. Great then was the +astonishment of the scientific world when the Bath organist announced +his discovery that the five planets which had been known from all +antiquity must now admit the company of a sixth. And this sixth +planet was, indeed, worthy on every ground to be received into the +ranks of the five glorious bodies of antiquity. It was, no doubt, +not so large as Saturn, it was certainly very much less than Jupiter; +on the other hand, the new body was very much larger than Mercury, +than Venus, or than Mars, and the earth itself seemed quite an +insignificant object in comparison with this newly added member of +the Solar System. In one respect, too, Herschel's new planet was a +much more imposing object than any one of the older bodies; it swept +around the sun in a majestic orbit, far outside that of Saturn, which +had previously been regarded as the boundary of the Solar System, and +its stately progress required a period of not less than eighty-one +years.</p> + +<p>King George the Third, hearing of the achievements of the Hanoverian +musician, felt much interest in his discovery, and accordingly +Herschel was bidden to come to Windsor, and to bring with him the +famous telescope, in order to exhibit the new planet to the King, and +to tell his Majesty all about it. The result of the interview was to +give Herschel the opportunity for which he had so long wished, of +being able to devote himself exclusively to science for the rest of +his life.</p> + +<p><a name="view_herschel_house" id="view_herschel_house"></a></p> + +<div class="figcenter" style="width: 416px;"> +<a href="images/ill_view_observatory_herschel_house.jpg"> +<img src="images/ill_view_observatory_herschel_house_sml.jpg" width="416" height="302" alt="VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>The King took so great a fancy to the astronomer that he first, as I +have already mentioned, duly pardoned his desertion from the army, +some twenty-five years previously. As a further mark of his favour +the King proposed to confer on Herschel the title of his Majesty's +own astronomer, to assign to him a residence near Windsor, to provide +him with a salary, and to furnish such funds as might be required for +the erection of great telescopes, and for the conduct of that mighty +scheme of celestial observation on which Herschel was so eager to +enter. Herschel's capacity for work would have been much impaired if +he had been deprived of the aid of his admirable sister, and to her, +therefore, the King also assigned a salary, and she was installed as +Herschel's assistant in his new post.</p> + +<p>With his usually impulsive determination, Herschel immediately cut +himself free from all his musical avocations at Bath, and at once +entered on the task of making and erecting the great telescopes at +Windsor. There, for more than thirty years, he and his faithful +sister prosecuted with unremitting ardour their nightly scrutiny of +the sky. Paper after paper was sent to the Royal Society, describing +the hundreds, indeed the thousands, of objects such as double stars; +nebulae and clusters, which were first revealed to human gaze during +those midnight vigils. To the end of his life he still continued at +every possible opportunity to devote himself to that beloved pursuit +in which he had such unparalleled success. No single discovery of +Herschel's later years was, however, of the same momentous +description as that which first brought him to fame.</p> + +<p><a name="telescope_slough" id="telescope_slough"></a></p> + +<div class="figcenter" style="width: 460px;"> +<a href="images/ill_telescope_herschel_house.jpg"> +<img src="images/ill_telescope_herschel_house_sml.jpg" width="460" height="354" alt="THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH." title="" /></a> +<span class="caption">THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH.</span> +</div> + +<p>Herschel married when considerably advanced in life and he lived to +enjoy the indescribable pleasure of finding that his only son, +afterwards Sir John Herschel, was treading worthily in his footsteps, +and attaining renown as an astronomical observer, second only to that +of his father. The elder Herschel died in 1822, and his illustrious +sister Caroline then returned to Hanover, where she lived for many +years to receive the respect and attention which were so justly +hers. She died at a very advanced age in 1848.</p> + +<h3><a name="LAPLACE" id="LAPLACE"></a>LAPLACE.</h3> +<p>The author of the "Mecanique Celeste" was born at Beaumont-en-Auge, +near Honfleur, in 1749, just thirteen years later than his renowned +friend Lagrange. His father was a farmer, but appears to have been +in a position to provide a good education for a son who seemed +promising. Considering the unorthodoxy in religious matters which is +generally said to have characterized Laplace in later years, it is +interesting to note that when he was a boy the subject which first +claimed his attention was theology. He was, however, soon introduced +to the study of mathematics, in which he presently became so +proficient, that while he was still no more than eighteen years old, +he obtained employment as a mathematical teacher in his native town.</p> + +<p>Desiring wider opportunities for study and for the acquisition of +fame than could be obtained in the narrow associations of provincial +life, young Laplace started for Paris, being provided with letters of +introduction to D'Alembert, who then occupied the most prominent +position as a mathematician in France, if not in the whole of +Europe. D'Alembert's fame was indeed so brilliant that Catherine the +Great wrote to ask him to undertake the education of her Son, and +promised the splendid income of a hundred thousand francs. He +preferred, however, a quiet life of research in Paris, although there +was but a modest salary attached to his office. The philosopher +accordingly declined the alluring offer to go to Russia, even though +Catherine wrote again to say: "I know that your refusal arises from +your desire to cultivate your studies and your friendships in quiet. +But this is of no consequence: bring all your friends with you, and I +promise you that both you and they shall have every accommodation in +my power." With equal firmness the illustrious mathematician +resisted the manifold attractions with which Frederick the Great +sought to induce him, to take up his residence at Berlin. In reading +of these invitations we cannot but be struck at the extraordinary +respect which was then paid to scientific distinction. It must be +remembered that the discoveries of such a man as D'Alembert were +utterly incapable of being appreciated except by those who possessed +a high degree of mathematical culture. We nevertheless find the +potentates of Russia and Prussia entreating and, as it happens, +vainly entreating, the most distinguished mathematician in France to +accept the positions that they were proud to offer him.</p> + +<p>It was to D'Alembert, the profound mathematician, that young Laplace, +the son of the country farmer, presented his letters of +introduction. But those letters seem to have elicited no reply, +whereupon Laplace wrote to D'Alembert submitting a discussion on some +point in Dynamics. This letter instantly produced the desired +effect. D'Alembert thought that such mathematical talent as the +young man displayed was in itself the best of introductions to his +favour. It could not be overlooked, and accordingly he invited +Laplace to come and see him. Laplace, of course, presented himself, +and ere long D'Alembert obtained for the rising philosopher a +professorship of mathematics in the Military School in Paris. This +gave the brilliant young mathematician the opening for which he +sought, and he quickly availed himself of it.</p> + +<p>Laplace was twenty-three years old when his first memoir on a +profound mathematical subject appeared in the Memoirs of the Academy +at Turin. From this time onwards we find him publishing one memoir +after another in which he attacks, and in many cases successfully +vanquishes, profound difficulties in the application of the Newtonian +theory of gravitation to the explanation of the solar system. Like +his great contemporary Lagrange, he loftily attempted problems which +demanded consummate analytical skill for their solution. The +attention of the scientific world thus became riveted on the splendid +discoveries which emanated from these two men, each gifted with +extraordinary genius.</p> + +<p>Laplace's most famous work is, of course, the "Mecanique Celeste," in +which he essayed a comprehensive attempt to carry out the principles +which Newton had laid down, into much greater detail than Newton had +found practicable. The fact was that Newton had not only to +construct the theory of gravitation, but he had to invent the +mathematical tools, so to speak, by which his theory could be applied +to the explanation of the movements of the heavenly bodies. In the +course of the century which had elapsed between the time of Newton +and the time of Laplace, mathematics had been extensively developed. +In particular, that potent instrument called the infinitesimal +calculus, which Newton had invented for the investigation of nature, +had become so far perfected that Laplace, when he attempted to +unravel the movements of the heavenly bodies, found himself provided +with a calculus far more efficient than that which had been available +to Newton. The purely geometrical methods which Newton employed, +though they are admirably adapted for demonstrating in a general way +the tendencies of forces and for explaining the more obvious +phenomena by which the movements of the heavenly bodies are +disturbed, are yet quite inadequate for dealing with the more subtle +effects of the Law of Gravitation. The disturbances which one planet +exercises upon the rest can only be fully ascertained by the aid of +long calculation, and for these calculations analytical methods are +required.</p> + +<p>With an armament of mathematical methods which had been perfected +since the days of Newton by the labours of two or three generations +of consummate mathematical inventors, Laplace essayed in the +"Mecanique Celeste" to unravel the mysteries of the heavens. It will +hardly be disputed that the book which he has produced is one of the +most difficult books to understand that has ever been written. In +great part, of course, this difficulty arises from the very nature of +the subject, and is so far unavoidable. No one need attempt to read +the "Mecanique Celeste" who has not been naturally endowed with +considerable mathematical aptitude which he has cultivated by years +of assiduous study. The critic will also note that there are grave +defects in Laplace's method of treatment. The style is often +extremely obscure, and the author frequently leaves great gaps in his +argument, to the sad discomfiture of his reader. Nor does it mend +matters to say, as Laplace often does say, that it is "easy to see" +how one step follows from another. Such inferences often present +great difficulties even to excellent mathematicians. Tradition +indeed tells us that when Laplace had occasion to refer to his own +book, it sometimes happened that an argument which he had dismissed +with his usual formula, "Il est facile a voir," cost the illustrious +author himself an hour or two of hard thinking before he could +recover the train of reasoning which had been omitted. But there are +certain parts of this great work which have always received the +enthusiastic admiration of mathematicians. Laplace has, in fact, +created whole tracts of science, some of which have been subsequently +developed with much advantage in the prosecution of the study of +Nature.</p> + +<p>Judged by a modern code the gravest defect of Laplace's great work is +rather of a moral than of a mathematical nature. Lagrange and he +advanced together in their study of the mechanics of the heavens, at +one time perhaps along parallel lines, while at other times they +pursued the same problem by almost identical methods. Sometimes the +important result was first reached by Lagrange, sometimes it was +Laplace who had the good fortune to make the discovery. It would +doubtless be a difficult matter to draw the line which should exactly +separate the contributions to astronomy made by one of these +illustrious mathematicians, and the contributions made by the other. +But in his great work Laplace in the loftiest manner disdained to +accord more than the very barest recognition to Lagrange, or to any +of the other mathematicians, Newton alone excepted, who had advanced +our knowledge of the mechanism of the heavens. It would be quite +impossible for a student who confined his reading to the "Mecanique +Celeste" to gather from any indications that it contains whether the +discoveries about which he was reading had been really made by +Laplace himself or whether they had not been made by Lagrange, or by +Euler, or by Clairaut. With our present standard of morality in such +matters, any scientific man who now brought forth a work in which he +presumed to ignore in this wholesale fashion the contributions of +others to the subject on which he was writing, would be justly +censured and bitter controversies would undoubtedly arise. Perhaps +we ought not to judge Laplace by the standard of our own time, and in +any case I do not doubt that Laplace might have made a plausible +defence. It is well known that when two investigators are working at +the same subjects, and constantly publishing their results, it +sometimes becomes difficult for each investigator himself to +distinguish exactly between what he has accomplished and that which +must be credited to his rival. Laplace may probably have said to +himself that he was going to devote his energies to a great work on +the interpretation of Nature, that it would take all his time and all +his faculties, and all the resources of knowledge that he could +command, to deal justly with the mighty problems before him. He +would not allow himself to be distracted by any side issue. He could +not tolerate that pages should be wasted in merely discussing to whom +we owe each formula, and to whom each deduction from such formula is +due. He would rather endeavour to produce as complete a picture as +he possibly could of the celestial mechanics, and whether it were by +means of his mathematics alone, or whether the discoveries of others +may have contributed in any degree to the result, is a matter so +infinitesimally insignificant in comparison with the grandeur of his +subject that he would altogether neglect it. "If Lagrange should +think," Laplace might say, "that his discoveries had been unduly +appropriated, the proper course would be for him to do exactly what I +have done. Let him also write a "Mecanique Celeste," let him employ +those consummate talents which he possesses in developing his noble +subject to the utmost. Let him utilise every result that I or any +other mathematician have arrived at, but not trouble himself unduly +with unimportant historical details as to who discovered this, and +who discovered that; let him produce such a work as he could write, +and I shall heartily welcome it as a splendid contribution to our +science." Certain it is that Laplace and Lagrange continued the best +of friends, and on the death of the latter it was Laplace who was +summoned to deliver the funeral oration at the grave of his great +rival.</p> + +<p>The investigations of Laplace are, generally speaking, of too +technical a character to make it possible to set forth any account of +them in such a work as the present. He did publish, however, one +treatise, called the "Systeme du Monde," in which, without +introducing mathematical symbols, he was able to give a general +account of the theories of the celestial movements, and of the +discoveries to which he and others had been led. In this work the +great French astronomer sketched for the first time that remarkable +doctrine by which his name is probably most generally known to those +readers of astronomical books who are not specially mathematicians. +It is in the "Systeme du Monde" that Laplace laid down the principles +of the Nebular Theory which, in modern days, has been generally +accepted by those philosophers who are competent to judge, as +substantially a correct expression of a great historical fact.</p> + +<p><a name="laplace_ill" id="laplace_ill"></a></p> + +<div class="figcenter" style="width: 423px;"> +<a href="images/ill_laplace.jpg"> +<img src="images/ill_laplace_sml.jpg" width="423" height="488" alt="LAPLACE." title="" /></a> +<span class="caption">LAPLACE.</span> +</div> + +<p>The Nebular Theory gives a physical account of the origin of the +solar system, consisting of the sun in the centre, with the planets +and their attendant satellites. Laplace perceived the significance +of the fact that all the planets revolved in the same direction +around the sun; he noticed also that the movements of rotation of the +planets on their axes were performed in the same direction as that in +which a planet revolves around the sun; he saw that the orbits of the +satellites, so far at least as he knew them, revolved around their +primaries also in the same direction. Nor did it escape his +attention that the sun itself rotated on its axis in the same sense. +His philosophical mind was led to reflect that such a remarkable +unanimity in the direction of the movements in the solar system +demanded some special explanation. It would have been in the highest +degree improbable that there should have been this unanimity unless +there had been some physical reason to account for it. To appreciate +the argument let us first concentrate our attention on three +particular bodies, namely the earth, the sun, and the moon. First +the earth revolves around the sun in a certain direction, and the +earth also rotates on its axis. The direction in which the earth +turns in accordance with this latter movement might have been that in +which it revolves around the sun, or it might of course have been +opposite thereto. As a matter of fact the two agree. The moon in +its monthly revolution around the earth follows also the same +direction, and our satellite rotates on its axis in the same period +as its monthly revolution, but in doing so is again observing this +same law. We have therefore in the earth and moon four movements, +all taking place in the same direction, and this is also identical +with that in which the sun rotates once every twenty-five days. Such +a coincidence would be very unlikely unless there were some physical +reason for it. Just as unlikely would it be that in tossing a coin +five heads or five tails should follow each other consecutively. If +we toss a coin five times the chances that it will turn up all heads +or all tails is but a small one. The probability of such an event is +only one-sixteenth.</p> + +<p>There are, however, in the solar system many other bodies besides the +three just mentioned which are animated by this common movement. +Among them are, of course, the great planets, Jupiter, Saturn, Mars, +Venus, and Mercury, and the satellites which attend on these +planets. All these planets rotate on their axes in the same +direction as they revolve around the sun, and all their satellites +revolve also in the same way. Confining our attention merely to the +earth, the sun, and the five great planets with which Laplace was +acquainted, we have no fewer than six motions of revolution and seven +motions of rotation, for in the latter we include the rotation of the +sun. We have also sixteen satellites of the planets mentioned whose +revolutions round their primaries are in the same direction. The +rotation of the moon on its axis may also be reckoned, but as to the +rotations of the satellites of the other planets we cannot speak with +any confidence, as they are too far off to be observed with the +necessary accuracy. We have thus thirty circular movements in the +solar system connected with the sun and moon and those great planets +than which no others were known in the days of Laplace. The +significant fact is that all these thirty movements take place in the +same direction. That this should be the case without some physical +reason would be just as unlikely as that in tossing a coin thirty +times it should turn up all heads or all tails every time without +exception.</p> + +<p>We can express the argument numerically. Calculation proves that +such an event would not generally happen oftener than once out of +five hundred millions of trials. To a philosopher of Laplace's +penetration, who had made a special study of the theory of +probabilities, it seemed well-nigh inconceivable that there should +have been such unanimity in the celestial movements, unless there had +been some adequate reason to account for it. We might, indeed, add +that if we were to include all the objects which are now known to +belong to the solar system, the argument from probability might be +enormously increased in strength. To Laplace the argument appeared +so conclusive that he sought for some physical cause of the +remarkable phenomenon which the solar system presented. Thus it was +that the famous Nebular Hypothesis took its rise. Laplace devised a +scheme for the origin of the sun and the planetary system, in which +it would be a necessary consequence that all the movements should +take place in the same direction as they are actually observed to do.</p> + +<p>Let us suppose that in the beginning there was a gigantic mass of +nebulous material, so highly heated that the iron and other +substances which now enter into the composition of the earth and +planets were then suspended in a state of vapour. There is nothing +unreasonable in such a supposition indeed, we know as a matter of +fact that there are thousands of such nebulae to be discerned at +present through our telescopes. It would be extremely unlikely that +any object could exist without possessing some motion of rotation; we +may in fact assert that for rotation to be entirety absent from the +great primeval nebula would be almost infinitely improbable. As ages +rolled on, the nebula gradually dispersed away by radiation its +original stores of heat, and, in accordance with well-known physical +principles, the materials of which it was formed would tend to +coalesce. The greater part of those materials would become +concentrated in a mighty mass surrounded by outlying uncondensed +vapours. There would, however, also be regions throughout the extent +of the nebula, in which subsidiary centres of condensation would be +found. In its long course of cooling, the nebula would, therefore, +tend ultimately to form a mighty central body with a number of +smaller bodies disposed around it. As the nebula was initially +endowed with a movement of rotation, the central mass into which it +had chiefly condensed would also revolve, and the subsidiary bodies +would be animated by movements of revolution around the central +body. These movements would be all pursued in one common direction, +and it follows, from well-known mechanical principles, that each of +the subsidiary masses, besides participating in the general +revolution around the central body, would also possess a rotation +around its axis, which must likewise be performed in the same +direction. Around the subsidiary bodies other objects still smaller +would be formed, just as they themselves were formed relatively to +the great central mass.</p> + +<p>As the ages sped by, and the heat of these bodies became gradually +dissipated, the various objects would coalesce, first into molten +liquid masses, and thence, at a further stage of cooling, they would +assume the appearance of solid masses, thus producing the planetary +bodies such as we now know them. The great central mass, on account +of its preponderating dimensions, would still retain, for further +uncounted ages, a large quantity of its primeval heat, and would thus +display the splendours of a glowing sun. In this way Laplace was +able to account for the remarkable phenomena presented in the +movements of the bodies of the solar system. There are many other +points also in which the nebular theory is known to tally with the +facts of observation. In fact, each advance in science only seems to +make it more certain that the Nebular Hypothesis substantially +represents the way in which our solar system has grown to its present +form.</p> + +<p>Not satisfied with a career which should be merely scientific, +Laplace sought to connect himself with public affairs. Napoleon +appreciated his genius, and desired to enlist him in the service of +the State. Accordingly he appointed Laplace to be Minister of the +Interior. The experiment was not successful, for he was not by +nature a statesman. Napoleon was much disappointed at the ineptitude +which the great mathematician showed for official life, and, in +despair of Laplace's capacity as an administrator, declared that he +carried the spirit of his infinitesimal calculus into the management +of business. Indeed, Laplace's political conduct hardly admits of +much defence. While he accepted the honours which Napoleon showered +on him in the time of his prosperity, he seems to have forgotten all +this when Napoleon could no longer render him service. Laplace was +made a Marquis by Louis XVIII., a rank which he transmitted to his +son, who was born in 1789. During the latter part of his life the +philosopher lived in a retired country place at Arcueile. Here he +pursued his studies, and by strict abstemiousness, preserved himself +from many of the infirmities of old age. He died on March the 5th, +1827, in his seventy-eighth year, his last words being, "What we know +is but little, what we do not know is immense."</p> + +<h3><a name="BRINKLEY" id="BRINKLEY"></a>BRINKLEY.</h3> +<p>Provost Baldwin held absolute sway in the University of Dublin for +forty-one years. His memory is well preserved there. The Bursar +still dispenses the satisfactory revenues which Baldwin left to the +College. None of us ever can forget the marble angels round the +figure of the dying Provost on which we used to gaze during the pangs +of the Examination Hall.</p> + +<p>Baldwin died in 1785, and was succeeded by Francis Andrews, a Fellow +of seventeen years' standing. As to the scholastic acquirements of +Andrews, all I can find is a statement that he was complimented by +the polite Professors of Padua on the elegance and purity with which +he discoursed to them in Latin. Andrews was also reputed to be a +skilful lawyer. He was certainly a Privy Councillor and a prominent +member of the Irish House of Commons, and his social qualities were +excellent. Perhaps it was Baldwin's example that stimulated a desire +in Andrews to become a benefactor to his college. He accordingly +bequeathed a sum of 3,000 pounds and an annual income of 250 pounds +wherewith to build and endow an astronomical Observatory in the +University. The figures just stated ought to be qualified by the +words of cautious Ussher (afterwards the first Professor of +Astronomy), that "this money was to arise from an accumulation of a +part of his property, to commence upon a particular contingency +happening to his family." The astronomical endowment was soon in +jeopardy by litigation. Andrews thought he had provided for his +relations by leaving to them certain leasehold interests connected +with the Provost's estate. The law courts, however, held that these +interests were not at the disposal of the testator, and handed them +over to Hely Hutchinson, the next Provost. The disappointed +relations then petitioned the Irish Parliament to redress this +grievance by transferring to them the moneys designed by Andrews for +the Observatory. It would not be right, they contended, that the +kindly intentions of the late Provost towards his kindred should be +frustrated for the sake of maintaining what they described as "a +purely ornamental institution." The authorities of the College +protested against this claim. Counsel were heard, and a Committee of +the House made a report declaring the situation of the relations to +be a hard one. Accordingly, a compromise was made, and the dispute +terminated.</p> + +<p>The selection of a site for the new astronomical Observatory was made +by the Board of Trinity College. The beautiful neighbourhood of +Dublin offered a choice of excellent localities. On the north side +of the Liffey an Observatory could have been admirably placed, either +on the remarkable promontory of Howth or on the elevation of which +Dunsink is the summit. On the south side of Dublin there are several +eminences that would have been suitable: the breezy heaths at +Foxrock combine all necessary conditions; the obelisk hill at +Killiney would have given one of the most picturesque sites for an +Observatory in the world; while near Delgany two or three other good +situations could be mentioned. But the Board of those pre-railway +days was naturally guided by the question of proximity. Dunsink was +accordingly chosen as the most suitable site within the distance of a +reasonable walk from Trinity College.</p> + +<p>The northern boundary of the Phoenix Park approaches the little river +Tolka, which winds through a succession of delightful bits of sylvan +scenery, such as may be found in the wide demesne of Abbotstown and +the classic shades of Glasnevin. From the banks of the Tolka, on the +opposite side of the park, the pastures ascend in a gentle slope to +culminate at Dunsink, where at a distance of half a mile from the +stream, of four miles from Dublin, and at a height of 300 feet above +the sea, now stands the Observatory. From the commanding position of +Dunsink a magnificent view is obtained. To the east the sea is +visible, while the southern prospect over the valley of the Liffey is +bounded by a range of hills and mountains extending from Killiney to +Bray Head, thence to the little Sugar Loaf, the Two Rock and the +Three Rock Mountains, over the flank of which the summit of the Great +Sugar Loaf is just perceptible. Directly in front opens the fine +valley of Glenasmole, with Kippure Mountain, while the range can be +followed to its western extremity at Lyons. The climate of Dunsink +is well suited for astronomical observation. No doubt here, as +elsewhere in Ireland, clouds are abundant, but mists or haze are +comparatively unusual, and fogs are almost unknown.</p> + +<p>The legal formalities to be observed in assuming occupation exacted a +delay of many months; accordingly, it was not until the 10th +December, 1782, that a contract could be made with Mr. Graham Moyers +for the erection of a meridian-room and a dome for an equatorial, in +conjunction with a becoming residence for the astronomer. Before the +work was commenced at Dunsink, the Board thought it expedient to +appoint the first Professor of Astronomy. They met for this purpose +on the 22nd January, 1783, and chose the Rev. Henry Ussher, a Senior +Fellow of Trinity College, Dublin. The wisdom of the appointment was +immediately shown by the assiduity with which Ussher engaged in +founding the observatory. In three years he had erected the +buildings and equipped them with instruments, several of which were +of his own invention. On the 19th of February, 1785, a special grant +of 200 pounds was made by the Board to Dr. Ussher as some recompense +for his labours. It happened that the observatory was not the only +scientific institution which came into being in Ireland at this +period; the newly-kindled ardour for the pursuit of knowledge led, at +the same time, to the foundation of the Royal Irish Academy. By a +fitting coincidence, the first memoir published in the "Transactions +Of The Royal Irish Academy," was by the first Andrews, Professor of +Astronomy. It was read on the 13th of June, 1785, and bore the +title, "Account of the Observatory belonging to Trinity College," by +the Rev. H. Ussher, D.D., M.R.I.A., F.R.S. This communication shows +the extensive design that had been originally intended for Dunsink, +only a part of which was, however, carried out. For instance, two +long corridors, running north and south from the central edifice, +which are figured in the paper, never developed into bricks and +mortar. We are not told why the original scheme had to be +contracted; but perhaps the reason may be not unconnected with a +remark of Ussher's, that the College had already advanced from its +own funds a sum considerably exceeding the original bequest. The +picture of the building shows also the dome for the South equatorial, +which was erected many years later.</p> + +<p>Ussher died in 1790. During his brief career at the observatory, he +observed eclipses, and is stated to have done other scientific work. +The minutes of the Board declare that the infant institution had +already obtained celebrity by his labours, and they urge the claims +of his widow to a pension, on the ground that the disease from which +he died had been contracted by his nightly vigils. The Board also +promised a grant of fifty guineas as a help to bring out Dr. Ussher's +sermons. They advanced twenty guineas to his widow towards the +publication of his astronomical papers. They ordered his bust to be +executed for the observatory, and offered "The Death of Ussher" as +the subject of a prize essay; but, so far as I can find, neither the +sermons nor the papers, neither the bust nor the prize essay, ever +came into being.</p> + +<p>There was keen competition for the chair of Astronomy which the death +of Ussher vacated. The two candidates were Rev. John Brinkley, of +Caius College, Cambridge, a Senior Wrangler (born at Woodbridge, +Suffolk, in 1763), and Mr. Stack, Fellow of Trinity College, Dublin, +and author of a book on Optics. A majority of the Board at first +supported Stack, while Provost Hely Hutchinson and one or two others +supported Brinkley. In those days the Provost had a veto at +elections, so that ultimately Stack was withdrawn and Brinkley was +elected. This took place on the 11th December, 1790. The national +press of the day commented on the preference shown to the young +Englishman, Brinkley, over his Irish rival. An animated controversy +ensued. The Provost himself condescended to enter the lists and to +vindicate his policy by a long letter in the "Public Register" or +"Freeman's Journal," of 21st December, 1790. This letter was +anonymous, but its authorship is obvious. It gives the +correspondence with Maskelyne and other eminent astronomers, whose +advice and guidance had been sought by the Provost. It also contends +that "the transactions of the Board ought not to be canvassed in the +newspapers." For this reference, as well as for much other +information, I am indebted to my friend, the Rev. John Stubbs, D.D.</p> + +<p><a name="dunsink" id="dunsink"></a></p> + +<div class="figcenter" style="width: 747px;"> +<a href="images/ill_observatory_dunsink.jpg"> +<img src="images/ill_observatory_dunsink_sml.jpg" width="747" height="451" alt="THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin." title="" /></a> +<span class="caption">THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin.</span> +</div> + +<p>The next event in the history of the Observatory was the issue of +Letters Patent (32 Geo. III., A.D. 1792), in which it is recited that +"We grant and ordain that there shall be forever hereafter a +Professor of Astronomy, on the foundation of Dr. Andrews, to be +called and known by the name of the Royal Astronomer of Ireland." The +letters prescribe the various duties of the astronomer and the mode +of his election. They lay down regulations as to the conduct of the +astronomical work, and as to the choice of an assistant. They direct +that the Provost and the Senior Fellows shall make a thorough +inspection of the observatory once every year in June or July; and +this duty was first undertaken on the 5th of July, 1792. It may be +noted that the date on which the celebration of the tercentenary of +the University was held happens to coincide with the centenary of the +first visitation of the observatory. The visitors on the first +occasion were A. Murray, Matthew Young, George Hall, and John +Barrett. They record that they find the buildings, books and +instruments in good condition; but the chief feature in this report, +as well as in many which followed it, related to a circumstance to +which we have not yet referred.</p> + +<p>In the original equipment of the observatory, Ussher, with the +natural ambition of a founder, desired to place in it a telescope of +more magnificent proportions than could be found anywhere else. The +Board gave a spirited support to this enterprise, and negotiations +were entered into with the most eminent instrument-maker of those +days. This was Jesse Ramsden (1735-1800), famous as the improver of +the sextant, as the constructor of the great theodolite used by +General Roy in the English Survey, and as the inventor of the +dividing engine for graduating astronomical instruments. Ramsden had +built for Sir George Schuckburgh the largest and most perfect +equatorial ever attempted. He had constructed mural quadrants for +Padua and Verona, which elicited the wonder of astronomers when Dr. +Maskelyne declared he could detect no error in their graduation so +large as two seconds and a half. But Ramsden maintained that even +better results would be obtained by superseding the entire quadrant +by the circle. He obtained the means of testing this prediction when +he completed a superb circle for Palermo of five feet diameter. +Finding his anticipations were realised, he desired to apply the same +principles on a still grander scale. Ramsden was in this mood when +he met with Dr. Ussher. The enthusiasm of the astronomer and the +instrument-maker communicated itself to the Board, and a tremendous +circle, to be ten feet in diameter, was forthwith projected.</p> + +<p>Projected, but never carried out. After Ramsden had to some extent +completed a 10-foot circle, he found such difficulties that he tried +a 9-foot, and this again he discarded for an 8-foot, which was +ultimately accomplished, though not entirely by himself. +Notwithstanding the contraction from the vast proportions originally +designed, the completed instrument must still be regarded as a +colossal piece of astronomical workmanship. Even at this day I do +not know that any other observatory can show a circle eight feet in +diameter graduated all round.</p> + +<p>I think it is Professor Piazzi Smith who tells us how grateful he was +to find a large telescope he had ordered finished by the opticians on +the very day they had promised it. The day was perfectly correct; it +was only the year that was wrong. A somewhat remarkable experience +in this direction is chronicled by the early reports of the visitors +to Dunsink Observatory. I cannot find the date on which the great +circle was ordered from Ramsden, but it is fixed with sufficient +precision by an allusion in Ussher's paper to the Royal Irish +Academy, which shows that by the 13th June, 1785, the order had been +given, but that the abandonment of the 10-foot scale had not then +been contemplated. It was reasonable that the board should allow +Ramsden ample time for the completion of a work at once so elaborate +and so novel. It could not have been finished in a year, nor would +there have been much reason for complaint if the maker had found he +required two or even three years more.</p> + +<p>Seven years gone, and still no telescope, was the condition in which +the Board found matters at their first visitation in 1792. They had, +however, assurances from Ramsden that the instrument would be +completed within the year; but, alas for such promises, another seven +years rolled on, and in 1799 the place for the great circle was still +vacant at Dunsink. Ramsden had fallen into bad health, and the Board +considerately directed that "inquiries should be made." Next year +there was still no progress, so the Board were roused to threaten +Ramsden with a suit at law; but the menace was never executed, for +the malady of the great optician grew worse, and he died that year.</p> + +<p>Affairs had now assumed a critical aspect, for the college had +advanced much money to Ramsden during these fifteen years, and the +instrument was still unfinished. An appeal was made by the Provost +to Dr. Maskelyne, the Astronomer Royal of England, for his advice and +kindly offices in this emergency. Maskelyne responds—in terms +calculated to allay the anxiety of the Bursar—"Mr. Ramsden has left +property behind him, and the College can be in no danger of losing +both their money and the instrument." The business of Ramsden was +then undertaken by Berge, who proceeded to finish the circle quite as +deliberately as his predecessor. After four years Berge promised the +instrument in the following August, but it did not come. Two years +later (1806) the professor complains that he can get no answer from +Berge. In 1807, it is stated that Berge will send the telescope in a +month. He did not; but in the next year (1808), about twenty-three +years after the great circle was ordered, it was erected at Dunsink, +where it is still to be seen.</p> + +<p>The following circumstances have been authenticated by the signatures +of Provosts, Proctors, Bursars, and other College dignitaries:—In +1793 the Board ordered two of the clocks at the observatory to be +sent to Mr. Crosthwaite for repairs. Seven years later, in 1800, Mr. +Crosthwaite was asked if the clocks were ready. This impatience was +clearly unreasonable, for even in four more years, 1804, we find the +two clocks were still in hand. Two years later, in 1806, the Board +determined to take vigorous action by asking the Bursar to call upon +Crosthwaite. This evidently produced some effect, for in the +following year, 1807, the Professor had no doubt that the clocks +would be speedily returned. After eight years more, in 1815, one of +the clocks was still being repaired, and so it was in 1816, which is +the last record we have of these interesting time-pieces. Astronomers +are, however, accustomed to deal with such stupendous periods in +their calculations, that even the time taken to repair a clock seems +but small in comparison.</p> + +<p>The long tenure of the chair of Astronomy by Brinkley is divided into +two nearly equal periods by the year in which the great circle was +erected. Brinkley was eighteen years waiting for his telescope, and +he had eighteen years more in which to use it. During the first of +these periods Brinkley devoted himself to mathematical research; +during the latter he became a celebrated astronomer. Brinkley's +mathematical labours procured for their author some reputation as a +mathematician. They appear to be works of considerable mathematical +elegance, but not indicating any great power of original thought. +Perhaps it has been prejudicial to Brinkley's fame in this direction, +that he was immediately followed in his chair by so mighty a genius +as William Rowan Hamilton.</p> + +<p>After the great circle had been at last erected, Brinkley was able to +begin his astronomical work in earnest. Nor was there much time to +lose. He was already forty-five years old, a year older than was +Herschel when he commenced his immortal career at Slough. Stimulated +by the consciousness of having the command of an instrument of unique +perfection, Brinkley loftily attempted the very highest class of +astronomical research. He resolved to measure anew with his own eye +and with his own hand the constants of aberration and of nutation. He +also strove to solve that great problem of the universe, the +discovery of the distance of a fixed star.</p> + +<p>These were noble problems, and they were nobly attacked. But to +appraise with justice this work of Brinkley, done seventy years ago, +we must not apply to it the same criterion as we would think right to +apply to similar work were it done now. We do not any longer use +Brinkley's constant of aberration, nor do we now think that +Brinkley's determinations of the star distances were reliable. But, +nevertheless, his investigations exercised a marked influence on the +progress of science; they stimulated the study of the principles on +which exact measurements were to be conducted.</p> + +<p>Brinkley had another profession in addition to that of an +astronomer. He was a divine. When a man endeavours to pursue two +distinct occupations concurrently, it will be equally easy to explain +why his career should be successful, or why it should be the +reverse. If he succeeds, he will, of course, exemplify the wisdom of +having two strings to his bow. Should he fail, it is, of course, +because he has attempted to sit on two stools at once. In Brinkley's +case, his two professions must be likened to the two strings rather +than to the two stools. It is true that his practical experience of +his clerical life was very slender. He had made no attempt to +combine the routine of a parish with his labours in the observatory. +Nor do we associate a special eminence in any department of religious +work with his name. If, however, we are to measure Brinkley's merits +as a divine by the ecclesiastical preferment which he received, his +services to theology must have rivalled his services to astronomy. +Having been raised step by step in the Church, he was at last +appointed to the See of Cloyne, in 1826, as the successor of Bishop +Berkeley.</p> + +<p>Now, though it was permissible for the Archdeacon to be also the +Andrews Professor, yet when the Archdeacon became a Bishop, it was +understood that he should transfer his residence from the observatory +to the palace. The chair of Astronomy accordingly became vacant. +Brinkley's subsequent career seems to have been devoted entirely to +ecclesiastical matters, and for the last ten years of his life he did +not contribute a paper to any scientific society. Arago, after a +characteristic lament that Brinkley should have forsaken the pursuit +of science for the temporal and spiritual attractions of a bishopric, +pays a tribute to the conscientiousness of the quondam astronomer, +who would not even allow a telescope to be brought into the palace +lest his mind should be distracted from his sacred duties.</p> + +<p>The good bishop died on the 13th September, 1835. He was buried in +the chapel of Trinity College, and a fine monument to his memory is a +familiar object at the foot of the noble old staircase of the library. +The best memorial of Brinkley is his admirable book on the "Elements +of Plane Astronomy." It passed through many editions in his lifetime, +and even at the present day the same work, revised first by Dr. Luby, +and more recently by the Rev. Dr. Stubbs and Dr. Brunnow, has a large +and well-merited circulation.</p> + +<h3><a name="JOHN_HERSCHEL" id="JOHN_HERSCHEL"></a>JOHN HERSCHEL.</h3> +<p>This illustrious son of an illustrious father was born at Slough, +near Windsor, on the 7th March, 1792. He was the only child of Sir +William Herschel, who had married somewhat late in life, as we have +already mentioned.</p> + +<p><a name="astronometer" id="astronometer"></a></p> + +<div class="figcenter" style="width: 438px;"> +<a href="images/ill_astronometer_herschel.jpg"> +<img src="images/ill_astronometer_herschel_sml.jpg" width="438" height="232" alt="ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon." title="" /></a> +<span class="caption">ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon.</span> +</div> + +<p>The surroundings among which the young astronomer was reared afforded +him an excellent training for that career on which he was to enter, +and in which he was destined to attain a fame only less brilliant +than that of his father. The circumstances of his youth permitted +him to enjoy one great advantage which was denied to the elder +Herschel. He was able, from his childhood, to devote himself almost +exclusively to intellectual pursuits. William Herschel, in the early +part of his career, had only been able to snatch occasional hours for +study from his busy life as a professional musician. But the son, +having been born with a taste for the student's life, was fortunate +enough to have been endowed with the leisure and the means to enjoy +it from the commencement. His early years have been so well +described by the late Professor Pritchard in the "Report of the +Council of the Royal Astronomical Society for 1872," that I venture +to make an extract here:—</p> + +<p>"A few traits of John Herschel's boyhood, mentioned by himself in his +maturer life, have been treasured up by those who were dear to him, +and the record of some of them may satisfy a curiosity as pardonable +as inevitable, which craves to learn through what early steps great +men or great nations become illustrious. His home was singular, and +singularly calculated to nurture into greatness any child born as +John Herschel was with natural gifts, capable of wide development. At +the head of the house there was the aged, observant, reticent +philosopher, and rarely far away his devoted sister, Caroline +Herschel, whose labours and whose fame are still cognisable as a +beneficent satellite to the brighter light of her illustrious +brother. It was in the companionship of these remarkable persons, +and under the shadow of his father's wonderful telescope, that John +Herschel passed his boyish years. He saw them, in silent but +ceaseless industry, busied about things which had no apparent concern +with the world outside the walls of that well-known house, but which, +at a later period of his life, he, with an unrivalled eloquence, +taught his countrymen to appreciate as foremost among those living +influences which but satisfy and elevate the noblest instincts of our +nature. What sort of intercourse passed between the father and the +boy may be gathered from an incident or two which he narrated as +having impressed themselves permanently on the memory of his youth. +He once asked his father what he thought was the oldest of all +things. The father replied, after the Socratic method, by putting +another question: 'And what do you yourself suppose is the oldest of +all things?' The boy was not successful in his answers, thereon the +old astronomer took up a small stone from the garden walk: 'There, my +child, there is the oldest of all the things that I certainly know.' +On another occasion his father is said to have asked the boy, 'What +sort of things, do you think, are most alike?' The delicate, +blue-eyed boy, after a short pause, replied, 'The leaves of the same +tree are most like each other.' 'Gather, then, a handful of leaves of +that tree,' rejoined the philosopher, 'and choose two that are +alike.' The boy failed; but he hid the lesson in his heart, and his +thoughts were revealed after many days. These incidents may be +trifles; nor should we record them here had not John Herschel +himself, though singularly reticent about his personal emotions, +recorded them as having made a strong impression on his mind. Beyond +all doubt we can trace therein, first, that grasp and grouping of +many things in one, implied in the stone as the oldest of things; +and, secondly, that fine and subtle discrimination of each thing out +of many like things as forming the main features which characterized +the habit of our venerated friend's philosophy."</p> + +<p>John Herschel entered St. John's College, Cambridge, when he was +seventeen years of age. His university career abundantly fulfilled +his father's eager desire, that his only son should develop a +capacity for the pursuit of science. After obtaining many lesser +distinctions, he finally came out as Senior Wrangler in 1813. It +was, indeed, a notable year in the mathematical annals of the +University. Second on that list, in which Herschel's name was first, +appeared that of the illustrious Peacock, afterwards Dean of Ely, who +remained throughout life one of Herschel's most intimate friends.</p> + +<p>Almost immediately after taking his degree, Herschel gave evidence of +possessing a special aptitude for original scientific investigation. +He sent to the Royal Society a mathematical paper which was published +in the PHILOSOPHICAL TRANSACTIONS. Doubtless the splendour that +attached to the name he bore assisted him in procuring early +recognition of his own great powers. Certain it is that he was made +a Fellow of the Royal Society at the unprecedentedly early age of +twenty-one. Even after this remarkable encouragement to adopt a +scientific career as the business of his life, it does not seem that +John Herschel at first contemplated devoting himself exclusively to +science. He commenced to prepare for the profession of the Law by +entering as a student at the Middle Temple, and reading with a +practising barrister.</p> + +<p>But a lawyer John Herschel was not destined to become. Circumstances +brought him into association with some leading scientific men. He +presently discovered that his inclinations tended more and more in +the direction of purely scientific pursuits. Thus it came to pass +that the original intention as to the calling which he should follow +was gradually abandoned. Fortunately for science Herschel found its +pursuit so attractive that he was led, as his father had been before +him, to give up his whole life to the advancement of knowledge. Nor +was it unnatural that a Senior Wrangler, who had once tasted the +delights of mathematical research, should have been tempted to devote +much time to this fascinating pursuit. By the time John Herschel was +twenty-nine he had published so much mathematical work, and his +researches were considered to possess so much merit, that the Royal +Society awarded him the Copley Medal, which was the highest +distinction it was capable of conferring.</p> + +<p>At the death of his father in 1822, John Herschel, with his tastes +already formed for a scientific career, found himself in the +possession of ample means. To him also passed all his father's great +telescopes and apparatus. These material aids, together with a +dutiful sense of filial obligation, decided him to make practical +astronomy the main work of his life. He decided to continue to its +completion that great survey of the heavens which had already been +inaugurated, and, indeed, to a large extent accomplished, by his +father.</p> + +<p>The first systematic piece of practical astronomical work which John +Herschel undertook was connected with the measurement of what are +known as "Double Stars." It should be observed, that there are in +the heavens a number of instances in which two stars are seen in very +close association. In the case of those objects to which the +expression "Double Stars" is generally applied, the two luminous +points are so close together that even though they might each be +quite bright enough to be visible to the unaided eye, yet their +proximity is such that they cannot be distinguished as two separate +objects without optical aid. The two stars seem fused together into +one. In the telescope, however, the bodies may be discerned +separately, though they are frequently so close together that it +taxes the utmost power of the instrument to indicate the division +between them.</p> + +<p>The appearance presented by a double star might arise from the +circumstance that the two stars, though really separated from each +other by prodigious distances, happened to lie nearly in the same +line of vision, as seen from our point of view. No doubt, many of +the so-called double stars could be accounted for on this +supposition. Indeed, in the early days when but few double stars +were known, and when telescopes were not powerful enough to exhibit +the numerous close doubles which have since been brought to light, +there seems to have been a tendency to regard all double stars as +merely such perspective effects. It was not at first suggested that +there could be any physical connection between the components of each +pair. The appearance presented was regarded as merely due to the +circumstance that the line joining the two bodies happened to pass +near the earth.</p> + +<p><a name="john_herschel_ill" id="john_herschel_ill"></a></p> + +<div class="figcenter" style="width: 439px;"> +<a href="images/ill_john_herschel.jpg"> +<img src="images/ill_john_herschel_sml.jpg" width="439" height="516" alt="SIR JOHN HERSCHEL." title="" /></a> +<span class="caption">SIR JOHN HERSCHEL.</span> +</div> + +<p>In the early part of his career, Sir William Herschel seems to have +entertained the view then generally held by other astronomers with +regard to the nature of these stellar pairs. The great observer +thought that the double stars could therefore be made to afford a +means of solving that problem in which so many of the observers of +the skies had been engaged, namely, the determination of the +distances of the stars from the earth. Herschel saw that the +displacement of the earth in its annual movement round the sun would +produce an apparent shift in the place of the nearer of the two stars +relatively to the other, supposed to be much more remote. If this +shift could be measured, then the distance of the nearer of the stars +could be estimated with some degree of precision.</p> + +<p>As has not unfrequently happened in the history of science, an effect +was perceived of a very different nature from that which had been +anticipated. If the relative places of the two stars had been +apparently deranged merely in consequence of the motion of the earth, +then the phenomenon would be an annual one. After the lapse of a +year the two stars would have regained their original relative +positions. This was the effect for which William Herschel was +looking. In certain of the so called double stars, he, no doubt, did +find a movement. He detected the remarkable fact that both the +apparent distance and the relative positions of the two bodies were +changing. But what was his surprise to observe that these +alterations were not of an annually periodic character. It became +evident then that in some cases one of the component stars was +actually revolving around the other, in an orbit which required many +years for its completion. Here was indeed a remarkable discovery. It +was clearly impossible to suppose that movements of this kind could +be mere apparent displacements, arising from the annual shift in our +point of view, in consequence of the revolution of the earth. +Herschel's discovery established the interesting fact that, in +certain of these double stars, or binary stars, as these particular +objects are more expressively designated, there is an actual orbital +revolution of a character similar to that which the earth performs +around the sun. Thus it was demonstrated that in these particular +double stars the nearness of the two components was not merely +apparent. The objects must actually lie close together at a distance +which is small in comparison with the distance at which either of +them is separated from the earth. The fact that the heavens contain +pairs of twin suns in mutual revolution was thus brought to light.</p> + +<p>In consequence of this beautiful discovery, the attention of +astronomers was directed to the subject of double stars with a degree +of interest which these objects had never before excited. It was +therefore not unnatural that John Herschel should have been attracted +to this branch of astronomical work. Admiration for his father's +discovery alone might have suggested that the son should strive to +develop this territory newly opened up to research. But it also +happened that the mathematical talents of the younger Herschel +inclined his inquiries in the same direction. He saw clearly that, +when sufficient observations of any particular binary star had been +accumulated, it would then be within the power of the mathematician +to elicit from those observations the shape and the position in space +of the path which each of the revolving stars described around the +other. Indeed, in some cases he would be able to perform the +astonishing feat of determining from his calculations the weight of +these distant suns, and thus be enabled to compare them with the mass +of our own sun.</p> + +<p><a name="nebula" id="nebula"></a></p> + +<div class="figleft" style="width: 188px;"> +<a href="images/ill_nebula_drawn_john_herschel.jpg"> +<img src="images/ill_nebula_drawn_john_herschel_sml.jpg" width="188" height="249" alt="NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel." title="" /></a> +<span class="caption">NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel.</span> +</div> + +<p>But this work must follow the observations, it could not precede +them. The first step was therefore to observe and to measure with +the utmost care the positions and distances of those particular +double stars which appear to offer the greatest promise in this +particular research. In 1821, Herschel and a friend of his, Mr. +James South, agreed to work together with this object. South was a +medical man with an ardent devotion to science, and possessed of +considerable wealth. He procured the best astronomical instruments +that money could obtain, and became a most enthusiastic astronomer +and a practical observer of tremendous energy.</p> + +<p>South and John Herschel worked together for two years in the +observation and measurement of the double stars discovered by Sir +William Herschel. In the course of this time their assiduity was +rewarded by the accumulation of so great a mass of careful +measurements that when published, they formed quite a volume in the +"Philosophical Transactions." The value and accuracy of the work, +when estimated by standards which form proper criteria for that +period, is universally recognised. It greatly promoted the progress +of sidereal astronomy, and the authors were in consequence awarded +medals from the Royal Society, and the Royal Astronomical Society, +as well as similar testimonials from various foreign institutions.</p> + +<p>This work must, however, be regarded as merely introductory to the +main labours of John Herschel's life. His father devoted the greater +part of his years as an observer to what he called his "sweeps" of +the heavens. The great reflecting telescope, twenty feet long, was +moved slowly up and down through an arc of about two degrees towards +and from the pole, while the celestial panorama passed slowly in the +course of the diurnal motion before the keenly watching eye of the +astronomer. Whenever a double star traversed the field Herschel +described it to his sister Caroline, who, as we have already +mentioned, was his invariable assistant in his midnight watches. When +a nebula appeared, then he estimated its size and its brightness, he +noticed whether it had a nucleus, or whether it had stars disposed in +any significant manner with regard to it. He also dictated any other +circumstance which he deemed worthy of record. These observations +were duly committed to writing by the same faithful and indefatigable +scribe, whose business it also was to take a memorandum of the exact +position of the object as indicated by a dial placed in front of her +desk, and connected with the telescope.</p> + +<p>John Herschel undertook the important task of re-observing the +various double stars and nebulae which had been discovered during +these memorable vigils. The son, however, lacked one inestimable +advantage which had been possessed by the father. John Herschel had +no assistant to discharge all those duties which Caroline had so +efficiently accomplished. He had, therefore, to modify the system of +sweeping previously adopted in order to enable all the work both of +observing and of recording to be done by himself. This, in many +ways, was a great drawback to the work of the younger astronomer. The +division of labour between the observer and the scribe enables a +greatly increased quantity of work to be got through. It is also +distinctly disadvantageous to an observer to have to use his eye at +the telescope directly after he has been employing it for reading the +graduations on a circle, by the light of a lamp, or for entering +memoranda in a note book. Nebulae, especially, are often so +excessively faint that they can only be properly observed by an eye +which is in that highly sensitive condition which is obtained by long +continuance in darkness. The frequent withdrawal of the eye from the +dark field of the telescope, and the application of it to reading by +artificial light, is very prejudicial to its use for the more +delicate purpose. John Herschel, no doubt, availed himself of every +precaution to mitigate the ill effects of this inconvenience as much +as possible, but it must have told upon his labours as compared with +those of his father.</p> + +<p>But nevertheless John Herschel did great work during his "sweeps." He +was specially particular to note all the double stars which presented +themselves to his observation. Of course some little discretion must +be allowed in deciding as to what degree of proximity in adjacent +stars does actually bring them within the category of "double +stars." Sir John set down all such objects as seemed to him likely +to be of interest, and the results of his discoveries in this branch +of astronomy amount to some thousands. Six or seven great memoirs in +the TRANSACTIONS of the Royal Astronomical Society have been devoted +to giving an account of his labours in this department of astronomy.</p> + +<p><a name="centaur" id="centaur"></a></p> + +<div class="figcenter" style="width: 328px;"> +<a href="images/ill_cluster_centaur.jpg"> +<img src="images/ill_cluster_centaur_sml.jpg" width="328" height="314" alt="THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel." title="" /></a> +<span class="caption">THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.</span> +</div> + +<p>One of the achievements by which Sir John Herschel is best known is +his invention of a method by which the orbits of binary stars could +be determined. It will be observed that when one star revolves +around another in consequence of the law of gravitation, the orbit +described must be an ellipse. This ellipse, however, generally +speaking, appears to us more or less foreshortened, for it is easily +seen that only under highly exceptional circumstances would the plane +in which the stars move happen to be directly square to the line of +view. It therefore follows that what we observe is not exactly the +track of one star around the other; it is rather the projection of +that track as seen on the surface of the sky. Now it is remarkable +that this apparent path is still an ellipse. Herschel contrived a +very ingenious and simple method by which he could discover from the +observations the size and position of the ellipse in which the +revolution actually takes place. He showed how, from the study of +the apparent orbit of the star, and from certain measurements which +could easily be effected upon it, the determination of the true +ellipse in which the movement is performed could be arrived at. In +other words, Herschel solved in a beautiful manner the problem of +finding the true orbits of double stars. The importance of this work +may be inferred from the fact that it has served as the basis on +which scores of other investigators have studied the fascinating +subject of the movement of binary stars.</p> + +<p>The labours, both in the discovery and measurement of the double +stars, and in the discussion of the observations with the object of +finding the orbits of such stars as are in actual revolution, +received due recognition in yet another gold medal awarded by the +Royal Society. An address was delivered on the occasion by the Duke +of Sussex (30th November, 1833), in the course of which, after +stating that the medal had been conferred on Sir John Herschel, he +remarks:—</p> + +<p>"It has been said that distance of place confers the same privilege +as distance of time, and I should gladly avail myself of the +privilege which is thus afforded me by Sir John Herschel's separation +from his country and friends, to express my admiration of his +character in stronger terms than I should otherwise venture to use; +for the language of panegyric, however sincerely it may flow from the +heart, might be mistaken for that of flattery, if it could not thus +claim somewhat of an historical character; but his great attainments +in almost every department of human knowledge, his fine powers as a +philosophical writer, his great services and his distinguished +devotion to science, the high principles which have regulated his +conduct in every relation of life, and, above all, his engaging +modesty, which is the crown of all his other virtues, presenting such +a model of an accomplished philosopher as can rarely be found beyond +the regions of fiction, demand abler pens than mine to describe them +in adequate terms, however much inclined I might feel to undertake +the task."</p> + +<p>The first few lines of the eulogium just quoted allude to Herschel's +absence from England. This was not merely an episode of interest in +the career of Herschel, it was the occasion of one of the greatest +scientific expeditions in the whole history of astronomy.</p> + +<p>Herschel had, as we have seen, undertaken a revision of his father's +"sweeps" for new objects, in those skies which are visible from our +latitudes in the northern hemisphere. He had well-nigh completed +this task. Zone by zone the whole of the heavens which could be +observed from Windsor had passed under his review. He had added +hundreds to the list of nebulae discovered by his father. He had +announced thousands of double stars. At last, however, the great +survey was accomplished. The contents of the northern hemisphere, so +far at least as they could be disclosed by his telescope of twenty +feet focal length, had been revealed.</p> + +<p><a name="herschel_observatory_feldhausen" id="herschel_observatory_feldhausen"></a></p> + +<div class="figcenter" style="width: 442px;"> +<a href="images/ill_john_herschel_observatory_feldhausen.jpg"> +<img src="images/ill_john_herschel_observatory_feldhausen_sml.jpg" width="442" height="373" alt="SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope." title="" /></a> +<span class="caption">SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope.</span> +</div> + +<p>But Herschel felt that this mighty task had to be supplemented by +another of almost equal proportions, before it could be said that the +twenty-foot telescope had done its work. It was only the northern +half of the celestial sphere which had been fully explored. The +southern half was almost virgin territory, for no other astronomer +was possessed of a telescope of such power as those which the +Herschels had used. It is true, of course, that as a certain margin +of the southern hemisphere was visible from these latitudes, it had +been more or less scrutinized by observers in northern skies. And +the glimpses which had thus been obtained of the celestial objects in +the southern sky, were such as to make an eager astronomer long for a +closer acquaintance with the celestial wonders of the south. The +most glorious object in the sidereal heavens, the Great Nebula in +Orion, lies indeed in that southern hemisphere to which the younger +Herschel's attention now became directed. It fortunately happens, +however, for votaries of astronomy all the world over, that Nature +has kindly placed her most astounding object, the great Nebula in +Orion, in such a favoured position, near the equator, that from a +considerable range of latitudes, both north and south, the wonders of +the Nebula can be explored. There are grounds for thinking that the +southern heavens contain noteworthy objects which, on the whole, are +nearer to the solar system than are the noteworthy objects in the +northern skies. The nearest star whose distance is known, Alpha +Centauri, lies in the southern hemisphere, and so also does the most +splendid cluster of stars.</p> + +<p>Influenced by the desire to examine these objects, Sir John Herschel +determined to take his great telescope to a station in the southern +hemisphere, and thus complete his survey of the sidereal heavens. The +latitude of the Cape of Good Hope is such that a suitable site could +be there found for his purpose. The purity of the skies in South +Africa promised to provide for the astronomer those clear nights +which his delicate task of surveying the nebulae would require.</p> + +<p>On November 13, 1833, Sir John Herschel, who had by this time +received the honour of knighthood from William IV., sailed from +Portsmouth for the Cape of Good Hope, taking with him his gigantic +instruments. After a voyage of two months, which was considered to +be a fair passage in those days, he landed in Table Bay, and having +duly reconnoitred various localities, he decided to place his +observatory at a place called Feldhausen, about six miles from Cape +Town, near the base of the Table Mountain. A commodious residence +was there available, and in it he settled with his family. A +temporary building was erected to contain the equatorial, but the +great twenty-foot telescope was accommodated with no more shelter +than is provided by the open canopy of heaven.</p> + +<p>As in his earlier researches at home, the attention of the great +astronomer at the Cape of Good Hope was chiefly directed to the +measurement of the relative positions and distances apart of the +double stars, and to the close examination of the nebulae. In the +delineation of the form of these latter objects Herschel found ample +employment for his skilful pencil. Many of the drawings he has made +of the celestial wonders in the southern sky are admirable examples +of celestial portraiture.</p> + +<p>The number of the nebulae and of those kindred objects, the star +clusters, which Herschel studied in the southern heavens, during four +years of delightful labour, amount in all to one thousand seven +hundred and seven. His notes on their appearance, and the +determinations of their positions, as well as his measurements of +double stars, and much other valuable astronomical research, were +published in a splendid volume, brought out at the cost of the Duke +of Northumberland. This is, indeed, a monumental work, full of +interesting and instructive reading for any one who has a taste for +astronomy.</p> + +<p>Herschel had the good fortune to be at the Cape on the occasion of +the periodical return of Halley's great comet in 1833. To the study +of this body he gave assiduous attention, and the records of his +observations form one of the most interesting chapters in that +remarkable volume to which we have just referred.</p> + +<p><a name="column" id="column"></a></p> + +<div class="figcenter" style="width: 412px;"> +<a href="images/ill_granite_column_feldhausen.jpg"> +<img src="images/ill_granite_column_feldhausen_sml.jpg" width="412" height="304" alt="COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens." title="" /></a> +<span class="caption">COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens.</span> +</div> + +<p>Early in 1838 Sir John Herschel returned to England. He had made +many friends at the Cape, who deeply sympathised with his self- +imposed labours while he was resident among them. They desired to +preserve the recollection of this visit, which would always, they +considered, be a source of gratification in the colony. Accordingly, +a number of scientific friends in that part of the world raised a +monument with a suitable inscription, on the spot which had been +occupied by the great twenty-foot reflector at Feldhausen.</p> + +<p>His return to England after five years of absence was naturally an +occasion for much rejoicing among the lovers of astronomy. He was +entertained at a memorable banquet, and the Queen, at her coronation, +made him a baronet. His famous aunt Caroline, at that time aged +eighty, was still in the enjoyment of her faculties, and was able to +estimate at its true value the further lustre which was added to the +name she bore. But there is reason to believe that her satisfaction +was not quite unmixed with other feelings. With whatever favour she +might regard her nephew, he was still not the brother to whom her +life had been devoted. So jealous was this vigorous old lady of the +fame of the great brother William, that she could hardly hear with +patience of the achievements of any other astronomer, and this +failing existed in some degree even when that other astronomer +happened to be her illustrious nephew.</p> + +<p>With Sir John Herschel's survey of the Southern Hemisphere it may be +said that his career as an observing astronomer came to a close. He +did not again engage in any systematic telescopic research. But it +must not be inferred from this statement that he desisted from active +astronomical work. It has been well observed that Sir John Herschel +was perhaps the only astronomer who has studied with success, and +advanced by original research, every department of the great science +with which his name is associated. It was to some other branches of +astronomy besides those concerned with looking through telescopes, +that the rest of the astronomer's life was to be devoted.</p> + +<p>To the general student Sir John Herschel is best known by the volume +which he published under the title of "Outlines of Astronomy." This +is, indeed, a masterly work, in which the characteristic difficulties +of the subject are resolutely faced and expounded with as much +simplicity as their nature will admit. As a literary effort this +work is admirable, both on account of its picturesque language and +the ennobling conceptions of the universe which it unfolds. The +student who desires to become acquainted with those recondite +departments of astronomy, in which the effects of the disturbing +action of one planet upon the motions of another planet are +considered, will turn to the chapters in Herschel's famous work on +the subject. There he will find this complex matter elucidated, +without resort to difficult mathematics. Edition after edition of +this valuable work has appeared, and though the advances of modern +astronomy have left it somewhat out of date in certain departments, +yet the expositions it contains of the fundamental parts of the +science still remain unrivalled.</p> + +<p>Another great work which Sir John undertook after his return from the +Cape, was a natural climax to those labours on which his father and +he had been occupied for so many years. We have already explained +how the work of both these observers had been mainly devoted to the +study of the nebulae and the star clusters. The results of their +discoveries had been announced to the world in numerous isolated +memoirs. The disjointed nature of these publications made their use +very inconvenient. But still it was necessary for those who desired +to study the marvellous objects discovered by the Herschels, to have +frequent recourse to the original works. To incorporate all the +several observations of nebular into one great systematic catalogue, +seemed, therefore, to be an indispensable condition of progress in +this branch of knowledge. No one could have been so fitted for this +task as Sir John Herschel. He, therefore, attacked and carried +through the great undertaking. Thus at last a grand catalogue of +nebulae and clusters was produced. Never before was there so +majestic an inventory. If we remember that each of the nebulae is an +object so vast, that the whole of the solar system would form an +inconsiderable speck by comparison, what are we to think of a +collection in which these objects are enumerated in thousands? In +this great catalogue we find arranged in systematic order all the +nebulae and all the clusters which had been revealed by the diligence +of the Herschels, father and son, in the Northern Hemisphere, and of +the son alone in the Southern Hemisphere. Nor should we omit to +mention that the labours of other astronomers were likewise +incorporated. It was unavoidable that the descriptions given to each +of the objects should be very slight. Abbreviations are used, which +indicate that a nebula is bright, or very bright, or extremely +bright, or faint, or very faint, or extremely faint. Such phrases +have certainly but a relative and technical meaning in such a +catalogue. The nebulae entered as extremely bright by the +experienced astronomer are only so described by way of contrast to +the great majority of these delicate telescopic objects. Most of the +nebulae, indeed, are so difficult to see, that they admit of but very +slight description. It should be observed that Herschel's catalogue +augmented the number of known nebulous objects to more than ten times +that collected into any catalogue which had ever been compiled before +the days of William Herschel's observing began. But the study of +these objects still advances, and the great telescopes now in use +could probably show at least twice as many of these objects as are +contained in the list of Herschel, of which a new and enlarged +edition has since been brought out by Dr. Dreyer.</p> + +<p>One of the best illustrations of Sir John Herschel's literary powers +is to be found in the address which he delivered at the Royal +Astronomical Society, on the occasion of presenting a medal to Mr. +Francis Baily, in recognition of his catalogue of stars. The passage +I shall here cite places in its proper aspect the true merit of the +laborious duty involved in such a task as that which Mr. Baily had +carried through with such success:—</p> + +<p>"If we ask to what end magnificent establishments are maintained by +states and sovereigns, furnished with masterpieces of art, and placed +under the direction of men of first-rate talent and high-minded +enthusiasm, sought out for those qualities among the foremost in the +ranks of science, if we demand QUI BONO? for what good a Bradley has +toiled, or a Maskelyne or a Piazzi has worn out his venerable age in +watching, the answer is—not to settle mere speculative points in the +doctrine of the universe; not to cater for the pride of man by +refined inquiries into the remoter mysteries of nature; not to trace +the path of our system through space, or its history through past and +future eternities. These, indeed, are noble ends and which I am far +from any thought of depreciating; the mind swells in their +contemplation, and attains in their pursuit an expansion and a +hardihood which fit it for the boldest enterprise. But the direct +practical utility of such labours is fully worthy of their +speculative grandeur. The stars are the landmarks of the universe; +and, amidst the endless and complicated fluctuations of our system, +seem placed by its Creator as guides and records, not merely to +elevate our minds by the contemplation of what is vast, but to teach +us to direct our actions by reference to what is immutable in His +works. It is, indeed, hardly possible to over-appreciate their value +in this point of view. Every well-determined star, from the moment +its place is registered, becomes to the astronomer, the geographer, +the navigator, the surveyor, a point of departure which can never +deceive or fail him, the same for ever and in all places, of a +delicacy so extreme as to be a test for every instrument yet invented +by man, yet equally adapted for the most ordinary purposes; as +available for regulating a town clock as for conducting a navy to the +Indies; as effective for mapping down the intricacies of a petty +barony as for adjusting the boundaries of Transatlantic empires. When +once its place has been thoroughly ascertained and carefully +recorded, the brazen circle with which that useful work was done may +moulder, the marble pillar may totter on its base, and the astronomer +himself survive only in the gratitude of posterity; but the record +remains, and transfuses all its own exactness into every +determination which takes it for a groundwork, giving to inferior +instruments—nay, even to temporary contrivances, and to the +observations of a few weeks or days—all the precision attained +originally at the cost of so much time, labour, and expense."</p> + +<p>Sir John Herschel wrote many other works besides those we have +mentioned. His "Treatise on Meteorology" is, indeed, a standard work +on this subject, and numerous articles from the same pen on +miscellaneous subjects, which have been collected and reprinted, +seemed as a relaxation from his severe scientific studies. Like +certain other great mathematicians Herschel was also a poet, and he +published a translation of the Iliad into blank verse.</p> + +<p>In his later years Sir John Herschel lived a retired life. For a +brief period he had, indeed, been induced to accept the office of +Master of the Mint. It was, however, evident that the routine of +such an occupation was not in accordance with his tastes, and he +gladly resigned it, to return to the seclusion of his study in his +beautiful home at Collingwood, in Kent.</p> + +<p>His health having gradually failed, he died on the 11th May, 1871, in +the seventy-ninth year of his age.</p> + +<h3><a name="THE_EARL_OF_ROSSE" id="THE_EARL_OF_ROSSE"></a>THE EARL OF ROSSE.</h3> +<p>The subject of our present sketch occupies quite a distinct position +in scientific history. Unlike many others who have risen by their +scientific discoveries from obscurity to fame, the great Earl of +Rosse was himself born in the purple. His father, who, under the +title of Sir Lawrence Parsons, had occupied a distinguished position +in the Irish Parliament, succeeded on the death of his father to the +Earldom which had been recently created. The subject of our present +memoir was, therefore, the third of the Earls of Rosse, and he was +born in York on June 17, 1800. Prior to his father's death in 1841, +he was known as Lord Oxmantown.</p> + +<p>The University education of the illustrious astronomer was begun in +Dublin and completed at Oxford. We do not hear in his case of any +very remarkable University career. Lord Rosse was, however, a +diligent student, and obtained a first-class in mathematics. He +always took a great deal of interest in social questions, and was a +profound student of political economy. He had a seat in the House of +Commons, as member for King's County, from 1821 to 1834, his +ancestral estate being situated in this part of Ireland.</p> + +<p><a name="rosse_ill" id="rosse_ill"></a></p> + +<div class="figcenter" style="width: 409px;"> +<a href="images/ill_earl_rosse.jpg"> +<img src="images/ill_earl_rosse_sml.jpg" width="409" height="476" alt="THE EARL OF ROSSE." title="" /></a> +<span class="caption">THE EARL OF ROSSE.</span> +</div> + +<p>Lord Rosse was endowed by nature with a special taste for mechanical +pursuits. Not only had he the qualifications of a scientific +engineer, but he had the manual dexterity which qualified him +personally to carry out many practical arts. Lord Rosse was, in +fact, a skilful mechanic, an experienced founder, and an ingenious +optician. His acquaintances were largely among those who were +interested in mechanical pursuits, and it was his delight to visit +the works or engineering establishments where refined processes in +the arts were being carried on. It has often been stated—and as I +have been told by members of his family, truly stated—that on one +occasion, after he had been shown over some large works in the north +of England, the proprietor bluntly said that he was greatly in want +of a foreman, and would indeed be pleased if his visitor, who had +evinced such extraordinary capacity for mechanical operations, would +accept the post. Lord Rosse produced his card, and gently explained +that he was not exactly the right man, but he appreciated the +compliment, and this led to a pleasant dinner, and was the basis of a +long friendship.</p> + +<p>I remember on one occasion hearing Lord Rosse explain how it was that +he came to devote his attention to astronomy. It appears that when +he found himself in the possession of leisure and of means, he +deliberately cast around to think how that means and that leisure +could be most usefully employed. Nor was it surprising that he +should search for a direction which would offer special scope for his +mechanical tastes. He came to the conclusion that the building of +great telescopes was an art which had received no substantial advance +since the great days of William Herschel. He saw that to construct +mighty instruments for studying the heavens required at once the +command of time and the command of wealth, while he also felt that +this was a subject the inherent difficulties of which would tax to +the uttermost whatever mechanical skill he might possess. Thus it +was he decided that the construction of great telescopes should +become the business of his life.</p> + +<p><a name="birr" id="birr"></a></p> + +<div class="figcenter" style="width: 651px;"> +<a href="images/ill_birr_castle.jpg"> +<img src="images/ill_birr_castle_sml.jpg" width="651" height="428" alt="BIRR CASTLE." /></a> +<span class="caption">BIRR CASTLE.</span> +</div> + +<p><a name="mall" id="mall"></a></p> + +<div class="figcenter" style="width: 651px;"> +<a href="images/ill_mall_parsonstown.jpg"> +<img src="images/ill_mall_parsonstown_sml.jpg" width="651" height="432" alt="THE MALL, PARSONSTOWN." title="" /></a> +<span class="caption">THE MALL, PARSONSTOWN.</span> +</div> + +<p>In the centre of Ireland, seventy miles from Dublin, on the border +between King's County and Tipperary, is a little town whereof we must +be cautious before writing the name. The inhabitants of that town +frequently insist that its name is Birr,[<a name="ast" id="ast"></a><a href="#note">*</a>] while the official +designation is Parsonstown, and to this day for every six people who +apply one name to the town, there will be half a dozen who use the +other. But whichever it may be, Birr or Parsonstown—and I shall +generally call it by the latter name—it is a favourable specimen of +an Irish county town. The widest street is called the Oxmantown +Mall. It is bordered by the dwelling-houses of the chief residents, +and adorned with rows of stately trees. At one end of this +distinctly good feature in the town is the Parish Church, while at +the opposite end are the gates leading into Birr Castle, the +ancestral home of the house of Parsons. Passing through the gates +the visitor enters a spacious demesne, possessing much beauty of wood +and water, one of the most pleasing features being the junction of +the two rivers, which unite at a spot ornamented by beautiful +timber. At various points illustrations of the engineering skill of +the great Earl will be observed. The beauty of the park has been +greatly enhanced by the construction of an ample lake, designed with +the consummate art by which art is concealed. Even in mid-summer it +is enlivened by troops of wild ducks preening themselves in that +confidence which they enjoy in those happy localities where the sound +of a gun is seldom heard. The water is led into the lake by a tube +which passes under one of the two rivers just mentioned, while the +overflow from the lake turns a water-wheel, which works a pair of +elevators ingeniously constructed for draining the low-lying parts of +the estate.</p> + +<div class="footnote"> +<a name="note" id="note"></a> +<p>[<a href="#ast">*</a>] Considering the fame acquired by Parsonstown from Lord Rosse's + mirrors, it may be interesting to note the following extract from + "The Natural History of Ireland," by Dr. Gerard Boate, Thomas + Molyneux M.D., F.R.S., and others, which shows that 150 years ago + Parsonstown was famous for its glass:—</p> + +<p>"We shall conclude this chapter with the glass, there having been + several glasshouses set up by the English in Ireland, none in Dublin + or other cities, but all of them in the country; amongst which the + principal was that of Birre, a market town, otherwise called + Parsonstown, after one Sir Lawrence Parsons, who, having purchased + that lordship, built a goodly house upon it; his son William Parsons + having succeeded him in the possession of it; which town is situate + in Queen's County, about fifty miles (Irish) to the southwest of + Dublin, upon the borders of the two provinces of Leinster and Munster; + from this place Dublin was furnished with all sorts of window and + drinking glasses, and such other as commonly are in use. One part of + the materials, viz., the sand, they had out of England; the other, + to wit the ashes, they made in the place of ash-tree, and used no + other. The chiefest difficulty was to get the clay for the pots to + melt the materials in; this they had out of the north."—Chap. XXI., + Sect. VIII. "Of the Glass made in Ireland."</p> +</div> + +<p>Birr Castle itself is a noble mansion with reminiscences from the +time of Cromwell. It is surrounded by a moat and a drawbridge of +modern construction, and from its windows beautiful views can be had +over the varied features of the park. But while the visitors to +Parsonstown will look with great interest on this residence of an +Irish landlord, whose delight it was to dwell in his own country, and +among his own people, yet the feature which they have specially come +to observe is not to be found in the castle itself. On an extensive +lawn, sweeping down from the moat towards the lake, stand two noble +masonry walls. They are turreted and clad with ivy, and considerably +loftier than any ordinary house. As the visitor approaches, he will +see between those walls what may at first sight appear to him to be +the funnel of a steamer lying down horizontally. On closer approach +he will find that it is an immense wooden tube, sixty feet long, and +upwards of six feet in diameter. It is in fact large enough to admit +of a tall man entering into it and walking erect right through from +one end to the other. This is indeed the most gigantic instrument +which has ever been constructed for the purpose of exploring the +heavens. Closely adjoining the walls between which the great tube +swings, is a little building called "The Observatory." In this the +smaller instruments are contained, and there are kept the books which +are necessary for reference. The observatory also offers shelter to +the observers, and provides the bright fire and the cup of warm tea, +which are so acceptable in the occasional intervals of a night's +observation passed on the top of the walls with no canopy but the +winter sky.</p> + +<p>Almost the first point which would strike the visitor to Lord Rosse's +telescope is that the instrument at which he is looking is not only +enormously greater than anything of the kind that he has ever seen +before, but also that it is something of a totally different nature. +In an ordinary telescope he is accustomed to find a tube with lenses +of glass at either end, while the large telescopes that we see in our +observatories are also in general constructed on the same principle. +At one end there is the object-glass, and at the other end the +eye-piece, and of course it is obvious that with an instrument of +this construction it is to the lower end of the tube that the eye of +the observer must be placed when the telescope is pointed to the +skies. But in Lord Rosse's telescope you would look in vain for +these glasses, and it is not at the lower end of the instrument that +you are to take your station when you are going to make your +observations. The astronomer at Parsonstown has rather to avail +himself of the ingenious system of staircases and galleries, by which +he is enabled to obtain access to the mouth of the great tube. The +colossal telescope which swings between the great walls, like +Herschel's great telescope already mentioned, is a reflector, the +original invention of which is due of course to Newton. The optical +work which is accomplished by the lenses in the ordinary telescope is +effected in the type of instrument constructed by Lord Rosse by a +reflecting mirror which is placed at the lower end of the vast tube. +The mirror in this instrument is made of a metal consisting of two +parts of copper to one of tin. As we have already seen, this mixture +forms an alloy of a very peculiar nature. The copper and the tin +both surrender their distinctive qualities, and unite to form a +material of a very different physical character. The copper is tough +and brown, the tin is no doubt silvery in hue, but soft and almost +fibrous in texture. When the two metals are mixed together in the +proportions I have stated, the alloy obtained is intensely hard and +quite brittle being in both these respects utterly unlike either of +the two ingredients of which it is composed. It does, however, +resemble the tin in its whiteness, but it acquires a lustre far +brighter than tin; in fact, this alloy hardly falls short of silver +itself in its brilliance when polished.</p> + +<p><a name="lord_rosse_telescope" id="lord_rosse_telescope"></a></p> + +<div class="figcenter" style="width: 641px;"> +<a href="images/ill_rosse_telescope.jpg"> +<img src="images/ill_rosse_telescope_sml.jpg" width="641" height="475" alt="LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin." title="" /></a> +<span class="caption">LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin.</span> +</div> + +<p>The first duty that Lord Rosse had to undertake was the construction +of this tremendous mirror, six feet across, and about four or five +inches thick. The dimensions were far in excess of those which had +been contemplated in any previous attempt of the same kind. Herschel +had no doubt fashioned one mirror of four feet in diameter, and many +others of smaller dimensions, but the processes which he employed had +never been fully published, and it was obvious that, with a large +increase in dimensions, great additional difficulties had to be +encountered. Difficulties began at the very commencement of the +process, and were experienced in one form or another at every +subsequent stage. In the first place, the mere casting of a great +disc of this mixture of tin and copper, weighing something like three +or four tons, involved very troublesome problems. No doubt a casting +of this size, if the material had been, for example, iron, would have +offered no difficulties beyond those with which every practical +founder is well acquainted, and which he has to encounter daily in +the course of his ordinary work. But speculum metal is a material of +a very intractable description. There is, of course, no practical +difficulty in melting the copper, nor in adding the proper proportion +of tin when the copper has been melted. There may be no great +difficulty in arranging an organization by which several crucibles, +filled with the molten material, shall be poured simultaneously so as +to obtain the requisite mass of metal, but from this point the +difficulties begin. For speculum metal when cold is excessively +brittle, and were the casting permitted to cool like an ordinary +copper or iron casting, the mirror would inevitably fly into pieces. +Lord Rosse, therefore, found it necessary to anneal the casting with +extreme care by allowing it to cool very slowly. This was +accomplished by drawing the disc of metal as soon as it had entered +into the solid state, though still glowing red, into an annealing +oven. There the temperature was allowed to subside so gradually, +that six weeks elapsed before the mirror had reached the temperature +of the external air. The necessity for extreme precaution in the +operation of annealing will be manifest if we reflect on one of the +accidents which happened. On a certain occasion, after the cooling +of a great casting had been completed, it was found, on withdrawing +the speculum, that it was cracked into two pieces. This mishap was +eventually traced to the fact that one of the walls of the oven had +only a single brick in its thickness, and that therefore the heat had +escaped more easily through that side than through the other sides +which were built of double thickness. The speculum had, +consequently, not cooled uniformly, and hence the fracture had +resulted. Undeterred, however, by this failure, as well as by not a +few other difficulties, into a description of which we cannot now +enter, Lord Rosse steadily adhered to his self-imposed task, and at +last succeeded in casting two perfect discs on which to commence the +tedious processes of grinding and polishing. The magnitude of the +operations involved may perhaps be appreciated if I mention that the +value of the mere copper and tin entering into the composition of +each of the mirrors was about 500 pounds.</p> + +<p>In no part of his undertaking was Lord Rosse's mechanical ingenuity +more taxed than in the devising of the mechanism for carrying out the +delicate operations of grinding and polishing the mirrors, whose +casting we have just mentioned. In the ordinary operations of the +telescope-maker, such processes had hitherto been generally effected +by hand, but, of course, such methods became impossible when dealing +with mirrors which were as large as a good-sized dinner table, and +whose weight was measured by tons. The rough grinding was effected +by means of a tool of cast iron about the same size as the mirror, +which was moved by suitable machinery both backwards and forwards, +and round and round, plenty of sand and water being supplied between +the mirror and the tool to produce the necessary attrition. As the +process proceeded and as the surface became smooth, emery was used +instead of sand; and when this stage was complete, the grinding tool +was removed and the polishing tool was substituted. The essential +part of this was a surface of pitch, which, having been temporarily +softened by heat, was then placed on the mirror, and accepted from +the mirror the proper form. Rouge was then introduced as the +polishing powder, and the operation was continued about nine hours, +by which time the great mirror had acquired the appearance of highly +polished silver. When completed, the disc of speculum metal was +about six feet across and four inches thick. The depression in the +centre was about half an inch. Mounted on a little truck, the great +speculum was then conveyed to the instrument, to be placed in its +receptacle at the bottom of the tube, the length of which was sixty +feet, this being the focal distance of the mirror. Another small +reflector was inserted in the great tube sideways, so as to direct +the gaze of the observer down upon the great reflector. Thus was +completed the most colossal instrument for the exploration of the +heavens which the art of man has ever constructed.</p> + +<p><a name="roman" id="roman"></a></p> + +<div class="figcenter" style="width: 655px;"> +<a href="images/ill_church_parsonstown.jpg"> +<img src="images/ill_church_parsonstown_sml.jpg" width="655" height="483" alt="ROMAN CATHOLIC CHURCH AT PARSONSTOWN." title="" /></a> +<span class="caption">ROMAN CATHOLIC CHURCH AT PARSONSTOWN.</span> +</div> + +<p>It was once my privilege to be one of those to whom the illustrious +builder of the great telescope entrusted its use. For two seasons in +1865 and 1866 I had the honour of being Lord Rosse's astronomer. +During that time I passed many a fine night in the observer's +gallery, examining different objects in the heavens with the aid of +this remarkable instrument. At the time I was there, the objects +principally studied were the nebulae, those faint stains of light +which lie on the background of the sky. Lord Rosse's telescope was +specially suited for the scrutiny of these objects, inasmuch as their +delicacy required all the light-grasping power which could be +provided.</p> + +<p>One of the greatest discoveries made by Lord Rosse, when his huge +instrument was first turned towards the heavens, consisted in the +detection of the spiral character of some of the nebulous forms. +When the extraordinary structure of these objects was first +announced, the discovery was received with some degree of +incredulity. Other astronomers looked at the same objects, and when +they failed to discern—and they frequently did fail to discern—the +spiral structure which Lord Rosse had indicated, they drew the +conclusion that this spiral structure did not exist. They thought it +must be due possibly to some instrumental defect or to the +imagination of the observer. It was, however, hardly possible for +any one who was both willing and competent to examine into the +evidence, to doubt the reality of Lord Rosse's discoveries. It +happens, however, that they have been recently placed beyond all +doubt by testimony which it is impossible to gainsay. A witness +never influenced by imagination has now come forward, and the +infallible photographic plate has justified Lord Rosse. Among the +remarkable discoveries which Dr. Isaac Roberts has recently made in +the application of his photographic apparatus to the heavens, there +is none more striking than that which declares, not only that the +nebulae which Lord Rosse described as spirals, actually do possess +the character so indicated, but that there are many others of the +same description. He has even brought to light the astonishingly +interesting fact that there are invisible objects of this class which +have never been seen by human eye, but whose spiral character is +visible to the peculiar delicacy of the photographic telescope.</p> + +<p>In his earlier years, Lord Rosse himself used to be a diligent +observer of the heavenly bodies with the great telescope which was +completed in the year 1845. But I think that those who knew Lord +Rosse well, will agree that it was more the mechanical processes +incidental to the making of the telescope which engaged his interest +than the actual observations with the telescope when it was +completed. Indeed one who was well acquainted with him believed Lord +Rosse's special interest in the great telescope ceased when the last +nail had been driven into it. But the telescope was never allowed to +lie idle, for Lord Rosse always had associated with him some ardent +young astronomer, whose delight it was to employ to the uttermost the +advantages of his position in exploring the wonders of the sky. Among +those who were in this capacity in the early days of the great +telescope, I may mention my esteemed friend Dr. Johnston Stoney.</p> + +<p>Such was the renown of Lord Rosse himself, brought about by his +consummate mechanical genius and his astronomical discoveries, and +such the interest which gathered around the marvellous workshops at +Birr castle, wherein his monumental exhibitions of optical skill were +constructed, that visitors thronged to see him from all parts of the +world. His home at Parsonstown became one of the most remarkable +scientific centres in Great Britain; thither assembled from time to +time all the leading men of science in the country, as well as many +illustrious foreigners. For many years Lord Rosse filled with marked +distinction the exalted position of President of the Royal Society, +and his advice and experience in practical mechanical matters were +always at the disposal of those who sought his assistance. Personally +and socially Lord Rosse endeared himself to all with whom he came in +contact. I remember one of the attendants telling me that on one +occasion he had the misfortune to let fall and break one of the small +mirrors on which Lord Rosse had himself expended many hours of hard +personal labour. The only remark of his lordship was that "accidents +will happen."</p> + +<p>The latter years of his life Lord Rosse passed in comparative +seclusion; he occasionally went to London for a brief sojourn during +the season, and he occasionally went for a cruise in his yacht; but +the greater part of the year he spent at Birr Castle, devoting +himself largely to the study of political and social questions, and +rarely going outside the walls of his demesne, except to church on +Sunday mornings. He died on October 31, 1867.</p> + +<p>He was succeeded by his eldest son, the present Earl of Rosse, who +has inherited his father's scientific abilities, and done much +notable work with the great telescope.</p> + +<h3><a name="AIRY" id="AIRY"></a>AIRY.</h3> +<p>In our sketch of the life of Flamsteed, we have referred to the +circumstances under which the famous Observatory that crowns +Greenwich Hill was founded. We have also had occasion to mention +that among the illustrious successors of Flamsteed both Halley and +Bradley are to be included. But a remarkable development of +Greenwich Observatory from the modest establishment of early days +took place under the direction of the distinguished astronomer whose +name is at the head of this chapter. By his labours this temple of +science was organised to such a degree of perfection that it has +served in many respects as a model for other astronomical +establishments in various parts of the world. An excellent account +of Airy's career has been given by Professor H. H. Turner, in the +obituary notice published by the Royal Astronomical Society. To this +I am indebted for many of the particulars here to be set down +concerning the life of the illustrious Astronomer Royal.</p> + +<p>The family from which Airy took his origin came from Kentmere, in +Westmoreland. His father, William Airy, belonged to a Lincolnshire +branch of the same stock. His mother's maiden name was Ann Biddell, +and her family resided at Playford, near Ipswich. William Airy held +some small government post which necessitated an occasional change of +residence to different parts of the country, and thus it was that his +son, George Biddell, came to be born at Alnwick, on 27th July, 1801. +The boy's education, so far as his school life was concerned was +partly conducted at Hereford and partly at Colchester. He does not, +however, seem to have derived much benefit from the hours which he +passed in the schoolroom. But it was delightful to him to spend his +holidays on the farm at Playford, where his uncle, Arthur Biddell, +showed him much kindness. The scenes of his early youth remained +dear to Airy throughout his life, and in subsequent years he himself +owned a house at Playford, to which it was his special delight to +resort for relaxation during the course of his arduous career. In +spite of the defects of his school training he seems to have +manifested such remarkable abilities that his uncle decided to enter +him in Cambridge University. He accordingly joined Trinity College +as a sizar in 1819, and after a brilliant career in mathematical and +physical science he graduated as Senior Wrangler in 1823. It may be +noted as an exceptional circumstance that, notwithstanding the +demands on his time in studying for his tripos, he was able, after +his second term of residence, to support himself entirely by taking +private pupils. In the year after he had taken his degree he was +elected to a Fellowship at Trinity College.</p> + +<p>Having thus gained an independent position, Airy immediately entered +upon that career of scientific work which he prosecuted without +intermission almost to the very close of his life. One of his most +interesting researches in these early days is on the subject of +Astigmatism, which defect he had discovered in his own eyes. His +investigations led him to suggest a means of correcting this defect +by using a pair of spectacles with lenses so shaped as to counteract +the derangement which the astigmatic eye impressed upon the rays of +light. His researches on this subject were of a very complete +character, and the principles he laid down are to the present day +practically employed by oculists in the treatment of this +malformation.</p> + +<p>On the 7th of December, 1826, Airy was elected to the Lucasian +Professorship of Mathematics in the University of Cambridge, the +chair which Newton's occupancy had rendered so illustrious. His +tenure of this office only lasted for two years, when he exchanged it +for the Plumian Professorship. The attraction which led him to +desire this change is doubtless to be found in the circumstance that +the Plumian Professorship of Astronomy carried with it at that time +the appointment of director of the new astronomical observatory, the +origin of which must now be described.</p> + +<p>Those most interested in the scientific side of University life +decided in 1820 that it would be proper to found an astronomical +observatory at Cambridge. Donations were accordingly sought for this +purpose, and upwards of 6,000 pounds were contributed by members of +the University and the public. To this sum 5,000 pounds were added +by a grant from the University chest, and in 1824 further sums +amounting altogether to 7,115 pounds were given by the University for +the same object. The regulations as to the administration of the new +observatory placed it under the management of the Plumian Professor, +who was to be provided with two assistants. Their duties were to +consist in making meridian observations of the sun, moon, and the +stars, and the observations made each year were to be printed and +published. The observatory was also to be used in the educational +work of the University, for it was arranged that smaller instruments +were to be provided by which students could be instructed in the +practical art of making astronomical observations.</p> + +<p>The building of the Cambridge Astronomical Observatory was completed +in 1824, but in 1828, when Airy entered on the discharge of his +duties as Director, the establishment was still far from completion, +in so far as its organisation was concerned. Airy commenced his work +so energetically that in the next year after his appointment he was +able to publish the first volume of "Cambridge Astronomical +Observations," notwithstanding that every part of the work, from the +making of observations to the revising of the proof-sheets, had to be +done by himself.</p> + +<p>It may here be remarked that these early volumes of the publications +of the Cambridge Observatory contained the first exposition of those +systematic methods of astronomical work which Airy afterwards +developed to such a great extent at Greenwich, and which have been +subsequently adopted in many other places. No more profitable +instruction for the astronomical beginner can be found than that +which can be had by the study of these volumes, in which the Plumian +Professor has laid down with admirable clearness the true principles +on which meridian work should be conducted.</p> + +<p><a name="sir_airy" id="sir_airy"></a></p> + +<div class="figcenter" style="width: 451px;"> +<a href="images/ill_george_airy.jpg"> +<img src="images/ill_george_airy_sml.jpg" width="451" height="517" alt="SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich." title="" /></a> +<span class="caption">SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich.</span> +</div> + +<p>Airy gradually added to the instruments with which the observatory +was originally equipped. A mural circle was mounted in 1832, and in +the same year a small equatorial was erected by Jones. This was made +use of by Airy in a well-known series of observations of Jupiter's +fourth satellite for the determination of the mass of the great +planet. His memoir on this subject fully expounds the method of +finding the weight of a planet from observations of the movements of +a satellite by which the planet is attended. This is, indeed, a +valuable investigation which no student of astronomy can afford to +neglect. The ardour with which Airy devoted himself to astronomical +studies may be gathered from a remarkable report on the progress of +astronomy during the present century, which he communicated to the +British Association at its second meeting in 1832. In the early +years of his life at Cambridge his most famous achievement was +connected with a research in theoretical astronomy for which +consummate mathematical power was required. We can only give a brief +account of the Subject, for to enter into any full detail with regard +to it would be quite out of the question.</p> + +<p>Venus is a planet of about the same size and the same weight as the +earth, revolving in an orbit which lies within that described by our +globe. Venus, consequently, takes less time than the earth to +accomplish one revolution round the sun, and it happens that the +relative movements of Venus and the earth are so proportioned that in +the time in which our earth accomplishes eight of her revolutions the +other planet will have accomplished almost exactly thirteen. It, +therefore, follows that if the earth and Venus are in line with the +sun at one date, then in eight years later both planets will again be +found at the same points in their orbits. In those eight years the +earth has gone round eight times, and has, therefore, regained its +original position, while in the same period Venus has accomplished +thirteen complete revolutions, and, therefore, this planet also has +reached the same spot where it was at first. Venus and the earth, of +course, attract each other, and in consequence of these mutual +attractions the earth is swayed from the elliptic track which it +would otherwise pursue. In like manner Venus is also forced by the +attraction of the earth to revolve in a track which deviates from +that which it would otherwise follow. Owing to the fact that the sun +is of such preponderating magnitude (being, in fact, upwards of +300,000 times as heavy as either Venus or the earth), the +disturbances induced in the motion of either planet, in consequence +of the attraction of the other, are relatively insignificant to the +main controlling agency by which each of the movements is governed. +It is, however, possible under certain circumstances that the +disturbing effects produced upon one planet by the other can become +so multiplied as to produce peculiar effects which attain measurable +dimensions. Suppose that the periodic times in which the earth and +Venus revolved had no simple relation to each other, then the points +of their tracks in which the two planets came into line with the sun +would be found at different parts of the orbits, and consequently the +disturbances would to a great extent neutralise each other, and +produce but little appreciable effect. As, however, Venus and the +earth come back every eight years to nearly the same positions at the +same points of their track, an accumulative effect is produced. For +the disturbance of one planet upon the other will, of course, be +greatest when those two planets are nearest, that is, when they lie +in line with the sun and on the same side of it. Every eight years a +certain part of the orbit of the earth is, therefore, disturbed by +the attraction of Venus with peculiar vigour. The consequence is +that, owing to the numerical relation between the movements of the +planets to which I have referred, disturbing effects become +appreciable which would otherwise be too small to permit of +recognition. Airy proposed to himself to compute the effects which +Venus would have on the movement of the earth in consequence of the +circumstance that eight revolutions of the one planet required almost +the same time as thirteen revolutions of the other. This is a +mathematical inquiry of the most arduous description, but the Plumian +Professor succeeded in working it out, and he had, accordingly, the +gratification of announcing to the Royal Society that he had detected +the influence which Venus was thus able to assert on the movement of +our earth around the sun. This remarkable investigation gained for +its author the gold medal of the Royal Astronomical Society in the +year 1832.</p> + +<p>In consequence of his numerous discoveries, Airy's scientific fame +had become so well recognised that the Government awarded him a +special pension, and in 1835, when Pond, who was then Astronomer +Royal, resigned, Airy was offered the post at Greenwich. There was +in truth, no scientific inducement to the Plumian Professor to leave +the comparatively easy post he held at Cambridge, in which he had +ample leisure to devote himself to those researches which specially +interested him, and accept that of the much more arduous observatory +at Greenwich. There were not even pecuniary inducements to make the +change; however, he felt it to be his duty to accede to the request +which the Government had made that he would take up the position +which Pond had vacated, and accordingly Airy went to Greenwich as +Astronomer Royal on October 1st, 1835.</p> + +<p>He immediately began with his usual energy to organise the systematic +conduct of the business of the National Observatory. To realise one +of the main characteristics of Airy's great work at Greenwich, it is +necessary to explain a point that might not perhaps be understood +without a little explanation by those who have no practical +experience in an observatory. In the work of an establishment such +as Greenwich, an observation almost always consists of a measurement +of some kind. The observer may, for instance, be making a +measurement of the time at which a star passes across a spider line +stretched through the field of view; on another occasion his object +may be the measurement of an angle which is read off by examining +through a microscope the lines of division on a graduated circle when +the telescope is so pointed that the star is placed on a certain mark +in the field of view. In either case the immediate result of the +astronomical observation is a purely numerical one, but it rarely +happens, indeed we may say it never happens, that the immediate +numerical result which the observation gives expresses directly the +quantity which we are really seeking for. No doubt the observation +has been so designed that the quantity we want to find can be +obtained from the figures which the measurement gives, but the object +sought is not those figures, for there are always a multitude of +other influences by which those figures are affected. For example, +if an observation were to be perfect, then the telescope with which +the observation is made should be perfectly placed in the exact +position which it ought to occupy; this is, however, never the case, +for no mechanic can ever construct or adjust a telescope so perfectly +as the wants of the astronomer demand. The clock also by which we +determine the time of the observation should be correct, but this is +rarely if ever the case. We have to correct our observations for +such errors, that is to say, we have to determine the errors in the +positions of our telescopes and the errors in the going of our +clocks, and then we have to determine what the observations would +have been had our telescopes been absolutely perfect, and had our +clocks been absolutely correct. There are also many other matters +which have to be attended to in order to reduce our observations so +as to obtain from the figures as yielded to the observer at the +telescope the actual quantities which it is his object to determine.</p> + +<p>The work of effecting these reductions is generally a very intricate +and laborious matter, so that it has not unfrequently happened that +while observations have accumulated in an observatory, yet the +tedious duty of reducing these observations has been allowed to fall +into arrear. When Airy entered on his duties at Greenwich he found +there an enormous mass of observations which, though implicitly +containing materials of the greatest value to astronomers, were, in +their unreduced form, entirely unavailable for any useful purpose. +He, therefore, devoted himself to coping with the reduction of the +observations of his predecessors. He framed systematic methods by +which the reductions were to be effected, and he so arranged the work +that little more than careful attention to numerical accuracy would +be required for the conduct of the operations. Encouraged by the +Admiralty, for it is under this department that Greenwich Observatory +is placed, the Astronomer Royal employed a large force of computers +to deal with the work. BY his energy and admirable organisation he +managed to reduce an extremely valuable series of planetary +observations, and to publish the results, which have been of the +greatest importance to astronomical investigation.</p> + +<p>The Astronomer Royal was a capable, practical engineer as well as an +optician, and he presently occupied himself by designing astronomical +instruments of improved pattern, which should replace the antiquated +instruments he found in the observatory. In the course of years the +entire equipment underwent a total transformation. He ordered a +great meridian circle, every part of which may be said to have been +formed from his own designs. He also designed the mounting for a +fine equatorial telescope worked by a driving clock, which he had +himself invented. Gradually the establishment at Greenwich waxed +great under his incessant care. It was the custom for the +observatory to be inspected every year by a board of visitors, whose +chairman was the President of the Royal Society. At each annual +visitation, held on the first Saturday in June, the visitors received +a report from the Astronomer Royal, in which he set forth the +business which had been accomplished during the past year. It was on +these occasions that applications were made to the Admiralty, either +for new instruments or for developing the work of the observatory in +some other way. After the more official business of the inspection +was over, the observatory was thrown open to visitors, and hundreds +of people enjoyed on that day the privilege of seeing the national +observatory. These annual gatherings are happily still continued, +and the first Saturday in June is known to be the occasion of one of +the most interesting reunions of scientific men which takes place in +the course of the year.</p> + +<p>Airy's scientific work was, however, by no means confined to the +observatory. He interested himself largely in expeditions for the +observation of eclipses and in projects for the measurement of arcs +on the earth. He devoted much attention to the collection of magnetic +observations from various parts of the world. Especially will it be +remembered that the circumstances of the transits of Venus, which +occurred in 1874 and in 1882, were investigated by him, and under his +guidance expeditions were sent forth to observe the transits from +those localities in remote parts of the earth where observations most +suitable for the determination of the sun's distance from the earth +could be obtained. The Astronomer Royal also studied tidal +phenomena, and he rendered great service to the country in the +restoration of the standards of length and weight which had been +destroyed in the great fire at the House of Parliament in October, +1834. In the most practical scientific matters his advice was often +sought, and was as cheerfully rendered. Now we find him engaged in +an investigation of the irregularities of the compass in iron ships, +with a view to remedying its defects; now we find him reporting on +the best gauge for railways. Among the most generally useful +developments of the observatory must be mentioned the telegraphic +method for the distribution of exact time. By arrangement with the +Post Office, the astronomers at Greenwich despatch each morning a +signal from the observatory to London at ten o'clock precisely. By +special apparatus, this signal is thence distributed automatically +over the country, so as to enable the time to be known everywhere +accurately to a single second. It was part of the same system that a +time ball should be dropped daily at one o'clock at Deal, as well as +at other places, for the purpose of enabling ship's chronometers to +be regulated.</p> + +<p>Airy's writings were most voluminous, and no fewer than forty-eight +memoirs by him are mentioned in the "Catalogue of Scientific +Memoirs," published by the Royal Society up to the year 1873, and +this only included ten years out of an entire life of most +extraordinary activity. Many other subjects besides those of a +purely scientific character from time to time engaged his attention. +He wrote, for instance, a very interesting treatise on the Roman +invasion of Britain, especially with a view of determining the port +from which Caesar set forth from Gaul, and the point at which he +landed on the British coast. Airy was doubtless led to this +investigation by his study of the tidal phenomena in the Straits of +Dover. Perhaps the Astronomer Royal is best known to the general +reading public by his excellent lectures on astronomy, delivered at +the Ipswich Museum in 1848. This book has passed through many +editions, and it gives a most admirable account of the manner in +which the fundamental problems in astronomy have to be attacked.</p> + +<p>As years rolled by almost every honour and distinction that could be +conferred upon a scientific man was awarded to Sir George Airy. He +was, indeed, the recipient of other honours not often awarded for +scientific distinction. Among these we may mention that in 1875 he +received the freedom of the City of London, "as a recognition of his +indefatigable labours in astronomy, and of his eminent services in +the advancement of practical science, whereby he has so materially +benefited the cause of commerce and civilisation."</p> + +<p>Until his eightieth year Airy continued to discharge his labours at +Greenwich with unflagging energy. At last, on August 15th, 1881, he +resigned the office which he had held so long with such distinction +to himself and such benefit to his country. He had married in 1830 +the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died +in 1875, and three sons and three daughters survived him. One +daughter is the wife of Dr. Routh, of Cambridge, and his other +daughters were the constant companions of their father during the +declining years of his life. Up to the age of ninety he enjoyed +perfect physical health, but an accidental fall which then occurred +was attended with serious results. He died on Saturday, January 2nd, +1892, and was buried in the churchyard at Playford.</p> + +<h3><a name="HAMILTON" id="HAMILTON"></a>HAMILTON.</h3> +<p>William Rowan Hamilton was born at midnight between the 3rd and 4th +of August, 1805, at Dublin, in the house which was then 29, but +subsequently 36, Dominick Street. His father, Archibald Hamilton, +was a solicitor, and William was the fourth of a family of nine. With +reference to his descent, it may be sufficient to notice that his +ancestors appear to have been chiefly of gentle Irish families, but +that his maternal grandmother was of Scottish birth. When he was +about a year old, his father and mother decided to hand over the +education of the child to his uncle, James Hamilton, a clergyman of +Trim, in County Meath. James Hamilton's sister, Sydney, resided with +him, and it was in their home that the days of William's childhood +were passed.</p> + +<p>In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of +letters will be found, in which Aunt Sydney details the progress of +the boy to his mother in Dublin. Probably there is no record of an +infant prodigy more extraordinary than that which these letters +contain. At three years old his aunt assured the mother that William +is "a hopeful blade," but at that time it was his physical vigour to +which she apparently referred; for the proofs of his capacity, which +she adduces, related to his prowess in making boys older than himself +fly before him. In the second letter, a month later, we hear that +William is brought in to read the Bible for the purpose of putting to +shame other boys double his age who could not read nearly so well. +Uncle James appears to have taken much pains with William's +schooling, but his aunt said that "how he picks up everything is +astonishing, for he never stops playing and jumping about." When he +was four years and three months old, we hear that he went out to dine +at the vicar's, and amused the company by reading for them equally +well whether the book was turned upside down or held in any other +fashion. His aunt assures the mother that "Willie is a most sensible +little creature, but at the same time has a great deal of roguery." +At four years and five months old he came up to pay his mother a +visit in town, and she writes to her sister a description of the +boy;—</p> + +<p>"His reciting is astonishing, and his clear and accurate knowledge of +geography is beyond belief; he even draws the countries with a pencil +on paper, and will cut them out, though not perfectly accurate, yet +so well that a anybody knowing the countries could not mistake them; +but, you will think this nothing when I tell you that he reads Latin, +Greek, and Hebrew."</p> + +<p>Aunt Sydney recorded that the moment Willie got back to Trim he was +desirous of at once resuming his former pursuits. He would not eat +his breakfast till his uncle had heard him his Hebrew, and he +comments on the importance of proper pronunciation. At five he was +taken to see a friend, to whom he repeated long passages from +Dryden. A gentleman present, who was not unnaturally sceptical about +Willie's attainments, desired to test him in Greek, and took down a +copy of Homer which happened to have the contracted type, and to his +amazement Willie went on with the greatest ease. At six years and +nine months he was translating Homer and Virgil; a year later his +uncle tells us that William finds so little difficulty in learning +French and Italian, that he wishes to read Homer in French. He is +enraptured with the Iliad, and carries it about with him, repeating +from it whatever particularly pleases him. At eight years and one +month the boy was one of a party who visited the Scalp in the Dublin +mountains, and he was so delighted with the scenery that he forthwith +delivered an oration in Latin. At nine years and six months he is +not satisfied until he learns Sanscrit; three months later his thirst +for the Oriental languages is unabated, and at ten years and four +months he is studying Arabic and Persian. When nearly twelve he +prepared a manuscript ready for publication. It was a "Syriac +Grammar," in Syriac letters and characters compiled from that of +Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was +fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a +visit to Dublin, and, as a practical exercise in his Oriental +languages, the young scholar addressed to his Excellency a letter in +Persian; a translation of which production is given by Mr. Graves. +When William was fourteen he had the misfortune to lose his father; +and he had lost his mother two years previously. The boy and his +three sisters were kindly provided for by different members of the +family on both sides.</p> + +<p>It was when William was about fifteen that his attention began to be +turned towards scientific subjects. These were at first regarded +rather as a relaxation from the linguistic studies with which he had +been so largely occupied. On November 22nd, 1820, he notes in his +journal that he had begun Newton's "Principia": he commenced also the +study of astronomy by observing eclipses, occultations, and similar +phenomena. When he was sixteen we learn that he had read conic +sections, and that he was engaged in the study of pendulums. After +an attack of illness, he was moved for change to Dublin, and in May, +1822, we find him reading the differential calculus and Laplace's +"Mecanique Celeste." He criticises an important part of Laplace's +work relative to the demonstration of the parallelogram of forces. In +this same year appeared the first gushes of those poems which +afterwards flowed in torrents.</p> + +<p>His somewhat discursive studies had, however, now to give place to a +more definite course of reading in preparation for entrance to the +University of Dublin. The tutor under whom he entered, Charles +Boyton, was himself a distinguished man, but he frankly told the +young William that he could be of little use to him as a tutor, for +his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom +this is recorded, adds, "But there is one thing which Boyton would +promise to be to him, and that was a FRIEND; and that one proof he +would give of this should be that, if ever he saw William beginning +to be UPSET by the sensation he would excite, and the notice he would +attract, he would tell him of it." At the beginning of his college +career he distanced all his competitors in every intellectual +pursuit. At his first term examination in the University he was +first in Classics and first in Mathematics, while he received the +Chancellor's prize for a poem on the Ionian Islands, and another for +his poem on Eustace de St. Pierre.</p> + +<p>There is abundant testimony that Hamilton had "a heart for friendship +formed." Among the warmest of the friends whom he made in these +early days was the gifted Maria Edgeworth, who writes to her sister +about "young Mr. Hamilton, an admirable Crichton of eighteen, a real +prodigy of talents, who Dr. Brinkley says may be a second Newton, +quiet, gentle, and simple." His sister Eliza, to whom he was +affectionately attached, writes to him in 1824:—</p> + +<p>"I had been drawing pictures of you in my mind in your study at +Cumberland Street with 'Xenophon,' &c., on the table, and you, with +your most awfully sublime face of thought, now sitting down, and now +walking about, at times rubbing your hands with an air of +satisfaction, and at times bursting forth into some very heroical +strain of poetry in an unknown language, and in your own internal +solemn ventriloquist-like voice, when you address yourself to the +silence and solitude of your own room, and indeed, at times, even +when your mysterious poetical addresses are not quite unheard."</p> + +<p>This letter is quoted because it refers to a circumstance which all +who ever met with Hamilton, even in his latest years, will remember. +He was endowed with two distinct voices, one a high treble, the other +a deep bass, and he alternately employed these voices not only in +ordinary conversation, but when he was delivering an address on the +profundities of Quaternions to the Royal Irish Academy, or on +similar occasions. His friends had long grown so familiar with this +peculiarity that they were sometimes rather surprised to find how +ludicrous it appeared to strangers.</p> + +<p>Hamilton was fortunate in finding, while still at a very early age, a +career open before him which was worthy of his talents. He had not +ceased to be an undergraduate before he was called to fill an +illustrious chair in his university. The circumstances are briefly +as follows.</p> + +<p>We have already mentioned that, in 1826, Brinkley was appointed +Bishop of Cloyne, and the professorship of astronomy thereupon became +vacant. Such was Hamilton's conspicuous eminence that, +notwithstanding he was still an undergraduate, and had only just +completed his twenty-first year, he was immediately thought of as a +suitable successor to the chair. Indeed, so remarkable were his +talents in almost every direction that had the vacancy been in the +professorship of classics or of mathematics, of English literature or +of metaphysics, of modern or of Oriental languages, it seems +difficult to suppose that he would not have occurred to every one as +a possible successor. The chief ground, however, on which the +friends of Hamilton urged his appointment was the earnest of original +power which he had already shown in a research on the theory of +Systems of Rays. This profound work created a new branch of optics, +and led a few years later to a superb discovery, by which the fame of +its author became world-wide.</p> + +<p>At first Hamilton thought it would be presumption for him to apply +for so exalted a position; he accordingly retired to the country, and +resumed his studies for his degree. Other eminent candidates came +forward, among them some from Cambridge, and a few of the Fellows +from Trinity College, Dublin, also sent in their claims. It was not +until Hamilton received an urgent letter from his tutor Boyton, in +which he was assured of the favourable disposition of the Board +towards his candidature, that he consented to come forward, and on +June 16th, 1827, he was unanimously chosen to succeed the Bishop of +Cloyne as Professor of Astronomy in the University. The appointment +met with almost universal approval. It should, however, be noted +that Brinkley, whom Hamilton succeeded, did not concur in the general +sentiment. No one could have formed a higher opinion than he had +done of Hamilton's transcendent powers; indeed, it was on that very +ground that he seemed to view the appointment with disapprobation. +He considered that it would have been wiser for Hamilton to have +obtained a Fellowship, in which capacity he would have been able to +exercise a greater freedom in his choice of intellectual pursuits. +The bishop seems to have thought, and not without reason, that +Hamilton's genius would rather recoil from much of the routine work +of an astronomical establishment. Now that Hamilton's whole life is +before us, it is easy to see that the bishop was entirely wrong. It +is quite true that Hamilton never became a skilled astronomical +observer; but the seclusion of the observatory was eminently +favourable to those gigantic labours to which his life was devoted, +and which have shed so much lustre, not only on Hamilton himself, but +also on his University and his country.</p> + +<p>In his early years at Dunsink, Hamilton did make some attempts at a +practical use of the telescopes, but he possessed no natural aptitude +for such work, while exposure which it involved seems to have acted +injuriously on his health. He, therefore, gradually allowed his +attention to be devoted to those mathematical researches in which he +had already given such promise of distinction. Although it was in +pure mathematics that he ultimately won his greatest fame, yet he +always maintained and maintained with justice, that he had ample +claims to the title of an astronomer. In his later years he set +forth this position himself in a rather striking manner. De Morgan +had written commending to Hamilton's notice Grant's "History of +Physical Astronomy." After becoming acquainted with the book, +Hamilton writes to his friend as follows:—</p> + +<p>"The book is very valuable, and very creditable to its composer. But +your humble servant may be pardoned if he finds himself somewhat +amused at the title, 'History of Physical Astronomy from the Earliest +Ages to the Middle of the Nineteenth Century,' when he fails to +observe any notice of the discoveries of Sir W. R. Hamilton in the +theory of the 'Dynamics of the Heavens.'"</p> + +<p>The intimacy between the two correspondents will account for the tone +of this letter; and, indeed, Hamilton supplies in the lines which +follow ample grounds for his complaint. He tells how Jacobi spoke of +him in Manchester in 1842 as "le Lagrange de votre pays," and how +Donkin had said that, "The Analytical Theory of Dynamics as it exists +at present is due mainly to the labours of La Grange Poisson, +Sir W. R. Hamilton, and Jacobi, whose researches on this subject +present a series of discoveries hardly paralleled for their elegance +and importance in any other branch of mathematics." In the same +letter Hamilton also alludes to the success which had attended the +applications of his methods in other hands than his own to the +elucidation of the difficult subject of Planetary Perturbations. +Even had his contributions to science amounted to no more than these +discoveries, his tenure of the chair would have been an illustrious +one. It happens, however, that in the gigantic mass of his +intellectual work these researches, though intrinsically of such +importance, assume what might almost be described as a relative +insignificance.</p> + +<p>The most famous achievement of Hamilton's earlier years at the +observatory was the discovery of conical refraction. This was one of +those rare events in the history of science, in which a sagacious +calculation has predicted a result of an almost startling character, +subsequently confirmed by observation. At once this conferred on the +young professor a world-wide renown. Indeed, though he was still +only twenty-seven, he had already lived through an amount of +intellectual activity which would have been remarkable for a man of +threescore and ten.</p> + +<p>Simultaneously with his growth in fame came the growth of his several +friendships. There were, in the first place, his scientific +friendships with Herschel, Robinson, and many others with whom he had +copious correspondence. In the excellent biography to which I have +referred, Hamilton's correspondence with Coleridge may be read, as +can also the letters to his lady correspondents, among them being +Maria Edgeworth, Lady Dunraven, and Lady Campbell. Many of these +sheets relate to literary matters, but they are largely intermingled +With genial pleasantry, and serve at all events to show the affection +and esteem with which he was regarded by all who had the privilege of +knowing him. There are also the letters to the sisters whom he +adored, letters brimming over with such exalted sentiment, that most +ordinary sisters would be tempted to receive them with a smile in the +excessively improbable event of their still more ordinary brothers +attempting to pen such effusions. There are also indications of +letters to and from other young ladies who from time to time were the +objects of Hamilton's tender admiration. We use the plural +advisedly, for, as Mr. Graves has set forth, Hamilton's love affairs +pursued a rather troubled course. The attention which he lavished on +one or two fair ones was not reciprocated, and even the intense +charms of mathematical discovery could not assuage the pangs which +the disappointed lover experienced. At last he reached the haven of +matrimony in 1833, when he was married to Miss Bayly. Of his married +life Hamilton said, many years later to De Morgan, that it was as +happy as he expected, and happier than he deserved. He had two sons, +William and Archibald, and one daughter, Helen, who became the wife +of Archdeacon O'Regan.</p> + +<p><a name="rowan_hamilton" id="rowan_hamilton"></a></p> + +<div class="figcenter" style="width: 418px;"> +<a href="images/ill_rowan_hamilton.jpg"> +<img src="images/ill_rowan_hamilton_sml.jpg" width="418" height="479" alt="SIR W. ROWAN HAMILTON." title="" /></a> +<span class="caption">SIR W. ROWAN HAMILTON.</span> +</div> + +<p>The most remarkable of Hamilton's friendships in his early years was +unquestionably that with Wordsworth. It commenced with Hamilton's +visit to Keswick; and on the first evening, when the poet met the +young mathematician, an incident occurred which showed the mutual +interest that was aroused. Hamilton thus describes it in a letter to +his sister Eliza:—</p> + +<p>"He (Wordsworth) walked back with our party as far as their lodge, +and then, on our bidding Mrs. Harrison good-night, I offered to walk +back with him while my party proceeded to the hotel. This offer he +accepted, and our conversation had become so interesting that when we +had arrived at his home, a distance of about a mile, he proposed to +walk back with me on my way to Ambleside, a proposal which you may be +sure I did not reject; so far from it that when he came to turn once +more towards his home I also turned once more along with him. It was +very late when I reached the hotel after all this walking."</p> + +<p>Hamilton also submitted to Wordsworth an original poem, entitled +"It Haunts me Yet." The reply of Wordsworth is worth repeating:—</p> + +<p>"With a safe conscience I can assure you that, in my judgment, your +verses are animated with the poetic spirit, as they are evidently the +product of strong feeling. The sixth and seventh stanzas affected me +much, even to the dimming of my eyes and faltering of my voice while +I was reading them aloud. Having said this, I have said enough. Now +for the per contra. You will not, I am sure, be hurt when I tell you +that the workmanship (what else could be expected from so young a +writer?) is not what it ought to be. . .</p> + +<p>"My household desire to be remembered to you in no formal way. +Seldom have I parted—never, I was going to say—with one whom after +so short an acquaintance I lost sight of with more regret. I trust +we shall meet again."</p> + +<p>The further affectionate intercourse between Hamilton and Wordsworth +is fully set forth, and to Hamilton's latest years a recollection of +his "Rydal hours" was carefully treasured and frequently referred +to. Wordsworth visited Hamilton at the observatory, where a +beautiful shady path in the garden is to the present day spoken of as +"Wordsworth's Walk."</p> + +<p>It was the practice of Hamilton to produce a sonnet on almost every +occasion which admitted of poetical treatment, and it was his delight +to communicate his verses to his friends all round. When Whewell was +producing his "Bridgewater Treatises," he writes to Hamilton in +1833:—</p> + +<p>"Your sonnet which you showed me expressed much better than I could +express it the feeling with which I tried to write this book, and I +once intended to ask your permission to prefix the sonnet to my book, +but my friends persuaded me that I ought to tell my story in my own +prose, however much better your verse might be."</p> + +<p>The first epoch-marking contribution to Theoretical Dynamics after +the time of Newton was undoubtedly made by Lagrange, in his discovery +of the general equations of Motion. The next great step in the same +direction was that taken by Hamilton in his discovery of a still more +comprehensive method. Of this contribution Hamilton writes to +Whewell, March 31st, 1834:—</p> + +<p>"As to my late paper, a day or two ago sent off to London, it is +merely mathematical and deductive. I ventured, indeed, to call it +the 'Mecanique Analytique' of Lagrange, 'a scientific poem'; and +spoke of Dynamics, or the Science of Force, as treating of 'Power +acting by Law in Space and Time.' In other respects it is as +unpoetical and unmetaphysical as my gravest friends could desire."</p> + +<p>It may well be doubted whether there is a more beautiful chapter in +the whole of mathematical philosophy than that which contains +Hamilton's dynamical theory. It is disfigured by no tedious +complexity of symbols; it condescends not to any particular problems; +it is an all embracing theory, which gives an intellectual grasp of +the most appropriate method for discovering the result of the +application of force to matter. It is the very generality of this +doctrine which has somewhat impeded the applications of which it is +susceptible. The exigencies of examinations are partly responsible +for the fact that the method has not become more familiar to students +of the higher mathematics. An eminent professor has complained that +Hamilton's essay on dynamics was of such an extremely abstract +character, that he found himself unable to extract from it problems +suitable for his examination papers.</p> + +<p>The following extract is from a letter of Professor Sylvester to +Hamilton, dated 20th of September, 1841. It will show how his works +were appreciated by so consummate a mathematician as the writer:—</p> + +<p>"Believe me, sir, it is not the least of my regrets in quitting this +empire to feel that I forego the casual occasion of meeting those +masters of my art, yourself chief amongst the number, whose +acquaintance, whose conversation, or even notice, have in themselves +the power to inspire, and almost to impart fresh vigour to the +understanding, and the courage and faith without which the efforts of +invention are in vain. The golden moments I enjoyed under your +hospitable roof at Dunsink, or moments such as they were, may +probably never again fall to my lot.</p> + +<p>"At a vast distance, and in an humble eminence, I still promise myself +the calm satisfaction of observing your blazing course in the +elevated regions of discovery. Such national honour as you are able +to confer on your country is, perhaps, the only species of that +luxury for the rich (I mean what is termed one's glory) which is not +bought at the expense of the comforts of the million."</p> + +<p>The study of metaphysics was always a favourite recreation when +Hamilton sought for a change from the pursuit of mathematics. In the +year 1834 we find him a diligent student of Kant; and, to show the +views of the author of Quaternions and of Algebra as the Science of +Pure Time on the "Critique of the Pure Reason," we quote the +following letter, dated 18th of July, 1834, from Hamilton to Viscount +Adare:—</p> + +<p>"I have read a large part of the 'Critique of the Pure Reason,' and +find it wonderfully clear, and generally quite convincing. +Notwithstanding some previous preparation from Berkeley, and from my +own thoughts, I seem to have learned much from Kant's own statement +of his views of 'Space and Time.' Yet, on the whole, a large part of +my pleasure consists in recognising through Kant's works, opinions, +or rather views, which have been long familiar to myself, although +far more clearly and systematically expressed and combined by him. +. . . Kant is, I think, much more indebted than he owns, or, perhaps +knows, to Berkeley, whom he calls by a sneer, 'GUTEM Berkeley'. . . +as it were, 'good soul, well meaning man,' who was able for all that +to shake to its centre the world of human thought, and to effect a +revolution among the early consequences of which was the growth of +Kant himself."</p> + +<p>At several meetings of the British Association Hamilton was a very +conspicuous figure. Especially was this the case in 1835, when the +Association met in Dublin, and when Hamilton, though then but thirty +years old, had attained such celebrity that even among a very +brilliant gathering his name was perhaps the most renowned. A +banquet was given at Trinity College in honour of the meeting. The +distinguished visitors assembled in the Library of the University. +The Earl of Mulgrave, then Lord Lieutenant of Ireland, made this the +opportunity of conferring on Hamilton the honour of knighthood, +gracefully adding, as he did so: "I but set the royal, and therefore +the national mark, on a distinction already acquired by your genius +and labours."</p> + +<p>The banquet followed, writes Mr. Graves. "It was no little addition +to the honour Hamilton had already received that, when Professor +Whewell returned thanks for the toast of the University of Cambridge, +he thought it appropriate to add the words, 'There was one point +which strongly pressed upon him at that moment: it was now one +hundred and thirty years since a great man in another Trinity College +knelt down before his sovereign, and rose up Sir Isaac Newton.' The +compliment was welcomed by immense applause."</p> + +<p>A more substantial recognition of the labours of Hamilton took place +subsequently. He thus describes it in a letter to Mr. Graves of 14th +of November, 1843:—</p> + +<p>"The Queen has been pleased—and you will not doubt that it was +entirely unsolicited, and even unexpected, on my part—'to express +her entire approbation of the grant of a pension of two hundred +pounds per annum from the Civil List' to me for scientific services. +The letters from Sir Robert Peel and from the Lord Lieutenant of +Ireland in which this grant has been communicated or referred to have +been really more gratifying to my feelings than the addition to my +income, however useful, and almost necessary, that may have been."</p> + +<p>The circumstances we have mentioned might lead to the supposition +that Hamilton was then at the zenith of his fame but this was not +so. It might more truly be said, that his achievements up to this +point were rather the preliminary exercises which fitted him for the +gigantic task of his life. The name of Hamilton is now chiefly +associated with his memorable invention of the calculus of +Quaternions. It was to the creation of this branch of mathematics +that the maturer powers of his life were devoted; in fact he gives us +himself an illustration of how completely habituated he became to the +new modes of thought which Quaternions originated. In one of his +later years he happened to take up a copy of his famous paper on +Dynamics, a paper which at the time created such a sensation among +mathematicians, and which is at this moment regarded as one of the +classics of dynamical literature. He read, he tells us, his paper +with considerable interest, and expressed his feelings of +gratification that he found himself still able to follow its +reasoning without undue effort. But it seemed to him all the time as +a work belonging to an age of analysis now entirely superseded.</p> + +<p>In order to realise the magnitude of the revolution which Hamilton +has wrought in the application of symbols to mathematical +investigation, it is necessary to think of what Hamilton did beside +the mighty advance made by Descartes. To describe the character of +the quaternion calculus would be unsuited to the pages of this work, +but we may quote an interesting letter, written by Hamilton from his +death-bed, twenty-two years later, to his son Archibald, in which he +has recorded the circumstances of the discovery:—</p> + +<p>"Indeed, I happen to be able to put the finger of memory upon the year +and month—October, 1843—when having recently returned from visits +to Cork and Parsonstown, connected with a meeting of the British +Association, the desire to discover the laws of multiplication +referred to, regained with me a certain strength and earnestness +which had for years been dormant, but was then on the point of being +gratified, and was occasionally talked of with you. Every morning in +the early part of the above-cited month, on my coming down to +breakfast, your (then) little brother William Edwin, and yourself, +used to ask me, 'Well papa, can you multiply triplets?' Whereto I +was always obliged to reply, with a sad shake of the head: 'No, I +can only ADD and subtract them,'</p> + +<p>"But on the 16th day of the same month—which happened to be Monday, +and a Council day of the Royal Irish Academy—I was walking in to +attend and preside, and your mother was walking with me along the +Royal Canal, to which she had perhaps driven; and although she talked +with me now and then, yet an UNDERCURRENT of thought was going on in +my mind which gave at last a RESULT, whereof it is not too much to +say that I felt AT ONCE the importance. An ELECTRIC circuit seemed +to CLOSE; and a spark flashed forth the herald (as I FORESAW +IMMEDIATELY) of many long years to come of definitely directed +thought and work by MYSELF, if spared, and, at all events, on the +part of OTHERS if I should even be allowed to live long enough +distinctly to communicate the discovery. Nor could I resist the +impulse—unphilosophical as it may have been—to cut with a knife on +a stone of Brougham Bridge as we passed it, the fundamental formula +which contains the SOLUTION of the PROBLEM, but, of course, the +inscription has long since mouldered away. A more durable notice +remains, however, on the Council Books of the Academy for that day +(October 16, 1843), which records the fact that I then asked for and +obtained leave to read a Paper on 'Quaternions,' at the First General +Meeting of the Session; which reading took place accordingly, on +Monday, the 13th of November following."</p> + +<p>Writing to Professor Tait, Hamilton gives further particulars of the +same event. And again in a letter to the Rev. J. W. Stubbs:—</p> + +<p>"To-morrow will be the fifteenth birthday of the Quaternions. They +started into life full-grown on the 16th October, 1843, as I was +walking with Lady Hamilton to Dublin, and came up to Brougham +Bridge—which my boys have since called Quaternion Bridge. I pulled +out a pocketbook which still exists, and made entry, on which at the +very moment I felt that it might be worth my while to expend the +labour of at least ten or fifteen years to come. But then it is fair +to say that this was because I felt a problem to have been at that +moment solved, an intellectual want relieved which had haunted me for +at least fifteen years before.</p> + +<p>"But did the thought of establishing such a system, in which +geometrically opposite facts—namely, two lines (or areas) which are +opposite IN SPACE give ALWAYS a positive product—ever come into +anybody's head till I was led to it in October, 1843, by trying to +extend my old theory of algebraic couples, and of algebra as the +science of pure time? As to my regarding geometrical addition of +lines as equivalent to composition of motions (and as performed by +the same rules), that is indeed essential in my theory but not +peculiar to it; on the contrary, I am only one of many who have been +led to this view of addition."</p> + +<p>Pilgrims in future ages will doubtless visit the spot commemorated by +the invention of Quaternions. Perhaps as they look at that by no +means graceful structure Quaternion Bridge, they will regret that the +hand of some Old Mortality had not been occasionally employed in +cutting the memorable inscription afresh. It is now irrecoverably +lost.</p> + +<p>It was ten years after the discovery that the great volume appeared +under the title of "Lectures on Quaternions," Dublin, 1853. The +reception of this work by the scientific world was such as might have +been expected from the extraordinary reputation of its author, and +the novelty and importance of the new calculus. His valued friend, +Sir John Herschel, writes to him in that style of which he was a +master:—</p> + +<p>"Now, most heartily let me congratulate you on getting out your +book—on having found utterance, ore rotundo, for all that labouring +and seething mass of thought which has been from time to time sending +out sparks, and gleams, and smokes, and shaking the soil about you; +but now breaks into a good honest eruption, with a lava stream and a +shower of fertilizing ashes.</p> + +<p>"Metaphor and simile apart, there is work for a twelve-month to any +man to read such a book, and for half a lifetime to digest it, and I +am glad to see it brought to a conclusion."</p> + +<p>We may also record Hamilton's own opinion expressed to Humphrey +Lloyd:—</p> + +<p>"In general, although in one sense I hope that I am actually growing +modest about the quaternions, from my seeing so many peeps and vistas +into future expansions of their principles, I still must assert that +this discovery appears to me to be as important for the middle of the +nineteenth century as the discovery of fluxions was for the close of +the seventeenth."</p> + +<p>Bartholomew Lloyd died in 1837. He had been the Provost of Trinity +College, and the President of the Royal Irish Academy. Three +candidates were put forward by their respective friends for the +vacant Presidency. One was Humphrey Lloyd, the son of the late +Provost, and the two others were Hamilton and Archbishop Whately. +Lloyd from the first urged strongly the claims of Hamilton, and +deprecated the putting forward of his own name. Hamilton in like +manner desired to withdraw in favour of Lloyd. The wish was strongly +felt by many of the Fellows of the College that Lloyd should be +elected, in consequence of his having a more intimate association +with collegiate life than Hamilton; while his scientific eminence was +world-wide. The election ultimately gave Hamilton a considerable +majority over Lloyd, behind whom the Archbishop followed at a +considerable distance. All concluded happily, for both Lloyd and the +Archbishop expressed, and no doubt felt, the pre-eminent claims of +Hamilton, and both of them cordially accepted the office of a +Vice-President, to which, according to the constitution of the +Academy, it is the privilege of the incoming President to nominate.</p> + +<p>In another chapter I have mentioned as a memorable episode in +astronomical history, that Sir J. Herschel went for a prolonged +sojourn to the Cape of Good Hope, for the purpose of submitting the +southern skies to the same scrutiny with the great telescope that his +father had given to the northern skies. The occasion of Herschel's +return after the brilliant success of his enterprise, was celebrated +by a banquet. On June 15th, 1838, Hamilton was assigned the high +honour of proposing the health of Herschel. This banquet is +otherwise memorable in Hamilton's career as being one of the two +occasions in which he was in the company of his intimate friend De +Morgan.</p> + +<p>In the year 1838 a scheme was adopted by the Royal Irish Academy for +the award of medals to the authors of papers which appeared to +possess exceptionally high merit. At the institution of the medal +two papers were named in competition for the prize. One was +Hamilton's "Memoir on Algebra, as the Science of Pure Time." The +other was Macullagh's paper on the "Laws of Crystalline Reflection +and Refraction." Hamilton expresses his gratification that, mainly +in consequence of his own exertions, he succeeded in having the medal +awarded to Macullagh rather than to himself. Indeed, it would almost +appear as if Hamilton had procured a letter from Sir J. Herschel, +which indicated the importance of Macullagh's memoir in such a way as +to decide the issue. It then became Hamilton's duty to award the +medal from the chair, and to deliver an address in which he expressed +his own sense of the excellence of Macullagh's scientific work. It +is the more necessary to allude to these points, because in the whole +of his scientific career it would seem that Macullagh was the only +man with whom Hamilton had ever even an approach to a dispute about +priority. The incident referred to took place in connection with the +discovery of conical refraction, the fame of which Macullagh made a +preposterous attempt to wrest from Hamilton. This is evidently +alluded to in Hamilton's letter to the Marquis of Northampton, dated +June 28th, 1838, in which we read:—</p> + +<p>"And though some former circumstances prevented me from applying to +the person thus distinguished the sacred name of FRIEND, I had the +pleasure of doing justice...to his high intellectual merits... I +believe he was not only gratified but touched, and may, perhaps, +regard me in future with feelings more like those which I long to +entertain towards him."</p> + +<p>Hamilton was in the habit, from time to time, of commencing the +keeping of a journal, but it does not appear to have been +systematically conducted. Whatever difficulties the biographer may +have experienced from its imperfections and irregularities, seem to +be amply compensated for by the practice which Hamilton had of +preserving copies of his letters, and even of comparatively +insignificant memoranda. In fact, the minuteness with which +apparently trivial matters were often noted down appears almost +whimsical. He frequently made a memorandum of the name of the person +who carried a letter to the post, and of the hour in which it was +despatched. On the other hand, the letters which he received were +also carefully preserved in a mighty mass of manuscripts, with which +his study was encumbered, and with which many other parts of the +house were not unfrequently invaded. If a letter was laid aside for +a few hours, it would become lost to view amid the seething mass of +papers, though occasionally, to use his own expression, it might be +seen "eddying" to the surface in some later disturbance.</p> + +<p>The great volume of "Lectures on Quaternions" had been issued, and +the author had received the honours which the completion of such a +task would rightfully bring him. The publication of an immortal work +does not, however, necessarily provide the means for paying the +printer's bill. The printing of so robust a volume was necessarily +costly; and even if all the copies could be sold, which at the time +did not seem very likely, they would hardly have met the inevitable +expenses. The provision of the necessary funds was, therefore, a +matter for consideration. The Board of Trinity College had already +contributed 200 pounds to the printing, but yet another hundred was +required. Even the discoverer of Quaternions found this a source of +much anxiety. However, the board, urged by the representation of +Humphrey Lloyd, now one of its members, and, as we have already seen, +one of Hamilton's staunchest friends, relieved him of all liability. +We may here note that, notwithstanding the pension which Hamilton +enjoyed in addition to the salary of his chair, he seems always to +have been in some what straitened circumstances, or, to use his own +words in one of his letters to De Morgan, "Though not an embarrassed +man, I am anything rather than a rich one." It appears that, +notwithstanding the world-wide fame of Hamilton's discoveries, the +only profit in a pecuniary sense that he ever obtained from any of +his works was by the sale of what he called his Icosian Game. Some +enterprising publisher, on the urgent representations of one of +Hamilton's friends in London, bought the copyright of the Icosian +Game for 25 pounds. Even this little speculation proved unfortunate +for the purchaser, as the public could not be induced to take the +necessary interest in the matter.</p> + +<p>After the completion of his great book, Hamilton appeared for awhile +to permit himself a greater indulgence than usual in literary +relaxations. He had copious correspondence with his intimate friend, +Aubrey de Vere, and there were multitudes of letters from those +troops of friends whom it was Hamilton's privilege to possess. He +had been greatly affected by the death of his beloved sister Eliza, a +poetess of much taste and feeling. She left to him her many papers +to preserve or to destroy, but he said it was only after the +expiration of four years of mourning that he took courage to open her +pet box of letters.</p> + +<p>The religious side of Hamilton's character is frequently illustrated +in these letters; especially is this brought out in the +correspondence with De Vere, who had seceded to the Church of Rome. +Hamilton writes, August 4, 1855:—</p> + +<p>"If, then, it be painfully evident to both, that under such +circumstances there CANNOT (whatever we may both DESIRE) be NOW in +the nature of things, or of minds, the same degree of INTIMACY +between us as of old; since we could no longer TALK with the same +degree of unreserve on every subject which happened to present +itself, but MUST, from the simplest instincts of courtesy, be each on +his guard not to say what might be offensive, or, at least, painful +to the other; yet WE were ONCE so intimate, and retain still, and, as +I trust, shall always retain, so much of regard and esteem and +appreciation for each other, made tender by so many associations of +my early youth and your boyhood, which can never be forgotten by +either of us, that (as times go) TWO OR THREE VERY RESPECTABLE +FRIENDSHIPS might easily be carved out from the fragments of our +former and ever-to-be-remembered INTIMACY. It would be no +exaggeration to quote the words: 'Heu! quanto minus est cum reliquis +versari, quam tui meminisse!'"</p> + +<p>In 1858 a correspondence on the subject of Quaternions commenced +between Professor Tait and Sir William Hamilton. It was particularly +gratifying to the discoverer that so competent a mathematician as +Professor Tait should have made himself acquainted with the new +calculus. It is, of course, well known that Professor Tait +subsequently brought out a most valuable elementary treatise on +Quaternions, to which those who are anxious to become acquainted with +the subject will often turn in preference to the tremendous work of +Hamilton.</p> + +<p>In the year 1861 gratifying information came to hand of the progress +which the study of Quaternions was making abroad. Especially did the +subject attract the attention of that accomplished mathematician, +Moebius, who had already in his "Barycentrische Calculus" been led to +conceptions which bore more affinity to Quaternions than could be +found in the writings of any other mathematician. Such notices of +his work were always pleasing to Hamilton, and they served, perhaps, +as incentives to that still closer and more engrossing labour by +which he became more and more absorbed. During the last few years of +his life he was observed to be even more of a recluse than he had +hitherto been. His powers of long and continuous study seemed to +grow with advancing years, and his intervals of relaxation, such as +they were, became more brief and more infrequent.</p> + +<p>It was not unusual for him to work for twelve hours at a stretch. +The dawn would frequently surprise him as he looked up to snuff his +candles after a night of fascinating labour at original research. +Regularity in habits was impossible to a student who had prolonged +fits of what he called his mathematical trances. Hours for rest and +hours for meals could only be snatched in the occasional the lucid +intervals between one attack of Quaternions and the next. When +hungry, he would go to see whether anything could be found on the +sideboard; when thirsty, he would visit the locker, and the one +blemish in the man's personal character is that these latter visits +were sometimes paid too often.</p> + +<p>As an example of one of Hamilton's rare diversions from the all- +absorbing pursuit of Quaternions, we find that he was seized with +curiosity to calculate back to the date of the Hegira, which he found +on the 15th July, 622. He speaks of the satisfaction with which he +ascertained subsequently that Herschel had assigned precisely the +same date. Metaphysics remained also, as it had ever been, a +favourite subject of Hamilton's readings and meditations and of +correspondence with his friends. He wrote a very long letter to Dr. +Ingleby on the subject of his "Introduction to Metaphysics." In it +Hamilton alludes, as he has done also in other places, to a +peculiarity of his own vision. It was habitual to him, by some +defect in the correlation of his eyes, to see always a distinct image +with each; in fact, he speaks of the remarkable effect which the use +of a good stereoscope had on his sensations of vision. It was then, +for the first time, that he realised how the two images which he had +always seen hitherto would, under normal circumstances, be blended +into one. He cites this fact as bearing on the phenomena of +binocular vision, and he draws from it the inference that the +necessity of binocular vision for the correct appreciation of +distance is unfounded. "I am quite sure," he says, "that I SEE +DISTANCE with EACH EYE SEPARATELY."</p> + +<p>The commencement of 1865, the last year of his life saw Hamilton as +diligent as ever, and corresponding with Salmon and Cayley. On April +26th he writes to a friend to say, that his health has not been good +for years past, and that so much work has injured his constitution; +and he adds, that it is not conducive to good spirits to find that he +is accumulating another heavy bill with the printer for the +publication of the "Elements." This was, indeed, up to the day of +his death, a cause for serious anxiety. It may, however, be +mentioned that the whole cost, which amounted to nearly 500 pounds, +was, like that of the previous volume, ultimately borne by the +College. Contrary to anticipation, the enterprise, even in a +pecuniary sense, cannot have been a very unprofitable one. The whole +edition has long been out of print, and as much as 5 pounds has since +been paid for a single copy.</p> + +<p>It was on the 9th of May, 1865, that Hamilton was in Dublin for the +last time. A few days later he had a violent attack of gout, and on +the 4th of June he became alarmingly ill, and on the next day had an +attack of epileptic convulsions. However, he slightly rallied, so +that before the end of the month he was again at work at the +"Elements." A gratifying incident brightened some of the last days +of his life. The National Academy of Science in America had then +been just formed. A list of foreign Associates had to be chosen from +the whole world, and a discussion took place as to what name should +be placed first on the list. Hamilton was informed by private +communication that this great distinction was awarded to him by a +majority of two-thirds.</p> + +<p>In August he was still at work on the table of contents of the +"Elements," and one of his very latest efforts was his letter to Mr. +Gould, in America, communicating his acknowledgements of the honour +which had been just conferred upon him by the National Academy. On +the 2nd of September Mr. Graves went to the observatory, in response +to a summons, and the great mathematician at once admitted to his +friend that he felt the end was approaching. He mentioned that he +had found in the 145th Psalm a wonderfully suitable expression of his +thoughts and feelings, and he wished to testify his faith and +thankfulness as a Christian by partaking of the Lord's Supper. He +died at half-past two on the afternoon of the 2nd of September, 1865, +aged sixty years and one month. He was buried in Mount Jerome +Cemetery on the 7th of September.</p> + +<p>Many were the letters and other more public manifestations of the +feelings awakened by Hamilton's death. Sir John Herschel wrote to +the widow:—</p> + +<p>"Permit me only to add that among the many scientific friends whom +time has deprived me of, there has been none whom I more deeply +lament, not only for his splendid talents, but for the excellence of +his disposition and the perfect simplicity of his manners—so great, +and yet devoid of pretensions."</p> + +<p>De Morgan, his old mathematical crony, as Hamilton affectionately +styled him, also wrote to Lady Hamilton:—</p> + +<p>"I have called him one of my dearest friends, and most truly; for I +know not how much longer than twenty-five years we have been in +intimate correspondence, of most friendly agreement or disagreement, +of most cordial interest in each other. And yet we did not know each +other's faces. I met him about 1830 at Babbage's breakfast table, +and there for the only time in our lives we conversed. I saw him, a +long way off, at the dinner given to Herschel (about 1838) on his +return from the Cape and there we were not near enough, nor on that +crowded day could we get near enough, to exchange a word. And this +is all I ever saw, and, so it has pleased God, all I shall see in +this world of a man whose friendly communications were among my +greatest social enjoyments, and greatest intellectual treats."</p> + +<p>There is a very interesting memoir of Hamilton written by De Morgan, +in the "Gentleman's Magazine" for 1866, in which he produces an +excellent sketch of his friend, illustrated by personal reminiscences +and anecdotes. He alludes, among other things, to the picturesque +confusion of the papers in his study. There was some sort of order +in the mass, discernible however, by Hamilton alone, and any invasion +of the domestics, with a view to tidying up, would throw the +mathematician as we are informed, into "a good honest thundering +passion."</p> + +<p>Hardly any two men, who were both powerful mathematicians, could have +been more dissimilar in every other respect than were Hamilton and De +Morgan. The highly poetical temperament of Hamilton was remarkably +contrasted with the practical realism of De Morgan. Hamilton sends +sonnets to his friend, who replies by giving the poet advice about +making his will. The metaphysical subtleties, with which Hamilton +often filled his sheets, did not seem to have the same attraction for +De Morgan that he found in battles about the quantification of the +Predicate. De Morgan was exquisitely witty, and though his jokes +were always appreciated by his correspondent, yet Hamilton seldom +ventured on anything of the same kind in reply; indeed his rare +attempts at humour only produced results of the most ponderous +description. But never were two scientific correspondents more +perfectly in sympathy with each other. Hamilton's work on +Quaternions, his labours in Dynamics, his literary tastes, his +metaphysics, and his poetry, were all heartily welcomed by his +friend, whose letters in reply invariably evince the kindliest +interest in all Hamilton's concerns. In a similar way De Morgan's +letters to Hamilton always met with a heartfelt response.</p> + +<p>Alike for the memory of Hamilton, for the credit of his University, +and for the benefit of science, let us hope that a collected edition +of his works will ere long appear—a collection which shall show +those early achievements in splendid optical theory, those +achievements of his more mature powers which made him the Lagrange of +his country, and finally those creations of the Quaternion Calculus +by which new capabilities have been bestowed on the human intellect.</p> + +<h3><a name="LE_VERRIER" id="LE_VERRIER"></a>LE VERRIER.</h3> +<p>The name of Le Verrier is one that goes down to fame on account of +very different discoveries from those which have given renown to +several of the other astronomers whom we have mentioned. We are +sometimes apt to identify the idea of an astronomer with that of a +man who looks through a telescope at the stars; but the word +astronomer has really much wider significance. No man who ever lived +has been more entitled to be designated an astronomer than Le +Verrier, and yet it is certain that he never made a telescopic +discovery of any kind. Indeed, so far as his scientific achievements +have been concerned, he might never have looked through a telescope +at all.</p> + +<p>For the full interpretation of the movements of the heavenly bodies, +mathematical knowledge of the most advanced character is demanded. +The mathematician at the outset calls upon the astronomer who uses +the instruments in the observatory, to ascertain for him at various +times the exact positions occupied by the sun, the moon, and the +planets. These observations, obtained with the greatest care, and +purified as far as possible from the errors by which they may be +affected form, as it were, the raw material on which the +mathematician exercises his skill. It is for him to elicit from the +observed places the true laws which govern the movements of the +heavenly bodies. Here is indeed a task in which the highest powers +of the human intellect may be worthily employed.</p> + +<p>Among those who have laboured with the greatest success in the +interpretation of the observations made with instruments of +precision, Le Verrier holds a highly honoured place. To him it has +been given to provide a superb illustration of the success with which +the mind of man can penetrate the deep things of Nature.</p> + +<p>The illustrious Frenchman, Urban Jean Joseph Le Verrier, was born on +the 11th March, 1811, at St. Lo, in the department of Manche. He +received his education in that famous school for education in the +higher branches of science, the Ecole Polytechnique, and acquired +there considerable fame as a mathematician. On leaving the school Le +Verrier at first purposed to devote himself to the public service, in +the department of civil engineering; and it is worthy of note that +his earliest scientific work was not in those mathematical researches +in which he was ultimately to become so famous. His duties in the +engineering department involved practical chemical research in the +laboratory. In this he seems to have become very expert, and +probably fame as a chemist would have been thus attained, had not +destiny led him into another direction. As it was, he did engage in +some original chemical research. His first contributions to science +were the fruits of his laboratory work; one of his papers was on the +combination of phosphorus and hydrogen, and another on the +combination of phosphorus and oxygen.</p> + +<p>His mathematical labours at the Ecole Polytechnique had, however, +revealed to Le Verrier that he was endowed with the powers requisite +for dealing with the subtlest instruments of mathematical analysis. +When he was twenty-eight years old, his first great astronomical +investigation was brought forth. It will be necessary to enter into +some explanation as to the nature of this, inasmuch as it was the +commencement of the life-work which he was to pursue.</p> + +<p>If but a single planet revolved around the sun, then the orbit of +that planet would be an ellipse, and the shape and size, as well as +the position of the ellipse, would never alter. One revolution after +another would be traced out, exactly in the same manner, in +compliance with the force continuously exerted by the sun. Suppose, +however, that a second planet be introduced into the system. The sun +will exert its attraction on this second planet also, and it will +likewise describe an orbit round the central globe. We can, however, +no longer assert that the orbit in which either of the planets moves +remains exactly an ellipse. We may, indeed, assume that the mass of +the sun is enormously greater than that of either of the planets. In +this case the attraction of the sun is a force of such preponderating +magnitude, that the actual path of each planet remains nearly the +same as if the other planet were absent. But it is impossible for +the orbit of each planet not to be affected in some degree by the +attraction of the other planet. The general law of nature asserts +that every body in space attracts every other body. So long as there +is only a single planet, it is the single attraction between the sun +and that planet which is the sole controlling principle of the +movement, and in consequence of it the ellipse is described. But +when a second planet is introduced, each of the two bodies is not +only subject to the attraction of the sun, but each one of the +planets attracts the other. It is true that this mutual attraction +is but small, but, nevertheless, it produces some effect. It +"disturbs," as the astronomer says, the elliptic orbit which would +otherwise have been pursued. Hence it follows that in the actual +planetary system where there are several planets disturbing each +other, it is not true to say that the orbits are absolutely elliptic.</p> + +<p>At the same time in any single revolution a planet may for most +practical purposes be said to be actually moving in an ellipse. As, +however, time goes on, the ellipse gradually varies. It alters its +shape, it alters its plane, and it alters its position in that +plane. If, therefore, we want to study the movements of the planets, +when great intervals of time are concerned, it is necessary to have +the means of learning the nature of the movement of the orbit in +consequence of the disturbances it has experienced.</p> + +<p>We may illustrate the matter by supposing the planet to be running +like a railway engine on a track which has been laid in a long +elliptic path. We may suppose that while the planet is coursing +along, the shape of the track is gradually altering. But this +alteration may be so slow, that it does not appreciably affect the +movement of the engine in a single revolution. We can also suppose +that the plane in which the rails have been laid has a slow +oscillation in level, and that the whole orbit is with more or less +uniformity moved slowly about in the plane.</p> + +<p>In short periods of time the changes in the shapes and positions of +the planetary orbits, in consequence of their mutual attractions, are +of no great consequence. When, however, we bring thousands of years +into consideration, then the displacements of the planetary orbits +attain considerable dimensions, and have, in fact, produced a +profound effect on the system.</p> + +<p>It is of the utmost interest to investigate the extent to which one +planet can affect another in virtue of their mutual attractions. Such +investigations demand the exercise of the highest mathematical +gifts. But not alone is intellectual ability necessary for success +in such inquiries. It must be united with a patient capacity for +calculations of an arduous type, protracted, as they frequently have +to be, through many years of labour. Le Verrier soon found in these +profound inquiries adequate scope for the exercise of his peculiar +gifts. His first important astronomical publication contained an +investigation of the changes which the orbits of several of the +planets, including the earth, have undergone in times past, and which +they will undergo in times to come.</p> + +<p>As an illustration of these researches, we may take the case of the +planet in which we are, of course, especially interested, namely, the +earth, and we can investigate the changes which, in the lapse of +time, the earth's orbit has undergone, in consequence of the +disturbance to which it has been subjected by the other planets. In +a century, or even in a thousand years, there is but little +recognisable difference in the shape of the track pursued by the +earth. Vast periods of time are required for the development of the +large consequences of planetary perturbation. Le Verrier has, +however, given us the particulars of what the earth's journey through +space has been at intervals of 20,000 years back from the present +date. His furthest calculation throws our glance back to the state +of the earth's track 100,000 years ago, while, with a bound forward, +he shows us what the earth's orbit is to be in the future, at +successive intervals of 20,000 years, till a date is reached which is +100,000 years in advance of A.D. 1800.</p> + +<p>The talent which these researches displayed brought Le Verrier into +notice. At that time the Paris Observatory was presided over by +Arago, a SAVANT who occupies a distinguished position in French +scientific annals. Arago at once perceived that Le Verrier was just +the man who possessed the qualifications suitable for undertaking a +problem of great importance and difficulty that had begun to force +itself on the attention of astronomers. What this great problem was, +and how astonishing was the solution it received, must now be +considered.</p> + +<p>Ever since Herschel brought himself into fame by his superb discovery +of the great planet Uranus, the movements of this new addition to the +solar system were scrutinized with care and attention. The position +of Uranus was thus accurately determined from time to time. At +length, when sufficient observations of this remote planet had been +brought together, the route which the newly-discovered body pursued +through the heavens was ascertained by those calculations with which +astronomers are familiar. It happens, however, that Uranus possesses +a superficial resemblance to a star. Indeed the resemblance is so +often deceptive that long ere its detection as a planet by Herschel, +it had been observed time after time by skilful astronomers, who +little thought that the star-like point at which they looked was +anything but a star. From these early observations it was possible +to determine the track of Uranus, and it was found that the great +planet takes a period of no less than eighty-four years to accomplish +a circuit. Calculations were made of the shape of the orbit in which +it revolved before its discovery by Herschel, and these were compared +with the orbit which observations showed the same body to pursue in +those later years when its planetary character was known. It could +not, of course, be expected that the orbit should remain unaltered; +the fact that the great planets Jupiter and Saturn revolve in the +vicinity of Uranus must necessarily imply that the orbit of the +latter undergoes considerable changes. When, however, due allowance +has been made for whatever influence the attraction of Jupiter and +Saturn, and we may add of the earth and all the other Planets, could +possibly produce, the movements of Uranus were still inexplicable. It +was perfectly obvious that there must be some other influence at work +besides that which could be attributed to the planets already known.</p> + +<p>Astronomers could only recognise one solution of such a difficulty. +It was impossible to doubt that there must be some other planet in +addition to the bodies at that time known, and that the perturbations +of Uranus hitherto unaccounted for, were due to the disturbances +caused by the action of this unknown planet. Arago urged Le Verrier +to undertake the great problem of searching for this body, whose +theoretical existence seemed demonstrated. But the conditions of the +search were such that it must needs be conducted on principles wholly +different from any search which had ever before been undertaken for a +celestial object. For this was not a case in which mere survey with +a telescope might be expected to lead to the discovery.</p> + +<p>Certain facts might be immediately presumed with reference to the +unknown object. There could be no doubt that the unknown disturber +of Uranus must be a large body with a mass far exceeding that of the +earth. It was certain, however, that it must be so distant that it +could only appear from our point of view as a very small object. +Uranus itself lay beyond the range, or almost beyond the range, of +unassisted vision. It could be shown that the planet by which the +disturbance was produced revolved in an orbit which must lie outside +that of Uranus. It seemed thus certain that the planet could not be +a body visible to the unaided eye. Indeed, had it been at all +conspicuous its planetary character would doubtless have been +detected ages ago. The unknown body must therefore be a planet which +would have to be sought for by telescopic aid.</p> + +<p>There is, of course, a profound physical difference between a planet +and a star, for the star is a luminous sun, and the planet is merely +a dark body, rendered visible by the sunlight which falls upon it. +Notwithstanding that a star is a sun thousands of times larger than +the planet and millions of times more remote, yet it is a singular +fact that telescopic planets possess an illusory resemblance to the +stars among which their course happens to lie. So far as actual +appearance goes, there is indeed only one criterion by which a planet +of this kind can be discriminated from a star. If the planet be +large enough the telescope will show that it possesses a disc, and +has a visible and measurable circular outline. This feature a star +does not exhibit. The stars are indeed so remote that no matter how +large they may be intrinsically, they only exhibit radiant points of +light, which the utmost powers of the telescope fail to magnify into +objects with an appreciable diameter. The older and well-known +planets, such as Jupiter and Mars, possess discs, which, though not +visible to the unaided eye, were clearly enough discernible with the +slightest telescopic power. But a very remote planet like Uranus, +though it possessed a disc large enough to be quickly appreciated by +the consummate observing skill of Herschel, was nevertheless so +stellar in its appearance, that it had been observed no fewer than +seventeen times by experienced astronomers prior to Herschel. In +each case the planetary nature of the object had been overlooked, and +it had been taken for granted that it was a star. It presented no +difference which was sufficient to arrest attention.</p> + +<p>As the unknown body by which Uranus was disturbed was certainly much +more remote than Uranus, it seemed to be certain that though it might +show a disc perceptible to very close inspection, yet that the disc +must be so minute as not to be detected except with extreme care. In +other words, it seemed probable that the body which was to be sought +for could not readily be discriminated from a small star, to which +class of object it bore a superficial resemblance, though, as a +matter of fact, there was the profoundest difference between the two +bodies.</p> + +<p>There are on the heavens many hundreds of thousands of stars, and the +problem of identifying the planet, if indeed it should lie among +these stars, seemed a very complex matter. Of course it is the +abundant presence of the stars which causes the difficulty. If the +stars could have been got rid of, a sweep over the heavens would at +once disclose all the planets which are bright enough to be visible +with the telescopic power employed. It is the fortuitous resemblance +of the planet to the stars which enables it to escape detection. To +discriminate the planet among stars everywhere in the sky would be +almost impossible. If, however, some method could be devised for +localizing that precise region in which the planet's existence might +be presumed, then the search could be undertaken with some prospect +of success.</p> + +<p>To a certain extent the problem of localizing the region on the sky +in which the planet might be expected admitted of an immediate +limitation. It is known that all the planets, or perhaps I ought +rather to say, all the great planets, confine their movements to a +certain zone around the heavens. This zone extends some way on +either side of that line called the ecliptic in which the earth +pursues its journey around the sun. It was therefore to be inferred +that the new planet need not be sought for outside this zone. It is +obvious that this consideration at once reduces the area to be +scrutinized to a small fraction of the entire heavens. But even +within the zone thus defined there are many thousands of stars. It +would seem a hopeless task to detect the new planet unless some +further limitation to its position could be assigned.</p> + +<p>It was accordingly suggested to Le Verrier that he should endeavour +to discover in what particular part of the strip of the celestial +sphere which we have indicated the search for the unknown planet +should be instituted. The materials available to the mathematician +for the solution of this problem were to be derived solely from the +discrepancies between the calculated places in which Uranus should be +found, taking into account the known causes of disturbance, and the +actual places in which observation had shown the planet to exist. +Here was indeed an unprecedented problem, and one of extraordinary +difficulty. Le Verrier, however, faced it, and, to the astonishment +of the world, succeeded in carrying it through to a brilliant +solution. We cannot here attempt to enter into any account of the +mathematical investigations that were necessary. All that we can do +is to give a general indication of the method which had to be +adopted.</p> + +<p>Let us suppose that a planet is revolving outside Uranus, at a +distance which is suggested by the several distances at which the +other planets are dispersed around the sun. Let us assume that this +outer planet has started on its course, in a prescribed path, and +that it has a certain mass. It will, of course, disturb the motion +of Uranus, and in consequence of that disturbance Uranus will follow +a path the nature of which can be determined by calculation. It +will, however, generally be found that the path so ascertained does +not tally with the actual path which observations have indicated for +Uranus. This demonstrates that the assumed circumstances of the +unknown planet must be in some respects erroneous, and the astronomer +commences afresh with an amended orbit. At last after many trials, +Le Verrier ascertained that, by assuming a certain size, shape, and +position for the unknown Planet's orbit, and a certain value for the +mass of the hypothetical body, it would be possible to account for +the observed disturbances of Uranus. Gradually it became clear to +the perception of this consummate mathematician, not only that the +difficulties in the movements of Uranus could be thus explained, but +that no other explanation need be sought for. It accordingly +appeared that a planet possessing the mass which he had assigned, and +moving in the orbit which his calculations had indicated, must indeed +exist, though no eye had ever beheld any such body. Here was, +indeed, an astonishing result. The mathematician sitting at his +desk, by studying the observations which had been supplied to him of +one planet, is able to discover the existence of another planet, and +even to assign the very position which it must occupy, ere ever the +telescope is invoked for its discovery.</p> + +<p>Thus it was that the calculations of Le Verrier narrowed greatly the +area to be scrutinised in the telescopic search which was presently +to be instituted. It was already known, as we have just pointed out, +that the planet must lie somewhere on the ecliptic. The French +mathematician had now further indicated the spot on the ecliptic at +which, according to his calculations, the planet must actually be +found. And now for an episode in this history which will be +celebrated so long as science shall endure. It is nothing less than +the telescopic confirmation of the existence of this new planet, +which had previously been indicated only by mathematical +calculation. Le Verrier had not himself the instruments necessary +for studying the heavens, nor did he possess the skill of the +practical astronomer. He, therefore, wrote to Dr. Galle, of the +Observatory at Berlin, requesting him to undertake a telescopic +search for the new planet in the vicinity which the mathematical +calculation had indicated for the whereabouts of the planet at that +particular time. Le Verrier added that he thought the planet ought +to admit of being recognised by the possession of a disc sufficiently +definite to mark the distinction between it and the surrounding +stars.</p> + +<p>It was the 23rd September, 1846, when the request from Le Verrier +reached the Berlin Observatory, and the night was clear, so that the +memorable search was made on the same evening. The investigation was +facilitated by the circumstance that a diligent observer had recently +compiled elaborate star maps for certain tracts of the heavens lying +in a sufficiently wide zone on both sides of the equator. These maps +were as yet only partially complete, but it happened that Hora. XXI., +which included the very spot which Le Verrier's results referred to, +had been just issued. Dr. Galle had thus before his eyes a chart of +all the stars which were visible in that part of the heavens at the +time when the map was made. The advantage of such an assistance to +the search could hardly be over-estimated. It at once gave the +astronomer another method of recognising the planet besides that +afforded by its possible possession of a disc. For as the planet was +a moving body, it would not have been in the same place relatively to +the stars at the time when the map was constructed, as it occupied +some years later when the search was being made. If the body should +be situated in the spot which Le Verrier's calculations indicated in +the autumn of 1846, then it might be regarded as certain that it +would not be found in that same place on a map drawn some years +previously.</p> + +<p>The search to be undertaken consisted in a comparison made point by +point between the bodies shown on the map, and those stars in the sky +which Dr. Galle's telescope revealed. In the course of this +comparison it presently appeared that a star-like object of the +eighth magnitude, which was quite a conspicuous body in the +telescope, was not represented in the map. This at once attracted +the earnest attention of the astronomer, and raised his hopes that +here was indeed the planet. Nor were these hopes destined to be +disappointed. It could not be supposed that a star of the eighth +magnitude would have been overlooked in the preparation of a chart +whereon stars of many lower degrees of brightness were set down. One +other supposition was of course conceivable. It might have been that +this suspicious object belonged to the class of variables, for there +are many such stars whose brightness fluctuates, and if it had +happened that the map was constructed at a time when the star in +question had but feeble brilliance, it might have escaped notice. It +is also well known that sometimes new stars suddenly develop, so that +the possibility that what Dr. Galle saw should have been a variable +star or should have been a totally new star had to be provided +against.</p> + +<p>Fortunately a test was immediately available to decide whether the +new object was indeed the long sought for planet, or whether it was a +star of one of the two classes to which I have just referred. A star +remains fixed, but a planet is in motion. No doubt when a planet +lies at the distance at which this new planet was believed to be +situated, its apparent motion would be so slow that it would not be +easy to detect any change in the course of a single night's +observation. Dr. Galle, however, addressed himself with much skill +to the examination of the place of the new body. Even in the course +of the night he thought he detected slight movements, and he awaited +with much anxiety the renewal of his observations on the subsequent +evenings. His suspicions as to the movement of the body were then +amply confirmed, and the planetary nature of the new object was thus +unmistakably detected.</p> + +<p>Great indeed was the admiration of the scientific world at this +superb triumph. Here was a mighty planet whose very existence was +revealed by the indications afforded by refined mathematical +calculation. At once the name of Le Verrier, already known to those +conversant with the more profound branches of astronomy, became +everywhere celebrated. It soon, however, appeared, that the fame +belonging to this great achievement had to be shared between Le +Verrier and another astronomer, J. C. Adams, of Cambridge. In our +chapter on this great English mathematician we shall describe the +manner in which he was independently led to the same discovery.</p> + +<p>Directly the planetary nature of the newly-discovered body had been +established, the great observatories naturally included this +additional member of the solar system in their working lists, so that +day after day its place was carefully determined. When sufficient +time had elapsed the shape and position of the orbit of the body +became known. Of course, it need hardly be said that observations +applied to the planet itself must necessarily provide a far more +accurate method of determining the path which it follows, than would +be possible to Le Verrier, when all he had to base his calculations +upon was the influence of the planet reflected, so to speak, from +Uranus. It may be noted that the true elements of the planet, when +revealed by direct observation, showed that there was a considerable +discrepancy between the track of the planet which Le Verrier had +announced, and that which the planet was actually found to pursue.</p> + +<p>The name of the newly-discovered body had next to be considered. As +the older members of the system were already known by the same names +as great heathen divinities, it was obvious that some similar source +should be invoked for a suggestion as to a name for the most recent +planet. The fact that this body was so remote in the depths of +space, not unnaturally suggested the name "Neptune." Such is +accordingly the accepted designation of that mighty globe which +revolves in the track that at present seems to trace out the +frontiers of our system.</p> + +<p>Le Verrier attained so much fame by this discovery, that when, in +1854, Arago's place had to be filled at the head of the great Paris +Observatory, it was universally felt that the discoverer of Neptune +was the suitable man to assume the office which corresponds in France +to that of the Astronomer Royal in England. It was true that the +work of the astronomical mathematician had hitherto been of an +abstract character. His discoveries had been made at his desk and +not in the observatory, and he had no practical acquaintance with the +use of astronomical instruments. However, he threw himself into the +technical duties of the observatory with vigour and determination. He +endeavoured to inspire the officers of the establishment with +enthusiasm for that systematic work which is so necessary for the +accomplishment of useful astronomical research. It must, however, be +admitted that Le Verrier was not gifted with those natural qualities +which would make him adapted for the successful administration of +such an establishment. Unfortunately disputes arose between the +Director and his staff. At last the difficulties of the situation +became so great that the only possible solution was to supersede Le +Verrier, and he was accordingly obliged to retire. He was succeeded +in his high office by another eminent mathematician, M. Delaunay, +only less distinguished than Le Verrier himself.</p> + +<p>Relieved of his official duties, Le Verrier returned to the +mathematics he loved. In his non-official capacity he continued to +work with the greatest ardour at his researches on the movements of +the planets. After the death of M. Delaunay, who was accidentally +drowned in 1873, Le Verrier was restored to the directorship of the +observatory, and he continued to hold the office until his death.</p> + +<p>The nature of the researches to which the life of Le Verrier was +subsequently devoted are not such as admit of description in a +general sketch like this, where the language, and still less the +symbols, of mathematics could not be suitably introduced. It may, +however, be said in general that he was particularly engaged with the +study of the effects produced on the movements of the planets by +their mutual attractions. The importance of this work to astronomy +consists, to a considerable extent, in the fact that by such +calculations we are enabled to prepare tables by which the places of +the different heavenly bodies can be predicted for our almanacs. To +this task Le Verrier devoted himself, and the amount of work he has +accomplished would perhaps have been deemed impossible had it not +been actually done.</p> + +<p>The superb success which had attended Le Verrier's efforts to explain +the cause of the perturbations of Uranus, naturally led this +wonderful computer to look for a similar explanation of certain other +irregularities in planetary movements. To a large extent he +succeeded in showing how the movements of each of the great planets +could be satisfactorily accounted for by the influence of the +attractions of the other bodies of the same class. One circumstance +in connection with these investigations is sufficiently noteworthy to +require a few words here. Just as at the opening of his career, Le +Verrier had discovered that Uranus, the outermost planet of the then +known system, exhibited the influence of an unknown external body, so +now it appeared to him that Mercury, the innermost body of our +system, was also subjected to some disturbances, which could not be +satisfactorily accounted for as consequences of any known agents of +attraction. The ellipse in which Mercury revolved was animated by a +slow movement, which caused it to revolve in its plane. It appeared +to Le Verrier that this displacement was incapable of explanation by +the action of any of the known bodies of our system. He was, +therefore, induced to try whether he could not determine from the +disturbances of Mercury the existence of some other planet, at +present unknown, which revolved inside the orbit of the known +planet. Theory seemed to indicate that the observed alteration in +the track of the planet could be thus accounted for. He naturally +desired to obtain telescopic confirmation which might verify the +existence of such a body in the same way as Dr. Galle verified the +existence of Neptune. If there were, indeed, an intramercurial +planet, then it must occasionally cross between the earth and the +sun, and might now and then be expected to be witnessed in the actual +act of transit. So confident did Le Verrier feel in the existence of +such a body that an observation of a dark object in transit, by +Lescarbault on 26th March, 1859, was believed by the mathematician to +be the object which his theory indicated. Le Verrier also thought it +likely that another transit of the same object would be seen in +March, 1877. Nothing of the kind was, however, witnessed, +notwithstanding that an assiduous watch was kept, and the explanation +of the change in Mercury's orbit must, therefore, be regarded as +still to be sought for.</p> + +<p>Le Verrier naturally received every honour that could be bestowed +upon a man of science. The latter part of his life was passed during +the most troubled period of modern French history. He was a +supporter of the Imperial Dynasty, and during the Commune he +experienced much anxiety; indeed, at one time grave fears were +entertained for his personal safety.</p> + +<p>Early in 1877 his health, which had been gradually failing for some +years, began to give way. He appeared to rally somewhat in the +summer, but in September he sank rapidly, and died on Sunday, the +23rd of that month.</p> + +<p>His remains were borne to the cemetery on Mont Parnasse in a public +funeral. Among his pallbearers were leading men of science, from +other countries as well as France, and the memorial discourses +pronounced at the grave expressed their admiration of his talents and +of the greatness of the services he had rendered to science.</p> + +<h3><a name="ADAMS" id="ADAMS"></a>ADAMS.</h3> +<p>The illustrious mathematician who, among Englishmen, at all events, +was second only to Newton by his discoveries in theoretical +astronomy, was born on June the 5th, 1819, at the farmhouse of +Lidcot, seven miles from Launceston, in Cornwall. His early +education was imparted under the guidance of the Rev. John Couch +Grylls, a first cousin of his mother. He appears to have received an +education of the ordinary school type in classics and mathematics, +but his leisure hours were largely devoted to studying what +astronomical books he could find in the library of the Mechanics' +Institute at Devonport. He was twenty years old when he entered St. +John's College, Cambridge. His career in the University was one of +almost unparalleled distinction, and it is recorded that his +answering at the Wranglership examination, where he came out at the +head of the list in 1843, was so high that he received more than +double the marks awarded to the Second Wrangler.</p> + +<p>Among the papers found after his death was the following memorandum, +dated July the 3rd, 1841: "Formed a design at the beginning of this +week of investigating, as soon as possible after taking my degree, +the irregularities in the motion of Uranus, which are as yet +unaccounted for, in order to find whether they may be attributed to +the action of an undiscovered planet beyond it; and, if possible, +thence to determine the elements of its orbit approximately, which +would lead probably to its discovery."</p> + +<p>After he had taken his degree, and had thus obtained a little +relaxation from the lines within which his studies had previously +been necessarily confined, Adams devoted himself to the study of the +perturbations of Uranus, in accordance with the resolve which we have +just seen that he formed while he was still an undergraduate. As a +first attempt he made the supposition that there might be a planet +exterior to Uranus, at a distance which was double that of Uranus +from the sun. Having completed his calculation as to the effect +which such a hypothetical planet might exercise upon the movement of +Uranus, he came to the conclusion that it would be quite possible to +account completely for the unexplained difficulties by the action of +an exterior planet, if only that planet were of adequate size and had +its orbit properly placed. It was necessary, however, to follow up +the problem more precisely, and accordingly an application was made +through Professor Challis, the Director of the Cambridge Observatory, +to the Astronomer Royal, with the object of obtaining from the +observations made at Greenwich Observatory more accurate values for +the disturbances suffered by Uranus. Basing his work on the more +precise materials thus available, Adams undertook his calculations +anew, and at last, with his completed results, he called at Greenwich +Observatory on October the 21st, 1845. He there left for the +Astronomer Royal a paper which contained the results at which he had +arrived for the mass and the mean distance of the hypothetical planet +as well as the other elements necessary for calculating its exact +position.</p> + +<p><a name="john" id="john"></a></p> + +<div class="figcenter" style="width: 433px;"> +<a href="images/ill_john_adams.jpg"> +<img src="images/ill_john_adams_sml.jpg" width="433" height="496" alt="JOHN COUCH ADAMS." title="" /></a> +<span class="caption">JOHN COUCH ADAMS.</span> +</div> + +<p>As we have seen in the preceding chapter, Le Verrier had been also +investigating the same problem. The place which Le Verrier assigned +to the hypothetical disturbing planet for the beginning of the year +1847, was within a degree of that to which Adams's computations +pointed, and which he had communicated to the Astronomer Royal seven +months before Le Verrier's work appeared. On July the 29th, 1846, +Professor Challis commenced to search for the unknown object with the +Northumberland telescope belonging to the Cambridge Observatory. He +confined his attention to a limited region in the heavens, extending +around that point to which Mr. Adams' calculations pointed. The +relative places of all the stars, or rather star-like objects within +this area, were to be carefully measured. When the same observations +were repeated a week or two later, then the distances of the several +pairs of stars from each other would be found unaltered, but any +planet which happened to lie among the objects measured would +disclose its existence by the alterations in distance due to its +motion in the interval. This method of search, though no doubt it +must ultimately have proved successful, was necessarily a very +tedious one, but to Professor Challis, unfortunately, no other method +was available. Thus it happened that, though Challis commenced his +search at Cambridge two months earlier than Galle at Berlin, yet, as +we have already explained, the possession of accurate star-maps by +Dr. Galle enabled him to discover the planet on the very first night +that he looked for it.</p> + +<p>The rival claims of Adams and Le Verrier to the discovery of Neptune, +or rather, we should say, the claims put forward by their respective +champions, for neither of the illustrious investigators themselves +condescended to enter into the personal aspect of the question, need +not be further discussed here. The main points of the controversy +have been long since settled, and we cannot do better than quote the +words of Sir John Herschel when he addressed the Royal Astronomical +Society in 1848:—</p> + +<p>"As genius and destiny have joined the names of Le Verrier and Adams, +I shall by no means put them asunder; nor will they ever be +pronounced apart so long as language shall celebrate the triumphs of +science in her sublimest walks. On the great discovery of Neptune, +which may be said to have surpassed, by intelligible and legitimate +means, the wildest pretensions of clairvoyance, it Would now be quite +superfluous for me to dilate. That glorious event and the steps +which led to it, and the various lights in which it has been placed, +are already familiar to every one having the least tincture of +science. I will only add that as there is not, nor henceforth ever +can be, the slightest rivalry on the subject between these two +illustrious men—as they have met as brothers, and as such will, I +trust, ever regard each other—we have made, we could make, no +distinction between then, on this occasion. May they both long adorn +and augment our science, and add to their own fame already so high +and pure, by fresh achievements."</p> + +<p>Adams was elected a Fellow of St. John's College, Cambridge, in 1843; +but as he did not take holy orders, his Fellowship, in accordance +with the rules then existing came to an end in 1852. In the +following year he was, however, elected to a Fellowship at Pembroke +College, which he retained until the end of his life. In 1858 he was +appointed Professor of Mathematics in the University of St. Andrews, +but his residence in the north was only a brief one, for in the same +year he was recalled to Cambridge as Lowndean Professor of Astronomy +and Geometry, in succession to Peacock. In 1861 Challis retired from +the Directorship of the Cambridge Observatory, and Adams was +appointed to succeed him.</p> + +<p>The discovery of Neptune was a brilliant inauguration of the +astronomical career of Adams. He worked at, and wrote upon, the +theory of the motions of Biela's comet; he made important corrections +to the theory of Saturn; he investigated the mass of Uranus, a +subject in which he was naturally interested from its importance in +the theory of Neptune; he also improved the methods of computing the +orbits of double stars. But all these must be regarded as his minor +labours, for next to the discovery of Neptune the fame of Adams +mainly rests on his researches upon certain movements of the moon, +and upon the November meteors.</p> + +<p>The periodic time of the moon is the interval required for one +circuit of its orbit. This interval is known with accuracy at the +present day, and by means of the ancient eclipses the period of the +moon's revolution two thousand years ago can be also ascertained. It +had been discovered by Halley that the period which the moon requires +to accomplish each of its revolutions around the earth has been +steadily, though no doubt slowly, diminishing. The change thus +produced is not appreciable when only small intervals of time are +considered, but it becomes appreciable when we have to deal with +intervals of thousands of years. The actual effect which is produced +by the lunar acceleration, for so this phenomenon is called, may be +thus estimated. If we suppose that the moon had, throughout the +ages, revolved around the earth in precisely the same periodic time +which it has at present, and if from this assumption we calculate +back to find where the moon must have been about two thousand years +ago, we obtain a position which the ancient eclipses show to be +different from that in which the moon was actually situated. The +interval between the position in which the moon would have been found +two thousand years ago if there had been no acceleration, and the +position in which the moon was actually placed, amounts to about a +degree, that is to say, to an arc on the heavens which is twice the +moon's apparent diameter.</p> + +<p>If no other bodies save the earth and the moon were present in the +universe, it seems certain that the motion of the moon would never +have exhibited this acceleration. In such a simple case as that +which I have supposed the orbit of the moon would have remained for +ever absolutely unchanged. It is, however, well known that the +presence of the sun exerts a disturbing influence upon the movements +of the moon. In each revolution our satellite is continually drawn +aside by the action of the sun from the place which it would +otherwise have occupied. These irregularities are known as the +perturbations of the lunar orbit, they have long been studied, and +the majority of them have been satisfactorily accounted for. It +seems, however, to those who first investigated the question that the +phenomenon of the lunar acceleration could not be explained as a +consequence of solar perturbation, and, as no other agent competent +to produce such effects was recognised by astronomers, the lunar +acceleration presented an unsolved enigma.</p> + +<p>At the end of the last century the illustrious French mathematician +Laplace undertook a new investigation of the famous problem, and was +rewarded with a success which for a long time appeared to be quite +complete. Let us suppose that the moon lies directly between the +earth and the sun, then both earth and moon are pulled towards the +sun by the solar attraction; as, however, the moon is the nearer of +the two bodies to the attracting centre it is pulled the more +energetically, and consequently there is an increase in the distance +between the earth and the moon. Similarly when the moon happens to +lie on the other side of the earth, so that the earth is interposed +directly between the moon and the sun, the solar attraction exerted +upon the earth is more powerful than the same influence upon the +moon. Consequently in this case, also, the distance of the moon from +the earth is increased by the solar disturbance. These instances +will illustrate the general truth, that, as one of the consequences +of the disturbing influence exerted by the sun upon the earth-moon +system, there is an increase in the dimensions of the average orbit +which the moon describes around the earth. As the time required by +the moon to accomplish a journey round the earth depends upon its +distance from the earth, it follows that among the influences of the +sun upon the moon there must be an enlargement of the periodic time, +from what it would have been had there been no solar disturbing +action.</p> + +<p>This was known long before the time of Laplace, but it did not +directly convey any explanation of the lunar acceleration. It no +doubt amounted to the assertion that the moon's periodic time was +slightly augmented by the disturbance, but it did not give any +grounds for suspecting that there was a continuous change in +progress. It was, however, apparent that the periodic time was +connected with the solar disturbance, so that, if there were any +alteration in the amount of the sun's disturbing effect, there must +be a corresponding alteration in the moon's periodic time. Laplace, +therefore, perceived that, if he could discover any continuous change +in the ability of the sun for disturbing the moon, he would then have +accounted for a continuous change in the moon's periodic time, and +that thus an explanation of the long-vexed question of the lunar +acceleration might be forthcoming.</p> + +<p>The capability of the sun for disturbing the earth-moon system is +obviously connected with the distance of the earth from the sun. If +the earth moved in an orbit which underwent no change whatever, then +the efficiency of the sun as a disturbing agent would not undergo any +change of the kind which was sought for. But if there were any +alteration in the shape or size of the earth's orbit, then that might +involve such changes in the distance between the earth and the sun as +would possibly afford the desired agent for producing the observed +lunar effect. It is known that the earth revolves in an orbit which, +though nearly circular, is strictly an ellipse. If the earth were +the only planet revolving around the sun then that ellipse would +remain unaltered from age to age. The earth is, however, only one of +a large number of planets which circulate around the great luminary, +and are guided and controlled by his supreme attracting power. These +planets mutually attract each other, and in consequence of their +mutual attractions the orbits of the planets are disturbed from the +simple elliptic form which they would otherwise possess. The +movement of the earth, for instance, is not, strictly speaking, +performed in an elliptical orbit. We may, however, regard it as +revolving in an ellipse provided we admit that the ellipse is itself +in slow motion.</p> + +<p>It is a remarkable characteristic of the disturbing effects of the +planets that the ellipse in which the earth is at any moment moving +always retains the same length; that is to say, its longest diameter +is invariable. In all other respects the ellipse is continually +changing. It alters its position, it changes its plane, and, most +important of all, it changes its eccentricity. Thus, from age to age +the shape of the track which the earth describes may at one time be +growing more nearly a circle, or at another time may be departing +more widely from a circle. These alterations are very small in +amount, and they take place with extreme slowness, but they are in +incessant progress, and their amount admits of being accurately +calculated. At the present time, and for thousands of years past, as +well as for thousands of years to come, the eccentricity of the +earth's orbit is diminishing, and consequently the orbit described by +the earth each year is becoming more nearly circular. We must, +however, remember that under all circumstances the length of the +longest axis of the ellipse is unaltered, and consequently the size +of the track which the earth describes around the sun is gradually +increasing. In other words, it may be said that during the present +ages the average distance between the earth and the sun is waxing +greater in consequence of the perturbations which the earth +experiences from the attraction of the other planets. We have, +however, already seen that the efficiency of the solar attraction for +disturbing the moon's movement depends on the distance between the +earth and the sun. As therefore the average distance between the +earth and the sun is increasing, at all events during the thousands +of years over which our observations extend, it follows that the +ability of the sun for disturbing the moon must be gradually +diminishing.</p> + +<p><a name="cambridge" id="cambridge"></a></p> + +<div class="figcenter" style="width: 720px;"> +<a href="images/ill_cambridge_observatory.jpg"> +<img src="images/ill_cambridge_observatory_sml.jpg" width="720" height="425" alt="CAMBRIDGE OBSERVATORY." title="" /></a> +<span class="caption">CAMBRIDGE OBSERVATORY.</span> +</div> + +<p>It has been pointed out that, in consequence of the solar +disturbance, the orbit of the moon must be some what enlarged. As it +now appears that the solar disturbance is on the whole declining, it +follows that the orbit of the moon, which has to be adjusted +relatively to the average value of the solar disturbance, must also +be gradually declining. In other words, the moon must be approaching +nearer to the earth in consequence of the alterations in the +eccentricity of the earth's orbit produced by the attraction of the +other planets. It is true that the change in the moon's position +thus arising is an extremely small one, and the consequent effect in +accelerating the moon's motion is but very slight. It is in fact +almost imperceptible, except when great periods of time are +involved. Laplace undertook a calculation on this subject. He knew +what the efficiency of the planets in altering the dimensions of the +earth's orbit amounted to; from this he was able to determine the +changes that would be propagated into the motion of the moon. Thus +he ascertained, or at all events thought he had ascertained, that the +acceleration of the moon's motion, as it had been inferred from the +observations of the ancient eclipses which have been handed down to +us, could be completely accounted for as a consequence of planetary +perturbation. This was regarded as a great scientific triumph. Our +belief in the universality of the law of gravitation would, in fact, +have been seriously challenged unless some explanation of the lunar +acceleration had been forthcoming. For about fifty years no one +questioned the truth of Laplace's investigation. When a +mathematician of his eminence had rendered an explanation of the +remarkable facts of observation which seemed so complete, it is not +surprising that there should have been but little temptation to doubt +it. On undertaking a new calculation of the same question, Professor +Adams found that Laplace had not pursued this approximation +sufficiently far, and that consequently there was a considerable +error in the result of his analysis. Adams, it must be observed, did +not impugn the value of the lunar acceleration which Halley had +deduced from the observations, but what he did show was, that the +calculation by which Laplace thought he had provided an explanation +of this acceleration was erroneous. Adams, in fact, proved that the +planetary influence which Laplace had detected only possessed about +half the efficiency which the great French mathematician had +attributed to it. There were not wanting illustrious mathematicians +who came forward to defend the calculations of Laplace. They +computed the question anew and arrived at results practically +coincident with those he had given. On the other hand certain +distinguished mathematicians at home and abroad verified the results +of Adams. The issue was merely a mathematical one. It had only one +correct solution. Gradually it appeared that those who opposed Adams +presented a number of different solutions, all of them discordant +with his, and, usually, discordant with each other. Adams showed +distinctly where each of these investigators had fallen into error, +and at last it became universally admitted that the Cambridge +Professor had corrected Laplace in a very fundamental point of +astronomical theory.</p> + +<p>Though it was desirable to have learned the truth, yet the breach +between observation and calculation which Laplace was believed to +have closed thus became reopened. Laplace's investigation, had it +been correct, would have exactly explained the observed facts. It +was, however, now shown that his solution was not correct, and that +the lunar acceleration, when strictly calculated as a consequence of +solar perturbations, only produced about half the effect which was +wanted to explain the ancient eclipses completely. It now seems +certain that there is no means of accounting for the lunar +acceleration as a direct consequence of the laws of gravitation, if +we suppose, as we have been in the habit of supposing, that the +members of the solar system concerned may be regarded as rigid +particles. It has, however, been suggested that another explanation +of a very interesting kind may be forthcoming, and this we must +endeavour to set forth.</p> + +<p>It will be remembered that we have to explain why the period of +revolution of the moon is now shorter than it used to be. If we +imagine the length of the period to be expressed in terms of days and +fractions of a day, that is to say, in terms of the rotations of the +earth around its axis, then the difficulty encountered is, that the +moon now requires for each of its revolutions around the earth rather +a smaller number of rotations of the earth around its axis than used +formerly to be the case. Of course this may be explained by the fact +that the moon is now moving more swiftly than of yore, but it is +obvious that an explanation of quite a different kind might be +conceivable. The moon may be moving just at the same pace as ever, +but the length of the day may be increasing. If the length of the +day is increasing, then, of course, a smaller number of days will be +required for the moon to perform each revolution even though the +moon's period was itself really unchanged. It would, therefore, seem +as if the phenomenon known as the lunar acceleration is the result of +the two causes. The first of these is that discovered by Laplace, +though its value was over-estimated by him, in which the perturbations +of the earth by the planets indirectly affect the motion of the +moon. The remaining part of the acceleration of our satellite is +apparent rather than real, it is not that the moon is moving more +quickly, but that our time-piece, the earth, is revolving more +slowly, and is thus actually losing time. It is interesting to note +that we can detect a physical explanation for the apparent checking +of the earth's motion which is thus manifested. The tides which ebb +and flow on the earth exert a brake-like action on the revolving +globe, and there can be no doubt that they are gradually reducing its +speed, and thus lengthening the day. It has accordingly been +suggested that it is this action of the tides which produces the +supplementary effect necessary to complete the physical explanation +of the lunar acceleration, though it would perhaps be a little +premature to assert that this has been fully demonstrated.</p> + +<p>The third of Professor Adams' most notable achievements was connected +with the great shower of November meteors which astonished the world +in 1866. This splendid display concentrated the attention of +astronomers on the theory of the movements of the little objects by +which the display was produced. For the definite discovery of the +track in which these bodies revolve, we are indebted to the labours +of Professor Adams, who, by a brilliant piece of mathematical work, +completed the edifice whose foundations had been laid by Professor +Newton, of Yale, and other astronomers.</p> + +<p>Meteors revolve around the sun in a vast swarm, every individual +member of which pursues an orbit in accordance with the well-known +laws of Kepler. In order to understand the movements of these +objects, to account satisfactorily for their periodic recurrence, and +to predict the times of their appearance, it became necessary to +learn the size and the shape of the track which the swarm followed, +as well as the position which it occupied. Certain features of the +track could no doubt be readily assigned. The fact that the shower +recurs on one particular day of the year, viz., November 13th, +defines one point through which the orbit must pass. The position on +the heavens of the radiant point from which the meteors appear to +diverge, gives another element in the track. The sun must of course +be situated at the focus, so that only one further piece of +information, namely, the periodic time, will be necessary to complete +our knowledge of the movements of the system. Professor H. Newton, +of Yale, had shown that the choice of possible orbits for the +meteoric swarm is limited to five. There is, first, the great +ellipse in which we now know the meteors revolve once every thirty +three and one quarter years. There is next an orbit of a nearly +circular kind in which the periodic time would be a little more than +a year. There is a similar track in which the periodic time would be +a few days short of a year, while two other smaller orbits would also +be conceivable. Professor Newton had pointed out a test by which it +would be possible to select the true orbit, which we know must be one +or other of these five. The mathematical difficulties which attended +the application of this test were no doubt great, but they did not +baffle Professor Adams.</p> + +<p>There is a continuous advance in the date of this meteoric shower. +The meteors now cross our track at the point occupied by the earth on +November 13th, but this point is gradually altering. The only +influence known to us which could account for the continuous change +in the plane of the meteor's orbit arises from the attraction of the +various planets. The problem to be solved may therefore be attacked +in this manner. A specified amount of change in the plane of the +orbit of the meteors is known to arise, and the changes which ought +to result from the attraction of the planets can be computed for each +of the five possible orbits, in one of which it is certain that the +meteors must revolve. Professor Adams undertook the work. Its +difficulty principally arises from the high eccentricity of the +largest of the orbits, which renders the more ordinary methods of +calculation inapplicable. After some months of arduous labour the +work was completed, and in April, 1867, Adams announced his solution +of the problem. He showed that if the meteors revolved in the +largest of the five orbits, with the periodic time of thirty three +and one quarter years, the perturbations of Jupiter would account for +a change to the extent of twenty minutes of arc in the point in which +the orbit crosses the earth's track. The attraction of Saturn would +augment this by seven minutes, and Uranus would add one minute more, +while the influence of the Earth and of the other planets would be +inappreciable. The accumulated effect is thus twenty-eight minutes, +which is practically coincident with the observed value as determined +by Professor Newton from an examination of all the showers of which +there is any historical record. Having thus showed that the great +orbit was a possible path for the meteors, Adams next proved that no +one of the other four orbits would be disturbed in the same manner. +Indeed, it appeared that not half the observed amount of change could +arise in any orbit except in that one with the long period. Thus was +brought to completion the interesting research which demonstrated the +true relation of the meteor swarm to the solar system.</p> + +<p>Besides those memorable scientific labours with which his attention +was so largely engaged, Professor Adams found time for much other +study. He occasionally allowed himself to undertake as a relaxation +some pieces of numerical calculation, so tremendously long that we +can only look on them with astonishment. He has calculated certain +important mathematical constants accurately to more than two hundred +places of decimals. He was a diligent reader of works on history, +geology, and botany, and his arduous labours were often beguiled by +novels, of which, like many other great men, he was very fond. He +had also the taste of a collector, and he brought together about +eight hundred volumes of early printed works, many of considerable +rarity and value. As to his personal character, I may quote the +words of Dr. Glaisher when he says, "Strangers who first met him were +invariably struck by his simple and unaffected manner. He was a +delightful companion, always cheerful and genial, showing in society +but few traces of his really shy and retiring disposition. His +nature was sympathetic and generous, and in few men have the moral +and intellectual qualities been more perfectly balanced."</p> + +<p>In 1863 he married the daughter of Haliday Bruce, Esq., of Dublin and +up to the close of his life he lived at the Cambridge Observatory, +pursuing his mathematical work and enjoying the society of his +friends.</p> + +<p>He died, after a long illness, on 21st January, 1892, and was +interred in St. Giles's Cemetery, on the Huntingdon Road, Cambridge.</p> + +<div>*** END OF THE PROJECT GUTENBERG EBOOK 2298 ***</div> +</body> +</html> + diff --git a/2298-h/images/ill_041.jpg b/2298-h/images/ill_041.jpg Binary files differnew file mode 100644 index 0000000..e70e5b6 --- /dev/null +++ b/2298-h/images/ill_041.jpg diff --git a/2298-h/images/ill_041_sml.jpg b/2298-h/images/ill_041_sml.jpg Binary files differnew file mode 100644 index 0000000..366b55b --- /dev/null +++ b/2298-h/images/ill_041_sml.jpg diff --git a/2298-h/images/ill_7_new_king_st.jpg 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S. Ball + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Great Astronomers + +Author: R. S. Ball + +Posting Date: October 24, 2010 [EBook #2298] +Release Date: August 2000 [EBook #2298] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK GREAT ASTRONOMERS *** + + + + +Produced by Chris Brennen cbrennen@freenet.co.uk +Jill R. Diffendal, Barb Grow pebareka@iexpress.net.au +Christine L. Hall Goleta, CA. USA +Pamela L. Hall pamhall@www.edu +HTML version produced by Chuck Greif + + + + + +</pre> + + +<div class="figcenter" style="width: 550px;"> +<a href="images/ill_front.jpg"> +<img src="images/ill_front_sml.jpg" width="550" height="338" alt="GREENWICH OBSERVATORY." title="" /></a> +<span class="caption">GREENWICH OBSERVATORY.</span> +</div> + +<h1>GREAT ASTRONOMERS</h1> + +<p class="c"><b>by</b></p> + +<p class="c"><b><big>SIR ROBERT S. BALL D.Sc. LL.D. F.R.S.</big></b></p> + +<p class="c"><b><small>Lowndean Professor of Astronomy and Geometry in the +University of Cambridge<br /> +Author of "In Starry Realms" "In the High Heavens" etc.</small></b></p> + +<p class="c"><b>WITH NUMEROUS ILLUSTRATIONS</b></p> + +<p><a name="greenwich" id="greenwich"></a></p> + +<h3><a name="PREFACE" id="PREFACE"></a>PREFACE.</h3> +<p>It has been my object in these pages to present the life of each +astronomer in such detail as to enable the reader to realise in +some degree the man's character and surroundings; and I have +endeavoured to indicate as clearly as circumstances would permit +the main features of the discoveries by which he has become known.</p> + +<p>There are many types of astronomers—from the stargazer who merely +watches the heavens, to the abstract mathematician who merely +works at his desk; it has, consequently, been necessary in the +case of some lives to adopt a very different treatment from that +which seemed suitable for others.</p> + +<p>While the work was in progress, some of the sketches appeared in +"Good Words." The chapter on Brinkley has been chiefly derived from +an article on the "History of Dunsink Observatory," which was +published on the occasion of the tercentenary celebration of the +University of Dublin in 1892, and the life of Sir William Rowan +Hamilton is taken, with a few alterations and omissions, from an +article contributed to the "Quarterly Review" on Graves' life of +the great mathematician. The remaining chapters now appear for +the first time. For many of the facts contained in the sketch of +the late Professor Adams, I am indebted to the obituary notice +written by my friend Dr. J. W. L. Glaisher, for the Royal Astronomical +Society; while with regard to the late Sir George Airy, I have a +similar acknowledgment to make to Professor H. H. Turner. To my +friend Dr. Arthur A. Rambaut I owe my hearty thanks for his +kindness in aiding me in the revision of the work.</p> + +<p class="r">R.S.B.</p> +<p class="nind"><small>The Observatory, Cambridge.<br /> +October, 1895</small></p> + +<h3><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h3> +<table border="0" cellpadding="0" cellspacing="0" summary=""> +<tr><td align="left"><a href="#PREFACE">P<small>REFACE</small>.</a></td></tr> +<tr><td align="left"><a href="#INTRODUCTION">I<small>NTRODUCTION</small>.</a></td></tr> +<tr><td align="left"><a href="#PTOLEMY">P<small>TOLEMY</small>.</a></td></tr> +<tr><td align="left"><a href="#COPERNICUS">C<small>OPERNICUS</small>.</a></td></tr> +<tr><td align="left"><a href="#TYCHO_BRAHE">T<small>YCHO</small> B<small>RAHE</small>.</a></td></tr> +<tr><td align="left"><a href="#GALILEO">G<small>ALILEO</small>.</a></td></tr> +<tr><td align="left"><a href="#KEPLER">K<small>EPLER</small>.</a></td></tr> +<tr><td align="left"><a href="#ISAAC_NEWTON">I<small>SAAC</small> N<small>EWTON</small>.</a></td></tr> +<tr><td align="left"><a href="#FLAMSTEED">F<small>LAMSTEED</small>.</a></td></tr> +<tr><td align="left"><a href="#HALLEY">H<small>ALLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#BRADLEY">B<small>RADLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#WILLIAM_HERSCHEL">W<small>ILLIAM</small> H<small>ERSCHEL</small>.</a></td></tr> +<tr><td align="left"><a href="#LAPLACE">L<small>APLACE</small>.</a></td></tr> +<tr><td align="left"><a href="#BRINKLEY">B<small>RINKLEY</small>.</a></td></tr> +<tr><td align="left"><a href="#JOHN_HERSCHEL">J<small>OHN</small> H<small>ERSCHEL</small>.</a></td></tr> +<tr><td align="left"><a href="#THE_EARL_OF_ROSSE">T<small>HE</small> E<small>ARL OF</small> R<small>OSSE</small>.</a></td></tr> +<tr><td align="left"><a href="#AIRY">A<small>IRY</small>.</a></td></tr> +<tr><td align="left"><a href="#HAMILTON">H<small>AMILTON</small>.</a></td></tr> +<tr><td align="left"><a href="#LE_VERRIER">L<small>E</small> V<small>ERRIER</small>.</a></td></tr> +<tr><td align="left"><a href="#ADAMS">A<small>DAMS</small>.</a></td></tr> +</table> + +<h3><a name="LIST_OF_ILLUSTRATIONS" id="LIST_OF_ILLUSTRATIONS"></a>LIST OF ILLUSTRATIONS.</h3> + +<p class="c"><small>[Note of etext transcriber: The illustrations by be seen enlarged by clicking on them.]</small></p> + +<ul> +<li><a href="#greenwich">THE OBSERVATORY, GREENWICH.</a></li> + +<li><a href="#PTOLEMY">PTOLEMY.</a></li> + +<li><a href="#fig_1">PTOLEMY'S PLANETARY SCHEME.</a></li> + +<li><a href="#fig_2">PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.</a></li> + +<li><a href="#thorn">THORN, FROM AN OLD PRINT.</a></li> + +<li><a href="#copernicus_ill">COPERNICUS.</a></li> + +<li><a href="#frauenburg">FRAUENBURG, FROM AN OLD PRINT.</a></li> + +<li><a href="#explanation">EXPLANATION OF PLANETARY MOVEMENTS.</a></li> + +<li><a href="#tycho">TYCHO BRAHE.</a></li> + +<li><a href="#tycho_ill">TYCHO'S CROSS STAFF.</a></li> + +<li><a href="#new_star">TYCHO'S "NEW STAR" SEXTANT OF 1572.</a></li> + +<li><a href="#trigonic_sextant">TYCHO'S TRIGONIC SEXTANT.</a></li> + +<li><a href="#astronomic_sextant">TYCHO'S ASTRONOMIC SEXTANT.</a></li> + +<li><a href="#equatorial_armillary">TYCHO'S EQUATORIAL ARMILLARY.</a></li> + +<li><a href="#augsburg_quadrant">THE GREAT AUGSBURG QUADRANT.</a></li> + +<li><a href="#new_scheme">TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.</a></li> + +<li><a href="#uraniborg">URANIBORG AND ITS GROUNDS.</a></li> + +<li><a href="#grnd_pln_uraniborg">GROUND-PLAN OF THE OBSERVATORY.</a></li> + +<li><a href="#uraniborg_hven">THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.</a></li> + +<li><a href="#effigy">EFFIGY ON TYCHO'S TOMB AT PRAGUE.</a> +<ul><li>By Permission of Messrs. A. & C. Black.</li></ul></li> +<li><a href="#quadrant">TYCHO'S MURAL QUADRANT, URANIBORG.</a></li> + +<li><a href="#galileo_pendulum">GALILEO'S PENDULUM.</a></li> + +<li><a href="#portrait">GALILEO.</a></li> + +<li><a href="#arcetri">THE VILLA ARCETRI.</a></li> + +<li><a href="#facsimile">FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.</a></li> + +<li><a href="#crest">CREST OF GALILEO'S FAMILY.</a></li> + +<li><a href="#solids">KEPLER'S SYSTEM OF REGULAR SOLIDS.</a></li> + +<li><a href="#kepler_ill">KEPLER.</a></li> + +<li><a href="#symbolical">SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.</a></li> + +<li><a href="#commemoration">THE COMMEMORATION OF THE RUDOLPHINE TABLES.</a></li> + +<li><a href="#woolsthorpe">WOOLSTHORPE MANOR.</a></li> + +<li><a href="#trinity">TRINITY COLLEGE, CAMBRIDGE.</a></li> + +<li><a href="#diagram">DIAGRAM OF A SUNBEAM.</a></li> + +<li><a href="#isaac">ISAAC NEWTON.</a></li> + +<li><a href="#newton_reflector">SIR ISAAC NEWTON'S LITTLE REFLECTOR.</a></li> + +<li><a href="#sun-dial">SIR ISAAC NEWTON'S SUN-DIAL.</a></li> + +<li><a href="#newton_telescope">SIR ISAAC NEWTON'S TELESCOPE.</a></li> + +<li><a href="#newton_astrolabe">SIR ISAAC NEWTON'S ASTROLABE.</a></li> + +<li><a href="#royal_society">SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.</a></li> + +<li><a href="#flamsteed_house">FLAMSTEED'S HOUSE.</a></li> + +<li><a href="#flamsteed_ill">FLAMSTEED.</a></li> + +<li><a href="#halley_ill">HALLEY.</a></li> + +<li><a href="#greenwich_observatory">GREENWICH OBSERVATORY IN HALLEY'S TIME.</a></li> + +<li><a href="#new_king">7, NEW KING STREET, BATH.</a><ul> +<li>From a Photograph by John Poole, Bath.</li></ul></li> + +<li><a href="#william">WILLIAM HERSCHEL.</a></li> + +<li><a href="#caroline">CAROLINE HERSCHEL.</a></li> + +<li><a href="#street">STREET VIEW, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#garden">GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#view_herschel_house">OBSERVATORY, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#telescope_slough">THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH.</a><ul> +<li>From a Photograph by Hill & Saunders, Eton.</li></ul></li> + +<li><a href="#laplace_ill">LAPLACE.</a></li> + +<li><a href="#dunsink">THE OBSERVATORY, DUNSINK.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#astronometer">ASTRONOMETER MADE BY SIR JOHN HERSCHEL.</a></li> + +<li><a href="#john_herschel_ill">SIR JOHN HERSCHEL.</a></li> + +<li><a href="#nebula">NEBULA IN SOUTHERN HEMISPHERE.</a></li> + +<li><a href="#centaur">THE CLUSTER IN THE CENTAUR.</a></li> + +<li><a href="#herschel_observatory_feldhausen">OBSERVATORY AT FELDHAUSEN.</a></li> + +<li><a href="#column">GRANITE COLUMN AT FELDHAUSEN.</a></li> + +<li><a href="#rosse_ill">THE EARL OF ROSSE.</a></li> + +<li><a href="#birr">BIRR CASTLE.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#mall">THE MALL, PARSONSTOWN.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#lord_rosse_telescope">LORD ROSSE'S TELESCOPE.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#roman">ROMAN CATHOLIC CHURCH, PARSONSTOWN.</a><ul> +<li>From a Photograph by W. Lawrence, Dublin.</li></ul></li> + +<li><a href="#sir_airy">AIRY.</a><ul> +<li>From a Photograph by E.P. Adams, Greenwich.</li></ul></li> + +<li><a href="#rowan_hamilton">HAMILTON.</a></li> + +<li><a href="#john">ADAMS.</a></li> + +<li><a href="#cambridge">THE OBSERVATORY, CAMBRIDGE.</a></li> +</ul> +<h3><a name="INTRODUCTION" id="INTRODUCTION"></a>INTRODUCTION.</h3> +<p>Of all the natural sciences there is not one which offers such +sublime objects to the attention of the inquirer as does the science +of astronomy. From the earliest ages the study of the stars has +exercised the same fascination as it possesses at the present day. +Among the most primitive peoples, the movements of the sun, the moon, +and the stars commanded attention from their supposed influence on +human affairs.</p> + +<p>The practical utilities of astronomy were also obvious in primeval +times. Maxims of extreme antiquity show how the avocations of the +husbandman are to be guided by the movements of the heavenly bodies. +The positions of the stars indicated the time to plough, and the time +to sow. To the mariner who was seeking a way across the trackless +ocean, the heavenly bodies offered the only reliable marks by which +his path could be guided. There was, accordingly, a stimulus both +from intellectual curiosity and from practical necessity to follow +the movements of the stars. Thus began a search for the causes of +the ever-varying phenomena which the heavens display.</p> + +<p>Many of the earliest discoveries are indeed prehistoric. The great +diurnal movement of the heavens, and the annual revolution of the +sun, seem to have been known in times far more ancient than those to +which any human monuments can be referred. The acuteness of the +early observers enabled them to single out the more important of the +wanderers which we now call planets. They saw that the star-like +objects, Jupiter, Saturn, and Mars, with the more conspicuous Venus, +constituted a class of bodies wholly distinct from the fixed stars +among which their movements lay, and to which they bear such a +superficial resemblance. But the penetration of the early +astronomers went even further, for they recognized that Mercury also +belongs to the same group, though this particular object is seen so +rarely. It would seem that eclipses and other phenomena were +observed at Babylon from a very remote period, while the most ancient +records of celestial observations that we possess are to be found in +the Chinese annals.</p> + +<p>The study of astronomy, in the sense in which we understand the word, +may be said to have commenced under the reign of the Ptolemies at +Alexandria. The most famous name in the science of this period is +that of Hipparchus who lived and worked at Rhodes about the year +160BC. It was his splendid investigations that first wrought the +observed facts into a coherent branch of knowledge. He recognized +the primary obligation which lies on the student of the heavens to +compile as complete an inventory as possible of the objects which are +there to be found. Hipparchus accordingly commenced by undertaking, +on a small scale, a task exactly similar to that on which modern +astronomers, with all available appliances of meridian circles, and +photographic telescopes, are constantly engaged at the present day. +He compiled a catalogue of the principal fixed stars, which is of +special value to astronomers, as being the earliest work of its kind +which has been handed down. He also studied the movements of the sun +and the moon, and framed theories to account for the incessant +changes which he saw in progress. He found a much more difficult +problem in his attempt to interpret satisfactorily the complicated +movements of the planets. With the view of constructing a theory +which should give some coherent account of the subject, he made many +observations of the places of these wandering stars. How great were +the advances which Hipparchus accomplished may be appreciated if we +reflect that, as a preliminary task to his more purely astronomical +labours, he had to invent that branch of mathematical science by +which alone the problems he proposed could be solved. It was for +this purpose that he devised the indispensable method of calculation +which we now know so well as trigonometry. Without the aid rendered +by this beautiful art it would have been impossible for any really +important advance in astronomical calculation to have been effected.</p> + +<p>But the discovery which shows, beyond all others, that Hipparchus +possessed one of the master-minds of all time was the detection of +that remarkable celestial movement known as the precession of the +equinoxes. The inquiry which conducted to this discovery involved a +most profound investigation, especially when it is remembered that in +the days of Hipparchus the means of observation of the heavenly +bodies were only of the rudest description, and the available +observations of earlier dates were extremely scanty. We can but look +with astonishment on the genius of the man who, in spite of such +difficulties, was able to detect such a phenomenon as the precession, +and to exhibit its actual magnitude. I shall endeavour to explain +the nature of this singular celestial movement, for it may be said to +offer the first instance in the history of science in which we find +that combination of accurate observation with skilful interpretation, +of which, in the subsequent development of astronomy, we have so many +splendid examples.</p> + +<p>The word equinox implies the condition that the night is equal to the +day. To a resident on the equator the night is no doubt equal to the +day at all times in the year, but to one who lives on any other part +of the earth, in either hemisphere, the night and the day are not +generally equal. There is, however, one occasion in spring, and +another in autumn, on which the day and the night are each twelve +hours at all places on the earth. When the night and day are equal +in spring, the point which the sun occupies on the heavens is termed +the vernal equinox. There is similarly another point in which the +sun is situated at the time of the autumnal equinox. In any +investigation of the celestial movements the positions of these two +equinoxes on the heavens are of primary importance, and Hipparchus, +with the instinct of genius, perceived their significance, and +commenced to study them. It will be understood that we can always +define the position of a point on the sky with reference to the +surrounding stars. No doubt we do not see the stars near the sun +when the sun is shining, but they are there nevertheless. The +ingenuity of Hipparchus enabled him to determine the positions of +each of the two equinoxes relatively to the stars which lie in its +immediate vicinity. After examination of the celestial places of +these points at different periods, he was led to the conclusion that +each equinox was moving relatively to the stars, though that movement +was so slow that twenty five thousand years would necessarily elapse +before a complete circuit of the heavens was accomplished. Hipparchus +traced out this phenomenon, and established it on an impregnable +basis, so that all astronomers have ever since recognised the +precession of the equinoxes as one of the fundamental facts of +astronomy. Not until nearly two thousand years after Hipparchus had +made this splendid discovery was the explanation of its cause given +by Newton.</p> + +<p>From the days of Hipparchus down to the present hour the science of +astronomy has steadily grown. One great observer after another has +appeared from time to time, to reveal some new phenomenon with regard +to the celestial bodies or their movements, while from time to time +one commanding intellect after another has arisen to explain the true +import of the facts of observations. The history of astronomy thus +becomes inseparable from the history of the great men to whose +labours its development is due.</p> + +<p>In the ensuing chapters we have endeavoured to sketch the lives and +the work of the great philosophers, by whose labours the science of +astronomy has been created. We shall commence with Ptolemy, who, +after the foundations of the science had been laid by Hipparchus, +gave to astronomy the form in which it was taught throughout the +Middle Ages. We shall next see the mighty revolution in our +conceptions of the universe which are associated with the name of +Copernicus. We then pass to those periods illumined by the genius of +Galileo and Newton, and afterwards we shall trace the careers of +other more recent discoverers, by whose industry and genius the +boundaries of human knowledge have been so greatly extended. Our +history will be brought down late enough to include some of the +illustrious astronomers who laboured in the generation which has just +passed away.</p> + +<h3><a name="PTOLEMY" id="PTOLEMY"></a>PTOLEMY.</h3> + +<div class="figcenter" style="width: 410px;"> +<a href="images/ill_ptolemy.jpg"> +<img src="images/ill_ptolemy_sml.jpg" width="410" height="486" alt="PTOLEMY." title="" /></a> +<span class="caption">PTOLEMY.</span> +</div> + +<p>The career of the famous man whose name stands at the head of this +chapter is one of the most remarkable in the history of human +learning. There may have been other discoverers who have done more +for science than ever Ptolemy accomplished, but there never has been +any other discoverer whose authority on the subject of the movements +of the heavenly bodies has held sway over the minds of men for so +long a period as the fourteen centuries during which his opinions +reigned supreme. The doctrines he laid down in his famous book, "The +Almagest," prevailed throughout those ages. No substantial addition +was made in all that time to the undoubted truths which this work +contained. No important correction was made of the serious errors +with which Ptolemy's theories were contaminated. The authority of +Ptolemy as to all things in the heavens, and as to a good many things +on the earth (for the same illustrious man was also a diligent +geographer), was invariably final.</p> + +<p>Though every child may now know more of the actual truths of the +celestial motions than ever Ptolemy knew, yet the fact that his work +exercised such an astonishing effect on the human intellect for some +sixty generations, shows that it must have been an extraordinary +production. We must look into the career of this wonderful man to +discover wherein lay the secret of that marvellous success which made +him the unchallenged instructor of the human race for such a +protracted period.</p> + +<p>Unfortunately, we know very little as to the personal history of +Ptolemy. He was a native of Egypt, and though it has been sometimes +conjectured that he belonged to the royal families of the same name, +yet there is nothing to support such a belief. The name, Ptolemy, +appears to have been a common one in Egypt in those days. The time +at which he lived is fixed by the fact that his first recorded +observation was made in 127 AD, and his last in 151 AD. When we add +that he seems to have lived in or near Alexandria, or to use his own +words, "on the parallel of Alexandria," we have said everything that +can be said so far as his individuality is concerned.</p> + +<p>Ptolemy is, without doubt, the greatest figure in ancient astronomy. +He gathered up the wisdom of the philosophers who had preceded him. +He incorporated this with the results of his own observations, and +illumined it with his theories. His speculations, even when they +were, as we now know, quite erroneous, had such an astonishing +verisimilitude to the actual facts of nature that they commanded +universal assent. Even in these modern days we not unfrequently find +lovers of paradox who maintain that Ptolemy's doctrines not only seem +true, but actually are true.</p> + +<p>In the absence of any accurate knowledge of the science of mechanics, +philosophers in early times were forced to fall back on certain +principles of more or less validity, which they derived from their +imagination as to what the natural fitness of things ought to be. +There was no geometrical figure so simple and so symmetrical as a +circle, and as it was apparent that the heavenly bodies pursued +tracks which were not straight lines, the conclusion obviously +followed that their movements ought to be circular. There was no +argument in favour of this notion, other than the merely imaginary +reflection that circular movement, and circular movement alone, was +"perfect," whatever "perfect" may have meant. It was further +believed to be impossible that the heavenly bodies could have any +other movements save those which were perfect. Assuming this, it +followed, in Ptolemy's opinion, and in that of those who came after +him for fourteen centuries, that all the tracks of the heavenly +bodies were in some way or other to be reduced to circles.</p> + +<p>Ptolemy succeeded in devising a scheme by which the apparent changes +that take place in the heavens could, so far as he knew them, be +explained by certain combinations of circular movement. This seemed +to reconcile so completely the scheme of things celestial with the +geometrical instincts which pointed to the circle as the type of +perfect movement, that we can hardly wonder Ptolemy's theory met with +the astonishing success that attended it. We shall, therefore, set +forth with sufficient detail the various steps of this famous +doctrine.</p> + +<p>Ptolemy commences with laying down the undoubted truth that the shape +of the earth is globular. The proofs which he gives of this +fundamental fact are quite satisfactory; they are indeed the same +proofs as we give today. There is, first of all, the well-known +circumstance of which our books on geography remind us, that when an +object is viewed at a distance across the sea, the lower part of the +object appears cut off by the interposing curved mass of water.</p> + +<p>The sagacity of Ptolemy enabled him to adduce another argument, +which, though not quite so obvious as that just mentioned, +demonstrates the curvature of the earth in a very impressive manner +to anyone who will take the trouble to understand it. Ptolemy +mentions that travellers who went to the south reported, that, as +they did so, the appearance of the heavens at night underwent a +gradual change. Stars that they were familiar with in the northern +skies gradually sank lower in the heavens. The constellation of the +Great Bear, which in our skies never sets during its revolution round +the pole, did set and rise when a sufficient southern latitude had +been attained. On the other hand, constellations new to the +inhabitants of northern climes were seen to rise above the southern +horizon. These circumstances would be quite incompatible with the +supposition that the earth was a flat surface. Had this been so, a +little reflection will show that no such changes in the apparent +movements of the stars would be the consequence of a voyage to the +south. Ptolemy set forth with much insight the significance of this +reasoning, and even now, with the resources of modern discoveries to +help us, we can hardly improve upon his arguments.</p> + +<p>Ptolemy, like a true philosopher disclosing a new truth to the world, +illustrated and enforced his subject by a variety of happy +demonstrations. I must add one of them, not only on account of its +striking nature, but also because it exemplifies Ptolemy's +acuteness. If the earth were flat, said this ingenious reasoner, +sunset must necessarily take place at the same instant, no matter in +what country the observer may happen to be placed. Ptolemy, however, +proved that the time of sunset did vary greatly as the observer's +longitude was altered. To us, of course, this is quite obvious; +everybody knows that the hour of sunset may have been reached in +Great Britain while it is still noon on the western coast of +America. Ptolemy had, however, few of those sources of knowledge +which are now accessible. How was he to show that the sun actually +did set earlier at Alexandria than it would in a city which lay a +hundred miles to the west? There was no telegraph wire by which +astronomers at the two Places could communicate. There was no +chronometer or watch which could be transported from place to place; +there was not any other reliable contrivance for the keeping of +time. Ptolemy's ingenuity, however, pointed out a thoroughly +satisfactory method by which the times of sunset at two places could +be compared. He was acquainted with the fact, which must indeed have +been known from the very earliest times, that the illumination of the +moon is derived entirely from the sun. He knew that an eclipse of +the moon was due to the interposition of the earth which cuts off the +light of the sun. It was, therefore, plain that an eclipse of the +moon must be a phenomenon which would begin at the same instant from +whatever part of the earth the moon could be seen at the time. +Ptolemy, therefore, brought together from various quarters the local +times at which different observers had recorded the beginning of a +lunar eclipse. He found that the observers to the west made the time +earlier and earlier the further away their stations were from +Alexandria. On the other hand, the eastern observers set down the +hour as later than that at which the phenomenon appeared at +Alexandria. As these observers all recorded something which indeed +appeared to them simultaneously, the only interpretation was, that +the more easterly a place the later its time. Suppose there were a +number of observers along a parallel of latitude, and each noted the +hour of sunset to be six o'clock, then, since the eastern times are +earlier than western times, 6 p.m. at one station A will correspond +to 5 p.m. at a station B sufficiently to the west. If, therefore, +it is sunset to the observer at A, the hour of sunset will not yet be +reached for the observer at B. This proves conclusively that the +time of sunset is not the same all over the earth. We have, however, +already seen that the apparent time of sunset would be the same from +all stations if the earth were flat. When Ptolemy, therefore, +demonstrated that the time of sunset was not the same at various +places, he showed conclusively that the earth was not flat.</p> + +<p>As the same arguments applied to all parts of the earth where Ptolemy +had either been himself, or from which he could gain the necessary +information, it followed that the earth, instead of being the flat +plain, girdled with an illimitable ocean, as was generally supposed, +must be in reality globular. This led at once to a startling +consequence. It was obvious that there could be no supports of any +kind by which this globe was sustained; it therefore followed that +the mighty object must be simply poised in space. This is indeed an +astonishing doctrine to anyone who relies on what merely seems the +evidence of the senses, without giving to that evidence its due +intellectual interpretation. According to our ordinary experience, +the very idea of an object poised without support in space, appears +preposterous. Would it not fall? we are immediately asked. Yes, +doubtless it could not remain poised in any way in which we try the +experiment. We must, however, observe that there are no such ideas +as upwards or downwards in relation to open space. To say that a +body falls downwards, merely means that it tries to fall as nearly as +possible towards the centre of the earth. There is no one direction +along which a body will tend to move in space, in preference to any +other. This may be illustrated by the fact that a stone let fall at +New Zealand will, in its approach towards the earth's centre, be +actually moving upwards as far as any locality in our hemisphere is +concerned. Why, then, argued Ptolemy, may not the earth remain +poised in space, for as all directions are equally upward or equally +downward, there seems no reason why the earth should require any +support? By this reasoning he arrives at the fundamental conclusion +that the earth is a globular body freely lying in space, and +surrounded above, below, and on all sides by the glittering stars of +heaven.</p> + +<p>The perception of this sublime truth marks a notable epoch in the +history of the gradual development of the human intellect. No doubt, +other philosophers, in groping after knowledge, may have set forth +certain assertions that are more or less equivalent to this +fundamental truth. It is to Ptolemy we must give credit, however, +not only for announcing this doctrine, but for demonstrating it by +clear and logical argument. We cannot easily project our minds back +to the conception of an intellectual state in which this truth was +unfamiliar. It may, however, be well imagined that, to one who +thought the earth was a flat plain of indefinite extent, it would be +nothing less than an intellectual convulsion for him to be forced to +believe that he stood upon a spherical earth, forming merely a +particle relatively to the immense sphere of the heavens.</p> + +<p>What Ptolemy saw in the movements of the stars led him to the +conclusion that they were bright points attached to the inside of a +tremendous globe. The movements of this globe which carried the +stars were only compatible with the supposition that the earth +occupied its centre. The imperceptible effect produced by a change +in the locality of the observer on the apparent brightness of the +stars made it plain that the dimensions of the terrestrial globe must +be quite insignificant in comparison with those of the celestial +sphere. The earth might, in fact, be regarded as a grain of sand +while the stars lay upon a globe many yards in diameter.</p> + +<p>So tremendous was the revolution in human knowledge implied by this +discovery, that we can well imagine how Ptolemy, dazzled as it were +by the fame which had so justly accrued to him, failed to make one +further step. Had he made that step, it would have emancipated the +human intellect from the bondage of fourteen centuries of servitude +to a wholly monstrous notion of this earth's importance in the scheme +of the heavens. The obvious fact that the sun, the moon, and the +stars rose day by day, moved across the sky in a glorious +never-ending procession, and duly set when their appointed courses +had been run, demanded some explanation. The circumstance that the +fixed stars preserved their mutual distances from year to year, and +from age to age, appeared to Ptolemy to prove that the sphere which +contained those stars, and on whose surface they were believed by him +to be fixed, revolved completely around the earth once every day. He +would thus account for all the phenomena of rising and setting +consistently with the supposition that our globe was stationary. +Probably this supposition must have appeared monstrous, even to +Ptolemy. He knew that the earth was a gigantic object, but, large as +it may have been, he knew that it was only a particle in comparison +with the celestial sphere, yet he apparently believed, and certainly +succeeded in persuading other men to believe, that the celestial +sphere did actually perform these movements.</p> + +<p>Ptolemy was an excellent geometer. He knew that the rising and the +setting of the sun, the moon, and the myriad stars, could have been +accounted for in a different way. If the earth turned round +uniformly once a day while poised at the centre of the sphere of the +heavens, all the phenomena of rising and setting could be completely +explained. This is, indeed, obvious after a moment's reflection. +Consider yourself to be standing on the earth at the centre of the +heavens. There are stars over your head, and half the contents of +the heavens are visible, while the other half are below your +horizon. As the earth turns round, the stars over your head will +change, and unless it should happen that you have taken up your +position at either of the poles, new stars will pass into your view, +and others will disappear, for at no time can you have more than half +of the whole sphere visible. The observer on the earth would, +therefore, say that some stars were rising, and that some stars were +setting. We have, therefore, two totally distinct methods, each of +which would completely explain all the observed facts of the diurnal +movement. One of these suppositions requires that the celestial +sphere, bearing with it the stars and other celestial bodies, turns +uniformly around an invisible axis, while the earth remains +stationary at the centre. The other supposition would be, that it is +the stupendous celestial sphere which remains stationary, while the +earth at the centre rotates about the same axis as the celestial +sphere did before, but in an opposite direction, and with a uniform +velocity which would enable it to complete one turn in twenty-four +hours. Ptolemy was mathematician enough to know that either of these +suppositions would suffice for the explanation of the observed +facts. Indeed, the phenomena of the movements of the stars, so far +as he could observe them, could not be called upon to pronounce which +of these views was true, and which was false.</p> + +<p>Ptolemy had, therefore, to resort for guidance to indirect lines of +reasoning. One of these suppositions must be true, and yet it +appeared that the adoption of either was accompanied by a great +difficulty. It is one of his chief merits to have demonstrated that +the celestial sphere was so stupendous that the earth itself was +absolutely insignificant in comparison therewith. If, then, this +stupendous sphere rotated once in twenty-four hours, the speed with +which the movement of some of the stars must be executed would be so +portentous as to seem well-nigh impossible. It would, therefore, +seem much simpler on this ground to adopt the other alternative, and +to suppose the diurnal movements were due to the rotation of the +earth. Here Ptolemy saw, or at all events fancied he saw, objections +of the weightiest description. The evidence of the senses appeared +directly to controvert the supposition that this earth is anything +but stationary. Ptolemy might, perhaps, have dismissed this +objection on the ground that the testimony of the senses on such a +matter should be entirely subordinated to the interpretation which +our intelligence would place upon the facts to which the senses +deposed. Another objection, however, appeared to him to possess the +gravest moment. It was argued that if the earth were rotating, there +is nothing to make the air participate in this motion, mankind would +therefore be swept from the earth by the furious blasts which would +arise from the movement of the earth through an atmosphere at rest. +Even if we could imagine that the air were carried round with the +earth, the same would not apply, so thought Ptolemy, to any object +suspended in the air. So long as a bird was perched on a tree, he +might very well be carried onward by the moving earth, but the moment +he took wing, the ground would slip from under him at a frightful +pace, so that when he dropped down again he would find himself at a +distance perhaps ten times as great as that which a carrier-pigeon or +a swallow could have traversed in the same time. Some vague delusion +of this description seems even still to crop up occasionally. I +remember hearing of a proposition for balloon travelling of a very +remarkable kind. The voyager who wanted to reach any other place in +the same latitude was simply to ascend in a balloon, and wait there +till the rotation of the earth conveyed the locality which happened +to be his destination directly beneath him, whereupon he was to let +out the gas and drop down! Ptolemy knew quite enough natural +philosophy to be aware that such a proposal for locomotion would be +an utter absurdity; he knew that there was no such relative shift +between the air and the earth as this motion would imply. It +appeared to him to be necessary that the air should lag behind, if +the earth had been animated by a movement of rotation. In this he +was, as we know, entirely wrong. There were, however, in his days no +accurate notions on the subject of the laws of motion.</p> + +<p>Assiduous as Ptolemy may have been in the study of the heavenly +bodies, it seems evident that he cannot have devoted much thought to +the phenomena of motion of terrestrial objects. Simple, indeed, are +the experiments which might have convinced a philosopher much less +acute than Ptolemy, that, if the earth did revolve, the air must +necessarily accompany it. If a rider galloping on horseback tosses a +ball into the air, it drops again into his hand, just as it would +have done had he been remaining at rest during the ball's flight; the +ball in fact participates in the horizontal motion, so that though it +really describes a curve as any passer-by would observe, yet it +appears to the rider himself merely to move up and down in a straight +line. This fact, and many others similar to it, demonstrate clearly +that if the earth were endowed with a movement of rotation, the +atmosphere surrounding it must participate in that movement. Ptolemy +did not know this, and consequently he came to the conclusion that +the earth did not rotate, and that, therefore, notwithstanding the +tremendous improbability of so mighty an object as the celestial +sphere spinning round once in every twenty-four hours, there was no +course open except to believe that this very improbable thing did +really happen. Thus it came to pass that Ptolemy adopted as the +cardinal doctrine of his system a stationary earth poised at the +centre of the celestial sphere, which stretched around on all sides +at a distance so vast that the diameter of the earth was an +inappreciable point in comparison therewith.</p> + +<p>Ptolemy having thus deliberately rejected the doctrine of the earth's +rotation, had to make certain other entirely erroneous suppositions. +It was easily seen that each star required exactly the same period +for the performance of a complete revolution of the heavens. Ptolemy +knew that the stars were at enormous distances from the earth, though +no doubt his notions on this point came very far short of what we +know to be the reality. If the stars had been at very varied +distances, then it would be so wildly improbable that they should all +accomplish their revolutions in the same time, that Ptolemy came to +the conclusion that they must be all at the same distance, that is, +that they must be all on the surface of a sphere. This view, however +erroneous, was corroborated by the obvious fact that the stars in the +constellations preserved their relative places unaltered for +centuries. Thus it was that Ptolemy came to the conclusion that they +were all fixed on one spherical surface, though we are not informed +as to the material of this marvellous setting which sustained the +stars like jewels.</p> + +<p>Nor should we hastily pronounce this doctrine to be absurd. The +stars do appear to lie on the surface of a sphere, of which the +observer is at the centre; not only is this the aspect which the +skies present to the untechnical observer, but it is the aspect in +which the skies are presented to the most experienced astronomer of +modern days. No doubt he knows well that the stars are at the most +varied distances from him; he knows that certain stars are ten times, +or a hundred times, or a thousand times, as far as other stars. +Nevertheless, to his eye the stars appear on the surface of the +sphere, it is on that surface that his measurements of the relative +places of the stars are made; indeed, it may be said that almost all +the accurate observations in the observatory relate to the places of +the stars, not as they really are, but as they appear to be projected +on that celestial sphere whose conception we owe to the genius of +Ptolemy.</p> + +<p>This great philosopher shows very ingeniously that the earth must be +at the centre of the sphere. He proves that, unless this were the +case, each star would not appear to move with the absolute uniformity +which does, as a matter of fact, characterise it. In all these +reasonings we cannot but have the most profound admiration for the +genius of Ptolemy, even though he had made an error so enormous in +the fundamental point of the stability of the earth. Another error +of a somewhat similar kind seemed to Ptolemy to be demonstrated. He +had shown that the earth was an isolated object in space, and being +such was, of course, capable of movement. It could either be turned +round, or it could be moved from one place to another. We know that +Ptolemy deliberately adopted the view that the earth did not turn +round; he had then to investigate the other question, as to whether +the earth was animated by any movement of translation. He came to +the conclusion that to attribute any motion to the earth would be +incompatible with the truths at which he had already arrived. The +earth, argued Ptolemy, lies at the centre of the celestial sphere. +If the earth were to be endowed with movement, it would not lie +always at this point, it must, therefore, shift to some other part of +the sphere. The movements of the stars, however, preclude the +possibility of this; and, therefore, the earth must be as devoid of +any movement of translation as it is devoid of rotation. Thus it was +that Ptolemy convinced himself that the stability of the earth, as it +appeared to the ordinary senses, had a rational philosophical +foundation.</p> + +<p>Not unfrequently it is the lot of the philosophers to contend against +the doctrines of the vulgar, but when it happens, as in the case of +Ptolemy's researches, that the doctrines of the vulgar are +corroborated by philosophical investigation which bear the stamp of +the highest authority, it is not to be wondered at that such +doctrines should be deemed well-nigh impregnable. In this way we +may, perhaps, account for the remarkable fact that the theories of +Ptolemy held unchallenged sway over the human intellect for the vast +period already mentioned.</p> + +<p>Up to the present we have been speaking only of those primary motions +of the heavens, by which the whole sphere appeared to revolve once +every twenty-four hours. We have now to discuss the remarkable +theories by which Ptolemy endeavoured to account for the monthly +movement of the moon, for the annual movement of the sun, and for the +periodic movements of the planets which had gained for them the +titles of the wandering stars.</p> + +<p>Possessed with the idea that these movements must be circular, or +must be capable, directly or indirectly, of being explained by +circular movements, it seemed obvious to Ptolemy, as indeed it had +done to previous astronomers, that the track of the moon through the +stars was a circle of which the earth is the centre. A similar +movement with a yearly period must also be attributed to the sun, for +the changes in the positions of the constellations in accordance with +the progress of the seasons, placed it beyond doubt that the sun made +a circuit of the celestial sphere, even though the bright light of +the sun prevented the stars in its vicinity, from being seen in +daylight. Thus the movements both of the sun and the moon, as well +as the diurnal rotation of the celestial sphere, seemed to justify +the notion that all celestial movements must be "perfect," that is to +say, described uniformly in those circles which were the only perfect +curves.</p> + +<p>The simplest observations, however, show that the movements of the +planets cannot be explained in this simple fashion. Here the +geometrical genius of Ptolemy shone forth, and he devised a scheme by +which the apparent wanderings of the planets could be accounted for +without the introduction of aught save "perfect" movements.</p> + +<p>To understand his reasoning, let us first set forth clearly those +facts of observation which require to be explained. I shall take, in +particular, two planets, Venus and Mars, as these illustrate, in the +most striking manner, the peculiarities of the inner and the outer +planets respectively. The simplest observations would show that +Venus did not move round the heavens in the same fashion as the sun +or the moon. Look at the evening star when brightest, as it appears +in the west after sunset. Instead of moving towards the east among +the stars, like the sun or the moon, we find, week after week, that +Venus is drawing in towards the sun, until it is lost in the +sunbeams. Then the planet emerges on the other side, not to be seen +as an evening star, but as a morning star. In fact, it was plain +that in some ways Venus accompanied the sun in its annual movement. +Now it is found advancing in front of the sun to a certain limited +distance, and now it is lagging to an equal extent behind the sun.</p> + +<p><a name="fig_1" id="fig_1"></a></p> + +<div class="figcenter" style="width: 303px;"> +<a href="images/ill_fig1.jpg"> +<img src="images/ill_fig1_sml.jpg" width="303" height="286" alt="FIG. 1. PTOLEMY'S PLANETARY SCHEME." title="" /></a> +<span class="caption">FIG. 1. PTOLEMY'S PLANETARY SCHEME.</span> +</div> + +<p>These movements were wholly incompatible with the supposition that +the journeys of Venus were described by a single motion of the kind +regarded as perfect. It was obvious that the movement was connected +in some strange manner with the revolution of the sun, and here was +the ingenious method by which Ptolemy sought to render account of +it. Imagine a fixed arm to extend from the earth to the sun, as +shown in the accompanying figure (Fig. 1), then this arm will move +round uniformly, in consequence of the sun's movement. At a point P +on this arm let a small circle be described. Venus is supposed to +revolve uniformly in this small circle, while the circle itself is +carried round continuously by the movement of the sun. In this way +it was possible to account for the chief peculiarities in the +movement of Venus. It will be seen that, in consequence of the +revolution around P, the spectator on the earth will sometimes see +Venus on one side of the sun, and sometimes on the other side, so +that the planet always remains in the sun's vicinity. By properly +proportioning the movements, this little contrivance simulated the +transitions from the morning star to the evening star. Thus the +changes of Venus could be accounted for by a Combination of the +"perfect" movement of P in the circle which it described uniformly +round the earth, combined with the "perfect" motion of Venus in the +circle which it described uniformly around the moving centre.</p> + +<p>In a precisely similar manner Ptolemy rendered an explanation of the +fitful apparitions of Mercury. Now just on one side of the sun, and +now just on the other, this rarely-seen planet moved like Venus on a +circle whereof the centre was also carried by the line joining the +sun and the earth. The circle, however, in which Mercury actually +revolved had to be smaller than that of Venus, in order to account +for the fact that Mercury lies always much closer to the sun than the +better-known planet.</p> + +<p><a name="fig_2" id="fig_2"></a></p> + +<div class="figcenter" style="width: 356px;"> +<a href="images/ill_fig2.jpg"> +<img src="images/ill_fig2_sml.jpg" width="356" height="327" alt="FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS." title="" /></a> +<span class="caption">FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.</span> +</div> + +<p>The explanation of the movement of an outer planet like Mars could +also be deduced from the joint effect of two perfect motions. The +changes through which Mars goes are, however, so different from the +movements of Venus that quite a different disposition of the circles +is necessary. For consider the facts which characterise the +movements of an outer planet such as Mars. In the first place, Mars +accomplishes an entire circuit of the heaven. In this respect, no +doubt, it may be said to resemble the sun or the moon. A little +attention will, however, show that there are extraordinary +irregularities in the movement of the planet. Generally speaking, it +speeds its way from west to east among the stars, but sometimes the +attentive observer will note that the speed with which the planet +advances is slackening, and then it will seem to become stationary. +Some days later the direction of the planet's movement will be +reversed, and it will be found moving from the east towards the +west. At first it proceeds slowly and then quickens its pace, until +a certain speed is attained, which afterwards declines until a second +stationary position is reached. After a due pause the original +motion from west to east is resumed, and is continued until a similar +cycle of changes again commences. Such movements as these were +obviously quite at variance with any perfect movement in a single +circle round the earth. Here, again, the geometrical sagacity of +Ptolemy provided him with the means of representing the apparent +movements of Mars, and, at the same time, restricting the explanation +to those perfect movements which he deemed so essential. In Fig. 2 +we exhibit Ptolemy's theory as to the movement of Mars. We have, as +before, the earth at the centre, and the sun describing its circular +orbit around that centre. The path of Mars is to be taken as +exterior to that of the sun. We are to suppose that at a point +marked M there is a fictitious planet, which revolves around the +earth uniformly, in a circle called the DEFERENT. This point M, +which is thus animated by a perfect movement, is the centre of a +circle which is carried onwards with M, and around the circumference +of which Mars revolves uniformly. It is easy to show that the +combined effect of these two perfect movements is to produce exactly +that displacement of Mars in the heavens which observation +discloses. In the position represented in the figure, Mars is +obviously pursuing a course which will appear to the observer as a +movement from west to east. When, however, the planet gets round to +such a position as R, it is then moving from east to west in +consequence of its revolution in the moving circle, as indicated by +the arrow-head. On the other hand, the whole circle is carried +forward in the opposite direction. If the latter movement be less +rapid than the former, then we shall have the backward movement of +Mars on the heavens which it was desired to explain. By a proper +adjustment of the relative lengths of these arms the movements of the +planet as actually observed could be completely accounted for.</p> + +<p>The other outer planets with which Ptolemy was acquainted, namely, +Jupiter and Saturn, had movements of the same general character as +those of Mars. Ptolemy was equally successful in explaining the +movements they performed by the supposition that each planet had +perfect rotation in a circle of its own, which circle itself had +perfect movement around the earth in the centre.</p> + +<p>It is somewhat strange that Ptolemy did not advance one step further, +as by so doing he would have given great simplicity to his system. He +might, for instance, have represented the movements of Venus equally +well by putting the centre of the moving circle at the sun itself, +and correspondingly enlarging the circle in which Venus revolved. He +might, too, have arranged that the several circles which the outer +planets traversed should also have had their centres at the sun. The +planetary system would then have consisted of an earth fixed at the +centre, of a sun revolving uniformly around it, and of a system of +planets each describing its own circle around a moving centre placed +in the sun. Perhaps Ptolemy had not thought of this, or perhaps he +may have seen arguments against it. This important step was, +however, taken by Tycho. He considered that all the planets revolved +around the sun in circles, and that the sun itself, bearing all these +orbits, described a mighty circle around the earth. This point +having been reached, only one more step would have been necessary to +reach the glorious truths that revealed the structure of the solar +system. That last step was taken by Copernicus.</p> + +<h3><a name="COPERNICUS" id="COPERNICUS"></a>COPERNICUS.</h3> +<p><a name="thorn" id="thorn"></a></p> + +<div class="figcenter" style="width: 585px;"> +<a href="images/ill_thorn.jpg"> +<img src="images/ill_thorn_sml.jpg" width="585" height="242" alt="THORN, FROM AN OLD PRINT." title="" /></a> +<span class="caption">THORN, FROM AN OLD PRINT.</span> +</div> + +<p>The quaint town of Thorn, on the Vistula, was more than two centuries +old when Copernicus was born there on the 19th of February, 1473. The +situation of this town on the frontier between Prussia and Poland, +with the commodious waterway offered by the river, made it a place of +considerable trade. A view of the town, as it was at the time of the +birth of Copernicus, is here given. The walls, with their +watch-towers, will be noted, and the strategic importance which the +situation of Thorn gave to it in the fifteenth century still belongs +thereto, so much so that the German Government recently constituted +the town a fortress of the first class.</p> + +<p>Copernicus, the astronomer, whose discoveries make him the great +predecessor of Kepler and Newton, did not come from a noble family, +as certain other early astronomers have done, for his father was a +tradesman. Chroniclers are, however, careful to tell us that one of +his uncles was a bishop. We are not acquainted with any of those +details of his childhood or youth which are often of such interest in +other cases where men have risen to exalted fame. It would appear +that the young Nicolaus, for such was his Christian name, received +his education at home until such time as he was deemed sufficiently +advanced to be sent to the University at Cracow. The education that +he there obtained must have been in those days of a very primitive +description, but Copernicus seems to have availed himself of it to +the utmost. He devoted himself more particularly to the study of +medicine, with the view of adopting its practice as the profession of +his life. The tendencies of the future astronomer were, however, +revealed in the fact that he worked hard at mathematics, and, like +one of his illustrious successors, Galileo, the practice of the art +of painting had for him a very great interest, and in it he obtained +some measure of success.</p> + +<p>By the time he was twenty-seven years old, it would seem that +Copernicus had given up the notion of becoming a medical +practitioner, and had resolved to devote himself to science. He was +engaged in teaching mathematics, and appears to have acquired some +reputation. His growing fame attracted the notice of his uncle the +bishop, at whose suggestion Copernicus took holy orders, and he was +presently appointed to a canonry in the cathedral of Frauenburg, near +the mouth of the Vistula.</p> + +<p>To Frauenburg, accordingly, this man of varied gifts retired. +Possessing somewhat of the ascetic spirit, he resolved to devote his +life to work of the most serious description. He eschewed all +ordinary society, restricting his intimacies to very grave and +learned companions, and refusing to engage in conversation of any +useless kind. It would seem as if his gifts for painting were +condemned as frivolous; at all events, we do not learn that he +continued to practise them. In addition to the discharge of his +theological duties, his life was occupied partly in ministering +medically to the wants of the poor, and partly with his researches in +astronomy and mathematics. His equipment in the matter of +instruments for the study of the heavens seems to have been of a very +meagre description. He arranged apertures in the walls of his house +at Allenstein, so that he could observe in some fashion the passage +of the stars across the meridian. That he possessed some talent for +practical mechanics is proved by his construction of a contrivance +for raising water from a stream, for the use of the inhabitants of +Frauenburg. Relics of this machine are still to be seen.</p> + +<p><a name="copernicus_ill" id="copernicus_ill"></a></p> + +<div class="figcenter" style="width: 395px;"> +<a href="images/ill_copernicus.jpg"> +<img src="images/ill_copernicus_sml.jpg" width="395" height="469" alt="COPERNICUS." title="" /></a> +<span class="caption">COPERNICUS.</span> +</div> + +<p>The intellectual slumber of the Middle Ages was destined to be +awakened by the revolutionary doctrines of Copernicus. It may be +noted, as an interesting circumstance, that the time at which he +discovered the scheme of the solar system has coincided with a +remarkable epoch in the world's history. The great astronomer had +just reached manhood at the time when Columbus discovered the new +world.</p> + +<p>Before the publication of the researches of Copernicus, the orthodox +scientific creed averred that the earth was stationary, and that the +apparent movements of the heavenly bodies were indeed real +movements. Ptolemy had laid down this doctrine 1,400 years before. +In his theory this huge error was associated with so much important +truth, and the whole presented such a coherent scheme for the +explanation of the heavenly movements, that the Ptolemaic theory was +not seriously questioned until the great work of Copernicus +appeared. No doubt others, before Copernicus, had from time to time +in some vague fashion surmised, with more or less plausibility, that +the sun, and not the earth, was the centre about which the system +really revolved. It is, however, one thing to state a scientific +fact; it is quite another thing to be in possession of the train of +reasoning, founded on observation or experiment, by which that fact +may be established. Pythagoras, it appears, had indeed told his +disciples that it was the sun, and not the earth, which was the +centre of movement, but it does not seem at all certain that +Pythagoras had any grounds which science could recognise for the +belief which is attributed to him. So far as information is +available to us, it would seem that Pythagoras associated his scheme +of things celestial with a number of preposterous notions in natural +philosophy. He may certainly have made a correct statement as to +which was the most important body in the solar system, but he +certainly did not provide any rational demonstration of the fact. +Copernicus, by a strict train of reasoning, convinced those who would +listen to him that the sun was the centre of the system. It is +useful for us to consider the arguments which he urged, and by which +he effected that intellectual revolution which is always connected +with his name.</p> + +<p>The first of the great discoveries which Copernicus made relates to +the rotation of the earth on its axis. That general diurnal +movement, by which the stars and all other celestial bodies appear to +be carried completely round the heavens once every twenty-four hours, +had been accounted for by Ptolemy on the supposition that the +apparent movements were the real movements. As we have already seen, +Ptolemy himself felt the extraordinary difficulty involved in the +supposition that so stupendous a fabric as the celestial sphere +should spin in the way supposed. Such movements required that many +of the stars should travel with almost inconceivable velocity. +Copernicus also saw that the daily rising and setting of the heavenly +bodies could be accounted for either by the supposition that the +celestial sphere moved round and that the earth remained at rest, or +by the supposition that the celestial sphere was at rest while the +earth turned round in the opposite direction. He weighed the +arguments on both sides as Ptolemy had done, and, as the result of +his deliberations, Copernicus came to an opposite conclusion from +Ptolemy. To Copernicus it appeared that the difficulties attending +the supposition that the celestial sphere revolved, were vastly +greater than those which appeared so weighty to Ptolemy as to force +him to deny the earth's rotation.</p> + +<p>Copernicus shows clearly how the observed phenomena could be +accounted for just as completely by a rotation of the earth as by a +rotation of the heavens. He alludes to the fact that, to those on +board a vessel which is moving through smooth water, the vessel +itself appears to be at rest, while the objects on shore seem to be +moving past. If, therefore, the earth were rotating uniformly, we +dwellers upon the earth, oblivious of our own movement, would wrongly +attribute to the stars the displacement which was actually the +consequence of our own motion.</p> + +<p>Copernicus saw the futility of the arguments by which Ptolemy had +endeavoured to demonstrate that a revolution of the earth was +impossible. It was plain to him that there was nothing whatever to +warrant refusal to believe in the rotation of the earth. In his +clear-sightedness on this matter we have specially to admire the +sagacity of Copernicus as a natural philosopher. It had been urged +that, if the earth moved round, its motion would not be imparted to +the air, and that therefore the earth would be uninhabitable by the +terrific winds which would be the result of our being carried through +the air. Copernicus convinced himself that this deduction was +preposterous. He proved that the air must accompany the earth, just +as his coat remains round him, notwithstanding the fact that he is +walking down the street. In this way he was able to show that all a +priori objections to the earth's movements were absurd, and therefore +he was able to compare together the plausibilities of the two rival +schemes for explaining the diurnal movement.</p> + +<p><a name="frauenburg" id="frauenburg"></a></p> + +<div class="figcenter" style="width: 571px;"> +<a href="images/ill_frauenburg.jpg"> +<img src="images/ill_frauenburg_sml.jpg" width="571" height="392" alt="FRAUENBURG, FROM AN OLD PRINT." title="" /></a> +<span class="caption">FRAUENBURG, FROM AN OLD PRINT.</span> +</div> + +<p>Once the issue had been placed in this form, the result could not be +long in doubt. Here is the question: Which is it more likely—that +the earth, like a grain of sand at the centre of a mighty globe, +should turn round once in twenty-four hours, or that the whole of +that vast globe should complete a rotation in the opposite direction +in the same time? Obviously, the former is far the more simple +supposition. But the case is really much stronger than this. Ptolemy +had supposed that all the stars were attached to the surface of a +sphere. He had no ground whatever for this supposition, except that +otherwise it would have been well-nigh impossible to have devised a +scheme by which the rotation of the heavens around a fixed earth +could have been arranged. Copernicus, however, with the just +instinct of a philosopher, considered that the celestial sphere, +however convenient from a geometrical point of view, as a means of +representing apparent phenomena, could not actually have a material +existence. In the first place, the existence of a material celestial +sphere would require that all the myriad stars should be at exactly +the same distances from the earth. Of course, no one will say that +this or any other arbitrary disposition of the stars is actually +impossible, but as there was no conceivable physical reason why the +distances of all the stars from the earth should be identical, it +seemed in the very highest degree improbable that the stars should be +so placed.</p> + +<p>Doubtless, also, Copernicus felt a considerable difficulty as to the +nature of the materials from which Ptolemy's wonderful sphere was to +be constructed. Nor could a philosopher of his penetration have +failed to observe that, unless that sphere were infinitely large, +there must have been space outside it, a consideration which would +open up other difficult questions. Whether infinite or not, it was +obvious that the celestial sphere must have a diameter at least many +thousands of times as great as that of the earth. From these +considerations Copernicus deduced the important fact that the stars +and the other celestial bodies must all be vast objects. He was thus +enabled to put the question in such a form that it could hardly +receive any answer but the correct one. Which is it more rational to +suppose, that the earth should turn round on its axis once in +twenty-four hours, or that thousands of mighty stars should circle +round the earth in the same time, many of them having to describe +circles many thousands of times greater in circumference than the +circuit of the earth at the equator? The obvious answer pressed upon +Copernicus with so much force that he was compelled to reject +Ptolemy's theory of the stationary earth, and to attribute the +diurnal rotation of the heavens to the revolution of the earth on its +axis.</p> + +<p>Once this tremendous step had been taken, the great difficulties +which beset the monstrous conception of the celestial sphere +vanished, for the stars need no longer be regarded as situated at +equal distances from the earth. Copernicus saw that they might lie +at the most varied degrees of remoteness, some being hundreds or +thousands of times farther away than others. The complicated +structure of the celestial sphere as a material object disappeared +altogether; it remained only as a geometrical conception, whereon we +find it convenient to indicate the places of the stars. Once the +Copernican doctrine had been fully set forth, it was impossible for +anyone, who had both the inclination and the capacity to understand +it, to withhold acceptance of its truth. The doctrine of a +stationary earth had gone for ever.</p> + +<p>Copernicus having established a theory of the celestial movements +which deliberately set aside the stability of the earth, it seemed +natural that he should inquire whether the doctrine of a moving earth +might not remove the difficulties presented in other celestial +phenomena. It had been universally admitted that the earth lay +unsupported in space. Copernicus had further shown that it possessed +a movement of rotation. Its want of stability being thus recognised, +it seemed reasonable to suppose that the earth might also have some +other kinds of movements as well. In this, Copernicus essayed to +solve a problem far more difficult than that which had hitherto +occupied his attention. It was a comparatively easy task to show how +the diurnal rising and setting could be accounted for by the rotation +of the earth. It was a much more difficult undertaking to +demonstrate that the planetary movements, which Ptolemy had +represented with so much success, could be completely explained by +the supposition that each of those planets revolved uniformly round +the sun, and that the earth was also a planet, accomplishing a +complete circuit of the sun once in the course of a year.</p> + +<p><a name="explanation" id="explanation"></a></p> + +<div class="figcenter" style="width: 291px;"> +<a href="images/ill_041.jpg"> +<img src="images/ill_041_sml.jpg" width="291" height="325" alt="EXPLANATION OF PLANETARY MOVEMENTS." title="" /></a> +<span class="caption">EXPLANATION OF PLANETARY MOVEMENTS.</span> +</div> + +<p>It would be impossible in a sketch like the present to enter into any +detail as to the geometrical propositions on which this beautiful +investigation of Copernicus depended. We can only mention a few of +the leading principles. It may be laid down in general that, if an +observer is in movement, he will, if unconscious of the fact, +attribute to the fixed objects around him a movement equal and +opposite to that which he actually possesses. A passenger on a +canal-boat sees the objects on the banks apparently moving backward +with a speed equal to that by which he is himself advancing +forwards. By an application of this principle, we can account for +all the phenomena of the movements of the planets, which Ptolemy had +so ingeniously represented by his circles. Let us take, for +instance, the most characteristic feature in the irregularities of +the outer planets. We have already remarked that Mars, though +generally advancing from west to east among the stars, occasionally +pauses, retraces his steps for awhile, again pauses, and then resumes +his ordinary onward progress. Copernicus showed clearly how this +effect was produced by the real motion of the earth, combined with +the real motion of Mars. In the adjoining figure we represent a +portion of the circular tracks in which the earth and Mars move in +accordance with the Copernican doctrine. I show particularly the +case where the earth comes directly between the planet and the sun, +because it is on such occasions that the retrograde movement (for so +this backward movement of Mars is termed) is at its highest. Mars is +then advancing in the direction shown by the arrow-head, and the +earth is also advancing in the same direction. We, on the earth, +however, being unconscious of our own motion, attribute, by the +principle I have already explained, an equal and opposite motion to +Mars. The visible effect upon the planet is, that Mars has two +movements, a real onward movement in one direction, and an apparent +movement in the opposite direction. If it so happened that the earth +was moving with the same speed as Mars, then the apparent movement +would exactly neutralise the real movement, and Mars would seem to be +at rest relatively to the surrounding stars. Under the actual +circumstances represented, however, the earth is moving faster than +Mars, and the consequence is, that the apparent movement of the +planet backwards exceeds the real movement forwards, the net result +being an apparent retrograde movement.</p> + +<p>With consummate skill, Copernicus showed how the applications of the +same principles could account for the characteristic movements of the +planets. His reasoning in due time bore down all opposition. The +supreme importance of the earth in the system vanished. It had now +merely to take rank as one of the planets.</p> + +<p>The same great astronomer now, for the first time, rendered something +like a rational account of the changes of the seasons. Nor did +certain of the more obscure astronomical phenomena escape his +attention.</p> + +<p>He delayed publishing his wonderful discoveries to the world until he +was quite an old man. He had a well-founded apprehension of the +storm of opposition which they would arouse. However, he yielded at +last to the entreaties of his friends, and his book was sent to the +press. But ere it made its appearance to the world, Copernicus was +seized by mortal illness. A copy of the book was brought to him on +May 23, 1543. We are told that he was able to see it and to touch +it, but no more, and he died a few hours afterwards. He was buried +in that Cathedral of Frauenburg, with which his life had been so +closely associated.</p> + +<h3><a name="TYCHO_BRAHE" id="TYCHO_BRAHE"></a>TYCHO BRAHE.</h3> +<p>The most picturesque figure in the history of astronomy is +undoubtedly that of the famous old Danish astronomer whose name +stands at the head of this chapter. Tycho Brahe was alike notable +for his astronomical genius and for the extraordinary vehemence of a +character which was by no means perfect. His romantic career as a +philosopher, and his taste for splendour as a Danish noble, his +ardent friendships and his furious quarrels, make him an ideal +subject for a biographer, while the magnificent astronomical work +which he accomplished, has given him imperishable fame.</p> + +<p>The history of Tycho Brahe has been admirably told by Dr. Dreyer, the +accomplished astronomer who now directs the observatory at Armagh, +though himself a countryman of Tycho. Every student of the career of +the great Dane must necessarily look on Dr. Dreyer's work as the +chief authority on the subject. Tycho sprang from an illustrious +stock. His family had flourished for centuries, both in Sweden and +in Denmark, where his descendants are to be met with at the present +day. The astronomer's father was a privy councillor, and having +filled important positions in the Danish government, he was +ultimately promoted to be governor of Helsingborg Castle, where he +spent the last years of his life. His illustrious son Tycho was born +in 1546, and was the second child and eldest boy in a family of ten.</p> + +<p>It appears that Otto, the father of Tycho, had a brother named +George, who was childless. George, however, desired to adopt a boy +on whom he could lavish his affection and to whom he could bequeath +his wealth. A somewhat singular arrangement was accordingly entered +into by the brothers at the time when Otto was married. It was +agreed that the first son who might be born to Otto should be +forthwith handed over by the parents to George to be reared and +adopted by him. In due time little Tycho appeared, and was +immediately claimed by George in pursuance of the compact. But it +was not unnatural that the parental instinct, which had been dormant +when the agreement was made, should here interpose. Tycho's father +and mother receded from the bargain, and refused to part with their +son. George thought he was badly treated. However, he took no +violent steps until a year later, when a brother was born to Tycho. +The uncle then felt no scruple in asserting what he believed to be +his rights by the simple process of stealing the first-born nephew, +which the original bargain had promised him. After a little time it +would seem that the parents acquiesced in the loss, and thus it was +in Uncle George's home that the future astronomer passed his +childhood.</p> + +<p>When we read that Tycho was no more than thirteen years old at the +time he entered the University of Copenhagen, it might be at first +supposed that even in his boyish years he must have exhibited some of +those remarkable talents with which he was afterwards to astonish the +world. Such an inference should not, however, be drawn. The fact is +that in those days it was customary for students to enter the +universities at a much earlier age than is now the case. Not, +indeed, that the boys of thirteen knew more then than the boys of +thirteen know now. But the education imparted in the universities at +that time was of a much more rudimentary kind than that which we +understand by university education at present. In illustration of +this Dr. Dreyer tells us how, in the University of Wittenberg, one of +the professors, in his opening address, was accustomed to point out +that even the processes of multiplication and division in arithmetic +might be learned by any student who possessed the necessary +diligence.</p> + +<p>It was the wish and the intention of his uncle that Tycho's education +should be specially directed to those branches of rhetoric and +philosophy which were then supposed to be a necessary preparation for +the career of a statesman. Tycho, however, speedily made it plain to +his teachers that though he was an ardent student, yet the things +which interested him were the movements of the heavenly bodies and +not the subtleties of metaphysics.</p> + +<p><a name="tycho" id="tycho"></a></p> + +<div class="figcenter" style="width: 451px;"> +<a href="images/ill_brahe.jpg"> +<img src="images/ill_brahe_sml.jpg" width="451" height="572" alt="TYCHO BRAHE." title="" /></a> +<span class="caption">TYCHO BRAHE.</span> +</div> + +<p>On the 21st October, 1560, an eclipse of the sun occurred, which was +partially visible at Copenhagen. Tycho, boy though he was, took the +utmost interest in this event. His ardour and astonishment in +connection with the circumstance were chiefly excited by the fact +that the time of the occurrence of the phenomenon could be predicted +with so much accuracy. Urged by his desire to understand the matter +thoroughly, Tycho sought to procure some book which might explain +what he so greatly wanted to know. In those days books of any kind +were but few and scarce, and scientific books were especially +unattainable. It so happened, however, that a Latin version of +Ptolemy's astronomical works had appeared a few years before the +eclipse took place, and Tycho managed to buy a copy of this book, +which was then the chief authority on celestial matters. Young as +the boy astronomer was, he studied hard, although perhaps not always +successfully, to understand Ptolemy, and to this day his copy of the +great work, copiously annotated and marked by the schoolboy hand, is +preserved as one of the chief treasures in the library of the +University at Prague.</p> + +<p>After Tycho had studied for about three years at the University of +Copenhagen, his uncle thought it would be better to send him, as was +usual in those days, to complete his education by a course of study +in some foreign university. The uncle cherished the hope that in +this way the attention of the young astronomer might be withdrawn +from the study of the stars and directed in what appeared to him a +more useful way. Indeed, to the wise heads of those days, the +pursuit of natural science seemed so much waste of good time which +might otherwise be devoted to logic or rhetoric or some other branch +of study more in vogue at that time. To assist in this attempt to +wean Tycho from his scientific tastes, his uncle chose as a tutor to +accompany him an intelligent and upright young man named Vedel, who +was four years senior to his pupil, and accordingly, in 1562, we find +the pair taking up their abode at the University of Leipzig.</p> + +<p>The tutor, however, soon found that he had undertaken a most hopeless +task. He could not succeed in imbuing Tycho with the slightest taste +for the study of the law or the other branches of knowledge which +were then thought so desirable. The stars, and nothing but the +stars, engrossed the attention of his pupil. We are told that all +the money he could obtain was spent secretly in buying astronomical +books and instruments. He learned the name of the stars from a +little globe, which he kept hidden from Vedel, and only ventured to +use during the latter's absence. No little friction was at first +caused by all this, but in after years a fast and enduring friendship +grew up between Tycho and his tutor, each of whom learned to respect +and to love the other.</p> + +<p>Before Tycho was seventeen he had commenced the difficult task of +calculating the movements of the planets and the places which they +occupied on the sky from time to time. He was not a little surprised +to find that the actual positions of the planets differed very widely +from those which were assigned to them by calculations from the best +existing works of astronomers. With the insight of genius he saw +that the only true method of investigating the movements of the +heavenly bodies would be to carry on a protracted series of +measurements of their places. This, which now seems to us so +obvious, was then entirely new doctrine. Tycho at once commenced +regular observations in such fashion as he could. His first +instrument was, indeed, a very primitive one, consisting of a simple +pair of compasses, which he used in this way. He placed his eye at +the hinge, and then opened the legs of the compass so that one leg +pointed to one star and the other leg to the other star. The compass +was then brought down to a divided circle, by which means the number +of degrees in the apparent angular distance of the two stars was +determined.</p> + +<p>His next advance in instrumental equipment was to provide himself +with the contrivance known as the "cross-staff," which he used to +observe the stars whenever opportunity offered. It must, of course, +be remembered that in those days there were no telescopes. In the +absence of optical aid, such as lenses afford the modern observers, +astronomers had to rely on mechanical appliances alone to measure the +places of the stars. Of such appliances, perhaps the most ingenious +was one known before Tycho's time, which we have represented in the +adjoining figure.</p> + +<p><a name="tycho_ill" id="tycho_ill"></a></p> + +<div class="figcenter" style="width: 279px;"> +<a href="images/ill_cross_staff.jpg"> +<img src="images/ill_cross_staff_sml.jpg" width="279" height="290" alt="TYCHO'S CROSS STAFF." title="" /></a> +</div> + +<p>Let us suppose that it be desired to measure the angle between two +stars, then if the angle be not too large it can be determined in the +following manner. Let the rod AB be divided into inches and parts of +an inch, and let another rod, CD, slide up and down along AB in such +a way that the two always remain perpendicular to each other. +"Sights," like those on a rifle, are placed at A and C, and there is +a pin at D. It will easily be seen that, by sliding the movable bar +along the fixed one, it must always be possible when the stars are +not too far apart to bring the sights into such positions that one +star can be seen along DC and the other along DA. This having been +accomplished, the length from A to the cross-bar is read off on the +scale, and then, by means of a table previously prepared, the value +of the required angular distance is obtained. If the angle between +the two stars were greater than it would be possible to measure in +the way already described, then there was a provision by which the +pin at D might be moved along CD into some other position, so as to +bring the angular distance of the stars within the range of the +instrument.</p> + +<p><a name="new_star" id="new_star"></a></p> + +<div class="figright" style="width: 257px;"> +<a href="images/ill_new_star.jpg"> +<img src="images/ill_new_star_sml.jpg" width="257" height="410" alt="TYCHO'S "NEW STAR" SEXTANT OF 1572. +(The arms, of walnut wood, are about 5 1/2 ft. long.)" title="" /></a> +<span class="caption">TYCHO'S "NEW STAR" SEXTANT OF 1572. +<br />(The arms, of walnut wood, are about 5 1/2 ft. long.)</span> +</div> + +<p>No doubt the cross-staff is a very primitive contrivance, but when +handled by one so skilful as Tycho it afforded results of +considerable accuracy. I would recommend any reader who may have a +taste for such pursuits to construct a cross-staff for himself, and +see what measurements he can accomplish with its aid.</p> + +<p>To employ this little instrument Tycho had to evade the vigilance of +his conscientious tutor, who felt it his duty to interdict all such +occupations as being a frivolous waste of time. It was when Vedel +was asleep that Tycho managed to escape with his cross staff and +measure the places of the heavenly bodies. Even at this early age +Tycho used to conduct his observations on those thoroughly sound +principles which lie at the foundation of all accurate modern +astronomy. Recognising the inevitable errors of workmanship in his +little instrument, he ascertained their amount and allowed for their +influence on the results which he deduced. This principle, employed +by the boy with his cross-staff in 1564, is employed at the present +day by the Astronomer Royal at Greenwich with the most superb +instruments that the skill of modern opticians has been able to +construct.</p> + +<p><a name="trigonic_sextant" id="trigonic_sextant"></a></p> + +<div class="figleft" style="width: 260px;"> +<a href="images/ill_trigonic_sextant.jpg"> +<img src="images/ill_trigonic_sextant_sml.jpg" width="260" height="411" alt="TYCHO'S TRIGONIC SEXTANT. +(The arms, AB and AC, are about 5 1/2 ft. long.)" title="" /></a> +<span class="caption">TYCHO'S TRIGONIC SEXTANT. +<br />(The arms, AB and AC, are about 5 1/2 ft. long.)</span> +</div> + +<p>After the death of his uncle, when Tycho was nineteen years of age, +it appears that the young philosopher was no longer interfered with +in so far as the line which his studies were to take was concerned. +Always of a somewhat restless temperament, we now find that he +shifted his abode to the University of Rostock, where he speedily +made himself notable in connection with an eclipse of the moon on +28th October, 1566. Like every other astronomer of those days, Tycho +had always associated astronomy with astrology. He considered that +the phenomena of the heavenly bodies always had some significance in +connection with human affairs. Tycho was also a poet, and in the +united capacity of poet, astrologer, and astronomer, he posted up +some verses in the college at Rostock announcing that the lunar +eclipse was a prognostication of the death of the great Turkish +Sultan, whose mighty deeds at that time filled men's minds. Presently +news did arrive of the death of the Sultan, and Tycho was accordingly +triumphant; but a little later it appeared that the decease had taken +place BEFORE the eclipse, a circumstance which caused many a laugh at +Tycho's expense.</p> + +<p><a name="astronomic_sextant" id="astronomic_sextant"></a></p> + +<div class="figright" style="width: 274px;"> +<a href="images/ill_astronomic_sextant.jpg"> +<img src="images/ill_astronomic_sextant_sml.jpg" width="274" height="433" alt="TYCHO'S ASTRONOMIC SEXTANT. +(Made of steel; the arms, A B, A C, measure 4ft.)" title="" /></a> +<span class="caption">TYCHO'S ASTRONOMIC SEXTANT.<br /> +(Made of steel; the arms, A B, A C, measure 4ft.)</span> +</div> + +<p><a name="equatorial_armillary" id="equatorial_armillary"></a></p> + +<div class="figleft" style="width: 257px;"> +<a href="images/ill_equatorial_armillary.jpg"> +<img src="images/ill_equatorial_armillary_sml.jpg" width="257" height="414" alt="TYCHO'S EQUATORIAL ARMILLARY. +(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)" title="" /></a> +<span class="caption">TYCHO'S EQUATORIAL ARMILLARY. +<br />(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)</span> +</div> + +<p>Tycho being of a somewhat turbulent disposition, it appears that, +while at the University of Rostock, he had a serious quarrel with +another Danish nobleman. We are not told for certain what was the +cause of the dispute. It does not, however, seem to have had any +more romantic origin than a difference of opinion as to which of them +knew the more mathematics. They fought, as perhaps it was becoming +for two astronomers to fight, under the canopy of heaven in utter +darkness at the dead of night, and the duel was honourably terminated +when a slice was taken off Tycho's nose by the insinuating sword of +his antagonist. For the repair of this injury the ingenuity of the +great instrument-maker was here again useful, and he made a +substitute for his nose "with a composition of gold and silver." The +imitation was so good that it is declared to have been quite equal to +the original. Dr. Lodge, however, pointedly observes that it does +not appear whether this remark was made by a friend or an enemy.</p> + +<p><a name="augsburg_quadrant" id="augsburg_quadrant"></a></p> + +<div class="figright" style="width: 268px;clear:both;"> +<a href="images/ill_augsburg_quadrant.jpg"> +<img src="images/ill_augsburg_quadrant_sml.jpg" +width="268" height="409" alt="THE GREAT AUGSBURG QUADRANT" +title="" /></a> +<span class="caption">THE GREAT AUGSBURG QUADRANT.</span> +</div> +<p><a name="new_scheme" id="new_scheme"></a></p> + +<div class="figcenter" style="width: 446px;clear:both;"> +<a href="images/ill_new_scheme.jpg"> +<img src="images/ill_new_scheme_sml.jpg" width="446" height="446" alt="TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577." title="" /></a> +<span class="caption">TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.</span> +</div> + +<p>The next few years Tycho spent in various places ardently pursuing +somewhat varied branches of scientific study. At one time we hear of +him assisting an astronomical alderman, in the ancient city of +Augsburg, to erect a tremendous wooden machine—a quadrant of 19-feet +radius—to be used in observing the heavens. At another time we +learn that the King of Denmark had recognised the talents of his +illustrious subject, and promised to confer on him a pleasant +sinecure in the shape of a canonry, which would assist him with the +means for indulging his scientific pursuits. Again we are told that +Tycho is pursuing experiments in chemistry with the greatest energy, +nor is this so incompatible as might at first be thought with his +devotion to astronomy. In those early days of knowledge the +different sciences seemed bound together by mysterious bonds. +Alchemists and astrologers taught that the several planets were +correlated in some mysterious manner with the several metals. It +was, therefore hardly surprising that Tycho should have included a +study of the properties of the metals in the programme of his +astronomical work.</p> + +<p><a name="uraniborg" id="uraniborg"></a></p> + +<div class="figcenter" style="width: 449px;"> +<a href="images/ill_uraniborg.jpg"> +<img src="images/ill_uraniborg_sml.jpg" width="449" height="444" alt="URANIBORG AND ITS GROUNDS. + +PLATE: GROUND-PLAN OF THE OBSERVATORY." title="" /></a> +<span class="caption">URANIBORG AND ITS GROUNDS.</span> +</div> +<p><a name="grnd_pln_uraniborg" id="grnd_pln_uraniborg"></a></p> + +<div class="figcenter" style="width: 401px;"> +<a href="images/ill_grnd_pln_observatory.jpg"> +<img src="images/ill_grnd_pln_observatory_sml.jpg" width="401" height="279" alt="GROUND-PLAN OF THE OBSERVATORY." title="" /></a> +<span class="caption">GROUND-PLAN OF THE OBSERVATORY.</span> +</div> + +<p>An event, however, occurred in 1572 which stimulated Tycho's +astronomical labours, and started him on his life's work. On the +11th of November in that year, he was returning home to supper after +a day's work in his laboratory, when he happened to lift his face to +the sky, and there he beheld a brilliant new star. It was in the +constellation of Cassiopeia, and occupied a position in which there +had certainly been no bright star visible when his attention had last +been directed to that part of the heavens. Such a phenomenon was so +startling that he found it hard to trust the evidence of his senses. +He thought he must be the subject of some hallucination. He +therefore called to the servants who were accompanying him, and asked +them whether they, too, could see a brilliant object in the direction +in which he pointed. They certainly could, and thus he became +convinced that this marvellous object was no mere creation of the +fancy, but a veritable celestial body—a new star of surpassing +splendour which had suddenly burst forth. In these days of careful +scrutiny of the heavens, we are accustomed to the occasional outbreak +of new stars. It is not, however, believed that any new star which +has ever appeared has displayed the same phenomenal brilliance as was +exhibited by the star of 1572.</p> + +<p>This object has a value in astronomy far greater than it might at +first appear. It is true, in one sense, that Tycho discovered the +new star, but it is equally true, in a different sense, that it was +the new star which discovered Tycho. Had it not been for this +opportune apparition, it is quite possible that Tycho might have +found a career in some direction less beneficial to science than that +which he ultimately pursued.</p> + +<p><a name="uraniborg_hven" id="uraniborg_hven"></a></p> + +<div class="figcenter" style="width: 433px;"> +<a href="images/ill_observatory_hven.jpg"> +<img src="images/ill_observatory_hven_sml.jpg" width="433" height="321" alt="THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN." title="" /></a> +<span class="caption">THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.</span> +</div> + +<p>When he reached his home on this memorable evening, Tycho immediately +applied his great quadrant to the measurement of the place of the new +star. His observations were specially directed to the determination +of the distance of the object. He rightly conjectured that if it +were very much nearer to us than the stars in its vicinity, the +distance of the brilliant body might be determined in a short time by +the apparent changes in its distance from the surrounding points. It +was speedily demonstrated that the new star could not be as near as +the moon, by the simple fact that its apparent place, as compared +with the stars in its neighbourhood, was not appreciably altered when +it was observed below the pole, and again above the pole at an +interval of twelve hours. Such observations were possible, inasmuch +as the star was bright enough to be seen in full daylight. Tycho +thus showed conclusively that the body was so remote that the +diameter of the earth bore an insignificant ratio to the star's +distance. His success in this respect is the more noteworthy when we +find that many other observers, who studied the same object, came to +the erroneous conclusion that the new star was quite as near as the +moon, or even much nearer. In fact, it may be said, that with regard +to this object Tycho discovered everything which could possibly have +been discovered in the days before telescopes were invented. He not +only proved that the star's distance was too great for measurement, +but he showed that it had no proper motion on the heavens. He +recorded the successive changes in its brightness from week to week, +as well as the fluctuations in hue with which the alterations in +lustre were accompanied.</p> + +<p>It seems, nowadays, strange to find that such thoroughly scientific +observations of the new star as those which Tycho made, possessed, +even in the eyes of the great astronomer himself, a profound +astrological significance. We learn from Dr. Dreyer that, in Tycho's +opinion, "the star was at first like Venus and Jupiter, and its +effects will therefore, first, be pleasant; but as it then became +like Mars, there will next come a period of wars, seditions, +captivity, and death of princes, and destruction of cities, together +with dryness and fiery meteors in the air, pestilence, and venomous +snakes. Lastly, the star became like Saturn, and thus will finally +come a time of want, death, imprisonment, and all kinds of sad +things!" Ideas of this kind were, however, universally entertained. +It seemed, indeed, obvious to learned men of that period that such an +apparition must forebode startling events. One of the chief theories +then held was, that just as the Star of Bethlehem announced the first +coming of Christ, so the second coming, and the end of the world, was +heralded by the new star of 1572.</p> + +<p>The researches of Tycho on this object were the occasion of his first +appearance as an author. The publication of his book was however, +for some time delayed by the urgent remonstrances of his friends, who +thought it was beneath the dignity of a nobleman to condescend to +write a book. Happily, Tycho determined to brave the opinion of his +order; the book appeared, and was the first of a series of great +astronomical productions from the same pen.</p> + +<p><a name="effigy" id="effigy"></a></p> + +<div class="figright" style="width: 221px;"> +<a href="images/ill_tomb_effigy.jpg"> +<img src="images/ill_tomb_effigy_sml.jpg" width="221" height="384" alt="EFFIGY ON TYCHO'S TOMB AT PRAGUE." title="" /></a> +<span class="caption">EFFIGY ON TYCHO'S TOMB AT PRAGUE.</span> +</div> + +<p>The fame of the noble Dane being now widespread, the King of Denmark +entreated him to return to his native country, and to deliver a +course of lectures on astronomy in the University of Copenhagen. With +some reluctance he consented, and his introductory oration has been +preserved. He dwells, in fervent language, upon the beauty and the +interest of the celestial phenomena. He points out the imperative +necessity of continuous and systematic observation of the heavenly +bodies in order to extend our knowledge. He appeals to the practical +utility of the science, for what civilised nation could exist without +having the means of measuring time? He sets forth how the study of +these beautiful objects "exalts the mind from earthly and trivial +things to heavenly ones;" and then he winds up by assuring them that +"a special use of astronomy is that it enables us to draw conclusions +from the movements in the celestial regions as to human fate."</p> + +<p>An interesting event, which occurred in 1572, distracted Tycho's +attention from astronomical matters. He fell in love. The young +girl on whom his affections were set appears to have sprung from +humble origin. Here again his august family friends sought to +dissuade him from a match they thought unsuitable for a nobleman. +But Tycho never gave way in anything. It is suggested that he did +not seek a wife among the highborn dames of his own rank from the +dread that the demands of a fashionable lady would make too great an +inroad on the time that he wished to devote to science. At all +events, Tycho's union seems to have been a happy one, and he had a +large family of children; none of whom, however, inherited their +father's talents.</p> + +<p><a name="quadrant" id="quadrant"></a></p> + +<div class="figcenter" style="width: 419px;"> +<a href="images/ill_mural_quadrant.jpg"> +<img src="images/ill_mural_quadrant_sml.jpg" width="419" height="570" alt="TYCHO'S MURAL QUADRANT PICTURE, URANIBORG." title="" /></a> +<span class="caption">TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.</span> +</div> + +<p>Tycho had many scientific friends in Germany, among whom his work was +held in high esteem. The treatment that he there met with seemed to +him so much more encouraging than that which he received in Denmark +that he formed the notion of emigrating to Basle and making it his +permanent abode. A whisper of this intention was conveyed to the +large-hearted King of Denmark, Frederick II. He wisely realised how +great would be the fame which would accrue to his realm if he could +induce Tycho to remain within Danish territory and carry on there the +great work of his life. A resolution to make a splendid proposal to +Tycho was immediately formed. A noble youth was forthwith despatched +as a messenger, and ordered to travel day and night until he reached +Tycho, whom he was to summon to the king. The astronomer was in bed +on the morning of 11th February, 1576, when the message was +delivered. Tycho, of course, set off at once and had an audience of +the king at Copenhagen. The astronomer explained that what he wanted +was the means to pursue his studies unmolested, whereupon the king +offered him the Island of Hven, in the Sound near Elsinore. There he +would enjoy all the seclusion that he could desire. The king further +promised that he would provide the funds necessary for building a +house and for founding the greatest observatory that had ever yet +been reared for the study of the heavens. After due deliberation and +consultation with his friends, Tycho accepted the king's offer. He +was forthwith granted a pension, and a deed was drawn up formally +assigning the Island of Hven to his use all the days of his life.</p> + +<p>The foundation of the famous castle of Uraniborg was laid on 30th +August, 1576. The ceremony was a formal and imposing one, in +accordance with Tycho's ideas of splendour. A party of scientific +friends had assembled, and the time had been chosen so that the +heavenly bodies were auspiciously placed. Libations of costly wines +were poured forth, and the stone was placed with due solemnity. The +picturesque character of this wonderful temple for the study of the +stars may be seen in the figures with which this chapter is +illustrated.</p> + +<p>One of the most remarkable instruments that has ever been employed in +studying the heavens was the mural quadrant which Tycho erected in +one of the apartments of Uraniborg. By its means the altitudes of +the celestial bodies could be observed with much greater accuracy +than had been previously attainable. This wonderful contrivance is +represented on the preceding page. It will be observed that the +walls of the room are adorned by pictures with a lavishness of +decoration not usually to be found in scientific establishments.</p> + +<p>A few years later, when the fame of the observatory at Hven became +more widely spread, a number of young men flocked to Tycho to study +under his direction. He therefore built another observatory for +their use in which the instruments were placed in subterranean rooms +of which only the roofs appeared above the ground. There was a +wonderful poetical inscription over the entrance to this underground +observatory, expressing the astonishment of Urania at finding, even +in the interior of the earth, a cavern devoted to the study of the +heavens. Tycho was indeed always fond of versifying, and he lost no +opportunity of indulging this taste whenever an occasion presented +itself.</p> + +<p>Around the walls of the subterranean observatory were the pictures of +eight astronomers, each with a suitable inscription—one of these of +course represented Tycho himself, and beneath were written words to +the effect that posterity should judge of his work. The eighth +picture depicted an astronomer who has not yet come into existence. +Tychonides was his name, and the inscription presses the modest hope +that when he does appear he will be worthy of his great predecessor. +The vast expenses incurred in the erection and the maintenance of +this strange establishment were defrayed by a succession of grants +from the royal purse.</p> + +<p>For twenty years Tycho laboured hard at Uraniborg in the pursuit of +science. His work mainly consisted in the determination of the +places of the moon, the planets, and the stars on the celestial +sphere. The extraordinary pains taken by Tycho to have his +observations as accurate as his instruments would permit, have justly +entitled him to the admiration of all succeeding astronomers. His +island home provided the means of recreation as well as a place for +work. He was surrounded by his family, troops of friends were not +wanting, and a pet dwarf seems to have been an inmate of his curious +residence. By way of change from his astronomical labours he used +frequently to work with his students in his chemical laboratory. It +is not indeed known what particular problems in chemistry occupied +his attention. We are told, however, that he engaged largely in the +production of medicines, and as these appear to have been dispensed +gratuitously there was no lack of patients.</p> + +<p>Tycho's imperious and grasping character frequently brought him into +difficulties, which seem to have increased with his advancing years. +He had ill-treated one of his tenants on Hven, and an adverse +decision by the courts seems to have greatly exasperated the +astronomer. Serious changes also took place in his relations to the +court at Copenhagen. When the young king was crowned in 1596, he +reversed the policy of his predecessor with reference to Hven. The +liberal allowances to Tycho were one after another withdrawn, and +finally even his pension was stopped. Tycho accordingly abandoned +Hven in a tumult of rage and mortification. A few years later we +find him in Bohemia a prematurely aged man, and he died on the 24th +October, 1601.</p> + +<h3><a name="GALILEO" id="GALILEO"></a>GALILEO.</h3> +<p>Among the ranks of the great astronomers it would be difficult to +find one whose life presents more interesting features and remarkable +vicissitudes than does that of Galileo. We may consider him as the +patient investigator and brilliant discoverer. We may consider him +in his private relations, especially to his daughter, Sister Maria +Celeste, a woman of very remarkable character; and we have also the +pathetic drama at the close of Galileo's life, when the philosopher +drew down upon himself the thunders of the Inquisition.</p> + +<p>The materials for the sketch of this astonishing man are sufficiently +abundant. We make special use in this place of those charming +letters which his daughter wrote to him from her convent home. More +than a hundred of these have been preserved, and it may well be +doubted whether any more beautiful and touching series of letters +addressed to a parent by a dearly loved child have ever been +written. An admirable account of this correspondence is contained in +a little book entitled "The Private Life of Galileo," published +anonymously by Messrs. Macmillan in 1870, and I have been much +indebted to the author of that volume for many of the facts contained +in this chapter.</p> + +<p>Galileo was born at Pisa, on 18th February, 1564. He was the eldest +son of Vincenzo de' Bonajuti de' Galilei, a Florentine noble. +Notwithstanding his illustrious birth and descent, it would seem that +the home in which the great philosopher's childhood was spent was an +impoverished one. It was obvious at least that the young Galileo +would have to be provided with some profession by which he might earn +a livelihood. From his father he derived both by inheritance and by +precept a keen taste for music, and it appears that he became an +excellent performer on the lute. He was also endowed with +considerable artistic power, which he cultivated diligently. Indeed, +it would seem that for some time the future astronomer entertained +the idea of devoting himself to painting as a profession. His +father, however, decided that he should study medicine. Accordingly, +we find that when Galileo was seventeen years of age, and had added a +knowledge of Greek and Latin to his acquaintance with the fine arts, +he was duly entered at the University of Pisa.</p> + +<p>Here the young philosopher obtained some inkling of mathematics, +whereupon he became so much interested in this branch of science, +that he begged to be allowed to study geometry. In compliance with +his request, his father permitted a tutor to be engaged for this +purpose; but he did so with reluctance, fearing that the attention of +the young student might thus be withdrawn from that medical work +which was regarded as his primary occupation. The event speedily +proved that these anxieties were not without some justification. The +propositions of Euclid proved so engrossing to Galileo that it was +thought wise to avoid further distraction by terminating the +mathematical tutor's engagement. But it was too late for the desired +end to be attained. Galileo had now made such progress that he was +able to continue his geometrical studies by himself. Presently he +advanced to that famous 47th proposition which won his lively +admiration, and on he went until he had mastered the six books of +Euclid, which was a considerable achievement for those days.</p> + +<p>The diligence and brilliance of the young student at Pisa did not, +however, bring him much credit with the University authorities. In +those days the doctrines of Aristotle were regarded as the embodiment +of all human wisdom in natural science as well as in everything +else. It was regarded as the duty of every student to learn +Aristotle off by heart, and any disposition to doubt or even to +question the doctrines of the venerated teacher was regarded as +intolerable presumption. But young Galileo had the audacity to think +for himself about the laws of nature. He would not take any +assertion of fact on the authority of Aristotle when he had the means +of questioning nature directly as to its truth or falsehood. His +teachers thus came to regard him as a somewhat misguided youth, +though they could not but respect the unflagging industry with which +he amassed all the knowledge he could acquire.</p> + +<p><a name="galileo_pendulum" id="galileo_pendulum"></a></p> + +<div class="figcenter" style="width: 313px;"> +<a href="images/ill_galileo_pendulum.jpg"> +<img src="images/ill_galileo_pendulum_sml.jpg" width="313" height="448" alt="GALILEO'S PENDULUM." title="" /></a> +<span class="caption">GALILEO'S PENDULUM.</span> +</div> + +<p>We are so accustomed to the use of pendulums in our clocks that +perhaps we do not often realise that the introduction of this method +of regulating time-pieces was really a notable invention worthy the +fame of the great astronomer to whom it was due. It appears that +sitting one day in the Cathedral of Pisa, Galileo's attention became +concentrated on the swinging of a chandelier which hung from the +ceiling. It struck him as a significant point, that whether the arc +through which the pendulum oscillated was a long one or a short one, +the time occupied in each vibration was sensibly the same. This +suggested to the thoughtful observer that a pendulum would afford the +means by which a time-keeper might be controlled, and accordingly +Galileo constructed for the first time a clock on this principle. The +immediate object sought in this apparatus was to provide a means of +aiding physicians in counting the pulses of their patients.</p> + +<p>The talents of Galileo having at length extorted due recognition from +the authorities, he was appointed, at the age of twenty-five, +Professor of Mathematics at the University of Pisa. Then came the +time when he felt himself strong enough to throw down the gauntlet to +the adherents of the old philosophy. As a necessary part of his +doctrine on the movement of bodies Aristotle had asserted that the +time occupied by a stone in falling depends upon its weight, so that +the heavier the stone the less time would it require to fall from a +certain height to the earth. It might have been thought that a +statement so easily confuted by the simplest experiments could never +have maintained its position in any accepted scheme of philosophy. +But Aristotle had said it, and to anyone who ventured to express a +doubt the ready sneer was forthcoming, "Do you think yourself a +cleverer man than Aristotle?" Galileo determined to demonstrate in +the most emphatic manner the absurdity of a doctrine which had for +centuries received the sanction of the learned. The summit of the +Leaning Tower of Pisa offered a highly dramatic site for the great +experiment. The youthful professor let fall from the overhanging top +a large heavy body and a small light body simultaneously. According +to Aristotle the large body ought to have reached the ground much +sooner than the small one, but such was found not to be the case. In +the sight of a large concourse of people the simple fact was +demonstrated that the two bodies fell side by side, and reached the +ground at the same time. Thus the first great step was taken in the +overthrow of that preposterous system of unquestioning adhesion to +dogma, which had impeded the development of the knowledge of nature +for nearly two thousand years.</p> + +<p>This revolutionary attitude towards the ancient beliefs was not +calculated to render Galileo's relations with the University +authorities harmonious. He had also the misfortune to make enemies +in other quarters. Don Giovanni de Medici, who was then the Governor +of the Port of Leghorn, had designed some contrivance by which he +proposed to pump out a dock. But Galileo showed up the absurdity of +this enterprise in such an aggressive manner that Don Giovanni took +mortal offence, nor was he mollified when the truths of Galileo's +criticisms were abundantly verified by the total failure of his +ridiculous invention. In various ways Galileo was made to feel his +position at Pisa so unpleasant that he was at length compelled to +abandon his chair in the University. The active exertions of his +friends, of whom Galileo was so fortunate as to have had throughout +his life an abundant supply, then secured his election to the +Professorship of Mathematics at Padua, whither he went in 1592.</p> + +<p><a name="portrait" id="portrait"></a></p> + +<div class="figcenter" style="width: 427px;"> +<a href="images/ill_portrait_galileo.jpg"> +<img src="images/ill_portrait_galileo_sml.jpg" width="427" height="533" alt="PORTRAIT OF GALILEO." title="" /></a> +<span class="caption">PORTRAIT OF GALILEO.</span> +</div> + +<p>It was in this new position that Galileo entered on that marvellous +career of investigation which was destined to revolutionize science. +The zeal with which he discharged his professorial duties was indeed +of the most unremitting character. He speedily drew such crowds to +listen to his discourses on Natural Philosophy that his lecture-room +was filled to overflowing. He also received many private pupils in +his house for special instruction. Every moment that could be spared +from these labours was devoted to his private study and to his +incessant experiments.</p> + +<p>Like many another philosopher who has greatly extended our knowledge +of nature, Galileo had a remarkable aptitude for the invention of +instruments designed for philosophical research. To facilitate his +practical work, we find that in 1599 he had engaged a skilled workman +who was to live in his house, and thus be constantly at hand to try +the devices for ever springing from Galileo's fertile brain. Among +the earliest of his inventions appears to have been the thermometer, +which he constructed in 1602. No doubt this apparatus in its +primitive form differed in some respects from the contrivance we call +by the same name. Galileo at first employed water as the agent, by +the expansion of which the temperature was to be measured. He +afterwards saw the advantage of using spirits for the same purpose. +It was not until about half a century later that mercury came to be +recognised as the liquid most generally suitable for the thermometer.</p> + +<p>The time was now approaching when Galileo was to make that mighty +step in the advancement of human knowledge which followed on the +application of the telescope to astronomy. As to how his idea of +such an instrument originated, we had best let him tell us in his own +words. The passage is given in a letter which he writes to his +brother-in-law, Landucci.</p> + +<p>"I write now because I have a piece of news for you, though whether +you will be glad or sorry to hear it I cannot say; for I have now no +hope of returning to my own country, though the occurrence which has +destroyed that hope has had results both useful and honourable. You +must know, then, that two months ago there was a report spread here +that in Flanders some one had presented to Count Maurice of Nassau a +glass manufactured in such a way as to make distant objects appear +very near, so that a man at the distance of two miles could be +clearly seen. This seemed to me so marvellous that I began to think +about it. As it appeared to me to have a foundation in the Theory of +Perspective, I set about contriving how to make it, and at length I +found out, and have succeeded so well that the one I have made is far +superior to the Dutch telescope. It was reported in Venice that I +had made one, and a week since I was commanded to show it to his +Serenity and to all the members of the senate, to their infinite +amazement. Many gentlemen and senators, even the oldest, have +ascended at various times the highest bell-towers in Venice to spy +out ships at sea making sail for the mouth of the harbour, and have +seen them clearly, though without my telescope they would have been +invisible for more than two hours. The effect of this instrument is +to show an object at a distance of say fifty miles, as if it were but +five miles."</p> + +<p>The remarkable properties of the telescope at once commanded +universal attention among intellectual men. Galileo received +applications from several quarters for his new instrument, of which +it would seem that he manufactured a large number to be distributed +as gifts to various illustrious personages.</p> + +<p>But it was reserved for Galileo himself to make that application of +the instrument to the celestial bodies by which its peculiar powers +were to inaugurate the new era in astronomy. The first discovery +that was made in this direction appears to have been connected with +the number of the stars. Galileo saw to his amazement that through +his little tube he could count ten times as many stars in the sky as +his unaided eye could detect. Here was, indeed, a surprise. We are +now so familiar with the elementary facts of astronomy that it is not +always easy to realise how the heavens were interpreted by the +observers in those ages prior to the invention of the telescope. We +can hardly, indeed, suppose that Galileo, like the majority of those +who ever thought of such matters, entertained the erroneous belief +that the stars were on the surface of a sphere at equal distances +from the observer. No one would be likely to have retained his +belief in such a doctrine when he saw how the number of visible stars +could be increased tenfold by means of Galileo's telescope. It would +have been almost impossible to refuse to draw the inference that the +stars thus brought into view were still more remote objects which the +telescope was able to reveal, just in the same way as it showed +certain ships to the astonished Venetians, when at the time these +ships were beyond the reach of unaided vision.</p> + +<p>Galileo's celestial discoveries now succeeded each other rapidly. +That beautiful Milky Way, which has for ages been the object of +admiration to all lovers of nature, never disclosed its true nature +to the eye of man till the astronomer of Padua turned on it his magic +tube. The splendid zone of silvery light was then displayed as +star-dust scattered over the black background of the sky. It was +observed that though the individual stars were too small to be seen +severally without optical aid, yet such was their incredible number +that the celestial radiance produced that luminosity with which every +stargazer was so familiar.</p> + +<p>But the greatest discovery made by the telescope in these early days, +perhaps, indeed, the greatest discovery that the telescope has ever +accomplished, was the detection of the system of four satellites +revolving around the great planet Jupiter. This phenomenon was so +wholly unexpected by Galileo that, at first, he could hardly believe +his eyes. However, the reality of the existence of a system of four +moons attending the great planet was soon established beyond all +question. Numbers of great personages crowded to Galileo to see for +themselves this beautiful miniature representing the sun with its +system of revolving planets.</p> + +<p>Of course there were, as usual, a few incredulous people who refused +to believe the assertion that four more moving bodies had to be added +to the planetary system. They scoffed at the notion; they said the +satellites may have been in the telescope, but that they were not in +the sky. One sceptical philosopher is reported to have affirmed, +that even if he saw the moons of Jupiter himself he would not believe +in them, as their existence was contrary to the principles of +common-sense!</p> + +<p>There can be no doubt that a special significance attached to the new +discovery at this particular epoch in the history of science. It +must be remembered that in those days the doctrine of Copernicus, +declaring that the sun, and not the earth, was the centre of the +system, that the earth revolved on its axis once a day, and that it +described a mighty circle round the sun once a year, had only +recently been promulgated. This new view of the scheme of nature had +been encountered with the most furious opposition. It may possibly +have been that Galileo himself had not felt quite confident in the +soundness of the Copernican theory, prior to the discovery of the +satellites of Jupiter. But when a picture was there exhibited in +which a number of relatively small globes were shown to be revolving +around a single large globe in the centre, it seemed impossible not +to feel that the beautiful spectacle so displayed was an emblem of +the relations of the planets to the sun. It was thus made manifest +to Galileo that the Copernican theory of the planetary system must be +the true one. The momentous import of this opinion upon the future +welfare of the great philosopher will presently appear.</p> + +<p>It would seem that Galileo regarded his residence at Padua as a state +of undesirable exile from his beloved Tuscany. He had always a +yearning to go back to his own country and at last the desired +opportunity presented itself. For now that Galileo's fame had become +so great, the Grand Duke of Tuscany desired to have the philosopher +resident at Florence, in the belief that he would shed lustre on the +Duke's dominions. Overtures were accordingly made to Galileo, and +the consequence was that in 1616 we find him residing at Florence, +bearing the title of Mathematician and Philosopher to the Grand Duke.</p> + +<p>Two daughters, Polissena and Virginia, and one son, Vincenzo, had +been born to Galileo in Padua. It was the custom in those days that +as soon as the daughter of an Italian gentleman had grown up, her +future career was somewhat summarily decided. Either a husband was +to be forthwith sought out, or she was to enter the convent with the +object of taking the veil as a professed nun. It was arranged that +the two daughters of Galileo, while still scarcely more than +children, should both enter the Franciscan convent of St. Matthew, at +Arcetri. The elder daughter Polissena, took the name of Sister Maria +Celeste, while Virginia became Sister Arcangela. The latter seems to +have been always delicate and subject to prolonged melancholy, and +she is of but little account in the narrative of the life of +Galileo. But Sister Maria Celeste, though never leaving the convent, +managed to preserve a close intimacy with her beloved father. This +was maintained only partly by Galileo's visits, which were very +irregular and were, indeed, often suspended for long intervals. But +his letters to this daughter were evidently frequent and +affectionate, especially in the latter part of his life. Most +unfortunately, however, all his letters have been lost. There are +grounds for believing that they were deliberately destroyed when +Galileo was seized by the Inquisition, lest they should have been +used as evidence against him, or lest they should have compromised +the convent where they were received. But Sister Maria Celeste's +letters to her father have happily been preserved, and most touching +these letters are. We can hardly read them without thinking how the +sweet and gentle nun would have shrunk from the idea of their +publication.</p> + +<p>Her loving little notes to her "dearest lord and father," as she used +affectionately to call Galileo, were almost invariably accompanied by +some gift, trifling it may be, but always the best the poor nun had +to bestow. The tender grace of these endearing communications was +all the more precious to him from the fact that the rest of Galileo's +relatives were of quite a worthless description. He always +acknowledged the ties of his kindred in the most generous way, but +their follies and their vices, their selfishness and their +importunities, were an incessant source of annoyance to him, almost +to the last day of his life.</p> + +<p>On 19th December, 1625, Sister Maria Celeste writes:—</p> + +<p>"I send two baked pears for these days of vigil. But as the greatest +treat of all, I send you a rose, which ought to please you extremely, +seeing what a rarity it is at this season; and with the rose you must +accept its thorns, which represent the bitter passion of our Lord, +whilst the green leaves represent the hope we may entertain that +through the same sacred passion we, having passed through the +darkness of the short winter of our mortal life, may attain to the +brightness and felicity of an eternal spring in heaven."</p> + +<p>When the wife and children of Galileo's shiftless brother came to +take up their abode in the philosopher's home, Sister Maria Celeste +feels glad to think that her father has now some one who, however +imperfectly, may fulfil the duty of looking after him. A graceful +note on Christmas Eve accompanies her little gifts. She hopes that—</p> + +<p>"In these holy days the peace of God may rest on him and all the +house. The largest collar and sleeves I mean for Albertino, the +other two for the two younger boys, the little dog for baby, and the +cakes for everybody, except the spice-cakes, which are for you. +Accept the good-will which would readily do much more."</p> + +<p>The extraordinary forbearance with which Galileo continually placed +his time, his purse, and his influence at the service of those who +had repeatedly proved themselves utterly unworthy of his countenance, +is thus commented on by the good nun.—</p> + +<p>"Now it seems to me, dearest lord and father, that your lordship is +walking in the right path, since you take hold of every occasion that +presents itself to shower continual benefits on those who only repay +you with ingratitude. This is an action which is all the more +virtuous and perfect as it is the more difficult."</p> + +<p>When the plague was raging in the neighbourhood, the loving +daughter's solicitude is thus shown:—</p> + +<p>"I send you two pots of electuary as a preventive against the +plague. The one without the label consists of dried figs, walnuts, +rue, and salt, mixed together with honey. A piece of the size of a +walnut to be taken in the morning, fasting, with a little Greek +wine."</p> + +<p>The plague increasing still more, Sister Maria Celeste obtained with +much difficulty, a small quantity of a renowned liqueur, made by +Abbess Ursula, an exceptionally saintly nun. This she sends to her +father with the words:—</p> + +<p>"I pray your lordship to have faith in this remedy. For if you have +so much faith in my poor miserable prayers, much more may you have in +those of such a holy person; indeed, through her merits you may feel +sure of escaping all danger from the plague."</p> + +<p>Whether Galileo took the remedy we do not know, but at all events +he escaped the plague.</p> + +<p><a name="arcetri" id="arcetri"></a></p> + +<div class="figcenter" style="width: 406px;"> +<a href="images/ill_villa_arcetri.jpg"> +<img src="images/ill_villa_arcetri_sml.jpg" width="406" height="312" alt="THE VILLA ARCETRI. +Galileo's residence, where Milton visited him." title="" /></a> +<span class="caption">THE VILLA ARCETRI. +Galileo's residence, where Milton visited him.</span> +</div> + +<p>From Galileo's new home in Florence the telescope was again directed +to the skies, and again did astounding discoveries reward the +astronomer's labours. The great success which he had met with in +studying Jupiter naturally led Galileo to look at Saturn. Here he +saw a spectacle which was sufficiently amazing, though he failed to +interpret it accurately. It was quite manifest that Saturn did not +exhibit a simple circular disc like Jupiter, or like Mars. It seemed +to Galileo as if the planet consisted of three bodies, a large globe +in the centre, and a smaller one on each side. The enigmatical +nature of the discovery led Galileo to announce it in an enigmatical +manner. He published a string of letters which, when duly +transposed, made up a sentence which affirmed that the planet Saturn +was threefold. Of course we now know that this remarkable appearance +of the planet was due to the two projecting portions of the ring. +With the feeble power of Galileo's telescope, these seemed merely +like small globes or appendages to the large central body.</p> + +<p>The last of Galileo's great astronomical discoveries related to the +libration of the moon. I think that the detection of this phenomenon +shows his acuteness of observation more remarkably than does any one +of his other achievements with the telescope. It is well known that +the moon constantly keeps the same face turned towards the earth. +When, however, careful measurements have been made with regard to the +spots and marks on the lunar surface, it is found that there is a +slight periodic variation which permits us to see now a little to the +east or to the west, now a little to the north or to the south of +the average lunar disc.</p> + +<p>But the circumstances which make the career of Galileo so especially +interesting from the biographer's point of view, are hardly so much +the triumphs that he won as the sufferings that he endured. The +sufferings and the triumphs were, however, closely connected, and it +is fitting that we should give due consideration to what was perhaps +the greatest drama in the history of science.</p> + +<p>On the appearance of the immortal work of Copernicus, in which it was +taught that the earth rotated on its axis, and that the earth, like +the other planets, revolved round the sun, orthodoxy stood aghast. +The Holy Roman Church submitted this treatise, which bore the name +"De Revolutionibus Orbium Coelestium," to the Congregation of the +Index. After due examination it was condemned as heretical in 1615. +Galileo was suspected, on no doubt excellent grounds, of entertaining +the objectionable views of Copernicus. He was accordingly privately +summoned before Cardinal Bellarmine on 26th February 1616, and duly +admonished that he was on no account to teach or to defend the +obnoxious doctrines. Galileo was much distressed by this +intimation. He felt it a serious matter to be deprived of the +privilege of discoursing with his friends about the Copernican +system, and of instructing his disciples in the principles of the +great theory of whose truth he was perfectly convinced. It pained +him, however, still more to think, devout Catholic as he was, that +such suspicions of his fervent allegiance to his Church should ever +have existed, as were implied by the words and monitions of Cardinal +Bellarmine.</p> + +<p>In 1616, Galileo had an interview with Pope Paul V., who received the +great astronomer very graciously, and walked up and down with him in +conversation for three-quarters of an hour. Galileo complained to +his Holiness of the attempts made by his enemies to embarrass him +with the authorities of the Church, but the Pope bade him be +comforted. His Holiness had himself no doubts of Galileo's +orthodoxy, and he assured him that the Congregation of the Index +should give Galileo no further trouble so long as Paul V. was in the +chair of St. Peter.</p> + +<p>On the death of Paul V. in 1623, Maffeo Barberini was elected Pope, +as Urban VIII. This new Pope, while a cardinal, had been an intimate +friend of Galileo's, and had indeed written Latin verses in praise of +the great astronomer and his discoveries. It was therefore not +unnatural for Galileo to think that the time had arrived when, with +the use of due circumspection, he might continue his studies and his +writings, without fear of incurring the displeasure of the Church. +Indeed, in 1624, one of Galileo's friends writing from Rome, urges +Galileo to visit the city again, and added that—</p> + +<p>"Under the auspices of this most excellent, learned, and benignant +Pontiff, science must flourish. Your arrival will be welcome to his +Holiness. He asked me if you were coming, and when, and in short, he +seems to love and esteem you more than ever."</p> + +<p>The visit was duly paid, and when Galileo returned to Florence, the +Pope wrote a letter from which the following is an extract, +commanding the philosopher to the good offices of the young +Ferdinand, who had shortly before succeeded his father in the Grand +Duchy of Tuscany.</p> + +<p>"We find in Galileo not only literary distinction, but also the love +of piety, and he is also strong in those qualities by which the +pontifical good-will is easily obtained. And now, when he has been +brought to this city to congratulate us on our elevation, we have +very lovingly embraced him; nor can we suffer him to return to the +country whither your liberality calls him, without an ample provision +of pontifical love. And that you may know how dear he is to us, we +have willed to give him this honourable testimonial of virtue and +piety. And we further signify that every benefit which you shall +confer upon him, imitating or even surpassing your father's +liberality, will conduce to our gratification."</p> + +<p>The favourable reception which had been accorded to him by Pope Urban +VIII. seems to have led Galileo to expect that there might be some +corresponding change in the attitude of the Papal authorities on the +great question of the stability of the earth. He accordingly +proceeded with the preparation of the chief work of his life, "The +Dialogue of the two Systems." It was submitted for inspection by the +constituted authorities. The Pope himself thought that, if a few +conditions which he laid down were duly complied with, there could be +no objection to the publication of the work. In the first place, the +title of the book was to be so carefully worded as to show plainly +that the Copernican doctrine was merely to be regarded as an +hypothesis, and not as a scientific fact. Galileo was also +instructed to conclude the book with special arguments which had been +supplied by the Pope himself, and which appeared to his Holiness to +be quite conclusive against the new doctrine of Copernicus.</p> + +<p>Formal leave for the publication of the Dialogue was then given to +Galileo by the Inquisitor General, and it was accordingly sent to the +press. It might be thought that the anxieties of the astronomer +about his book would then have terminated. As a matter of fact, they +had not yet seriously begun. Riccardi, the Master of the Sacred +Palace, having suddenly had some further misgivings, sent to Galileo +for the manuscript while the work was at the printer's, in order that +the doctrine it implied might be once again examined. Apparently, +Riccardi had come to the conclusion that he had not given the matter +sufficient attention, when the authority to go to press had been +first and, perhaps, hastily given. Considerable delay in the issue +of the book was the result of these further deliberations. At last, +however, in June, 1632, Galileo's great work, "The Dialogue of the +two Systems," was produced for the instruction of the world, though +the occasion was fraught with ruin to the immortal author.</p> + +<p><a name="facsimile" id="facsimile"></a></p> + +<div class="figcenter" style="width: 297px;"> +<a href="images/ill_sketch_lunar_sfc.jpg"> +<img src="images/ill_sketch_lunar_sfc_sml.jpg" width="297" height="294" alt="FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO." title="" /></a> +<span class="caption">FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.</span> +</div> + +<p>The book, on its publication, was received and read with the greatest +avidity. But presently the Master of The Sacred Palace found reason +to regret that he had given his consent to its appearance. He +accordingly issued a peremptory order to sequestrate every copy in +Italy. This sudden change in the Papal attitude towards Galileo +formed the subject of a strong remonstrance addressed to the Roman +authorities by the Grand Duke of Tuscany. The Pope himself seemed to +have become impressed all at once with the belief that the work +contained matter of an heretical description. The general +interpretation put upon the book seems to have shown the authorities +that they had mistaken its true tendency, notwithstanding the fact +that it had been examined again and again by theologians deputed for +the duty. To the communication from the Grand Duke the Pope returned +answer, that he had decided to submit the book to a congregation of +"learned, grave, and saintly men," who would weigh every word in it. +The views of his Holiness personally on the subject were expressed in +his belief that the Dialogue contained the most perverse matter that +could come into a reader's hands.</p> + +<p>The Master of the Sacred Palace was greatly blamed by the authorities +for having given his sanction to its issue. He pleaded that the book +had not been printed in the precise terms of the original manuscript +which had been submitted to him. It was also alleged that Galileo +had not adhered to his promise of inserting properly the arguments +which the Pope himself had given in support of the old and orthodox +view. One of these had, no doubt, been introduced, but, so far from +mending Galileo's case, it had made matters really look worse for the +poor philosopher. The Pope's argument had been put into the mouth of +one of the characters in the Dialogue named "Simplicio." Galileo's +enemies maintained that by adopting such a method for the expression +of his Holiness's opinion, Galileo had intended to hold the Pope +himself up to ridicule. Galileo's friends maintained that nothing +could have been farther from his intention. It seems, however, +highly probable that the suspicions thus aroused had something to say +to the sudden change of front on the part of the Papal authorities.</p> + +<p>On 1st October, 1632, Galileo received an order to appear before the +Inquisition at Rome on the grave charge of heresy. Galileo, of +course, expressed his submission, but pleaded for a respite from +compliance with the summons, on the ground of his advanced age and +his failing health. The Pope was, however, inexorable; he said that +he had warned Galileo of his danger while he was still his friend. +The command could not be disobeyed. Galileo might perform the +journey as slowly as he pleased, but it was imperatively necessary +for him to set forth and at once.</p> + +<p>On 20th January, 1633, Galileo started on his weary journey to Rome, +in compliance with this peremptory summons. On 13th February he was +received as the guest of Niccolini, the Tuscan ambassador, who had +acted as his wise and ever-kind friend throughout the whole affair. +It seemed plain that the Holy Office were inclined to treat Galileo +with as much clemency and consideration as was consistent with the +determination that the case against him should be proceeded with to +the end. The Pope intimated that in consequence of his respect for +the Grand Duke of Tuscany he should permit Galileo to enjoy the +privilege, quite unprecedented for a prisoner charged with heresy, of +remaining as an inmate in the ambassador's house. He ought, +strictly, to have been placed in the dungeons of the Inquisition. +When the examination of the accused had actually commenced, Galileo +was confined, not, indeed, in the dungeons, but in comfortable rooms +at the Holy Office.</p> + +<p>By the judicious and conciliatory language of submission which +Niccolini had urged Galileo to use before the Inquisitors, they were +so far satisfied that they interceded with the Pope for his release. +During the remainder of the trial Galileo was accordingly permitted +to go back to the ambassador's, where he was most heartily welcomed. +Sister Maria Celeste, evidently thinking this meant that the whole +case was at an end, thus expresses herself:—</p> + +<p>"The joy that your last dear letter brought me, and the having to +read it over and over to the nuns, who made quite a jubilee on +hearing its contents, put me into such an excited state that at last +I got a severe attack of headache."</p> + +<p>In his defence Galileo urged that he had already been acquitted in +1616 by Cardinal Bellarmine, when a charge of heresy was brought +against him, and he contended that anything he might now have done, +was no more than he had done on the preceding occasion, when the +orthodoxy of his doctrines received solemn confirmation. The +Inquisition seemed certainly inclined to clemency, but the Pope was +not satisfied. Galileo was accordingly summoned again on the 21st +June. He was to be threatened with torture if he did not forthwith +give satisfactory explanations as to the reasons which led him to +write the Dialogue. In this proceeding the Pope assured the Tuscan +ambassador that he was treating Galileo with the utmost consideration +possible in consequence of his esteem and regard for the Grand Duke, +whose servant Galileo was. It was, however, necessary that some +exemplary punishment be meted out to the astronomer, inasmuch as by +the publication of the Dialogue he had distinctly disobeyed the +injunction of silence laid upon him by the decree of 1616. Nor was +it admissible for Galileo to plead that his book had been sanctioned +by the Master of the Sacred College, to whose inspection it had been +again and again submitted. It was held, that if the Master of the +Sacred College had been unaware of the solemn warning the philosopher +had already received sixteen years previously, it was the duty of +Galileo to have drawn his attention to that fact.</p> + +<p>On the 22nd June, 1633, Galileo was led to the great hall of the +Inquisition, and compelled to kneel before the cardinals there +assembled and hear his sentence. In a long document, most +elaborately drawn up, it is definitely charged against Galileo that, +in publishing the Dialogue, he committed the essentially grave error +of treating the doctrine of the earth's motion as open to +discussion. Galileo knew, so the document affirmed, that the Church +had emphatically pronounced this notion to be contrary to Holy Writ, +and that for him to consider a doctrine so stigmatized as having any +shadow of probability in its favour was an act of disrespect to the +authority of the Church which could not be overlooked. It was also +charged against Galileo that in his Dialogue he has put the strongest +arguments into the mouth, not of those who supported the orthodox +doctrine, but of those who held the theory as to the earth's motion +which the Church had so deliberately condemned.</p> + +<p>After due consideration of the defence made by the prisoner, it was +thereupon decreed that he had rendered himself vehemently suspected +of heresy by the Holy Office, and in consequence had incurred all the +censures and penalties of the sacred canons, and other decrees +promulgated against such persons. The graver portion of these +punishments would be remitted, if Galileo would solemnly repudiate +the heresies referred to by an abjuration to be pronounced by him in +the terms laid down.</p> + +<p>At the same time it was necessary to mark, in some emphatic manner, +the serious offence which had been committed, so that it might serve +both as a punishment to Galileo and as a warning to others. It was +accordingly decreed that he should be condemned to imprisonment in +the Holy Office during the pleasure of the Papal authorities, and +that he should recite once a week for three years the seven +Penitential Psalms.</p> + +<p>Then followed that ever-memorable scene in the great hall of the +Inquisition, in which the aged and infirm Galileo, the inventor of +the telescope and the famous astronomer, knelt down to abjure before +the most eminent and reverend Lords Cardinal, Inquisitors General +throughout the Christian Republic against heretical depravity. With +his hands on the Gospels, Galileo was made to curse and detest the +false opinion that the sun was the centre of the universe and +immovable, and that the earth was not the centre of the same, and +that it moved. He swore that for the future he will never say nor +write such things as may bring him under suspicion, and that if he +does so he submits to all the pains and penalties of the sacred +canons. This abjuration was subsequently read in Florence before +Galileo's disciples, who had been specially summoned to attend.</p> + +<p>It has been noted that neither on the first occasion, in 1616, nor on +the second in 1633, did the reigning Pope sign the decrees concerning +Galileo. The contention has accordingly been made that Paul V. and +Urban VIII. are both alike vindicated from any technical +responsibility for the attitude of the Romish Church towards the +Copernican doctrines. The significance of this circumstance has been +commented on in connection with the doctrine of the infallibility of +the Pope.</p> + +<p>We can judge of the anxiety felt by Sister Maria Celeste about her +beloved father during these terrible trials. The wife of the +ambassador Niccolini, Galileo's steadfast friend, most kindly wrote +to give the nun whatever quieting assurances the case would permit. +There is a renewed flow of these touching epistles from the daughter +to her father. Thus she sends word—</p> + +<p>"The news of your fresh trouble has pierced my soul with grief all +the more that it came quite unexpectedly."</p> + +<p>And again, on hearing that he had been permitted to leave Rome, +she writes—</p> + +<p>"I wish I could describe the rejoicing of all the mothers and sisters +on hearing of your happy arrival at Siena. It was indeed most +extraordinary. On hearing the news the Mother Abbess and many of the +nuns ran to me, embracing me and weeping for joy and tenderness."</p> + +<p>The sentence of imprisonment was at first interpreted leniently by +the Pope. Galileo was allowed to reside in qualified durance in the +archbishop's house at Siena. Evidently the greatest pain that he +endured arose from the forced separation from that daughter, whom he +had at last learned to love with an affection almost comparable with +that she bore to him. She had often told him that she never had any +pleasure equal to that with which she rendered any service to her +father. To her joy, she discovers that she can relieve him from the +task of reciting the seven Penitential Psalms which had been imposed +as a Penance:—</p> + +<p>"I began to do this a while ago," she writes, "and it gives me much +pleasure. First, because I am persuaded that prayer in obedience to +Holy Church must be efficacious; secondly, in order to save you the +trouble of remembering it. If I had been able to do more, most +willingly would I have entered a straiter prison than the one I live +in now, if by so doing I could have set you at liberty."</p> + +<p><a name="crest" id="crest"></a></p> + +<div class="figcenter" style="width: 281px;"> +<a href="images/ill_fm_crest_galileo.jpg"> +<img src="images/ill_fm_crest_galileo_sml.jpg" width="281" height="258" alt="CREST OF GALILEO'S FAMILY." title="" /></a> +<span class="caption">CREST OF GALILEO'S FAMILY.</span> +</div> + +<p>Sister Maria Celeste was gradually failing in health, but the great +privilege was accorded to her of being able once again to embrace her +beloved lord and master. Galileo had, in fact, been permitted to +return to his old home; but on the very day when he heard of his +daughter's death came the final decree directing him to remain in his +own house in perpetual solitude.</p> + +<p>Amid the advancing infirmities of age, the isolation from friends, +and the loss of his daughter, Galileo once again sought consolation +in hard work. He commenced his famous dialogue on Motion. Gradually, +however, his sight began to fail, and blindness was at last added to +his other troubles. On January 2nd, 1638, he writes to Diodati:—</p> + +<p>"Alas, your dear friend and servant, Galileo, has been for the last +month perfectly blind, so that this heaven, this earth, this universe +which I by my marvellous discoveries and clear demonstrations have +enlarged a hundred thousand times beyond the belief of the wise men +of bygone ages, henceforward is for me shrunk into such a small space +as is filled by my own bodily sensations."</p> + +<p>But the end was approaching—the great philosopher, was attacked by +low fever, from which he died on the 8th January, 1643.</p> + +<h3><a name="KEPLER" id="KEPLER"></a>KEPLER.</h3> +<p>While the illustrious astronomer, Tycho Brahe, lay on his death-bed, +he had an interview which must ever rank as one of the important +incidents in the history of science. The life of Tycho had been +passed, as we have seen, in the accumulation of vast stores of +careful observations of the positions of the heavenly bodies. It was +not given to him to deduce from his splendid work the results to +which they were destined to lead. It was reserved for another +astronomer to distil, so to speak, from the volumes in which Tycho's +figures were recorded, the great truths of the universe which those +figures contained. Tycho felt that his work required an interpreter, +and he recognised in the genius of a young man with whom he was +acquainted the agent by whom the world was to be taught some of the +great truths of nature. To the bedside of the great Danish +astronomer the youthful philosopher was summoned, and with his last +breath Tycho besought of him to spare no labour in the performance of +those calculations, by which alone the secrets of the movements of +the heavens could be revealed. The solemn trust thus imposed was +duly accepted, and the man who accepted it bore the immortal name of +Kepler.</p> + +<p>Kepler was born on the 27th December, 1571, at Weil, in the Duchy of +Wurtemberg. It would seem that the circumstances of his childhood +must have been singularly unhappy. His father, sprung from a +well-connected family, was but a shiftless and idle adventurer; nor +was the great astronomer much more fortunate in his other parent. His +mother was an ignorant and ill-tempered woman; indeed, the +ill-assorted union came to an abrupt end through the desertion of the +wife by her husband when their eldest son John, the hero of our +present sketch, was eighteen years old. The childhood of this lad, +destined for such fame, was still further embittered by the +circumstance that when he was four years old he had a severe attack +of small-pox. Not only was his eyesight permanently injured, but +even his constitution appears to have been much weakened by this +terrible malady.</p> + +<p>It seems, however, that the bodily infirmities of young John Kepler +were the immediate cause of his attention being directed to the +pursuit of knowledge. Had the boy been fitted like other boys for +ordinary manual work, there can be hardly any doubt that to manual +work his life must have been devoted. But, though his body was +feeble, he soon gave indications of the possession of considerable +mental power. It was accordingly thought that a suitable sphere for +his talents might be found in the Church which, in those days, was +almost the only profession that afforded an opening for an +intellectual career. We thus find that by the time John Kepler was +seventeen years old he had attained a sufficient standard of +knowledge to entitle him to admission on the foundation of the +University at Tubingen.</p> + +<p>In the course of his studies at this institution he seems to have +divided his attention equally between astronomy and divinity. It not +unfrequently happens that when a man has attained considerable +proficiency in two branches of knowledge he is not able to see very +clearly in which of the two pursuits his true vocation lies. His +friends and onlookers are often able to judge more wisely than he +himself can do as to which of the two lines it would be better for +him to pursue. This incapacity for perceiving the path in which +greatness awaited him, existed in the case of Kepler. Personally, he +inclined to enter the ministry, in which a promising career seemed +open to him. He yielded, however, to friends, who evidently knew him +better than he knew himself, and accepted in 1594, the important +Professorship of astronomy which had been offered to him in the +University of Gratz.</p> + +<p>It is difficult for us in these modern days to realise the somewhat +extraordinary duties which were expected from an astronomical +professor in the sixteenth century. He was, of course, required to +employ his knowledge of the heavens in the prediction of eclipses, +and of the movements of the heavenly bodies generally. This seems +reasonable enough; but what we are not prepared to accept is the +obligation which lay on the astronomers to predict the fates of +nations and the destinies of individuals.</p> + +<p>It must be remembered that it was the almost universal belief in +those days, that all the celestial spheres revolved in some +mysterious fashion around the earth, which appeared by far the most +important body in the universe. It was imagined that the sun, the +moon, and the stars indicated, in the vicissitudes of their +movements, the careers of nations and of individuals. Such being the +generally accepted notion, it seemed to follow that a professor who +was charged with the duty of expounding the movements of the heavenly +bodies must necessarily be looked to for the purpose of deciphering +the celestial decrees regarding the fate of man which the heavenly +luminaries were designed to announce.</p> + +<p>Kepler threw himself with characteristic ardour into even this +fantastic phase of the labours of the astronomical professor; he +diligently studied the rules of astrology, which the fancies of +antiquity had compiled. Believing sincerely as he did in the +connection between the aspect of the stars and the state of human +affairs, he even thought that he perceived, in the events of his own +life, a corroboration of the doctrine which affirmed the influence of +the planets upon the fate of individuals.</p> + +<p><a name="solids" id="solids"></a></p> + +<div class="figcenter" style="width: 276px;"> +<a href="images/ill_kepler_solids.jpg"> +<img src="images/ill_kepler_solids_sml.jpg" width="276" height="257" alt="KEPLER'S SYSTEM OF REGULAR SOLIDS." title="" /></a> +<span class="caption">KEPLER'S SYSTEM OF REGULAR SOLIDS.</span> +</div> + +<p>But quite independently of astrology there seem to have been many +other delusions current among the philosophers of Kepler's time. It +is now almost incomprehensible how the ablest men of a few centuries +ago should have entertained such preposterous notions, as they did, +with respect to the system of the universe. As an instance of what +is here referred to, we may cite the extraordinary notion which, +under the designation of a discovery, first brought Kepler into +fame. Geometers had long known that there were five, but no more +than five, regular solid figures. There is, for instance, the cube +with six sides, which is, of course, the most familiar of these +solids. Besides the cube there are other figures of four, eight, +twelve, and twenty sides respectively. It also happened that there +were five planets, but no more than five, known to the ancients, +namely, Mercury, Venus, Mars, Jupiter, and Saturn. To Kepler's +lively imaginations this coincidence suggested the idea that the five +regular solids corresponded to the five planets, and a number of +fancied numerical relations were adduced on the subject. The +absurdity of this doctrine is obvious enough, especially when we +observe that, as is now well known, there are two large planets, and +a host of small planets, over and above the magical number of the +regular solids. In Kepler's time, however, this doctrine was so far +from being regarded as absurd, that its announcement was hailed as a +great intellectual triumph. Kepler was at once regarded with +favour. It seems, indeed, to have been the circumstance which +brought him into correspondence with Tycho Brahe. By its means also +he became known to Galileo.</p> + +<p>The career of a scientific professor in those early days appears +generally to have been marked by rather more striking vicissitudes +than usually befall a professor in a modern university. Kepler was a +Protestant, and as such he had been appointed to his professorship at +Gratz. A change, however, having taken place in the religious belief +entertained by the ruling powers of the University, the Protestant +professors were expelled. It seems that special influence having +been exerted in Kepler's case on account of his exceptional eminence, +he was recalled to Gratz and reinstated in the tenure of his chair. +But his pupils had vanished, so that the great astronomer was glad to +accept a post offered him by Tycho Brahe in the observatory which the +latter had recently established near Prague.</p> + +<p>On Tycho's death, which occurred soon after, an opening presented +itself which gave Kepler the opportunity his genius demanded. He was +appointed to succeed Tycho in the position of imperial mathematician. +But a far more important point, both for Kepler and for science, +was that to him was confided the use of Tycho's observations. It was, +indeed, by the discussion of Tycho's results that Kepler was enabled +to make the discoveries which form such an important part of +astronomical history.</p> + +<p>Kepler must also be remembered as one of the first great astronomers +who ever had the privilege of viewing celestial bodies through a +telescope. It was in 1610 that he first held in his hands one of +those little instruments which had been so recently applied to the +heavens by Galileo. It should, however, be borne in mind that the +epoch-making achievements of Kepler did not arise from any telescopic +observations that he made, or, indeed, that any one else made. They +were all elaborately deduced from Tycho's measurements of the +positions of the planets, obtained with his great instruments, which +were unprovided with telescopic assistance.</p> + +<p>To realise the tremendous advance which science received from +Kepler's great work, it is to be understood that all the astronomers +who laboured before him at the difficult subject of the celestial +motions, took it for granted that the planets must revolve in +circles. If it did not appear that a planet moved in a fixed circle, +then the ready answer was provided by Ptolemy's theory that the +circle in which the planet did move was itself in motion, so that its +centre described another circle.</p> + +<p>When Kepler had before him that wonderful series of observations of +the planet, Mars, which had been accumulated by the extraordinary +skill of Tycho, he proved, after much labour, that the movements of +the planet refused to be represented in a circular form. Nor would +it do to suppose that Mars revolved in one circle, the centre of +which revolved in another circle. On no such supposition could the +movements of the planets be made to tally with those which Tycho had +actually observed. This led to the astonishing discovery of the true +form of a planet's orbit. For the first time in the history of +astronomy the principle was laid down that the movement of a planet +could not be represented by a circle, nor even by combinations of +circles, but that it could be represented by an elliptic path. In +this path the sun is situated at one of those two points in the +ellipse which are known as its foci.</p> + +<p><a name="kepler_ill" id="kepler_ill"></a></p> + +<div class="figcenter" style="width: 425px;"> +<a href="images/ill_kepler.jpg"> +<img src="images/ill_kepler_sml.jpg" width="425" height="526" alt="KEPLER." title="" /></a> +<span class="caption">KEPLER.</span> +</div> + +<p>Very simple apparatus is needed for the drawing of one of those +ellipses which Kepler has shown to possess such astonishing +astronomical significance. Two pins are stuck through a sheet of +paper on a board, the point of a pencil is inserted in a loop of +string which passes over the pins, and as the pencil is moved round +in such a way as to keep the string stretched, that beautiful curve +known as the ellipse is delineated, while the positions of the pins +indicate the two foci of the curve. If the length of the loop of +string is unchanged then the nearer the pins are together, the +greater will be the resemblance between the ellipse and the circle, +whereas the more the pins are separated the more elongated does the +ellipse become. The orbit of a great planet is, in general, one of +those ellipses which approaches a nearly circular form. It +fortunately happens, however, that the orbit of Mars makes a wider +departure from the circular form than any of the other important +planets. It is, doubtless, to this circumstance that we must +attribute the astonishing success of Kepler in detecting the true +shape of a planetary orbit. Tycho's observations would not have been +sufficiently accurate to have exhibited the elliptic nature of a +planetary orbit which, like that of Venus, differed very little from +a circle.</p> + +<p>The more we ponder on this memorable achievement the more striking +will it appear. It must be remembered that in these days we know of +the physical necessity which requires that a planet shall revolve in +an ellipse and not in any other curve. But Kepler had no such +knowledge. Even to the last hour of his life he remained in +ignorance of the existence of any natural cause which ordained that +planets should follow those particular curves which geometers know so +well. Kepler's assignment of the ellipse as the true form of the +planetary orbit is to be regarded as a brilliant guess, the truth of +which Tycho's observations enabled him to verify. Kepler also +succeeded in pointing out the law according to which the velocity of +a planet at different points of its path could be accurately +specified. Here, again, we have to admire the sagacity with which +this marvellously acute astronomer guessed the deep truth of nature. +In this case also he was quite unprovided with any reason for +expecting from physical principles that such a law as he discovered +must be obeyed. It is quite true that Kepler had some slight +knowledge of the existence of what we now know as gravitation. He +had even enunciated the remarkable doctrine that the ebb and flow of +the tide must be attributed to the attraction of the moon on the +waters of the earth. He does not, however, appear to have had any +anticipation of those wonderful discoveries which Newton was destined +to make a little later, in which he demonstrated that the laws +detected by Kepler's marvellous acumen were necessary consequences of +the principle of universal gravitation.</p> + +<p><a name="symbolical" id="symbolical"></a></p> + +<div class="figcenter" style="width: 320px;"> +<a href="images/ill_symbolic_planetary_system.jpg"> +<img src="images/ill_symbolic_planetary_system_sml.jpg" width="320" height="362" alt="SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM." title="" /></a> +<span class="caption">SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.</span> +</div> + +<p>To appreciate the relations of Kepler and Tycho it is necessary to +note the very different way in which these illustrious astronomers +viewed the system of the heavens. It should be observed that +Copernicus had already expounded the true system, which located the +sun at the centre of the planetary system. But in the days of Tycho +Brahe this doctrine had not as yet commanded universal assent. In +fact, the great observer himself did not accept the new views of +Copernicus. It appeared to Tycho that the earth not only appeared to +be the centre of things celestial, but that it actually was the +centre. It is, indeed, not a little remarkable that a student of the +heavens so accurate as Tycho should have deliberately rejected the +Copernican doctrine in favour of the system which now seems so +preposterous. Throughout his great career, Tycho steadily observed +the places of the sun, the moon, and the planets, and as steadily +maintained that all those bodies revolved around the earth fixed in +the centre. Kepler, however, had the advantage of belonging to the +new school. He utilised the observations of Tycho in developing the +great Copernican theory whose teaching Tycho stoutly resisted.</p> + +<p>Perhaps a chapter in modern science may illustrate the intellectual +relation of these great men. The revolution produced by Copernicus +in the doctrine of the heavens has often been likened to the +revolution which the Darwinian theory produced in the views held by +biologists as to life on this earth. The Darwinian theory did not at +first command universal assent even among those naturalists whose +lives had been devoted with the greatest success to the study of +organisms. Take, for instance, that great naturalist, Professor +Owen, by whose labours vast extension has been given to our knowledge +of the fossil animals which dwelt on the earth in past ages. Now, +though Owens researches were intimately connected with the great +labours of Darwin, and afforded the latter material for his +epoch-making generalization, yet Owen deliberately refused to accept +the new doctrines. Like Tycho, he kept on rigidly accumulating his +facts under the influence of a set of ideas as to the origin of +living forms which are now universally admitted to be erroneous. If, +therefore, we liken Darwin to Copernicus, and Owen to Tycho, we may +liken the biologists of the present day to Kepler, who interpreted +the results of accurate observation upon sound theoretical +principles.</p> + +<p>In reading the works of Kepler in the light of our modern knowledge +we are often struck by the extent to which his perception of the +sublimest truths in nature was associated with the most extravagant +errors and absurdities. But, of course, it must be remembered that +he wrote in an age in which even the rudiments of science, as we now +understand it, were almost entirely unknown.</p> + +<p>It may well be doubted whether any joy experienced by mortals is more +genuine than that which rewards the successful searcher after natural +truths. Every science-worker, be his efforts ever so humble, will be +able to sympathise with the enthusiastic delight of Kepler when at +last, after years of toil, the glorious light broke forth, and that +which he considered to be the greatest of his astonishing laws first +dawned upon him. Kepler rightly judged that the number of days which +a planet required to perform its voyage round the sun must be +connected in some manner with the distance from the planet to the +sun; that is to say, with the radius of the planet's orbit, inasmuch +as we may for our present object regard the planet's orbit as +circular.</p> + +<p>Here, again, in his search for the unknown law, Kepler had no +accurate dynamical principles to guide his steps. Of course, we now +know not only what the connection between the planet's distance and +the planet's periodic time actually is, but we also know that it is a +necessary consequence of the law of universal gravitation. Kepler, +it is true, was not without certain surmises on the subject, but they +were of the most fanciful description. His notions of the planets, +accurate as they were in certain important respects, were mixed up +with vague ideas as to the properties of metals and the geometrical +relations of the regular solids. Above all, his reasoning was +penetrated by the supposed astrological influences of the stars and +their significant relation to human fate. Under the influence of +such a farrago of notions, Kepler resolved to make all sorts of +trials in his search for the connection between the distance of a +planet from the sun and the time in which the revolution of that +planet was accomplished.</p> + +<p>It was quite easily demonstrated that the greater the distance of the +planet from the sun the longer was the time required for its +journey. It might have been thought that the time would be directly +proportional to the distance. It was, however, easy to show that +this supposition did not agree with the fact. Finding that this +simple relation would not do, Kepler undertook a vast series of +calculations to find out the true method of expressing the +connection. At last, after many vain attempts, he found, to his +indescribable joy, that the square of the time in which a planet +revolves around the sun was proportional to the cube of the average +distance of the planet from that body.</p> + +<p>The extraordinary way in which Kepler's views on celestial matters +were associated with the wildest speculations, is well illustrated in +the work in which he propounded his splendid discovery just referred +to. The announcement of the law connecting the distances of the +planets from the sun with their periodic times, was then mixed up +with a preposterous conception about the properties of the different +planets. They were supposed to be associated with some profound +music of the spheres inaudible to human ears, and performed only for +the benefit of that being whose soul formed the animating spirit of +the sun.</p> + +<p>Kepler was also the first astronomer who ever ventured to predict the +occurrence of that remarkable phenomenon, the transit of a planet in +front of the sun's disc. He published, in 1629, a notice to the +curious in things celestial, in which he announced that both of the +planets, Mercury and Venus, were to make a transit across the sun on +specified days in the winter of 1631. The transit of Mercury was +duly observed by Gassendi, and the transit of Venus also took place, +though, as we now know, the circumstances were such that it was not +possible for the phenomenon to be witnessed by any European +astronomer.</p> + +<p>In addition to Kepler's discoveries already mentioned, with which his +name will be for ever associated, his claim on the gratitude of +astronomers chiefly depends on the publication of his famous +Rudolphine tables. In this remarkable work means are provided for +finding the places of the planets with far greater accuracy than had +previously been attainable.</p> + +<p>Kepler, it must be always remembered, was not an astronomical +observer. It was his function to deal with the observations made by +Tycho, and, from close study and comparison of the results, to work +out the movements of the heavenly bodies. It was, in fact, Tycho who +provided as it were the raw material, while it was the genius of +Kepler which wrought that material into a beautiful and serviceable +form. For more than a century the Rudolphine tables were regarded as +a standard astronomical work. In these days we are accustomed to +find the movements of the heavenly bodies set forth with all +desirable exactitude in the NAUTICAL ALMANACK, and the similar +publication issued by foreign Governments. Let it be remembered that +it was Kepler who first imparted the proper impulse in this +direction.</p> + +<p><a name="commemoration" id="commemoration"></a></p> + +<div class="figcenter" style="width: 447px;"> +<a href="images/ill_commemoration_rudolphine_tables.jpg"> +<img src="images/ill_commemoration_rudolphine_tables_sml.jpg" width="447" height="692" alt="THE COMMEMORATION OF THE RUDOLPHINE TABLES." title="" /></a> +<span class="caption">THE COMMEMORATION OF THE RUDOLPHINE TABLES.</span> +</div> + +<p>When Kepler was twenty-six he married an heiress from Styria, who, +though only twenty-three years old, had already had some experience +in matrimony. Her first husband had died; and it was after her +second husband had divorced her that she received the addresses of +Kepler. It will not be surprising to hear that his domestic affairs +do not appear to have been particularly happy, and his wife died in +1611. Two years later, undeterred by the want of success in his +first venture, he sought a second partner, and he evidently +determined not to make a mistake this time. Indeed, the methodical +manner in which he made his choice of the lady to whom he should +propose has been duly set forth by him and preserved for our +edification. With some self-assurance he asserts that there were no +fewer than eleven spinsters desirous of sharing his joys and +sorrows. He has carefully estimated and recorded the merits and +demerits of each of these would-be brides. The result of his +deliberations was that he awarded himself to an orphan girl, +destitute even of a portion. Success attended his choice, and his +second marriage seems to have proved a much more suitable union than +his first. He had five children by the first wife and seven by the +second.</p> + +<p>The years of Kepler's middle life were sorely distracted by a trouble +which, though not uncommon in those days, is one which we find it +difficult to realise at the present time. His mother, Catherine +Kepler, had attained undesirable notoriety by the suspicion that she +was guilty of witchcraft. Years were spent in legal investigations, +and it was only after unceasing exertions on the part of the +astronomer for upwards of a twelve-month that he was finally able to +procure her acquittal and release from prison.</p> + +<p>It is interesting for us to note that at one time there was a +proposal that Kepler should forsake his native country and adopt +England as a home. It arose in this wise. The great man was +distressed throughout the greater part of his life by pecuniary +anxieties. Finding him in a strait of this description, the English +ambassador in Venice, Sir Henry Wotton, in the year 1620, besought +Kepler to come over to England, where he assured him that he would +obtain a favourable reception, and where, he was able to add, +Kepler's great scientific work was already highly esteemed. But his +efforts were unavailing; Kepler would not leave his own country. He +was then forty-nine years of age, and doubtless a home in a foreign +land, where people spoke a strange tongue, had not sufficient +attraction for him, even when accompanied with the substantial +inducements which the ambassador was able to offer. Had Kepler +accepted this invitation, he would, in transferring his home to +England, have anticipated the similar change which took place in the +career of another great astronomer two centuries later. It will be +remembered that Herschel, in his younger days, did transfer himself +to England, and thus gave to England the imperishable fame of +association with his triumphs.</p> + +<p>The publication of the Rudolphine tables of the celestial movements +entailed much expense. A considerable part of this was defrayed by +the Government at Venice but the balance occasioned no little trouble +and anxiety to Kepler. No doubt the authorities of those days were +even less willing to spend money on scientific matters than are the +Governments of more recent times. For several years the imperial +Treasury was importuned to relieve him from his anxieties. The +effects of so much worry, and of the long journeys which were +involved, at last broke down Kepler's health completely. As we have +already mentioned, he had never been strong from infancy, and he +finally succumbed to a fever in November, 1630, at the age of +fifty-nine. He was interred at St. Peter's Church at Ratisbon.</p> + +<p>Though Kepler had not those personal characteristics which have made +his great predecessor, Tycho Brahe, such a romantic figure, yet a +picturesque element in Kepler's character is not wanting. It was, +however, of an intellectual kind. His imagination, as well as his +reasoning faculties, always worked together. He was incessantly +prompted by the most extraordinary speculations. The great majority +of them were in a high degree wild and chimerical, but every now and +then one of his fancies struck right to the heart of nature, and an +immortal truth was brought to light.</p> + +<p>I remember visiting the observatory of one of our greatest modern +astronomers, and in a large desk he showed me a multitude of +photographs which he had attempted but which had not been successful, +and then he showed me the few and rare pictures which had succeeded, +and by which important truths had been revealed. With a felicity of +expression which I have often since thought of, he alluded to the +contents of the desk as the "chips." They were useless, but they +were necessary incidents in the truly successful work. So it is in +all great and good work. Even the most skilful man of science +pursues many a wrong scent. Time after time he goes off on some +track that plays him false. The greater the man's genius and +intellectual resource, the more numerous will be the ventures which +he makes, and the great majority of those ventures are certain to be +fruitless. They are in fact, the "chips." In Kepler's case the +chips were numerous enough. They were of the most extraordinary +variety and structure. But every now and then a sublime discovery +was made of such a character as to make us regard even the most +fantastic of Kepler's chips with the greatest veneration and respect.</p> + +<h3><a name="ISAAC_NEWTON" id="ISAAC_NEWTON"></a>ISAAC NEWTON.</h3> +<p>It was just a year after the death of Galileo, that an infant came +into the world who was christened Isaac Newton. Even the great fame +of Galileo himself must be relegated to a second place in comparison +with that of the philosopher who first expounded the true theory of +the universe.</p> + +<p>Isaac Newton was born on the 25th of December (old style), 1642, at +Woolsthorpe, in Lincolnshire, about a half-mile from Colsterworth, +and eight miles south of Grantham. His father, Mr. Isaac Newton, had +died a few months after his marriage to Harriet Ayscough, the +daughter of Mr. James Ayscough, of Market Overton, in Rutlandshire. +The little Isaac was at first so excessively frail and weakly that +his life was despaired of. The watchful mother, however, tended her +delicate child with such success that he seems to have thriven better +than might have been expected from the circumstances of his infancy, +and he ultimately acquired a frame strong enough to outlast the +ordinary span of human life.</p> + +<p>For three years they continued to live at Woolsthorpe, the widow's +means of livelihood being supplemented by the income from another +small estate at Sewstern, in a neighbouring part of Leicestershire.</p> + +<p><a name="woolsthorpe" id="woolsthorpe"></a></p> + +<div class="figcenter" style="width: 312px;"> +<a href="images/ill_woolsthorpe_manor.jpg"> +<img src="images/ill_woolsthorpe_manor_sml.jpg" width="312" height="185" alt="WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy." title="" /></a> +<span class="caption">WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy.</span> +</div> + +<p>In 1645, Mrs. Newton took as a second husband the Rev. Barnabas +Smith, and on moving to her new home, about a mile from Woolsthorpe, +she entrusted little Isaac to her mother, Mrs. Ayscough. In due +time we find that the boy was sent to the public school at Grantham, +the name of the master being Stokes. For the purpose of being near +his work, the embryo philosopher was boarded at the house of Mr. +Clark, an apothecary at Grantham. We learn from Newton himself that +at first he had a very low place in the class lists of the school, +and was by no means one of those model school-boys who find favour in +the eyes of the school-master by attention to Latin grammar. Isaac's +first incentive to diligent study seems to have been derived from the +circumstance that he was severely kicked by one of the boys who was +above him in the class. This indignity had the effect of stimulating +young Newton's activity to such an extent that he not only attained +the desired object of passing over the head of the boy who had +maltreated him, but continued to rise until he became the head of the +school.</p> + +<p>The play-hours of the great philosopher were devoted to pursuits very +different from those of most school-boys. His chief amusement was +found in making mechanical toys and various ingenious contrivances. +He watched day by day with great interest the workmen engaged in +constructing a windmill in the neighbourhood of the school, the +result of which was that the boy made a working model of the windmill +and of its machinery, which seems to have been much admired, as +indicating his aptitude for mechanics. We are told that Isaac also +indulged in somewhat higher flights of mechanical enterprise. He +constructed a carriage, the wheels of which were to be driven by the +hands of the occupant, while the first philosophical instrument he +made was a clock, which was actuated by water. He also devoted much +attention to the construction of paper kites, and his skill in this +respect was highly appreciated by his school-fellows. Like a true +philosopher, even at this stage he experimented on the best methods +of attaching the string, and on the proportions which the tail ought +to have. He also made lanthorns of paper to provide himself with +light as he walked to school in the dark winter mornings.</p> + +<p>The only love affair in Newton's life appears to have commenced while +he was still of tender years. The incidents are thus described in +Brewster's "Life of Newton," a work to which I am much indebted in +this chapter.</p> + +<p>"In the house where he lodged there were some female inmates, in +whose company he appears to have taken much pleasure. One of these, +a Miss Storey, sister to Dr. Storey, a physician at Buckminster, near +Colsterworth, was two or three years younger than Newton and to great +personal attractions she seems to have added more than the usual +allotment of female talent. The society of this young lady and her +companions was always preferred to that of his own school-fellows, +and it was one of his most agreeable occupations to construct for +them little tables and cupboards, and other utensils for holding +their dolls and their trinkets. He had lived nearly six years in the +same house with Miss Storey, and there is reason to believe that +their youthful friendship gradually rose to a higher passion; but the +smallness of her portion, and the inadequacy of his own fortune, +appear to have prevented the consummation of their happiness. Miss +Storey was afterwards twice married, and under the name of Mrs. +Vincent, Dr. Stukeley visited her at Grantham in 1727, at the age of +eighty-two, and obtained from her many particulars respecting the +early history of our author. Newton's esteem for her continued +unabated during his life. He regularly visited her when he went to +Lincolnshire, and never failed to relieve her from little pecuniary +difficulties which seem to have beset her family."</p> + +<p>The schoolboy at Grantham was only fourteen years of age when his +mother became a widow for the second time. She then returned to the +old family home at Woolsthorpe, bringing with her the three children +of her second marriage. Her means appear to have been somewhat +scanty, and it was consequently thought necessary to recall Isaac +from the school. His recently-born industry had been such that he +had already made good progress in his studies, and his mother hoped +that he would now lay aside his books, and those silent meditations +to which, even at this early age, he had become addicted. It was +expected that, instead of such pursuits, which were deemed quite +useless, the boy would enter busily into the duties of the farm and +the details of a country life. But before long it became manifest +that the study of nature and the pursuit of knowledge had such a +fascination for the youth that he could give little attention to +aught else. It was plain that he would make but an indifferent +farmer. He greatly preferred experimenting on his water-wheels to +looking after labourers, while he found that working at mathematics +behind a hedge was much more interesting than chaffering about the +price of bullocks in the market place. Fortunately for humanity his +mother, like a wise woman, determined to let her boy's genius have +the scope which it required. He was accordingly sent back to +Grantham school, with the object of being trained in the knowledge +which would fit him for entering the University of Cambridge.</p> + +<p><a name="trinity" id="trinity"></a></p> + +<div class="figcenter" style="width: 325px;"> +<a href="images/ill_trinity_college.jpg"> +<img src="images/ill_trinity_college_sml.jpg" width="325" height="410" alt="TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope." title="" /></a> +<span class="caption">TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope.</span> +</div> + +<p>It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen, +was enrolled as an undergraduate of Trinity College, Cambridge. +Little did those who sent him there dream that this boy was destined +to be the most illustrious student who ever entered the portals of +that great seat of learning. Little could the youth himself have +foreseen that the rooms near the gateway which he occupied would +acquire a celebrity from the fact that he dwelt in them, or that the +ante-chapel of his college was in good time to be adorned by that +noble statue, which is regarded as one of the chief art treasures of +Cambridge University, both on account of its intrinsic beauty and the +fact that it commemorates the fame of her most distinguished alumnus, +Isaac Newton, the immortal astronomer. Indeed, his advent at the +University seemed to have been by no means auspicious or brilliant. +His birth was, as we have seen, comparatively obscure, and though he +had already given indication of his capacity for reflecting on +philosophical matters, yet he seems to have been but ill-equipped +with the routine knowledge which youths are generally expected to +take with them to the Universities.</p> + +<p>From the outset of his college career, Newton's attention seems to +have been mainly directed to mathematics. Here he began to give +evidence of that marvellous insight into the deep secrets of nature +which more than a century later led so dispassionate a judge as +Laplace to pronounce Newton's immortal work as pre-eminent above all +the productions of the human intellect. But though Newton was one of +the very greatest mathematicians that ever lived, he was never a +mathematician for the mere sake of mathematics. He employed his +mathematics as an instrument for discovering the laws of nature. His +industry and genius soon brought him under the notice of the +University authorities. It is stated in the University records that +he obtained a Scholarship in 1664. Two years later we find that +Newton, as well as many residents in the University, had to leave +Cambridge temporarily on account of the breaking out of the plague. +The philosopher retired for a season to his old home at Woolsthorpe, +and there he remained until he was appointed a Fellow of Trinity +College, Cambridge, in 1667. From this time onwards, Newton's +reputation as a mathematician and as a natural philosopher steadily +advanced, so that in 1669, while still but twenty-seven years of age, +he was appointed to the distinguished position of Lucasian Professor +of Mathematics at Cambridge. Here he found the opportunity to +continue and develop that marvellous career of discovery which formed +his life's work.</p> + +<p>The earliest of Newton's great achievements in natural philosophy was +his detection of the composite character of light. That a beam of +ordinary sunlight is, in fact, a mixture of a very great number of +different-coloured lights, is a doctrine now familiar to every one +who has the slightest education in physical science. We must, +however, remember that this discovery was really a tremendous advance +in knowledge at the time when Newton announced it.</p> + +<p><a name="diagram" id="diagram"></a></p> + +<div class="figcenter" style="width: 390px;"> +<a href="images/ill_diagram_sunbeam.jpg"> +<img src="images/ill_diagram_sunbeam_sml.jpg" width="390" height="163" alt="DIAGRAM OF A SUNBEAM." title="" /></a> +<span class="caption">DIAGRAM OF A SUNBEAM.</span> +</div> + +<p>We here give the little diagram originally drawn by Newton, to +explain the experiment by which he first learned the composition of +light. A sunbeam is admitted into a darkened room through an +opening, H, in a shutter. This beam when not interfered with will +travel in a straight line to the screen, and there reproduce a bright +spot of the same shape as the hole in the shutter. If, however, a +prism of glass, A B C, be introduced so that the beam traverse it, +then it will be seen at once that the light is deflected from its +original track. There is, however, a further and most important +change which takes place. The spot of light is not alone removed to +another part of the screen, but it becomes spread out into a long +band beautifully coloured, and exhibiting the hues of the rainbow. At +the top are the violet rays, and then in descending order we have the +indigo, blue, green, yellow, orange, and red.</p> + +<p>The circumstance in this phenomenon which appears to have +particularly arrested Newton's attention, was the elongation which +the luminous spot underwent in consequence of its passage through the +prism. When the prism was absent the spot was nearly circular, but +when the prism was introduced the spot was about five times as long +as it was broad. To ascertain the explanation of this was the first +problem to be solved. It seemed natural to suppose that it might be +due to the thickness of the glass in the prism which the light +traversed, or to the angle of incidence at which the light fell upon +the prism. He found, however, upon careful trial, that the phenomenon +could not be thus accounted for. It was not until after much patient +labour that the true explanation dawned upon him. He discovered that +though the beam of white light looks so pure and so simple, yet in +reality it is composed of differently coloured lights blended +together. These are, of course, indistinguishable in the compound +beam, but they are separated or disentangled, so to speak, by the +action of the prism. The rays at the blue end of the spectrum are +more powerfully deflected by the action of the glass than are the +rays at the red end. Thus, the rays variously coloured red, orange, +yellow, green, blue, indigo, violet, are each conducted to a +different part of the screen. In this way the prism has the effect +of exhibiting the constitution of the composite beam of light.</p> + +<p>To us this now seems quite obvious, but Newton did not adopt it +hastily. With characteristic caution he verified the explanation by +many different experiments, all of which confirmed his discovery. One +of these may be mentioned. He made a hole in the screen at that part +on which the violet rays fell. Thus a violet ray was allowed to pass +through, all the rest of the light being intercepted, and on this +beam so isolated he was able to try further experiments. For +instance, when he interposed another prism in its path, he found, as +he expected, that it was again deflected, and he measured the amount +of the deflection. Again he tried the same experiment with one of +the red rays from the opposite end of the coloured band. He allowed +it to pass through the same aperture in the screen, and he tested the +amount by which the second prism was capable of producing deflection. +He thus found, as he had expected to find, that the second prism was +more efficacious in bending the violet rays than in bending the red +rays. Thus he confirmed the fact that the various hues of the +rainbow were each bent by a prism to a different extent, violet being +acted upon the most, and red the least.</p> + +<p><a name="isaac" id="isaac"></a></p> + +<div class="figcenter" style="width: 390px;"> +<a href="images/ill_newton.jpg"> +<img src="images/ill_newton_sml.jpg" width="390" height="469" alt="ISAAC NEWTON." title="" /></a> +<span class="caption">ISAAC NEWTON.</span> +</div> + +<p>Not only did Newton decompose a white beam into its constituent +colours, but conversely by interposing a second prism with its angle +turned upwards, he reunited the different colours, and thus +reproduced the original beam of white light. In several other ways +also he illustrated his famous proposition, which then seemed so +startling, that white light was the result of a mixture of all hues +of the rainbow. By combining painters' colours in the right +proportion he did not indeed succeed in producing a mixture which +would ordinarily be called white, but he obtained a grey pigment. +Some of this he put on the floor of his room for comparison with a +piece of white paper. He allowed a beam of bright sunlight to fall +upon the paper and the mixed colours side by side, and a friend he +called in for his opinion pronounced that under these circumstances +the mixed colours looked the whiter of the two.</p> + +<p>By repeated demonstrations Newton thus established his great +discovery of the composite character of light. He at once perceived +that his researches had an important bearing upon the principles +involved in the construction of a telescope. Those who employed the +telescope for looking at the stars, had been long aware of the +imperfections which prevented all the various rays from being +conducted to the same focus. But this imperfection had hitherto been +erroneously accounted for. It had been supposed that the reason why +success had not been attained in the construction of a refracting +telescope was due to the fact that the object glass, made as it then +was of a single piece, had not been properly shaped. Mathematicians +had abundantly demonstrated that a single lens, if properly figured, +must conduct all rays of light to the same focus, provided all rays +experienced equal refraction in passing through the glass. Until +Newton's discovery of the composition of white light, it had been +taken for granted that the several rays in a white beam were equally +refrangible. No doubt if this had been the case, a perfect telescope +could have been produced by properly shaping the object glass. But +when Newton had demonstrated that light was by no means so simple as +had been supposed, it became obvious that a satisfactory refracting +telescope was an impossibility when only a single object lens was +employed, however carefully that lens might have been wrought. Such +an objective might, no doubt, be made to conduct any one group of +rays of a particular shade to the same focus, but the rays of other +colours in the beam of white light must necessarily travel somewhat +astray. In this way Newton accounted for a great part of the +difficulties which had hitherto beset the attempts to construct a +perfect refracting telescope.</p> + +<p>We now know how these difficulties can be, to a great extent, +overcome, by employing for the objective a composite lens made of two +pieces of glass possessing different qualities. To these achromatic +object glasses, as they are called, the great development of +astronomical knowledge, since Newton's time, is due. But it must be +remarked that, although the theoretical possibility of constructing +an achromatic lens was investigated by Newton, he certainly came to +the conclusion that the difficulty could not be removed by employing +a composite objective, with two different kinds of glass. In this +his marvellous sagacity in the interpretation of nature seems for +once to have deserted him. We can, however, hardly regret that +Newton failed to discover the achromatic objective, when we observe +that it was in consequence of his deeming an achromatic objective to +be impossible that he was led to the invention of the reflecting +telescope. Finding, as he believed, that the defects of the +telescope could not be remedied by any application of the principle +of refraction he was led to look in quite a different direction for +the improvement of the tool on which the advancement of astronomy +depended. The REFRACTION of light depended as he had found, upon the +colour of the light. The laws of REFLECTION were, however, quite +independent of the colour. Whether rays be red or green, blue or +yellow, they are all reflected in precisely the same manner from a +mirror. Accordingly, Newton perceived that if he could construct a +telescope the action of which depended upon reflection, instead of +upon refraction, the difficulty which had hitherto proved an +insuperable obstacle to the improvement of the instrument would be +evaded.</p> + +<p><a name="newton_reflector" id="newton_reflector"></a></p> + +<div class="figcenter" style="width: 278px;"> +<a href="images/ill_little_reflector.jpg"> +<img src="images/ill_little_reflector_sml.jpg" width="278" height="284" alt="SIR ISAAC NEWTON'S LITTLE REFLECTOR." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S LITTLE REFLECTOR.</span> +</div> + +<p>For this purpose Newton fashioned a concave mirror from a mixture of +copper and tin, a combination which gives a surface with almost the +lustre of silver. When the light of a star fell upon the surface, an +image of the star was produced in the focus of this mirror, and then +this image was examined by a magnifying eye-piece. Such is the +principle of the famous reflecting telescope which bears the name of +Newton. The little reflector which he constructed, represented in +the adjoining figure, is still preserved as one of the treasures of +the Royal Society. The telescope tube had the very modest dimension +of one inch in diameter. It was, however, the precursor of a whole +series of magnificent instruments, each outstripping the other in +magnitude, until at last the culminating point was attained in 1845, +by the construction of Lord Rosse's mammoth reflector of six feet in +aperture.</p> + +<p>Newton's discovery of the composition of light led to an embittered +controversy, which caused no little worry to the great Philosopher. +Some of those who attacked him enjoyed considerable and, it must be +admitted, even well-merited repute in the ranks of science. They +alleged, however, that the elongation of the coloured band which +Newton had noticed was due to this, to that, or to the other—to +anything, in fact, rather than to the true cause which Newton +assigned. With characteristic patience and love of truth, Newton +steadily replied to each such attack. He showed most completely how +utterly his adversaries had misunderstood the subject, and how slight +indeed was their acquaintance with the natural phenomenon in +question. In reply to each point raised, he was ever able to cite +fresh experiments and adduce fresh illustrations, until at last his +opponents retired worsted from the combat.</p> + +<p>It has been often a matter for surprise that Newton, throughout his +whole career, should have taken so much trouble to expose the errors +of those who attacked his views. He used even to do this when it +plainly appeared that his adversaries did not understand the subject +they were discussing. A philosopher might have said, "I know I am +right, and whether others think I am right or not may be a matter of +concern to them, but it is certainly not a matter about which I need +trouble. If after having been told the truth they elect to remain in +error, so much the worse for them; my time can be better employed +than in seeking to put such people right." This, however, was not +Newton's method. He spent much valuable time in overthrowing +objections which were often of a very futile description. Indeed, he +suffered a great deal of annoyance from the persistency, and in some +cases one might almost say from the rancour, of the attacks which +were made upon him. Unfortunately for himself, he did not possess +that capacity for sublime indifference to what men may say, which is +often the happy possession of intellects greatly inferior to his.</p> + +<p>The subject of optics still continuing to engross Newton's attention, +he followed up his researches into the structure of the sunbeam by +many other valuable investigations in connection with light. Every +one has noticed the beautiful colours manifested in a soap-bubble. +Here was a subject which not unnaturally attracted the attention of +one who had expounded the colours of the spectrum with such success. +He perceived that similar hues were produced by other thin plates of +transparent material besides soap-bubbles, and his ingenuity was +sufficient to devise a method by which the thicknesses of the +different films could be measured. We can hardly, indeed, say that a +like success attended his interpretation of these phenomena to that +which had been so conspicuous in his explanation of the spectrum. It +implies no disparagement to the sublime genius of Newton to admit +that the doctrines he put forth as to the causes of the colours in +the soap-bubbles can be no longer accepted. We must remember that +Newton was a pioneer in accounting for the physical properties of +light. The facts that he established are indeed unquestionable, but +the explanations which he was led to offer of some of them are seen +to be untenable in the fuller light of our present knowledge.</p> + +<p><a name="sun-dial" id="sun-dial"></a></p> + +<div class="figcenter" style="width: 402px;"> +<a href="images/ill_newton_sundial.jpg"> +<img src="images/ill_newton_sundial_sml.jpg" width="402" height="485" alt="SIR ISAAC NEWTON'S SUN-DIAL." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S SUN-DIAL.</span> +</div> + +<p>Had Newton done nothing beyond making his wonderful discoveries in +light, his fame would have gone down to posterity as one of the +greatest of Nature's interpreters. But it was reserved for him to +accomplish other discoveries, which have pushed even his analysis of +the sunbeam into the background; it is he who has expounded the +system of the universe by the discovery of the law of universal +gravitation.</p> + +<p>The age had indeed become ripe for the advent of the genius of +Newton. Kepler had discovered with marvellous penetration the laws +which govern the movements of the planets around the sun, and in +various directions it had been more or less vaguely felt that the +explanation of Kepler's laws, as well as of many other phenomena, +must be sought for in connection with the attractive power of +matter. But the mathematical analysis which alone could deal with +this subject was wanting; it had to be created by Newton.</p> + +<p>At Woolsthorpe, in the year 1666, Newton's attention appears to have +been concentrated upon the subject of gravitation. Whatever may be +the extent to which we accept the more or less mythical story as to +how the fall of an apple first directed the attention of the +philosopher to the fact that gravitation must extend through space, +it seems, at all events, certain that this is an excellent +illustration of the line of reasoning which he followed. He argued +in this way. The earth attracts the apple; it would do so, no matter +how high might be the tree from which that apple fell. It would then +seem to follow that this power which resides in the earth by which it +can draw all external bodies towards it, extends far beyond the +altitude of the loftiest tree. Indeed, we seem to find no limit to +it. At the greatest elevation that has ever been attained, the +attractive power of the earth is still exerted, and though we cannot +by any actual experiment reach an altitude more than a few miles +above the earth, yet it is certain that gravitation would extend to +elevations far greater. It is plain, thought Newton, that an apple +let fall from a point a hundred miles above this earth's surface, +would be drawn down by the attraction, and would continually gather +fresh velocity until it reached the ground. From a hundred miles it +was natural to think of what would happen at a thousand miles, or at +hundreds of thousands of miles. No doubt the intensity of the +attraction becomes weaker with every increase in the altitude, but +that action would still exist to some extent, however lofty might be +the elevation which had been attained.</p> + +<p>It then occurred to Newton, that though the moon is at a distance of +two hundred and forty thousand miles from the earth, yet the +attractive power of the earth must extend to the moon. He was +particularly led to think of the moon in this connection, not only +because the moon is so much closer to the earth than are any other +celestial bodies, but also because the moon is an appendage to the +earth, always revolving around it. The moon is certainly attracted +to the earth, and yet the moon does not fall down; how is this to be +accounted for? The explanation was to be found in the character of +the moon's present motion. If the moon were left for a moment at +rest, there can be no doubt that the attraction of the earth would +begin to draw the lunar globe in towards our globe. In the course of +a few days our satellite would come down on the earth with a most +fearful crash. This catastrophe is averted by the circumstance that +the moon has a movement of revolution around the earth. Newton was +able to calculate from the known laws of mechanics, which he had +himself been mainly instrumental in discovering, what the attractive +power of the earth must be, so that the moon shall move precisely as +we find it to move. It then appeared that the very power which makes +an apple fall at the earth's surface is the power which guides the +moon in its orbit.</p> + +<p><a name="newton_telescope" id="newton_telescope"></a></p> + +<div class="figcenter" style="width: 378px;"> +<a href="images/ill_newton_telescope.jpg"> +<img src="images/ill_newton_telescope_sml.jpg" width="378" height="202" alt="SIR ISAAC NEWTON'S TELESCOPE." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S TELESCOPE.</span> +</div> + +<p>Once this step had been taken, the whole scheme of the universe might +almost be said to have become unrolled before the eye of the +philosopher. It was natural to suppose that just as the moon was +guided and controlled by the attraction of the earth, so the earth +itself, in the course of its great annual progress, should be guided +and controlled by the supreme attractive power of the sun. If this +were so with regard to the earth, then it would be impossible to +doubt that in the same way the movements of the planets could be +explained to be consequences of solar attraction.</p> + +<p>It was at this point that the great laws of Kepler became especially +significant. Kepler had shown how each of the planets revolves in an +ellipse around the sun, which is situated on one of the foci. This +discovery had been arrived at from the interpretation of +observations. Kepler had himself assigned no reason why the orbit of +a planet should be an ellipse rather than any other of the infinite +number of closed curves which might be traced around the sun. Kepler +had also shown, and here again he was merely deducing the results +from observation, that when the movements of two planets were +compared together, the squares of the periodic times in which each +planet revolved were proportional to the cubes of their mean +distances from the sun. This also Kepler merely knew to be true as a +fact, he gave no demonstration of the reason why nature should have +adopted this particular relation between the distance and the +periodic time rather than any other. Then, too, there was the law by +which Kepler with unparalleled ingenuity, explained the way in which +the velocity of a planet varies at the different points of its track, +when he showed how the line drawn from the sun to the planet +described equal areas around the sun in equal times. These were the +materials with which Newton set to work. He proposed to infer from +these the actual laws regulating the force by which the sun guides +the planets. Here it was that his sublime mathematical genius came +into play. Step by step Newton advanced until he had completely +accounted for all the phenomena.</p> + +<p>In the first place, he showed that as the planet describes equal +areas in equal times about the sun, the attractive force which the +sun exerts upon it must necessarily be directed in a straight line +towards the sun itself. He also demonstrated the converse truth, +that whatever be the nature of the force which emanated from a sun, +yet so long as that force was directed through the sun's centre, any +body which revolved around it must describe equal areas in equal +times, and this it must do, whatever be the actual character of the +law according to which the intensity of the force varies at different +parts of the planet's journey. Thus the first advance was taken in +the exposition of the scheme of the universe.</p> + +<p>The next step was to determine the law according to which the force +thus proved to reside in the sun varied with the distance of the +planet. Newton presently showed by a most superb effort of +mathematical reasoning, that if the orbit of a planet were an ellipse +and if the sun were at one of the foci of that ellipse, the intensity +of the attractive force must vary inversely as the square of the +planet's distance. If the law had any other expression than the +inverse square of the distance, then the orbit which the planet must +follow would not be an ellipse; or if an ellipse, it would, at all +events, not have the sun in the focus. Hence he was able to show +from Kepler's laws alone that the force which guided the planets was +an attractive power emanating from the sun, and that the intensity of +this attractive power varied with the inverse square of the distance +between the two bodies.</p> + +<p>These circumstances being known, it was then easy to show that the +last of Kepler's three laws must necessarily follow. If a number of +planets were revolving around the sun, then supposing the materials +of all these bodies were equally affected by gravitation, it can be +demonstrated that the square of the periodic time in which each +planet completes its orbit is proportional to the cube of the +greatest diameter in that orbit.</p> + +<p><a name="newton_astrolabe" id="newton_astrolabe"></a></p> + +<div class="figcenter" style="width: 419px;"> +<a href="images/ill_newton_astrolabe.jpg"> +<img src="images/ill_newton_astrolabe_sml.jpg" width="419" height="511" alt="SIR ISAAC NEWTON'S ASTROLABE." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S ASTROLABE.</span> +</div> + +<p>These superb discoveries were, however, but the starting point from +which Newton entered on a series of researches, which disclosed many +of the profoundest secrets in the scheme of celestial mechanics. His +natural insight showed that not only large masses like the sun and +the earth, and the moon, attract each other, but that every particle +in the universe must attract every other particle with a force which +varies inversely as the square of the distance between them. If, for +example, the two particles were placed twice as far apart, then the +intensity of the force which sought to bring them together would be +reduced to one-fourth. If two particles, originally ten miles +asunder, attracted each other with a certain force, then, when the +distance was reduced to one mile, the intensity of the attraction +between the two particles would be increased one-hundred-fold. This +fertile principle extends throughout the whole of nature. In some +cases, however, the calculation of its effect upon the actual +problems of nature would be hardly possible, were it not for another +discovery which Newton's genius enabled him to accomplish. In the +case of two globes like the earth and the moon, we must remember that +we are dealing not with particles, but with two mighty masses of +matter, each composed of innumerable myriads of particles. Every +particle in the earth does attract every particle in the moon with a +force which varies inversely as the square of their distance. The +calculation of such attractions is rendered feasible by the following +principle. Assuming that the earth consists of materials +symmetrically arranged in shells of varying densities, we may then, +in calculating its attraction, regard the whole mass of the globe as +concentrated at its centre. Similarly we may regard the moon as +concentrated at the centre of its mass. In this way the earth and +the moon can both be regarded as particles in point of size, each +particle having, however, the entire mass of the corresponding +globe. The attraction of one particle for another is a much more +simple matter to investigate than the attraction of the myriad +different points of the earth upon the myriad different points of the +moon.</p> + +<p>Many great discoveries now crowded in upon Newton. He first of all +gave the explanation of the tides that ebb and flow around our +shores. Even in the earliest times the tides had been shown to be +related to the moon. It was noticed that the tides were specially +high during full moon or during new moon, and this circumstance +obviously pointed to the existence of some connection between the +moon and these movements of the water, though as to what that +connection was no one had any accurate conception until Newton +announced the law of gravitation. Newton then made it plain that the +rise and fall of the water was simply a consequence of the attractive +power which the moon exerted upon the oceans lying upon our globe. He +showed also that to a certain extent the sun produces tides, and he +was able to explain how it was that when the sun and the moon both +conspire, the joint result was to produce especially high tides, +which we call "spring tides"; whereas if the solar tide was low, +while the lunar tide was high, then we had the phenomenon of "neap" +tides.</p> + +<p>But perhaps the most signal of Newton's applications of the law of +gravitation was connected with certain irregularities in the +movements of the moon. In its orbit round the earth our satellite +is, of course, mainly guided by the great attraction of our globe. If +there were no other body in the universe, then the centre of the moon +must necessarily perform an ellipse, and the centre of the earth +would lie in the focus of that ellipse. Nature, however, does not +allow the movements to possess the simplicity which this arrangement +would imply, for the sun is present as a source of disturbance. The +sun attracts the moon, and the sun attracts the earth, but in +different degrees, and the consequence is that the moon's movement +with regard to the earth is seriously affected by the influence of +the sun. It is not allowed to move exactly in an ellipse, nor is the +earth exactly in the focus. How great was Newton's achievement in +the solution of this problem will be appreciated if we realise that +he not only had to determine from the law of gravitation the nature +of the disturbance of the moon, but he had actually to construct the +mathematical tools by which alone such calculations could be +effected.</p> + +<p>The resources of Newton's genius seemed, however, to prove equal to +almost any demand that could be made upon it. He saw that each +planet must disturb the other, and in that way he was able to render +a satisfactory account of certain phenomena which had perplexed all +preceding investigators. That mysterious movement by which the pole +of the earth sways about among the stars had been long an unsolved +enigma, but Newton showed that the moon grasped with its attraction +the protuberant mass at the equatorial regions of the earth, and thus +tilted the earth's axis in a way that accounted for the phenomenon +which had been known but had never been explained for two thousand +years. All these discoveries were brought together in that immortal +work, Newton's "Principia."</p> + +<p>Down to the year 1687, when the "Principia" was published, Newton had +lived the life of a recluse at Cambridge, being entirely occupied +with those transcendent researches to which we have referred. But in +that year he issued from his seclusion under circumstances of +considerable historical interest. King James the Second attempted an +invasion of the rights and privileges of the University of Cambridge +by issuing a command that Father Francis, a Benedictine monk, should +be received as a Master of Arts in the University, without having taken +the oaths of allegiance and supremacy. With this arbitrary command +the University sternly refused to comply. The Vice-Chancellor was +accordingly summoned to answer for an act of contempt to the authority +of the Crown. Newton was one of nine delegates who were chosen to +defend the independence of the University before the High Court. +They were able to show that Charles the Second, who had issued a +MANDAMUS under somewhat similar circumstances, had been induced after +due consideration to withdraw it. This argument appeared satisfactory, +and the University gained their case. Newton's next step in public +life was his election, by a narrow majority, as member for the +University, and during the years 1688 and 1689, he seems to have +attended to his parliamentary duties with considerable regularity.</p> + +<p>An incident which happened in 1692 was apparently the cause of +considerable disturbance in Newton's equanimity, if not in his +health. He had gone to early morning chapel, leaving a lighted +candle among his papers on his desk. Tradition asserts that his +little dog "Diamond" upset the candle; at all events, when Newton +came back he found that many valuable papers had perished in a +conflagration. The loss of these manuscripts seems to have had a +serious effect. Indeed, it has been asserted that the distress +reduced Newton to a state of mental aberration for a considerable +time. This has, apparently, not been confirmed, but there is no +doubt that he experienced considerable disquiet, for in writing on +September 13th, 1693, to Mr. Pepys, he says:</p> + +<p>"I am extremely troubled at the embroilment I am in, and have +neither ate nor slept well this twelve-month, nor have my former +consistency of mind."</p> + +<p>Notwithstanding the fame which Newton had achieved, by the +publication of his, "Principia," and by all his researches, the State +had not as yet taken any notice whatever of the most illustrious man +of science that this or any other country has ever produced. Many of +his friends had exerted themselves to procure him some permanent +appointment, but without success. It happened, however, that Mr. +Montagu, who had sat with Newton in Parliament, was appointed +Chancellor of the Exchequer in 1694. Ambitious of distinction in his +new office, Mr. Montagu addressed himself to the improvement of the +current coin, which was then in a very debased condition. It +fortunately happened that an opportunity occurred of appointing a new +official in the Mint; and Mr. Montagu on the 19th of March, 1695, +wrote to offer Mr. Newton the position of warden. The salary was to +be five or six hundred a year, and the business would not require +more attendance than Newton could spare. The Lucasian professor +accepted this post, and forthwith entered upon his new duties.</p> + +<p>The knowledge of physics which Newton had acquired by his experiments +was of much use in connection with his duties at the Mint. He +carried out the re-coinage with great skill in the course of two +years, and as a reward for his exertions, he was appointed, in 1697, +to the Mastership of the Mint, with a salary between 1,200 Pounds and +1,500 Pounds per annum. In 1701, his duties at the Mint being so +engrossing, he resigned his Lucasian professorship at Cambridge, and +at the same time he had to surrender his fellowship at Trinity +College. This closed his connection with the University of +Cambridge. It should, however, be remarked that at a somewhat +earlier stage in his career he was very nearly being appointed to an +office which might have enabled the University to retain the great +philosopher within its precincts. Some of his friends had almost +succeeded in securing his nomination to the Provostship of King's +College, Cambridge; the appointment, however, fell through, inasmuch +as the statute could not be evaded, which required that the Provost +of King's College should be in holy orders.</p> + +<p>In those days it was often the custom for illustrious mathematicians, +when they had discovered a solution for some new and striking +problem, to publish that problem as a challenge to the world, while +withholding their own solution. A famous instance of this is found +in what is known as the Brachistochrone problem, which was solved by +John Bernouilli. The nature of this problem may be mentioned. It +was to find the shape of the curve along which a body would slide +down from one point (A) to another point (B) in the shortest time. It +might at first be thought that the straight line from A to B, as it +is undoubtedly the shortest distance between the points, would also +be the path of quickest descent; but this is not so. There is a +curved line, down which a bead, let us say, would run on a smooth +wire from A to B in a shorter time than the same bead would require +to run down the straight wire. Bernouilli's problem was to find out +what that curve must be. Newton solved it correctly; he showed that +the curve was a part of what is termed a cycloid—that is to say, a +curve like that which is described by a point on the rim of a +carriage-wheel as the wheel runs along the ground. Such was Newton's +geometrical insight that he was able to transmit a solution of the +problem on the day after he had received it, to the President of the +Royal Society.</p> + +<p>In 1703 Newton, whose world wide fame was now established, was +elected President of the Royal Society. Year after year he was +re-elected to this distinguished position, and his tenure, which +lasted twenty-five years, only terminated with his life. It was in +discharge of his duties as President of the Royal Society that Newton +was brought into contact with Prince George of Denmark. In April, +1705, the Queen paid a visit to Cambridge as the guest of Dr. +Bentley, the then Master of Trinity, and in a court held at Trinity +Lodge on April 15th, 1705, the honour of knighthood was conferred +upon the discoverer of gravitation.</p> + +<p>Urged by illustrious friends, who sought the promotion of knowledge, +Newton gave his attention to the publication of a new edition of the +"Principia." His duties at the Mint, however, added to the supreme +duty of carrying on his original investigations, left him but little +time for the more ordinary task of the revision. He was accordingly +induced to associate with himself for this purpose a distinguished +young mathematician, Roger Coates, a Fellow of Trinity College, +Cambridge, who had recently been appointed Plumian Professor of +Astronomy. On July 27th, 1713, Newton, by this time a favourite at +Court, waited on the Queen, and presented her with a copy of the new +edition of the "Principia."</p> + +<p>Throughout his life Newton appears to have been greatly interested in +theological studies, and he specially devoted his attention to the +subject of prophecy. He left behind him a manuscript on the +prophecies of Daniel and the Apocalypse of St. John, and he also +wrote various theological papers. Many other subjects had from time +to time engaged his attention. He studied the laws of heat; he +experimented in pursuit of the dreams of the Alchymist; while the +philosopher who had revealed the mechanism of the heavens found +occasional relaxation in trying to interpret hieroglyphics. In the +last few years of his life he bore with fortitude a painful ailment, +and on Monday, March 20th, 1727, he died in the eighty-fifth year of +his age. On Tuesday, March 28th, he was buried in Westminster Abbey.</p> + +<p>Though Newton lived long enough to receive the honour that his +astonishing discoveries so justly merited, and though for many years +of his life his renown was much greater than that of any of his +contemporaries, yet it is not too much to say that, in the years +which have since elapsed, Newton's fame has been ever steadily +advancing, so that it never stood higher than it does at this moment.</p> + +<p>We hardly know whether to admire more the sublime discoveries at +which he arrived, or the extraordinary character of the intellectual +processes by which those discoveries were reached. Viewed from +either standpoint, Newton's "Principia" is incomparably the greatest +work on science that has ever yet been produced.</p> + +<p><a name="royal_society" id="royal_society"></a></p> + +<div class="figcenter" style="width: 327px;"> +<a href="images/ill_newtons_sundial_royal_society.jpg"> +<img src="images/ill_newtons_sundial_royal_society_sml.jpg" width="327" height="192" alt="SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY." title="" /></a> +<span class="caption">SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.</span> +</div> + +<h3><a name="FLAMSTEED" id="FLAMSTEED"></a>FLAMSTEED.</h3> +<p>Among the manuscripts preserved at Greenwich Observatory are certain +documents in which Flamsteed gives an account of his own life. We +may commence our sketch by quoting the following passage from this +autobiography:—"To keep myself from idleness, and to recreate +myself, I have intended here to give some account of my life, in my +youth, before the actions thereof, and the providences of God +therein, be too far passed out of my memory; and to observe the +accidents of all my years, and inclinations of my mind, that +whosoever may light upon these papers may see I was not so wholly +taken up, either with my father's business or my mathematics, but +that I both admitted and found time for other as weighty +considerations."</p> + +<p>The chief interest which attaches to the name of Flamsteed arises +from the fact that he was the first of the illustrious series of +Astronomers Royal who have presided over Greenwich Observatory. In +that capacity Flamsteed was able to render material assistance to +Newton by providing him with the observations which his lunar theory +required.</p> + +<p>John Flamsteed was born at Denby, in Derbyshire, on the 19th of +August, 1646. His mother died when he was three years old, and the +second wife, whom his father took three years later, only lived until +Flamsteed was eight, there being also two younger sisters. In his +boyhood the future astronomer tells us that he was very fond of those +romances which affect boy's imagination, but as he writes, "At twelve +years of age I left all the wild ones and betook myself to read the +better sort of them, which, though they were not probable, yet +carried no seeming impossibility in the picturing." By the time +Flamsteed was fifteen years old he had embarked in still more serious +work, for he had read Plutarch's "Lives," Tacitus' "Roman History," +and many other books of a similar description. In 1661 he became ill +with some serious rheumatic affection, which obliged him to be +withdrawn from school. It was then for the first time that he +received the rudiments of a scientific education. He had, however, +attained his sixteenth year before he made any progress in +arithmetic. He tells us how his father taught him "the doctrine of +fractions," and "the golden rule of three"—lessons which he seemed +to have learned easily and quickly. One of the books which he read +at this time directed his attention to astronomical instruments, and +he was thus led to construct for himself a quadrant, by which he +could take some simple astronomical observations. He further +calculated a table to give the sun's altitudes at different hours, +and thus displayed those tastes for practical astronomy which he +lived to develop so greatly. It appears that these scientific +studies were discountenanced by his father, who designed that his son +should follow a business career. Flamsteed's natural inclination, +however, forced him to prosecute astronomical work, notwithstanding +the impediments that lay in his path. Unfortunately, his +constitutional delicacy seems to have increased, and he had just +completed his eighteenth year, "when," to use his own words, "the +winter came on and thrust me again into the chimney, whence the heat +and the dryness of the preceding summer had happily once before +withdrawn me. But, it not being a fit season for physic, it was +thought fit to let me alone this winter, and try the skill of another +physician on me in the spring."</p> + +<p>It appears that at this time a quack named Valentine Greatrackes, was +reputed to have effected most astonishing cures in Ireland merely by +the stroke of his hands, without the application of any medicine +whatever. Flamsteed's father, despairing of any remedy for his son +from the legitimate branch of the profession, despatched him to +Ireland on August 26th, 1665, he being then, as recorded with +astronomical accuracy, "nineteen years, six days, and eleven hours +old." The young astronomer, accompanied by a friend, arrived on a +Tuesday at Liverpool but the wind not being favourable, they remained +there till the following Friday, when a shift of the wind to the east +took place. They embarked accordingly on a vessel called the SUPPLY +at noon, and on Saturday night came in sight of Dublin. Ere they +could land, however, they were nearly being wrecked on Lambay +Island. This peril safely passed, there was a long delay for +quarantine before they were at last allowed on shore. On Thursday, +September 6th, they set out from Dublin, where they had been +sojourning at the "Ship" Hotel, in Dame Street, towards Assaune, +where Greatrackes received his patients.</p> + +<p><a name="flamsteed_house" id="flamsteed_house"></a></p> + +<div class="figcenter" style="width: 420px;"> +<a href="images/ill_flamsteeds_house.jpg"> +<img src="images/ill_flamsteeds_house_sml.jpg" width="420" height="313" alt="FLAMSTEED'S HOUSE." title="" /></a> +<span class="caption">FLAMSTEED'S HOUSE.</span> +</div> + +<p>Flamsteed gives an interesting account of his travels in Ireland. +They dined at Naas on the first day, and on September 8th they +reached Carlow, a town which is described as one of the fairest they +saw on their journey. By Sunday morning, September 10th, having lost +their way several times, they reached Castleton, called commonly Four +Mile Waters. Flamsteed inquired of the host in the inn where they +might find a church, but was told that the minister lived twelve +miles away, and that they had no sermon except when he came to +receive his tithes once a year, and a woman added that "they had +plenty enough of everything necessary except the word of God." The +travellers accordingly went on to Cappoquin, which lies up the river +Blackwater, on the road to Lismore, eight miles from Youghal. Thence +they immediately started on foot to Assaune. About a mile from +Cappoquin, and entering into the house of Mr. Greatrackes, they saw +him touch several patients, "whereof some were nearly cured, others +were on the mending hand, and some on whom his strokes had no +effect." Flamsteed was touched by the famous quack on the afternoon +of September 11th, but we are hardly surprised to hear his remark +that "he found not his disease to stir." Next morning the astronomer +came again to see Mr. Greatrackes, who had "a kind of majestical yet +affable presence, and a composed carriage." Even after the third +touching had been submitted to, no benefit seems to have been +derived. We must, however record, to the credit of Mr. Greatrackes, +that he refused to accept any payment from Flamsteed, because he was +a stranger.</p> + +<p>Finding it useless to protract his stay any longer, Flamsteed and his +friend set out on their return to Dublin. In the course of his +journey he seems to have been much impressed with Clonmel, which he +describes as an "exceedingly pleasantly seated town." But in those +days a journey to Ireland was so serious an enterprise that when +Flamsteed did arrive safely back at Derby after an absence of a +month, he adds, "For God's providence in this journey, His name be +praised, Amen."</p> + +<p>As to the expected benefits to his health from the expedition we may +quote his own words: "In the winter following I was indifferent +hearty, and my disease was not so violent as it used to be at that +time formerly. But whether through God's mercy I received this +through Mr. Greatrackes' touch, or my journey and vomiting at sea, I +am uncertain; but, by some circumstances, I guess that I received a +benefit from both."</p> + +<p>It is evident that by this time Flamsteed's interest in all +astronomical matters had greatly increased. He studied the +construction of sun-dials, he formed a catalogue of seventy of the +fixed stars, with their places on the heavens, and he computed the +circumstances of the solar eclipse which was to happen on June 22nd, +1666. It is interesting to note that even in those days the +doctrines of the astrologers still found a considerable degree of +credence, and Flamsteed spent a good deal of his time in astrological +studies and computations. He investigated the methods of casting a +nativity, but a suspicion, or, indeed, rather more than a suspicion, +seems to have crossed his mind as to the value of these astrological +predictions, for he says in fine, "I found astrology to give +generally strong conjectural hints, not perfect declarations."</p> + +<p>All this time, however, the future Astronomer Royal was steadily +advancing in astronomical inquiries of a recondite nature. He had +investigated the obliquity of the ecliptic with extreme care, so far +as the circumstances of astronomical observation would at that time +permit. He had also sought to discover the sun's distance from the +earth in so far as it could be obtained by determining when the moon +was exactly half illuminated, and he had measured, with much +accuracy, the length of the tropical year. It will thus be seen +that, even at the age of twenty, Flamsteed had made marked progress, +considering how much his time had been interfered with by ill-health.</p> + +<p>Other branches of astronomy began also to claim his attention. We +learn that in 1669 and 1670 he compared the planets Jupiter and Mars +with certain fixed stars near which they passed. His instrumental +means, though very imperfect, were still sufficient to enable him to +measure the intervals on the celestial sphere between the planets and +the stars. As the places of the stars were known, Flamsteed was thus +able to obtain the places of the planets. This is substantially the +way in which astronomers of the present day still proceed when they +desire to determine the places of the planets, inasmuch as, directly +or indirectly those places are always obtained relatively to the +fixed stars. By his observations at this early period, Flamsteed +was, it is true, not able to obtain any great degree of accuracy; he +succeeded, however, in proving that the tables by which the places of +the planets were ordinarily given were not to be relied upon.</p> + +<p><a name="flamsteed_ill" id="flamsteed_ill"></a></p> + +<div class="figcenter" style="width: 382px;"> +<a href="images/ill_flamsteed.jpg"> +<img src="images/ill_flamsteed_sml.jpg" width="382" height="478" alt="FLAMSTEED." title="" /></a> +<span class="caption">FLAMSTEED.</span> +</div> + +<p>Flamsteed's labours in astronomy and in the allied branches of +science were now becoming generally known, and he gradually came to +correspond with many distinguished men of learning. One of the first +occasions which brought the talents of the young astronomer into fame +was the publication of some calculations concerning certain +astronomical phenomena which were to happen in the year 1670. In the +monthly revolution of the moon its disc passes over those stars which +lie along its track. The disappearance of a star by the +interposition of the moon is called an "occultation." Owing to the +fact that our satellite is comparatively near us, the position which +the moon appears to occupy on the heavens varies from different parts +of the earth, it consequently happens that a star which would be +occulted to an observer in one locality, would often not be occulted +to an observer who was situated elsewhere. Even when an occultation +is visible from both places, the times at which the star disappears +from view will, generally speaking, be different. Much calculation +is therefore necessary to decide the circumstances under which the +occultations of stars may be visible from any particular station. +Having a taste for such computations, Flamsteed calculated the +occultations which were to happen in the year 1670, it being the case +that several remarkable stars would be passed over by the moon during +this year. Of course at the present time, we find such information +duly set forth in the NAUTICAL ALMANAC, but a couple of centuries ago +there was no such source of astronomical knowledge as is now to be +found in that invaluable publication, which astronomers and +navigators know so well. Flamsteed accordingly sent the results of +his work to the President of the Royal Society. The paper which +contained them was received very favourably, and at once brought +Flamsteed into notice among the most eminent members of that +illustrious body, one of whom, Mr. Collins, became through life his +faithful friend and constant correspondent. Flamsteed's father was +naturally gratified with the remarkable notice which his son was +receiving from the great and learned; accordingly he desired him to +go to London, that he might make the personal acquaintance of those +scientific friends whom he had only known by correspondence +previously. Flamsteed was indeed glad to avail himself of this +opportunity. Thus he became acquainted with Dr. Barrow, and +especially with Newton, who was then Lucasian Professor of +Mathematics at Cambridge. It seems to have been in consequence of +this visit to London that Flamsteed entered himself as a member of +Jesus College, Cambridge. We have but little information as to his +University career, but at all events he took his degree of M.A. on +June 5th, 1674.</p> + +<p>Up to this time it would seem that Flamsteed had been engaged, to a +certain extent, in the business carried on by his father. It is true +that he does not give any explicit details, yet there are frequent +references to journeys which he had to take on business matters. But +the time now approached when Flamsteed was to start on an independent +career, and it appears that he took his degree in Cambridge with the +object of entering into holy orders, so that he might settle in a +small living near Derby, which was in the gift of a friend of his +father, and would be at the disposal of the young astronomer. This +scheme was, however, not carried out, but Flamsteed does not tell us +why it failed, his only remark being, that "the good providence of +God that had designed me for another station ordered it otherwise."</p> + +<p>Sir Jonas Moore, one of the influential friends whom Flamsteed's +talents had attracted, seems to have procured for him the position of +king's astronomer, with a salary of 100 pounds per annum. A larger +salary appears to have been designed at first for this office, which +was now being newly created, but as Flamsteed was resolved on taking +holy orders, a lesser salary was in his case deemed sufficient. The +building of the observatory, in which the first Astronomer Royal was +to be installed, seems to have been brought about, or, at all events, +its progress was accelerated, in a somewhat curious manner.</p> + +<p>A Frenchman, named Le Sieur de S. Pierre, came over to London to +promulgate a scheme for discovering longitudes, then a question of +much importance. He brought with him introductions to distinguished +people, and his mission attracted a great deal of attention. The +proposals which he made came under Flamsteed's notice, who pointed +out that the Frenchman's projects were quite inapplicable in the +present state of astronomical science, inasmuch as the places of the +stars were not known with the degree of accuracy which would be +necessary if such methods were to be rendered available. Flamsteed +then goes on to say:—"I heard no more of the Frenchman after this; +but was told that my letters had been shown King Charles. He was +startled at the assertion of the fixed stars' places being false in +the catalogue, and said, with some vehemence, he must have them anew +observed, examined, and corrected, for the use of his seamen."</p> + +<p>The first question to be settled was the site for the new +observatory. Hyde Park and Chelsea College were both mentioned as +suitable localities, but, at Sir Christopher Wren's suggestion, +Greenwich Hill was finally resolved upon. The king made a grant of +five hundred pounds of money. He gave bricks from Tilbury Fort, +while materials, in the shape of wood, iron, and lead, were available +from a gatehouse demolished in the Tower. The king also promised +whatever further material aid might be shown to be necessary. The +first stone of the Royal Observatory was laid on August 10th, 1675, +and within a few years a building was erected in which the art of +modern practical astronomy was to be created. Flamsteed strove with +extraordinary diligence, and in spite of many difficulties, to obtain +a due provision of astronomical instruments, and to arrange for the +carrying on of his observations. Notwithstanding the king's +promises, the astronomer was, however, but scantily provided with +means, and he had no assistants to help him in his work. It follows +that all the observations, as well as the reductions, and, indeed, +all the incidental work of the observatory, had to be carried on by +himself alone. Flamsteed, as we have seen, had, however, many +staunch friends. Sir Jonas Moore in particular at all times rendered +him most valuable assistance, and encouraged him by the warm sympathy +and keen interest which he showed in astronomy. The work of the +first Astronomer Royal was frequently interrupted by recurrent +attacks of the complaints to which we have already referred. He says +himself that "his distempers stick so close that that he cannot +remove them," and he lost much time by prostration from headaches, as +well as from more serious affections.</p> + +<p>The year 1678 found him in the full tide of work in his observatory. +He was specially engaged on the problem of the earth's motion, which +he sought to derive from observations of the sun and of Venus. But +this, as well as many other astronomical researches which he +undertook, were only subsidiary to that which he made the main task +of his life, namely, the formation of a catalogue of fixed stars. At +the time when Flamsteed commenced his career, the only available +catalogue of fixed stars was that of Tycho Brahe. This work had been +published at the commencement of the seventeenth century, and it +contained about a thousand stars. The positions assigned to these +stars, though obtained with wonderful skill, considering the many +difficulties under which Tycho laboured, were quite inaccurate when +judged by our modern standards. Tycho's instruments were necessarily +most rudely divided, and he had, of course, no telescopes to aid him. +Consequently it was merely by a process of sighting that he could +obtain the places of the stars. It must further be remembered that +Tycho had no clocks, and no micrometers. He had, indeed, but little +correct knowledge of the motions of the heavenly bodies to guide +him. To determine the longitudes of a few principal stars he +conceived the ingenious idea of measuring by day the position of +Venus with respect to the sun, an observation which the exceptional +brightness of this planet rendered possible without telescopic aid, +and then by night he observed the position of Venus with regard to +the stars.</p> + +<p>It has been well remarked by Mr. Baily, in his introduction to the +"British Catalogue of Stars," that "Flamsteed's observations, by a +fortunate combination of circumstances, commenced a new and a +brilliant era. It happened that, at that period, the powerful mind +of Newton was directed to this subject; a friendly intercourse then +existed between these two distinguished characters; and thus the +first observations that could lay any claim to accuracy were at once +brought in aid of those deep researches in which our illustrious +geometer was then engaged. The first edition of the 'Principia' +bears testimony to the assistance afforded by Flamsteed to Newton in +these inquiries; although the former considers that the +acknowledgment is not so ample as it ought to have been."</p> + +<p>Although Flamsteed's observations can hardly be said to possess the +accuracy of those made in more recent times, when instruments so much +superior to his have been available, yet they possess an interest of +a special kind from their very antiquity. This circumstance renders +them of particular importance to the astronomer, inasmuch as they are +calculated to throw light on the proper motions of the stars. +Flamsteed's work may, indeed, be regarded as the origin of all +subsequent catalogues, and the nomenclature which he adopted, though +in some respects it can hardly be said to be very defensible, is, +nevertheless, that which has been adopted by all subsequent +astronomers. There were also a great many errors, as might be +expected in a work of such extent, composed almost entirely of +numerical detail. Many of these errors have been corrected by Baily +himself, the assiduous editor of "Flamsteed's Life and Works," for +Flamsteed was so harassed from various causes in the latter part of +his life, and was so subject to infirmities all through his career, +that he was unable to revise his computations with the care that +would have been necessary. Indeed, he observed many additional stars +which he never included in the British Catalogue. It is, as Baily +well remarks, "rather a matter of astonishment that he accomplished +so much, considering his slender means, his weak frame, and the +vexations which he constantly experienced."</p> + +<p>Flamsteed had the misfortune, in the latter part of his life, to +become estranged from his most eminent scientific contemporaries. He +had supplied Newton with places of the moon, at the urgent +solicitation of the author of the "Principia," in order that the +lunar theory should be carefully compared with observation. But +Flamsteed appears to have thought that in Newton's further request +for similar information, he appeared to be demanding as a right that +which Flamsteed considered he was only called upon to render as a +favour. A considerable dispute grew out of this matter, and there +are many letters and documents, bearing on the difficulties which +subsequently arose, that are not, perhaps, very creditable to either +party.</p> + +<p>Notwithstanding his feeble constitution, Flamsteed lived to the age +of seventy-three, his death occurring on the last day of the year +1719.</p> + +<h3><a name="HALLEY" id="HALLEY"></a>HALLEY.</h3> +<p>Isaac Newton was just fourteen years of age when the birth of Edmund +Halley, who was destined in after years to become Newton's warmly +attached friend, and one of his most illustrious scientific +contemporaries, took place. There can be little doubt that the fame +as an astronomer which Halley ultimately acquired, great as it +certainly was, would have been even greater still had it not been +somewhat impaired by the misfortune that he had to shine in the same +sky as that which was illumined by the unparalleled genius of Newton.</p> + +<p>Edmund Halley was born at Haggerston, in the Parish of St. Leonard's, +Shoreditch, on October 29th, 1656. His father, who bore the same +name as his famous son, was a soap-boiler in Winchester Street, +London, and he had conducted his business with such success that he +accumulated an ample fortune. I have been unable to obtain more than +a very few particulars with respect to the early life of the future +astronomer. It would, however, appear that from boyhood he showed +considerable aptitude for the acquisition of various kinds of +learning, and he also had some capacity for mechanical invention. +Halley seems to have received a sound education at St. Paul's School, +then under the care of Dr. Thomas Gale.</p> + +<p>Here, the young philosopher rapidly distanced his competitors in the +various branches of ordinary school instruction. His superiority +was, however, most conspicuous in mathematical studies, and, as a +natural development of such tastes, we learn that by the time he had +left school he had already made good progress in astronomy. At the +age of seventeen he was entered as a commoner at Queen's College, +Oxford, and the reputation that he brought with him to the University +may be inferred from the remark of the writer of "Athenae +Oxonienses," that Halley came to Oxford "with skill in Latin, Greek, +and Hebrew, and such a knowledge of geometry as to make a complete +dial." Though his studies were thus of a somewhat multifarious +nature, yet it is plain that from the first his most favourite +pursuit was astronomy. His earliest efforts in practical observation +were connected with an eclipse which he observed from his father's +house in Winchester Street. It also appears that he had studied +theoretical branches of astronomy so far as to be conversant with the +application of mathematics to somewhat abstruse problems.</p> + +<p>Up to the time of Kepler, philosophers had assumed almost as an axiom +that the heavenly bodies must revolve in circles and that the motion +of the planet around the orbit which it described must be uniform. We +have already seen how that great philosopher, after very persevering +labour, succeeded in proving that the orbits of the planets were not +circles, but that they were ellipses of small eccentricity. Kepler +was, however, unable to shake himself free from the prevailing notion +that the angular motion of the planet ought to be of a uniform +character around some point. He had indeed proved that the motion +round the focus of the ellipse in which the sun lies is not of this +description. One of his most important discoveries even related to +the fact that at some parts of its orbit a planet swings around the +sun with greater angular velocity than at others. But it so happens +that in elliptic tracks which differ but little from circles, as is +the case with all the more important planetary orbits, the motion +round the empty focus of the ellipse is very nearly uniform. It +seemed natural to assume, that this was exactly the case, in which +event each of the two foci of the ellipse would have had a special +significance in relation to the movement of the planet. The youthful +Halley, however, demonstrated that so far as the empty focus was +concerned, the movement of the planet around it, though so nearly +uniform, was still not exactly so, and at the age of nineteen, he +published a treatise on the subject which at once placed him in the +foremost rank amongst theoretical astronomers.</p> + +<p>But Halley had no intention of being merely an astronomer with his +pen. He longed to engage in the practical work of observing. He saw +that the progress of exact astronomy must depend largely on the +determination of the positions of the stars with all attainable +accuracy. He accordingly determined to take up this branch of work, +which had been so successfully initiated by Tycho Brahe.</p> + +<p>At the present day, astronomers of the great national observatories +are assiduously engaged in the determination of the places of the +stars. A knowledge of the exact positions of these bodies is indeed +of the most fundamental importance, not alone for the purposes of +scientific astronomy, but also for navigation and for extensive +operations of surveying in which accuracy is desired. The fact that +Halley determined to concentrate himself on this work shows clearly +the scientific acumen of the young astronomer.</p> + +<p>Halley, however, found that Hevelius, at Dantzig, and Flamsteed, the +Astronomer Royal at Greenwich, were both engaged on work of this +character. He accordingly determined to direct his energies in a way +that he thought would be more useful to science. He resigned to the +two astronomers whom I have named the investigation of the stars in +the northern hemisphere, and he sought for himself a field hitherto +almost entirely unworked. He determined to go to the southern +hemisphere, there to measure and survey those stars which were +invisible in Europe, so that his work should supplement the labours +of the northern astronomers, and that the joint result of his labours +and of theirs might be a complete survey of the most important stars +on the surface of the heavens.</p> + +<p>In these days, after so many ardent students everywhere have devoted +themselves to the study of Nature, it seems difficult for a beginner +to find a virgin territory in which to commence his explorations. +Halley may, however, be said to have enjoyed the privilege of +commencing to work in a magnificent region, the contents of which +were previously almost entirely unknown. Indeed none of the stars +which were so situated as to have been invisible from Tycho Brahe's +observatory at Uraniborg, in Denmark, could be said to have been +properly observed. There was, no doubt, a rumour that a Dutchman had +observed southern stars from the island of Sumatra, and certain stars +were indicated in the southern heavens on a celestial globe. On +examination, however, Halley found that no reliance could be placed +on the results which had been obtained, so that practically the field +before him may be said to have been unworked.</p> + +<p>At the age of twenty, without having even waited to take that degree +at the university which the authorities would have been glad to +confer on so promising an undergraduate, this ardent student of +Nature sought his father's permission to go to the southern +hemisphere for the purpose of studying the stars which lie around the +southern pole. His father possessed the necessary means, and he had +likewise the sagacity to encourage the young astronomer. He was +indeed most anxious to make everything as easy as possible for so +hopeful a son. He provided him with an allowance of 300 pounds a +year, which was regarded as a very munificent provision in those +days. Halley was also furnished with letters of recommendation from +King Charles II., as well as from the directors of the East India +Company. He accordingly set sail with his instruments in the year +1676, in one of the East India Company's ships, for the island of St. +Helena, which he had selected as the scene of his labours.</p> + +<p><a name="halley_ill" id="halley_ill"></a></p> + +<div class="figcenter" style="width: 407px;"> +<a href="images/ill_haley.jpg"> +<img src="images/ill_haley_sml.jpg" width="407" height="484" alt="HALLEY." title="" /></a> +<span class="caption">HALLEY.</span> +</div> + +<p>After an uneventful voyage of three months, the astronomer landed on +St. Helena, with his sextant of five and a half feet radius, and a +telescope 24 feet long, and forthwith plunged with ardour into his +investigation of the southern skies. He met, however, with one very +considerable disappointment. The climate of this island had been +represented to him as most favourable for astronomical observation; +but instead of the pure blue skies he had been led to expect, he +found that they were almost always more or less clouded, and that +rain was frequent, so that his observations were very much +interrupted. On this account he only remained at St. Helena for a +single year, having, during that time, and in spite of many +difficulties, accomplished a piece of work which earned for him the +title of "our southern Tycho." Thus did Halley establish his fame as +an astronomer on the same lonely rock in mid-Atlantic, which nearly a +century and a-half later became the scene of Napoleon's imprisonment, +when his star, in which he believed so firmly, had irretrievably set.</p> + +<p>On his return to England, Halley prepared a map which showed the +result of his labours, and he presented it to the king, in 1677. +Like his great predecessor Tycho, Halley did not altogether disdain +the arts of the courtier, for he endeavoured to squeeze a new +constellation into the group around the southern pole which he styled +"The Royal Oak," adding a description to the effect that the +incidents of which "The Royal Oak" was a symbol were of sufficient +importance to be inscribed on the surface of the heavens.</p> + +<p>There is reason to think that Charles II. duly appreciated the +scientific renown which one of his subjects had achieved, and it was +probably through the influence of the king that Halley was made a +Master of Arts at Oxford on November 18th, 1678. Special reference +was made on the occasion to his observations at St. Helena, as +evidence of unusual attainments in mathematics and astronomy. This +degree was no small honour to such a young man, who, as we have seen, +quitted his university before he had the opportunity of graduating in +the ordinary manner.</p> + +<p>On November 30th, in the same year, the astronomer received a further +distinction in being elected a Fellow of the Royal Society. From +this time forward he took a most active part in the affairs of the +Society, and the numerous papers which he read before it form a very +valuable part of that notable series of volumes known as the +"Philosophical Transactions." He was subsequently elected to the +important office of secretary to the Royal Society, and he discharged +the duties of his post until his appointment to Greenwich +necessitated his resignation.</p> + +<p>Within a year of Halley's election as a Fellow of the Royal Society, +he was chosen by the Society to represent them in a discussion which +had arisen with Hevelius. The nature of this discussion, or rather +the fact that any discussion should have been necessary, may seem +strange to modern astronomers, for the point is one on which it would +now seem impossible for there to be any difference of opinion. We +must, however, remember that the days of Halley were, comparatively +speaking, the days of infancy as regards the art of astronomical +observation, and issues that now seem obvious were often, in those +early times, the occasions of grave and anxious consideration. The +particular question on which Halley had to represent the Royal +Society may be simply stated. When Tycho Brahe made his memorable +investigations into the places of the stars, he had no telescopes to +help him. The famous instruments at Uraniborg were merely provided +with sights, by which the telescope was pointed to a star on the same +principle as a rifle is sighted for a target. Shortly after Tycho's +time, Galileo invented the telescope. Of course every one admitted +at once the extraordinary advantages which the telescope had to +offer, so far as the mere question of the visibility of objects was +concerned. But the bearing of Galileo's invention upon what we may +describe as the measuring part of astronomy was not so immediately +obvious. If a star be visible to the unaided eye, we can determine +its place by such instruments as those which Tycho used, in which no +telescope is employed. We can, however, also avail ourselves of an +instrument in which we view the star not directly but through the +intervention of the telescope. Can the place of the star be +determined more accurately by the latter method than it can when the +telescope is dispensed with? With our present knowledge, of course, +there is no doubt about the answer; every one conversant with +instruments knows that we can determine the place of a star far more +accurately with the telescope than is possible by any mere sighting +apparatus. In fact an observer would be as likely to make an error +of a minute with the sighting apparatus in Tycho's instrument, as he +would be to make an error of a second with the modern telescope, or, +to express the matter somewhat differently, we may say, speaking +quite generally, that the telescopic method of determining the places +of the stars does not lead to errors more than one-sixtieth part as +great as which are unavoidable when we make use of Tycho's method.</p> + +<p>But though this is so apparent to the modern astronomer, it was not +at all apparent in the days of Halley, and accordingly he was sent +off to discuss the question with the Continental astronomers. +Hevelius, as the representative of the older method, which Tycho had +employed with such success, maintained that an instrument could be +pointed more accurately at a star by the use of sights than by the +use of a telescope, and vigorously disputed the claims put forward by +those who believed that the latter method was the more suitable. On +May 14th, 1679, Halley started for Dantzig, and the energetic +character of the man may be judged from the fact that on the very +night of his arrival he commenced to make the necessary +observations. In those days astronomical telescopes had only +obtained a fractional part of the perfection possessed by the +instruments in our modern observatories, and therefore it may not be +surprising that the results of the trial were not immediately +conclusive. Halley appears to have devoted much time to the +investigation; indeed, he remained at Dantzig for more than a +twelve-month. On his return to England, he spoke highly of the skill +which Hevelius exhibited in the use of his antiquated methods, but +Halley was nevertheless too sagacious an observer to be shaken in his +preference for the telescopic method of observation.</p> + +<p>The next year we find our young astronomer starting for a Continental +tour, and we, who complain if the Channel passage lasts more than an +hour or two, may note Halley's remark in writing to Hooke on June +15th, 1680: "Having fallen in with bad weather we took forty hours in +the journey from Dover to Calais." The scientific distinction which +he had already attained was such that he was received in Paris with +marked attention. A great deal of his time seems to have been passed +in the Paris observatory, where Cassini, the presiding genius, +himself an astronomer of well-deserved repute, had extended a hearty +welcome to his English visitor. They made observations together of +the place of the splendid comet which was then attracting universal +attention, and Halley found the work thus done of much use when he +subsequently came to investigate the path pursued by this body. +Halley was wise enough to spare no pains to derive all possible +advantages from his intercourse with the distinguished savants of the +French capital. In the further progress of his tour he visited the +principal cities of the Continent, leaving behind him everywhere the +memory of an amiable disposition and of a rare intelligence.</p> + +<p>After Halley's return to England, in 1682, he married a young lady +named Mary Tooke, with whom he lived happily, till her death +fifty-five years later. On his marriage, he took up his abode in +Islington, where he erected his instruments and recommenced his +observations.</p> + +<p>It has often been the good fortune of astronomers to render practical +services to humanity by their investigations, and Halley's +achievements in this respect deserve to be noted. A few years after +he had settled in England, he published an important paper on the +variation of the magnetic compass, for so the departure of the needle +from the true north is termed. This subject had indeed early engaged +his attention, and he continued to feel much interest in it up to the +end of his life. With respect to his labours in this direction, Sir +John Herschel says: "To Halley we owe the first appreciation of the +real complexity of the subject of magnetism. It is wonderful indeed, +and a striking proof of the penetration and sagacity of this +extraordinary man, that with his means of information he should have +been able to draw such conclusions, and to take so large and +comprehensive a view of the subject as he appears to have done." In +1692, Halley explained his theory of terrestrial magnetism, and +begged captains of ships to take observations of the variations of +the compass in all parts of the world, and to communicate them to the +Royal Society, "in order that all the facts may be readily available +to those who are hereafter to complete this difficult and complicated +subject."</p> + +<p>The extent to which Halley was in advance of his contemporaries, in +the study of terrestrial magnetism, may be judged from the fact that +the subject was scarcely touched after his time till the year 1811. +The interest which he felt in it was not of a merely theoretical +kind, nor was it one which could be cultivated in an easy-chair. Like +all true investigators, he longed to submit his theory to the test of +experiment, and for that purpose Halley determined to observe the +magnetic variation for himself. He procured from King William III. +the command of a vessel called the "Paramour Pink," with which he +started for the South Seas in 1694. This particular enterprise was +not, however, successful; for, on crossing the line, some of his men +fell sick and one of his lieutenants mutinied, so that he was obliged +to return the following year with his mission unaccomplished. The +government cashiered the lieutenant, and Halley having procured a +second smaller vessel to accompany the "Paramour Pink," started once +more in September, 1699. He traversed the Atlantic to the 52nd +degree of southern latitude, beyond which his further advance was +stopped. "In these latitudes," he writes to say, "we fell in with +great islands of ice of so incredible height and magnitude, that I +scarce dare write my thoughts of it."</p> + +<p>On his return in 1700, Halley published a general chart, showing the +variation of the compass at the different places which he had +visited. On these charts he set down lines connecting those +localities at which the magnetic variation was identical. He thus +set an example of the graphic representation of large masses of +complex facts, in such a manner as to appeal at once to the eye, a +method of which we make many applications in the present day.</p> + +<p>But probably the greatest service which Halley ever rendered to human +knowledge was the share in which he took in bringing Newton's +"Principia" before the world. In fact, as Dr. Glaisher, writing in +1888, has truly remarked, "but for Halley the 'Principia' would not +have existed."</p> + +<p>It was a visit from Halley in the year 1684 which seems to have first +suggested to Newton the idea of publishing the results of his +investigations on gravitation. Halley, and other scientific +contemporaries, had no doubt some faint glimmering of the great truth +which only Newton's genius was able fully to reveal. Halley had +indeed shown how, on the assumptions that the planets move in +circular orbits round the sun, and that the squares of their periodic +times are proportional to the cubes of their mean distances, it may +be proved that the force acting on each planet must vary inversely as +the square of its distance from the sun. Since, however, each of the +planets actually moves in an ellipse, and therefore, at continually +varying distances from the sun, it becomes a much more difficult +matter to account mathematically for the body's motions on the +supposition that the attractive force varies inversely as the square +of the distance. This was the question with which Halley found +himself confronted, but which his mathematical abilities were not +adequate to solve. It would seem that both Hooke and Sir Christopher +Wren were interested in the same problem; in fact, the former claimed +to have arrived at a solution, but declined to make known his +results, giving as an excuse his desire that others having tried and +failed might learn to value his achievements all the more. Halley, +however, confessed that his attempts at the solution were +unsuccessful, and Wren, in order to encourage the other two +philosophers to pursue the inquiry, offered to present a book of +forty shillings value to either of them who should in the space of +two months bring him a convincing proof of it. Such was the value +which Sir Christopher set on the Law of Gravitation, upon which the +whole fabric of modern astronomy may be said to stand.</p> + +<p>Finding himself unequal to the task, Halley went down to Cambridge to +see Newton on the subject, and was delighted to learn that the great +mathematician had already completed the investigation. He showed +Halley that the motions of all the planets could be completely +accounted for on the hypothesis of a force of attraction directed +towards the sun, which varies inversely as the square of the distance +from that body.</p> + +<p>Halley had the genius to perceive the tremendous importance of +Newton's researches, and he ceased not to urge upon the recluse man +of science the necessity for giving his new discoveries publication. +He paid another visit to Cambridge with the object of learning more +with regard to the mathematical methods which had already conducted +Newton to such sublime truths, and he again encouraged the latter +both to pursue his investigations, and to give some account of them +to the world. In December of the same year Halley had the +gratification of announcing to the Royal Society that Newton had +promised to send that body a paper containing his researches on +Gravitation.</p> + +<p>It seems that at this epoch the finances of the Royal Society were at +a very low ebb. This impecuniosity was due to the fact that a book +by Willoughby, entitled "De Historia Piscium," had been recently +printed by the society at great expense. In fact, the coffers were +so low that they had some difficulty in paying the salaries of their +permanent officials. It appears that the public did not care about +the history of fishes, or at all events the volume did not meet with +the ready demand which was expected for it. Indeed, it has been +recorded that when Halley had undertaken to measure the length of a +degree of the earth's surface, at the request of the Royal Society, +it was ordered that his expenses be defrayed either in 50 pounds +sterling, or in fifty books of fishes. Thus it happened that on June +2nd, the Council, after due consideration of ways and means in +connection with the issue of the Principia, "ordered that Halley +should undertake the business of looking after the book and printing +it at his own charge," which he engaged to do.</p> + +<p>It was, as we have elsewhere mentioned, characteristic of Newton that +he detested controversies, and he was, in fact, inclined to suppress +the third book of the "Principia" altogether rather than have any +conflict with Hooke with respect to the discoveries there +enunciated. He also thought of changing the name of the work to De +Motu Corporum Libri Duo, but upon second thoughts, he retained the +original title, remarking, as he wrote to Halley, "It will help the +sale of the book, which I ought not to diminish, now it is yours," a +sentence which shows conclusively, if further proof were necessary, +that Halley had assumed the responsibility of its publication.</p> + +<p>Halley spared no pains in pushing forward the publication of his +illustrious friend's great work, so that in the same year he was in a +position to present a complete copy to King James II., with a proper +discourse of his own. Halley also wrote a set of Latin hexameters in +praise of Newton's genius, which he printed at the beginning of the +work. The last line of this specimen of Halley's poetic muse may be +thus rendered: "Nor mortals nearer may approach the gods."</p> + +<p>The intimate friendship between the two greatest astronomers of the +time continued without interruption till the death of Newton. It +has, indeed, been alleged that some serious cause of estrangement +arose between them. There is, however, no satisfactory ground for +this statement; indeed, it may be regarded as effectually disposed of +by the fact that, in the year 1727, Halley took up the defence of his +friend, and wrote two learned papers in support of Newton's "System +of Chronology," which had been seriously attacked by a certain +ecclesiastic. It is quite evident to any one who has studied these +papers that Halley's friendship for Newton was as ardent as ever.</p> + +<p>The generous zeal with which Halley adopted and defended the +doctrines of Newton with regard to the movements of the celestial +bodies was presently rewarded by a brilliant discovery, which has +more than any of his other researches rendered his name a familiar +one to astronomers. Newton, having explained the movement of the +planets, was naturally led to turn his attention to comets. He +perceived that their journeyings could be completely accounted for as +consequences of the attraction of the sun, and he laid down the +principles by which the orbit of a comet could be determined, +provided that observations of its positions were obtained at three +different dates. The importance of these principles was by no one +more quickly recognised than by Halley, who saw at once that it +provided the means of detecting something like order in the movements +of these strange wanderers. The doctrine of Gravitation seemed to +show that just as the planets revolved around the sun in ellipses, so +also must the comets. The orbit, however, in the case of the comet, +is so extremely elongated that the very small part of the elliptic +path within which the comet is both near enough and bright enough to +be seen from the earth, is indistinguishable from a parabola. +Applying these principles, Halley thought it would be instructive to +study the movements of certain bright comets, concerning which +reliable observations could be obtained. At the expense of much +labour, he laid down the paths pursued by twenty-four of these +bodies, which had appeared between the years 1337 and 1698. Amongst +them he noticed three, which followed tracks so closely resembling +each other, that he was led to conclude the so called three comets +could only have been three different appearances of the same body. +The first of these occurred in 1531, the second was seen by Kepler in +1607, and the third by Halley himself in 1682. These dates suggested +that the observed phenomena might be due to the successive returns of +one and the same comet after intervals of seventy-five or seventy-six +years. On the further examination of ancient records, Halley found +that a comet had been seen in the year 1456, a date, it will be +observed, seventy-five years before 1531. Another had been observed +seventy-six years earlier than 1456, viz., in 1380, and another +seventy-five years before that, in 1305.</p> + +<p>As Halley thus found that a comet had been recorded on several +occasions at intervals of seventy-five or seventy-six years, he was +led to the conclusion that these several apparitions related to one +and the same object, which was an obedient vassal of the sun, +performing an eccentric journey round that luminary in a period of +seventy-five or seventy-six years. To realise the importance of this +discovery, it should be remembered that before Halley's time a comet, +if not regarded merely as a sign of divine displeasure, or as an omen +of intending disaster, had at least been regarded as a chance visitor +to the solar system, arriving no one knew whence, and going no one +knew whither.</p> + +<p>A supreme test remained to be applied to Halley's theory. The +question arose as to the date at which this comet would be seen +again. We must observe that the question was complicated by the fact +that the body, in the course of its voyage around the sun, was +exposed to the incessant disturbing action produced by the attraction +of the several planets. The comet therefore, does not describe a +simple ellipse as it would do if the attraction of the sun were the +only force by which its movement were controlled. Each of the +planets solicits the comet to depart from its track, and though the +amount of these attractions may be insignificant in comparison with +the supreme controlling force of the sun, yet the departure from the +ellipse is quite sufficient to produce appreciable irregularities in +the comet's movement. At the time when Halley lived, no means +existed of calculating with precision the effect of the disturbance a +comet might experience from the action of the different planets. +Halley exhibited his usual astronomical sagacity in deciding that +Jupiter would retard the return of the comet to some extent. Had it +not been for this disturbance the comet would apparently have been +due in 1757 or early in 1758. But the attraction of the great planet +would cause delay, so that Halley assigned, for the date of its +re-appearance, either the end of 1758 or the beginning of 1759. +Halley knew that he could not himself live to witness the fulfilment +of his prediction, but he says: "If it should return, according to +our predictions, about the year 1758, impartial posterity will not +refuse to acknowledge that this was first discovered by an +Englishman." This was, indeed, a remarkable prediction of an event +to occur fifty-three years after it had been uttered. The way in +which it was fulfilled forms one of the most striking episodes in the +history of astronomy. The comet was first seen on Christmas Day, +1758, and passed through its nearest point to the sun on March 13th, +1759. Halley had then been lying in his grave for seventeen years, +yet the verification of his prophecy reflects a glory on his name +which will cause it to live for ever in the annals of astronomy. The +comet paid a subsequent visit in 1835, and its next appearance is due +about 1910.</p> + +<p>Halley next entered upon a labour which, if less striking to the +imagination than his discoveries with regard to comets, is still of +inestimable value in astronomy. He undertook a series of +investigations with the object of improving our knowledge of the +movements of the planets. This task was practically finished in +1719, though the results of it were not published until after his +death in 1749. In the course of it he was led to investigate closely +the motion of Venus, and thus he came to recognise for the first time +the peculiar importance which attaches to the phenomenon of the +transit of this planet across the sun. Halley saw that the transit, +which was to take place in the year 1761, would afford a favourable +opportunity for determining the distance of the sun, and thus +learning the scale of the solar system. He predicted the +circumstances of the phenomenon with an astonishing degree of +accuracy, considering his means of information, and it is +unquestionably to the exertions of Halley in urging the importance of +the matter upon astronomers that we owe the unexampled degree of +interest taken in the event, and the energy which scientific men +exhibited in observing it. The illustrious astronomer had no hope of +being himself a witness of the event, for it could not happen till +many years after his death. This did not, however, diminish his +anxiety to impress upon those who would then be alive, the importance +of the occurrence, nor did it lead him to neglect anything which +might contribute to the success of the observations. As we now know, +Halley rather over-estimated the value of the transit of Venus, as a +means of determining the solar distance. The fact is that the +circumstances are such that the observation of the time of contact +between the edge of the planet and the edge of the sun cannot be made +with the accuracy which he had expected.</p> + +<p>In 1691, Halley became a candidate for the Savilian Professorship of +Astronomy at Oxford. He was not, however, successful, for his +candidature was opposed by Flamsteed, the Astronomer Royal of the +time, and another was appointed. He received some consolation for +this particular disappointment by the fact that, in 1696, owing to +Newton's friendly influence, he was appointed deputy Controller of +the Mint at Chester, an office which he did not retain for long, as +it was abolished two years later. At last, in 1703, he received what +he had before vainly sought, and he was appointed to the Savilian +chair.</p> + +<p>His observations of the eclipse of the sun, which occurred in 1715, +added greatly to Halley's reputation. This phenomenon excited +special attention, inasmuch as it was the first total eclipse of the +sun which had been visible in London since the year 1140. Halley +undertook the necessary calculations, and predicted the various +circumstances with a far higher degree of precision than the official +announcement. He himself observed the phenomenon from the Royal +Society's rooms, and he minutely describes the outer atmosphere of +the sun, now known as the corona; without, however, offering an +opinion as to whether it was a solar or a lunar appendage.</p> + +<p>At last Halley was called to the dignified office which he of all men +was most competent to fill. On February 9th, 1720, he was appointed +Astronomer Royal in succession to Flamsteed. He found things at the +Royal Observatory in a most unsatisfactory state. Indeed, there were +no instruments, nor anything else that was movable; for such things, +being the property of Flamsteed, had been removed by his widow, and +though Halley attempted to purchase from that lady some of the +instruments which his predecessor had employed, the unhappy personal +differences which had existed between him and Flamsteed, and which, +as we have already seen, prevented his election as Savilian Professor +of Astronomy, proved a bar to the negotiation. Greenwich Observatory +wore a very different appearance in those days, from that which the +modern visitor, who is fortunate enough to gain admission, may now +behold. Not only did Halley find it bereft of instruments, we learn +besides that he had no assistants, and was obliged to transact the +whole business of the establishment single-handed.</p> + +<p>In 1721, however, he obtained a grant of 500 pounds from the Board of +Ordnance, and accordingly a transit instrument was erected in the +same year. Some time afterwards he procured an eight-foot quadrant, +and with these instruments, at the age of sixty-four, he commenced a +series of observations on the moon. He intended, if his life was +spared, to continue his observations for a period of eighteen years, +this being, as astronomers know, a very important cycle in connection +with lunar movements. The special object of this vast undertaking +was to improve the theory of the moon's motion, so that it might +serve more accurately to determine longitudes at sea. This +self-imposed task Halley lived to carry to a successful termination, +and the tables deduced from his observations, and published after his +death, were adopted almost universally by astronomers, those of the +French nation being the only exception.</p> + +<p>Throughout his life Halley had been singularly free from illness of +every kind, but in 1737 he had a stroke of paralysis. Notwithstanding +this, however, he worked diligently at his telescope till 1739, after +which his health began rapidly to give way. He died on January 14th, +1742, in the eighty-sixth year of his age, retaining his mental +faculties to the end. He was buried in the cemetery of the church of +Lee in Kent, in the same grave as his wife, who had died five years +previously. We are informed by Admiral Smyth that Pond, a later +Astronomer Royal, was afterwards laid in the same tomb.</p> + +<p>Halley's disposition seems to have been generous and candid, and +wholly free from anything like jealousy or rancour. In person he was +rather above the middle height, and slight in build; his complexion +was fair, and he is said to have always spoken, as well as acted, +with uncommon sprightliness. In the eloge pronounced upon him at the +Paris Academie Des Sciences, of which Halley had been made a member +in 1719 it was said, "he possessed all the qualifications which were +necessary to please princes who were desirous of instruction, with a +great extent of knowledge and a constant presence of mind; his +answers were ready, and at the same time pertinent, judicious, polite +and sincere."</p> + +<p><a name="greenwich_observatory" id="greenwich_observatory"></a></p> + +<div class="figcenter" style="width: 705px;"> +<a href="images/ill_grnch_oberservatory_halleys_time.jpg"> +<img src="images/ill_grnch_oberservatory_halleys_time_sml.jpg" width="705" height="429" alt="GREENWICH OBSERVATORY IN HALLEY'S TIME." title="" /></a> +<span class="caption">GREENWICH OBSERVATORY IN HALLEY'S TIME.</span> +</div> + +<p>Thus we find that Peter the Great was one of his most ardent +admirers. He consulted the astronomer on matters connected with +shipbuilding, and invited him to his own table. But Halley possessed +nobler qualifications than the capacity of pleasing Princes. He was +able to excite and to retain the love and admiration of his equals. +This was due to the warmth of his attachments, the unselfishness of +his devotion to his friends, and to a vein of gaiety and good-humour +which pervaded all his conversation.</p> + +<h3><a name="BRADLEY" id="BRADLEY"></a>BRADLEY.</h3> +<p>James Bradley was descended from an ancient family in the county of +Durham. He was born in 1692 or 1693, at Sherbourne, in +Gloucestershire, and was educated in the Grammar School at +Northleach. From thence he proceeded in due course to Oxford, where +he was admitted a commoner at Balliol College, on March 15th, 1711. +Much of his time, while an undergraduate, was passed in Essex with +his maternal uncle, the Rev. James Pound, who was a well-known man of +science and a diligent observer of the stars. It was doubtless by +intercourse with his uncle that young Bradley became so expert in the +use of astronomical instruments, but the immortal discoveries he +subsequently made show him to have been a born astronomer.</p> + +<p>The first exhibition of Bradley's practical skill seems to be +contained in two observations which he made in 1717 and 1718. They +have been published by Halley, whose acuteness had led him to +perceive the extraordinary scientific talents of the young +astronomer. Another illustration of the sagacity which Bradley +manifested, even at the very commencement of his astronomical career, +is contained in a remark of Halley's, who says: "Dr. Pound and his +nephew, Mr. Bradley, did, myself being present, in the last +opposition of the sun and Mars this way demonstrate the extreme +minuteness of the sun's parallax, and that it was not more than +twelve seconds nor less than nine seconds." To make the significance +of this plain, it should be observed that the determination of the +sun's parallax is equivalent to the determination of the distance +from the earth to the sun. At the time of which we are now writing, +this very important unit of celestial measurement was only very +imperfectly known, and the observations of Pound and Bradley may be +interpreted to mean that, from their observations, they had come to +the conclusion that the distance from the earth to the sun must be +more than 94 millions of miles, and less than 125 millions. We now, +of course, know that they were not exactly right, for the true +distance of the sun is about 93 millions of miles. We cannot, +however, but think that it was a very remarkable approach for the +veteran astronomer and his brilliant nephew to make towards the +determination of a magnitude which did not become accurately known +till fifty years later.</p> + +<p>Among the earliest parts of astronomical work to which Bradley's +attention was directed, were the eclipses of Jupiter's satellites. +These phenomena are specially attractive inasmuch as they can be so +readily observed, and Bradley found it extremely interesting to +calculate the times at which the eclipses should take place, and then +to compare his observations with the predicted times. From the +success that he met with in this work, and from his other labours, +Bradley's reputation as an astronomer increased so greatly that on +November the 6th, 1718, he was elected a Fellow of the Royal Society.</p> + +<p>Up to this time the astronomical investigations of Bradley had been +more those of an amateur than of a professional astronomer, and as it +did not at first seem likely that scientific work would lead to any +permanent provision, it became necessary for the youthful astronomer +to choose a profession. It had been all along intended that he +should enter the Church, though for some reason which is not told us, +he did not take orders as soon as his age would have entitled him to +do so. In 1719, however, the Bishop of Hereford offered Bradley the +Vicarage of Bridstow, near Ross, in Monmouthshire, and on July 25th, +1720, he having then taken priest's orders, was duly instituted in +his vicarage. In the beginning of the next year, Bradley had some +addition to his income from the proceeds of a Welsh living, which, +being a sinecure, he was able to hold with his appointment at +Bridstow. It appears, however, that his clerical occupations were +not very exacting in their demands upon his time, for he was still +able to pay long and often-repeated visits to his uncle at +Wandsworth, who, being himself a clergyman, seems to have received +occasional assistance in his ministerial duties from his astronomical +nephew.</p> + +<p>The time, however, soon arrived when Bradley was able to make a +choice between continuing to exercise his profession as a divine, or +devoting himself to a scientific career. The Savilian Professorship +of Astronomy in the University of Oxford became vacant by the death +of Dr. John Keill. The statutes forbade that the Savilian Professor +should also hold a clerical appointment, and Mr. Pound would +certainly have been elected to the professorship had he consented to +surrender his preferments in the Church. But Pound was unwilling to +sacrifice his clerical position, and though two or three other +candidates appeared in the field, yet the talents of Bradley were so +conspicuous that he was duly elected, his willingness to resign the +clerical profession having been first ascertained.</p> + +<p>There can be no doubt that, with such influential friends as Bradley +possessed, he would have made great advances had he adhered to his +profession as a divine. Bishop Hoadly, indeed, with other marks of +favour, had already made the astronomer his chaplain. The engrossing +nature of Bradley's interest in astronomy decided him, however, to +sacrifice all other prospects in comparison with the opening afforded +by the Savilian Professorship. It was not that Bradley found himself +devoid of interest in clerical matters, but he felt that the true +scope for such abilities as he possessed would be better found in the +discharge of the scientific duties of the Oxford chair than in the +spiritual charge of a parish. On April the 26th, 1722, Bradley read +his inaugural lecture in that new position on which he was destined +to confer such lustre.</p> + +<p>It must, of course, be remembered that in those early days the art of +constructing the astronomical telescope was very imperfectly +understood. The only known method for getting over the peculiar +difficulties presented in the construction of the refracting +telescope, was to have it of the most portentous length. In fact, +Bradley made several of his observations with an instrument of two +hundred and twelve feet focus. In such a case, no tube could be +used, and the object glass was merely fixed at the top of a high +pole. Notwithstanding the inconvenience and awkwardness of such an +instrument, Bradley by its means succeeded in making many careful +measurements. He observed, for example, the transit of Mercury over +the sun's disc, on October 9th, 1723; he also observed the dimensions +of the planet Venus, while a comet which Halley discovered on October +the 9th, 1723, was assiduously observed at Wanstead up to the middle +of the ensuing month. The first of Bradley's remarkable +contributions to the "Philosophical Transactions" relates to this +comet, and the extraordinary amount of work that he went through in +connection therewith may be seen from an examination of his book of +Calculations which is still extant.</p> + +<p>The time was now approaching when Bradley was to make the first of +those two great discoveries by which his name has acquired a lustre +that has placed him in the very foremost rank of astronomical +discoverers. As has been often the case in the history of science, +the first of these great successes was attained while he was pursuing +a research intended for a wholly different purpose. It had long been +recognised that as the earth describes a vast orbit, nearly two +hundred million miles in diameter, in its annual journey round the +sun, the apparent places of the stars should alter, to some extent, +in correspondence with the changes in the earth's position. The +nearer the star the greater the shift in its apparent place on the +heavens, which must arise from the fact that it was seen from +different positions in the earth's orbit. It had been pointed out +that these apparent changes in the places of the stars, due to the +movement of the earth, would provide the means of measuring the +distances of the stars. As, however, these distances are enormously +great in comparison with the orbit which the earth describes around +the sun, the attempt to determine the distances of the stars by the +shift in their positions had hitherto proved ineffectual. Bradley +determined to enter on this research once again; he thought that by +using instruments of greater power, and by making measurements of +increased delicacy, he would be able to perceive and to measure +displacements which had proved so small as to elude the skill of the +other astronomers who had previously made efforts in the same +direction. In order to simplify the investigation as much as +possible, Bradley devoted his attention to one particular star, Beta +Draconis, which happened to pass near his zenith. The object of +choosing a star in this position was to avoid the difficulties which +would be introduced by refraction had the star occupied any other +place in the heavens than that directly overhead.</p> + +<p>We are still able to identify the very spot on which the telescope +stood which was used in this memorable research. It was erected at +the house then occupied by Molyneux, on the western extremity of Kew +Green. The focal length was 24 feet 3 inches, and the eye-glass was +3 and a half feet above the ground floor. The instrument was first +set up on November 26th, 1725. If there had been any appreciable +disturbance in the place of Beta Draconis in consequence of the +movement of the earth around the sun, the star must appear to have +the smallest latitude when in conjunction with the sun, and the +greatest when in opposition. The star passed the meridian at noon in +December, and its position was particularly noticed by Molyneux on +the third of that month. Any perceptible displacement by +parallax—for so the apparent change in position, due to the earth's +motion, is called—would would have made the star shift towards the +north. Bradley, however, when observing it on the 17th, was +surprised to find that the apparent place of the star, so far from +shifting towards the north, as they had perhaps hoped it would, was +found to lie a little more to the south than when it was observed +before. He took extreme care to be sure that there was no mistake in +his observation, and, true astronomer as he was, he scrutinized with +the utmost minuteness all the circumstances of the adjustment of his +instruments. Still the star went to the south, and it continued so +advancing in the same direction until the following March, by which +time it had moved no less than twenty seconds south from the place +which it occupied when the first observation was made. After a brief +pause, in which no apparent movement was perceptible, the star by the +middle of April appeared to be returning to the north. Early in June +it reached the same distance from the zenith which it had in +December. By September the star was as much as thirty-nine seconds +more to the north than it had been in March, then it returned towards +the south, regaining in December the same situation which it had +occupied twelve months before.</p> + +<p>This movement of the star being directly opposite to the movements +which would have been the consequence of parallax, seemed to show +that even if the star had any parallax its effects upon the apparent +place were entirely masked by a much larger motion of a totally +different description. Various attempts were made to account for the +phenomenon, but they were not successful. Bradley accordingly +determined to investigate the whole subject in a more thorough +manner. One of his objects was to try whether the same movements +which he had observed in one star were in any similar degree +possessed by other stars. For this purpose he set up a new +instrument at Wanstead, and there he commenced a most diligent +scrutiny of the apparent places of several stars which passed at +different distances from the zenith. He found in the course of this +research that other stars exhibited movements of a similar +description to those which had already proved so perplexing. For a +long time the cause of these apparent movements seemed a mystery. At +last, however, the explanation of these remarkable phenomena dawned +upon him, and his great discovery was made.</p> + +<p>One day when Bradley was out sailing he happened to remark that every +time the boat was laid on a different tack the vane at the top of the +boat's mast shifted a little, as if there had been a slight change in +the direction of the wind. After he had noticed this three or four +times he made a remark to the sailors to the effect that it was very +strange the wind should always happen to change just at the moment +when the boat was going about. The sailors, however, said there had +been no change in the wind, but that the alteration in the vane was +due to the fact that the boat's course had been altered. In fact, +the position of the vane was determined both by the course of the +boat and the direction of the wind, and if either of these were +altered there would be a corresponding change in the direction of the +vane. This meant, of course, that the observer in the boat which was +moving along would feel the wind coming from a point different from +that in which the wind appeared to be blowing when the boat was at +rest, or when it was sailing in some different direction. Bradley's +sagacity saw in this observation the clue to the Difficulty which had +so long troubled him.</p> + +<p>It had been discovered before the time of Bradley that the passage of +light through space is not an instantaneous phenomenon. Light +requires time for its journey. Galileo surmised that the sun may +have reached the horizon before we see it there, and it was indeed +sufficiently obvious that a physical action, like the transmission of +light, could hardly take place without requiring some lapse of time. +The speed with which light actually travelled was, however, so rapid +that its determination eluded all the means of experimenting which +were available in those days. The penetration of Roemer had +previously detected irregularities in the observed times of the +eclipses of Jupiter's satellites, which were undoubtedly due to the +interval which light required for stretching across the +interplanetary spaces. Bradley argued that as light can only travel +with a certain speed, it may in a measure be regarded like the wind, +which he noticed in the boat. If the observer were at rest, that is +to say, if the earth were a stationary object, the direction in which +the light actually does come would be different from that in which it +appears to come when the earth is in motion. It is true that the +earth travels but eighteen miles a second, while the velocity with +which light is borne along attains to as much as 180,000 miles a +second. The velocity of light is thus ten thousand times greater +than the speed of the earth. But even though the wind blew ten +thousand times faster than the speed with which the boat was sailing +there would still be some change, though no doubt a very small +change, in the position of the vane when the boat was in progress +from the position it would have if the boat were at rest. It +therefore occurred to this most acute of astronomers that when the +telescope was pointed towards a star so as to place it apparently in +the centre of the field of view, yet it was not generally the true +position of the star. It was not, in fact, the position in which the +star would have been observed had the earth been at rest. Provided +with this suggestion, he explained the apparent movements of the +stars by the principle known as the "aberration of light." Every +circumstance was accounted for as a consequence of the relative +movements of the earth and of the light from the star. This +beautiful discovery not only established in the most forcible manner +the nature of the movement of light; not only did it illustrate the +truth of the Copernican theory which asserted that the earth revolved +around the sun, but it was also of the utmost importance in the +improvement of practical astronomy. Every observer now knows that, +generally speaking, the position which the star appears to have is +not exactly the position in which the star does actually lie. The +observer is, however, able, by the application of the principles +which Bradley so clearly laid down, to apply to an observation the +correction which is necessary to obtain from it the true place in +which the object is actually situated. This memorable achievement at +once conferred on Bradley the highest astronomical fame. He tested +his discovery in every way, but only to confirm its truth in the most +complete manner.</p> + +<p>Halley, the Astronomer Royal, died on the 14th, January, 1742, and +Bradley was immediately pointed out as his successor. He was +accordingly appointed Astronomer Royal in February, 1742. On first +taking up his abode at Greenwich he was unable to conduct his +observations owing to the wretched condition in which he found the +instruments. He devoted himself, however, assiduously to their +repair, and his first transit observation is recorded on the 25th +July, 1742. He worked with such energy that on one day it appears +that 255 transit observations were taken by himself alone, and in +September, 1747, he had completed the series of observations which +established his second great discovery, the nutation of the earth's +axis. The way in which he was led to the detection of the nutation +is strikingly illustrative of the extreme care with which Bradley +conducted his observations. He found that in the course of a +twelve-month, when the star had completed the movement which was due +to aberration, it did not return exactly to the same position which +it had previously occupied. At first he thought this must be due to +some instrumental error, but after closer examination and repeated +study of the effect as manifested by many different stars, he came to +the conclusion that its origin must be sought in some quite different +source. The fact is that a certain change takes place in the +apparent position of the stars which is not due to the movement of +the star itself, but is rather to be attributed to changes in the +points from which the star's positions are measured.</p> + +<p>We may explain the matter in this way. As the earth is not a sphere, +but has protuberant parts at the equator, the attraction of the moon +exercises on those protuberant parts a pulling effect which +continually changes the direction of the earth's axis, and +consequently the position of the pole must be in a state of incessant +fluctuation. The pole to which the earth's axis points on the sky +is, therefore, slowly changing. At present it happens to lie near +the Pole Star, but it will not always remain there. It describes a +circle around the pole of the Ecliptic, requiring about 25,000 years +for a complete circuit. In the course of its progress the pole will +gradually pass now near one star and now near another, so that many +stars will in the lapse of ages discharge the various functions which +the present Pole Star does for us. In about 12,000 years, for +instance, the pole will have come near the bright star, Vega. This +movement of the pole had been known for ages. But what Bradley +discovered was that the pole, instead of describing an uniform +movement as had been previously supposed, followed a sinuous course +now on one side and now on the other of its mean place. This he +traced to the fluctuations of the moon's orbit, which undergoes a +continuous change in a period of nineteen years. Thus the efficiency +with which the moon acts on the protuberant mass of the earth varies, +and thus the pole is caused to oscillate.</p> + +<p>This subtle discovery, if perhaps in some ways less impressive than +Bradley's earlier achievements of the detection of the aberration of +light, is regarded by astronomers as testifying even in a higher +degree to his astonishing care and skill as an observer, and justly +entitles him to a unique place among the astronomers whose +discoveries have been effected by consummate practical skill in the +use of astronomical instruments.</p> + +<p>Of Bradley's private or domestic life there is but little to tell. In +1744, soon after he became Astronomer Royal, he married a daughter of +Samuel Peach, of Chalford, in Gloucestershire. There was but one +child, a daughter, who became the wife of her cousin, Rev. Samuel +Peach, rector of Compton, Beauchamp, in Berkshire.</p> + +<p>Bradley's last two years of life were clouded by a melancholy +depression of spirits, due to an apprehension that he should survive +his rational faculties. It seems, however, that the ill he dreaded +never came upon him, for he retained his mental powers to the close. +He died on 13th July, 1762, aged seventy, and was buried at +Michinghamton.</p> + +<h3><a name="WILLIAM_HERSCHEL" id="WILLIAM_HERSCHEL"></a>WILLIAM HERSCHEL.</h3> +<p>William Herschel, one of the greatest astronomers that has ever +lived, was born at Hanover, on the 15th November, 1738. His father, +Isaac Herschel, was a man evidently of considerable ability, whose +life was devoted to the study and practice of music, by which he +earned a somewhat precarious maintenance. He had but few worldly +goods to leave to his children, but he more than compensated for this +by bequeathing to them a splendid inheritance of genius. Touches of +genius were, indeed, liberally scattered among the members of Isaac's +large family, and in the case of his forth child, William, and of a +sister several years younger, it was united with that determined +perseverance and rigid adherence to principle which enabled genius to +fulfil its perfect work.</p> + +<p>A faithful chronicler has given us an interesting account of the way +in which Isaac Herschel educated his sons; the narrative is taken +from the recollections of one who, at the time we are speaking of, +was an unnoticed little girl five or six years old. She writes:—</p> + +<p>"My brothers were often introduced as solo performers and assistants +in the orchestra at the Court, and I remember that I was frequently +prevented from going to sleep by the lively criticisms on music on +coming from a concert. Often I would keep myself awake that I might +listen to their animating remarks, for it made me so happy to see +them so happy. But generally their conversation would branch out on +philosophical subjects, when my brother William and my father often +argued with such warmth that my mother's interference became +necessary, when the names—Euler, Leibnitz, and Newton—sounded +rather too loud for the repose of her little ones, who had to be at +school by seven in the morning." The child whose reminiscences are +here given became afterwards the famous Caroline Herschel. The +narrative of her life, by Mrs. John Herschel, is a most interesting +book, not only for the account it contains of the remarkable woman +herself, but also because it provides the best picture we have of the +great astronomer to whom Caroline devoted her life.</p> + +<p>This modest family circle was, in a measure, dispersed at the +outbreak of the Seven Years' War in 1756. The French proceeded to +invade Hanover, which, it will be remembered, belonged at this time +to the British dominions. Young William Herschel had already +obtained the position of a regular performer in the regimental band +of the Hanoverian Guards, and it was his fortune to obtain some +experience of actual warfare in the disastrous battle of Hastenbeck. +He was not wounded, but he had to spend the night after the battle in +a ditch, and his meditations on the occasion convinced him that +soldiering was not the profession exactly adapted to his tastes. We +need not attempt to conceal the fact that he left his regiment by the +very simple but somewhat risky process of desertion. He had, it +would seem, to adopt disguises to effect his escape. At all events, +by some means he succeeded in eluding detection and reached England +in safety. It is interesting to have learned on good authority that +many years after this offence was committed it was solemnly +forgiven. When Herschel had become the famous astronomer, and as +such visited King George at Windsor, the King at their first meeting +handed to him his pardon for deserting from the army, written out in +due form by his Majesty himself.</p> + +<p>It seems that the young musician must have had some difficulty in +providing for his maintenance during the first few years of his abode +in England. It was not until he had reached the age of twenty-two +that he succeeded in obtaining any regular appointment. He was then +made Instructor of Music to the Durham Militia. Shortly afterwards, +his talents being more widely recognised, he was appointed as +organist at the parish church at Halifax, and his prospects in life +now being fairly favourable, and the Seven Years' War being over, he +ventured to pay a visit to Hanover to see his father. We can imagine +the delight with which old Isaac Herschel welcomed his promising son, +as well as his parental pride when a concert was given at which some +of William's compositions were performed. If the father was so +intensely gratified on this occasion, what would his feelings have +been could he have lived to witness his son's future career? But +this pleasure was not to be his, for he died many years before +William became an astronomer.</p> + +<p>In 1766, about a couple of years after his return to England from +This visit to his old home, we find that Herschel had received a +further promotion to be organist in the Octagon Chapel, at Bath. +Bath was then, as now, a highly fashionable resort, and many notable +personages patronised the rising musician. Herschel had other points +in his favour besides his professional skill; his appearance was +good, his address was prepossessing, and even his nationality was a +distinct advantage, inasmuch as he was a Hanoverian in the reign of +King George the Third. On Sundays he played the organ, to the great +delight of the congregation, and on week-days he was occupied by +giving lessons to private pupils, and in preparation for public +performances. He thus came to be busily employed, and seems to have +been in the enjoyment of comfortable means.</p> + +<p><a name="new_king" id="new_king"></a></p> + +<div class="figcenter" style="width: 292px;"> +<a href="images/ill_7_new_king_st.jpg"> +<img src="images/ill_7_new_king_st_sml.jpg" width="292" height="532" alt="7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED." title="" /></a> +<span class="caption">7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.</span> +</div> + +<p>From his earliest youth Herschel had been endowed with that +invaluable characteristic, an eager curiosity for knowledge. He was +naturally desirous of perfecting himself in the theory of music, and +thus he was led to study mathematics. When he had once tasted the +charms of mathematics, he saw vast regions of knowledge unfolded +before him, and in this way he was induced to direct his attention to +astronomy. More and more this pursuit seems to have engrossed his +attention, until at last it had become an absorbing passion. Herschel +was, however, still obliged, by the exigency of procuring a +livelihood, to give up the best part of his time to his profession as +a musician; but his heart was eagerly fixed on another science, and +every spare moment was steadily devoted to astronomy. For many +years, however, he continued to labour at his original calling, nor +was it until he had attained middle age and become the most +celebrated astronomer of the time, that he was enabled to concentrate +his attention exclusively on his favourite pursuit.</p> + +<p>It was with quite a small telescope which had been lent him by a +friend that Herschel commenced his career as an observer. However, +he speedily discovered that to see all he wanted to see, a telescope +of far greater power would be necessary, and he determined to obtain +this more powerful instrument by actually making it with his own +hands. At first it may seem scarcely likely that one whose +occupation had previously been the study and practice of music should +meet with success in so technical an operation as the construction of +a telescope. It may, however, be mentioned that the kind of +instrument which Herschel designed to construct was formed on a very +different principle from the refracting telescopes with which we are +ordinarily familiar. His telescope was to be what is termed a +reflector. In this type of instrument the optical power is obtained +by the use of a mirror at the bottom of the tube, and the astronomer +looks down through the tube TOWARDS HIS MIRROR and views the +reflection of the stars with its aid. Its efficiency as a telescope +depends entirely on the accuracy with which the requisite form has +been imparted to the mirror. The surface has to be hollowed out a +little, and this has to be done so truly that the slightest deviation +from good workmanship in this essential particular would be fatal to +efficient performance of the telescope.</p> + +<p><a name="william" id="william"></a></p> + +<div class="figcenter" style="width: 411px;"> +<a href="images/ill_herschel.jpg"> +<img src="images/ill_herschel_sml.jpg" width="411" height="495" alt="WILLIAM HERSCHEL." title="" /></a> +<span class="caption">WILLIAM HERSCHEL.</span> +</div> + +<p>The mirror that Herschel employed was composed of a mixture of two +parts of copper to one of tin; the alloy thus obtained is an +intensely hard material, very difficult to cast into the proper +shape, and very difficult to work afterwards. It possesses, however, +when polished, a lustre hardly inferior to that of silver itself. +Herschel has recorded hardly any particulars as to the actual process +by which he cast and figured his reflectors. We are however, told +that in later years, after his telescopes had become famous, he made +a considerable sum of money by the manufacture and sale of great +instruments. Perhaps this may be the reason why he never found it +expedient to publish any very explicit details as to the means by +which his remarkable successes were obtained.</p> + +<p><a name="caroline" id="caroline"></a></p> + +<div class="figcenter" style="width: 406px;"> +<a href="images/ill_caroline_herschel.jpg"> +<img src="images/ill_caroline_herschel_sml.jpg" width="406" height="509" alt="CAROLINE HERSCHEL." title="" /></a> +<span class="caption">CAROLINE HERSCHEL.</span> +</div> + +<p>Since Herschel's time many other astronomers, notably the late Earl +of Rosse, have experimented in the same direction, and succeeded in +making telescopes certainly far greater, and probably more perfect, +than any which Herschel appears to have constructed. The details of +these later methods are now well known, and have been extensively +practised. Many amateurs have thus been able to make telescopes by +following the instructions so clearly laid down by Lord Rosse and the +other authorities. Indeed, it would seem that any one who has a +little mechanical skill and a good deal of patience ought now to +experience no great difficulty in constructing a telescope quite as +powerful as that which first brought Herschel into fame. I should, +however, mention that in these modern days the material generally +used for the mirror is of a more tractable description than the +metallic substance which was employed by Herschel and by Lord Rosse. +A reflecting telescope of the present day would not be fitted with a +mirror composed of that alloy known as speculum metal, whose +composition I have already mentioned. It has been found more +advantageous to employ a glass mirror carefully figured and polished, +just as a metallic mirror would have been, and then to impart to the +polished glass surface a fine coating of silver laid down by a +chemical process. The silver-on-glass mirrors are so much lighter +and so much easier to construct that the more old-fashioned metallic +mirrors may be said to have fallen into almost total disuse. In one +respect however, the metallic mirror may still claim the advantage +that, with reasonable care, its surface will last bright and +untarnished for a much longer period than can the silver film on the +glass. However, the operation of re-silvering a glass has now become +such a simple one that the advantage this indicates is not relatively +so great as might at first be supposed.</p> + +<p><a name="street" id="street"></a></p> + +<div class="figcenter" style="width: 426px;"> +<a href="images/ill_herschel_house_slough.jpg"> +<img src="images/ill_herschel_house_slough_sml.jpg" width="426" height="318" alt="STREET VIEW, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">STREET VIEW, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>Some years elapsed after Herschel's attention had been first directed +to astronomy, before he reaped the reward of his exertions in the +possession of a telescope which would adequately reveal some of the +glories of the heavens. It was in 1774, when the astronomer was +thirty-six years old, that he obtained his first glimpse of the stars +with an instrument of his own construction. Night after night, as +soon as his musical labours were ended, his telescopes were brought +out, sometimes into the small back garden of his house at Bath, and +sometimes into the street in front of his hall-door. It was +characteristic of him that he was always endeavouring to improve his +apparatus. He was incessantly making fresh mirrors, or trying new +lenses, or combinations of lenses to act as eye-pieces, or projecting +alterations in the mounting by which the telescope was supported. +Such was his enthusiasm that his house, we are told, was incessantly +littered with the usual indications of the workman's presence, +greatly to the distress of his sister, who, at this time, had come to +take up her abode with him and look after his housekeeping. Indeed, +she complained that in his astronomical ardour he sometimes omitted +to take off, before going into his workshop, the beautiful lace +ruffles which he wore while conducting a concert, and that +consequently they became soiled with the pitch employed in the +polishing of his mirrors.</p> + +<p>This sister, who occupies such a distinct place in scientific history +is the same little girl to whom we have already referred. From her +earliest days she seems to have cherished a passionate admiration for +her brilliant brother William. It was the proudest delight of her +childhood as well as of her mature years to render him whatever +service she could; no man of science was ever provided with a more +capable or energetic helper than William Herschel found in this +remarkable woman. Whatever work had to be done she was willing to +bear her share in it, or even to toil at it unassisted if she could +be allowed to do so. She not only managed all his domestic affairs, +but in the grinding of the lenses and in the polishing of the mirrors +she rendered every assistance that was possible. At one stage of the +very delicate operation of fashioning a reflector, it is necessary +for the workman to remain with his hand on the mirror for many hours +in succession. When such labours were in progress, Caroline used to +sit by her brother, and enliven the time by reading stories aloud, +sometimes pausing to feed him with a spoon while his hands were +engaged on the task from which he could not desist for a moment.</p> + +<p>When mathematical work had to be done Caroline was ready for it; she +had taught herself sufficient to enable her to perform the kind of +calculations, not, perhaps, very difficult ones, that Herschel's work +required; indeed, it is not too much to say that the mighty life-work +which this man was enabled to perform could never have been accomplished +had it not been for the self-sacrifice of this ever-loving and faithful +sister. When Herschel was at the telescope at night, Caroline sat by +him at her desk, pen in hand, ready to write down the notes of the +observations as they fell from her brother's lips. This was no +insignificant toil. The telescope was, of course, in the open air, +and as Herschel not unfrequently continued his observations throughout +the whole of a long winter's night, there were but few women who could +have accomplished the task which Caroline so cheerfully executed. +From dusk till dawn, when the sky was clear, were Herschel's observing +hours, and what this sometimes implied we can realise from the fact +that Caroline assures us she had sometimes to desist because the ink +had actually frozen in her pen. The night's work over, a brief rest +was taken, and while William had his labours for the day to attend to, +Caroline carefully transcribed the observations made during the night +before, reduced all the figures and prepared everything in readiness +for the observations that were to follow on the ensuing evening.</p> + +<p>But we have here been anticipating a little of the future which lay +before the great astronomer; we must now revert to the history of his +early work, at Bath, in 1774, when Herschel's scrutiny of the skies +first commenced with an instrument of his own manufacture. For some +few years he did not attain any result of importance; no doubt he +made a few interesting observations, but the value of the work during +those years is to be found, not in any actual discoveries which were +accomplished, but in the practice which Herschel obtained in the use +of his instruments. It was not until 1782 that the great achievement +took place by which he at once sprang into fame.</p> + +<p><a name="garden" id="garden"></a></p> + +<div class="figcenter" style="width: 421px;"> +<a href="images/ill_garden_view_herschel_house_slough.jpg"> +<img src="images/ill_garden_view_herschel_house_slough_sml.jpg" width="421" height="340" alt="GARDEN VIEW, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>It is sometimes said that discoveries are made by accident, and, no +doubt, to a certain extent, but only, I fancy to a very small extent, +this statement may be true. It is, at all events, certain that such +lucky accidents do not often fall to the lot of people unless those +people have done much to deserve them. This was certainly the case +with Herschel. He appears to have formed a project for making a +close examination of all the stars above a certain magnitude. Perhaps +he intended to confine this research to a limited region of the sky, +but, at all events, he seems to have undertaken the work +energetically and systematically. Star after star was brought to the +centre of the field of view of his telescope, and after being +carefully examined was then displaced, while another star was brought +forward to be submitted to the same process. In the great majority +of cases such observations yield really nothing of importance; no +doubt even the smallest star in the heavens would, if we could find +out all about it, reveal far more than all the astronomers that were +ever on the earth have even conjectured. What we actually learn +about the great majority of stars is only information of the most +meagre description. We see that the star is a little point of light, +and we see nothing more.</p> + +<p>In the great review which Herschel undertook he doubtless examined +hundreds, or perhaps thousands of stars, allowing them to pass away +without note or comment. But on an ever-memorable night in March, +1782, it happened that he was pursuing his task among the stars in +the Constellation of Gemini. Doubtless, on that night, as on so many +other nights, one star after another was looked at only to be +dismissed, as not requiring further attention. On the evening in +question, however, one star was noticed which, to Herschel's acute +vision seemed different from the stars which in so many thousands are +strewn over the sky. A star properly so called appears merely as a +little point of light, which no increase of magnifying power will +ever exhibit with a true disc. But there was something in the +star-like object which Herschel saw that immediately arrested his +attention and made him apply to it a higher magnifying power. This +at once disclosed the fact that the object possessed a disc, that is, +a definite, measurable size, and that it was thus totally different +from any one of the hundreds and thousands of stars which exist +elsewhere in space. Indeed, we may say at once that this little +object was not a star at all; it was a planet. That such was its +true nature was confirmed, after a little further observation, by +perceiving that the body was shifting its place on the heavens +relatively to the stars. The organist at the Octagon Chapel at Bath +had, therefore, discovered a new planet with his home-made telescope.</p> + +<p>I can imagine some one will say, "Oh, there was nothing so wonderful +in that; are not planets always being discovered? Has not M. Palisa, +for instance, discovered about eighty of such objects, and are there +not hundreds of them known nowadays?" This is, to a certain extent, +quite true. I have not the least desire to detract from the credit +of those industrious and sharp-sighted astronomers who have in modern +days brought so many of these little objects within our cognisance. I +think, however, it must be admitted that such discoveries have a +totally different importance in the history of science from that +which belongs to the peerless achievement of Herschel. In the first +place, it must be observed that the minor planets now brought to +light are so minute that if a score of them were rolled to together +into one lump it would not be one-thousandth part of the size of the +grand planet discovered by Herschel. This is, nevertheless, not the +most important point. What marks Herschel's achievement as one of +the great epochs in the history of astronomy is the fact that the +detection of Uranus was the very first recorded occasion of the +discovery of any planet whatever.</p> + +<p>For uncounted ages those who watched the skies had been aware of the +existence of the five old planets—Jupiter, Mercury, Saturn, Venus, +and Mars. It never seems to have occurred to any of the ancient +philosophers that there could be other similar objects as yet +undetected over and above the well-known five. Great then was the +astonishment of the scientific world when the Bath organist announced +his discovery that the five planets which had been known from all +antiquity must now admit the company of a sixth. And this sixth +planet was, indeed, worthy on every ground to be received into the +ranks of the five glorious bodies of antiquity. It was, no doubt, +not so large as Saturn, it was certainly very much less than Jupiter; +on the other hand, the new body was very much larger than Mercury, +than Venus, or than Mars, and the earth itself seemed quite an +insignificant object in comparison with this newly added member of +the Solar System. In one respect, too, Herschel's new planet was a +much more imposing object than any one of the older bodies; it swept +around the sun in a majestic orbit, far outside that of Saturn, which +had previously been regarded as the boundary of the Solar System, and +its stately progress required a period of not less than eighty-one +years.</p> + +<p>King George the Third, hearing of the achievements of the Hanoverian +musician, felt much interest in his discovery, and accordingly +Herschel was bidden to come to Windsor, and to bring with him the +famous telescope, in order to exhibit the new planet to the King, and +to tell his Majesty all about it. The result of the interview was to +give Herschel the opportunity for which he had so long wished, of +being able to devote himself exclusively to science for the rest of +his life.</p> + +<p><a name="view_herschel_house" id="view_herschel_house"></a></p> + +<div class="figcenter" style="width: 416px;"> +<a href="images/ill_view_observatory_herschel_house.jpg"> +<img src="images/ill_view_observatory_herschel_house_sml.jpg" width="416" height="302" alt="VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH." title="" /></a> +<span class="caption">VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.</span> +</div> + +<p>The King took so great a fancy to the astronomer that he first, as I +have already mentioned, duly pardoned his desertion from the army, +some twenty-five years previously. As a further mark of his favour +the King proposed to confer on Herschel the title of his Majesty's +own astronomer, to assign to him a residence near Windsor, to provide +him with a salary, and to furnish such funds as might be required for +the erection of great telescopes, and for the conduct of that mighty +scheme of celestial observation on which Herschel was so eager to +enter. Herschel's capacity for work would have been much impaired if +he had been deprived of the aid of his admirable sister, and to her, +therefore, the King also assigned a salary, and she was installed as +Herschel's assistant in his new post.</p> + +<p>With his usually impulsive determination, Herschel immediately cut +himself free from all his musical avocations at Bath, and at once +entered on the task of making and erecting the great telescopes at +Windsor. There, for more than thirty years, he and his faithful +sister prosecuted with unremitting ardour their nightly scrutiny of +the sky. Paper after paper was sent to the Royal Society, describing +the hundreds, indeed the thousands, of objects such as double stars; +nebulae and clusters, which were first revealed to human gaze during +those midnight vigils. To the end of his life he still continued at +every possible opportunity to devote himself to that beloved pursuit +in which he had such unparalleled success. No single discovery of +Herschel's later years was, however, of the same momentous +description as that which first brought him to fame.</p> + +<p><a name="telescope_slough" id="telescope_slough"></a></p> + +<div class="figcenter" style="width: 460px;"> +<a href="images/ill_telescope_herschel_house.jpg"> +<img src="images/ill_telescope_herschel_house_sml.jpg" width="460" height="354" alt="THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH." title="" /></a> +<span class="caption">THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH.</span> +</div> + +<p>Herschel married when considerably advanced in life and he lived to +enjoy the indescribable pleasure of finding that his only son, +afterwards Sir John Herschel, was treading worthily in his footsteps, +and attaining renown as an astronomical observer, second only to that +of his father. The elder Herschel died in 1822, and his illustrious +sister Caroline then returned to Hanover, where she lived for many +years to receive the respect and attention which were so justly +hers. She died at a very advanced age in 1848.</p> + +<h3><a name="LAPLACE" id="LAPLACE"></a>LAPLACE.</h3> +<p>The author of the "Mecanique Celeste" was born at Beaumont-en-Auge, +near Honfleur, in 1749, just thirteen years later than his renowned +friend Lagrange. His father was a farmer, but appears to have been +in a position to provide a good education for a son who seemed +promising. Considering the unorthodoxy in religious matters which is +generally said to have characterized Laplace in later years, it is +interesting to note that when he was a boy the subject which first +claimed his attention was theology. He was, however, soon introduced +to the study of mathematics, in which he presently became so +proficient, that while he was still no more than eighteen years old, +he obtained employment as a mathematical teacher in his native town.</p> + +<p>Desiring wider opportunities for study and for the acquisition of +fame than could be obtained in the narrow associations of provincial +life, young Laplace started for Paris, being provided with letters of +introduction to D'Alembert, who then occupied the most prominent +position as a mathematician in France, if not in the whole of +Europe. D'Alembert's fame was indeed so brilliant that Catherine the +Great wrote to ask him to undertake the education of her Son, and +promised the splendid income of a hundred thousand francs. He +preferred, however, a quiet life of research in Paris, although there +was but a modest salary attached to his office. The philosopher +accordingly declined the alluring offer to go to Russia, even though +Catherine wrote again to say: "I know that your refusal arises from +your desire to cultivate your studies and your friendships in quiet. +But this is of no consequence: bring all your friends with you, and I +promise you that both you and they shall have every accommodation in +my power." With equal firmness the illustrious mathematician +resisted the manifold attractions with which Frederick the Great +sought to induce him, to take up his residence at Berlin. In reading +of these invitations we cannot but be struck at the extraordinary +respect which was then paid to scientific distinction. It must be +remembered that the discoveries of such a man as D'Alembert were +utterly incapable of being appreciated except by those who possessed +a high degree of mathematical culture. We nevertheless find the +potentates of Russia and Prussia entreating and, as it happens, +vainly entreating, the most distinguished mathematician in France to +accept the positions that they were proud to offer him.</p> + +<p>It was to D'Alembert, the profound mathematician, that young Laplace, +the son of the country farmer, presented his letters of +introduction. But those letters seem to have elicited no reply, +whereupon Laplace wrote to D'Alembert submitting a discussion on some +point in Dynamics. This letter instantly produced the desired +effect. D'Alembert thought that such mathematical talent as the +young man displayed was in itself the best of introductions to his +favour. It could not be overlooked, and accordingly he invited +Laplace to come and see him. Laplace, of course, presented himself, +and ere long D'Alembert obtained for the rising philosopher a +professorship of mathematics in the Military School in Paris. This +gave the brilliant young mathematician the opening for which he +sought, and he quickly availed himself of it.</p> + +<p>Laplace was twenty-three years old when his first memoir on a +profound mathematical subject appeared in the Memoirs of the Academy +at Turin. From this time onwards we find him publishing one memoir +after another in which he attacks, and in many cases successfully +vanquishes, profound difficulties in the application of the Newtonian +theory of gravitation to the explanation of the solar system. Like +his great contemporary Lagrange, he loftily attempted problems which +demanded consummate analytical skill for their solution. The +attention of the scientific world thus became riveted on the splendid +discoveries which emanated from these two men, each gifted with +extraordinary genius.</p> + +<p>Laplace's most famous work is, of course, the "Mecanique Celeste," in +which he essayed a comprehensive attempt to carry out the principles +which Newton had laid down, into much greater detail than Newton had +found practicable. The fact was that Newton had not only to +construct the theory of gravitation, but he had to invent the +mathematical tools, so to speak, by which his theory could be applied +to the explanation of the movements of the heavenly bodies. In the +course of the century which had elapsed between the time of Newton +and the time of Laplace, mathematics had been extensively developed. +In particular, that potent instrument called the infinitesimal +calculus, which Newton had invented for the investigation of nature, +had become so far perfected that Laplace, when he attempted to +unravel the movements of the heavenly bodies, found himself provided +with a calculus far more efficient than that which had been available +to Newton. The purely geometrical methods which Newton employed, +though they are admirably adapted for demonstrating in a general way +the tendencies of forces and for explaining the more obvious +phenomena by which the movements of the heavenly bodies are +disturbed, are yet quite inadequate for dealing with the more subtle +effects of the Law of Gravitation. The disturbances which one planet +exercises upon the rest can only be fully ascertained by the aid of +long calculation, and for these calculations analytical methods are +required.</p> + +<p>With an armament of mathematical methods which had been perfected +since the days of Newton by the labours of two or three generations +of consummate mathematical inventors, Laplace essayed in the +"Mecanique Celeste" to unravel the mysteries of the heavens. It will +hardly be disputed that the book which he has produced is one of the +most difficult books to understand that has ever been written. In +great part, of course, this difficulty arises from the very nature of +the subject, and is so far unavoidable. No one need attempt to read +the "Mecanique Celeste" who has not been naturally endowed with +considerable mathematical aptitude which he has cultivated by years +of assiduous study. The critic will also note that there are grave +defects in Laplace's method of treatment. The style is often +extremely obscure, and the author frequently leaves great gaps in his +argument, to the sad discomfiture of his reader. Nor does it mend +matters to say, as Laplace often does say, that it is "easy to see" +how one step follows from another. Such inferences often present +great difficulties even to excellent mathematicians. Tradition +indeed tells us that when Laplace had occasion to refer to his own +book, it sometimes happened that an argument which he had dismissed +with his usual formula, "Il est facile a voir," cost the illustrious +author himself an hour or two of hard thinking before he could +recover the train of reasoning which had been omitted. But there are +certain parts of this great work which have always received the +enthusiastic admiration of mathematicians. Laplace has, in fact, +created whole tracts of science, some of which have been subsequently +developed with much advantage in the prosecution of the study of +Nature.</p> + +<p>Judged by a modern code the gravest defect of Laplace's great work is +rather of a moral than of a mathematical nature. Lagrange and he +advanced together in their study of the mechanics of the heavens, at +one time perhaps along parallel lines, while at other times they +pursued the same problem by almost identical methods. Sometimes the +important result was first reached by Lagrange, sometimes it was +Laplace who had the good fortune to make the discovery. It would +doubtless be a difficult matter to draw the line which should exactly +separate the contributions to astronomy made by one of these +illustrious mathematicians, and the contributions made by the other. +But in his great work Laplace in the loftiest manner disdained to +accord more than the very barest recognition to Lagrange, or to any +of the other mathematicians, Newton alone excepted, who had advanced +our knowledge of the mechanism of the heavens. It would be quite +impossible for a student who confined his reading to the "Mecanique +Celeste" to gather from any indications that it contains whether the +discoveries about which he was reading had been really made by +Laplace himself or whether they had not been made by Lagrange, or by +Euler, or by Clairaut. With our present standard of morality in such +matters, any scientific man who now brought forth a work in which he +presumed to ignore in this wholesale fashion the contributions of +others to the subject on which he was writing, would be justly +censured and bitter controversies would undoubtedly arise. Perhaps +we ought not to judge Laplace by the standard of our own time, and in +any case I do not doubt that Laplace might have made a plausible +defence. It is well known that when two investigators are working at +the same subjects, and constantly publishing their results, it +sometimes becomes difficult for each investigator himself to +distinguish exactly between what he has accomplished and that which +must be credited to his rival. Laplace may probably have said to +himself that he was going to devote his energies to a great work on +the interpretation of Nature, that it would take all his time and all +his faculties, and all the resources of knowledge that he could +command, to deal justly with the mighty problems before him. He +would not allow himself to be distracted by any side issue. He could +not tolerate that pages should be wasted in merely discussing to whom +we owe each formula, and to whom each deduction from such formula is +due. He would rather endeavour to produce as complete a picture as +he possibly could of the celestial mechanics, and whether it were by +means of his mathematics alone, or whether the discoveries of others +may have contributed in any degree to the result, is a matter so +infinitesimally insignificant in comparison with the grandeur of his +subject that he would altogether neglect it. "If Lagrange should +think," Laplace might say, "that his discoveries had been unduly +appropriated, the proper course would be for him to do exactly what I +have done. Let him also write a "Mecanique Celeste," let him employ +those consummate talents which he possesses in developing his noble +subject to the utmost. Let him utilise every result that I or any +other mathematician have arrived at, but not trouble himself unduly +with unimportant historical details as to who discovered this, and +who discovered that; let him produce such a work as he could write, +and I shall heartily welcome it as a splendid contribution to our +science." Certain it is that Laplace and Lagrange continued the best +of friends, and on the death of the latter it was Laplace who was +summoned to deliver the funeral oration at the grave of his great +rival.</p> + +<p>The investigations of Laplace are, generally speaking, of too +technical a character to make it possible to set forth any account of +them in such a work as the present. He did publish, however, one +treatise, called the "Systeme du Monde," in which, without +introducing mathematical symbols, he was able to give a general +account of the theories of the celestial movements, and of the +discoveries to which he and others had been led. In this work the +great French astronomer sketched for the first time that remarkable +doctrine by which his name is probably most generally known to those +readers of astronomical books who are not specially mathematicians. +It is in the "Systeme du Monde" that Laplace laid down the principles +of the Nebular Theory which, in modern days, has been generally +accepted by those philosophers who are competent to judge, as +substantially a correct expression of a great historical fact.</p> + +<p><a name="laplace_ill" id="laplace_ill"></a></p> + +<div class="figcenter" style="width: 423px;"> +<a href="images/ill_laplace.jpg"> +<img src="images/ill_laplace_sml.jpg" width="423" height="488" alt="LAPLACE." title="" /></a> +<span class="caption">LAPLACE.</span> +</div> + +<p>The Nebular Theory gives a physical account of the origin of the +solar system, consisting of the sun in the centre, with the planets +and their attendant satellites. Laplace perceived the significance +of the fact that all the planets revolved in the same direction +around the sun; he noticed also that the movements of rotation of the +planets on their axes were performed in the same direction as that in +which a planet revolves around the sun; he saw that the orbits of the +satellites, so far at least as he knew them, revolved around their +primaries also in the same direction. Nor did it escape his +attention that the sun itself rotated on its axis in the same sense. +His philosophical mind was led to reflect that such a remarkable +unanimity in the direction of the movements in the solar system +demanded some special explanation. It would have been in the highest +degree improbable that there should have been this unanimity unless +there had been some physical reason to account for it. To appreciate +the argument let us first concentrate our attention on three +particular bodies, namely the earth, the sun, and the moon. First +the earth revolves around the sun in a certain direction, and the +earth also rotates on its axis. The direction in which the earth +turns in accordance with this latter movement might have been that in +which it revolves around the sun, or it might of course have been +opposite thereto. As a matter of fact the two agree. The moon in +its monthly revolution around the earth follows also the same +direction, and our satellite rotates on its axis in the same period +as its monthly revolution, but in doing so is again observing this +same law. We have therefore in the earth and moon four movements, +all taking place in the same direction, and this is also identical +with that in which the sun rotates once every twenty-five days. Such +a coincidence would be very unlikely unless there were some physical +reason for it. Just as unlikely would it be that in tossing a coin +five heads or five tails should follow each other consecutively. If +we toss a coin five times the chances that it will turn up all heads +or all tails is but a small one. The probability of such an event is +only one-sixteenth.</p> + +<p>There are, however, in the solar system many other bodies besides the +three just mentioned which are animated by this common movement. +Among them are, of course, the great planets, Jupiter, Saturn, Mars, +Venus, and Mercury, and the satellites which attend on these +planets. All these planets rotate on their axes in the same +direction as they revolve around the sun, and all their satellites +revolve also in the same way. Confining our attention merely to the +earth, the sun, and the five great planets with which Laplace was +acquainted, we have no fewer than six motions of revolution and seven +motions of rotation, for in the latter we include the rotation of the +sun. We have also sixteen satellites of the planets mentioned whose +revolutions round their primaries are in the same direction. The +rotation of the moon on its axis may also be reckoned, but as to the +rotations of the satellites of the other planets we cannot speak with +any confidence, as they are too far off to be observed with the +necessary accuracy. We have thus thirty circular movements in the +solar system connected with the sun and moon and those great planets +than which no others were known in the days of Laplace. The +significant fact is that all these thirty movements take place in the +same direction. That this should be the case without some physical +reason would be just as unlikely as that in tossing a coin thirty +times it should turn up all heads or all tails every time without +exception.</p> + +<p>We can express the argument numerically. Calculation proves that +such an event would not generally happen oftener than once out of +five hundred millions of trials. To a philosopher of Laplace's +penetration, who had made a special study of the theory of +probabilities, it seemed well-nigh inconceivable that there should +have been such unanimity in the celestial movements, unless there had +been some adequate reason to account for it. We might, indeed, add +that if we were to include all the objects which are now known to +belong to the solar system, the argument from probability might be +enormously increased in strength. To Laplace the argument appeared +so conclusive that he sought for some physical cause of the +remarkable phenomenon which the solar system presented. Thus it was +that the famous Nebular Hypothesis took its rise. Laplace devised a +scheme for the origin of the sun and the planetary system, in which +it would be a necessary consequence that all the movements should +take place in the same direction as they are actually observed to do.</p> + +<p>Let us suppose that in the beginning there was a gigantic mass of +nebulous material, so highly heated that the iron and other +substances which now enter into the composition of the earth and +planets were then suspended in a state of vapour. There is nothing +unreasonable in such a supposition indeed, we know as a matter of +fact that there are thousands of such nebulae to be discerned at +present through our telescopes. It would be extremely unlikely that +any object could exist without possessing some motion of rotation; we +may in fact assert that for rotation to be entirety absent from the +great primeval nebula would be almost infinitely improbable. As ages +rolled on, the nebula gradually dispersed away by radiation its +original stores of heat, and, in accordance with well-known physical +principles, the materials of which it was formed would tend to +coalesce. The greater part of those materials would become +concentrated in a mighty mass surrounded by outlying uncondensed +vapours. There would, however, also be regions throughout the extent +of the nebula, in which subsidiary centres of condensation would be +found. In its long course of cooling, the nebula would, therefore, +tend ultimately to form a mighty central body with a number of +smaller bodies disposed around it. As the nebula was initially +endowed with a movement of rotation, the central mass into which it +had chiefly condensed would also revolve, and the subsidiary bodies +would be animated by movements of revolution around the central +body. These movements would be all pursued in one common direction, +and it follows, from well-known mechanical principles, that each of +the subsidiary masses, besides participating in the general +revolution around the central body, would also possess a rotation +around its axis, which must likewise be performed in the same +direction. Around the subsidiary bodies other objects still smaller +would be formed, just as they themselves were formed relatively to +the great central mass.</p> + +<p>As the ages sped by, and the heat of these bodies became gradually +dissipated, the various objects would coalesce, first into molten +liquid masses, and thence, at a further stage of cooling, they would +assume the appearance of solid masses, thus producing the planetary +bodies such as we now know them. The great central mass, on account +of its preponderating dimensions, would still retain, for further +uncounted ages, a large quantity of its primeval heat, and would thus +display the splendours of a glowing sun. In this way Laplace was +able to account for the remarkable phenomena presented in the +movements of the bodies of the solar system. There are many other +points also in which the nebular theory is known to tally with the +facts of observation. In fact, each advance in science only seems to +make it more certain that the Nebular Hypothesis substantially +represents the way in which our solar system has grown to its present +form.</p> + +<p>Not satisfied with a career which should be merely scientific, +Laplace sought to connect himself with public affairs. Napoleon +appreciated his genius, and desired to enlist him in the service of +the State. Accordingly he appointed Laplace to be Minister of the +Interior. The experiment was not successful, for he was not by +nature a statesman. Napoleon was much disappointed at the ineptitude +which the great mathematician showed for official life, and, in +despair of Laplace's capacity as an administrator, declared that he +carried the spirit of his infinitesimal calculus into the management +of business. Indeed, Laplace's political conduct hardly admits of +much defence. While he accepted the honours which Napoleon showered +on him in the time of his prosperity, he seems to have forgotten all +this when Napoleon could no longer render him service. Laplace was +made a Marquis by Louis XVIII., a rank which he transmitted to his +son, who was born in 1789. During the latter part of his life the +philosopher lived in a retired country place at Arcueile. Here he +pursued his studies, and by strict abstemiousness, preserved himself +from many of the infirmities of old age. He died on March the 5th, +1827, in his seventy-eighth year, his last words being, "What we know +is but little, what we do not know is immense."</p> + +<h3><a name="BRINKLEY" id="BRINKLEY"></a>BRINKLEY.</h3> +<p>Provost Baldwin held absolute sway in the University of Dublin for +forty-one years. His memory is well preserved there. The Bursar +still dispenses the satisfactory revenues which Baldwin left to the +College. None of us ever can forget the marble angels round the +figure of the dying Provost on which we used to gaze during the pangs +of the Examination Hall.</p> + +<p>Baldwin died in 1785, and was succeeded by Francis Andrews, a Fellow +of seventeen years' standing. As to the scholastic acquirements of +Andrews, all I can find is a statement that he was complimented by +the polite Professors of Padua on the elegance and purity with which +he discoursed to them in Latin. Andrews was also reputed to be a +skilful lawyer. He was certainly a Privy Councillor and a prominent +member of the Irish House of Commons, and his social qualities were +excellent. Perhaps it was Baldwin's example that stimulated a desire +in Andrews to become a benefactor to his college. He accordingly +bequeathed a sum of 3,000 pounds and an annual income of 250 pounds +wherewith to build and endow an astronomical Observatory in the +University. The figures just stated ought to be qualified by the +words of cautious Ussher (afterwards the first Professor of +Astronomy), that "this money was to arise from an accumulation of a +part of his property, to commence upon a particular contingency +happening to his family." The astronomical endowment was soon in +jeopardy by litigation. Andrews thought he had provided for his +relations by leaving to them certain leasehold interests connected +with the Provost's estate. The law courts, however, held that these +interests were not at the disposal of the testator, and handed them +over to Hely Hutchinson, the next Provost. The disappointed +relations then petitioned the Irish Parliament to redress this +grievance by transferring to them the moneys designed by Andrews for +the Observatory. It would not be right, they contended, that the +kindly intentions of the late Provost towards his kindred should be +frustrated for the sake of maintaining what they described as "a +purely ornamental institution." The authorities of the College +protested against this claim. Counsel were heard, and a Committee of +the House made a report declaring the situation of the relations to +be a hard one. Accordingly, a compromise was made, and the dispute +terminated.</p> + +<p>The selection of a site for the new astronomical Observatory was made +by the Board of Trinity College. The beautiful neighbourhood of +Dublin offered a choice of excellent localities. On the north side +of the Liffey an Observatory could have been admirably placed, either +on the remarkable promontory of Howth or on the elevation of which +Dunsink is the summit. On the south side of Dublin there are several +eminences that would have been suitable: the breezy heaths at +Foxrock combine all necessary conditions; the obelisk hill at +Killiney would have given one of the most picturesque sites for an +Observatory in the world; while near Delgany two or three other good +situations could be mentioned. But the Board of those pre-railway +days was naturally guided by the question of proximity. Dunsink was +accordingly chosen as the most suitable site within the distance of a +reasonable walk from Trinity College.</p> + +<p>The northern boundary of the Phoenix Park approaches the little river +Tolka, which winds through a succession of delightful bits of sylvan +scenery, such as may be found in the wide demesne of Abbotstown and +the classic shades of Glasnevin. From the banks of the Tolka, on the +opposite side of the park, the pastures ascend in a gentle slope to +culminate at Dunsink, where at a distance of half a mile from the +stream, of four miles from Dublin, and at a height of 300 feet above +the sea, now stands the Observatory. From the commanding position of +Dunsink a magnificent view is obtained. To the east the sea is +visible, while the southern prospect over the valley of the Liffey is +bounded by a range of hills and mountains extending from Killiney to +Bray Head, thence to the little Sugar Loaf, the Two Rock and the +Three Rock Mountains, over the flank of which the summit of the Great +Sugar Loaf is just perceptible. Directly in front opens the fine +valley of Glenasmole, with Kippure Mountain, while the range can be +followed to its western extremity at Lyons. The climate of Dunsink +is well suited for astronomical observation. No doubt here, as +elsewhere in Ireland, clouds are abundant, but mists or haze are +comparatively unusual, and fogs are almost unknown.</p> + +<p>The legal formalities to be observed in assuming occupation exacted a +delay of many months; accordingly, it was not until the 10th +December, 1782, that a contract could be made with Mr. Graham Moyers +for the erection of a meridian-room and a dome for an equatorial, in +conjunction with a becoming residence for the astronomer. Before the +work was commenced at Dunsink, the Board thought it expedient to +appoint the first Professor of Astronomy. They met for this purpose +on the 22nd January, 1783, and chose the Rev. Henry Ussher, a Senior +Fellow of Trinity College, Dublin. The wisdom of the appointment was +immediately shown by the assiduity with which Ussher engaged in +founding the observatory. In three years he had erected the +buildings and equipped them with instruments, several of which were +of his own invention. On the 19th of February, 1785, a special grant +of 200 pounds was made by the Board to Dr. Ussher as some recompense +for his labours. It happened that the observatory was not the only +scientific institution which came into being in Ireland at this +period; the newly-kindled ardour for the pursuit of knowledge led, at +the same time, to the foundation of the Royal Irish Academy. By a +fitting coincidence, the first memoir published in the "Transactions +Of The Royal Irish Academy," was by the first Andrews, Professor of +Astronomy. It was read on the 13th of June, 1785, and bore the +title, "Account of the Observatory belonging to Trinity College," by +the Rev. H. Ussher, D.D., M.R.I.A., F.R.S. This communication shows +the extensive design that had been originally intended for Dunsink, +only a part of which was, however, carried out. For instance, two +long corridors, running north and south from the central edifice, +which are figured in the paper, never developed into bricks and +mortar. We are not told why the original scheme had to be +contracted; but perhaps the reason may be not unconnected with a +remark of Ussher's, that the College had already advanced from its +own funds a sum considerably exceeding the original bequest. The +picture of the building shows also the dome for the South equatorial, +which was erected many years later.</p> + +<p>Ussher died in 1790. During his brief career at the observatory, he +observed eclipses, and is stated to have done other scientific work. +The minutes of the Board declare that the infant institution had +already obtained celebrity by his labours, and they urge the claims +of his widow to a pension, on the ground that the disease from which +he died had been contracted by his nightly vigils. The Board also +promised a grant of fifty guineas as a help to bring out Dr. Ussher's +sermons. They advanced twenty guineas to his widow towards the +publication of his astronomical papers. They ordered his bust to be +executed for the observatory, and offered "The Death of Ussher" as +the subject of a prize essay; but, so far as I can find, neither the +sermons nor the papers, neither the bust nor the prize essay, ever +came into being.</p> + +<p>There was keen competition for the chair of Astronomy which the death +of Ussher vacated. The two candidates were Rev. John Brinkley, of +Caius College, Cambridge, a Senior Wrangler (born at Woodbridge, +Suffolk, in 1763), and Mr. Stack, Fellow of Trinity College, Dublin, +and author of a book on Optics. A majority of the Board at first +supported Stack, while Provost Hely Hutchinson and one or two others +supported Brinkley. In those days the Provost had a veto at +elections, so that ultimately Stack was withdrawn and Brinkley was +elected. This took place on the 11th December, 1790. The national +press of the day commented on the preference shown to the young +Englishman, Brinkley, over his Irish rival. An animated controversy +ensued. The Provost himself condescended to enter the lists and to +vindicate his policy by a long letter in the "Public Register" or +"Freeman's Journal," of 21st December, 1790. This letter was +anonymous, but its authorship is obvious. It gives the +correspondence with Maskelyne and other eminent astronomers, whose +advice and guidance had been sought by the Provost. It also contends +that "the transactions of the Board ought not to be canvassed in the +newspapers." For this reference, as well as for much other +information, I am indebted to my friend, the Rev. John Stubbs, D.D.</p> + +<p><a name="dunsink" id="dunsink"></a></p> + +<div class="figcenter" style="width: 747px;"> +<a href="images/ill_observatory_dunsink.jpg"> +<img src="images/ill_observatory_dunsink_sml.jpg" width="747" height="451" alt="THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin." title="" /></a> +<span class="caption">THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin.</span> +</div> + +<p>The next event in the history of the Observatory was the issue of +Letters Patent (32 Geo. III., A.D. 1792), in which it is recited that +"We grant and ordain that there shall be forever hereafter a +Professor of Astronomy, on the foundation of Dr. Andrews, to be +called and known by the name of the Royal Astronomer of Ireland." The +letters prescribe the various duties of the astronomer and the mode +of his election. They lay down regulations as to the conduct of the +astronomical work, and as to the choice of an assistant. They direct +that the Provost and the Senior Fellows shall make a thorough +inspection of the observatory once every year in June or July; and +this duty was first undertaken on the 5th of July, 1792. It may be +noted that the date on which the celebration of the tercentenary of +the University was held happens to coincide with the centenary of the +first visitation of the observatory. The visitors on the first +occasion were A. Murray, Matthew Young, George Hall, and John +Barrett. They record that they find the buildings, books and +instruments in good condition; but the chief feature in this report, +as well as in many which followed it, related to a circumstance to +which we have not yet referred.</p> + +<p>In the original equipment of the observatory, Ussher, with the +natural ambition of a founder, desired to place in it a telescope of +more magnificent proportions than could be found anywhere else. The +Board gave a spirited support to this enterprise, and negotiations +were entered into with the most eminent instrument-maker of those +days. This was Jesse Ramsden (1735-1800), famous as the improver of +the sextant, as the constructor of the great theodolite used by +General Roy in the English Survey, and as the inventor of the +dividing engine for graduating astronomical instruments. Ramsden had +built for Sir George Schuckburgh the largest and most perfect +equatorial ever attempted. He had constructed mural quadrants for +Padua and Verona, which elicited the wonder of astronomers when Dr. +Maskelyne declared he could detect no error in their graduation so +large as two seconds and a half. But Ramsden maintained that even +better results would be obtained by superseding the entire quadrant +by the circle. He obtained the means of testing this prediction when +he completed a superb circle for Palermo of five feet diameter. +Finding his anticipations were realised, he desired to apply the same +principles on a still grander scale. Ramsden was in this mood when +he met with Dr. Ussher. The enthusiasm of the astronomer and the +instrument-maker communicated itself to the Board, and a tremendous +circle, to be ten feet in diameter, was forthwith projected.</p> + +<p>Projected, but never carried out. After Ramsden had to some extent +completed a 10-foot circle, he found such difficulties that he tried +a 9-foot, and this again he discarded for an 8-foot, which was +ultimately accomplished, though not entirely by himself. +Notwithstanding the contraction from the vast proportions originally +designed, the completed instrument must still be regarded as a +colossal piece of astronomical workmanship. Even at this day I do +not know that any other observatory can show a circle eight feet in +diameter graduated all round.</p> + +<p>I think it is Professor Piazzi Smith who tells us how grateful he was +to find a large telescope he had ordered finished by the opticians on +the very day they had promised it. The day was perfectly correct; it +was only the year that was wrong. A somewhat remarkable experience +in this direction is chronicled by the early reports of the visitors +to Dunsink Observatory. I cannot find the date on which the great +circle was ordered from Ramsden, but it is fixed with sufficient +precision by an allusion in Ussher's paper to the Royal Irish +Academy, which shows that by the 13th June, 1785, the order had been +given, but that the abandonment of the 10-foot scale had not then +been contemplated. It was reasonable that the board should allow +Ramsden ample time for the completion of a work at once so elaborate +and so novel. It could not have been finished in a year, nor would +there have been much reason for complaint if the maker had found he +required two or even three years more.</p> + +<p>Seven years gone, and still no telescope, was the condition in which +the Board found matters at their first visitation in 1792. They had, +however, assurances from Ramsden that the instrument would be +completed within the year; but, alas for such promises, another seven +years rolled on, and in 1799 the place for the great circle was still +vacant at Dunsink. Ramsden had fallen into bad health, and the Board +considerately directed that "inquiries should be made." Next year +there was still no progress, so the Board were roused to threaten +Ramsden with a suit at law; but the menace was never executed, for +the malady of the great optician grew worse, and he died that year.</p> + +<p>Affairs had now assumed a critical aspect, for the college had +advanced much money to Ramsden during these fifteen years, and the +instrument was still unfinished. An appeal was made by the Provost +to Dr. Maskelyne, the Astronomer Royal of England, for his advice and +kindly offices in this emergency. Maskelyne responds—in terms +calculated to allay the anxiety of the Bursar—"Mr. Ramsden has left +property behind him, and the College can be in no danger of losing +both their money and the instrument." The business of Ramsden was +then undertaken by Berge, who proceeded to finish the circle quite as +deliberately as his predecessor. After four years Berge promised the +instrument in the following August, but it did not come. Two years +later (1806) the professor complains that he can get no answer from +Berge. In 1807, it is stated that Berge will send the telescope in a +month. He did not; but in the next year (1808), about twenty-three +years after the great circle was ordered, it was erected at Dunsink, +where it is still to be seen.</p> + +<p>The following circumstances have been authenticated by the signatures +of Provosts, Proctors, Bursars, and other College dignitaries:—In +1793 the Board ordered two of the clocks at the observatory to be +sent to Mr. Crosthwaite for repairs. Seven years later, in 1800, Mr. +Crosthwaite was asked if the clocks were ready. This impatience was +clearly unreasonable, for even in four more years, 1804, we find the +two clocks were still in hand. Two years later, in 1806, the Board +determined to take vigorous action by asking the Bursar to call upon +Crosthwaite. This evidently produced some effect, for in the +following year, 1807, the Professor had no doubt that the clocks +would be speedily returned. After eight years more, in 1815, one of +the clocks was still being repaired, and so it was in 1816, which is +the last record we have of these interesting time-pieces. Astronomers +are, however, accustomed to deal with such stupendous periods in +their calculations, that even the time taken to repair a clock seems +but small in comparison.</p> + +<p>The long tenure of the chair of Astronomy by Brinkley is divided into +two nearly equal periods by the year in which the great circle was +erected. Brinkley was eighteen years waiting for his telescope, and +he had eighteen years more in which to use it. During the first of +these periods Brinkley devoted himself to mathematical research; +during the latter he became a celebrated astronomer. Brinkley's +mathematical labours procured for their author some reputation as a +mathematician. They appear to be works of considerable mathematical +elegance, but not indicating any great power of original thought. +Perhaps it has been prejudicial to Brinkley's fame in this direction, +that he was immediately followed in his chair by so mighty a genius +as William Rowan Hamilton.</p> + +<p>After the great circle had been at last erected, Brinkley was able to +begin his astronomical work in earnest. Nor was there much time to +lose. He was already forty-five years old, a year older than was +Herschel when he commenced his immortal career at Slough. Stimulated +by the consciousness of having the command of an instrument of unique +perfection, Brinkley loftily attempted the very highest class of +astronomical research. He resolved to measure anew with his own eye +and with his own hand the constants of aberration and of nutation. He +also strove to solve that great problem of the universe, the +discovery of the distance of a fixed star.</p> + +<p>These were noble problems, and they were nobly attacked. But to +appraise with justice this work of Brinkley, done seventy years ago, +we must not apply to it the same criterion as we would think right to +apply to similar work were it done now. We do not any longer use +Brinkley's constant of aberration, nor do we now think that +Brinkley's determinations of the star distances were reliable. But, +nevertheless, his investigations exercised a marked influence on the +progress of science; they stimulated the study of the principles on +which exact measurements were to be conducted.</p> + +<p>Brinkley had another profession in addition to that of an +astronomer. He was a divine. When a man endeavours to pursue two +distinct occupations concurrently, it will be equally easy to explain +why his career should be successful, or why it should be the +reverse. If he succeeds, he will, of course, exemplify the wisdom of +having two strings to his bow. Should he fail, it is, of course, +because he has attempted to sit on two stools at once. In Brinkley's +case, his two professions must be likened to the two strings rather +than to the two stools. It is true that his practical experience of +his clerical life was very slender. He had made no attempt to +combine the routine of a parish with his labours in the observatory. +Nor do we associate a special eminence in any department of religious +work with his name. If, however, we are to measure Brinkley's merits +as a divine by the ecclesiastical preferment which he received, his +services to theology must have rivalled his services to astronomy. +Having been raised step by step in the Church, he was at last +appointed to the See of Cloyne, in 1826, as the successor of Bishop +Berkeley.</p> + +<p>Now, though it was permissible for the Archdeacon to be also the +Andrews Professor, yet when the Archdeacon became a Bishop, it was +understood that he should transfer his residence from the observatory +to the palace. The chair of Astronomy accordingly became vacant. +Brinkley's subsequent career seems to have been devoted entirely to +ecclesiastical matters, and for the last ten years of his life he did +not contribute a paper to any scientific society. Arago, after a +characteristic lament that Brinkley should have forsaken the pursuit +of science for the temporal and spiritual attractions of a bishopric, +pays a tribute to the conscientiousness of the quondam astronomer, +who would not even allow a telescope to be brought into the palace +lest his mind should be distracted from his sacred duties.</p> + +<p>The good bishop died on the 13th September, 1835. He was buried in +the chapel of Trinity College, and a fine monument to his memory is a +familiar object at the foot of the noble old staircase of the library. +The best memorial of Brinkley is his admirable book on the "Elements +of Plane Astronomy." It passed through many editions in his lifetime, +and even at the present day the same work, revised first by Dr. Luby, +and more recently by the Rev. Dr. Stubbs and Dr. Brunnow, has a large +and well-merited circulation.</p> + +<h3><a name="JOHN_HERSCHEL" id="JOHN_HERSCHEL"></a>JOHN HERSCHEL.</h3> +<p>This illustrious son of an illustrious father was born at Slough, +near Windsor, on the 7th March, 1792. He was the only child of Sir +William Herschel, who had married somewhat late in life, as we have +already mentioned.</p> + +<p><a name="astronometer" id="astronometer"></a></p> + +<div class="figcenter" style="width: 438px;"> +<a href="images/ill_astronometer_herschel.jpg"> +<img src="images/ill_astronometer_herschel_sml.jpg" width="438" height="232" alt="ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon." title="" /></a> +<span class="caption">ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon.</span> +</div> + +<p>The surroundings among which the young astronomer was reared afforded +him an excellent training for that career on which he was to enter, +and in which he was destined to attain a fame only less brilliant +than that of his father. The circumstances of his youth permitted +him to enjoy one great advantage which was denied to the elder +Herschel. He was able, from his childhood, to devote himself almost +exclusively to intellectual pursuits. William Herschel, in the early +part of his career, had only been able to snatch occasional hours for +study from his busy life as a professional musician. But the son, +having been born with a taste for the student's life, was fortunate +enough to have been endowed with the leisure and the means to enjoy +it from the commencement. His early years have been so well +described by the late Professor Pritchard in the "Report of the +Council of the Royal Astronomical Society for 1872," that I venture +to make an extract here:—</p> + +<p>"A few traits of John Herschel's boyhood, mentioned by himself in his +maturer life, have been treasured up by those who were dear to him, +and the record of some of them may satisfy a curiosity as pardonable +as inevitable, which craves to learn through what early steps great +men or great nations become illustrious. His home was singular, and +singularly calculated to nurture into greatness any child born as +John Herschel was with natural gifts, capable of wide development. At +the head of the house there was the aged, observant, reticent +philosopher, and rarely far away his devoted sister, Caroline +Herschel, whose labours and whose fame are still cognisable as a +beneficent satellite to the brighter light of her illustrious +brother. It was in the companionship of these remarkable persons, +and under the shadow of his father's wonderful telescope, that John +Herschel passed his boyish years. He saw them, in silent but +ceaseless industry, busied about things which had no apparent concern +with the world outside the walls of that well-known house, but which, +at a later period of his life, he, with an unrivalled eloquence, +taught his countrymen to appreciate as foremost among those living +influences which but satisfy and elevate the noblest instincts of our +nature. What sort of intercourse passed between the father and the +boy may be gathered from an incident or two which he narrated as +having impressed themselves permanently on the memory of his youth. +He once asked his father what he thought was the oldest of all +things. The father replied, after the Socratic method, by putting +another question: 'And what do you yourself suppose is the oldest of +all things?' The boy was not successful in his answers, thereon the +old astronomer took up a small stone from the garden walk: 'There, my +child, there is the oldest of all the things that I certainly know.' +On another occasion his father is said to have asked the boy, 'What +sort of things, do you think, are most alike?' The delicate, +blue-eyed boy, after a short pause, replied, 'The leaves of the same +tree are most like each other.' 'Gather, then, a handful of leaves of +that tree,' rejoined the philosopher, 'and choose two that are +alike.' The boy failed; but he hid the lesson in his heart, and his +thoughts were revealed after many days. These incidents may be +trifles; nor should we record them here had not John Herschel +himself, though singularly reticent about his personal emotions, +recorded them as having made a strong impression on his mind. Beyond +all doubt we can trace therein, first, that grasp and grouping of +many things in one, implied in the stone as the oldest of things; +and, secondly, that fine and subtle discrimination of each thing out +of many like things as forming the main features which characterized +the habit of our venerated friend's philosophy."</p> + +<p>John Herschel entered St. John's College, Cambridge, when he was +seventeen years of age. His university career abundantly fulfilled +his father's eager desire, that his only son should develop a +capacity for the pursuit of science. After obtaining many lesser +distinctions, he finally came out as Senior Wrangler in 1813. It +was, indeed, a notable year in the mathematical annals of the +University. Second on that list, in which Herschel's name was first, +appeared that of the illustrious Peacock, afterwards Dean of Ely, who +remained throughout life one of Herschel's most intimate friends.</p> + +<p>Almost immediately after taking his degree, Herschel gave evidence of +possessing a special aptitude for original scientific investigation. +He sent to the Royal Society a mathematical paper which was published +in the PHILOSOPHICAL TRANSACTIONS. Doubtless the splendour that +attached to the name he bore assisted him in procuring early +recognition of his own great powers. Certain it is that he was made +a Fellow of the Royal Society at the unprecedentedly early age of +twenty-one. Even after this remarkable encouragement to adopt a +scientific career as the business of his life, it does not seem that +John Herschel at first contemplated devoting himself exclusively to +science. He commenced to prepare for the profession of the Law by +entering as a student at the Middle Temple, and reading with a +practising barrister.</p> + +<p>But a lawyer John Herschel was not destined to become. Circumstances +brought him into association with some leading scientific men. He +presently discovered that his inclinations tended more and more in +the direction of purely scientific pursuits. Thus it came to pass +that the original intention as to the calling which he should follow +was gradually abandoned. Fortunately for science Herschel found its +pursuit so attractive that he was led, as his father had been before +him, to give up his whole life to the advancement of knowledge. Nor +was it unnatural that a Senior Wrangler, who had once tasted the +delights of mathematical research, should have been tempted to devote +much time to this fascinating pursuit. By the time John Herschel was +twenty-nine he had published so much mathematical work, and his +researches were considered to possess so much merit, that the Royal +Society awarded him the Copley Medal, which was the highest +distinction it was capable of conferring.</p> + +<p>At the death of his father in 1822, John Herschel, with his tastes +already formed for a scientific career, found himself in the +possession of ample means. To him also passed all his father's great +telescopes and apparatus. These material aids, together with a +dutiful sense of filial obligation, decided him to make practical +astronomy the main work of his life. He decided to continue to its +completion that great survey of the heavens which had already been +inaugurated, and, indeed, to a large extent accomplished, by his +father.</p> + +<p>The first systematic piece of practical astronomical work which John +Herschel undertook was connected with the measurement of what are +known as "Double Stars." It should be observed, that there are in +the heavens a number of instances in which two stars are seen in very +close association. In the case of those objects to which the +expression "Double Stars" is generally applied, the two luminous +points are so close together that even though they might each be +quite bright enough to be visible to the unaided eye, yet their +proximity is such that they cannot be distinguished as two separate +objects without optical aid. The two stars seem fused together into +one. In the telescope, however, the bodies may be discerned +separately, though they are frequently so close together that it +taxes the utmost power of the instrument to indicate the division +between them.</p> + +<p>The appearance presented by a double star might arise from the +circumstance that the two stars, though really separated from each +other by prodigious distances, happened to lie nearly in the same +line of vision, as seen from our point of view. No doubt, many of +the so-called double stars could be accounted for on this +supposition. Indeed, in the early days when but few double stars +were known, and when telescopes were not powerful enough to exhibit +the numerous close doubles which have since been brought to light, +there seems to have been a tendency to regard all double stars as +merely such perspective effects. It was not at first suggested that +there could be any physical connection between the components of each +pair. The appearance presented was regarded as merely due to the +circumstance that the line joining the two bodies happened to pass +near the earth.</p> + +<p><a name="john_herschel_ill" id="john_herschel_ill"></a></p> + +<div class="figcenter" style="width: 439px;"> +<a href="images/ill_john_herschel.jpg"> +<img src="images/ill_john_herschel_sml.jpg" width="439" height="516" alt="SIR JOHN HERSCHEL." title="" /></a> +<span class="caption">SIR JOHN HERSCHEL.</span> +</div> + +<p>In the early part of his career, Sir William Herschel seems to have +entertained the view then generally held by other astronomers with +regard to the nature of these stellar pairs. The great observer +thought that the double stars could therefore be made to afford a +means of solving that problem in which so many of the observers of +the skies had been engaged, namely, the determination of the +distances of the stars from the earth. Herschel saw that the +displacement of the earth in its annual movement round the sun would +produce an apparent shift in the place of the nearer of the two stars +relatively to the other, supposed to be much more remote. If this +shift could be measured, then the distance of the nearer of the stars +could be estimated with some degree of precision.</p> + +<p>As has not unfrequently happened in the history of science, an effect +was perceived of a very different nature from that which had been +anticipated. If the relative places of the two stars had been +apparently deranged merely in consequence of the motion of the earth, +then the phenomenon would be an annual one. After the lapse of a +year the two stars would have regained their original relative +positions. This was the effect for which William Herschel was +looking. In certain of the so called double stars, he, no doubt, did +find a movement. He detected the remarkable fact that both the +apparent distance and the relative positions of the two bodies were +changing. But what was his surprise to observe that these +alterations were not of an annually periodic character. It became +evident then that in some cases one of the component stars was +actually revolving around the other, in an orbit which required many +years for its completion. Here was indeed a remarkable discovery. It +was clearly impossible to suppose that movements of this kind could +be mere apparent displacements, arising from the annual shift in our +point of view, in consequence of the revolution of the earth. +Herschel's discovery established the interesting fact that, in +certain of these double stars, or binary stars, as these particular +objects are more expressively designated, there is an actual orbital +revolution of a character similar to that which the earth performs +around the sun. Thus it was demonstrated that in these particular +double stars the nearness of the two components was not merely +apparent. The objects must actually lie close together at a distance +which is small in comparison with the distance at which either of +them is separated from the earth. The fact that the heavens contain +pairs of twin suns in mutual revolution was thus brought to light.</p> + +<p>In consequence of this beautiful discovery, the attention of +astronomers was directed to the subject of double stars with a degree +of interest which these objects had never before excited. It was +therefore not unnatural that John Herschel should have been attracted +to this branch of astronomical work. Admiration for his father's +discovery alone might have suggested that the son should strive to +develop this territory newly opened up to research. But it also +happened that the mathematical talents of the younger Herschel +inclined his inquiries in the same direction. He saw clearly that, +when sufficient observations of any particular binary star had been +accumulated, it would then be within the power of the mathematician +to elicit from those observations the shape and the position in space +of the path which each of the revolving stars described around the +other. Indeed, in some cases he would be able to perform the +astonishing feat of determining from his calculations the weight of +these distant suns, and thus be enabled to compare them with the mass +of our own sun.</p> + +<p><a name="nebula" id="nebula"></a></p> + +<div class="figleft" style="width: 188px;"> +<a href="images/ill_nebula_drawn_john_herschel.jpg"> +<img src="images/ill_nebula_drawn_john_herschel_sml.jpg" width="188" height="249" alt="NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel." title="" /></a> +<span class="caption">NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel.</span> +</div> + +<p>But this work must follow the observations, it could not precede +them. The first step was therefore to observe and to measure with +the utmost care the positions and distances of those particular +double stars which appear to offer the greatest promise in this +particular research. In 1821, Herschel and a friend of his, Mr. +James South, agreed to work together with this object. South was a +medical man with an ardent devotion to science, and possessed of +considerable wealth. He procured the best astronomical instruments +that money could obtain, and became a most enthusiastic astronomer +and a practical observer of tremendous energy.</p> + +<p>South and John Herschel worked together for two years in the +observation and measurement of the double stars discovered by Sir +William Herschel. In the course of this time their assiduity was +rewarded by the accumulation of so great a mass of careful +measurements that when published, they formed quite a volume in the +"Philosophical Transactions." The value and accuracy of the work, +when estimated by standards which form proper criteria for that +period, is universally recognised. It greatly promoted the progress +of sidereal astronomy, and the authors were in consequence awarded +medals from the Royal Society, and the Royal Astronomical Society, +as well as similar testimonials from various foreign institutions.</p> + +<p>This work must, however, be regarded as merely introductory to the +main labours of John Herschel's life. His father devoted the greater +part of his years as an observer to what he called his "sweeps" of +the heavens. The great reflecting telescope, twenty feet long, was +moved slowly up and down through an arc of about two degrees towards +and from the pole, while the celestial panorama passed slowly in the +course of the diurnal motion before the keenly watching eye of the +astronomer. Whenever a double star traversed the field Herschel +described it to his sister Caroline, who, as we have already +mentioned, was his invariable assistant in his midnight watches. When +a nebula appeared, then he estimated its size and its brightness, he +noticed whether it had a nucleus, or whether it had stars disposed in +any significant manner with regard to it. He also dictated any other +circumstance which he deemed worthy of record. These observations +were duly committed to writing by the same faithful and indefatigable +scribe, whose business it also was to take a memorandum of the exact +position of the object as indicated by a dial placed in front of her +desk, and connected with the telescope.</p> + +<p>John Herschel undertook the important task of re-observing the +various double stars and nebulae which had been discovered during +these memorable vigils. The son, however, lacked one inestimable +advantage which had been possessed by the father. John Herschel had +no assistant to discharge all those duties which Caroline had so +efficiently accomplished. He had, therefore, to modify the system of +sweeping previously adopted in order to enable all the work both of +observing and of recording to be done by himself. This, in many +ways, was a great drawback to the work of the younger astronomer. The +division of labour between the observer and the scribe enables a +greatly increased quantity of work to be got through. It is also +distinctly disadvantageous to an observer to have to use his eye at +the telescope directly after he has been employing it for reading the +graduations on a circle, by the light of a lamp, or for entering +memoranda in a note book. Nebulae, especially, are often so +excessively faint that they can only be properly observed by an eye +which is in that highly sensitive condition which is obtained by long +continuance in darkness. The frequent withdrawal of the eye from the +dark field of the telescope, and the application of it to reading by +artificial light, is very prejudicial to its use for the more +delicate purpose. John Herschel, no doubt, availed himself of every +precaution to mitigate the ill effects of this inconvenience as much +as possible, but it must have told upon his labours as compared with +those of his father.</p> + +<p>But nevertheless John Herschel did great work during his "sweeps." He +was specially particular to note all the double stars which presented +themselves to his observation. Of course some little discretion must +be allowed in deciding as to what degree of proximity in adjacent +stars does actually bring them within the category of "double +stars." Sir John set down all such objects as seemed to him likely +to be of interest, and the results of his discoveries in this branch +of astronomy amount to some thousands. Six or seven great memoirs in +the TRANSACTIONS of the Royal Astronomical Society have been devoted +to giving an account of his labours in this department of astronomy.</p> + +<p><a name="centaur" id="centaur"></a></p> + +<div class="figcenter" style="width: 328px;"> +<a href="images/ill_cluster_centaur.jpg"> +<img src="images/ill_cluster_centaur_sml.jpg" width="328" height="314" alt="THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel." title="" /></a> +<span class="caption">THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.</span> +</div> + +<p>One of the achievements by which Sir John Herschel is best known is +his invention of a method by which the orbits of binary stars could +be determined. It will be observed that when one star revolves +around another in consequence of the law of gravitation, the orbit +described must be an ellipse. This ellipse, however, generally +speaking, appears to us more or less foreshortened, for it is easily +seen that only under highly exceptional circumstances would the plane +in which the stars move happen to be directly square to the line of +view. It therefore follows that what we observe is not exactly the +track of one star around the other; it is rather the projection of +that track as seen on the surface of the sky. Now it is remarkable +that this apparent path is still an ellipse. Herschel contrived a +very ingenious and simple method by which he could discover from the +observations the size and position of the ellipse in which the +revolution actually takes place. He showed how, from the study of +the apparent orbit of the star, and from certain measurements which +could easily be effected upon it, the determination of the true +ellipse in which the movement is performed could be arrived at. In +other words, Herschel solved in a beautiful manner the problem of +finding the true orbits of double stars. The importance of this work +may be inferred from the fact that it has served as the basis on +which scores of other investigators have studied the fascinating +subject of the movement of binary stars.</p> + +<p>The labours, both in the discovery and measurement of the double +stars, and in the discussion of the observations with the object of +finding the orbits of such stars as are in actual revolution, +received due recognition in yet another gold medal awarded by the +Royal Society. An address was delivered on the occasion by the Duke +of Sussex (30th November, 1833), in the course of which, after +stating that the medal had been conferred on Sir John Herschel, he +remarks:—</p> + +<p>"It has been said that distance of place confers the same privilege +as distance of time, and I should gladly avail myself of the +privilege which is thus afforded me by Sir John Herschel's separation +from his country and friends, to express my admiration of his +character in stronger terms than I should otherwise venture to use; +for the language of panegyric, however sincerely it may flow from the +heart, might be mistaken for that of flattery, if it could not thus +claim somewhat of an historical character; but his great attainments +in almost every department of human knowledge, his fine powers as a +philosophical writer, his great services and his distinguished +devotion to science, the high principles which have regulated his +conduct in every relation of life, and, above all, his engaging +modesty, which is the crown of all his other virtues, presenting such +a model of an accomplished philosopher as can rarely be found beyond +the regions of fiction, demand abler pens than mine to describe them +in adequate terms, however much inclined I might feel to undertake +the task."</p> + +<p>The first few lines of the eulogium just quoted allude to Herschel's +absence from England. This was not merely an episode of interest in +the career of Herschel, it was the occasion of one of the greatest +scientific expeditions in the whole history of astronomy.</p> + +<p>Herschel had, as we have seen, undertaken a revision of his father's +"sweeps" for new objects, in those skies which are visible from our +latitudes in the northern hemisphere. He had well-nigh completed +this task. Zone by zone the whole of the heavens which could be +observed from Windsor had passed under his review. He had added +hundreds to the list of nebulae discovered by his father. He had +announced thousands of double stars. At last, however, the great +survey was accomplished. The contents of the northern hemisphere, so +far at least as they could be disclosed by his telescope of twenty +feet focal length, had been revealed.</p> + +<p><a name="herschel_observatory_feldhausen" id="herschel_observatory_feldhausen"></a></p> + +<div class="figcenter" style="width: 442px;"> +<a href="images/ill_john_herschel_observatory_feldhausen.jpg"> +<img src="images/ill_john_herschel_observatory_feldhausen_sml.jpg" width="442" height="373" alt="SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope." title="" /></a> +<span class="caption">SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope.</span> +</div> + +<p>But Herschel felt that this mighty task had to be supplemented by +another of almost equal proportions, before it could be said that the +twenty-foot telescope had done its work. It was only the northern +half of the celestial sphere which had been fully explored. The +southern half was almost virgin territory, for no other astronomer +was possessed of a telescope of such power as those which the +Herschels had used. It is true, of course, that as a certain margin +of the southern hemisphere was visible from these latitudes, it had +been more or less scrutinized by observers in northern skies. And +the glimpses which had thus been obtained of the celestial objects in +the southern sky, were such as to make an eager astronomer long for a +closer acquaintance with the celestial wonders of the south. The +most glorious object in the sidereal heavens, the Great Nebula in +Orion, lies indeed in that southern hemisphere to which the younger +Herschel's attention now became directed. It fortunately happens, +however, for votaries of astronomy all the world over, that Nature +has kindly placed her most astounding object, the great Nebula in +Orion, in such a favoured position, near the equator, that from a +considerable range of latitudes, both north and south, the wonders of +the Nebula can be explored. There are grounds for thinking that the +southern heavens contain noteworthy objects which, on the whole, are +nearer to the solar system than are the noteworthy objects in the +northern skies. The nearest star whose distance is known, Alpha +Centauri, lies in the southern hemisphere, and so also does the most +splendid cluster of stars.</p> + +<p>Influenced by the desire to examine these objects, Sir John Herschel +determined to take his great telescope to a station in the southern +hemisphere, and thus complete his survey of the sidereal heavens. The +latitude of the Cape of Good Hope is such that a suitable site could +be there found for his purpose. The purity of the skies in South +Africa promised to provide for the astronomer those clear nights +which his delicate task of surveying the nebulae would require.</p> + +<p>On November 13, 1833, Sir John Herschel, who had by this time +received the honour of knighthood from William IV., sailed from +Portsmouth for the Cape of Good Hope, taking with him his gigantic +instruments. After a voyage of two months, which was considered to +be a fair passage in those days, he landed in Table Bay, and having +duly reconnoitred various localities, he decided to place his +observatory at a place called Feldhausen, about six miles from Cape +Town, near the base of the Table Mountain. A commodious residence +was there available, and in it he settled with his family. A +temporary building was erected to contain the equatorial, but the +great twenty-foot telescope was accommodated with no more shelter +than is provided by the open canopy of heaven.</p> + +<p>As in his earlier researches at home, the attention of the great +astronomer at the Cape of Good Hope was chiefly directed to the +measurement of the relative positions and distances apart of the +double stars, and to the close examination of the nebulae. In the +delineation of the form of these latter objects Herschel found ample +employment for his skilful pencil. Many of the drawings he has made +of the celestial wonders in the southern sky are admirable examples +of celestial portraiture.</p> + +<p>The number of the nebulae and of those kindred objects, the star +clusters, which Herschel studied in the southern heavens, during four +years of delightful labour, amount in all to one thousand seven +hundred and seven. His notes on their appearance, and the +determinations of their positions, as well as his measurements of +double stars, and much other valuable astronomical research, were +published in a splendid volume, brought out at the cost of the Duke +of Northumberland. This is, indeed, a monumental work, full of +interesting and instructive reading for any one who has a taste for +astronomy.</p> + +<p>Herschel had the good fortune to be at the Cape on the occasion of +the periodical return of Halley's great comet in 1833. To the study +of this body he gave assiduous attention, and the records of his +observations form one of the most interesting chapters in that +remarkable volume to which we have just referred.</p> + +<p><a name="column" id="column"></a></p> + +<div class="figcenter" style="width: 412px;"> +<a href="images/ill_granite_column_feldhausen.jpg"> +<img src="images/ill_granite_column_feldhausen_sml.jpg" width="412" height="304" alt="COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens." title="" /></a> +<span class="caption">COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens.</span> +</div> + +<p>Early in 1838 Sir John Herschel returned to England. He had made +many friends at the Cape, who deeply sympathised with his self- +imposed labours while he was resident among them. They desired to +preserve the recollection of this visit, which would always, they +considered, be a source of gratification in the colony. Accordingly, +a number of scientific friends in that part of the world raised a +monument with a suitable inscription, on the spot which had been +occupied by the great twenty-foot reflector at Feldhausen.</p> + +<p>His return to England after five years of absence was naturally an +occasion for much rejoicing among the lovers of astronomy. He was +entertained at a memorable banquet, and the Queen, at her coronation, +made him a baronet. His famous aunt Caroline, at that time aged +eighty, was still in the enjoyment of her faculties, and was able to +estimate at its true value the further lustre which was added to the +name she bore. But there is reason to believe that her satisfaction +was not quite unmixed with other feelings. With whatever favour she +might regard her nephew, he was still not the brother to whom her +life had been devoted. So jealous was this vigorous old lady of the +fame of the great brother William, that she could hardly hear with +patience of the achievements of any other astronomer, and this +failing existed in some degree even when that other astronomer +happened to be her illustrious nephew.</p> + +<p>With Sir John Herschel's survey of the Southern Hemisphere it may be +said that his career as an observing astronomer came to a close. He +did not again engage in any systematic telescopic research. But it +must not be inferred from this statement that he desisted from active +astronomical work. It has been well observed that Sir John Herschel +was perhaps the only astronomer who has studied with success, and +advanced by original research, every department of the great science +with which his name is associated. It was to some other branches of +astronomy besides those concerned with looking through telescopes, +that the rest of the astronomer's life was to be devoted.</p> + +<p>To the general student Sir John Herschel is best known by the volume +which he published under the title of "Outlines of Astronomy." This +is, indeed, a masterly work, in which the characteristic difficulties +of the subject are resolutely faced and expounded with as much +simplicity as their nature will admit. As a literary effort this +work is admirable, both on account of its picturesque language and +the ennobling conceptions of the universe which it unfolds. The +student who desires to become acquainted with those recondite +departments of astronomy, in which the effects of the disturbing +action of one planet upon the motions of another planet are +considered, will turn to the chapters in Herschel's famous work on +the subject. There he will find this complex matter elucidated, +without resort to difficult mathematics. Edition after edition of +this valuable work has appeared, and though the advances of modern +astronomy have left it somewhat out of date in certain departments, +yet the expositions it contains of the fundamental parts of the +science still remain unrivalled.</p> + +<p>Another great work which Sir John undertook after his return from the +Cape, was a natural climax to those labours on which his father and +he had been occupied for so many years. We have already explained +how the work of both these observers had been mainly devoted to the +study of the nebulae and the star clusters. The results of their +discoveries had been announced to the world in numerous isolated +memoirs. The disjointed nature of these publications made their use +very inconvenient. But still it was necessary for those who desired +to study the marvellous objects discovered by the Herschels, to have +frequent recourse to the original works. To incorporate all the +several observations of nebular into one great systematic catalogue, +seemed, therefore, to be an indispensable condition of progress in +this branch of knowledge. No one could have been so fitted for this +task as Sir John Herschel. He, therefore, attacked and carried +through the great undertaking. Thus at last a grand catalogue of +nebulae and clusters was produced. Never before was there so +majestic an inventory. If we remember that each of the nebulae is an +object so vast, that the whole of the solar system would form an +inconsiderable speck by comparison, what are we to think of a +collection in which these objects are enumerated in thousands? In +this great catalogue we find arranged in systematic order all the +nebulae and all the clusters which had been revealed by the diligence +of the Herschels, father and son, in the Northern Hemisphere, and of +the son alone in the Southern Hemisphere. Nor should we omit to +mention that the labours of other astronomers were likewise +incorporated. It was unavoidable that the descriptions given to each +of the objects should be very slight. Abbreviations are used, which +indicate that a nebula is bright, or very bright, or extremely +bright, or faint, or very faint, or extremely faint. Such phrases +have certainly but a relative and technical meaning in such a +catalogue. The nebulae entered as extremely bright by the +experienced astronomer are only so described by way of contrast to +the great majority of these delicate telescopic objects. Most of the +nebulae, indeed, are so difficult to see, that they admit of but very +slight description. It should be observed that Herschel's catalogue +augmented the number of known nebulous objects to more than ten times +that collected into any catalogue which had ever been compiled before +the days of William Herschel's observing began. But the study of +these objects still advances, and the great telescopes now in use +could probably show at least twice as many of these objects as are +contained in the list of Herschel, of which a new and enlarged +edition has since been brought out by Dr. Dreyer.</p> + +<p>One of the best illustrations of Sir John Herschel's literary powers +is to be found in the address which he delivered at the Royal +Astronomical Society, on the occasion of presenting a medal to Mr. +Francis Baily, in recognition of his catalogue of stars. The passage +I shall here cite places in its proper aspect the true merit of the +laborious duty involved in such a task as that which Mr. Baily had +carried through with such success:—</p> + +<p>"If we ask to what end magnificent establishments are maintained by +states and sovereigns, furnished with masterpieces of art, and placed +under the direction of men of first-rate talent and high-minded +enthusiasm, sought out for those qualities among the foremost in the +ranks of science, if we demand QUI BONO? for what good a Bradley has +toiled, or a Maskelyne or a Piazzi has worn out his venerable age in +watching, the answer is—not to settle mere speculative points in the +doctrine of the universe; not to cater for the pride of man by +refined inquiries into the remoter mysteries of nature; not to trace +the path of our system through space, or its history through past and +future eternities. These, indeed, are noble ends and which I am far +from any thought of depreciating; the mind swells in their +contemplation, and attains in their pursuit an expansion and a +hardihood which fit it for the boldest enterprise. But the direct +practical utility of such labours is fully worthy of their +speculative grandeur. The stars are the landmarks of the universe; +and, amidst the endless and complicated fluctuations of our system, +seem placed by its Creator as guides and records, not merely to +elevate our minds by the contemplation of what is vast, but to teach +us to direct our actions by reference to what is immutable in His +works. It is, indeed, hardly possible to over-appreciate their value +in this point of view. Every well-determined star, from the moment +its place is registered, becomes to the astronomer, the geographer, +the navigator, the surveyor, a point of departure which can never +deceive or fail him, the same for ever and in all places, of a +delicacy so extreme as to be a test for every instrument yet invented +by man, yet equally adapted for the most ordinary purposes; as +available for regulating a town clock as for conducting a navy to the +Indies; as effective for mapping down the intricacies of a petty +barony as for adjusting the boundaries of Transatlantic empires. When +once its place has been thoroughly ascertained and carefully +recorded, the brazen circle with which that useful work was done may +moulder, the marble pillar may totter on its base, and the astronomer +himself survive only in the gratitude of posterity; but the record +remains, and transfuses all its own exactness into every +determination which takes it for a groundwork, giving to inferior +instruments—nay, even to temporary contrivances, and to the +observations of a few weeks or days—all the precision attained +originally at the cost of so much time, labour, and expense."</p> + +<p>Sir John Herschel wrote many other works besides those we have +mentioned. His "Treatise on Meteorology" is, indeed, a standard work +on this subject, and numerous articles from the same pen on +miscellaneous subjects, which have been collected and reprinted, +seemed as a relaxation from his severe scientific studies. Like +certain other great mathematicians Herschel was also a poet, and he +published a translation of the Iliad into blank verse.</p> + +<p>In his later years Sir John Herschel lived a retired life. For a +brief period he had, indeed, been induced to accept the office of +Master of the Mint. It was, however, evident that the routine of +such an occupation was not in accordance with his tastes, and he +gladly resigned it, to return to the seclusion of his study in his +beautiful home at Collingwood, in Kent.</p> + +<p>His health having gradually failed, he died on the 11th May, 1871, in +the seventy-ninth year of his age.</p> + +<h3><a name="THE_EARL_OF_ROSSE" id="THE_EARL_OF_ROSSE"></a>THE EARL OF ROSSE.</h3> +<p>The subject of our present sketch occupies quite a distinct position +in scientific history. Unlike many others who have risen by their +scientific discoveries from obscurity to fame, the great Earl of +Rosse was himself born in the purple. His father, who, under the +title of Sir Lawrence Parsons, had occupied a distinguished position +in the Irish Parliament, succeeded on the death of his father to the +Earldom which had been recently created. The subject of our present +memoir was, therefore, the third of the Earls of Rosse, and he was +born in York on June 17, 1800. Prior to his father's death in 1841, +he was known as Lord Oxmantown.</p> + +<p>The University education of the illustrious astronomer was begun in +Dublin and completed at Oxford. We do not hear in his case of any +very remarkable University career. Lord Rosse was, however, a +diligent student, and obtained a first-class in mathematics. He +always took a great deal of interest in social questions, and was a +profound student of political economy. He had a seat in the House of +Commons, as member for King's County, from 1821 to 1834, his +ancestral estate being situated in this part of Ireland.</p> + +<p><a name="rosse_ill" id="rosse_ill"></a></p> + +<div class="figcenter" style="width: 409px;"> +<a href="images/ill_earl_rosse.jpg"> +<img src="images/ill_earl_rosse_sml.jpg" width="409" height="476" alt="THE EARL OF ROSSE." title="" /></a> +<span class="caption">THE EARL OF ROSSE.</span> +</div> + +<p>Lord Rosse was endowed by nature with a special taste for mechanical +pursuits. Not only had he the qualifications of a scientific +engineer, but he had the manual dexterity which qualified him +personally to carry out many practical arts. Lord Rosse was, in +fact, a skilful mechanic, an experienced founder, and an ingenious +optician. His acquaintances were largely among those who were +interested in mechanical pursuits, and it was his delight to visit +the works or engineering establishments where refined processes in +the arts were being carried on. It has often been stated—and as I +have been told by members of his family, truly stated—that on one +occasion, after he had been shown over some large works in the north +of England, the proprietor bluntly said that he was greatly in want +of a foreman, and would indeed be pleased if his visitor, who had +evinced such extraordinary capacity for mechanical operations, would +accept the post. Lord Rosse produced his card, and gently explained +that he was not exactly the right man, but he appreciated the +compliment, and this led to a pleasant dinner, and was the basis of a +long friendship.</p> + +<p>I remember on one occasion hearing Lord Rosse explain how it was that +he came to devote his attention to astronomy. It appears that when +he found himself in the possession of leisure and of means, he +deliberately cast around to think how that means and that leisure +could be most usefully employed. Nor was it surprising that he +should search for a direction which would offer special scope for his +mechanical tastes. He came to the conclusion that the building of +great telescopes was an art which had received no substantial advance +since the great days of William Herschel. He saw that to construct +mighty instruments for studying the heavens required at once the +command of time and the command of wealth, while he also felt that +this was a subject the inherent difficulties of which would tax to +the uttermost whatever mechanical skill he might possess. Thus it +was he decided that the construction of great telescopes should +become the business of his life.</p> + +<p><a name="birr" id="birr"></a></p> + +<div class="figcenter" style="width: 651px;"> +<a href="images/ill_birr_castle.jpg"> +<img src="images/ill_birr_castle_sml.jpg" width="651" height="428" alt="BIRR CASTLE." /></a> +<span class="caption">BIRR CASTLE.</span> +</div> + +<p><a name="mall" id="mall"></a></p> + +<div class="figcenter" style="width: 651px;"> +<a href="images/ill_mall_parsonstown.jpg"> +<img src="images/ill_mall_parsonstown_sml.jpg" width="651" height="432" alt="THE MALL, PARSONSTOWN." title="" /></a> +<span class="caption">THE MALL, PARSONSTOWN.</span> +</div> + +<p>In the centre of Ireland, seventy miles from Dublin, on the border +between King's County and Tipperary, is a little town whereof we must +be cautious before writing the name. The inhabitants of that town +frequently insist that its name is Birr,[<a name="ast" id="ast"></a><a href="#note">*</a>] while the official +designation is Parsonstown, and to this day for every six people who +apply one name to the town, there will be half a dozen who use the +other. But whichever it may be, Birr or Parsonstown—and I shall +generally call it by the latter name—it is a favourable specimen of +an Irish county town. The widest street is called the Oxmantown +Mall. It is bordered by the dwelling-houses of the chief residents, +and adorned with rows of stately trees. At one end of this +distinctly good feature in the town is the Parish Church, while at +the opposite end are the gates leading into Birr Castle, the +ancestral home of the house of Parsons. Passing through the gates +the visitor enters a spacious demesne, possessing much beauty of wood +and water, one of the most pleasing features being the junction of +the two rivers, which unite at a spot ornamented by beautiful +timber. At various points illustrations of the engineering skill of +the great Earl will be observed. The beauty of the park has been +greatly enhanced by the construction of an ample lake, designed with +the consummate art by which art is concealed. Even in mid-summer it +is enlivened by troops of wild ducks preening themselves in that +confidence which they enjoy in those happy localities where the sound +of a gun is seldom heard. The water is led into the lake by a tube +which passes under one of the two rivers just mentioned, while the +overflow from the lake turns a water-wheel, which works a pair of +elevators ingeniously constructed for draining the low-lying parts of +the estate.</p> + +<div class="footnote"> +<a name="note" id="note"></a> +<p>[<a href="#ast">*</a>] Considering the fame acquired by Parsonstown from Lord Rosse's + mirrors, it may be interesting to note the following extract from + "The Natural History of Ireland," by Dr. Gerard Boate, Thomas + Molyneux M.D., F.R.S., and others, which shows that 150 years ago + Parsonstown was famous for its glass:—</p> + +<p>"We shall conclude this chapter with the glass, there having been + several glasshouses set up by the English in Ireland, none in Dublin + or other cities, but all of them in the country; amongst which the + principal was that of Birre, a market town, otherwise called + Parsonstown, after one Sir Lawrence Parsons, who, having purchased + that lordship, built a goodly house upon it; his son William Parsons + having succeeded him in the possession of it; which town is situate + in Queen's County, about fifty miles (Irish) to the southwest of + Dublin, upon the borders of the two provinces of Leinster and Munster; + from this place Dublin was furnished with all sorts of window and + drinking glasses, and such other as commonly are in use. One part of + the materials, viz., the sand, they had out of England; the other, + to wit the ashes, they made in the place of ash-tree, and used no + other. The chiefest difficulty was to get the clay for the pots to + melt the materials in; this they had out of the north."—Chap. XXI., + Sect. VIII. "Of the Glass made in Ireland."</p> +</div> + +<p>Birr Castle itself is a noble mansion with reminiscences from the +time of Cromwell. It is surrounded by a moat and a drawbridge of +modern construction, and from its windows beautiful views can be had +over the varied features of the park. But while the visitors to +Parsonstown will look with great interest on this residence of an +Irish landlord, whose delight it was to dwell in his own country, and +among his own people, yet the feature which they have specially come +to observe is not to be found in the castle itself. On an extensive +lawn, sweeping down from the moat towards the lake, stand two noble +masonry walls. They are turreted and clad with ivy, and considerably +loftier than any ordinary house. As the visitor approaches, he will +see between those walls what may at first sight appear to him to be +the funnel of a steamer lying down horizontally. On closer approach +he will find that it is an immense wooden tube, sixty feet long, and +upwards of six feet in diameter. It is in fact large enough to admit +of a tall man entering into it and walking erect right through from +one end to the other. This is indeed the most gigantic instrument +which has ever been constructed for the purpose of exploring the +heavens. Closely adjoining the walls between which the great tube +swings, is a little building called "The Observatory." In this the +smaller instruments are contained, and there are kept the books which +are necessary for reference. The observatory also offers shelter to +the observers, and provides the bright fire and the cup of warm tea, +which are so acceptable in the occasional intervals of a night's +observation passed on the top of the walls with no canopy but the +winter sky.</p> + +<p>Almost the first point which would strike the visitor to Lord Rosse's +telescope is that the instrument at which he is looking is not only +enormously greater than anything of the kind that he has ever seen +before, but also that it is something of a totally different nature. +In an ordinary telescope he is accustomed to find a tube with lenses +of glass at either end, while the large telescopes that we see in our +observatories are also in general constructed on the same principle. +At one end there is the object-glass, and at the other end the +eye-piece, and of course it is obvious that with an instrument of +this construction it is to the lower end of the tube that the eye of +the observer must be placed when the telescope is pointed to the +skies. But in Lord Rosse's telescope you would look in vain for +these glasses, and it is not at the lower end of the instrument that +you are to take your station when you are going to make your +observations. The astronomer at Parsonstown has rather to avail +himself of the ingenious system of staircases and galleries, by which +he is enabled to obtain access to the mouth of the great tube. The +colossal telescope which swings between the great walls, like +Herschel's great telescope already mentioned, is a reflector, the +original invention of which is due of course to Newton. The optical +work which is accomplished by the lenses in the ordinary telescope is +effected in the type of instrument constructed by Lord Rosse by a +reflecting mirror which is placed at the lower end of the vast tube. +The mirror in this instrument is made of a metal consisting of two +parts of copper to one of tin. As we have already seen, this mixture +forms an alloy of a very peculiar nature. The copper and the tin +both surrender their distinctive qualities, and unite to form a +material of a very different physical character. The copper is tough +and brown, the tin is no doubt silvery in hue, but soft and almost +fibrous in texture. When the two metals are mixed together in the +proportions I have stated, the alloy obtained is intensely hard and +quite brittle being in both these respects utterly unlike either of +the two ingredients of which it is composed. It does, however, +resemble the tin in its whiteness, but it acquires a lustre far +brighter than tin; in fact, this alloy hardly falls short of silver +itself in its brilliance when polished.</p> + +<p><a name="lord_rosse_telescope" id="lord_rosse_telescope"></a></p> + +<div class="figcenter" style="width: 641px;"> +<a href="images/ill_rosse_telescope.jpg"> +<img src="images/ill_rosse_telescope_sml.jpg" width="641" height="475" alt="LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin." title="" /></a> +<span class="caption">LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin.</span> +</div> + +<p>The first duty that Lord Rosse had to undertake was the construction +of this tremendous mirror, six feet across, and about four or five +inches thick. The dimensions were far in excess of those which had +been contemplated in any previous attempt of the same kind. Herschel +had no doubt fashioned one mirror of four feet in diameter, and many +others of smaller dimensions, but the processes which he employed had +never been fully published, and it was obvious that, with a large +increase in dimensions, great additional difficulties had to be +encountered. Difficulties began at the very commencement of the +process, and were experienced in one form or another at every +subsequent stage. In the first place, the mere casting of a great +disc of this mixture of tin and copper, weighing something like three +or four tons, involved very troublesome problems. No doubt a casting +of this size, if the material had been, for example, iron, would have +offered no difficulties beyond those with which every practical +founder is well acquainted, and which he has to encounter daily in +the course of his ordinary work. But speculum metal is a material of +a very intractable description. There is, of course, no practical +difficulty in melting the copper, nor in adding the proper proportion +of tin when the copper has been melted. There may be no great +difficulty in arranging an organization by which several crucibles, +filled with the molten material, shall be poured simultaneously so as +to obtain the requisite mass of metal, but from this point the +difficulties begin. For speculum metal when cold is excessively +brittle, and were the casting permitted to cool like an ordinary +copper or iron casting, the mirror would inevitably fly into pieces. +Lord Rosse, therefore, found it necessary to anneal the casting with +extreme care by allowing it to cool very slowly. This was +accomplished by drawing the disc of metal as soon as it had entered +into the solid state, though still glowing red, into an annealing +oven. There the temperature was allowed to subside so gradually, +that six weeks elapsed before the mirror had reached the temperature +of the external air. The necessity for extreme precaution in the +operation of annealing will be manifest if we reflect on one of the +accidents which happened. On a certain occasion, after the cooling +of a great casting had been completed, it was found, on withdrawing +the speculum, that it was cracked into two pieces. This mishap was +eventually traced to the fact that one of the walls of the oven had +only a single brick in its thickness, and that therefore the heat had +escaped more easily through that side than through the other sides +which were built of double thickness. The speculum had, +consequently, not cooled uniformly, and hence the fracture had +resulted. Undeterred, however, by this failure, as well as by not a +few other difficulties, into a description of which we cannot now +enter, Lord Rosse steadily adhered to his self-imposed task, and at +last succeeded in casting two perfect discs on which to commence the +tedious processes of grinding and polishing. The magnitude of the +operations involved may perhaps be appreciated if I mention that the +value of the mere copper and tin entering into the composition of +each of the mirrors was about 500 pounds.</p> + +<p>In no part of his undertaking was Lord Rosse's mechanical ingenuity +more taxed than in the devising of the mechanism for carrying out the +delicate operations of grinding and polishing the mirrors, whose +casting we have just mentioned. In the ordinary operations of the +telescope-maker, such processes had hitherto been generally effected +by hand, but, of course, such methods became impossible when dealing +with mirrors which were as large as a good-sized dinner table, and +whose weight was measured by tons. The rough grinding was effected +by means of a tool of cast iron about the same size as the mirror, +which was moved by suitable machinery both backwards and forwards, +and round and round, plenty of sand and water being supplied between +the mirror and the tool to produce the necessary attrition. As the +process proceeded and as the surface became smooth, emery was used +instead of sand; and when this stage was complete, the grinding tool +was removed and the polishing tool was substituted. The essential +part of this was a surface of pitch, which, having been temporarily +softened by heat, was then placed on the mirror, and accepted from +the mirror the proper form. Rouge was then introduced as the +polishing powder, and the operation was continued about nine hours, +by which time the great mirror had acquired the appearance of highly +polished silver. When completed, the disc of speculum metal was +about six feet across and four inches thick. The depression in the +centre was about half an inch. Mounted on a little truck, the great +speculum was then conveyed to the instrument, to be placed in its +receptacle at the bottom of the tube, the length of which was sixty +feet, this being the focal distance of the mirror. Another small +reflector was inserted in the great tube sideways, so as to direct +the gaze of the observer down upon the great reflector. Thus was +completed the most colossal instrument for the exploration of the +heavens which the art of man has ever constructed.</p> + +<p><a name="roman" id="roman"></a></p> + +<div class="figcenter" style="width: 655px;"> +<a href="images/ill_church_parsonstown.jpg"> +<img src="images/ill_church_parsonstown_sml.jpg" width="655" height="483" alt="ROMAN CATHOLIC CHURCH AT PARSONSTOWN." title="" /></a> +<span class="caption">ROMAN CATHOLIC CHURCH AT PARSONSTOWN.</span> +</div> + +<p>It was once my privilege to be one of those to whom the illustrious +builder of the great telescope entrusted its use. For two seasons in +1865 and 1866 I had the honour of being Lord Rosse's astronomer. +During that time I passed many a fine night in the observer's +gallery, examining different objects in the heavens with the aid of +this remarkable instrument. At the time I was there, the objects +principally studied were the nebulae, those faint stains of light +which lie on the background of the sky. Lord Rosse's telescope was +specially suited for the scrutiny of these objects, inasmuch as their +delicacy required all the light-grasping power which could be +provided.</p> + +<p>One of the greatest discoveries made by Lord Rosse, when his huge +instrument was first turned towards the heavens, consisted in the +detection of the spiral character of some of the nebulous forms. +When the extraordinary structure of these objects was first +announced, the discovery was received with some degree of +incredulity. Other astronomers looked at the same objects, and when +they failed to discern—and they frequently did fail to discern—the +spiral structure which Lord Rosse had indicated, they drew the +conclusion that this spiral structure did not exist. They thought it +must be due possibly to some instrumental defect or to the +imagination of the observer. It was, however, hardly possible for +any one who was both willing and competent to examine into the +evidence, to doubt the reality of Lord Rosse's discoveries. It +happens, however, that they have been recently placed beyond all +doubt by testimony which it is impossible to gainsay. A witness +never influenced by imagination has now come forward, and the +infallible photographic plate has justified Lord Rosse. Among the +remarkable discoveries which Dr. Isaac Roberts has recently made in +the application of his photographic apparatus to the heavens, there +is none more striking than that which declares, not only that the +nebulae which Lord Rosse described as spirals, actually do possess +the character so indicated, but that there are many others of the +same description. He has even brought to light the astonishingly +interesting fact that there are invisible objects of this class which +have never been seen by human eye, but whose spiral character is +visible to the peculiar delicacy of the photographic telescope.</p> + +<p>In his earlier years, Lord Rosse himself used to be a diligent +observer of the heavenly bodies with the great telescope which was +completed in the year 1845. But I think that those who knew Lord +Rosse well, will agree that it was more the mechanical processes +incidental to the making of the telescope which engaged his interest +than the actual observations with the telescope when it was +completed. Indeed one who was well acquainted with him believed Lord +Rosse's special interest in the great telescope ceased when the last +nail had been driven into it. But the telescope was never allowed to +lie idle, for Lord Rosse always had associated with him some ardent +young astronomer, whose delight it was to employ to the uttermost the +advantages of his position in exploring the wonders of the sky. Among +those who were in this capacity in the early days of the great +telescope, I may mention my esteemed friend Dr. Johnston Stoney.</p> + +<p>Such was the renown of Lord Rosse himself, brought about by his +consummate mechanical genius and his astronomical discoveries, and +such the interest which gathered around the marvellous workshops at +Birr castle, wherein his monumental exhibitions of optical skill were +constructed, that visitors thronged to see him from all parts of the +world. His home at Parsonstown became one of the most remarkable +scientific centres in Great Britain; thither assembled from time to +time all the leading men of science in the country, as well as many +illustrious foreigners. For many years Lord Rosse filled with marked +distinction the exalted position of President of the Royal Society, +and his advice and experience in practical mechanical matters were +always at the disposal of those who sought his assistance. Personally +and socially Lord Rosse endeared himself to all with whom he came in +contact. I remember one of the attendants telling me that on one +occasion he had the misfortune to let fall and break one of the small +mirrors on which Lord Rosse had himself expended many hours of hard +personal labour. The only remark of his lordship was that "accidents +will happen."</p> + +<p>The latter years of his life Lord Rosse passed in comparative +seclusion; he occasionally went to London for a brief sojourn during +the season, and he occasionally went for a cruise in his yacht; but +the greater part of the year he spent at Birr Castle, devoting +himself largely to the study of political and social questions, and +rarely going outside the walls of his demesne, except to church on +Sunday mornings. He died on October 31, 1867.</p> + +<p>He was succeeded by his eldest son, the present Earl of Rosse, who +has inherited his father's scientific abilities, and done much +notable work with the great telescope.</p> + +<h3><a name="AIRY" id="AIRY"></a>AIRY.</h3> +<p>In our sketch of the life of Flamsteed, we have referred to the +circumstances under which the famous Observatory that crowns +Greenwich Hill was founded. We have also had occasion to mention +that among the illustrious successors of Flamsteed both Halley and +Bradley are to be included. But a remarkable development of +Greenwich Observatory from the modest establishment of early days +took place under the direction of the distinguished astronomer whose +name is at the head of this chapter. By his labours this temple of +science was organised to such a degree of perfection that it has +served in many respects as a model for other astronomical +establishments in various parts of the world. An excellent account +of Airy's career has been given by Professor H. H. Turner, in the +obituary notice published by the Royal Astronomical Society. To this +I am indebted for many of the particulars here to be set down +concerning the life of the illustrious Astronomer Royal.</p> + +<p>The family from which Airy took his origin came from Kentmere, in +Westmoreland. His father, William Airy, belonged to a Lincolnshire +branch of the same stock. His mother's maiden name was Ann Biddell, +and her family resided at Playford, near Ipswich. William Airy held +some small government post which necessitated an occasional change of +residence to different parts of the country, and thus it was that his +son, George Biddell, came to be born at Alnwick, on 27th July, 1801. +The boy's education, so far as his school life was concerned was +partly conducted at Hereford and partly at Colchester. He does not, +however, seem to have derived much benefit from the hours which he +passed in the schoolroom. But it was delightful to him to spend his +holidays on the farm at Playford, where his uncle, Arthur Biddell, +showed him much kindness. The scenes of his early youth remained +dear to Airy throughout his life, and in subsequent years he himself +owned a house at Playford, to which it was his special delight to +resort for relaxation during the course of his arduous career. In +spite of the defects of his school training he seems to have +manifested such remarkable abilities that his uncle decided to enter +him in Cambridge University. He accordingly joined Trinity College +as a sizar in 1819, and after a brilliant career in mathematical and +physical science he graduated as Senior Wrangler in 1823. It may be +noted as an exceptional circumstance that, notwithstanding the +demands on his time in studying for his tripos, he was able, after +his second term of residence, to support himself entirely by taking +private pupils. In the year after he had taken his degree he was +elected to a Fellowship at Trinity College.</p> + +<p>Having thus gained an independent position, Airy immediately entered +upon that career of scientific work which he prosecuted without +intermission almost to the very close of his life. One of his most +interesting researches in these early days is on the subject of +Astigmatism, which defect he had discovered in his own eyes. His +investigations led him to suggest a means of correcting this defect +by using a pair of spectacles with lenses so shaped as to counteract +the derangement which the astigmatic eye impressed upon the rays of +light. His researches on this subject were of a very complete +character, and the principles he laid down are to the present day +practically employed by oculists in the treatment of this +malformation.</p> + +<p>On the 7th of December, 1826, Airy was elected to the Lucasian +Professorship of Mathematics in the University of Cambridge, the +chair which Newton's occupancy had rendered so illustrious. His +tenure of this office only lasted for two years, when he exchanged it +for the Plumian Professorship. The attraction which led him to +desire this change is doubtless to be found in the circumstance that +the Plumian Professorship of Astronomy carried with it at that time +the appointment of director of the new astronomical observatory, the +origin of which must now be described.</p> + +<p>Those most interested in the scientific side of University life +decided in 1820 that it would be proper to found an astronomical +observatory at Cambridge. Donations were accordingly sought for this +purpose, and upwards of 6,000 pounds were contributed by members of +the University and the public. To this sum 5,000 pounds were added +by a grant from the University chest, and in 1824 further sums +amounting altogether to 7,115 pounds were given by the University for +the same object. The regulations as to the administration of the new +observatory placed it under the management of the Plumian Professor, +who was to be provided with two assistants. Their duties were to +consist in making meridian observations of the sun, moon, and the +stars, and the observations made each year were to be printed and +published. The observatory was also to be used in the educational +work of the University, for it was arranged that smaller instruments +were to be provided by which students could be instructed in the +practical art of making astronomical observations.</p> + +<p>The building of the Cambridge Astronomical Observatory was completed +in 1824, but in 1828, when Airy entered on the discharge of his +duties as Director, the establishment was still far from completion, +in so far as its organisation was concerned. Airy commenced his work +so energetically that in the next year after his appointment he was +able to publish the first volume of "Cambridge Astronomical +Observations," notwithstanding that every part of the work, from the +making of observations to the revising of the proof-sheets, had to be +done by himself.</p> + +<p>It may here be remarked that these early volumes of the publications +of the Cambridge Observatory contained the first exposition of those +systematic methods of astronomical work which Airy afterwards +developed to such a great extent at Greenwich, and which have been +subsequently adopted in many other places. No more profitable +instruction for the astronomical beginner can be found than that +which can be had by the study of these volumes, in which the Plumian +Professor has laid down with admirable clearness the true principles +on which meridian work should be conducted.</p> + +<p><a name="sir_airy" id="sir_airy"></a></p> + +<div class="figcenter" style="width: 451px;"> +<a href="images/ill_george_airy.jpg"> +<img src="images/ill_george_airy_sml.jpg" width="451" height="517" alt="SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich." title="" /></a> +<span class="caption">SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich.</span> +</div> + +<p>Airy gradually added to the instruments with which the observatory +was originally equipped. A mural circle was mounted in 1832, and in +the same year a small equatorial was erected by Jones. This was made +use of by Airy in a well-known series of observations of Jupiter's +fourth satellite for the determination of the mass of the great +planet. His memoir on this subject fully ex pounds the method of +finding the weight of a planet from observations of the movements of +a satellite by which the planet is attended. This is, indeed, a +valuable investigation which no student of astronomy can afford to +neglect. The ardour with which Airy devoted himself to astronomical +studies may be gathered from a remarkable report on the progress of +astronomy during the present century, which he communicated to the +British Association at its second meeting in 1832. In the early +years of his life at Cambridge his most famous achievement was +connected with a research in theoretical astronomy for which +consummate mathematical power was required. We can only give a brief +account of the Subject, for to enter into any full detail with regard +to it would be quite out of the question.</p> + +<p>Venus is a planet of about the same size and the same weight as the +earth, revolving in an orbit which lies within that described by our +globe. Venus, consequently, takes less time than the earth to +accomplish one revolution round the sun, and it happens that the +relative movements of Venus and the earth are so proportioned that in +the time in which our earth accomplishes eight of her revolutions the +other planet will have accomplished almost exactly thirteen. It, +therefore, follows that if the earth and Venus are in line with the +sun at one date, then in eight years later both planets will again be +found at the same points in their orbits. In those eight years the +earth has gone round eight times, and has, therefore, regained its +original position, while in the same period Venus has accomplished +thirteen complete revolutions, and, therefore, this planet also has +reached the same spot where it was at first. Venus and the earth, of +course, attract each other, and in consequence of these mutual +attractions the earth is swayed from the elliptic track which it +would otherwise pursue. In like manner Venus is also forced by the +attraction of the earth to revolve in a track which deviates from +that which it would otherwise follow. Owing to the fact that the sun +is of such preponderating magnitude (being, in fact, upwards of +300,000 times as heavy as either Venus or the earth), the +disturbances induced in the motion of either planet, in consequence +of the attraction of the other, are relatively insignificant to the +main controlling agency by which each of the movements is governed. +It is, however, possible under certain circumstances that the +disturbing effects produced upon one planet by the other can become +so multiplied as to produce peculiar effects which attain measurable +dimensions. Suppose that the periodic times in which the earth and +Venus revolved had no simple relation to each other, then the points +of their tracks in which the two planets came into line with the sun +would be found at different parts of the orbits, and consequently the +disturbances would to a great extent neutralise each other, and +produce but little appreciable effect. As, however, Venus and the +earth come back every eight years to nearly the same positions at the +same points of their track, an accumulative effect is produced. For +the disturbance of one planet upon the other will, of course, be +greatest when those two planets are nearest, that is, when they lie +in line with the sun and on the same side of it. Every eight years a +certain part of the orbit of the earth is, therefore, disturbed by +the attraction of Venus with peculiar vigour. The consequence is +that, owing to the numerical relation between the movements of the +planets to which I have referred, disturbing effects become +appreciable which would otherwise be too small to permit of +recognition. Airy proposed to himself to compute the effects which +Venus would have on the movement of the earth in consequence of the +circumstance that eight revolutions of the one planet required almost +the same time as thirteen revolutions of the other. This is a +mathematical inquiry of the most arduous description, but the Plumian +Professor succeeded in working it out, and he had, accordingly, the +gratification of announcing to the Royal Society that he had detected +the influence which Venus was thus able to assert on the movement of +our earth around the sun. This remarkable investigation gained for +its author the gold medal of the Royal Astronomical Society in the +year 1832.</p> + +<p>In consequence of his numerous discoveries, Airy's scientific fame +had become so well recognised that the Government awarded him a +special pension, and in 1835, when Pond, who was then Astronomer +Royal, resigned, Airy was offered the post at Greenwich. There was +in truth, no scientific inducement to the Plumian Professor to leave +the comparatively easy post he held at Cambridge, in which he had +ample leisure to devote himself to those researches which specially +interested him, and accept that of the much more arduous observatory +at Greenwich. There were not even pecuniary inducements to make the +change; however, he felt it to be his duty to accede to the request +which the Government had made that he would take up the position +which Pond had vacated, and accordingly Airy went to Greenwich as +Astronomer Royal on October 1st, 1835.</p> + +<p>He immediately began with his usual energy to organise the systematic +conduct of the business of the National Observatory. To realise one +of the main characteristics of Airy's great work at Greenwich, it is +necessary to explain a point that might not perhaps be understood +without a little explanation by those who have no practical +experience in an observatory. In the work of an establishment such +as Greenwich, an observation almost always consists of a measurement +of some kind. The observer may, for instance, be making a +measurement of the time at which a star passes across a spider line +stretched through the field of view; on another occasion his object +may be the measurement of an angle which is read off by examining +through a microscope the lines of division on a graduated circle when +the telescope is so pointed that the star is placed on a certain mark +in the field of view. In either case the immediate result of the +astronomical observation is a purely numerical one, but it rarely +happens, indeed we may say it never happens, that the immediate +numerical result which the observation gives expresses directly the +quantity which we are really seeking for. No doubt the observation +has been so designed that the quantity we want to find can be +obtained from the figures which the measurement gives, but the object +sought is not those figures, for there are always a multitude of +other influences by which those figures are affected. For example, +if an observation were to be perfect, then the telescope with which +the observation is made should be perfectly placed in the exact +position which it ought to occupy; this is, however, never the case, +for no mechanic can ever construct or adjust a telescope so perfectly +as the wants of the astronomer demand. The clock also by which we +determine the time of the observation should be correct, but this is +rarely if ever the case. We have to correct our observations for +such errors, that is to say, we have to determine the errors in the +positions of our telescopes and the errors in the going of our +clocks, and then we have to determine what the observations would +have been had our telescopes been absolutely perfect, and had our +clocks been absolutely correct. There are also many other matters +which have to be attended to in order to reduce our observations so +as to obtain from the figures as yielded to the observer at the +telescope the actual quantities which it is his object to determine.</p> + +<p>The work of effecting these reductions is generally a very intricate +and laborious matter, so that it has not unfrequently happened that +while observations have accumulated in an observatory, yet the +tedious duty of reducing these observations has been allowed to fall +into arrear. When Airy entered on his duties at Greenwich he found +there an enormous mass of observations which, though implicitly +containing materials of the greatest value to astronomers, were, in +their unreduced form, entirely unavailable for any useful purpose. +He, therefore, devoted himself to coping with the reduction of the +observations of his predecessors. He framed systematic methods by +which the reductions were to be effected, and he so arranged the work +that little more than careful attention to numerical accuracy would +be required for the conduct of the operations. Encouraged by the +Admiralty, for it is under this department that Greenwich Observatory +is placed, the Astronomer Royal employed a large force of computers +to deal with the work. BY his energy and admirable organisation he +managed to reduce an extremely valuable series of planetary +observations, and to publish the results, which have been of the +greatest importance to astronomical investigation.</p> + +<p>The Astronomer Royal was a capable, practical engineer as well as an +optician, and he presently occupied himself by designing astronomical +instruments of improved pattern, which should replace the antiquated +instruments he found in the observatory. In the course of years the +entire equipment underwent a total transformation. He ordered a +great meridian circle, every part of which may be said to have been +formed from his own designs. He also designed the mounting for a +fine equatorial telescope worked by a driving clock, which he had +himself invented. Gradually the establishment at Greenwich waxed +great under his incessant care. It was the custom for the +observatory to be inspected every year by a board of visitors, whose +chairman was the President of the Royal Society. At each annual +visitation, held on the first Saturday in June, the visitors received +a report from the Astronomer Royal, in which he set forth the +business which had been accomplished during the past year. It was on +these occasions that applications were made to the Admiralty, either +for new instruments or for developing the work of the observatory in +some other way. After the more official business of the inspection +was over, the observatory was thrown open to visitors, and hundreds +of people enjoyed on that day the privilege of seeing the national +observatory. These annual gatherings are happily still continued, +and the first Saturday in June is known to be the occasion of one of +the most interesting reunions of scientific men which takes place in +the course of the year.</p> + +<p>Airy's scientific work was, however, by no means confined to the +observatory. He interested himself largely in expeditions for the +observation of eclipses and in projects for the measurement of arcs +on the earth. He devoted much attention to the collection of magnetic +observations from various parts of the world. Especially will it be +remembered that the circumstances of the transits of Venus, which +occurred in 1874 and in 1882, were investigated by him, and under his +guidance expeditions were sent forth to observe the transits from +those localities in remote parts of the earth where observations most +suitable for the determination of the sun's distance from the earth +could be obtained. The Astronomer Royal also studied tidal +phenomena, and he rendered great service to the country in the +restoration of the standards of length and weight which had been +destroyed in the great fire at the House of Parliament in October, +1834. In the most practical scientific matters his advice was often +sought, and was as cheerfully rendered. Now we find him engaged in +an investigation of the irregularities of the compass in iron ships, +with a view to remedying its defects; now we find him reporting on +the best gauge for railways. Among the most generally useful +developments of the observatory must be mentioned the telegraphic +method for the distribution of exact time. By arrangement with the +Post Office, the astronomers at Greenwich despatch each morning a +signal from the observatory to London at ten o'clock precisely. By +special apparatus, this signal is thence distributed automatically +over the country, so as to enable the time to be known everywhere +accurately to a single second. It was part of the same system that a +time ball should be dropped daily at one o'clock at Deal, as well as +at other places, for the purpose of enabling ship's chronometers to +be regulated.</p> + +<p>Airy's writings were most voluminous, and no fewer than forty-eight +memoirs by him are mentioned in the "Catalogue of Scientific +Memoirs," published by the Royal Society up to the year 1873, and +this only included ten years out of an entire life of most +extraordinary activity. Many other subjects besides those of a +purely scientific character from time to time engaged his attention. +He wrote, for instance, a very interesting treatise on the Roman +invasion of Britain, especially with a view of determining the port +from which Caesar set forth from Gaul, and the point at which he +landed on the British coast. Airy was doubtless led to this +investigation by his study of the tidal phenomena in the Straits of +Dover. Perhaps the Astronomer Royal is best known to the general +reading public by his excellent lectures on astronomy, delivered at +the Ipswich Museum in 1848. This book has passed through many +editions, and it gives a most admirable account of the manner in +which the fundamental problems in astronomy have to be attacked.</p> + +<p>As years rolled by almost every honour and distinction that could be +conferred upon a scientific man was awarded to Sir George Airy. He +was, indeed, the recipient of other honours not often awarded for +scientific distinction. Among these we may mention that in 1875 he +received the freedom of the City of London, "as a recognition of his +indefatigable labours in astronomy, and of his eminent services in +the advancement of practical science, whereby he has so materially +benefited the cause of commerce and civilisation."</p> + +<p>Until his eightieth year Airy continued to discharge his labours at +Greenwich with unflagging energy. At last, on August 15th, 1881, he +resigned the office which he had held so long with such distinction +to himself and such benefit to his country. He had married in 1830 +the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died +in 1875, and three sons and three daughters survived him. One +daughter is the wife of Dr. Routh, of Cambridge, and his other +daughters were the constant companions of their father during the +declining years of his life. Up to the age of ninety he enjoyed +perfect physical health, but an accidental fall which then occurred +was attended with serious results. He died on Saturday, January 2nd, +1892, and was buried in the churchyard at Playford.</p> + +<h3><a name="HAMILTON" id="HAMILTON"></a>HAMILTON.</h3> +<p>William Rowan Hamilton was born at midnight between the 3rd and 4th +of August, 1805, at Dublin, in the house which was then 29, but +subsequently 36, Dominick Street. His father, Archibald Hamilton, +was a solicitor, and William was the fourth of a family of nine. With +reference to his descent, it may be sufficient to notice that his +ancestors appear to have been chiefly of gentle Irish families, but +that his maternal grandmother was of Scottish birth. When he was +about a year old, his father and mother decided to hand over the +education of the child to his uncle, James Hamilton, a clergyman of +Trim, in County Meath. James Hamilton's sister, Sydney, resided with +him, and it was in their home that the days of William's childhood +were passed.</p> + +<p>In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of +letters will be found, in which Aunt Sydney details the progress of +the boy to his mother in Dublin. Probably there is no record of an +infant prodigy more extraordinary than that which these letters +contain. At three years old his aunt assured the mother that William +is "a hopeful blade," but at that time it was his physical vigour to +which she apparently referred; for the proofs of his capacity, which +she adduces, related to his prowess in making boys older than himself +fly before him. In the second letter, a month later, we hear that +William is brought in to read the Bible for the purpose of putting to +shame other boys double his age who could not read nearly so well. +Uncle James appears to have taken much pains with William's +schooling, but his aunt said that "how he picks up everything is +astonishing, for he never stops playing and jumping about." When he +was four years and three months old, we hear that he went out to dine +at the vicar's, and amused the company by reading for them equally +well whether the book was turned upside down or held in any other +fashion. His aunt assures the mother that "Willie is a most sensible +little creature, but at the same time has a great deal of roguery." +At four years and five months old he came up to pay his mother a +visit in town, and she writes to her sister a description of the +boy;—</p> + +<p>"His reciting is astonishing, and his clear and accurate knowledge of +geography is beyond belief; he even draws the countries with a pencil +on paper, and will cut them out, though not perfectly accurate, yet +so well that a anybody knowing the countries could not mistake them; +but, you will think this nothing when I tell you that he reads Latin, +Greek, and Hebrew."</p> + +<p>Aunt Sydney recorded that the moment Willie got back to Trim he was +desirous of at once resuming his former pursuits. He would not eat +his breakfast till his uncle had heard him his Hebrew, and he +comments on the importance of proper pronunciation. At five he was +taken to see a friend, to whom he repeated long passages from +Dryden. A gentleman present, who was not unnaturally sceptical about +Willie's attainments, desired to test him in Greek, and took down a +copy of Homer which happened to have the contracted type, and to his +amazement Willie went on with the greatest ease. At six years and +nine months he was translating Homer and Virgil; a year later his +uncle tells us that William finds so little difficulty in learning +French and Italian, that he wishes to read Homer in French. He is +enraptured with the Iliad, and carries it about with him, repeating +from it whatever particularly pleases him. At eight years and one +month the boy was one of a party who visited the Scalp in the Dublin +mountains, and he was so delighted with the scenery that he forthwith +delivered an oration in Latin. At nine years and six months he is +not satisfied until he learns Sanscrit; three months later his thirst +for the Oriental languages is unabated, and at ten years and four +months he is studying Arabic and Persian. When nearly twelve he +prepared a manuscript ready for publication. It was a "Syriac +Grammar," in Syriac letters and characters compiled from that of +Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was +fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a +visit to Dublin, and, as a practical exercise in his Oriental +languages, the young scholar addressed to his Excellency a letter in +Persian; a translation of which production is given by Mr. Graves. +When William was fourteen he had the misfortune to lose his father; +and he had lost his mother two years previously. The boy and his +three sisters were kindly provided for by different members of the +family on both sides.</p> + +<p>It was when William was about fifteen that his attention began to be +turned towards scientific subjects. These were at first regarded +rather as a relaxation from the linguistic studies with which he had +been so largely occupied. On November 22nd, 1820, he notes in his +journal that he had begun Newton's "Principia": he commenced also the +study of astronomy by observing eclipses, occultations, and similar +phenomena. When he was sixteen we learn that he had read conic +sections, and that he was engaged in the study of pendulums. After +an attack of illness, he was moved for change to Dublin, and in May, +1822, we find him reading the differential calculus and Laplace's +"Mecanique Celeste." He criticises an important part of Laplace's +work relative to the demonstration of the parallelogram of forces. In +this same year appeared the first gushes of those poems which +afterwards flowed in torrents.</p> + +<p>His somewhat discursive studies had, however, now to give place to a +more definite course of reading in preparation for entrance to the +University of Dublin. The tutor under whom he entered, Charles +Boyton, was himself a distinguished man, but he frankly told the +young William that he could be of little use to him as a tutor, for +his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom +this is recorded, adds, "But there is one thing which Boyton would +promise to be to him, and that was a FRIEND; and that one proof he +would give of this should be that, if ever he saw William beginning +to be UPSET by the sensation he would excite, and the notice he would +attract, he would tell him of it." At the beginning of his college +career he distanced all his competitors in every intellectual +pursuit. At his first term examination in the University he was +first in Classics and first in Mathematics, while he received the +Chancellor's prize for a poem on the Ionian Islands, and another for +his poem on Eustace de St. Pierre.</p> + +<p>There is abundant testimony that Hamilton had "a heart for friendship +formed." Among the warmest of the friends whom he made in these +early days was the gifted Maria Edgeworth, who writes to her sister +about "young Mr. Hamilton, an admirable Crichton of eighteen, a real +prodigy of talents, who Dr. Brinkley says may be a second Newton, +quiet, gentle, and simple." His sister Eliza, to whom he was +affectionately attached, writes to him in 1824:—</p> + +<p>"I had been drawing pictures of you in my mind in your study at +Cumberland Street with 'Xenophon,' &c., on the table, and you, with +your most awfully sublime face of thought, now sitting down, and now +walking about, at times rubbing your hands with an air of +satisfaction, and at times bursting forth into some very heroical +strain of poetry in an unknown language, and in your own internal +solemn ventriloquist-like voice, when you address yourself to the +silence and solitude of your own room, and indeed, at times, even +when your mysterious poetical addresses are not quite unheard."</p> + +<p>This letter is quoted because it refers to a circumstance which all +who ever met with Hamilton, even in his latest years, will remember. +He was endowed with two distinct voices, one a high treble, the other +a deep bass, and he alternately employed these voices not only in +ordinary conversation, but when he was delivering an address on the +profundities of Quaternions to the Royal Irish Academy, or on +similar occasions. His friends had long grown so familiar with this +peculiarity that they were sometimes rather surprised to find how +ludicrous it appeared to strangers.</p> + +<p>Hamilton was fortunate in finding, while still at a very early age, a +career open before him which was worthy of his talents. He had not +ceased to be an undergraduate before he was called to fill an +illustrious chair in his university. The circumstances are briefly +as follows.</p> + +<p>We have already mentioned that, in 1826, Brinkley was appointed +Bishop of Cloyne, and the professorship of astronomy thereupon became +vacant. Such was Hamilton's conspicuous eminence that, +notwithstanding he was still an undergraduate, and had only just +completed his twenty-first year, he was immediately thought of as a +suitable successor to the chair. Indeed, so remarkable were his +talents in almost every direction that had the vacancy been in the +professorship of classics or of mathematics, of English literature or +of metaphysics, of modern or of Oriental languages, it seems +difficult to suppose that he would not have occurred to every one as +a possible successor. The chief ground, however, on which the +friends of Hamilton urged his appointment was the earnest of original +power which he had already shown in a research on the theory of +Systems of Rays. This profound work created a new branch of optics, +and led a few years later to a superb discovery, by which the fame of +its author became world-wide.</p> + +<p>At first Hamilton thought it would be presumption for him to apply +for so exalted a position; he accordingly retired to the country, and +resumed his studies for his degree. Other eminent candidates came +forward, among them some from Cambridge, and a few of the Fellows +from Trinity College, Dublin, also sent in their claims. It was not +until Hamilton received an urgent letter from his tutor Boyton, in +which he was assured of the favourable disposition of the Board +towards his candidature, that he consented to come forward, and on +June 16th, 1827, he was unanimously chosen to succeed the Bishop of +Cloyne as Professor of Astronomy in the University. The appointment +met with almost universal approval. It should, however, be noted +that Brinkley, whom Hamilton succeeded, did not concur in the general +sentiment. No one could have formed a higher opinion than he had +done of Hamilton's transcendent powers; indeed, it was on that very +ground that he seemed to view the appointment with disapprobation. +He considered that it would have been wiser for Hamilton to have +obtained a Fellowship, in which capacity he would have been able to +exercise a greater freedom in his choice of intellectual pursuits. +The bishop seems to have thought, and not without reason, that +Hamilton's genius would rather recoil from much of the routine work +of an astronomical establishment. Now that Hamilton's whole life is +before us, it is easy to see that the bishop was entirely wrong. It +is quite true that Hamilton never became a skilled astronomical +observer; but the seclusion of the observatory was eminently +favourable to those gigantic labours to which his life was devoted, +and which have shed so much lustre, not only on Hamilton himself, but +also on his University and his country.</p> + +<p>In his early years at Dunsink, Hamilton did make some attempts at a +practical use of the telescopes, but he possessed no natural aptitude +for such work, while exposure which it involved seems to have acted +injuriously on his health. He, therefore, gradually allowed his +attention to be devoted to those mathematical researches in which he +had already given such promise of distinction. Although it was in +pure mathematics that he ultimately won his greatest fame, yet he +always maintained and maintained with justice, that he had ample +claims to the title of an astronomer. In his later years he set +forth this position himself in a rather striking manner. De Morgan +had written commending to Hamilton's notice Grant's "History of +Physical Astronomy." After becoming acquainted with the book, +Hamilton writes to his friend as follows:—</p> + +<p>"The book is very valuable, and very creditable to its composer. But +your humble servant may be pardoned if he finds himself somewhat +amused at the title, 'History of Physical Astronomy from the Earliest +Ages to the Middle of the Nineteenth Century,' when he fails to +observe any notice of the discoveries of Sir W. R. Hamilton in the +theory of the 'Dynamics of the Heavens.'"</p> + +<p>The intimacy between the two correspondents will account for the tone +of this letter; and, indeed, Hamilton supplies in the lines which +follow ample grounds for his complaint. He tells how Jacobi spoke of +him in Manchester in 1842 as "le Lagrange de votre pays," and how +Donkin had said that, "The Analytical Theory of Dynamics as it exists +at present is due mainly to the labours of La Grange Poisson, +Sir W. R. Hamilton, and Jacobi, whose researches on this subject +present a series of discoveries hardly paralleled for their elegance +and importance in any other branch of mathematics." In the same +letter Hamilton also alludes to the success which had attended the +applications of his methods in other hands than his own to the +elucidation of the difficult subject of Planetary Perturbations. +Even had his contributions to science amounted to no more than these +discoveries, his tenure of the chair would have been an illustrious +one. It happens, however, that in the gigantic mass of his +intellectual work these researches, though intrinsically of such +importance, assume what might almost be described as a relative +insignificance.</p> + +<p>The most famous achievement of Hamilton's earlier years at the +observatory was the discovery of conical refraction. This was one of +those rare events in the history of science, in which a sagacious +calculation has predicted a result of an almost startling character, +subsequently confirmed by observation. At once this conferred on the +young professor a world-wide renown. Indeed, though he was still +only twenty-seven, he had already lived through an amount of +intellectual activity which would have been remarkable for a man of +threescore and ten.</p> + +<p>Simultaneously with his growth in fame came the growth of his several +friendships. There were, in the first place, his scientific +friendships with Herschel, Robinson, and many others with whom he had +copious correspondence. In the excellent biography to which I have +referred, Hamilton's correspondence with Coleridge may be read, as +can also the letters to his lady correspondents, among them being +Maria Edgeworth, Lady Dunraven, and Lady Campbell. Many of these +sheets relate to literary matters, but they are largely intermingled +With genial pleasantry, and serve at all events to show the affection +and esteem with which he was regarded by all who had the privilege of +knowing him. There are also the letters to the sisters whom he +adored, letters brimming over with such exalted sentiment, that most +ordinary sisters would be tempted to receive them with a smile in the +excessively improbable event of their still more ordinary brothers +attempting to pen such effusions. There are also indications of +letters to and from other young ladies who from time to time were the +objects of Hamilton's tender admiration. We use the plural +advisedly, for, as Mr. Graves has set forth, Hamilton's love affairs +pursued a rather troubled course. The attention which he lavished on +one or two fair ones was not reciprocated, and even the intense +charms of mathematical discovery could not assuage the pangs which +the disappointed lover experienced. At last he reached the haven of +matrimony in 1833, when he was married to Miss Bayly. Of his married +life Hamilton said, many years later to De Morgan, that it was as +happy as he expected, and happier than he deserved. He had two sons, +William and Archibald, and one daughter, Helen, who became the wife +of Archdeacon O'Regan.</p> + +<p><a name="rowan_hamilton" id="rowan_hamilton"></a></p> + +<div class="figcenter" style="width: 418px;"> +<a href="images/ill_rowan_hamilton.jpg"> +<img src="images/ill_rowan_hamilton_sml.jpg" width="418" height="479" alt="SIR W. ROWAN HAMILTON." title="" /></a> +<span class="caption">SIR W. ROWAN HAMILTON.</span> +</div> + +<p>The most remarkable of Hamilton's friendships in his early years was +unquestionably that with Wordsworth. It commenced with Hamilton's +visit to Keswick; and on the first evening, when the poet met the +young mathematician, an incident occurred which showed the mutual +interest that was aroused. Hamilton thus describes it in a letter to +his sister Eliza:—</p> + +<p>"He (Wordsworth) walked back with our party as far as their lodge, +and then, on our bidding Mrs. Harrison good-night, I offered to walk +back with him while my party proceeded to the hotel. This offer he +accepted, and our conversation had become so interesting that when we +had arrived at his home, a distance of about a mile, he proposed to +walk back with me on my way to Ambleside, a proposal which you may be +sure I did not reject; so far from it that when he came to turn once +more towards his home I also turned once more along with him. It was +very late when I reached the hotel after all this walking."</p> + +<p>Hamilton also submitted to Wordsworth an original poem, entitled +"It Haunts me Yet." The reply of Wordsworth is worth repeating:—</p> + +<p>"With a safe conscience I can assure you that, in my judgment, your +verses are animated with the poetic spirit, as they are evidently the +product of strong feeling. The sixth and seventh stanzas affected me +much, even to the dimming of my eyes and faltering of my voice while +I was reading them aloud. Having said this, I have said enough. Now +for the per contra. You will not, I am sure, be hurt when I tell you +that the workmanship (what else could be expected from so young a +writer?) is not what it ought to be. . .</p> + +<p>"My household desire to be remembered to you in no formal way. +Seldom have I parted—never, I was going to say—with one whom after +so short an acquaintance I lost sight of with more regret. I trust +we shall meet again."</p> + +<p>The further affectionate intercourse between Hamilton and Wordsworth +is fully set forth, and to Hamilton's latest years a recollection of +his "Rydal hours" was carefully treasured and frequently referred +to. Wordsworth visited Hamilton at the observatory, where a +beautiful shady path in the garden is to the present day spoken of as +"Wordsworth's Walk."</p> + +<p>It was the practice of Hamilton to produce a sonnet on almost every +occasion which admitted of poetical treatment, and it was his delight +to communicate his verses to his friends all round. When Whewell was +producing his "Bridgewater Treatises," he writes to Hamilton in +1833:—</p> + +<p>"Your sonnet which you showed me expressed much better than I could +express it the feeling with which I tried to write this book, and I +once intended to ask your permission to prefix the sonnet to my book, +but my friends persuaded me that I ought to tell my story in my own +prose, however much better your verse might be."</p> + +<p>The first epoch-marking contribution to Theoretical Dynamics after +the time of Newton was undoubtedly made by Lagrange, in his discovery +of the general equations of Motion. The next great step in the same +direction was that taken by Hamilton in his discovery of a still more +comprehensive method. Of this contribution Hamilton writes to +Whewell, March 31st, 1834:—</p> + +<p>"As to my late paper, a day or two ago sent off to London, it is +merely mathematical and deductive. I ventured, indeed, to call it +the 'Mecanique Analytique' of Lagrange, 'a scientific poem'; and +spoke of Dynamics, or the Science of Force, as treating of 'Power +acting by Law in Space and Time.' In other respects it is as +unpoetical and unmetaphysical as my gravest friends could desire."</p> + +<p>It may well be doubted whether there is a more beautiful chapter in +the whole of mathematical philosophy than that which contains +Hamilton's dynamical theory. It is disfigured by no tedious +complexity of symbols; it condescends not to any particular problems; +it is an all embracing theory, which gives an intellectual grasp of +the most appropriate method for discovering the result of the +application of force to matter. It is the very generality of this +doctrine which has somewhat impeded the applications of which it is +susceptible. The exigencies of examinations are partly responsible +for the fact that the method has not become more familiar to students +of the higher mathematics. An eminent professor has complained that +Hamilton's essay on dynamics was of such an extremely abstract +character, that he found himself unable to extract from it problems +suitable for his examination papers.</p> + +<p>The following extract is from a letter of Professor Sylvester to +Hamilton, dated 20th of September, 1841. It will show how his works +were appreciated by so consummate a mathematician as the writer:—</p> + +<p>"Believe me, sir, it is not the least of my regrets in quitting this +empire to feel that I forego the casual occasion of meeting those +masters of my art, yourself chief amongst the number, whose +acquaintance, whose conversation, or even notice, have in themselves +the power to inspire, and almost to impart fresh vigour to the +understanding, and the courage and faith without which the efforts of +invention are in vain. The golden moments I enjoyed under your +hospitable roof at Dunsink, or moments such as they were, may +probably never again fall to my lot.</p> + +<p>"At a vast distance, and in an humble eminence, I still promise myself +the calm satisfaction of observing your blazing course in the +elevated regions of discovery. Such national honour as you are able +to confer on your country is, perhaps, the only species of that +luxury for the rich (I mean what is termed one's glory) which is not +bought at the expense of the comforts of the million."</p> + +<p>The study of metaphysics was always a favourite recreation when +Hamilton sought for a change from the pursuit of mathematics. In the +year 1834 we find him a diligent student of Kant; and, to show the +views of the author of Quaternions and of Algebra as the Science of +Pure Time on the "Critique of the Pure Reason," we quote the +following letter, dated 18th of July, 1834, from Hamilton to Viscount +Adare:—</p> + +<p>"I have read a large part of the 'Critique of the Pure Reason,' and +find it wonderfully clear, and generally quite convincing. +Notwithstanding some previous preparation from Berkeley, and from my +own thoughts, I seem to have learned much from Kant's own statement +of his views of 'Space and Time.' Yet, on the whole, a large part of +my pleasure consists in recognising through Kant's works, opinions, +or rather views, which have been long familiar to myself, although +far more clearly and systematically expressed and combined by him. +. . . Kant is, I think, much more indebted than he owns, or, perhaps +knows, to Berkeley, whom he calls by a sneer, 'GUTEM Berkeley'. . . +as it were, 'good soul, well meaning man,' who was able for all that +to shake to its centre the world of human thought, and to effect a +revolution among the early consequences of which was the growth of +Kant himself."</p> + +<p>At several meetings of the British Association Hamilton was a very +conspicuous figure. Especially was this the case in 1835, when the +Association met in Dublin, and when Hamilton, though then but thirty +years old, had attained such celebrity that even among a very +brilliant gathering his name was perhaps the most renowned. A +banquet was given at Trinity College in honour of the meeting. The +distinguished visitors assembled in the Library of the University. +The Earl of Mulgrave, then Lord Lieutenant of Ireland, made this the +opportunity of conferring on Hamilton the honour of knighthood, +gracefully adding, as he did so: "I but set the royal, and therefore +the national mark, on a distinction already acquired by your genius +and labours."</p> + +<p>The banquet followed, writes Mr. Graves. "It was no little addition +to the honour Hamilton had already received that, when Professor +Whewell returned thanks for the toast of the University of Cambridge, +he thought it appropriate to add the words, 'There was one point +which strongly pressed upon him at that moment: it was now one +hundred and thirty years since a great man in another Trinity College +knelt down before his sovereign, and rose up Sir Isaac Newton.' The +compliment was welcomed by immense applause."</p> + +<p>A more substantial recognition of the labours of Hamilton took place +subsequently. He thus describes it in a letter to Mr. Graves of 14th +of November, 1843:—</p> + +<p>"The Queen has been pleased—and you will not doubt that it was +entirely unsolicited, and even unexpected, on my part—'to express +her entire approbation of the grant of a pension of two hundred +pounds per annum from the Civil List' to me for scientific services. +The letters from Sir Robert Peel and from the Lord Lieutenant of +Ireland in which this grant has been communicated or referred to have +been really more gratifying to my feelings than the addition to my +income, however useful, and almost necessary, that may have been."</p> + +<p>The circumstances we have mentioned might lead to the supposition +that Hamilton was then at the zenith of his fame but this was not +so. It might more truly be said, that his achievements up to this +point were rather the preliminary exercises which fitted him for the +gigantic task of his life. The name of Hamilton is now chiefly +associated with his memorable invention of the calculus of +Quaternions. It was to the creation of this branch of mathematics +that the maturer powers of his life were devoted; in fact he gives us +himself an illustration of how completely habituated he became to the +new modes of thought which Quaternions originated. In one of his +later years he happened to take up a copy of his famous paper on +Dynamics, a paper which at the time created such a sensation among +mathematicians, and which is at this moment regarded as one of the +classics of dynamical literature. He read, he tells us, his paper +with considerable interest, and expressed his feelings of +gratification that he found himself still able to follow its +reasoning without undue effort. But it seemed to him all the time as +a work belonging to an age of analysis now entirely superseded.</p> + +<p>In order to realise the magnitude of the revolution which Hamilton +has wrought in the application of symbols to mathematical +investigation, it is necessary to think of what Hamilton did beside +the mighty advance made by Descartes. To describe the character of +the quaternion calculus would be unsuited to the pages of this work, +but we may quote an interesting letter, written by Hamilton from his +death-bed, twenty-two years later, to his son Archibald, in which he +has recorded the circumstances of the discovery:—</p> + +<p>"Indeed, I happen to be able to put the finger of memory upon the year +and month—October, 1843—when having recently returned from visits +to Cork and Parsonstown, connected with a meeting of the British +Association, the desire to discover the laws of multiplication +referred to, regained with me a certain strength and earnestness +which had for years been dormant, but was then on the point of being +gratified, and was occasionally talked of with you. Every morning in +the early part of the above-cited month, on my coming down to +breakfast, your (then) little brother William Edwin, and yourself, +used to ask me, 'Well papa, can you multiply triplets?' Whereto I +was always obliged to reply, with a sad shake of the head: 'No, I +can only ADD and subtract them,'</p> + +<p>"But on the 16th day of the same month—which happened to be Monday, +and a Council day of the Royal Irish Academy—I was walking in to +attend and preside, and your mother was walking with me along the +Royal Canal, to which she had perhaps driven; and although she talked +with me now and then, yet an UNDERCURRENT of thought was going on in +my mind which gave at last a RESULT, whereof it is not too much to +say that I felt AT ONCE the importance. An ELECTRIC circuit seemed +to CLOSE; and a spark flashed forth the herald (as I FORESAW +IMMEDIATELY) of many long years to come of definitely directed +thought and work by MYSELF, if spared, and, at all events, on the +part of OTHERS if I should even be allowed to live long enough +distinctly to communicate the discovery. Nor could I resist the +impulse—unphilosophical as it may have been—to cut with a knife on +a stone of Brougham Bridge as we passed it, the fundamental formula +which contains the SOLUTION of the PROBLEM, but, of course, the +inscription has long since mouldered away. A more durable notice +remains, however, on the Council Books of the Academy for that day +(October 16, 1843), which records the fact that I then asked for and +obtained leave to read a Paper on 'Quaternions,' at the First General +Meeting of the Session; which reading took place accordingly, on +Monday, the 13th of November following."</p> + +<p>Writing to Professor Tait, Hamilton gives further particulars of the +same event. And again in a letter to the Rev. J. W. Stubbs:—</p> + +<p>"To-morrow will be the fifteenth birthday of the Quaternions. They +started into life full-grown on the 16th October, 1843, as I was +walking with Lady Hamilton to Dublin, and came up to Brougham +Bridge—which my boys have since called Quaternion Bridge. I pulled +out a pocketbook which still exists, and made entry, on which at the +very moment I felt that it might be worth my while to expend the +labour of at least ten or fifteen years to come. But then it is fair +to say that this was because I felt a problem to have been at that +moment solved, an intellectual want relieved which had haunted me for +at least fifteen years before.</p> + +<p>"But did the thought of establishing such a system, in which +geometrically opposite facts—namely, two lines (or areas) which are +opposite IN SPACE give ALWAYS a positive product—ever come into +anybody's head till I was led to it in October, 1843, by trying to +extend my old theory of algebraic couples, and of algebra as the +science of pure time? As to my regarding geometrical addition of +lines as equivalent to composition of motions (and as performed by +the same rules), that is indeed essential in my theory but not +peculiar to it; on the contrary, I am only one of many who have been +led to this view of addition."</p> + +<p>Pilgrims in future ages will doubtless visit the spot commemorated by +the invention of Quaternions. Perhaps as they look at that by no +means graceful structure Quaternion Bridge, they will regret that the +hand of some Old Mortality had not been occasionally employed in +cutting the memorable inscription afresh. It is now irrecoverably +lost.</p> + +<p>It was ten years after the discovery that the great volume appeared +under the title of "Lectures on Quaternions," Dublin, 1853. The +reception of this work by the scientific world was such as might have +been expected from the extraordinary reputation of its author, and +the novelty and importance of the new calculus. His valued friend, +Sir John Herschel, writes to him in that style of which he was a +master:—</p> + +<p>"Now, most heartily let me congratulate you on getting out your +book—on having found utterance, ore rotundo, for all that labouring +and seething mass of thought which has been from time to time sending +out sparks, and gleams, and smokes, and shaking the soil about you; +but now breaks into a good honest eruption, with a lava stream and a +shower of fertilizing ashes.</p> + +<p>"Metaphor and simile apart, there is work for a twelve-month to any +man to read such a book, and for half a lifetime to digest it, and I +am glad to see it brought to a conclusion."</p> + +<p>We may also record Hamilton's own opinion expressed to Humphrey +Lloyd:—</p> + +<p>"In general, although in one sense I hope that I am actually growing +modest about the quaternions, from my seeing so many peeps and vistas +into future expansions of their principles, I still must assert that +this discovery appears to me to be as important for the middle of the +nineteenth century as the discovery of fluxions was for the close of +the seventeenth."</p> + +<p>Bartholomew Lloyd died in 1837. He had been the Provost of Trinity +College, and the President of the Royal Irish Academy. Three +candidates were put forward by their respective friends for the +vacant Presidency. One was Humphrey Lloyd, the son of the late +Provost, and the two others were Hamilton and Archbishop Whately. +Lloyd from the first urged strongly the claims of Hamilton, and +deprecated the putting forward of his own name. Hamilton in like +manner desired to withdraw in favour of Lloyd. The wish was strongly +felt by many of the Fellows of the College that Lloyd should be +elected, in consequence of his having a more intimate association +with collegiate life than Hamilton; while his scientific eminence was +world-wide. The election ultimately gave Hamilton a considerable +majority over Lloyd, behind whom the Archbishop followed at a +considerable distance. All concluded happily, for both Lloyd and the +Archbishop expressed, and no doubt felt, the pre-eminent claims of +Hamilton, and both of them cordially accepted the office of a +Vice-President, to which, according to the constitution of the +Academy, it is the privilege of the incoming President to nominate.</p> + +<p>In another chapter I have mentioned as a memorable episode in +astronomical history, that Sir J. Herschel went for a prolonged +sojourn to the Cape of Good Hope, for the purpose of submitting the +southern skies to the same scrutiny with the great telescope that his +father had given to the northern skies. The occasion of Herschel's +return after the brilliant success of his enterprise, was celebrated +by a banquet. On June 15th, 1838, Hamilton was assigned the high +honour of proposing the health of Herschel. This banquet is +otherwise memorable in Hamilton's career as being one of the two +occasions in which he was in the company of his intimate friend De +Morgan.</p> + +<p>In the year 1838 a scheme was adopted by the Royal Irish Academy for +the award of medals to the authors of papers which appeared to +possess exceptionally high merit. At the institution of the medal +two papers were named in competition for the prize. One was +Hamilton's "Memoir on Algebra, as the Science of Pure Time." The +other was Macullagh's paper on the "Laws of Crystalline Reflection +and Refraction." Hamilton expresses his gratification that, mainly +in consequence of his own exertions, he succeeded in having the medal +awarded to Macullagh rather than to himself. Indeed, it would almost +appear as if Hamilton had procured a letter from Sir J. Herschel, +which indicated the importance of Macullagh's memoir in such a way as +to decide the issue. It then became Hamilton's duty to award the +medal from the chair, and to deliver an address in which he expressed +his own sense of the excellence of Macullagh's scientific work. It +is the more necessary to allude to these points, because in the whole +of his scientific career it would seem that Macullagh was the only +man with whom Hamilton had ever even an approach to a dispute about +priority. The incident referred to took place in connection with the +discovery of conical refraction, the fame of which Macullagh made a +preposterous attempt to wrest from Hamilton. This is evidently +alluded to in Hamilton's letter to the Marquis of Northampton, dated +June 28th, 1838, in which we read:—</p> + +<p>"And though some former circumstances prevented me from applying to +the person thus distinguished the sacred name of FRIEND, I had the +pleasure of doing justice...to his high intellectual merits... I +believe he was not only gratified but touched, and may, perhaps, +regard me in future with feelings more like those which I long to +entertain towards him."</p> + +<p>Hamilton was in the habit, from time to time, of commencing the +keeping of a journal, but it does not appear to have been +systematically conducted. Whatever difficulties the biographer may +have experienced from its imperfections and irregularities, seem to +be amply compensated for by the practice which Hamilton had of +preserving copies of his letters, and even of comparatively +insignificant memoranda. In fact, the minuteness with which +apparently trivial matters were often noted down appears almost +whimsical. He frequently made a memorandum of the name of the person +who carried a letter to the post, and of the hour in which it was +despatched. On the other hand, the letters which he received were +also carefully preserved in a mighty mass of manuscripts, with which +his study was encumbered, and with which many other parts of the +house were not unfrequently invaded. If a letter was laid aside for +a few hours, it would become lost to view amid the seething mass of +papers, though occasionally, to use his own expression, it might be +seen "eddying" to the surface in some later disturbance.</p> + +<p>The great volume of "Lectures on Quaternions" had been issued, and +the author had received the honours which the completion of such a +task would rightfully bring him. The publication of an immortal work +does not, however, necessarily provide the means for paying the +printer's bill. The printing of so robust a volume was necessarily +costly; and even if all the copies could be sold, which at the time +did not seem very likely, they would hardly have met the inevitable +expenses. The provision of the necessary funds was, therefore, a +matter for consideration. The Board of Trinity College had already +contributed 200 pounds to the printing, but yet another hundred was +required. Even the discoverer of Quaternions found this a source of +much anxiety. However, the board, urged by the representation of +Humphrey Lloyd, now one of its members, and, as we have already seen, +one of Hamilton's staunchest friends, relieved him of all liability. +We may here note that, notwithstanding the pension which Hamilton +enjoyed in addition to the salary of his chair, he seems always to +have been in some what straitened circumstances, or, to use his own +words in one of his letters to De Morgan, "Though not an embarrassed +man, I am anything rather than a rich one." It appears that, +notwithstanding the world-wide fame of Hamilton's discoveries, the +only profit in a pecuniary sense that he ever obtained from any of +his works was by the sale of what he called his Icosian Game. Some +enterprising publisher, on the urgent representations of one of +Hamilton's friends in London, bought the copyright of the Icosian +Game for 25 pounds. Even this little speculation proved unfortunate +for the purchaser, as the public could not be induced to take the +necessary interest in the matter.</p> + +<p>After the completion of his great book, Hamilton appeared for awhile +to permit himself a greater indulgence than usual in literary +relaxations. He had copious correspondence with his intimate friend, +Aubrey de Vere, and there were multitudes of letters from those +troops of friends whom it was Hamilton's privilege to possess. He +had been greatly affected by the death of his beloved sister Eliza, a +poetess of much taste and feeling. She left to him her many papers +to preserve or to destroy, but he said it was only after the +expiration of four years of mourning that he took courage to open her +pet box of letters.</p> + +<p>The religious side of Hamilton's character is frequently illustrated +in these letters; especially is this brought out in the +correspondence with De Vere, who had seceded to the Church of Rome. +Hamilton writes, August 4, 1855:—</p> + +<p>"If, then, it be painfully evident to both, that under such +circumstances there CANNOT (whatever we may both DESIRE) be NOW in +the nature of things, or of minds, the same degree of INTIMACY +between us as of old; since we could no longer TALK with the same +degree of unreserve on every subject which happened to present +itself, but MUST, from the simplest instincts of courtesy, be each on +his guard not to say what might be offensive, or, at least, painful +to the other; yet WE were ONCE so intimate, and retain still, and, as +I trust, shall always retain, so much of regard and esteem and +appreciation for each other, made tender by so many associations of +my early youth and your boyhood, which can never be forgotten by +either of us, that (as times go) TWO OR THREE VERY RESPECTABLE +FRIENDSHIPS might easily be carved out from the fragments of our +former and ever-to-be-remembered INTIMACY. It would be no +exaggeration to quote the words: 'Heu! quanto minus est cum reliquis +versari, quam tui meminisse!'"</p> + +<p>In 1858 a correspondence on the subject of Quaternions commenced +between Professor Tait and Sir William Hamilton. It was particularly +gratifying to the discoverer that so competent a mathematician as +Professor Tait should have made himself acquainted with the new +calculus. It is, of course, well known that Professor Tait +subsequently brought out a most valuable elementary treatise on +Quaternions, to which those who are anxious to become acquainted with +the subject will often turn in preference to the tremendous work of +Hamilton.</p> + +<p>In the year 1861 gratifying information came to hand of the progress +which the study of Quaternions was making abroad. Especially did the +subject attract the attention of that accomplished mathematician, +Moebius, who had already in his "Barycentrische Calculus" been led to +conceptions which bore more affinity to Quaternions than could be +found in the writings of any other mathematician. Such notices of +his work were always pleasing to Hamilton, and they served, perhaps, +as incentives to that still closer and more engrossing labour by +which he became more and more absorbed. During the last few years of +his life he was observed to be even more of a recluse than he had +hitherto been. His powers of long and continuous study seemed to +grow with advancing years, and his intervals of relaxation, such as +they were, became more brief and more infrequent.</p> + +<p>It was not unusual for him to work for twelve hours at a stretch. +The dawn would frequently surprise him as he looked up to snuff his +candles after a night of fascinating labour at original research. +Regularity in habits was impossible to a student who had prolonged +fits of what he called his mathematical trances. Hours for rest and +hours for meals could only be snatched in the occasional the lucid +intervals between one attack of Quaternions and the next. When +hungry, he would go to see whether anything could be found on the +sideboard; when thirsty, he would visit the locker, and the one +blemish in the man's personal character is that these latter visits +were sometimes paid too often.</p> + +<p>As an example of one of Hamilton's rare diversions from the all- +absorbing pursuit of Quaternions, we find that he was seized with +curiosity to calculate back to the date of the Hegira, which he found +on the 15th July, 622. He speaks of the satisfaction with which he +ascertained subsequently that Herschel had assigned precisely the +same date. Metaphysics remained also, as it had ever been, a +favourite subject of Hamilton's readings and meditations and of +correspondence with his friends. He wrote a very long letter to Dr. +Ingleby on the subject of his "Introduction to Metaphysics." In it +Hamilton alludes, as he has done also in other places, to a +peculiarity of his own vision. It was habitual to him, by some +defect in the correlation of his eyes, to see always a distinct image +with each; in fact, he speaks of the remarkable effect which the use +of a good stereoscope had on his sensations of vision. It was then, +for the first time, that he realised how the two images which he had +always seen hitherto would, under normal circumstances, be blended +into one. He cites this fact as bearing on the phenomena of +binocular vision, and he draws from it the inference that the +necessity of binocular vision for the correct appreciation of +distance is unfounded. "I am quite sure," he says, "that I SEE +DISTANCE with EACH EYE SEPARATELY."</p> + +<p>The commencement of 1865, the last year of his life saw Hamilton as +diligent as ever, and corresponding with Salmon and Cayley. On April +26th he writes to a friend to say, that his health has not been good +for years past, and that so much work has injured his constitution; +and he adds, that it is not conducive to good spirits to find that he +is accumulating another heavy bill with the printer for the +publication of the "Elements." This was, indeed, up to the day of +his death, a cause for serious anxiety. It may, however, be +mentioned that the whole cost, which amounted to nearly 500 pounds, +was, like that of the previous volume, ultimately borne by the +College. Contrary to anticipation, the enterprise, even in a +pecuniary sense, cannot have been a very unprofitable one. The whole +edition has long been out of print, and as much as 5 pounds has since +been paid for a single copy.</p> + +<p>It was on the 9th of May, 1865, that Hamilton was in Dublin for the +last time. A few days later he had a violent attack of gout, and on +the 4th of June he became alarmingly ill, and on the next day had an +attack of epileptic convulsions. However, he slightly rallied, so +that before the end of the month he was again at work at the +"Elements." A gratifying incident brightened some of the last days +of his life. The National Academy of Science in America had then +been just formed. A list of foreign Associates had to be chosen from +the whole world, and a discussion took place as to what name should +be placed first on the list. Hamilton was informed by private +communication that this great distinction was awarded to him by a +majority of two-thirds.</p> + +<p>In August he was still at work on the table of contents of the +"Elements," and one of his very latest efforts was his letter to Mr. +Gould, in America, communicating his acknowledgements of the honour +which had been just conferred upon him by the National Academy. On +the 2nd of September Mr. Graves went to the observatory, in response +to a summons, and the great mathematician at once admitted to his +friend that he felt the end was approaching. He mentioned that he +had found in the 145th Psalm a wonderfully suitable expression of his +thoughts and feelings, and he wished to testify his faith and +thankfulness as a Christian by partaking of the Lord's Supper. He +died at half-past two on the afternoon of the 2nd of September, 1865, +aged sixty years and one month. He was buried in Mount Jerome +Cemetery on the 7th of September.</p> + +<p>Many were the letters and other more public manifestations of the +feelings awakened by Hamilton's death. Sir John Herschel wrote to +the widow:—</p> + +<p>"Permit me only to add that among the many scientific friends whom +time has deprived me of, there has been none whom I more deeply +lament, not only for his splendid talents, but for the excellence of +his disposition and the perfect simplicity of his manners—so great, +and yet devoid of pretensions."</p> + +<p>De Morgan, his old mathematical crony, as Hamilton affectionately +styled him, also wrote to Lady Hamilton:—</p> + +<p>"I have called him one of my dearest friends, and most truly; for I +know not how much longer than twenty-five years we have been in +intimate correspondence, of most friendly agreement or disagreement, +of most cordial interest in each other. And yet we did not know each +other's faces. I met him about 1830 at Babbage's breakfast table, +and there for the only time in our lives we conversed. I saw him, a +long way off, at the dinner given to Herschel (about 1838) on his +return from the Cape and there we were not near enough, nor on that +crowded day could we get near enough, to exchange a word. And this +is all I ever saw, and, so it has pleased God, all I shall see in +this world of a man whose friendly communications were among my +greatest social enjoyments, and greatest intellectual treats."</p> + +<p>There is a very interesting memoir of Hamilton written by De Morgan, +in the "Gentleman's Magazine" for 1866, in which he produces an +excellent sketch of his friend, illustrated by personal reminiscences +and anecdotes. He alludes, among other things, to the picturesque +confusion of the papers in his study. There was some sort of order +in the mass, discernible however, by Hamilton alone, and any invasion +of the domestics, with a view to tidying up, would throw the +mathematician as we are informed, into "a good honest thundering +passion."</p> + +<p>Hardly any two men, who were both powerful mathematicians, could have +been more dissimilar in every other respect than were Hamilton and De +Morgan. The highly poetical temperament of Hamilton was remarkably +contrasted with the practical realism of De Morgan. Hamilton sends +sonnets to his friend, who replies by giving the poet advice about +making his will. The metaphysical subtleties, with which Hamilton +often filled his sheets, did not seem to have the same attraction for +De Morgan that he found in battles about the quantification of the +Predicate. De Morgan was exquisitely witty, and though his jokes +were always appreciated by his correspondent, yet Hamilton seldom +ventured on anything of the same kind in reply; indeed his rare +attempts at humour only produced results of the most ponderous +description. But never were two scientific correspondents more +perfectly in sympathy with each other. Hamilton's work on +Quaternions, his labours in Dynamics, his literary tastes, his +metaphysics, and his poetry, were all heartily welcomed by his +friend, whose letters in reply invariably evince the kindliest +interest in all Hamilton's concerns. In a similar way De Morgan's +letters to Hamilton always met with a heartfelt response.</p> + +<p>Alike for the memory of Hamilton, for the credit of his University, +and for the benefit of science, let us hope that a collected edition +of his works will ere long appear—a collection which shall show +those early achievements in splendid optical theory, those +achievements of his more mature powers which made him the Lagrange of +his country, and finally those creations of the Quaternion Calculus +by which new capabilities have been bestowed on the human intellect.</p> + +<h3><a name="LE_VERRIER" id="LE_VERRIER"></a>LE VERRIER.</h3> +<p>The name of Le Verrier is one that goes down to fame on account of +very different discoveries from those which have given renown to +several of the other astronomers whom we have mentioned. We are +sometimes apt to identify the idea of an astronomer with that of a +man who looks through a telescope at the stars; but the word +astronomer has really much wider significance. No man who ever lived +has been more entitled to be designated an astronomer than Le +Verrier, and yet it is certain that he never made a telescopic +discovery of any kind. Indeed, so far as his scientific achievements +have been concerned, he might never have looked through a telescope +at all.</p> + +<p>For the full interpretation of the movements of the heavenly bodies, +mathematical knowledge of the most advanced character is demanded. +The mathematician at the outset calls upon the astronomer who uses +the instruments in the observatory, to ascertain for him at various +times the exact positions occupied by the sun, the moon, and the +planets. These observations, obtained with the greatest care, and +purified as far as possible from the errors by which they may be +affected form, as it were, the raw material on which the +mathematician exercises his skill. It is for him to elicit from the +observed places the true laws which govern the movements of the +heavenly bodies. Here is indeed a task in which the highest powers +of the human intellect may be worthily employed.</p> + +<p>Among those who have laboured with the greatest success in the +interpretation of the observations made with instruments of +precision, Le Verrier holds a highly honoured place. To him it has +been given to provide a superb illustration of the success with which +the mind of man can penetrate the deep things of Nature.</p> + +<p>The illustrious Frenchman, Urban Jean Joseph Le Verrier, was born on +the 11th March, 1811, at St. Lo, in the department of Manche. He +received his education in that famous school for education in the +higher branches of science, the Ecole Polytechnique, and acquired +there considerable fame as a mathematician. On leaving the school Le +Verrier at first purposed to devote himself to the public service, in +the department of civil engineering; and it is worthy of note that +his earliest scientific work was not in those mathematical researches +in which he was ultimately to become so famous. His duties in the +engineering department involved practical chemical research in the +laboratory. In this he seems to have become very expert, and +probably fame as a chemist would have been thus attained, had not +destiny led him into another direction. As it was, he did engage in +some original chemical research. His first contributions to science +were the fruits of his laboratory work; one of his papers was on the +combination of phosphorus and hydrogen, and another on the +combination of phosphorus and oxygen.</p> + +<p>His mathematical labours at the Ecole Polytechnique had, however, +revealed to Le Verrier that he was endowed with the powers requisite +for dealing with the subtlest instruments of mathematical analysis. +When he was twenty-eight years old, his first great astronomical +investigation was brought forth. It will be necessary to enter into +some explanation as to the nature of this, inasmuch as it was the +commencement of the life-work which he was to pursue.</p> + +<p>If but a single planet revolved around the sun, then the orbit of +that planet would be an ellipse, and the shape and size, as well as +the position of the ellipse, would never alter. One revolution after +another would be traced out, exactly in the same manner, in +compliance with the force continuously exerted by the sun. Suppose, +however, that a second planet be introduced into the system. The sun +will exert its attraction on this second planet also, and it will +likewise describe an orbit round the central globe. We can, however, +no longer assert that the orbit in which either of the planets moves +remains exactly an ellipse. We may, indeed, assume that the mass of +the sun is enormously greater than that of either of the planets. In +this case the attraction of the sun is a force of such preponderating +magnitude, that the actual path of each planet remains nearly the +same as if the other planet were absent. But it is impossible for +the orbit of each planet not to be affected in some degree by the +attraction of the other planet. The general law of nature asserts +that every body in space attracts every other body. So long as there +is only a single planet, it is the single attraction between the sun +and that planet which is the sole controlling principle of the +movement, and in consequence of it the ellipse is described. But +when a second planet is introduced, each of the two bodies is not +only subject to the attraction of the sun, but each one of the +planets attracts the other. It is true that this mutual attraction +is but small, but, nevertheless, it produces some effect. It +"disturbs," as the astronomer says, the elliptic orbit which would +otherwise have been pursued. Hence it follows that in the actual +planetary system where there are several planets disturbing each +other, it is not true to say that the orbits are absolutely elliptic.</p> + +<p>At the same time in any single revolution a planet may for most +practical purposes be said to be actually moving in an ellipse. As, +however, time goes on, the ellipse gradually varies. It alters its +shape, it alters its plane, and it alters its position in that +plane. If, therefore, we want to study the movements of the planets, +when great intervals of time are concerned, it is necessary to have +the means of learning the nature of the movement of the orbit in +consequence of the disturbances it has experienced.</p> + +<p>We may illustrate the matter by supposing the planet to be running +like a railway engine on a track which has been laid in a long +elliptic path. We may suppose that while the planet is coursing +along, the shape of the track is gradually altering. But this +alteration may be so slow, that it does not appreciably affect the +movement of the engine in a single revolution. We can also suppose +that the plane in which the rails have been laid has a slow +oscillation in level, and that the whole orbit is with more or less +uniformity moved slowly about in the plane.</p> + +<p>In short periods of time the changes in the shapes and positions of +the planetary orbits, in consequence of their mutual attractions, are +of no great consequence. When, however, we bring thousands of years +into consideration, then the displacements of the planetary orbits +attain considerable dimensions, and have, in fact, produced a +profound effect on the system.</p> + +<p>It is of the utmost interest to investigate the extent to which one +planet can affect another in virtue of their mutual attractions. Such +investigations demand the exercise of the highest mathematical +gifts. But not alone is intellectual ability necessary for success +in such inquiries. It must be united with a patient capacity for +calculations of an arduous type, protracted, as they frequently have +to be, through many years of labour. Le Verrier soon found in these +profound inquiries adequate scope for the exercise of his peculiar +gifts. His first important astronomical publication contained an +investigation of the changes which the orbits of several of the +planets, including the earth, have undergone in times past, and which +they will undergo in times to come.</p> + +<p>As an illustration of these researches, we may take the case of the +planet in which we are, of course, especially interested, namely, the +earth, and we can investigate the changes which, in the lapse of +time, the earth's orbit has undergone, in consequence of the +disturbance to which it has been subjected by the other planets. In +a century, or even in a thousand years, there is but little +recognisable difference in the shape of the track pursued by the +earth. Vast periods of time are required for the development of the +large consequences of planetary perturbation. Le Verrier has, +however, given us the particulars of what the earth's journey through +space has been at intervals of 20,000 years back from the present +date. His furthest calculation throws our glance back to the state +of the earth's track 100,000 years ago, while, with a bound forward, +he shows us what the earth's orbit is to be in the future, at +successive intervals of 20,000 years, till a date is reached which is +100,000 years in advance of A.D. 1800.</p> + +<p>The talent which these researches displayed brought Le Verrier into +notice. At that time the Paris Observatory was presided over by +Arago, a SAVANT who occupies a distinguished position in French +scientific annals. Arago at once perceived that Le Verrier was just +the man who possessed the qualifications suitable for undertaking a +problem of great importance and difficulty that had begun to force +itself on the attention of astronomers. What this great problem was, +and how astonishing was the solution it received, must now be +considered.</p> + +<p>Ever since Herschel brought himself into fame by his superb discovery +of the great planet Uranus, the movements of this new addition to the +solar system were scrutinized with care and attention. The position +of Uranus was thus accurately determined from time to time. At +length, when sufficient observations of this remote planet had been +brought together, the route which the newly-discovered body pursued +through the heavens was ascertained by those calculations with which +astronomers are familiar. It happens, however, that Uranus possesses +a superficial resemblance to a star. Indeed the resemblance is so +often deceptive that long ere its detection as a planet by Herschel, +it had been observed time after time by skilful astronomers, who +little thought that the star-like point at which they looked was +anything but a star. From these early observations it was possible +to determine the track of Uranus, and it was found that the great +planet takes a period of no less than eighty-four years to accomplish +a circuit. Calculations were made of the shape of the orbit in which +it revolved before its discovery by Herschel, and these were compared +with the orbit which observations showed the same body to pursue in +those later years when its planetary character was known. It could +not, of course, be expected that the orbit should remain unaltered; +the fact that the great planets Jupiter and Saturn revolve in the +vicinity of Uranus must necessarily imply that the orbit of the +latter undergoes considerable changes. When, however, due allowance +has been made for whatever influence the attraction of Jupiter and +Saturn, and we may add of the earth and all the other Planets, could +possibly produce, the movements of Uranus were still inexplicable. It +was perfectly obvious that there must be some other influence at work +besides that which could be attributed to the planets already known.</p> + +<p>Astronomers could only recognise one solution of such a difficulty. +It was impossible to doubt that there must be some other planet in +addition to the bodies at that time known, and that the perturbations +of Uranus hitherto unaccounted for, were due to the disturbances +caused by the action of this unknown planet. Arago urged Le Verrier +to undertake the great problem of searching for this body, whose +theoretical existence seemed demonstrated. But the conditions of the +search were such that it must needs be conducted on principles wholly +different from any search which had ever before been undertaken for a +celestial object. For this was not a case in which mere survey with +a telescope might be expected to lead to the discovery.</p> + +<p>Certain facts might be immediately presumed with reference to the +unknown object. There could be no doubt that the unknown disturber +of Uranus must be a large body with a mass far exceeding that of the +earth. It was certain, however, that it must be so distant that it +could only appear from our point of view as a very small object. +Uranus itself lay beyond the range, or almost beyond the range, of +unassisted vision. It could be shown that the planet by which the +disturbance was produced revolved in an orbit which must lie outside +that of Uranus. It seemed thus certain that the planet could not be +a body visible to the unaided eye. Indeed, had it been at all +conspicuous its planetary character would doubtless have been +detected ages ago. The unknown body must therefore be a planet which +would have to be sought for by telescopic aid.</p> + +<p>There is, of course, a profound physical difference between a planet +and a star, for the star is a luminous sun, and the planet is merely +a dark body, rendered visible by the sunlight which falls upon it. +Notwithstanding that a star is a sun thousands of times larger than +the planet and millions of times more remote, yet it is a singular +fact that telescopic planets possess an illusory resemblance to the +stars among which their course happens to lie. So far as actual +appearance goes, there is indeed only one criterion by which a planet +of this kind can be discriminated from a star. If the planet be +large enough the telescope will show that it possesses a disc, and +has a visible and measurable circular outline. This feature a star +does not exhibit. The stars are indeed so remote that no matter how +large they may be intrinsically, they only exhibit radiant points of +light, which the utmost powers of the telescope fail to magnify into +objects with an appreciable diameter. The older and well-known +planets, such as Jupiter and Mars, possess discs, which, though not +visible to the unaided eye, were clearly enough discernible with the +slightest telescopic power. But a very remote planet like Uranus, +though it possessed a disc large enough to be quickly appreciated by +the consummate observing skill of Herschel, was nevertheless so +stellar in its appearance, that it had been observed no fewer than +seventeen times by experienced astronomers prior to Herschel. In +each case the planetary nature of the object had been overlooked, and +it had been taken for granted that it was a star. It presented no +difference which was sufficient to arrest attention.</p> + +<p>As the unknown body by which Uranus was disturbed was certainly much +more remote than Uranus, it seemed to be certain that though it might +show a disc perceptible to very close inspection, yet that the disc +must be so minute as not to be detected except with extreme care. In +other words, it seemed probable that the body which was to be sought +for could not readily be discriminated from a small star, to which +class of object it bore a superficial resemblance, though, as a +matter of fact, there was the profoundest difference between the two +bodies.</p> + +<p>There are on the heavens many hundreds of thousands of stars, and the +problem of identifying the planet, if indeed it should lie among +these stars, seemed a very complex matter. Of course it is the +abundant presence of the stars which causes the difficulty. If the +stars could have been got rid of, a sweep over the heavens would at +once disclose all the planets which are bright enough to be visible +with the telescopic power employed. It is the fortuitous resemblance +of the planet to the stars which enables it to escape detection. To +discriminate the planet among stars everywhere in the sky would be +almost impossible. If, however, some method could be devised for +localizing that precise region in which the planet's existence might +be presumed, then the search could be undertaken with some prospect +of success.</p> + +<p>To a certain extent the problem of localizing the region on the sky +in which the planet might be expected admitted of an immediate +limitation. It is known that all the planets, or perhaps I ought +rather to say, all the great planets, confine their movements to a +certain zone around the heavens. This zone extends some way on +either side of that line called the ecliptic in which the earth +pursues its journey around the sun. It was therefore to be inferred +that the new planet need not be sought for outside this zone. It is +obvious that this consideration at once reduces the area to be +scrutinized to a small fraction of the entire heavens. But even +within the zone thus defined there are many thousands of stars. It +would seem a hopeless task to detect the new planet unless some +further limitation to its position could be assigned.</p> + +<p>It was accordingly suggested to Le Verrier that he should endeavour +to discover in what particular part of the strip of the celestial +sphere which we have indicated the search for the unknown planet +should be instituted. The materials available to the mathematician +for the solution of this problem were to be derived solely from the +discrepancies between the calculated places in which Uranus should be +found, taking into account the known causes of disturbance, and the +actual places in which observation had shown the planet to exist. +Here was indeed an unprecedented problem, and one of extraordinary +difficulty. Le Verrier, however, faced it, and, to the astonishment +of the world, succeeded in carrying it through to a brilliant +solution. We cannot here attempt to enter into any account of the +mathematical investigations that were necessary. All that we can do +is to give a general indication of the method which had to be +adopted.</p> + +<p>Let us suppose that a planet is revolving outside Uranus, at a +distance which is suggested by the several distances at which the +other planets are dispersed around the sun. Let us assume that this +outer planet has started on its course, in a prescribed path, and +that it has a certain mass. It will, of course, disturb the motion +of Uranus, and in consequence of that disturbance Uranus will follow +a path the nature of which can be determined by calculation. It +will, however, generally be found that the path so ascertained does +not tally with the actual path which observations have indicated for +Uranus. This demonstrates that the assumed circumstances of the +unknown planet must be in some respects erroneous, and the astronomer +commences afresh with an amended orbit. At last after many trials, +Le Verrier ascertained that, by assuming a certain size, shape, and +position for the unknown Planet's orbit, and a certain value for the +mass of the hypothetical body, it would be possible to account for +the observed disturbances of Uranus. Gradually it became clear to +the perception of this consummate mathematician, not only that the +difficulties in the movements of Uranus could be thus explained, but +that no other explanation need be sought for. It accordingly +appeared that a planet possessing the mass which he had assigned, and +moving in the orbit which his calculations had indicated, must indeed +exist, though no eye had ever beheld any such body. Here was, +indeed, an astonishing result. The mathematician sitting at his +desk, by studying the observations which had been supplied to him of +one planet, is able to discover the existence of another planet, and +even to assign the very position which it must occupy, ere ever the +telescope is invoked for its discovery.</p> + +<p>Thus it was that the calculations of Le Verrier narrowed greatly the +area to be scrutinised in the telescopic search which was presently +to be instituted. It was already known, as we have just pointed out, +that the planet must lie somewhere on the ecliptic. The French +mathematician had now further indicated the spot on the ecliptic at +which, according to his calculations, the planet must actually be +found. And now for an episode in this history which will be +celebrated so long as science shall endure. It is nothing less than +the telescopic confirmation of the existence of this new planet, +which had previously been indicated only by mathematical +calculation. Le Verrier had not himself the instruments necessary +for studying the heavens, nor did he possess the skill of the +practical astronomer. He, therefore, wrote to Dr. Galle, of the +Observatory at Berlin, requesting him to undertake a telescopic +search for the new planet in the vicinity which the mathematical +calculation had indicated for the whereabouts of the planet at that +particular time. Le Verrier added that he thought the planet ought +to admit of being recognised by the possession of a disc sufficiently +definite to mark the distinction between it and the surrounding +stars.</p> + +<p>It was the 23rd September, 1846, when the request from Le Verrier +reached the Berlin Observatory, and the night was clear, so that the +memorable search was made on the same evening. The investigation was +facilitated by the circumstance that a diligent observer had recently +compiled elaborate star maps for certain tracts of the heavens lying +in a sufficiently wide zone on both sides of the equator. These maps +were as yet only partially complete, but it happened that Hora. XXI., +which included the very spot which Le Verrier's results referred to, +had been just issued. Dr. Galle had thus before his, eyes a chart of +all the stars which were visible in that part of the heavens at the +time when the map was made. The advantage of such an assistance to +the search could hardly be over-estimated. It at once gave the +astronomer another method of recognising the planet besides that +afforded by its possible possession of a disc. For as the planet was +a moving body, it would not have been in the same place relatively to +the stars at the time when the map was constructed, as it occupied +some years later when the search was being made. If the body should +be situated in the spot which Le Verrier's calculations indicated in +the autumn of 1846, then it might be regarded as certain that it +would not be found in that same place on a map drawn some years +previously.</p> + +<p>The search to be undertaken consisted in a comparison made point by +point between the bodies shown on the map, and those stars in the sky +which Dr. Galle's telescope revealed. In the course of this +comparison it presently appeared that a star-like object of the +eighth magnitude, which was quite a conspicuous body in the +telescope, was not represented in the map. This at once attracted +the earnest attention of the astronomer, and raised his hopes that +here was indeed the planet. Nor were these hopes destined to be +disappointed. It could not be supposed that a star of the eighth +magnitude would have been overlooked in the preparation of a chart +whereon stars of many lower degrees of brightness were set down. One +other supposition was of course conceivable. It might have been that +this suspicious object belonged to the class of variables, for there +are many such stars whose brightness fluctuates, and if it had +happened that the map was constructed at a time when the star in +question had but feeble brilliance, it might have escaped notice. It +is also well known that sometimes new stars suddenly develop, so that +the possibility that what Dr. Galle saw should have been a variable +star or should have been a totally new star had to be provided +against.</p> + +<p>Fortunately a test was immediately available to decide whether the +new object was indeed the long sought for planet, or whether it was a +star of one of the two classes to which I have just referred. A star +remains fixed, but a planet is in motion. No doubt when a planet +lies at the distance at which this new planet was believed to be +situated, its apparent motion would be so slow that it would not be +easy to detect any change in the course of a single night's +observation. Dr. Galle, however, addressed himself with much skill +to the examination of the place of the new body. Even in the course +of the night he thought he detected slight movements, and he awaited +with much anxiety the renewal of his observations on the subsequent +evenings. His suspicions as to the movement of the body were then +amply confirmed, and the planetary nature of the new object was thus +unmistakably detected.</p> + +<p>Great indeed was the admiration of the scientific world at this +superb triumph. Here was a mighty planet whose very existence was +revealed by the indications afforded by refined mathematical +calculation. At once the name of Le Verrier, already known to those +conversant with the more profound branches of astronomy, became +everywhere celebrated. It soon, however, appeared, that the fame +belonging to this great achievement had to be shared between Le +Verrier and another astronomer, J. C. Adams, of Cambridge. In our +chapter on this great English mathematician we shall describe the +manner in which he was independently led to the same discovery.</p> + +<p>Directly the planetary nature of the newly-discovered body had been +established, the great observatories naturally included this +additional member of the solar system in their working lists, so that +day after day its place was carefully determined. When sufficient +time had elapsed the shape and position of the orbit of the body +became known. Of course, it need hardly be said that observations +applied to the planet itself must necessarily provide a far more +accurate method of determining the path which it follows, than would +be possible to Le Verrier, when all he had to base his calculations +upon was the influence of the planet reflected, so to speak, from +Uranus. It may be noted that the true elements of the planet, when +revealed by direct observation, showed that there was a considerable +discrepancy between the track of the planet which Le Verrier had +announced, and that which the planet was actually found to pursue.</p> + +<p>The name of the newly-discovered body had next to be considered. As +the older members of the system were already known by the same names +as great heathen divinities, it was obvious that some similar source +should be invoked for a suggestion as to a name for the most recent +planet. The fact that this body was so remote in the depths of +space, not unnaturally suggested the name "Neptune." Such is +accordingly the accepted designation of that mighty globe which +revolves in the track that at present seems to trace out the +frontiers of our system.</p> + +<p>Le Verrier attained so much fame by this discovery, that when, in +1854, Arago's place had to be filled at the head of the great Paris +Observatory, it was universally felt that the discoverer of Neptune +was the suitable man to assume the office which corresponds in France +to that of the Astronomer Royal in England. It was true that the +work of the astronomical mathematician had hitherto been of an +abstract character. His discoveries had been made at his desk and +not in the observatory, and he had no practical acquaintance with the +use of astronomical instruments. However, he threw himself into the +technical duties of the observatory with vigour and determination. He +endeavoured to inspire the officers of the establishment with +enthusiasm for that systematic work which is so necessary for the +accomplishment of useful astronomical research. It must, however, be +admitted that Le Verrier was not gifted with those natural qualities +which would make him adapted for the successful administration of +such an establishment. Unfortunately disputes arose between the +Director and his staff. At last the difficulties of the situation +became so great that the only possible solution was to supersede Le +Verrier, and he was accordingly obliged to retire. He was succeeded +in his high office by another eminent mathematician, M. Delaunay, +only less distinguished than Le Verrier himself.</p> + +<p>Relieved of his official duties, Le Verrier returned to the +mathematics he loved. In his non-official capacity he continued to +work with the greatest ardour at his researches on the movements of +the planets. After the death of M. Delaunay, who was accidentally +drowned in 1873, Le Verrier was restored to the directorship of the +observatory, and he continued to hold the office until his death.</p> + +<p>The nature of the researches to which the life of Le Verrier was +subsequently devoted are not such as admit of description in a +general sketch like this, where the language, and still less the +symbols, of mathematics could not be suitably introduced. It may, +however, be said in general that he was particularly engaged with the +study of the effects produced on the movements of the planets by +their mutual attractions. The importance of this work to astronomy +consists, to a considerable extent, in the fact that by such +calculations we are enabled to prepare tables by which the places of +the different heavenly bodies can be predicted for our almanacs. To +this task Le Verrier devoted himself, and the amount of work he has +accomplished would perhaps have been deemed impossible had it not +been actually done.</p> + +<p>The superb success which had attended Le Verrier's efforts to explain +the cause of the perturbations of Uranus, naturally led this +wonderful computer to look for a similar explanation of certain other +irregularities in planetary movements. To a large extent he +succeeded in showing how the movements of each of the great planets +could be satisfactorily accounted for by the influence of the +attractions of the other bodies of the same class. One circumstance +in connection with these investigations is sufficiently noteworthy to +require a few words here. Just as at the opening of his career, Le +Verrier had discovered that Uranus, the outermost planet of the then +known system, exhibited the influence of an unknown external body, so +now it appeared to him that Mercury, the innermost body of our +system, was also subjected to some disturbances, which could not be +satisfactorily accounted for as consequences of any known agents of +attraction. The ellipse in which Mercury revolved was animated by a +slow movement, which caused it to revolve in its plane. It appeared +to Le Verrier that this displacement was incapable of explanation by +the action of any of the known bodies of our system. He was, +therefore, induced to try whether he could not determine from the +disturbances of Mercury the existence of some other planet, at +present unknown, which revolved inside the orbit of the known +planet. Theory seemed to indicate that the observed alteration in +the track of the planet could be thus accounted for. He naturally +desired to obtain telescopic confirmation which might verify the +existence of such a body in the same way as Dr. Galle verified the +existence of Neptune. If there were, indeed, an intramercurial +planet, then it must occasionally cross between the earth and the +sun, and might now and then be expected to be witnessed in the actual +act of transit. So confident did Le Verrier feel in the existence of +such a body that an observation of a dark object in transit, by +Lescarbault on 26th March, 1859, was believed by the mathematician to +be the object which his theory indicated. Le Verrier also thought it +likely that another transit of the same object would be seen in +March, 1877. Nothing of the kind was, however, witnessed, +notwithstanding that an assiduous watch was kept, and the explanation +of the change in Mercury's orbit must, therefore, be regarded as +still to be sought for.</p> + +<p>Le Verrier naturally received every honour that could be bestowed +upon a man of science. The latter part of his life was passed during +the most troubled period of modern French history. He was a +supporter of the Imperial Dynasty, and during the Commune he +experienced much anxiety; indeed, at one time grave fears were +entertained for his personal safety.</p> + +<p>Early in 1877 his health, which had been gradually failing for some +years, began to give way. He appeared to rally somewhat in the +summer, but in September he sank rapidly, and died on Sunday, the +23rd of that month.</p> + +<p>His remains were borne to the cemetery on Mont Parnasse in a public +funeral. Among his pallbearers were leading men of science, from +other countries as well as France, and the memorial discourses +pronounced at the grave expressed their admiration of his talents and +of the greatness of the services he had rendered to science.</p> + +<h3><a name="ADAMS" id="ADAMS"></a>ADAMS.</h3> +<p>The illustrious mathematician who, among Englishmen, at all events, +was second only to Newton by his discoveries in theoretical +astronomy, was born on June the 5th, 1819, at the farmhouse of +Lidcot, seven miles from Launceston, in Cornwall. His early +education was imparted under the guidance of the Rev. John Couch +Grylls, a first cousin of his mother. He appears to have received an +education of the ordinary school type in classics and mathematics, +but his leisure hours were largely devoted to studying what +astronomical books he could find in the library of the Mechanics' +Institute at Devonport. He was twenty years old when he entered St. +John's College, Cambridge. His career in the University was one of +almost unparalleled distinction, and it is recorded that his +answering at the Wranglership examination, where he came out at the +head of the list in 1843, was so high that he received more than +double the marks awarded to the Second Wrangler.</p> + +<p>Among the papers found after his death was the following memorandum, +dated July the 3rd, 1841: "Formed a design at the beginning of this +week of investigating, as soon as possible after taking my degree, +the irregularities in the motion of Uranus, which are as yet +unaccounted for, in order to find whether they may be attributed to +the action of an undiscovered planet beyond it; and, if possible, +thence to determine the elements of its orbit approximately, which +would lead probably to its discovery."</p> + +<p>After he had taken his degree, and had thus obtained a little +relaxation from the lines within which his studies had previously +been necessarily confined, Adams devoted himself to the study of the +perturbations of Uranus, in accordance with the resolve which we have +just seen that he formed while he was still an undergraduate. As a +first attempt he made the supposition that there might be a planet +exterior to Uranus, at a distance which was double that of Uranus +from the sun. Having completed his calculation as to the effect +which such a hypothetical planet might exercise upon the movement of +Uranus, he came to the conclusion that it would be quite possible to +account completely for the unexplained difficulties by the action of +an exterior planet, if only that planet were of adequate size and had +its orbit properly placed. It was necessary, however, to follow up +the problem more precisely, and accordingly an application was made +through Professor Challis, the Director of the Cambridge Observatory, +to the Astronomer Royal, with the object of obtaining from the +observations made at Greenwich Observatory more accurate values for +the disturbances suffered by Uranus. Basing his work on the more +precise materials thus available, Adams undertook his calculations +anew, and at last, with his completed results, he called at Greenwich +Observatory on October the 21st, 1845. He there left for the +Astronomer Royal a paper which contained the results at which he had +arrived for the mass and the mean distance of the hypothetical planet +as well as the other elements necessary for calculating its exact +position.</p> + +<p><a name="john" id="john"></a></p> + +<div class="figcenter" style="width: 433px;"> +<a href="images/ill_john_adams.jpg"> +<img src="images/ill_john_adams_sml.jpg" width="433" height="496" alt="JOHN COUCH ADAMS." title="" /></a> +<span class="caption">JOHN COUCH ADAMS.</span> +</div> + +<p>As we have seen in the preceding chapter, Le Verrier had been also +investigating the same problem. The place which Le Verrier assigned +to the hypothetical disturbing planet for the beginning of the year +1847, was within a degree of that to which Adams's computations +pointed, and which he had communicated to the Astronomer Royal seven +months before Le Verrier's work appeared. On July the 29th, 1846, +Professor Challis commenced to search for the unknown object with the +Northumberland telescope belonging to the Cambridge Observatory. He +confined his attention to a limited region in the heavens, extending +around that point to which Mr. Adams' calculations pointed. The +relative places of all the stars, or rather star-like objects within +this area, were to be carefully measured. When the same observations +were repeated a week or two later, then the distances of the several +pairs of stars from each other would be found unaltered, but any +planet which happened to lie among the objects measured would +disclose its existence by the alterations in distance due to its +motion in the interval. This method of search, though no doubt it +must ultimately have proved successful, was necessarily a very +tedious one, but to Professor Challis, unfortunately, no other method +was available. Thus it happened that, though Challis commenced his +search at Cambridge two months earlier than Galle at Berlin, yet, as +we have already explained, the possession of accurate star-maps by +Dr. Galle enabled him to discover the planet on the very first night +that he looked for it.</p> + +<p>The rival claims of Adams and Le Verrier to the discovery of Neptune, +or rather, we should say, the claims put forward by their respective +champions, for neither of the illustrious investigators themselves +condescended to enter into the personal aspect of the question, need +not be further discussed here. The main points of the controversy +have been long since settled, and we cannot do better than quote the +words of Sir John Herschel when he addressed the Royal Astronomical +Society in 1848:—</p> + +<p>"As genius and destiny have joined the names of Le Verrier and Adams, +I shall by no means put them asunder; nor will they ever be +pronounced apart so long as language shall celebrate the triumphs of +science in her sublimest walks. On the great discovery of Neptune, +which may be said to have surpassed, by intelligible and legitimate +means, the wildest pretensions of clairvoyance, it Would now be quite +superfluous for me to dilate. That glorious event and the steps +which led to it, and the various lights in which it has been placed, +are already familiar to every one having the least tincture of +science. I will only add that as there is not, nor henceforth ever +can be, the slightest rivalry on the subject between these two +illustrious men—as they have met as brothers, and as such will, I +trust, ever regard each other—we have made, we could make, no +distinction between then, on this occasion. May they both long adorn +and augment our science, and add to their own fame already so high +and pure, by fresh achievements."</p> + +<p>Adams was elected a Fellow of St. John's College, Cambridge, in 1843; +but as he did not take holy orders, his Fellowship, in accordance +with the rules then existing came to an end in 1852. In the +following year he was, however, elected to a Fellowship at Pembroke +College, which he retained until the end of his life. In 1858 he was +appointed Professor of Mathematics in the University of St. Andrews, +but his residence in the north was only a brief one, for in the same +year he was recalled to Cambridge as Lowndean Professor of Astronomy +and Geometry, in succession to Peacock. In 1861 Challis retired from +the Directorship of the Cambridge Observatory, and Adams was +appointed to succeed him.</p> + +<p>The discovery of Neptune was a brilliant inauguration of the +astronomical career of Adams. He worked at, and wrote upon, the +theory of the motions of Biela's comet; he made important corrections +to the theory of Saturn; he investigated the mass of Uranus, a +subject in which he was naturally interested from its importance in +the theory of Neptune; he also improved the methods of computing the +orbits of double stars. But all these must be regarded as his minor +labours, for next to the discovery of Neptune the fame of Adams +mainly rests on his researches upon certain movements of the moon, +and upon the November meteors.</p> + +<p>The periodic time of the moon is the interval required for one +circuit of its orbit. This interval is known with accuracy at the +present day, and by means of the ancient eclipses the period of the +moon's revolution two thousand years ago can be also ascertained. It +had been discovered by Halley that the period which the moon requires +to accomplish each of its revolutions around the earth has been +steadily, though no doubt slowly, diminishing. The change thus +produced is not appreciable when only small intervals of time are +considered, but it becomes appreciable when we have to deal with +intervals of thousands of years. The actual effect which is produced +by the lunar acceleration, for so this phenomenon is called, may be +thus estimated. If we suppose that the moon had, throughout the +ages, revolved around the earth in precisely the same periodic time +which it has at present, and if from this assumption we calculate +back to find where the moon must have been about two thousand years +ago, we obtain a position which the ancient eclipses show to be +different from that in which the moon was actually situated. The +interval between the position in which the moon would have been found +two thousand years ago if there had been no acceleration, and the +position in which the moon was actually placed, amounts to about a +degree, that is to say, to an arc on the heavens which is twice the +moon's apparent diameter.</p> + +<p>If no other bodies save the earth and the moon were present in the +universe, it seems certain that the motion of the moon would never +have exhibited this acceleration. In such a simple case as that +which I have supposed the orbit of the moon would have remained for +ever absolutely unchanged. It is, however, well known that the +presence of the sun exerts a disturbing influence upon the movements +of the moon. In each revolution our satellite is continually drawn +aside by the action of the sun from the place which it would +otherwise have occupied. These irregularities are known as the +perturbations of the lunar orbit, they have long been studied, and +the majority of them have been satisfactorily accounted for. It +seems, however, to those who first investigated the question that the +phenomenon of the lunar acceleration could not be explained as a +consequence of solar perturbation, and, as no other agent competent +to produce such effects was recognised by astronomers, the lunar +acceleration presented an unsolved enigma.</p> + +<p>At the end of the last century the illustrious French mathematician +Laplace undertook a new investigation of the famous problem, and was +rewarded with a success which for a long time appeared to be quite +complete. Let us suppose that the moon lies directly between the +earth and the sun, then both earth and moon are pulled towards the +sun by the solar attraction; as, however, the moon is the nearer of +the two bodies to the attracting centre it is pulled the more +energetically, and consequently there is an increase in the distance +between the earth and the moon. Similarly when the moon happens to +lie on the other side of the earth, so that the earth is interposed +directly between the moon and the sun, the solar attraction exerted +upon the earth is more powerful than the same influence upon the +moon. Consequently in this case, also, the distance of the moon from +the earth is increased by the solar disturbance. These instances +will illustrate the general truth, that, as one of the consequences +of the disturbing influence exerted by the sun upon the earth-moon +system, there is an increase in the dimensions of the average orbit +which the moon describes around the earth. As the time required by +the moon to accomplish a journey round the earth depends upon its +distance from the earth, it follows that among the influences of the +sun upon the moon there must be an enlargement of the periodic time, +from what it would have been had there been no solar disturbing +action.</p> + +<p>This was known long before the time of Laplace, but it did not +directly convey any explanation of the lunar acceleration. It no +doubt amounted to the assertion that the moon's periodic time was +slightly augmented by the disturbance, but it did not give any +grounds for suspecting that there was a continuous change in +progress. It was, however, apparent that the periodic time was +connected with the solar disturbance, so that, if there were any +alteration in the amount of the sun's disturbing effect, there must +be a corresponding alteration in the moon's periodic time. Laplace, +therefore, perceived that, if he could discover any continuous change +in the ability of the sun for disturbing the moon, he would then have +accounted for a continuous change in the moon's periodic time, and +that thus an explanation of the long-vexed question of the lunar +acceleration might be forthcoming.</p> + +<p>The capability of the sun for disturbing the earth-moon system is +obviously connected with the distance of the earth from the sun. If +the earth moved in an orbit which underwent no change whatever, then +the efficiency of the sun as a disturbing agent would not undergo any +change of the kind which was sought for. But if there were any +alteration in the shape or size of the earth's orbit, then that might +involve such changes in the distance between the earth and the sun as +would possibly afford the desired agent for producing the observed +lunar effect. It is known that the earth revolves in an orbit which, +though nearly circular, is strictly an ellipse. If the earth were +the only planet revolving around the sun then that ellipse would +remain unaltered from age to age. The earth is, however, only one of +a large number of planets which circulate around the great luminary, +and are guided and controlled by his supreme attracting power. These +planets mutually attract each other, and in consequence of their +mutual attractions the orbits of the planets are disturbed from the +simple elliptic form which they would otherwise possess. The +movement of the earth, for instance, is not, strictly speaking, +performed in an elliptical orbit. We may, however, regard it as +revolving in an ellipse provided we admit that the ellipse is itself +in slow motion.</p> + +<p>It is a remarkable characteristic of the disturbing effects of the +planets that the ellipse in which the earth is at any moment moving +always retains the same length; that is to say, its longest diameter +is invariable. In all other respects the ellipse is continually +changing. It alters its position, it changes its plane, and, most +important of all, it changes its eccentricity. Thus, from age to age +the shape of the track which the earth describes may at one time be +growing more nearly a circle, or at another time may be departing +more widely from a circle. These alterations are very small in +amount, and they take place with extreme slowness, but they are in +incessant progress, and their amount admits of being accurately +calculated. At the present time, and for thousands of years past, as +well as for thousands of years to come, the eccentricity of the +earth's orbit is diminishing, and consequently the orbit described by +the earth each year is becoming more nearly circular. We must, +however, remember that under all circumstances the length of the +longest axis of the ellipse is unaltered, and consequently the size +of the track which the earth describes around the sun is gradually +increasing. In other words, it may be said that during the present +ages the average distance between the earth and the sun is waxing +greater in consequence of the perturbations which the earth +experiences from the attraction of the other planets. We have, +however, already seen that the efficiency of the solar attraction for +disturbing the moon's movement depends on the distance between the +earth and the sun. As therefore the average distance between the +earth and the sun is increasing, at all events during the thousands +of years over which our observations extend, it follows that the +ability of the sun for disturbing the moon must be gradually +diminishing.</p> + +<p><a name="cambridge" id="cambridge"></a></p> + +<div class="figcenter" style="width: 720px;"> +<a href="images/ill_cambridge_observatory.jpg"> +<img src="images/ill_cambridge_observatory_sml.jpg" width="720" height="425" alt="CAMBRIDGE OBSERVATORY." title="" /></a> +<span class="caption">CAMBRIDGE OBSERVATORY.</span> +</div> + +<p>It has been pointed out that, in consequence of the solar +disturbance, the orbit of the moon must be some what enlarged. As it +now appears that the solar disturbance is on the whole declining, it +follows that the orbit of the moon, which has to be adjusted +relatively to the average value of the solar disturbance, must also +be gradually declining. In other words, the moon must be approaching +nearer to the earth in consequence of the alterations in the +eccentricity of the earth's orbit produced by the attraction of the +other planets. It is true that the change in the moon's position +thus arising is an extremely small one, and the consequent effect in +accelerating the moon's motion is but very slight. It is in fact +almost imperceptible, except when great periods of time are +involved. Laplace undertook a calculation on this subject. He knew +what the efficiency of the planets in altering the dimensions of the +earth's orbit amounted to; from this he was able to determine the +changes that would be propagated into the motion of the moon. Thus +he ascertained, or at all events thought he had ascertained, that the +acceleration of the moon's motion, as it had been inferred from the +observations of the ancient eclipses which have been handed down to +us, could be completely accounted for as a consequence of planetary +perturbation. This was regarded as a great scientific triumph. Our +belief in the universality of the law of gravitation would, in fact, +have been seriously challenged unless some explanation of the lunar +acceleration had been forthcoming. For about fifty years no one +questioned the truth of Laplace's investigation. When a +mathematician of his eminence had rendered an explanation of the +remarkable facts of observation which seemed so complete, it is not +surprising that there should have been but little temptation to doubt +it. On undertaking a new calculation of the same question, Professor +Adams found that Laplace had not pursued this approximation +sufficiently far, and that consequently there was a considerable +error in the result of his analysis. Adams, it must be observed, did +not impugn the value of the lunar acceleration which Halley had +deduced from the observations, but what he did show was, that the +calculation by which Laplace thought he had provided an explanation +of this acceleration was erroneous. Adams, in fact, proved that the +planetary influence which Laplace had detected only possessed about +half the efficiency which the great French mathematician had +attributed to it. There were not wanting illustrious mathematicians +who came forward to defend the calculations of Laplace. They +computed the question anew and arrived at results practically +coincident with those he had given. On the other hand certain +distinguished mathematicians at home and abroad verified the results +of Adams. The issue was merely a mathematical one. It had only one +correct solution. Gradually it appeared that those who opposed Adams +presented a number of different solutions, all of them discordant +with his, and, usually, discordant with each other. Adams showed +distinctly where each of these investigators had fallen into error, +and at last it became universally admitted that the Cambridge +Professor had corrected Laplace in a very fundamental point of +astronomical theory.</p> + +<p>Though it was desirable to have learned the truth, yet the breach +between observation and calculation which Laplace was believed to +have closed thus became reopened. Laplace's investigation, had it +been correct, would have exactly explained the observed facts. It +was, however, now shown that his solution was not correct, and that +the lunar acceleration, when strictly calculated as a consequence of +solar perturbations, only produced about half the effect which was +wanted to explain the ancient eclipses completely. It now seems +certain that there is no means of accounting for the lunar +acceleration as a direct consequence of the laws of gravitation, if +we suppose, as we have been in the habit of supposing, that the +members of the solar system concerned may be regarded as rigid +particles. It has, however, been suggested that another explanation +of a very interesting kind may be forthcoming, and this we must +endeavour to set forth.</p> + +<p>It will be remembered that we have to explain why the period of +revolution of the moon is now shorter than it used to be. If we +imagine the length of the period to be expressed in terms of days and +fractions of a day, that is to say, in terms of the rotations of the +earth around its axis, then the difficulty encountered is, that the +moon now requires for each of its revolutions around the earth rather +a smaller number of rotations of the earth around its axis than used +formerly to be the case. Of course this may be explained by the fact +that the moon is now moving more swiftly than of yore, but it is +obvious that an explanation of quite a different kind might be +conceivable. The moon may be moving just at the same pace as ever, +but the length of the day may be increasing. If the length of the +day is increasing, then, of course, a smaller number of days will be +required for the moon to perform each revolution even though the +moon's period was itself really unchanged. It would, therefore, seem +as if the phenomenon known as the lunar acceleration is the result of +the two causes. The first of these is that discovered by Laplace, +though its value was over-estimated by him, in which the perturbations +of the earth by the planets indirectly affect the motion of the +moon. The remaining part of the acceleration of our satellite is +apparent rather than real, it is not that the moon is moving more +quickly, but that our time-piece, the earth, is revolving more +slowly, and is thus actually losing time. It is interesting to note +that we can detect a physical explanation for the apparent checking +of the earth's motion which is thus manifested. The tides which ebb +and flow on the earth exert a brake-like action on the revolving +globe, and there can be no doubt that they are gradually reducing its +speed, and thus lengthening the day. It has accordingly been +suggested that it is this action of the tides which produces the +supplementary effect necessary to complete the physical explanation +of the lunar acceleration, though it would perhaps be a little +premature to assert that this has been fully demonstrated.</p> + +<p>The third of Professor Adams' most notable achievements was connected +with the great shower of November meteors which astonished the world +in 1866. This splendid display concentrated the attention of +astronomers on the theory of the movements of the little objects by +which the display was produced. For the definite discovery of the +track in which these bodies revolve, we are indebted to the labours +of Professor Adams, who, by a brilliant piece of mathematical work, +completed the edifice whose foundations had been laid by Professor +Newton, of Yale, and other astronomers.</p> + +<p>Meteors revolve around the sun in a vast swarm, every individual +member of which pursues an orbit in accordance with the well-known +laws of Kepler. In order to understand the movements of these +objects, to account satisfactorily for their periodic recurrence, and +to predict the times of their appearance, it became necessary to +learn the size and the shape of the track which the swarm followed, +as well as the position which it occupied. Certain features of the +track could no doubt be readily assigned. The fact that the shower +recurs on one particular day of the year, viz., November 13th, +defines one point through which the orbit must pass. The position on +the heavens of the radiant point from which the meteors appear to +diverge, gives another element in the track. The sun must of course +be situated at the focus, so that only one further piece of +information, namely, the periodic time, will be necessary to complete +our knowledge of the movements of the system. Professor H. Newton, +of Yale, had shown that the choice of possible orbits for the +meteoric swarm is limited to five. There is, first, the great +ellipse in which we now know the meteors revolve once every thirty +three and one quarter years. There is next an orbit of a nearly +circular kind in which the periodic time would be a little more than +a year. There is a similar track in which the periodic time would be +a few days short of a year, while two other smaller orbits would also +be conceivable. Professor Newton had pointed out a test by which it +would be possible to select the true orbit, which we know must be one +or other of these five. The mathematical difficulties which attended +the application of this test were no doubt great, but they did not +baffle Professor Adams.</p> + +<p>There is a continuous advance in the date of this meteoric shower. +The meteors now cross our track at the point occupied by the earth on +November 13th, but this point is gradually altering. The only +influence known to us which could account for the continuous change +in the plane of the meteor's orbit arises from the attraction of the +various planets. The problem to be solved may therefore be attacked +in this manner. A specified amount of change in the plane of the +orbit of the meteors is known to arise, and the changes which ought +to result from the attraction of the planets can be computed for each +of the five possible orbits, in one of which it is certain that the +meteors must revolve. Professor Adams undertook the work. Its +difficulty principally arises from the high eccentricity of the +largest of the orbits, which renders the more ordinary methods of +calculation inapplicable. After some months of arduous labour the +work was completed, and in April, 1867, Adams announced his solution +of the problem. He showed that if the meteors revolved in the +largest of the five orbits, with the periodic time of thirty three +and one quarter years, the perturbations of Jupiter would account for +a change to the extent of twenty minutes of arc in the point in which +the orbit crosses the earth's track. The attraction of Saturn would +augment this by seven minutes, and Uranus would add one minute more, +while the influence of the Earth and of the other planets would be +inappreciable. The accumulated effect is thus twenty-eight minutes, +which is practically coincident with the observed value as determined +by Professor Newton from an examination of all the showers of which +there is any historical record. Having thus showed that the great +orbit was a possible path for the meteors, Adams next proved that no +one of the other four orbits would be disturbed in the same manner. +Indeed, it appeared that not half the observed amount of change could +arise in any orbit except in that one with the long period. Thus was +brought to completion the interesting research which demonstrated the +true relation of the meteor swarm to the solar system.</p> + +<p>Besides those memorable scientific labours with which his attention +was so largely engaged, Professor Adams found time for much other +study. He occasionally allowed himself to undertake as a relaxation +some pieces of numerical calculation, so tremendously long that we +can only look on them with astonishment. He has calculated certain +important mathematical constants accurately to more than two hundred +places of decimals. He was a diligent reader of works on history, +geology, and botany, and his arduous labours were often beguiled by +novels, of which, like many other great men, he was very fond. He +had also the taste of a collector, and he brought together about +eight hundred volumes of early printed works, many of considerable +rarity and value. As to his personal character, I may quote the +words of Dr. Glaisher when he says, "Strangers who first met him were +invariably struck by his simple and unaffected manner. He was a +delightful companion, always cheerful and genial, showing in society +but few traces of his really shy and retiring disposition. His +nature was sympathetic and generous, and in few men have the moral +and intellectual qualities been more perfectly balanced."</p> + +<p>In 1863 he married the daughter of Haliday Bruce, Esq., of Dublin and +up to the close of his life he lived at the Cambridge Observatory, +pursuing his mathematical work and enjoying the society of his +friends.</p> + +<p>He died, after a long illness, on 21st January, 1892, and was +interred in St. Giles's Cemetery, on the Huntingdon Road, Cambridge.</p> + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Great Astronomers, by R. S. Ball + +*** END OF THIS PROJECT GUTENBERG EBOOK GREAT ASTRONOMERS *** + +***** This file should be named 2298-h.htm or 2298-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/2/9/2298/ + +Produced by Chris Brennen cbrennen@freenet.co.uk +Jill R. Diffendal, Barb Grow pebareka@iexpress.net.au +Christine L. Hall Goleta, CA. USA +Pamela L. 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b/old/old-2024-10-01/2298-h/images/ill_woolsthorpe_manor_sml.jpg Binary files differnew file mode 100644 index 0000000..8a88ed4 --- /dev/null +++ b/old/old-2024-10-01/2298-h/images/ill_woolsthorpe_manor_sml.jpg diff --git a/old/old-2024-10-01/2298.txt b/old/old-2024-10-01/2298.txt new file mode 100644 index 0000000..55de7ae --- /dev/null +++ b/old/old-2024-10-01/2298.txt @@ -0,0 +1,9655 @@ +The Project Gutenberg EBook of Great Astronomers, by R. S. Ball + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Great Astronomers + +Author: R. S. Ball + +Posting Date: October 24, 2010 [EBook #2298] +Release Date: August 2000 [EBook #2298] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK GREAT ASTRONOMERS *** + + + + +Produced by Chris Brennen cbrennen@freenet.co.uk +Jill R. Diffendal, Barb Grow pebareka@iexpress.net.au +Christine L. Hall Goleta, CA. USA +Pamela L. Hall pamhall@www.edu + + + + + + + + +GREAT ASTRONOMERS + +by + +SIR ROBERT S. BALL D.Sc. LL.D. F.R.S. + +Lowndean Professor of Astronomy and Geometry in the +University of Cambridge + +Author of "In Starry Realms" "In the High Heavens" etc. + +WITH NUMEROUS ILLUSTRATIONS + + +[PLATE: GREENWICH OBSERVATORY.] + + + + +PREFACE. + + +It has been my object in these pages to present the life of each +astronomer in such detail as to enable the reader to realise in +some degree the man's character and surroundings; and I have +endeavoured to indicate as clearly as circumstances would permit +the main features of the discoveries by which he has become known. + +There are many types of astronomers--from the stargazer who merely +watches the heavens, to the abstract mathematician who merely +works at his desk; it has, consequently, been necessary in the +case of some lives to adopt a very different treatment from that +which seemed suitable for others. + +While the work was in progress, some of the sketches appeared in +"Good Words." The chapter on Brinkley has been chiefly derived from +an article on the "History of Dunsink Observatory," which was +published on the occasion of the tercentenary celebration of the +University of Dublin in 1892, and the life of Sir William Rowan +Hamilton is taken, with a few alterations and omissions, from an +article contributed to the "Quarterly Review" on Graves' life of +the great mathematician. The remaining chapters now appear for +the first time. For many of the facts contained in the sketch of +the late Professor Adams, I am indebted to the obituary notice +written by my friend Dr. J. W. L. Glaisher, for the Royal Astronomical +Society; while with regard to the late Sir George Airy, I have a +similar acknowledgment to make to Professor H. H. Turner. To my +friend Dr. Arthur A. Rambaut I owe my hearty thanks for his +kindness in aiding me in the revision of the work. + +R.S.B. +The Observatory, Cambridge. +October, 1895 + + + + +CONTENTS. + + +INTRODUCTION. + +PTOLEMY. + +COPERNICUS. + +TYCHO BRAHE. + +GALILEO. + +KEPLER. + +ISAAC NEWTON. + +FLAMSTEED. + +HALLEY. + +BRADLEY. + +WILLIAM HERSCHEL. + +LAPLACE. + +BRINKLEY. + +JOHN HERSCHEL. + +THE EARL OF ROSSE. + +AIRY. + +HAMILTON. + +LE VERRIER. + +ADAMS. + + + + +LIST OF ILLUSTRATIONS. + +THE OBSERVATORY, GREENWICH. + +PTOLEMY. + +PTOLEMY'S PLANETARY SCHEME. + +PTOLEMY'S THEORY OF THE MOVEMENT OF MARS. + +THORN, FROM AN OLD PRINT. + +COPERNICUS. + +FRAUENBURG, FROM AN OLD PRINT. + +EXPLANATION OF PLANETARY MOVEMENTS. + +TYCHO BRAHE. + +TYCHO'S CROSS STAFF. + +TYCHO'S "NEW STAR" SEXTANT OF 1572. + +TYCHO'S TRIGONIC SEXTANT. + +TYCHO'S ASTRONOMIC SEXTANT. + +TYCHO'S EQUATORIAL ARMILLARY. + +THE GREAT AUGSBURG QUADRANT. + +TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577. + +URANIBORG AND ITS GROUNDS. + +GROUND-PLAN OF THE OBSERVATORY. + +THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN. + +EFFIGY ON TYCHO'S TOMB AT PRAGUE. + By Permission of Messrs. A. & C. Black. + +TYCHO'S MURAL QUADRANT, URANIBORG. + +GALILEO'S PENDULUM. + +GALILEO. + +THE VILLA ARCETRI. + +FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO. + +CREST OF GALILEO'S FAMILY. + +KEPLER'S SYSTEM OF REGULAR SOLIDS. + +KEPLER. + +SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM. + +THE COMMEMORATION OF THE RUDOLPHINE TABLES. + +WOOLSTHORPE MANOR. + +TRINITY COLLEGE, CAMBRIDGE. + +DIAGRAM OF A SUNBEAM. + +ISAAC NEWTON. + +SIR ISAAC NEWTON'S LITTLE REFLECTOR. + +SIR ISAAC NEWTON'S SUN-DIAL. + +SIR ISAAC NEWTON'S TELESCOPE. + +SIR ISAAC NEWTON'S ASTROLABE. + +SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY. + +FLAMSTEED'S HOUSE. + +FLAMSTEED. + +HALLEY. + +GREENWICH OBSERVATORY IN HALLEY'S TIME. + +7, NEW KING STREET, BATH. + From a Photograph by John Poole, Bath. + +WILLIAM HERSCHEL. + +CAROLINE HERSCHEL. + +STREET VIEW, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +GARDEN VIEW, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +OBSERVATORY, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH. + From a Photograph by Hill & Saunders, Eton. + +LAPLACE. + +THE OBSERVATORY, DUNSINK. + From a Photograph by W. Lawrence, Dublin. + +ASTRONOMETER MADE BY SIR JOHN HERSCHEL. + +SIR JOHN HERSCHEL. + +NEBULA IN SOUTHERN HEMISPHERE. + +THE CLUSTER IN THE CENTAUR. + +OBSERVATORY AT FELDHAUSEN. + +GRANITE COLUMN AT FELDHAUSEN. + +THE EARL OF ROSSE. + +BIRR CASTLE. + From a Photograph by W. Lawrence, Dublin. + +THE MALL, PARSONSTOWN. + From a Photograph by W. Lawrence, Dublin. + +LORD ROSSE'S TELESCOPE. + From a Photograph by W. Lawrence, Dublin. + +ROMAN CATHOLIC CHURCH, PARSONSTOWN. + From a Photograph by W. Lawrence, Dublin. + +AIRY. + From a Photograph by E.P. Adams, Greenwich. + +HAMILTON. + +ADAMS. + +THE OBSERVATORY, CAMBRIDGE. + + + + +INTRODUCTION. + + +Of all the natural sciences there is not one which offers such +sublime objects to the attention of the inquirer as does the science +of astronomy. From the earliest ages the study of the stars has +exercised the same fascination as it possesses at the present day. +Among the most primitive peoples, the movements of the sun, the moon, +and the stars commanded attention from their supposed influence on +human affairs. + +The practical utilities of astronomy were also obvious in primeval +times. Maxims of extreme antiquity show how the avocations of the +husbandman are to be guided by the movements of the heavenly bodies. +The positions of the stars indicated the time to plough, and the time +to sow. To the mariner who was seeking a way across the trackless +ocean, the heavenly bodies offered the only reliable marks by which +his path could be guided. There was, accordingly, a stimulus both +from intellectual curiosity and from practical necessity to follow +the movements of the stars. Thus began a search for the causes of +the ever-varying phenomena which the heavens display. + +Many of the earliest discoveries are indeed prehistoric. The great +diurnal movement of the heavens, and the annual revolution of the +sun, seem to have been known in times far more ancient than those to +which any human monuments can be referred. The acuteness of the +early observers enabled them to single out the more important of the +wanderers which we now call planets. They saw that the star-like +objects, Jupiter, Saturn, and Mars, with the more conspicuous Venus, +constituted a class of bodies wholly distinct from the fixed stars +among which their movements lay, and to which they bear such a +superficial resemblance. But the penetration of the early +astronomers went even further, for they recognized that Mercury also +belongs to the same group, though this particular object is seen so +rarely. It would seem that eclipses and other phenomena were +observed at Babylon from a very remote period, while the most ancient +records of celestial observations that we possess are to be found in +the Chinese annals. + +The study of astronomy, in the sense in which we understand the word, +may be said to have commenced under the reign of the Ptolemies at +Alexandria. The most famous name in the science of this period is +that of Hipparchus who lived and worked at Rhodes about the year +160BC. It was his splendid investigations that first wrought the +observed facts into a coherent branch of knowledge. He recognized +the primary obligation which lies on the student of the heavens to +compile as complete an inventory as possible of the objects which are +there to be found. Hipparchus accordingly commenced by undertaking, +on a small scale, a task exactly similar to that on which modern +astronomers, with all available appliances of meridian circles, and +photographic telescopes, are constantly engaged at the present day. +He compiled a catalogue of the principal fixed stars, which is of +special value to astronomers, as being the earliest work of its kind +which has been handed down. He also studied the movements of the sun +and the moon, and framed theories to account for the incessant +changes which he saw in progress. He found a much more difficult +problem in his attempt to interpret satisfactorily the complicated +movements of the planets. With the view of constructing a theory +which should give some coherent account of the subject, he made many +observations of the places of these wandering stars. How great were +the advances which Hipparchus accomplished may be appreciated if we +reflect that, as a preliminary task to his more purely astronomical +labours, he had to invent that branch of mathematical science by +which alone the problems he proposed could be solved. It was for +this purpose that he devised the indispensable method of calculation +which we now know so well as trigonometry. Without the aid rendered +by this beautiful art it would have been impossible for any really +important advance in astronomical calculation to have been effected. + +But the discovery which shows, beyond all others, that Hipparchus +possessed one of the master-minds of all time was the detection of +that remarkable celestial movement known as the precession of the +equinoxes. The inquiry which conducted to this discovery involved a +most profound investigation, especially when it is remembered that in +the days of Hipparchus the means of observation of the heavenly +bodies were only of the rudest description, and the available +observations of earlier dates were extremely scanty. We can but look +with astonishment on the genius of the man who, in spite of such +difficulties, was able to detect such a phenomenon as the precession, +and to exhibit its actual magnitude. I shall endeavour to explain +the nature of this singular celestial movement, for it may be said to +offer the first instance in the history of science in which we find +that combination of accurate observation with skilful interpretation, +of which, in the subsequent development of astronomy, we have so many +splendid examples. + +The word equinox implies the condition that the night is equal to the +day. To a resident on the equator the night is no doubt equal to the +day at all times in the year, but to one who lives on any other part +of the earth, in either hemisphere, the night and the day are not +generally equal. There is, however, one occasion in spring, and +another in autumn, on which the day and the night are each twelve +hours at all places on the earth. When the night and day are equal +in spring, the point which the sun occupies on the heavens is termed +the vernal equinox. There is similarly another point in which the +sun is situated at the time of the autumnal equinox. In any +investigation of the celestial movements the positions of these two +equinoxes on the heavens are of primary importance, and Hipparchus, +with the instinct of genius, perceived their significance, and +commenced to study them. It will be understood that we can always +define the position of a point on the sky with reference to the +surrounding stars. No doubt we do not see the stars near the sun +when the sun is shining, but they are there nevertheless. The +ingenuity of Hipparchus enabled him to determine the positions of +each of the two equinoxes relatively to the stars which lie in its +immediate vicinity. After examination of the celestial places of +these points at different periods, he was led to the conclusion that +each equinox was moving relatively to the stars, though that movement +was so slow that twenty five thousand years would necessarily elapse +before a complete circuit of the heavens was accomplished. Hipparchus +traced out this phenomenon, and established it on an impregnable +basis, so that all astronomers have ever since recognised the +precession of the equinoxes as one of the fundamental facts of +astronomy. Not until nearly two thousand years after Hipparchus had +made this splendid discovery was the explanation of its cause given +by Newton. + +From the days of Hipparchus down to the present hour the science of +astronomy has steadily grown. One great observer after another has +appeared from time to time, to reveal some new phenomenon with regard +to the celestial bodies or their movements, while from time to time +one commanding intellect after another has arisen to explain the true +import of the facts of observations. The history of astronomy thus +becomes inseparable from the history of the great men to whose +labours its development is due. + +In the ensuing chapters we have endeavoured to sketch the lives and +the work of the great philosophers, by whose labours the science of +astronomy has been created. We shall commence with Ptolemy, who, +after the foundations of the science had been laid by Hipparchus, +gave to astronomy the form in which it was taught throughout the +Middle Ages. We shall next see the mighty revolution in our +conceptions of the universe which are associated with the name of +Copernicus. We then pass to those periods illumined by the genius of +Galileo and Newton, and afterwards we shall trace the careers of +other more recent discoverers, by whose industry and genius the +boundaries of human knowledge have been so greatly extended. Our +history will be brought down late enough to include some of the +illustrious astronomers who laboured in the generation which has just +passed away. + + + + +PTOLEMY. + + +[PLATE: PTOLEMY.] + +The career of the famous man whose name stands at the head of this +chapter is one of the most remarkable in the history of human +learning. There may have been other discoverers who have done more +for science than ever Ptolemy accomplished, but there never has been +any other discoverer whose authority on the subject of the movements +of the heavenly bodies has held sway over the minds of men for so +long a period as the fourteen centuries during which his opinions +reigned supreme. The doctrines he laid down in his famous book, "The +Almagest," prevailed throughout those ages. No substantial addition +was made in all that time to the undoubted truths which this work +contained. No important correction was made of the serious errors +with which Ptolemy's theories were contaminated. The authority of +Ptolemy as to all things in the heavens, and as to a good many things +on the earth (for the same illustrious man was also a diligent +geographer), was invariably final. + +Though every child may now know more of the actual truths of the +celestial motions than ever Ptolemy knew, yet the fact that his work +exercised such an astonishing effect on the human intellect for some +sixty generations, shows that it must have been an extraordinary +production. We must look into the career of this wonderful man to +discover wherein lay the secret of that marvellous success which made +him the unchallenged instructor of the human race for such a +protracted period. + +Unfortunately, we know very little as to the personal history of +Ptolemy. He was a native of Egypt, and though it has been sometimes +conjectured that he belonged to the royal families of the same name, +yet there is nothing to support such a belief. The name, Ptolemy, +appears to have been a common one in Egypt in those days. The time +at which he lived is fixed by the fact that his first recorded +observation was made in 127 AD, and his last in 151 AD. When we add +that he seems to have lived in or near Alexandria, or to use his own +words, "on the parallel of Alexandria," we have said everything that +can be said so far as his individuality is concerned. + +Ptolemy is, without doubt, the greatest figure in ancient astronomy. +He gathered up the wisdom of the philosophers who had preceded him. +He incorporated this with the results of his own observations, and +illumined it with his theories. His speculations, even when they +were, as we now know, quite erroneous, had such an astonishing +verisimilitude to the actual facts of nature that they commanded +universal assent. Even in these modern days we not unfrequently find +lovers of paradox who maintain that Ptolemy's doctrines not only seem +true, but actually are true. + +In the absence of any accurate knowledge of the science of mechanics, +philosophers in early times were forced to fall back on certain +principles of more or less validity, which they derived from their +imagination as to what the natural fitness of things ought to be. +There was no geometrical figure so simple and so symmetrical as a +circle, and as it was apparent that the heavenly bodies pursued +tracks which were not straight lines, the conclusion obviously +followed that their movements ought to be circular. There was no +argument in favour of this notion, other than the merely imaginary +reflection that circular movement, and circular movement alone, was +"perfect," whatever "perfect" may have meant. It was further +believed to be impossible that the heavenly bodies could have any +other movements save those which were perfect. Assuming this, it +followed, in Ptolemy's opinion, and in that of those who came after +him for fourteen centuries, that all the tracks of the heavenly +bodies were in some way or other to be reduced to circles. + +Ptolemy succeeded in devising a scheme by which the apparent changes +that take place in the heavens could, so far as he knew them, be +explained by certain combinations of circular movement. This seemed +to reconcile so completely the scheme of things celestial with the +geometrical instincts which pointed to the circle as the type of +perfect movement, that we can hardly wonder Ptolemy's theory met with +the astonishing success that attended it. We shall, therefore, set +forth with sufficient detail the various steps of this famous +doctrine. + +Ptolemy commences with laying down the undoubted truth that the shape +of the earth is globular. The proofs which he gives of this +fundamental fact are quite satisfactory; they are indeed the same +proofs as we give today. There is, first of all, the well-known +circumstance of which our books on geography remind us, that when an +object is viewed at a distance across the sea, the lower part of the +object appears cut off by the interposing curved mass of water. + +The sagacity of Ptolemy enabled him to adduce another argument, +which, though not quite so obvious as that just mentioned, +demonstrates the curvature of the earth in a very impressive manner +to anyone who will take the trouble to understand it. Ptolemy +mentions that travellers who went to the south reported, that, as +they did so, the appearance of the heavens at night underwent a +gradual change. Stars that they were familiar with in the northern +skies gradually sank lower in the heavens. The constellation of the +Great Bear, which in our skies never sets during its revolution round +the pole, did set and rise when a sufficient southern latitude had +been attained. On the other hand, constellations new to the +inhabitants of northern climes were seen to rise above the southern +horizon. These circumstances would be quite incompatible with the +supposition that the earth was a flat surface. Had this been so, a +little reflection will show that no such changes in the apparent +movements of the stars would be the consequence of a voyage to the +south. Ptolemy set forth with much insight the significance of this +reasoning, and even now, with the resources of modern discoveries to +help us, we can hardly improve upon his arguments. + +Ptolemy, like a true philosopher disclosing a new truth to the world, +illustrated and enforced his subject by a variety of happy +demonstrations. I must add one of them, not only on account of its +striking nature, but also because it exemplifies Ptolemy's +acuteness. If the earth were flat, said this ingenious reasoner, +sunset must necessarily take place at the same instant, no matter in +what country the observer may happen to be placed. Ptolemy, however, +proved that the time of sunset did vary greatly as the observer's +longitude was altered. To us, of course, this is quite obvious; +everybody knows that the hour of sunset may have been reached in +Great Britain while it is still noon on the western coast of +America. Ptolemy had, however, few of those sources of knowledge +which are now accessible. How was he to show that the sun actually +did set earlier at Alexandria than it would in a city which lay a +hundred miles to the west? There was no telegraph wire by which +astronomers at the two Places could communicate. There was no +chronometer or watch which could be transported from place to place; +there was not any other reliable contrivance for the keeping of +time. Ptolemy's ingenuity, however, pointed out a thoroughly +satisfactory method by which the times of sunset at two places could +be compared. He was acquainted with the fact, which must indeed have +been known from the very earliest times, that the illumination of the +moon is derived entirely from the sun. He knew that an eclipse of +the moon was due to the interposition of the earth which cuts off the +light of the sun. It was, therefore, plain that an eclipse of the +moon must be a phenomenon which would begin at the same instant from +whatever part of the earth the moon could be seen at the time. +Ptolemy, therefore, brought together from various quarters the local +times at which different observers had recorded the beginning of a +lunar eclipse. He found that the observers to the west made the time +earlier and earlier the further away their stations were from +Alexandria. On the other hand, the eastern observers set down the +hour as later than that at which the phenomenon appeared at +Alexandria. As these observers all recorded something which indeed +appeared to them simultaneously, the only interpretation was, that +the more easterly a place the later its time. Suppose there were a +number of observers along a parallel of latitude, and each noted the +hour of sunset to be six o'clock, then, since the eastern times are +earlier than western times, 6 p.m. at one station A will correspond +to 5 p.m. at a station B sufficiently to the west. If, therefore, +it is sunset to the observer at A, the hour of sunset will not yet be +reached for the observer at B. This proves conclusively that the +time of sunset is not the same all over the earth. We have, however, +already seen that the apparent time of sunset would be the same from +all stations if the earth were flat. When Ptolemy, therefore, +demonstrated that the time of sunset was not the same at various +places, he showed conclusively that the earth was not flat. + +As the same arguments applied to all parts of the earth where Ptolemy +had either been himself, or from which he could gain the necessary +information, it followed that the earth, instead of being the flat +plain, girdled with an illimitable ocean, as was generally supposed, +must be in reality globular. This led at once to a startling +consequence. It was obvious that there could be no supports of any +kind by which this globe was sustained; it therefore followed that +the mighty object must be simply poised in space. This is indeed an +astonishing doctrine to anyone who relies on what merely seems the +evidence of the senses, without giving to that evidence its due +intellectual interpretation. According to our ordinary experience, +the very idea of an object poised without support in space, appears +preposterous. Would it not fall? we are immediately asked. Yes, +doubtless it could not remain poised in any way in which we try the +experiment. We must, however, observe that there are no such ideas +as upwards or downwards in relation to open space. To say that a +body falls downwards, merely means that it tries to fall as nearly as +possible towards the centre of the earth. There is no one direction +along which a body will tend to move in space, in preference to any +other. This may be illustrated by the fact that a stone let fall at +New Zealand will, in its approach towards the earth's centre, be +actually moving upwards as far as any locality in our hemisphere is +concerned. Why, then, argued Ptolemy, may not the earth remain +poised in space, for as all directions are equally upward or equally +downward, there seems no reason why the earth should require any +support? By this reasoning he arrives at the fundamental conclusion +that the earth is a globular body freely lying in space, and +surrounded above, below, and on all sides by the glittering stars of +heaven. + +The perception of this sublime truth marks a notable epoch in the +history of the gradual development of the human intellect. No doubt, +other philosophers, in groping after knowledge, may have set forth +certain assertions that are more or less equivalent to this +fundamental truth. It is to Ptolemy we must give credit, however, +not only for announcing this doctrine, but for demonstrating it by +clear and logical argument. We cannot easily project our minds back +to the conception of an intellectual state in which this truth was +unfamiliar. It may, however, be well imagined that, to one who +thought the earth was a flat plain of indefinite extent, it would be +nothing less than an intellectual convulsion for him to be forced to +believe that he stood upon a spherical earth, forming merely a +particle relatively to the immense sphere of the heavens. + +What Ptolemy saw in the movements of the stars led him to the +conclusion that they were bright points attached to the inside of a +tremendous globe. The movements of this globe which carried the +stars were only compatible with the supposition that the earth +occupied its centre. The imperceptible effect produced by a change +in the locality of the observer on the apparent brightness of the +stars made it plain that the dimensions of the terrestrial globe must +be quite insignificant in comparison with those of the celestial +sphere. The earth might, in fact, be regarded as a grain of sand +while the stars lay upon a globe many yards in diameter. + +So tremendous was the revolution in human knowledge implied by this +discovery, that we can well imagine how Ptolemy, dazzled as it were +by the fame which had so justly accrued to him, failed to make one +further step. Had he made that step, it would have emancipated the +human intellect from the bondage of fourteen centuries of servitude +to a wholly monstrous notion of this earth's importance in the scheme +of the heavens. The obvious fact that the sun, the moon, and the +stars rose day by day, moved across the sky in a glorious +never-ending procession, and duly set when their appointed courses +had been run, demanded some explanation. The circumstance that the +fixed stars preserved their mutual distances from year to year, and +from age to age, appeared to Ptolemy to prove that the sphere which +contained those stars, and on whose surface they were believed by him +to be fixed, revolved completely around the earth once every day. He +would thus account for all the phenomena of rising and setting +consistently with the supposition that our globe was stationary. +Probably this supposition must have appeared monstrous, even to +Ptolemy. He knew that the earth was a gigantic object, but, large as +it may have been, he knew that it was only a particle in comparison +with the celestial sphere, yet he apparently believed, and certainly +succeeded in persuading other men to believe, that the celestial +sphere did actually perform these movements. + +Ptolemy was an excellent geometer. He knew that the rising and the +setting of the sun, the moon, and the myriad stars, could have been +accounted for in a different way. If the earth turned round +uniformly once a day while poised at the centre of the sphere of the +heavens, all the phenomena of rising and setting could be completely +explained. This is, indeed, obvious after a moment's reflection. +Consider yourself to be standing on the earth at the centre of the +heavens. There are stars over your head, and half the contents of +the heavens are visible, while the other half are below your +horizon. As the earth turns round, the stars over your head will +change, and unless it should happen that you have taken up your +position at either of the poles, new stars will pass into your view, +and others will disappear, for at no time can you have more than half +of the whole sphere visible. The observer on the earth would, +therefore, say that some stars were rising, and that some stars were +setting. We have, therefore, two totally distinct methods, each of +which would completely explain all the observed facts of the diurnal +movement. One of these suppositions requires that the celestial +sphere, bearing with it the stars and other celestial bodies, turns +uniformly around an invisible axis, while the earth remains +stationary at the centre. The other supposition would be, that it is +the stupendous celestial sphere which remains stationary, while the +earth at the centre rotates about the same axis as the celestial +sphere did before, but in an opposite direction, and with a uniform +velocity which would enable it to complete one turn in twenty-four +hours. Ptolemy was mathematician enough to know that either of these +suppositions would suffice for the explanation of the observed +facts. Indeed, the phenomena of the movements of the stars, so far +as he could observe them, could not be called upon to pronounce which +of these views was true, and which was false. + +Ptolemy had, therefore, to resort for guidance to indirect lines of +reasoning. One of these suppositions must be true, and yet it +appeared that the adoption of either was accompanied by a great +difficulty. It is one of his chief merits to have demonstrated that +the celestial sphere was so stupendous that the earth itself was +absolutely insignificant in comparison therewith. If, then, this +stupendous sphere rotated once in twenty-four hours, the speed with +which the movement of some of the stars must be executed would be so +portentous as to seem well-nigh impossible. It would, therefore, +seem much simpler on this ground to adopt the other alternative, and +to suppose the diurnal movements were due to the rotation of the +earth. Here Ptolemy saw, or at all events fancied he saw, objections +of the weightiest description. The evidence of the senses appeared +directly to controvert the supposition that this earth is anything +but stationary. Ptolemy might, perhaps, have dismissed this +objection on the ground that the testimony of the senses on such a +matter should be entirely subordinated to the interpretation which +our intelligence would place upon the facts to which the senses +deposed. Another objection, however, appeared to him to possess the +gravest moment. It was argued that if the earth were rotating, there +is nothing to make the air participate in this motion, mankind would +therefore be swept from the earth by the furious blasts which would +arise from the movement of the earth through an atmosphere at rest. +Even if we could imagine that the air were carried round with the +earth, the same would not apply, so thought Ptolemy, to any object +suspended in the air. So long as a bird was perched on a tree, he +might very well be carried onward by the moving earth, but the moment +he took wing, the ground would slip from under him at a frightful +pace, so that when he dropped down again he would find himself at a +distance perhaps ten times as great as that which a carrier-pigeon or +a swallow could have traversed in the same time. Some vague delusion +of this description seems even still to crop up occasionally. I +remember hearing of a proposition for balloon travelling of a very +remarkable kind. The voyager who wanted to reach any other place in +the same latitude was simply to ascend in a balloon, and wait there +till the rotation of the earth conveyed the locality which happened +to be his destination directly beneath him, whereupon he was to let +out the gas and drop down! Ptolemy knew quite enough natural +philosophy to be aware that such a proposal for locomotion would be +an utter absurdity; he knew that there was no such relative shift +between the air and the earth as this motion would imply. It +appeared to him to be necessary that the air should lag behind, if +the earth had been animated by a movement of rotation. In this he +was, as we know, entirely wrong. There were, however, in his days no +accurate notions on the subject of the laws of motion. + +Assiduous as Ptolemy may have been in the study of the heavenly +bodies, it seems evident that he cannot have devoted much thought to +the phenomena of motion of terrestrial objects. Simple, indeed, are +the experiments which might have convinced a philosopher much less +acute than Ptolemy, that, if the earth did revolve, the air must +necessarily accompany it. If a rider galloping on horseback tosses a +ball into the air, it drops again into his hand, just as it would +have done had he been remaining at rest during the ball's flight; the +ball in fact participates in the horizontal motion, so that though it +really describes a curve as any passer-by would observe, yet it +appears to the rider himself merely to move up and down in a straight +line. This fact, and many others similar to it, demonstrate clearly +that if the earth were endowed with a movement of rotation, the +atmosphere surrounding it must participate in that movement. Ptolemy +did not know this, and consequently he came to the conclusion that +the earth did not rotate, and that, therefore, notwithstanding the +tremendous improbability of so mighty an object as the celestial +sphere spinning round once in every twenty-four hours, there was no +course open except to believe that this very improbable thing did +really happen. Thus it came to pass that Ptolemy adopted as the +cardinal doctrine of his system a stationary earth poised at the +centre of the celestial sphere, which stretched around on all sides +at a distance so vast that the diameter of the earth was an +inappreciable point in comparison therewith. + +Ptolemy having thus deliberately rejected the doctrine of the earth's +rotation, had to make certain other entirely erroneous suppositions. +It was easily seen that each star required exactly the same period +for the performance of a complete revolution of the heavens. Ptolemy +knew that the stars were at enormous distances from the earth, though +no doubt his notions on this point came very far short of what we +know to be the reality. If the stars had been at very varied +distances, then it would be so wildly improbable that they should all +accomplish their revolutions in the same time, that Ptolemy came to +the conclusion that they must be all at the same distance, that is, +that they must be all on the surface of a sphere. This view, however +erroneous, was corroborated by the obvious fact that the stars in the +constellations preserved their relative places unaltered for +centuries. Thus it was that Ptolemy came to the conclusion that they +were all fixed on one spherical surface, though we are not informed +as to the material of this marvellous setting which sustained the +stars like jewels. + +Nor should we hastily pronounce this doctrine to be absurd. The +stars do appear to lie on the surface of a sphere, of which the +observer is at the centre; not only is this the aspect which the +skies present to the untechnical observer, but it is the aspect in +which the skies are presented to the most experienced astronomer of +modern days. No doubt he knows well that the stars are at the most +varied distances from him; he knows that certain stars are ten times, +or a hundred times, or a thousand times, as far as other stars. +Nevertheless, to his eye the stars appear on the surface of the +sphere, it is on that surface that his measurements of the relative +places of the stars are made; indeed, it may be said that almost all +the accurate observations in the observatory relate to the places of +the stars, not as they really are, but as they appear to be projected +on that celestial sphere whose conception we owe to the genius of +Ptolemy. + +This great philosopher shows very ingeniously that the earth must be +at the centre of the sphere. He proves that, unless this were the +case, each star would not appear to move with the absolute uniformity +which does, as a matter of fact, characterise it. In all these +reasonings we cannot but have the most profound admiration for the +genius of Ptolemy, even though he had made an error so enormous in +the fundamental point of the stability of the earth. Another error +of a somewhat similar kind seemed to Ptolemy to be demonstrated. He +had shown that the earth was an isolated object in space, and being +such was, of course, capable of movement. It could either be turned +round, or it could be moved from one place to another. We know that +Ptolemy deliberately adopted the view that the earth did not turn +round; he had then to investigate the other question, as to whether +the earth was animated by any movement of translation. He came to +the conclusion that to attribute any motion to the earth would be +incompatible with the truths at which he had already arrived. The +earth, argued Ptolemy, lies at the centre of the celestial sphere. +If the earth were to be endowed with movement, it would not lie +always at this point, it must, therefore, shift to some other part of +the sphere. The movements of the stars, however, preclude the +possibility of this; and, therefore, the earth must be as devoid of +any movement of translation as it is devoid of rotation. Thus it was +that Ptolemy convinced himself that the stability of the earth, as it +appeared to the ordinary senses, had a rational philosophical +foundation. + +Not unfrequently it is the lot of the philosophers to contend against +the doctrines of the vulgar, but when it happens, as in the case of +Ptolemy's researches, that the doctrines of the vulgar are +corroborated by philosophical investigation which bear the stamp of +the highest authority, it is not to be wondered at that such +doctrines should be deemed well-nigh impregnable. In this way we +may, perhaps, account for the remarkable fact that the theories of +Ptolemy held unchallenged sway over the human intellect for the vast +period already mentioned. + +Up to the present we have been speaking only of those primary motions +of the heavens, by which the whole sphere appeared to revolve once +every twenty-four hours. We have now to discuss the remarkable +theories by which Ptolemy endeavoured to account for the monthly +movement of the moon, for the annual movement of the sun, and for the +periodic movements of the planets which had gained for them the +titles of the wandering stars. + +Possessed with the idea that these movements must be circular, or +must be capable, directly or indirectly, of being explained by +circular movements, it seemed obvious to Ptolemy, as indeed it had +done to previous astronomers, that the track of the moon through the +stars was a circle of which the earth is the centre. A similar +movement with a yearly period must also be attributed to the sun, for +the changes in the positions of the constellations in accordance with +the progress of the seasons, placed it beyond doubt that the sun made +a circuit of the celestial sphere, even though the bright light of +the sun prevented the stars in its vicinity, from being seen in +daylight. Thus the movements both of the sun and the moon, as well +as the diurnal rotation of the celestial sphere, seemed to justify +the notion that all celestial movements must be "perfect," that is to +say, described uniformly in those circles which were the only perfect +curves. + +The simplest observations, however, show that the movements of the +planets cannot be explained in this simple fashion. Here the +geometrical genius of Ptolemy shone forth, and he devised a scheme by +which the apparent wanderings of the planets could be accounted for +without the introduction of aught save "perfect" movements. + +To understand his reasoning, let us first set forth clearly those +facts of observation which require to be explained. I shall take, in +particular, two planets, Venus and Mars, as these illustrate, in the +most striking manner, the peculiarities of the inner and the outer +planets respectively. The simplest observations would show that +Venus did not move round the heavens in the same fashion as the sun +or the moon. Look at the evening star when brightest, as it appears +in the west after sunset. Instead of moving towards the east among +the stars, like the sun or the moon, we find, week after week, that +Venus is drawing in towards the sun, until it is lost in the +sunbeams. Then the planet emerges on the other side, not to be seen +as an evening star, but as a morning star. In fact, it was plain +that in some ways Venus accompanied the sun in its annual movement. +Now it is found advancing in front of the sun to a certain limited +distance, and now it is lagging to an equal extent behind the sun. + +[FIG. 1. PTOLEMY'S PLANETARY SCHEME.] + +These movements were wholly incompatible with the supposition that +the journeys of Venus were described by a single motion of the kind +regarded as perfect. It was obvious that the movement was connected +in some strange manner with the revolution of the sun, and here was +the ingenious method by which Ptolemy sought to render account of +it. Imagine a fixed arm to extend from the earth to the sun, as +shown in the accompanying figure (Fig. 1), then this arm will move +round uniformly, in consequence of the sun's movement. At a point P +on this arm let a small circle be described. Venus is supposed to +revolve uniformly in this small circle, while the circle itself is +carried round continuously by the movement of the sun. In this way +it was possible to account for the chief peculiarities in the +movement of Venus. It will be seen that, in consequence of the +revolution around P, the spectator on the earth will sometimes see +Venus on one side of the sun, and sometimes on the other side, so +that the planet always remains in the sun's vicinity. By properly +proportioning the movements, this little contrivance simulated the +transitions from the morning star to the evening star. Thus the +changes of Venus could be accounted for by a Combination of the +"perfect" movement of P in the circle which it described uniformly +round the earth, combined with the "perfect" motion of Venus in the +circle which it described uniformly around the moving centre. + +In a precisely similar manner Ptolemy rendered an explanation of the +fitful apparitions of Mercury. Now just on one side of the sun, and +now just on the other, this rarely-seen planet moved like Venus on a +circle whereof the centre was also carried by the line joining the +sun and the earth. The circle, however, in which Mercury actually +revolved had to be smaller than that of Venus, in order to account +for the fact that Mercury lies always much closer to the sun than the +better-known planet. + +[FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.] + +The explanation of the movement of an outer planet like Mars could +also be deduced from the joint effect of two perfect motions. The +changes through which Mars goes are, however, so different from the +movements of Venus that quite a different disposition of the circles +is necessary. For consider the facts which characterise the +movements of an outer planet such as Mars. In the first place, Mars +accomplishes an entire circuit of the heaven. In this respect, no +doubt, it may be said to resemble the sun or the moon. A little +attention will, however, show that there are extraordinary +irregularities in the movement of the planet. Generally speaking, it +speeds its way from west to east among the stars, but sometimes the +attentive observer will note that the speed with which the planet +advances is slackening, and then it will seem to become stationary. +Some days later the direction of the planet's movement will be +reversed, and it will be found moving from the east towards the +west. At first it proceeds slowly and then quickens its pace, until +a certain speed is attained, which afterwards declines until a second +stationary position is reached. After a due pause the original +motion from west to east is resumed, and is continued until a similar +cycle of changes again commences. Such movements as these were +obviously quite at variance with any perfect movement in a single +circle round the earth. Here, again, the geometrical sagacity of +Ptolemy provided him with the means of representing the apparent +movements of Mars, and, at the same time, restricting the explanation +to those perfect movements which he deemed so essential. In Fig. 2 +we exhibit Ptolemy's theory as to the movement of Mars. We have, as +before, the earth at the centre, and the sun describing its circular +orbit around that centre. The path of Mars is to be taken as +exterior to that of the sun. We are to suppose that at a point +marked M there is a fictitious planet, which revolves around the +earth uniformly, in a circle called the DEFERENT. This point M, +which is thus animated by a perfect movement, is the centre of a +circle which is carried onwards with M, and around the circumference +of which Mars revolves uniformly. It is easy to show that the +combined effect of these two perfect movements is to produce exactly +that displacement of Mars in the heavens which observation +discloses. In the position represented in the figure, Mars is +obviously pursuing a course which will appear to the observer as a +movement from west to east. When, however, the planet gets round to +such a position as R, it is then moving from east to west in +consequence of its revolution in the moving circle, as indicated by +the arrow-head. On the other hand, the whole circle is carried +forward in the opposite direction. If the latter movement be less +rapid than the former, then we shall have the backward movement of +Mars on the heavens which it was desired to explain. By a proper +adjustment of the relative lengths of these arms the movements of the +planet as actually observed could be completely accounted for. + +The other outer planets with which Ptolemy was acquainted, namely, +Jupiter and Saturn, had movements of the same general character as +those of Mars. Ptolemy was equally successful in explaining the +movements they performed by the supposition that each planet had +perfect rotation in a circle of its own, which circle itself had +perfect movement around the earth in the centre. + +It is somewhat strange that Ptolemy did not advance one step further, +as by so doing he would have given great simplicity to his system. He +might, for instance, have represented the movements of Venus equally +well by putting the centre of the moving circle at the sun itself, +and correspondingly enlarging the circle in which Venus revolved. He +might, too, have arranged that the several circles which the outer +planets traversed should also have had their centres at the sun. The +planetary system would then have consisted of an earth fixed at the +centre, of a sun revolving uniformly around it, and of a system of +planets each describing its own circle around a moving centre placed +in the sun. Perhaps Ptolemy had not thought of this, or perhaps he +may have seen arguments against it. This important step was, +however, taken by Tycho. He considered that all the planets revolved +around the sun in circles, and that the sun itself, bearing all these +orbits, described a mighty circle around the earth. This point +having been reached, only one more step would have been necessary to +reach the glorious truths that revealed the structure of the solar +system. That last step was taken by Copernicus. + + + + +COPERNICUS + + +[PLATE: THORN, FROM AN OLD PRINT.] + +The quaint town of Thorn, on the Vistula, was more than two centuries +old when Copernicus was born there on the 19th of February, 1473. The +situation of this town on the frontier between Prussia and Poland, +with the commodious waterway offered by the river, made it a place of +considerable trade. A view of the town, as it was at the time of the +birth of Copernicus, is here given. The walls, with their +watch-towers, will be noted, and the strategic importance which the +situation of Thorn gave to it in the fifteenth century still belongs +thereto, so much so that the German Government recently constituted +the town a fortress of the first class. + +Copernicus, the astronomer, whose discoveries make him the great +predecessor of Kepler and Newton, did not come from a noble family, +as certain other early astronomers have done, for his father was a +tradesman. Chroniclers are, however, careful to tell us that one of +his uncles was a bishop. We are not acquainted with any of those +details of his childhood or youth which are often of such interest in +other cases where men have risen to exalted fame. It would appear +that the young Nicolaus, for such was his Christian name, received +his education at home until such time as he was deemed sufficiently +advanced to be sent to the University at Cracow. The education that +he there obtained must have been in those days of a very primitive +description, but Copernicus seems to have availed himself of it to +the utmost. He devoted himself more particularly to the study of +medicine, with the view of adopting its practice as the profession of +his life. The tendencies of the future astronomer were, however, +revealed in the fact that he worked hard at mathematics, and, like +one of his illustrious successors, Galileo, the practice of the art +of painting had for him a very great interest, and in it he obtained +some measure of success. + +By the time he was twenty-seven years old, it would seem that +Copernicus had given up the notion of becoming a medical +practitioner, and had resolved to devote himself to science. He was +engaged in teaching mathematics, and appears to have acquired some +reputation. His growing fame attracted the notice of his uncle the +bishop, at whose suggestion Copernicus took holy orders, and he was +presently appointed to a canonry in the cathedral of Frauenburg, near +the mouth of the Vistula. + +To Frauenburg, accordingly, this man of varied gifts retired. +Possessing somewhat of the ascetic spirit, he resolved to devote his +life to work of the most serious description. He eschewed all +ordinary society, restricting his intimacies to very grave and +learned companions, and refusing to engage in conversation of any +useless kind. It would seem as if his gifts for painting were +condemned as frivolous; at all events, we do not learn that he +continued to practise them. In addition to the discharge of his +theological duties, his life was occupied partly in ministering +medically to the wants of the poor, and partly with his researches in +astronomy and mathematics. His equipment in the matter of +instruments for the study of the heavens seems to have been of a very +meagre description. He arranged apertures in the walls of his house +at Allenstein, so that he could observe in some fashion the passage +of the stars across the meridian. That he possessed some talent for +practical mechanics is proved by his construction of a contrivance +for raising water from a stream, for the use of the inhabitants of +Frauenburg. Relics of this machine are still to be seen. + +[PLATE: COPERNICUS.] + +The intellectual slumber of the Middle Ages was destined to be +awakened by the revolutionary doctrines of Copernicus. It may be +noted, as an interesting circumstance, that the time at which he +discovered the scheme of the solar system has coincided with a +remarkable epoch in the world's history. The great astronomer had +just reached manhood at the time when Columbus discovered the new +world. + +Before the publication of the researches of Copernicus, the orthodox +scientific creed averred that the earth was stationary, and that the +apparent movements of the heavenly bodies were indeed real +movements. Ptolemy had laid down this doctrine 1,400 years before. +In his theory this huge error was associated with so much important +truth, and the whole presented such a coherent scheme for the +explanation of the heavenly movements, that the Ptolemaic theory was +not seriously questioned until the great work of Copernicus +appeared. No doubt others, before Copernicus, had from time to time +in some vague fashion surmised, with more or less plausibility, that +the sun, and not the earth, was the centre about which the system +really revolved. It is, however, one thing to state a scientific +fact; it is quite another thing to be in possession of the train of +reasoning, founded on observation or experiment, by which that fact +may be established. Pythagoras, it appears, had indeed told his +disciples that it was the sun, and not the earth, which was the +centre of movement, but it does not seem at all certain that +Pythagoras had any grounds which science could recognise for the +belief which is attributed to him. So far as information is +available to us, it would seem that Pythagoras associated his scheme +of things celestial with a number of preposterous notions in natural +philosophy. He may certainly have made a correct statement as to +which was the most important body in the solar system, but he +certainly did not provide any rational demonstration of the fact. +Copernicus, by a strict train of reasoning, convinced those who would +listen to him that the sun was the centre of the system. It is +useful for us to consider the arguments which he urged, and by which +he effected that intellectual revolution which is always connected +with his name. + +The first of the great discoveries which Copernicus made relates to +the rotation of the earth on its axis. That general diurnal +movement, by which the stars and all other celestial bodies appear to +be carried completely round the heavens once every twenty-four hours, +had been accounted for by Ptolemy on the supposition that the +apparent movements were the real movements. As we have already seen, +Ptolemy himself felt the extraordinary difficulty involved in the +supposition that so stupendous a fabric as the celestial sphere +should spin in the way supposed. Such movements required that many +of the stars should travel with almost inconceivable velocity. +Copernicus also saw that the daily rising and setting of the heavenly +bodies could be accounted for either by the supposition that the +celestial sphere moved round and that the earth remained at rest, or +by the supposition that the celestial sphere was at rest while the +earth turned round in the opposite direction. He weighed the +arguments on both sides as Ptolemy had done, and, as the result of +his deliberations, Copernicus came to an opposite conclusion from +Ptolemy. To Copernicus it appeared that the difficulties attending +the supposition that the celestial sphere revolved, were vastly +greater than those which appeared so weighty to Ptolemy as to force +him to deny the earth's rotation. + +Copernicus shows clearly how the observed phenomena could be +accounted for just as completely by a rotation of the earth as by a +rotation of the heavens. He alludes to the fact that, to those on +board a vessel which is moving through smooth water, the vessel +itself appears to be at rest, while the objects on shore seem to be +moving past. If, therefore, the earth were rotating uniformly, we +dwellers upon the earth, oblivious of our own movement, would wrongly +attribute to the stars the displacement which was actually the +consequence of our own motion. + +Copernicus saw the futility of the arguments by which Ptolemy had +endeavoured to demonstrate that a revolution of the earth was +impossible. It was plain to him that there was nothing whatever to +warrant refusal to believe in the rotation of the earth. In his +clear-sightedness on this matter we have specially to admire the +sagacity of Copernicus as a natural philosopher. It had been urged +that, if the earth moved round, its motion would not be imparted to +the air, and that therefore the earth would be uninhabitable by the +terrific winds which would be the result of our being carried through +the air. Copernicus convinced himself that this deduction was +preposterous. He proved that the air must accompany the earth, just +as his coat remains round him, notwithstanding the fact that he is +walking down the street. In this way he was able to show that all a +priori objections to the earth's movements were absurd, and therefore +he was able to compare together the plausibilities of the two rival +schemes for explaining the diurnal movement. + +[PLATE: FRAUENBURG, FROM AN OLD PRINT.] + +Once the issue had been placed in this form, the result could not be +long in doubt. Here is the question: Which is it more likely--that +the earth, like a grain of sand at the centre of a mighty globe, +should turn round once in twenty-four hours, or that the whole of +that vast globe should complete a rotation in the opposite direction +in the same time? Obviously, the former is far the more simple +supposition. But the case is really much stronger than this. Ptolemy +had supposed that all the stars were attached to the surface of a +sphere. He had no ground whatever for this supposition, except that +otherwise it would have been well-nigh impossible to have devised a +scheme by which the rotation of the heavens around a fixed earth +could have been arranged. Copernicus, however, with the just +instinct of a philosopher, considered that the celestial sphere, +however convenient from a geometrical point of view, as a means of +representing apparent phenomena, could not actually have a material +existence. In the first place, the existence of a material celestial +sphere would require that all the myriad stars should be at exactly +the same distances from the earth. Of course, no one will say that +this or any other arbitrary disposition of the stars is actually +impossible, but as there was no conceivable physical reason why the +distances of all the stars from the earth should be identical, it +seemed in the very highest degree improbable that the stars should be +so placed. + +Doubtless, also, Copernicus felt a considerable difficulty as to the +nature of the materials from which Ptolemy's wonderful sphere was to +be constructed. Nor could a philosopher of his penetration have +failed to observe that, unless that sphere were infinitely large, +there must have been space outside it, a consideration which would +open up other difficult questions. Whether infinite or not, it was +obvious that the celestial sphere must have a diameter at least many +thousands of times as great as that of the earth. From these +considerations Copernicus deduced the important fact that the stars +and the other celestial bodies must all be vast objects. He was thus +enabled to put the question in such a form that it could hardly +receive any answer but the correct one. Which is it more rational to +suppose, that the earth should turn round on its axis once in +twenty-four hours, or that thousands of mighty stars should circle +round the earth in the same time, many of them having to describe +circles many thousands of times greater in circumference than the +circuit of the earth at the equator? The obvious answer pressed upon +Copernicus with so much force that he was compelled to reject +Ptolemy's theory of the stationary earth, and to attribute the +diurnal rotation of the heavens to the revolution of the earth on its +axis. + +Once this tremendous step had been taken, the great difficulties +which beset the monstrous conception of the celestial sphere +vanished, for the stars need no longer be regarded as situated at +equal distances from the earth. Copernicus saw that they might lie +at the most varied degrees of remoteness, some being hundreds or +thousands of times farther away than others. The complicated +structure of the celestial sphere as a material object disappeared +altogether; it remained only as a geometrical conception, whereon we +find it convenient to indicate the places of the stars. Once the +Copernican doctrine had been fully set forth, it was impossible for +anyone, who had both the inclination and the capacity to understand +it, to withhold acceptance of its truth. The doctrine of a +stationary earth had gone for ever. + +Copernicus having established a theory of the celestial movements +which deliberately set aside the stability of the earth, it seemed +natural that he should inquire whether the doctrine of a moving earth +might not remove the difficulties presented in other celestial +phenomena. It had been universally admitted that the earth lay +unsupported in space. Copernicus had further shown that it possessed +a movement of rotation. Its want of stability being thus recognised, +it seemed reasonable to suppose that the earth might also have some +other kinds of movements as well. In this, Copernicus essayed to +solve a problem far more difficult than that which had hitherto +occupied his attention. It was a comparatively easy task to show how +the diurnal rising and setting could be accounted for by the rotation +of the earth. It was a much more difficult undertaking to +demonstrate that the planetary movements, which Ptolemy had +represented with so much success, could be completely explained by +the supposition that each of those planets revolved uniformly round +the sun, and that the earth was also a planet, accomplishing a +complete circuit of the sun once in the course of a year. + +[PLATE: EXPLANATION OF PLANETARY MOVEMENTS.] + +It would be impossible in a sketch like the present to enter into any +detail as to the geometrical propositions on which this beautiful +investigation of Copernicus depended. We can only mention a few of +the leading principles. It may be laid down in general that, if an +observer is in movement, he will, if unconscious of the fact, +attribute to the fixed objects around him a movement equal and +opposite to that which he actually possesses. A passenger on a +canal-boat sees the objects on the banks apparently moving backward +with a speed equal to that by which he is himself advancing +forwards. By an application of this principle, we can account for +all the phenomena of the movements of the planets, which Ptolemy had +so ingeniously represented by his circles. Let us take, for +instance, the most characteristic feature in the irregularities of +the outer planets. We have already remarked that Mars, though +generally advancing from west to east among the stars, occasionally +pauses, retraces his steps for awhile, again pauses, and then resumes +his ordinary onward progress. Copernicus showed clearly how this +effect was produced by the real motion of the earth, combined with +the real motion of Mars. In the adjoining figure we represent a +portion of the circular tracks in which the earth and Mars move in +accordance with the Copernican doctrine. I show particularly the +case where the earth comes directly between the planet and the sun, +because it is on such occasions that the retrograde movement (for so +this backward movement of Mars is termed) is at its highest. Mars is +then advancing in the direction shown by the arrow-head, and the +earth is also advancing in the same direction. We, on the earth, +however, being unconscious of our own motion, attribute, by the +principle I have already explained, an equal and opposite motion to +Mars. The visible effect upon the planet is, that Mars has two +movements, a real onward movement in one direction, and an apparent +movement in the opposite direction. If it so happened that the earth +was moving with the same speed as Mars, then the apparent movement +would exactly neutralise the real movement, and Mars would seem to be +at rest relatively to the surrounding stars. Under the actual +circumstances represented, however, the earth is moving faster than +Mars, and the consequence is, that the apparent movement of the +planet backwards exceeds the real movement forwards, the net result +being an apparent retrograde movement. + +With consummate skill, Copernicus showed how the applications of the +same principles could account for the characteristic movements of the +planets. His reasoning in due time bore down all opposition. The +supreme importance of the earth in the system vanished. It had now +merely to take rank as one of the planets. + +The same great astronomer now, for the first time, rendered something +like a rational account of the changes of the seasons. Nor did +certain of the more obscure astronomical phenomena escape his +attention. + +He delayed publishing his wonderful discoveries to the world until he +was quite an old man. He had a well-founded apprehension of the +storm of opposition which they would arouse. However, he yielded at +last to the entreaties of his friends, and his book was sent to the +press. But ere it made its appearance to the world, Copernicus was +seized by mortal illness. A copy of the book was brought to him on +May 23, 1543. We are told that he was able to see it and to touch +it, but no more, and he died a few hours afterwards. He was buried +in that Cathedral of Frauenburg, with which his life had been so +closely associated. + + + + +TYCHO BRAHE. + + +The most picturesque figure in the history of astronomy is +undoubtedly that of the famous old Danish astronomer whose name +stands at the head of this chapter. Tycho Brahe was alike notable +for his astronomical genius and for the extraordinary vehemence of a +character which was by no means perfect. His romantic career as a +philosopher, and his taste for splendour as a Danish noble, his +ardent friendships and his furious quarrels, make him an ideal +subject for a biographer, while the magnificent astronomical work +which he accomplished, has given him imperishable fame. + +The history of Tycho Brahe has been admirably told by Dr. Dreyer, the +accomplished astronomer who now directs the observatory at Armagh, +though himself a countryman of Tycho. Every student of the career of +the great Dane must necessarily look on Dr. Dreyer's work as the +chief authority on the subject. Tycho sprang from an illustrious +stock. His family had flourished for centuries, both in Sweden and +in Denmark, where his descendants are to be met with at the present +day. The astronomer's father was a privy councillor, and having +filled important positions in the Danish government, he was +ultimately promoted to be governor of Helsingborg Castle, where he +spent the last years of his life. His illustrious son Tycho was born +in 1546, and was the second child and eldest boy in a family of ten. + +It appears that Otto, the father of Tycho, had a brother named +George, who was childless. George, however, desired to adopt a boy +on whom he could lavish his affection and to whom he could bequeath +his wealth. A somewhat singular arrangement was accordingly entered +into by the brothers at the time when Otto was married. It was +agreed that the first son who might be born to Otto should be +forthwith handed over by the parents to George to be reared and +adopted by him. In due time little Tycho appeared, and was +immediately claimed by George in pursuance of the compact. But it +was not unnatural that the parental instinct, which had been dormant +when the agreement was made, should here interpose. Tycho's father +and mother receded from the bargain, and refused to part with their +son. George thought he was badly treated. However, he took no +violent steps until a year later, when a brother was born to Tycho. +The uncle then felt no scruple in asserting what he believed to be +his rights by the simple process of stealing the first-born nephew, +which the original bargain had promised him. After a little time it +would seem that the parents acquiesced in the loss, and thus it was +in Uncle George's home that the future astronomer passed his +childhood. + +When we read that Tycho was no more than thirteen years old at the +time he entered the University of Copenhagen, it might be at first +supposed that even in his boyish years he must have exhibited some of +those remarkable talents with which he was afterwards to astonish the +world. Such an inference should not, however, be drawn. The fact is +that in those days it was customary for students to enter the +universities at a much earlier age than is now the case. Not, +indeed, that the boys of thirteen knew more then than the boys of +thirteen know now. But the education imparted in the universities at +that time was of a much more rudimentary kind than that which we +understand by university education at present. In illustration of +this Dr. Dreyer tells us how, in the University of Wittenberg, one of +the professors, in his opening address, was accustomed to point out +that even the processes of multiplication and division in arithmetic +might be learned by any student who possessed the necessary +diligence. + +It was the wish and the intention of his uncle that Tycho's education +should be specially directed to those branches of rhetoric and +philosophy which were then supposed to be a necessary preparation for +the career of a statesman. Tycho, however, speedily made it plain to +his teachers that though he was an ardent student, yet the things +which interested him were the movements of the heavenly bodies and +not the subtleties of metaphysics. + +[PLATE: TYCHO BRAHE.] + +On the 21st October, 1560, an eclipse of the sun occurred, which was +partially visible at Copenhagen. Tycho, boy though he was, took the +utmost interest in this event. His ardour and astonishment in +connection with the circumstance were chiefly excited by the fact +that the time of the occurrence of the phenomenon could be predicted +with so much accuracy. Urged by his desire to understand the matter +thoroughly, Tycho sought to procure some book which might explain +what he so greatly wanted to know. In those days books of any kind +were but few and scarce, and scientific books were especially +unattainable. It so happened, however, that a Latin version of +Ptolemy's astronomical works had appeared a few years before the +eclipse took place, and Tycho managed to buy a copy of this book, +which was then the chief authority on celestial matters. Young as +the boy astronomer was, he studied hard, although perhaps not always +successfully, to understand Ptolemy, and to this day his copy of the +great work, copiously annotated and marked by the schoolboy hand, is +preserved as one of the chief treasures in the library of the +University at Prague. + +After Tycho had studied for about three years at the University of +Copenhagen, his uncle thought it would be better to send him, as was +usual in those days, to complete his education by a course of study +in some foreign university. The uncle cherished the hope that in +this way the attention of the young astronomer might be withdrawn +from the study of the stars and directed in what appeared to him a +more useful way. Indeed, to the wise heads of those days, the +pursuit of natural science seemed so much waste of good time which +might otherwise be devoted to logic or rhetoric or some other branch +of study more in vogue at that time. To assist in this attempt to +wean Tycho from his scientific tastes, his uncle chose as a tutor to +accompany him an intelligent and upright young man named Vedel, who +was four years senior to his pupil, and accordingly, in 1562, we find +the pair taking up their abode at the University of Leipzig. + +The tutor, however, soon found that he had undertaken a most hopeless +task. He could not succeed in imbuing Tycho with the slightest taste +for the study of the law or the other branches of knowledge which +were then thought so desirable. The stars, and nothing but the +stars, engrossed the attention of his pupil. We are told that all +the money he could obtain was spent secretly in buying astronomical +books and instruments. He learned the name of the stars from a +little globe, which he kept hidden from Vedel, and only ventured to +use during the latter's absence. No little friction was at first +caused by all this, but in after years a fast and enduring friendship +grew up between Tycho and his tutor, each of whom learned to respect +and to love the other. + +Before Tycho was seventeen he had commenced the difficult task of +calculating the movements of the planets and the places which they +occupied on the sky from time to time. He was not a little surprised +to find that the actual positions of the planets differed very widely +from those which were assigned to them by calculations from the best +existing works of astronomers. With the insight of genius he saw +that the only true method of investigating the movements of the +heavenly bodies would be to carry on a protracted series of +measurements of their places. This, which now seems to us so +obvious, was then entirely new doctrine. Tycho at once commenced +regular observations in such fashion as he could. His first +instrument was, indeed, a very primitive one, consisting of a simple +pair of compasses, which he used in this way. He placed his eye at +the hinge, and then opened the legs of the compass so that one leg +pointed to one star and the other leg to the other star. The compass +was then brought down to a divided circle, by which means the number +of degrees in the apparent angular distance of the two stars was +determined. + +His next advance in instrumental equipment was to provide himself +with the contrivance known as the "cross-staff," which he used to +observe the stars whenever opportunity offered. It must, of course, +be remembered that in those days there were no telescopes. In the +absence of optical aid, such as lenses afford the modern observers, +astronomers had to rely on mechanical appliances alone to measure the +places of the stars. Of such appliances, perhaps the most ingenious +was one known before Tycho's time, which we have represented in the +adjoining figure. + +[PLATE: TYCHO'S CROSS STAFF.] + +Let us suppose that it be desired to measure the angle between two +stars, then if the angle be not too large it can be determined in the +following manner. Let the rod AB be divided into inches and parts of +an inch, and let another rod, CD, slide up and down along AB in such +a way that the two always remain perpendicular to each other. +"Sights," like those on a rifle, are placed at A and C, and there is +a pin at D. It will easily be seen that, by sliding the movable bar +along the fixed one, it must always be possible when the stars are +not too far apart to bring the sights into such positions that one +star can be seen along DC and the other along DA. This having been +accomplished, the length from A to the cross-bar is read off on the +scale, and then, by means of a table previously prepared, the value +of the required angular distance is obtained. If the angle between +the two stars were greater than it would be possible to measure in +the way already described, then there was a provision by which the +pin at D might be moved along CD into some other position, so as to +bring the angular distance of the stars within the range of the +instrument. + +[PLATE: TYCHO'S "NEW STAR" SEXTANT OF 1572. +(The arms, of walnut wood, are about 5 1/2 ft. long.)] + +No doubt the cross-staff is a very primitive contrivance, but when +handled by one so skilful as Tycho it afforded results of +considerable accuracy. I would recommend any reader who may have a +taste for such pursuits to construct a cross-staff for himself, and +see what measurements he can accomplish with its aid. + +To employ this little instrument Tycho had to evade the vigilance of +his conscientious tutor, who felt it his duty to interdict all such +occupations as being a frivolous waste of time. It was when Vedel +was asleep that Tycho managed to escape with his cross staff and +measure the places of the heavenly bodies. Even at this early age +Tycho used to conduct his observations on those thoroughly sound +principles which lie at the foundation of all accurate modern +astronomy. Recognising the inevitable errors of workmanship in his +little instrument, he ascertained their amount and allowed for their +influence on the results which he deduced. This principle, employed +by the boy with his cross-staff in 1564, is employed at the present +day by the Astronomer Royal at Greenwich with the most superb +instruments that the skill of modern opticians has been able to +construct. + +[PLATE: TYCHO'S TRIGONIC SEXTANT. +(The arms, AB and AC, are about 5 1/2 ft. long.)] + +After the death of his uncle, when Tycho was nineteen years of age, +it appears that the young philosopher was no longer interfered with +in so far as the line which his studies were to take was concerned. +Always of a somewhat restless temperament, we now find that he +shifted his abode to the University of Rostock, where he speedily +made himself notable in connection with an eclipse of the moon on +28th October, 1566. Like every other astronomer of those days, Tycho +had always associated astronomy with astrology. He considered that +the phenomena of the heavenly bodies always had some significance in +connection with human affairs. Tycho was also a poet, and in the +united capacity of poet, astrologer, and astronomer, he posted up +some verses in the college at Rostock announcing that the lunar +eclipse was a prognostication of the death of the great Turkish +Sultan, whose mighty deeds at that time filled men's minds. Presently +news did arrive of the death of the Sultan, and Tycho was accordingly +triumphant; but a little later it appeared that the decease had taken +place BEFORE the eclipse, a circumstance which caused many a laugh at +Tycho's expense. + +[PLATE: TYCHO'S ASTRONOMIC SEXTANT. +(Made of steel: the arms, AB, AC, measure 4 ft.) + +PLATE: TYCHO'S EQUATORIAL ARMILLARY. +(The meridian circle, E B C A D, made of solid steel, +is nearly 6 ft. in diameter.)] + +Tycho being of a somewhat turbulent disposition, it appears that, +while at the University of Rostock, he had a serious quarrel with +another Danish nobleman. We are not told for certain what was the +cause of the dispute. It does not, however, seem to have had any +more romantic origin than a difference of opinion as to which of them +knew the more mathematics. They fought, as perhaps it was becoming +for two astronomers to fight, under the canopy of heaven in utter +darkness at the dead of night, and the duel was honourably terminated +when a slice was taken off Tycho's nose by the insinuating sword of +his antagonist. For the repair of this injury the ingenuity of the +great instrument-maker was here again useful, and he made a +substitute for his nose "with a composition of gold and silver." The +imitation was so good that it is declared to have been quite equal to +the original. Dr. Lodge, however, pointedly observes that it does +not appear whether this remark was made by a friend or an enemy. + +[PLATE: THE GREAT AUGSBURG QUADRANT. +(Built of heart of oak; the radii about 19 ft.) + +PLATE: TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.] + +The next few years Tycho spent in various places ardently pursuing +somewhat varied branches of scientific study. At one time we hear of +him assisting an astronomical alderman, in the ancient city of +Augsburg, to erect a tremendous wooden machine--a quadrant of 19-feet +radius--to be used in observing the heavens. At another time we +learn that the King of Denmark had recognised the talents of his +illustrious subject, and promised to confer on him a pleasant +sinecure in the shape of a canonry, which would assist him with the +means for indulging his scientific pursuits. Again we are told that +Tycho is pursuing experiments in chemistry with the greatest energy, +nor is this so incompatible as might at first be thought with his +devotion to astronomy. In those early days of knowledge the +different sciences seemed bound together by mysterious bonds. +Alchemists and astrologers taught that the several planets were +correlated in some mysterious manner with the several metals. It +was, therefore hardly surprising that Tycho should have included a +study of the properties of the metals in the programme of his +astronomical work. + +[PLATE: URANIBORG AND ITS GROUNDS. + +PLATE: GROUND-PLAN OF THE OBSERVATORY.] + +An event, however, occurred in 1572 which stimulated Tycho's +astronomical labours, and started him on his life's work. On the +11th of November in that year, he was returning home to supper after +a day's work in his laboratory, when he happened to lift his face to +the sky, and there he beheld a brilliant new star. It was in the +constellation of Cassiopeia, and occupied a position in which there +had certainly been no bright star visible when his attention had last +been directed to that part of the heavens. Such a phenomenon was so +startling that he found it hard to trust the evidence of his senses. +He thought he must be the subject of some hallucination. He +therefore called to the servants who were accompanying him, and asked +them whether they, too, could see a brilliant object in the direction +in which he pointed. They certainly could, and thus he became +convinced that this marvellous object was no mere creation of the +fancy, but a veritable celestial body--a new star of surpassing +splendour which had suddenly burst forth. In these days of careful +scrutiny of the heavens, we are accustomed to the occasional outbreak +of new stars. It is not, however, believed that any new star which +has ever appeared has displayed the same phenomenal brilliance as was +exhibited by the star of 1572. + +This object has a value in astronomy far greater than it might at +first appear. It is true, in one sense, that Tycho discovered the +new star, but it is equally true, in a different sense, that it was +the new star which discovered Tycho. Had it not been for this +opportune apparition, it is quite possible that Tycho might have +found a career in some direction less beneficial to science than that +which he ultimately pursued. + +[PLATE: THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.] + +When he reached his home on this memorable evening, Tycho immediately +applied his great quadrant to the measurement of the place of the new +star. His observations were specially directed to the determination +of the distance of the object. He rightly conjectured that if it +were very much nearer to us than the stars in its vicinity, the +distance of the brilliant body might be determined in a short time by +the apparent changes in its distance from the surrounding points. It +was speedily demonstrated that the new star could not be as near as +the moon, by the simple fact that its apparent place, as compared +with the stars in its neighbourhood, was not appreciably altered when +it was observed below the pole, and again above the pole at an +interval of twelve hours. Such observations were possible, inasmuch +as the star was bright enough to be seen in full daylight. Tycho +thus showed conclusively that the body was so remote that the +diameter of the earth bore an insignificant ratio to the star's +distance. His success in this respect is the more noteworthy when we +find that many other observers, who studied the same object, came to +the erroneous conclusion that the new star was quite as near as the +moon, or even much nearer. In fact, it may be said, that with regard +to this object Tycho discovered everything which could possibly have +been discovered in the days before telescopes were invented. He not +only proved that the star's distance was too great for measurement, +but he showed that it had no proper motion on the heavens. He +recorded the successive changes in its brightness from week to week, +as well as the fluctuations in hue with which the alterations in +lustre were accompanied. + +It seems, nowadays, strange to find that such thoroughly scientific +observations of the new star as those which Tycho made, possessed, +even in the eyes of the great astronomer himself, a profound +astrological significance. We learn from Dr. Dreyer that, in Tycho's +opinion, "the star was at first like Venus and Jupiter, and its +effects will therefore, first, be pleasant; but as it then became +like Mars, there will next come a period of wars, seditions, +captivity, and death of princes, and destruction of cities, together +with dryness and fiery meteors in the air, pestilence, and venomous +snakes. Lastly, the star became like Saturn, and thus will finally +come a time of want, death, imprisonment, and all kinds of sad +things!" Ideas of this kind were, however, universally entertained. +It seemed, indeed, obvious to learned men of that period that such an +apparition must forebode startling events. One of the chief theories +then held was, that just as the Star of Bethlehem announced the first +coming of Christ, so the second coming, and the end of the world, was +heralded by the new star of 1572. + +The researches of Tycho on this object were the occasion of his first +appearance as an author. The publication of his book was however, +for some time delayed by the urgent remonstrances of his friends, who +thought it was beneath the dignity of a nobleman to condescend to +write a book. Happily, Tycho determined to brave the opinion of his +order; the book appeared, and was the first of a series of great +astronomical productions from the same pen. + +[PLATE: EFFIGY ON TYCHO'S TOMB AT PRAGUE.] + +The fame of the noble Dane being now widespread, the King of Denmark +entreated him to return to his native country, and to deliver a +course of lectures on astronomy in the University of Copenhagen. With +some reluctance he consented, and his introductory oration has been +preserved. He dwells, in fervent language, upon the beauty and the +interest of the celestial phenomena. He points out the imperative +necessity of continuous and systematic observation of the heavenly +bodies in order to extend our knowledge. He appeals to the practical +utility of the science, for what civilised nation could exist without +having the means of measuring time? He sets forth how the study of +these beautiful objects "exalts the mind from earthly and trivial +things to heavenly ones;" and then he winds up by assuring them that +"a special use of astronomy is that it enables us to draw conclusions +from the movements in the celestial regions as to human fate." + +An interesting event, which occurred in 1572, distracted Tycho's +attention from astronomical matters. He fell in love. The young +girl on whom his affections were set appears to have sprung from +humble origin. Here again his august family friends sought to +dissuade him from a match they thought unsuitable for a nobleman. +But Tycho never gave way in anything. It is suggested that he did +not seek a wife among the highborn dames of his own rank from the +dread that the demands of a fashionable lady would make too great an +inroad on the time that he wished to devote to science. At all +events, Tycho's union seems to have been a happy one, and he had a +large family of children; none of whom, however, inherited their +father's talents. + +[PLATE: TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.] + +Tycho had many scientific friends in Germany, among whom his work was +held in high esteem. The treatment that he there met with seemed to +him so much more encouraging than that which he received in Denmark +that he formed the notion of emigrating to Basle and making it his +permanent abode. A whisper of this intention was conveyed to the +large-hearted King of Denmark, Frederick II. He wisely realised how +great would be the fame which would accrue to his realm if he could +induce Tycho to remain within Danish territory and carry on there the +great work of his life. A resolution to make a splendid proposal to +Tycho was immediately formed. A noble youth was forthwith despatched +as a messenger, and ordered to travel day and night until he reached +Tycho, whom he was to summon to the king. The astronomer was in bed +on the morning of 11th February, 1576, when the message was +delivered. Tycho, of course, set off at once and had an audience of +the king at Copenhagen. The astronomer explained that what he wanted +was the means to pursue his studies unmolested, whereupon the king +offered him the Island of Hven, in the Sound near Elsinore. There he +would enjoy all the seclusion that he could desire. The king further +promised that he would provide the funds necessary for building a +house and for founding the greatest observatory that had ever yet +been reared for the study of the heavens. After due deliberation and +consultation with his friends, Tycho accepted the king's offer. He +was forthwith granted a pension, and a deed was drawn up formally +assigning the Island of Hven to his use all the days of his life. + +The foundation of the famous castle of Uraniborg was laid on 30th +August, 1576. The ceremony was a formal and imposing one, in +accordance with Tycho's ideas of splendour. A party of scientific +friends had assembled, and the time had been chosen so that the +heavenly bodies were auspiciously placed. Libations of costly wines +were poured forth, and the stone was placed with due solemnity. The +picturesque character of this wonderful temple for the study of the +stars may be seen in the figures with which this chapter is +illustrated. + +One of the most remarkable instruments that has ever been employed in +studying the heavens was the mural quadrant which Tycho erected in +one of the apartments of Uraniborg. By its means the altitudes of +the celestial bodies could be observed with much greater accuracy +than had been previously attainable. This wonderful contrivance is +represented on the preceding page. It will be observed that the +walls of the room are adorned by pictures with a lavishness of +decoration not usually to be found in scientific establishments. + +A few years later, when the fame of the observatory at Hven became +more widely spread, a number of young men flocked to Tycho to study +under his direction. He therefore built another observatory for +their use in which the instruments were placed in subterranean rooms +of which only the roofs appeared above the ground. There was a +wonderful poetical inscription over the entrance to this underground +observatory, expressing the astonishment of Urania at finding, even +in the interior of the earth, a cavern devoted to the study of the +heavens. Tycho was indeed always fond of versifying, and he lost no +opportunity of indulging this taste whenever an occasion presented +itself. + +Around the walls of the subterranean observatory were the pictures of +eight astronomers, each with a suitable inscription--one of these of +course represented Tycho himself, and beneath were written words to +the effect that posterity should judge of his work. The eighth +picture depicted an astronomer who has not yet come into existence. +Tychonides was his name, and the inscription presses the modest hope +that when he does appear he will be worthy of his great predecessor. +The vast expenses incurred in the erection and the maintenance of +this strange establishment were defrayed by a succession of grants +from the royal purse. + +For twenty years Tycho laboured hard at Uraniborg in the pursuit of +science. His work mainly consisted in the determination of the +places of the moon, the planets, and the stars on the celestial +sphere. The extraordinary pains taken by Tycho to have his +observations as accurate as his instruments would permit, have justly +entitled him to the admiration of all succeeding astronomers. His +island home provided the means of recreation as well as a place for +work. He was surrounded by his family, troops of friends were not +wanting, and a pet dwarf seems to have been an inmate of his curious +residence. By way of change from his astronomical labours he used +frequently to work with his students in his chemical laboratory. It +is not indeed known what particular problems in chemistry occupied +his attention. We are told, however, that he engaged largely in the +production of medicines, and as these appear to have been dispensed +gratuitously there was no lack of patients. + +Tycho's imperious and grasping character frequently brought him into +difficulties, which seem to have increased with his advancing years. +He had ill-treated one of his tenants on Hven, and an adverse +decision by the courts seems to have greatly exasperated the +astronomer. Serious changes also took place in his relations to the +court at Copenhagen. When the young king was crowned in 1596, he +reversed the policy of his predecessor with reference to Hven. The +liberal allowances to Tycho were one after another withdrawn, and +finally even his pension was stopped. Tycho accordingly abandoned +Hven in a tumult of rage and mortification. A few years later we +find him in Bohemia a prematurely aged man, and he died on the 24th +October, 1601. + + + + +GALILEO. + + +Among the ranks of the great astronomers it would be difficult to +find one whose life presents more interesting features and remarkable +vicissitudes than does that of Galileo. We may consider him as the +patient investigator and brilliant discoverer. We may consider him +in his private relations, especially to his daughter, Sister Maria +Celeste, a woman of very remarkable character; and we have also the +pathetic drama at the close of Galileo's life, when the philosopher +drew down upon himself the thunders of the Inquisition. + +The materials for the sketch of this astonishing man are sufficiently +abundant. We make special use in this place of those charming +letters which his daughter wrote to him from her convent home. More +than a hundred of these have been preserved, and it may well be +doubted whether any more beautiful and touching series of letters +addressed to a parent by a dearly loved child have ever been +written. An admirable account of this correspondence is contained in +a little book entitled "The Private Life of Galileo," published +anonymously by Messrs. Macmillan in 1870, and I have been much +indebted to the author of that volume for many of the facts contained +in this chapter. + +Galileo was born at Pisa, on 18th February, 1564. He was the eldest +son of Vincenzo de' Bonajuti de' Galilei, a Florentine noble. +Notwithstanding his illustrious birth and descent, it would seem that +the home in which the great philosopher's childhood was spent was an +impoverished one. It was obvious at least that the young Galileo +would have to be provided with some profession by which he might earn +a livelihood. From his father he derived both by inheritance and by +precept a keen taste for music, and it appears that he became an +excellent performer on the lute. He was also endowed with +considerable artistic power, which he cultivated diligently. Indeed, +it would seem that for some time the future astronomer entertained +the idea of devoting himself to painting as a profession. His +father, however, decided that he should study medicine. Accordingly, +we find that when Galileo was seventeen years of age, and had added a +knowledge of Greek and Latin to his acquaintance with the fine arts, +he was duly entered at the University of Pisa. + +Here the young philosopher obtained some inkling of mathematics, +whereupon he became so much interested in this branch of science, +that he begged to be allowed to study geometry. In compliance with +his request, his father permitted a tutor to be engaged for this +purpose; but he did so with reluctance, fearing that the attention of +the young student might thus be withdrawn from that medical work +which was regarded as his primary occupation. The event speedily +proved that these anxieties were not without some justification. The +propositions of Euclid proved so engrossing to Galileo that it was +thought wise to avoid further distraction by terminating the +mathematical tutor's engagement. But it was too late for the desired +end to be attained. Galileo had now made such progress that he was +able to continue his geometrical studies by himself. Presently he +advanced to that famous 47th proposition which won his lively +admiration, and on he went until he had mastered the six books of +Euclid, which was a considerable achievement for those days. + +The diligence and brilliance of the young student at Pisa did not, +however, bring him much credit with the University authorities. In +those days the doctrines of Aristotle were regarded as the embodiment +of all human wisdom in natural science as well as in everything +else. It was regarded as the duty of every student to learn +Aristotle off by heart, and any disposition to doubt or even to +question the doctrines of the venerated teacher was regarded as +intolerable presumption. But young Galileo had the audacity to think +for himself about the laws of nature. He would not take any +assertion of fact on the authority of Aristotle when he had the means +of questioning nature directly as to its truth or falsehood. His +teachers thus came to regard him as a somewhat misguided youth, +though they could not but respect the unflagging industry with which +he amassed all the knowledge he could acquire. + +[PLATE: GALILEO'S PENDULUM.] + +We are so accustomed to the use of pendulums in our clocks that +perhaps we do not often realise that the introduction of this method +of regulating time-pieces was really a notable invention worthy the +fame of the great astronomer to whom it was due. It appears that +sitting one day in the Cathedral of Pisa, Galileo's attention became +concentrated on the swinging of a chandelier which hung from the +ceiling. It struck him as a significant point, that whether the arc +through which the pendulum oscillated was a long one or a short one, +the time occupied in each vibration was sensibly the same. This +suggested to the thoughtful observer that a pendulum would afford the +means by which a time-keeper might be controlled, and accordingly +Galileo constructed for the first time a clock on this principle. The +immediate object sought in this apparatus was to provide a means of +aiding physicians in counting the pulses of their patients. + +The talents of Galileo having at length extorted due recognition from +the authorities, he was appointed, at the age of twenty-five, +Professor of Mathematics at the University of Pisa. Then came the +time when he felt himself strong enough to throw down the gauntlet to +the adherents of the old philosophy. As a necessary part of his +doctrine on the movement of bodies Aristotle had asserted that the +time occupied by a stone in falling depends upon its weight, so that +the heavier the stone the less time would it require to fall from a +certain height to the earth. It might have been thought that a +statement so easily confuted by the simplest experiments could never +have maintained its position in any accepted scheme of philosophy. +But Aristotle had said it, and to anyone who ventured to express a +doubt the ready sneer was forthcoming, "Do you think yourself a +cleverer man than Aristotle?" Galileo determined to demonstrate in +the most emphatic manner the absurdity of a doctrine which had for +centuries received the sanction of the learned. The summit of the +Leaning Tower of Pisa offered a highly dramatic site for the great +experiment. The youthful professor let fall from the overhanging top +a large heavy body and a small light body simultaneously. According +to Aristotle the large body ought to have reached the ground much +sooner than the small one, but such was found not to be the case. In +the sight of a large concourse of people the simple fact was +demonstrated that the two bodies fell side by side, and reached the +ground at the same time. Thus the first great step was taken in the +overthrow of that preposterous system of unquestioning adhesion to +dogma, which had impeded the development of the knowledge of nature +for nearly two thousand years. + +This revolutionary attitude towards the ancient beliefs was not +calculated to render Galileo's relations with the University +authorities harmonious. He had also the misfortune to make enemies +in other quarters. Don Giovanni de Medici, who was then the Governor +of the Port of Leghorn, had designed some contrivance by which he +proposed to pump out a dock. But Galileo showed up the absurdity of +this enterprise in such an aggressive manner that Don Giovanni took +mortal offence, nor was he mollified when the truths of Galileo's +criticisms were abundantly verified by the total failure of his +ridiculous invention. In various ways Galileo was made to feel his +position at Pisa so unpleasant that he was at length compelled to +abandon his chair in the University. The active exertions of his +friends, of whom Galileo was so fortunate as to have had throughout +his life an abundant supply, then secured his election to the +Professorship of Mathematics at Padua, whither he went in 1592. + +[PLATE: PORTRAIT OF GALILEO.] + +It was in this new position that Galileo entered on that marvellous +career of investigation which was destined to revolutionize science. +The zeal with which he discharged his professorial duties was indeed +of the most unremitting character. He speedily drew such crowds to +listen to his discourses on Natural Philosophy that his lecture-room +was filled to overflowing. He also received many private pupils in +his house for special instruction. Every moment that could be spared +from these labours was devoted to his private study and to his +incessant experiments. + +Like many another philosopher who has greatly extended our knowledge +of nature, Galileo had a remarkable aptitude for the invention of +instruments designed for philosophical research. To facilitate his +practical work, we find that in 1599 he had engaged a skilled workman +who was to live in his house, and thus be constantly at hand to try +the devices for ever springing from Galileo's fertile brain. Among +the earliest of his inventions appears to have been the thermometer, +which he constructed in 1602. No doubt this apparatus in its +primitive form differed in some respects from the contrivance we call +by the same name. Galileo at first employed water as the agent, by +the expansion of which the temperature was to be measured. He +afterwards saw the advantage of using spirits for the same purpose. +It was not until about half a century later that mercury came to be +recognised as the liquid most generally suitable for the thermometer. + +The time was now approaching when Galileo was to make that mighty +step in the advancement of human knowledge which followed on the +application of the telescope to astronomy. As to how his idea of +such an instrument originated, we had best let him tell us in his own +words. The passage is given in a letter which he writes to his +brother-in-law, Landucci. + +"I write now because I have a piece of news for you, though whether +you will be glad or sorry to hear it I cannot say; for I have now no +hope of returning to my own country, though the occurrence which has +destroyed that hope has had results both useful and honourable. You +must know, then, that two months ago there was a report spread here +that in Flanders some one had presented to Count Maurice of Nassau a +glass manufactured in such a way as to make distant objects appear +very near, so that a man at the distance of two miles could be +clearly seen. This seemed to me so marvellous that I began to think +about it. As it appeared to me to have a foundation in the Theory of +Perspective, I set about contriving how to make it, and at length I +found out, and have succeeded so well that the one I have made is far +superior to the Dutch telescope. It was reported in Venice that I +had made one, and a week since I was commanded to show it to his +Serenity and to all the members of the senate, to their infinite +amazement. Many gentlemen and senators, even the oldest, have +ascended at various times the highest bell-towers in Venice to spy +out ships at sea making sail for the mouth of the harbour, and have +seen them clearly, though without my telescope they would have been +invisible for more than two hours. The effect of this instrument is +to show an object at a distance of say fifty miles, as if it were but +five miles." + +The remarkable properties of the telescope at once commanded +universal attention among intellectual men. Galileo received +applications from several quarters for his new instrument, of which +it would seem that he manufactured a large number to be distributed +as gifts to various illustrious personages. + +But it was reserved for Galileo himself to make that application of +the instrument to the celestial bodies by which its peculiar powers +were to inaugurate the new era in astronomy. The first discovery +that was made in this direction appears to have been connected with +the number of the stars. Galileo saw to his amazement that through +his little tube he could count ten times as many stars in the sky as +his unaided eye could detect. Here was, indeed, a surprise. We are +now so familiar with the elementary facts of astronomy that it is not +always easy to realise how the heavens were interpreted by the +observers in those ages prior to the invention of the telescope. We +can hardly, indeed, suppose that Galileo, like the majority of those +who ever thought of such matters, entertained the erroneous belief +that the stars were on the surface of a sphere at equal distances +from the observer. No one would be likely to have retained his +belief in such a doctrine when he saw how the number of visible stars +could be increased tenfold by means of Galileo's telescope. It would +have been almost impossible to refuse to draw the inference that the +stars thus brought into view were still more remote objects which the +telescope was able to reveal, just in the same way as it showed +certain ships to the astonished Venetians, when at the time these +ships were beyond the reach of unaided vision. + +Galileo's celestial discoveries now succeeded each other rapidly. +That beautiful Milky Way, which has for ages been the object of +admiration to all lovers of nature, never disclosed its true nature +to the eye of man till the astronomer of Padua turned on it his magic +tube. The splendid zone of silvery light was then displayed as +star-dust scattered over the black background of the sky. It was +observed that though the individual stars were too small to be seen +severally without optical aid, yet such was their incredible number +that the celestial radiance produced that luminosity with which every +stargazer was so familiar. + +But the greatest discovery made by the telescope in these early days, +perhaps, indeed, the greatest discovery that the telescope has ever +accomplished, was the detection of the system of four satellites +revolving around the great planet Jupiter. This phenomenon was so +wholly unexpected by Galileo that, at first, he could hardly believe +his eyes. However, the reality of the existence of a system of four +moons attending the great planet was soon established beyond all +question. Numbers of great personages crowded to Galileo to see for +themselves this beautiful miniature representing the sun with its +system of revolving planets. + +Of course there were, as usual, a few incredulous people who refused +to believe the assertion that four more moving bodies had to be added +to the planetary system. They scoffed at the notion; they said the +satellites may have been in the telescope, but that they were not in +the sky. One sceptical philosopher is reported to have affirmed, +that even if he saw the moons of Jupiter himself he would not believe +in them, as their existence was contrary to the principles of +common-sense! + +There can be no doubt that a special significance attached to the new +discovery at this particular epoch in the history of science. It +must be remembered that in those days the doctrine of Copernicus, +declaring that the sun, and not the earth, was the centre of the +system, that the earth revolved on its axis once a day, and that it +described a mighty circle round the sun once a year, had only +recently been promulgated. This new view of the scheme of nature had +been encountered with the most furious opposition. It may possibly +have been that Galileo himself had not felt quite confident in the +soundness of the Copernican theory, prior to the discovery of the +satellites of Jupiter. But when a picture was there exhibited in +which a number of relatively small globes were shown to be revolving +around a single large globe in the centre, it seemed impossible not +to feel that the beautiful spectacle so displayed was an emblem of +the relations of the planets to the sun. It was thus made manifest +to Galileo that the Copernican theory of the planetary system must be +the true one. The momentous import of this opinion upon the future +welfare of the great philosopher will presently appear. + +It would seem that Galileo regarded his residence at Padua as a state +of undesirable exile from his beloved Tuscany. He had always a +yearning to go back to his own country and at last the desired +opportunity presented itself. For now that Galileo's fame had become +so great, the Grand Duke of Tuscany desired to have the philosopher +resident at Florence, in the belief that he would shed lustre on the +Duke's dominions. Overtures were accordingly made to Galileo, and +the consequence was that in 1616 we find him residing at Florence, +bearing the title of Mathematician and Philosopher to the Grand Duke. + +Two daughters, Polissena and Virginia, and one son, Vincenzo, had +been born to Galileo in Padua. It was the custom in those days that +as soon as the daughter of an Italian gentleman had grown up, her +future career was somewhat summarily decided. Either a husband was +to be forthwith sought out, or she was to enter the convent with the +object of taking the veil as a professed nun. It was arranged that +the two daughters of Galileo, while still scarcely more than +children, should both enter the Franciscan convent of St. Matthew, at +Arcetri. The elder daughter Polissena, took the name of Sister Maria +Celeste, while Virginia became Sister Arcangela. The latter seems to +have been always delicate and subject to prolonged melancholy, and +she is of but little account in the narrative of the life of +Galileo. But Sister Maria Celeste, though never leaving the convent, +managed to preserve a close intimacy with her beloved father. This +was maintained only partly by Galileo's visits, which were very +irregular and were, indeed, often suspended for long intervals. But +his letters to this daughter were evidently frequent and +affectionate, especially in the latter part of his life. Most +unfortunately, however, all his letters have been lost. There are +grounds for believing that they were deliberately destroyed when +Galileo was seized by the Inquisition, lest they should have been +used as evidence against him, or lest they should have compromised +the convent where they were received. But Sister Maria Celeste's +letters to her father have happily been preserved, and most touching +these letters are. We can hardly read them without thinking how the +sweet and gentle nun would have shrunk from the idea of their +publication. + +Her loving little notes to her "dearest lord and father," as she used +affectionately to call Galileo, were almost invariably accompanied by +some gift, trifling it may be, but always the best the poor nun had +to bestow. The tender grace of these endearing communications was +all the more precious to him from the fact that the rest of Galileo's +relatives were of quite a worthless description. He always +acknowledged the ties of his kindred in the most generous way, but +their follies and their vices, their selfishness and their +importunities, were an incessant source of annoyance to him, almost +to the last day of his life. + +On 19th December, 1625, Sister Maria Celeste writes:-- + +"I send two baked pears for these days of vigil. But as the greatest +treat of all, I send you a rose, which ought to please you extremely, +seeing what a rarity it is at this season; and with the rose you must +accept its thorns, which represent the bitter passion of our Lord, +whilst the green leaves represent the hope we may entertain that +through the same sacred passion we, having passed through the +darkness of the short winter of our mortal life, may attain to the +brightness and felicity of an eternal spring in heaven." + +When the wife and children of Galileo's shiftless brother came to +take up their abode in the philosopher's home, Sister Maria Celeste +feels glad to think that her father has now some one who, however +imperfectly, may fulfil the duty of looking after him. A graceful +note on Christmas Eve accompanies her little gifts. She hopes that-- + +"In these holy days the peace of God may rest on him and all the +house. The largest collar and sleeves I mean for Albertino, the +other two for the two younger boys, the little dog for baby, and the +cakes for everybody, except the spice-cakes, which are for you. +Accept the good-will which would readily do much more." + +The extraordinary forbearance with which Galileo continually placed +his time, his purse, and his influence at the service of those who +had repeatedly proved themselves utterly unworthy of his countenance, +is thus commented on by the good nun.-- + +"Now it seems to me, dearest lord and father, that your lordship is +walking in the right path, since you take hold of every occasion that +presents itself to shower continual benefits on those who only repay +you with ingratitude. This is an action which is all the more +virtuous and perfect as it is the more difficult." + +When the plague was raging in the neighbourhood, the loving +daughter's solicitude is thus shown:-- + +"I send you two pots of electuary as a preventive against the +plague. The one without the label consists of dried figs, walnuts, +rue, and salt, mixed together with honey. A piece of the size of a +walnut to be taken in the morning, fasting, with a little Greek +wine." + +The plague increasing still more, Sister Maria Celeste obtained with +much difficulty, a small quantity of a renowned liqueur, made by +Abbess Ursula, an exceptionally saintly nun. This she sends to her +father with the words:-- + +"I pray your lordship to have faith in this remedy. For if you have +so much faith in my poor miserable prayers, much more may you have in +those of such a holy person; indeed, through her merits you may feel +sure of escaping all danger from the plague." + +Whether Galileo took the remedy we do not know, but at all events +he escaped the plague. + +[PLATE: THE VILLA ARCETRI. +Galileo's residence, where Milton visited him.] + +From Galileo's new home in Florence the telescope was again directed +to the skies, and again did astounding discoveries reward the +astronomer's labours. The great success which he had met with in +studying Jupiter naturally led Galileo to look at Saturn. Here he +saw a spectacle which was sufficiently amazing, though he failed to +interpret it accurately. It was quite manifest that Saturn did not +exhibit a simple circular disc like Jupiter, or like Mars. It seemed +to Galileo as if the planet consisted of three bodies, a large globe +in the centre, and a smaller one on each side. The enigmatical +nature of the discovery led Galileo to announce it in an enigmatical +manner. He published a string of letters which, when duly +transposed, made up a sentence which affirmed that the planet Saturn +was threefold. Of course we now know that this remarkable appearance +of the planet was due to the two projecting portions of the ring. +With the feeble power of Galileo's telescope, these seemed merely +like small globes or appendages to the large central body. + +The last of Galileo's great astronomical discoveries related to the +libration of the moon. I think that the detection of this phenomenon +shows his acuteness of observation more remarkably than does any one +of his other achievements with the telescope. It is well known that +the moon constantly keeps the same face turned towards the earth. +When, however, careful measurements have been made with regard to the +spots and marks on the lunar surface, it is found that there is a +slight periodic variation which permits us to see now a little to the +east or to the west, now a little to the north or to the south of +the average lunar disc. + +But the circumstances which make the career of Galileo so especially +interesting from the biographer's point of view, are hardly so much +the triumphs that he won as the sufferings that he endured. The +sufferings and the triumphs were, however, closely connected, and it +is fitting that we should give due consideration to what was perhaps +the greatest drama in the history of science. + +On the appearance of the immortal work of Copernicus, in which it was +taught that the earth rotated on its axis, and that the earth, like +the other planets, revolved round the sun, orthodoxy stood aghast. +The Holy Roman Church submitted this treatise, which bore the name +"De Revolutionibus Orbium Coelestium," to the Congregation of the +Index. After due examination it was condemned as heretical in 1615. +Galileo was suspected, on no doubt excellent grounds, of entertaining +the objectionable views of Copernicus. He was accordingly privately +summoned before Cardinal Bellarmine on 26th February 1616, and duly +admonished that he was on no account to teach or to defend the +obnoxious doctrines. Galileo was much distressed by this +intimation. He felt it a serious matter to be deprived of the +privilege of discoursing with his friends about the Copernican +system, and of instructing his disciples in the principles of the +great theory of whose truth he was perfectly convinced. It pained +him, however, still more to think, devout Catholic as he was, that +such suspicions of his fervent allegiance to his Church should ever +have existed, as were implied by the words and monitions of Cardinal +Bellarmine. + +In 1616, Galileo had an interview with Pope Paul V., who received the +great astronomer very graciously, and walked up and down with him in +conversation for three-quarters of an hour. Galileo complained to +his Holiness of the attempts made by his enemies to embarrass him +with the authorities of the Church, but the Pope bade him be +comforted. His Holiness had himself no doubts of Galileo's +orthodoxy, and he assured him that the Congregation of the Index +should give Galileo no further trouble so long as Paul V. was in the +chair of St. Peter. + +On the death of Paul V. in 1623, Maffeo Barberini was elected Pope, +as Urban VIII. This new Pope, while a cardinal, had been an intimate +friend of Galileo's, and had indeed written Latin verses in praise of +the great astronomer and his discoveries. It was therefore not +unnatural for Galileo to think that the time had arrived when, with +the use of due circumspection, he might continue his studies and his +writings, without fear of incurring the displeasure of the Church. +Indeed, in 1624, one of Galileo's friends writing from Rome, urges +Galileo to visit the city again, and added that-- + +"Under the auspices of this most excellent, learned, and benignant +Pontiff, science must flourish. Your arrival will be welcome to his +Holiness. He asked me if you were coming, and when, and in short, he +seems to love and esteem you more than ever." + +The visit was duly paid, and when Galileo returned to Florence, the +Pope wrote a letter from which the following is an extract, +commanding the philosopher to the good offices of the young +Ferdinand, who had shortly before succeeded his father in the Grand +Duchy of Tuscany. + +"We find in Galileo not only literary distinction, but also the love +of piety, and he is also strong in those qualities by which the +pontifical good-will is easily obtained. And now, when he has been +brought to this city to congratulate us on our elevation, we have +very lovingly embraced him; nor can we suffer him to return to the +country whither your liberality calls him, without an ample provision +of pontifical love. And that you may know how dear he is to us, we +have willed to give him this honourable testimonial of virtue and +piety. And we further signify that every benefit which you shall +confer upon him, imitating or even surpassing your father's +liberality, will conduce to our gratification." + +The favourable reception which had been accorded to him by Pope Urban +VIII. seems to have led Galileo to expect that there might be some +corresponding change in the attitude of the Papal authorities on the +great question of the stability of the earth. He accordingly +proceeded with the preparation of the chief work of his life, "The +Dialogue of the two Systems." It was submitted for inspection by the +constituted authorities. The Pope himself thought that, if a few +conditions which he laid down were duly complied with, there could be +no objection to the publication of the work. In the first place, the +title of the book was to be so carefully worded as to show plainly +that the Copernican doctrine was merely to be regarded as an +hypothesis, and not as a scientific fact. Galileo was also +instructed to conclude the book with special arguments which had been +supplied by the Pope himself, and which appeared to his Holiness to +be quite conclusive against the new doctrine of Copernicus. + +Formal leave for the publication of the Dialogue was then given to +Galileo by the Inquisitor General, and it was accordingly sent to the +press. It might be thought that the anxieties of the astronomer +about his book would then have terminated. As a matter of fact, they +had not yet seriously begun. Riccardi, the Master of the Sacred +Palace, having suddenly had some further misgivings, sent to Galileo +for the manuscript while the work was at the printer's, in order that +the doctrine it implied might be once again examined. Apparently, +Riccardi had come to the conclusion that he had not given the matter +sufficient attention, when the authority to go to press had been +first and, perhaps, hastily given. Considerable delay in the issue +of the book was the result of these further deliberations. At last, +however, in June, 1632, Galileo's great work, "The Dialogue of the +two Systems," was produced for the instruction of the world, though +the occasion was fraught with ruin to the immortal author. + +[PLATE: FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.] + +The book, on its publication, was received and read with the greatest +avidity. But presently the Master of The Sacred Palace found reason +to regret that he had given his consent to its appearance. He +accordingly issued a peremptory order to sequestrate every copy in +Italy. This sudden change in the Papal attitude towards Galileo +formed the subject of a strong remonstrance addressed to the Roman +authorities by the Grand Duke of Tuscany. The Pope himself seemed to +have become impressed all at once with the belief that the work +contained matter of an heretical description. The general +interpretation put upon the book seems to have shown the authorities +that they had mistaken its true tendency, notwithstanding the fact +that it had been examined again and again by theologians deputed for +the duty. To the communication from the Grand Duke the Pope returned +answer, that he had decided to submit the book to a congregation of +"learned, grave, and saintly men," who would weigh every word in it. +The views of his Holiness personally on the subject were expressed in +his belief that the Dialogue contained the most perverse matter that +could come into a reader's hands. + +The Master of the Sacred Palace was greatly blamed by the authorities +for having given his sanction to its issue. He pleaded that the book +had not been printed in the precise terms of the original manuscript +which had been submitted to him. It was also alleged that Galileo +had not adhered to his promise of inserting properly the arguments +which the Pope himself had given in support of the old and orthodox +view. One of these had, no doubt, been introduced, but, so far from +mending Galileo's case, it had made matters really look worse for the +poor philosopher. The Pope's argument had been put into the mouth of +one of the characters in the Dialogue named "Simplicio." Galileo's +enemies maintained that by adopting such a method for the expression +of his Holiness's opinion, Galileo had intended to hold the Pope +himself up to ridicule. Galileo's friends maintained that nothing +could have been farther from his intention. It seems, however, +highly probable that the suspicions thus aroused had something to say +to the sudden change of front on the part of the Papal authorities. + +On 1st October, 1632, Galileo received an order to appear before the +Inquisition at Rome on the grave charge of heresy. Galileo, of +course, expressed his submission, but pleaded for a respite from +compliance with the summons, on the ground of his advanced age and +his failing health. The Pope was, however, inexorable; he said that +he had warned Galileo of his danger while he was still his friend. +The command could not be disobeyed. Galileo might perform the +journey as slowly as he pleased, but it was imperatively necessary +for him to set forth and at once. + +On 20th January, 1633, Galileo started on his weary journey to Rome, +in compliance with this peremptory summons. On 13th February he was +received as the guest of Niccolini, the Tuscan ambassador, who had +acted as his wise and ever-kind friend throughout the whole affair. +It seemed plain that the Holy Office were inclined to treat Galileo +with as much clemency and consideration as was consistent with the +determination that the case against him should be proceeded with to +the end. The Pope intimated that in consequence of his respect for +the Grand Duke of Tuscany he should permit Galileo to enjoy the +privilege, quite unprecedented for a prisoner charged with heresy, of +remaining as an inmate in the ambassador's house. He ought, +strictly, to have been placed in the dungeons of the Inquisition. +When the examination of the accused had actually commenced, Galileo +was confined, not, indeed, in the dungeons, but in comfortable rooms +at the Holy Office. + +By the judicious and conciliatory language of submission which +Niccolini had urged Galileo to use before the Inquisitors, they were +so far satisfied that they interceded with the Pope for his release. +During the remainder of the trial Galileo was accordingly permitted +to go back to the ambassador's, where he was most heartily welcomed. +Sister Maria Celeste, evidently thinking this meant that the whole +case was at an end, thus expresses herself:-- + +"The joy that your last dear letter brought me, and the having to +read it over and over to the nuns, who made quite a jubilee on +hearing its contents, put me into such an excited state that at last +I got a severe attack of headache." + +In his defence Galileo urged that he had already been acquitted in +1616 by Cardinal Bellarmine, when a charge of heresy was brought +against him, and he contended that anything he might now have done, +was no more than he had done on the preceding occasion, when the +orthodoxy of his doctrines received solemn confirmation. The +Inquisition seemed certainly inclined to clemency, but the Pope was +not satisfied. Galileo was accordingly summoned again on the 21st +June. He was to be threatened with torture if he did not forthwith +give satisfactory explanations as to the reasons which led him to +write the Dialogue. In this proceeding the Pope assured the Tuscan +ambassador that he was treating Galileo with the utmost consideration +possible in consequence of his esteem and regard for the Grand Duke, +whose servant Galileo was. It was, however, necessary that some +exemplary punishment be meted out to the astronomer, inasmuch as by +the publication of the Dialogue he had distinctly disobeyed the +injunction of silence laid upon him by the decree of 1616. Nor was +it admissible for Galileo to plead that his book had been sanctioned +by the Master of the Sacred College, to whose inspection it had been +again and again submitted. It was held, that if the Master of the +Sacred College had been unaware of the solemn warning the philosopher +had already received sixteen years previously, it was the duty of +Galileo to have drawn his attention to that fact. + +On the 22nd June, 1633, Galileo was led to the great hall of the +Inquisition, and compelled to kneel before the cardinals there +assembled and hear his sentence. In a long document, most +elaborately drawn up, it is definitely charged against Galileo that, +in publishing the Dialogue, he committed the essentially grave error +of treating the doctrine of the earth's motion as open to +discussion. Galileo knew, so the document affirmed, that the Church +had emphatically pronounced this notion to be contrary to Holy Writ, +and that for him to consider a doctrine so stigmatized as having any +shadow of probability in its favour was an act of disrespect to the +authority of the Church which could not be overlooked. It was also +charged against Galileo that in his Dialogue he has put the strongest +arguments into the mouth, not of those who supported the orthodox +doctrine, but of those who held the theory as to the earth's motion +which the Church had so deliberately condemned. + +After due consideration of the defence made by the prisoner, it was +thereupon decreed that he had rendered himself vehemently suspected +of heresy by the Holy Office, and in consequence had incurred all the +censures and penalties of the sacred canons, and other decrees +promulgated against such persons. The graver portion of these +punishments would be remitted, if Galileo would solemnly repudiate +the heresies referred to by an abjuration to be pronounced by him in +the terms laid down. + +At the same time it was necessary to mark, in some emphatic manner, +the serious offence which had been committed, so that it might serve +both as a punishment to Galileo and as a warning to others. It was +accordingly decreed that he should be condemned to imprisonment in +the Holy Office during the pleasure of the Papal authorities, and +that he should recite once a week for three years the seven +Penitential Psalms. + +Then followed that ever-memorable scene in the great hall of the +Inquisition, in which the aged and infirm Galileo, the inventor of +the telescope and the famous astronomer, knelt down to abjure before +the most eminent and reverend Lords Cardinal, Inquisitors General +throughout the Christian Republic against heretical depravity. With +his hands on the Gospels, Galileo was made to curse and detest the +false opinion that the sun was the centre of the universe and +immovable, and that the earth was not the centre of the same, and +that it moved. He swore that for the future he will never say nor +write such things as may bring him under suspicion, and that if he +does so he submits to all the pains and penalties of the sacred +canons. This abjuration was subsequently read in Florence before +Galileo's disciples, who had been specially summoned to attend. + +It has been noted that neither on the first occasion, in 1616, nor on +the second in 1633, did the reigning Pope sign the decrees concerning +Galileo. The contention has accordingly been made that Paul V. and +Urban VIII. are both alike vindicated from any technical +responsibility for the attitude of the Romish Church towards the +Copernican doctrines. The significance of this circumstance has been +commented on in connection with the doctrine of the infallibility of +the Pope. + +We can judge of the anxiety felt by Sister Maria Celeste about her +beloved father during these terrible trials. The wife of the +ambassador Niccolini, Galileo's steadfast friend, most kindly wrote +to give the nun whatever quieting assurances the case would permit. +There is a renewed flow of these touching epistles from the daughter +to her father. Thus she sends word-- + +"The news of your fresh trouble has pierced my soul with grief all +the more that it came quite unexpectedly." + +And again, on hearing that he had been permitted to leave Rome, +she writes-- + +"I wish I could describe the rejoicing of all the mothers and sisters +on hearing of your happy arrival at Siena. It was indeed most +extraordinary. On hearing the news the Mother Abbess and many of the +nuns ran to me, embracing me and weeping for joy and tenderness." + +The sentence of imprisonment was at first interpreted leniently by +the Pope. Galileo was allowed to reside in qualified durance in the +archbishop's house at Siena. Evidently the greatest pain that he +endured arose from the forced separation from that daughter, whom he +had at last learned to love with an affection almost comparable with +that she bore to him. She had often told him that she never had any +pleasure equal to that with which she rendered any service to her +father. To her joy, she discovers that she can relieve him from the +task of reciting the seven Penitential Psalms which had been imposed +as a Penance:-- + +"I began to do this a while ago," she writes, "and it gives me much +pleasure. First, because I am persuaded that prayer in obedience to +Holy Church must be efficacious; secondly, in order to save you the +trouble of remembering it. If I had been able to do more, most +willingly would I have entered a straiter prison than the one I live +in now, if by so doing I could have set you at liberty." + +[PLATE: CREST OF GALILEO'S FAMILY.] + +Sister Maria Celeste was gradually failing in health, but the great +privilege was accorded to her of being able once again to embrace her +beloved lord and master. Galileo had, in fact, been permitted to +return to his old home; but on the very day when he heard of his +daughter's death came the final decree directing him to remain in his +own house in perpetual solitude. + +Amid the advancing infirmities of age, the isolation from friends, +and the loss of his daughter, Galileo once again sought consolation +in hard work. He commenced his famous dialogue on Motion. Gradually, +however, his sight began to fail, and blindness was at last added to +his other troubles. On January 2nd, 1638, he writes to Diodati:-- + +"Alas, your dear friend and servant, Galileo, has been for the last +month perfectly blind, so that this heaven, this earth, this universe +which I by my marvellous discoveries and clear demonstrations have +enlarged a hundred thousand times beyond the belief of the wise men +of bygone ages, henceforward is for me shrunk into such a small space +as is filled by my own bodily sensations." + +But the end was approaching--the great philosopher, was attacked by +low fever, from which he died on the 8th January, 1643. + + + + +KEPLER. + + +While the illustrious astronomer, Tycho Brahe, lay on his death-bed, +he had an interview which must ever rank as one of the important +incidents in the history of science. The life of Tycho had been +passed, as we have seen, in the accumulation of vast stores of +careful observations of the positions of the heavenly bodies. It was +not given to him to deduce from his splendid work the results to +which they were destined to lead. It was reserved for another +astronomer to distil, so to speak, from the volumes in which Tycho's +figures were recorded, the great truths of the universe which those +figures contained. Tycho felt that his work required an interpreter, +and he recognised in the genius of a young man with whom he was +acquainted the agent by whom the world was to be taught some of the +great truths of nature. To the bedside of the great Danish +astronomer the youthful philosopher was summoned, and with his last +breath Tycho besought of him to spare no labour in the performance of +those calculations, by which alone the secrets of the movements of +the heavens could be revealed. The solemn trust thus imposed was +duly accepted, and the man who accepted it bore the immortal name of +Kepler. + +Kepler was born on the 27th December, 1571, at Weil, in the Duchy of +Wurtemberg. It would seem that the circumstances of his childhood +must have been singularly unhappy. His father, sprung from a +well-connected family, was but a shiftless and idle adventurer; nor +was the great astronomer much more fortunate in his other parent. His +mother was an ignorant and ill-tempered woman; indeed, the +ill-assorted union came to an abrupt end through the desertion of the +wife by her husband when their eldest son John, the hero of our +present sketch, was eighteen years old. The childhood of this lad, +destined for such fame, was still further embittered by the +circumstance that when he was four years old he had a severe attack +of small-pox. Not only was his eyesight permanently injured, but +even his constitution appears to have been much weakened by this +terrible malady. + +It seems, however, that the bodily infirmities of young John Kepler +were the immediate cause of his attention being directed to the +pursuit of knowledge. Had the boy been fitted like other boys for +ordinary manual work, there can be hardly any doubt that to manual +work his life must have been devoted. But, though his body was +feeble, he soon gave indications of the possession of considerable +mental power. It was accordingly thought that a suitable sphere for +his talents might be found in the Church which, in those days, was +almost the only profession that afforded an opening for an +intellectual career. We thus find that by the time John Kepler was +seventeen years old he had attained a sufficient standard of +knowledge to entitle him to admission on the foundation of the +University at Tubingen. + +In the course of his studies at this institution he seems to have +divided his attention equally between astronomy and divinity. It not +unfrequently happens that when a man has attained considerable +proficiency in two branches of knowledge he is not able to see very +clearly in which of the two pursuits his true vocation lies. His +friends and onlookers are often able to judge more wisely than he +himself can do as to which of the two lines it would be better for +him to pursue. This incapacity for perceiving the path in which +greatness awaited him, existed in the case of Kepler. Personally, he +inclined to enter the ministry, in which a promising career seemed +open to him. He yielded, however, to friends, who evidently knew him +better than he knew himself, and accepted in 1594, the important +Professorship of astronomy which had been offered to him in the +University of Gratz. + +It is difficult for us in these modern days to realise the somewhat +extraordinary duties which were expected from an astronomical +professor in the sixteenth century. He was, of course, required to +employ his knowledge of the heavens in the prediction of eclipses, +and of the movements of the heavenly bodies generally. This seems +reasonable enough; but what we are not prepared to accept is the +obligation which lay on the astronomers to predict the fates of +nations and the destinies of individuals. + +It must be remembered that it was the almost universal belief in +those days, that all the celestial spheres revolved in some +mysterious fashion around the earth, which appeared by far the most +important body in the universe. It was imagined that the sun, the +moon, and the stars indicated, in the vicissitudes of their +movements, the careers of nations and of individuals. Such being the +generally accepted notion, it seemed to follow that a professor who +was charged with the duty of expounding the movements of the heavenly +bodies must necessarily be looked to for the purpose of deciphering +the celestial decrees regarding the fate of man which the heavenly +luminaries were designed to announce. + +Kepler threw himself with characteristic ardour into even this +fantastic phase of the labours of the astronomical professor; he +diligently studied the rules of astrology, which the fancies of +antiquity had compiled. Believing sincerely as he did in the +connection between the aspect of the stars and the state of human +affairs, he even thought that he perceived, in the events of his own +life, a corroboration of the doctrine which affirmed the influence of +the planets upon the fate of individuals. + +[PLATE: KEPLER'S SYSTEM OF REGULAR SOLIDS.] + +But quite independently of astrology there seem to have been many +other delusions current among the philosophers of Kepler's time. It +is now almost incomprehensible how the ablest men of a few centuries +ago should have entertained such preposterous notions, as they did, +with respect to the system of the universe. As an instance of what +is here referred to, we may cite the extraordinary notion which, +under the designation of a discovery, first brought Kepler into +fame. Geometers had long known that there were five, but no more +than five, regular solid figures. There is, for instance, the cube +with six sides, which is, of course, the most familiar of these +solids. Besides the cube there are other figures of four, eight, +twelve, and twenty sides respectively. It also happened that there +were five planets, but no more than five, known to the ancients, +namely, Mercury, Venus, Mars, Jupiter, and Saturn. To Kepler's +lively imaginations this coincidence suggested the idea that the five +regular solids corresponded to the five planets, and a number of +fancied numerical relations were adduced on the subject. The +absurdity of this doctrine is obvious enough, especially when we +observe that, as is now well known, there are two large planets, and +a host of small planets, over and above the magical number of the +regular solids. In Kepler's time, however, this doctrine was so far +from being regarded as absurd, that its announcement was hailed as a +great intellectual triumph. Kepler was at once regarded with +favour. It seems, indeed, to have been the circumstance which +brought him into correspondence with Tycho Brahe. By its means also +he became known to Galileo. + +The career of a scientific professor in those early days appears +generally to have been marked by rather more striking vicissitudes +than usually befall a professor in a modern university. Kepler was a +Protestant, and as such he had been appointed to his professorship at +Gratz. A change, however, having taken place in the religious belief +entertained by the ruling powers of the University, the Protestant +professors were expelled. It seems that special influence having +been exerted in Kepler's case on account of his exceptional eminence, +he was recalled to Gratz and reinstated in the tenure of his chair. +But his pupils had vanished, so that the great astronomer was glad to +accept a post offered him by Tycho Brahe in the observatory which the +latter had recently established near Prague. + +On Tycho's death, which occurred soon after, an opening presented +itself which gave Kepler the opportunity his genius demanded. He was +appointed to succeed Tycho in the position of imperial mathematician. +But a far more important point, both for Kepler and for science, +was that to him was confided the use of Tycho's observations. It was, +indeed, by the discussion of Tycho's results that Kepler was enabled +to make the discoveries which form such an important part of +astronomical history. + +Kepler must also be remembered as one of the first great astronomers +who ever had the privilege of viewing celestial bodies through a +telescope. It was in 1610 that he first held in his hands one of +those little instruments which had been so recently applied to the +heavens by Galileo. It should, however, be borne in mind that the +epoch-making achievements of Kepler did not arise from any telescopic +observations that he made, or, indeed, that any one else made. They +were all elaborately deduced from Tycho's measurements of the +positions of the planets, obtained with his great instruments, which +were unprovided with telescopic assistance. + +To realise the tremendous advance which science received from +Kepler's great work, it is to be understood that all the astronomers +who laboured before him at the difficult subject of the celestial +motions, took it for granted that the planets must revolve in +circles. If it did not appear that a planet moved in a fixed circle, +then the ready answer was provided by Ptolemy's theory that the +circle in which the planet did move was itself in motion, so that its +centre described another circle. + +When Kepler had before him that wonderful series of observations of +the planet, Mars, which had been accumulated by the extraordinary +skill of Tycho, he proved, after much labour, that the movements of +the planet refused to be represented in a circular form. Nor would +it do to suppose that Mars revolved in one circle, the centre of +which revolved in another circle. On no such supposition could the +movements of the planets be made to tally with those which Tycho had +actually observed. This led to the astonishing discovery of the true +form of a planet's orbit. For the first time in the history of +astronomy the principle was laid down that the movement of a planet +could not be represented by a circle, nor even by combinations of +circles, but that it could be represented by an elliptic path. In +this path the sun is situated at one of those two points in the +ellipse which are known as its foci. + +[PLATE: KEPLER.] + +Very simple apparatus is needed for the drawing of one of those +ellipses which Kepler has shown to possess such astonishing +astronomical significance. Two pins are stuck through a sheet of +paper on a board, the point of a pencil is inserted in a loop of +string which passes over the pins, and as the pencil is moved round +in such a way as to keep the string stretched, that beautiful curve +known as the ellipse is delineated, while the positions of the pins +indicate the two foci of the curve. If the length of the loop of +string is unchanged then the nearer the pins are together, the +greater will be the resemblance between the ellipse and the circle, +whereas the more the pins are separated the more elongated does the +ellipse become. The orbit of a great planet is, in general, one of +those ellipses which approaches a nearly circular form. It +fortunately happens, however, that the orbit of Mars makes a wider +departure from the circular form than any of the other important +planets. It is, doubtless, to this circumstance that we must +attribute the astonishing success of Kepler in detecting the true +shape of a planetary orbit. Tycho's observations would not have been +sufficiently accurate to have exhibited the elliptic nature of a +planetary orbit which, like that of Venus, differed very little from +a circle. + +The more we ponder on this memorable achievement the more striking +will it appear. It must be remembered that in these days we know of +the physical necessity which requires that a planet shall revolve in +an ellipse and not in any other curve. But Kepler had no such +knowledge. Even to the last hour of his life he remained in +ignorance of the existence of any natural cause which ordained that +planets should follow those particular curves which geometers know so +well. Kepler's assignment of the ellipse as the true form of the +planetary orbit is to be regarded as a brilliant guess, the truth of +which Tycho's observations enabled him to verify. Kepler also +succeeded in pointing out the law according to which the velocity of +a planet at different points of its path could be accurately +specified. Here, again, we have to admire the sagacity with which +this marvellously acute astronomer guessed the deep truth of nature. +In this case also he was quite unprovided with any reason for +expecting from physical principles that such a law as he discovered +must be obeyed. It is quite true that Kepler had some slight +knowledge of the existence of what we now know as gravitation. He +had even enunciated the remarkable doctrine that the ebb and flow of +the tide must be attributed to the attraction of the moon on the +waters of the earth. He does not, however, appear to have had any +anticipation of those wonderful discoveries which Newton was destined +to make a little later, in which he demonstrated that the laws +detected by Kepler's marvellous acumen were necessary consequences of +the principle of universal gravitation. + +[PLATE: SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.] + +To appreciate the relations of Kepler and Tycho it is necessary to +note the very different way in which these illustrious astronomers +viewed the system of the heavens. It should be observed that +Copernicus had already expounded the true system, which located the +sun at the centre of the planetary system. But in the days of Tycho +Brahe this doctrine had not as yet commanded universal assent. In +fact, the great observer himself did not accept the new views of +Copernicus. It appeared to Tycho that the earth not only appeared to +be the centre of things celestial, but that it actually was the +centre. It is, indeed, not a little remarkable that a student of the +heavens so accurate as Tycho should have deliberately rejected the +Copernican doctrine in favour of the system which now seems so +preposterous. Throughout his great career, Tycho steadily observed +the places of the sun, the moon, and the planets, and as steadily +maintained that all those bodies revolved around the earth fixed in +the centre. Kepler, however, had the advantage of belonging to the +new school. He utilised the observations of Tycho in developing the +great Copernican theory whose teaching Tycho stoutly resisted. + +Perhaps a chapter in modern science may illustrate the intellectual +relation of these great men. The revolution produced by Copernicus +in the doctrine of the heavens has often been likened to the +revolution which the Darwinian theory produced in the views held by +biologists as to life on this earth. The Darwinian theory did not at +first command universal assent even among those naturalists whose +lives had been devoted with the greatest success to the study of +organisms. Take, for instance, that great naturalist, Professor +Owen, by whose labours vast extension has been given to our knowledge +of the fossil animals which dwelt on the earth in past ages. Now, +though Owens researches were intimately connected with the great +labours of Darwin, and afforded the latter material for his +epoch-making generalization, yet Owen deliberately refused to accept +the new doctrines. Like Tycho, he kept on rigidly accumulating his +facts under the influence of a set of ideas as to the origin of +living forms which are now universally admitted to be erroneous. If, +therefore, we liken Darwin to Copernicus, and Owen to Tycho, we may +liken the biologists of the present day to Kepler, who interpreted +the results of accurate observation upon sound theoretical +principles. + +In reading the works of Kepler in the light of our modern knowledge +we are often struck by the extent to which his perception of the +sublimest truths in nature was associated with the most extravagant +errors and absurdities. But, of course, it must be remembered that +he wrote in an age in which even the rudiments of science, as we now +understand it, were almost entirely unknown. + +It may well be doubted whether any joy experienced by mortals is more +genuine than that which rewards the successful searcher after natural +truths. Every science-worker, be his efforts ever so humble, will be +able to sympathise with the enthusiastic delight of Kepler when at +last, after years of toil, the glorious light broke forth, and that +which he considered to be the greatest of his astonishing laws first +dawned upon him. Kepler rightly judged that the number of days which +a planet required to perform its voyage round the sun must be +connected in some manner with the distance from the planet to the +sun; that is to say, with the radius of the planet's orbit, inasmuch +as we may for our present object regard the planet's orbit as +circular. + +Here, again, in his search for the unknown law, Kepler had no +accurate dynamical principles to guide his steps. Of course, we now +know not only what the connection between the planet's distance and +the planet's periodic time actually is, but we also know that it is a +necessary consequence of the law of universal gravitation. Kepler, +it is true, was not without certain surmises on the subject, but they +were of the most fanciful description. His notions of the planets, +accurate as they were in certain important respects, were mixed up +with vague ideas as to the properties of metals and the geometrical +relations of the regular solids. Above all, his reasoning was +penetrated by the supposed astrological influences of the stars and +their significant relation to human fate. Under the influence of +such a farrago of notions, Kepler resolved to make all sorts of +trials in his search for the connection between the distance of a +planet from the sun and the time in which the revolution of that +planet was accomplished. + +It was quite easily demonstrated that the greater the distance of the +planet from the sun the longer was the time required for its +journey. It might have been thought that the time would be directly +proportional to the distance. It was, however, easy to show that +this supposition did not agree with the fact. Finding that this +simple relation would not do, Kepler undertook a vast series of +calculations to find out the true method of expressing the +connection. At last, after many vain attempts, he found, to his +indescribable joy, that the square of the time in which a planet +revolves around the sun was proportional to the cube of the average +distance of the planet from that body. + +The extraordinary way in which Kepler's views on celestial matters +were associated with the wildest speculations, is well illustrated in +the work in which he propounded his splendid discovery just referred +to. The announcement of the law connecting the distances of the +planets from the sun with their periodic times, was then mixed up +with a preposterous conception about the properties of the different +planets. They were supposed to be associated with some profound +music of the spheres inaudible to human ears, and performed only for +the benefit of that being whose soul formed the animating spirit of +the sun. + +Kepler was also the first astronomer who ever ventured to predict the +occurrence of that remarkable phenomenon, the transit of a planet in +front of the sun's disc. He published, in 1629, a notice to the +curious in things celestial, in which he announced that both of the +planets, Mercury and Venus, were to make a transit across the sun on +specified days in the winter of 1631. The transit of Mercury was +duly observed by Gassendi, and the transit of Venus also took place, +though, as we now know, the circumstances were such that it was not +possible for the phenomenon to be witnessed by any European +astronomer. + +In addition to Kepler's discoveries already mentioned, with which his +name will be for ever associated, his claim on the gratitude of +astronomers chiefly depends on the publication of his famous +Rudolphine tables. In this remarkable work means are provided for +finding the places of the planets with far greater accuracy than had +previously been attainable. + +Kepler, it must be always remembered, was not an astronomical +observer. It was his function to deal with the observations made by +Tycho, and, from close study and comparison of the results, to work +out the movements of the heavenly bodies. It was, in fact, Tycho who +provided as it were the raw material, while it was the genius of +Kepler which wrought that material into a beautiful and serviceable +form. For more than a century the Rudolphine tables were regarded as +a standard astronomical work. In these days we are accustomed to +find the movements of the heavenly bodies set forth with all +desirable exactitude in the NAUTICAL ALMANACK, and the similar +publication issued by foreign Governments. Let it be remembered that +it was Kepler who first imparted the proper impulse in this +direction. + +[PLATE: THE COMMEMORATION OF THE RUDOLPHINE TABLES.] + +When Kepler was twenty-six he married an heiress from Styria, who, +though only twenty-three years old, had already had some experience +in matrimony. Her first husband had died; and it was after her +second husband had divorced her that she received the addresses of +Kepler. It will not be surprising to hear that his domestic affairs +do not appear to have been particularly happy, and his wife died in +1611. Two years later, undeterred by the want of success in his +first venture, he sought a second partner, and he evidently +determined not to make a mistake this time. Indeed, the methodical +manner in which he made his choice of the lady to whom he should +propose has been duly set forth by him and preserved for our +edification. With some self-assurance he asserts that there were no +fewer than eleven spinsters desirous of sharing his joys and +sorrows. He has carefully estimated and recorded the merits and +demerits of each of these would-be brides. The result of his +deliberations was that he awarded himself to an orphan girl, +destitute even of a portion. Success attended his choice, and his +second marriage seems to have proved a much more suitable union than +his first. He had five children by the first wife and seven by the +second. + +The years of Kepler's middle life were sorely distracted by a trouble +which, though not uncommon in those days, is one which we find it +difficult to realise at the present time. His mother, Catherine +Kepler, had attained undesirable notoriety by the suspicion that she +was guilty of witchcraft. Years were spent in legal investigations, +and it was only after unceasing exertions on the part of the +astronomer for upwards of a twelve-month that he was finally able to +procure her acquittal and release from prison. + +It is interesting for us to note that at one time there was a +proposal that Kepler should forsake his native country and adopt +England as a home. It arose in this wise. The great man was +distressed throughout the greater part of his life by pecuniary +anxieties. Finding him in a strait of this description, the English +ambassador in Venice, Sir Henry Wotton, in the year 1620, besought +Kepler to come over to England, where he assured him that he would +obtain a favourable reception, and where, he was able to add, +Kepler's great scientific work was already highly esteemed. But his +efforts were unavailing; Kepler would not leave his own country. He +was then forty-nine years of age, and doubtless a home in a foreign +land, where people spoke a strange tongue, had not sufficient +attraction for him, even when accompanied with the substantial +inducements which the ambassador was able to offer. Had Kepler +accepted this invitation, he would, in transferring his home to +England, have anticipated the similar change which took place in the +career of another great astronomer two centuries later. It will be +remembered that Herschel, in his younger days, did transfer himself +to England, and thus gave to England the imperishable fame of +association with his triumphs. + +The publication of the Rudolphine tables of the celestial movements +entailed much expense. A considerable part of this was defrayed by +the Government at Venice but the balance occasioned no little trouble +and anxiety to Kepler. No doubt the authorities of those days were +even less willing to spend money on scientific matters than are the +Governments of more recent times. For several years the imperial +Treasury was importuned to relieve him from his anxieties. The +effects of so much worry, and of the long journeys which were +involved, at last broke down Kepler's health completely. As we have +already mentioned, he had never been strong from infancy, and he +finally succumbed to a fever in November, 1630, at the age of +fifty-nine. He was interred at St. Peter's Church at Ratisbon. + +Though Kepler had not those personal characteristics which have made +his great predecessor, Tycho Brahe, such a romantic figure, yet a +picturesque element in Kepler's character is not wanting. It was, +however, of an intellectual kind. His imagination, as well as his +reasoning faculties, always worked together. He was incessantly +prompted by the most extraordinary speculations. The great majority +of them were in a high degree wild and chimerical, but every now and +then one of his fancies struck right to the heart of nature, and an +immortal truth was brought to light. + +I remember visiting the observatory of one of our greatest modern +astronomers, and in a large desk he showed me a multitude of +photographs which he had attempted but which had not been successful, +and then he showed me the few and rare pictures which had succeeded, +and by which important truths had been revealed. With a felicity of +expression which I have often since thought of, he alluded to the +contents of the desk as the "chips." They were useless, but they +were necessary incidents in the truly successful work. So it is in +all great and good work. Even the most skilful man of science +pursues many a wrong scent. Time after time he goes off on some +track that plays him false. The greater the man's genius and +intellectual resource, the more numerous will be the ventures which +he makes, and the great majority of those ventures are certain to be +fruitless. They are in fact, the "chips." In Kepler's case the +chips were numerous enough. They were of the most extraordinary +variety and structure. But every now and then a sublime discovery +was made of such a character as to make us regard even the most +fantastic of Kepler's chips with the greatest veneration and respect. + + + +ISAAC NEWTON. + + +It was just a year after the death of Galileo, that an infant came +into the world who was christened Isaac Newton. Even the great fame +of Galileo himself must be relegated to a second place in comparison +with that of the philosopher who first expounded the true theory of +the universe. + +Isaac Newton was born on the 25th of December (old style), 1642, at +Woolsthorpe, in Lincolnshire, about a half-mile from Colsterworth, +and eight miles south of Grantham. His father, Mr. Isaac Newton, had +died a few months after his marriage to Harriet Ayscough, the +daughter of Mr. James Ayscough, of Market Overton, in Rutlandshire. +The little Isaac was at first so excessively frail and weakly that +his life was despaired of. The watchful mother, however, tended her +delicate child with such success that he seems to have thriven better +than might have been expected from the circumstances of his infancy, +and he ultimately acquired a frame strong enough to outlast the +ordinary span of human life. + +For three years they continued to live at Woolsthorpe, the widow's +means of livelihood being supplemented by the income from another +small estate at Sewstern, in a neighbouring part of Leicestershire. + +[PLATE: WOOLSTHORPE MANOR. +Showing solar dial made by Newton when a boy.] + +In 1645, Mrs. Newton took as a second husband the Rev. Barnabas +Smith, and on moving to her new home, about a mile from Woolsthorpe, +she entrusted little Isaac to her mother, Mrs. Ayscough. In due +time we find that the boy was sent to the public school at Grantham, +the name of the master being Stokes. For the purpose of being near +his work, the embryo philosopher was boarded at the house of Mr. +Clark, an apothecary at Grantham. We learn from Newton himself that +at first he had a very low place in the class lists of the school, +and was by no means one of those model school-boys who find favour in +the eyes of the school-master by attention to Latin grammar. Isaac's +first incentive to diligent study seems to have been derived from the +circumstance that he was severely kicked by one of the boys who was +above him in the class. This indignity had the effect of stimulating +young Newton's activity to such an extent that he not only attained +the desired object of passing over the head of the boy who had +maltreated him, but continued to rise until he became the head of the +school. + +The play-hours of the great philosopher were devoted to pursuits very +different from those of most school-boys. His chief amusement was +found in making mechanical toys and various ingenious contrivances. +He watched day by day with great interest the workmen engaged in +constructing a windmill in the neighbourhood of the school, the +result of which was that the boy made a working model of the windmill +and of its machinery, which seems to have been much admired, as +indicating his aptitude for mechanics. We are told that Isaac also +indulged in somewhat higher flights of mechanical enterprise. He +constructed a carriage, the wheels of which were to be driven by the +hands of the occupant, while the first philosophical instrument he +made was a clock, which was actuated by water. He also devoted much +attention to the construction of paper kites, and his skill in this +respect was highly appreciated by his school-fellows. Like a true +philosopher, even at this stage he experimented on the best methods +of attaching the string, and on the proportions which the tail ought +to have. He also made lanthorns of paper to provide himself with +light as he walked to school in the dark winter mornings. + +The only love affair in Newton's life appears to have commenced while +he was still of tender years. The incidents are thus described in +Brewster's "Life of Newton," a work to which I am much indebted in +this chapter. + +"In the house where he lodged there were some female inmates, in +whose company he appears to have taken much pleasure. One of these, +a Miss Storey, sister to Dr. Storey, a physician at Buckminster, near +Colsterworth, was two or three years younger than Newton and to great +personal attractions she seems to have added more than the usual +allotment of female talent. The society of this young lady and her +companions was always preferred to that of his own school-fellows, +and it was one of his most agreeable occupations to construct for +them little tables and cupboards, and other utensils for holding +their dolls and their trinkets. He had lived nearly six years in the +same house with Miss Storey, and there is reason to believe that +their youthful friendship gradually rose to a higher passion; but the +smallness of her portion, and the inadequacy of his own fortune, +appear to have prevented the consummation of their happiness. Miss +Storey was afterwards twice married, and under the name of Mrs. +Vincent, Dr. Stukeley visited her at Grantham in 1727, at the age of +eighty-two, and obtained from her many particulars respecting the +early history of our author. Newton's esteem for her continued +unabated during his life. He regularly visited her when he went to +Lincolnshire, and never failed to relieve her from little pecuniary +difficulties which seem to have beset her family." + +The schoolboy at Grantham was only fourteen years of age when his +mother became a widow for the second time. She then returned to the +old family home at Woolsthorpe, bringing with her the three children +of her second marriage. Her means appear to have been somewhat +scanty, and it was consequently thought necessary to recall Isaac +from the school. His recently-born industry had been such that he +had already made good progress in his studies, and his mother hoped +that he would now lay aside his books, and those silent meditations +to which, even at this early age, he had become addicted. It was +expected that, instead of such pursuits, which were deemed quite +useless, the boy would enter busily into the duties of the farm and +the details of a country life. But before long it became manifest +that the study of nature and the pursuit of knowledge had such a +fascination for the youth that he could give little attention to +aught else. It was plain that he would make but an indifferent +farmer. He greatly preferred experimenting on his water-wheels to +looking after labourers, while he found that working at mathematics +behind a hedge was much more interesting than chaffering about the +price of bullocks in the market place. Fortunately for humanity his +mother, like a wise woman, determined to let her boy's genius have +the scope which it required. He was accordingly sent back to +Grantham school, with the object of being trained in the knowledge +which would fit him for entering the University of Cambridge. + +[PLATE: TRINITY COLLEGE, CAMBRIDGE. +Showing Newton's rooms; on the leads of the gateway he placed +his telescope.] + +It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen, +was enrolled as an undergraduate of Trinity College, Cambridge. +Little did those who sent him there dream that this boy was destined +to be the most illustrious student who ever entered the portals of +that great seat of learning. Little could the youth himself have +foreseen that the rooms near the gateway which he occupied would +acquire a celebrity from the fact that he dwelt in them, or that the +ante-chapel of his college was in good time to be adorned by that +noble statue, which is regarded as one of the chief art treasures of +Cambridge University, both on account of its intrinsic beauty and the +fact that it commemorates the fame of her most distinguished alumnus, +Isaac Newton, the immortal astronomer. Indeed, his advent at the +University seemed to have been by no means auspicious or brilliant. +His birth was, as we have seen, comparatively obscure, and though he +had already given indication of his capacity for reflecting on +philosophical matters, yet he seems to have been but ill-equipped +with the routine knowledge which youths are generally expected to +take with them to the Universities. + +From the outset of his college career, Newton's attention seems to +have been mainly directed to mathematics. Here he began to give +evidence of that marvellous insight into the deep secrets of nature +which more than a century later led so dispassionate a judge as +Laplace to pronounce Newton's immortal work as pre-eminent above all +the productions of the human intellect. But though Newton was one of +the very greatest mathematicians that ever lived, he was never a +mathematician for the mere sake of mathematics. He employed his +mathematics as an instrument for discovering the laws of nature. His +industry and genius soon brought him under the notice of the +University authorities. It is stated in the University records that +he obtained a Scholarship in 1664. Two years later we find that +Newton, as well as many residents in the University, had to leave +Cambridge temporarily on account of the breaking out of the plague. +The philosopher retired for a season to his old home at Woolsthorpe, +and there he remained until he was appointed a Fellow of Trinity +College, Cambridge, in 1667. From this time onwards, Newton's +reputation as a mathematician and as a natural philosopher steadily +advanced, so that in 1669, while still but twenty-seven years of age, +he was appointed to the distinguished position of Lucasian Professor +of Mathematics at Cambridge. Here he found the opportunity to +continue and develop that marvellous career of discovery which formed +his life's work. + +The earliest of Newton's great achievements in natural philosophy was +his detection of the composite character of light. That a beam of +ordinary sunlight is, in fact, a mixture of a very great number of +different-coloured lights, is a doctrine now familiar to every one +who has the slightest education in physical science. We must, +however, remember that this discovery was really a tremendous advance +in knowledge at the time when Newton announced it. + +[PLATE: DIAGRAM OF A SUNBEAM.] + +We here give the little diagram originally drawn by Newton, to +explain the experiment by which he first learned the composition of +light. A sunbeam is admitted into a darkened room through an +opening, H, in a shutter. This beam when not interfered with will +travel in a straight line to the screen, and there reproduce a bright +spot of the same shape as the hole in the shutter. If, however, a +prism of glass, A B C, be introduced so that the beam traverse it, +then it will be seen at once that the light is deflected from its +original track. There is, however, a further and most important +change which takes place. The spot of light is not alone removed to +another part of the screen, but it becomes spread out into a long +band beautifully coloured, and exhibiting the hues of the rainbow. At +the top are the violet rays, and then in descending order we have the +indigo, blue, green, yellow, orange, and red. + +The circumstance in this phenomenon which appears to have +particularly arrested Newton's attention, was the elongation which +the luminous spot underwent in consequence of its passage through the +prism. When the prism was absent the spot was nearly circular, but +when the prism was introduced the spot was about five times as long +as it was broad. To ascertain the explanation of this was the first +problem to be solved. It seemed natural to suppose that it might be +due to the thickness of the glass in the prism which the light +traversed, or to the angle of incidence at which the light fell upon +the prism. He found, however, upon careful trial, that the phenomenon +could not be thus accounted for. It was not until after much patient +labour that the true explanation dawned upon him. He discovered that +though the beam of white light looks so pure and so simple, yet in +reality it is composed of differently coloured lights blended +together. These are, of course, indistinguishable in the compound +beam, but they are separated or disentangled, so to speak, by the +action of the prism. The rays at the blue end of the spectrum are +more powerfully deflected by the action of the glass than are the +rays at the red end. Thus, the rays variously coloured red, orange, +yellow, green, blue, indigo, violet, are each conducted to a +different part of the screen. In this way the prism has the effect +of exhibiting the constitution of the composite beam of light. + +To us this now seems quite obvious, but Newton did not adopt it +hastily. With characteristic caution he verified the explanation by +many different experiments, all of which confirmed his discovery. One +of these may be mentioned. He made a hole in the screen at that part +on which the violet rays fell. Thus a violet ray was allowed to pass +through, all the rest of the light being intercepted, and on this +beam so isolated he was able to try further experiments. For +instance, when he interposed another prism in its path, he found, as +he expected, that it was again deflected, and he measured the amount +of the deflection. Again he tried the same experiment with one of +the red rays from the opposite end of the coloured band. He allowed +it to pass through the same aperture in the screen, and he tested the +amount by which the second prism was capable of producing deflection. +He thus found, as he had expected to find, that the second prism was +more efficacious in bending the violet rays than in bending the red +rays. Thus he confirmed the fact that the various hues of the +rainbow were each bent by a prism to a different extent, violet being +acted upon the most, and red the least. + +[PLATE: ISAAC NEWTON.] + +Not only did Newton decompose a white beam into its constituent +colours, but conversely by interposing a second prism with its angle +turned upwards, he reunited the different colours, and thus +reproduced the original beam of white light. In several other ways +also he illustrated his famous proposition, which then seemed so +startling, that white light was the result of a mixture of all hues +of the rainbow. By combining painters' colours in the right +proportion he did not indeed succeed in producing a mixture which +would ordinarily be called white, but he obtained a grey pigment. +Some of this he put on the floor of his room for comparison with a +piece of white paper. He allowed a beam of bright sunlight to fall +upon the paper and the mixed colours side by side, and a friend he +called in for his opinion pronounced that under these circumstances +the mixed colours looked the whiter of the two. + +By repeated demonstrations Newton thus established his great +discovery of the composite character of light. He at once perceived +that his researches had an important bearing upon the principles +involved in the construction of a telescope. Those who employed the +telescope for looking at the stars, had been long aware of the +imperfections which prevented all the various rays from being +conducted to the same focus. But this imperfection had hitherto been +erroneously accounted for. It had been supposed that the reason why +success had not been attained in the construction of a refracting +telescope was due to the fact that the object glass, made as it then +was of a single piece, had not been properly shaped. Mathematicians +had abundantly demonstrated that a single lens, if properly figured, +must conduct all rays of light to the same focus, provided all rays +experienced equal refraction in passing through the glass. Until +Newton's discovery of the composition of white light, it had been +taken for granted that the several rays in a white beam were equally +refrangible. No doubt if this had been the case, a perfect telescope +could have been produced by properly shaping the object glass. But +when Newton had demonstrated that light was by no means so simple as +had been supposed, it became obvious that a satisfactory refracting +telescope was an impossibility when only a single object lens was +employed, however carefully that lens might have been wrought. Such +an objective might, no doubt, be made to conduct any one group of +rays of a particular shade to the same focus, but the rays of other +colours in the beam of white light must necessarily travel somewhat +astray. In this way Newton accounted for a great part of the +difficulties which had hitherto beset the attempts to construct a +perfect refracting telescope. + +We now know how these difficulties can be, to a great extent, +overcome, by employing for the objective a composite lens made of two +pieces of glass possessing different qualities. To these achromatic +object glasses, as they are called, the great development of +astronomical knowledge, since Newton's time, is due. But it must be +remarked that, although the theoretical possibility of constructing +an achromatic lens was investigated by Newton, he certainly came to +the conclusion that the difficulty could not be removed by employing +a composite objective, with two different kinds of glass. In this +his marvellous sagacity in the interpretation of nature seems for +once to have deserted him. We can, however, hardly regret that +Newton failed to discover the achromatic objective, when we observe +that it was in consequence of his deeming an achromatic objective to +be impossible that he was led to the invention of the reflecting +telescope. Finding, as he believed, that the defects of the +telescope could not be remedied by any application of the principle +of refraction he was led to look in quite a different direction for +the improvement of the tool on which the advancement of astronomy +depended. The REFRACTION of light depended as he had found, upon the +colour of the light. The laws of REFLECTION were, however, quite +independent of the colour. Whether rays be red or green, blue or +yellow, they are all reflected in precisely the same manner from a +mirror. Accordingly, Newton perceived that if he could construct a +telescope the action of which depended upon reflection, instead of +upon refraction, the difficulty which had hitherto proved an +insuperable obstacle to the improvement of the instrument would be +evaded. + +[PLATE: SIR ISAAC NEWTON'S LITTLE REFLECTOR.] + +For this purpose Newton fashioned a concave mirror from a mixture of +copper and tin, a combination which gives a surface with almost the +lustre of silver. When the light of a star fell upon the surface, an +image of the star was produced in the focus of this mirror, and then +this image was examined by a magnifying eye-piece. Such is the +principle of the famous reflecting telescope which bears the name of +Newton. The little reflector which he constructed, represented in +the adjoining figure, is still preserved as one of the treasures of +the Royal Society. The telescope tube had the very modest dimension +of one inch in diameter. It was, however, the precursor of a whole +series of magnificent instruments, each outstripping the other in +magnitude, until at last the culminating point was attained in 1845, +by the construction of Lord Rosse's mammoth reflector of six feet in +aperture. + +Newton's discovery of the composition of light led to an embittered +controversy, which caused no little worry to the great Philosopher. +Some of those who attacked him enjoyed considerable and, it must be +admitted, even well-merited repute in the ranks of science. They +alleged, however, that the elongation of the coloured band which +Newton had noticed was due to this, to that, or to the other--to +anything, in fact, rather than to the true cause which Newton +assigned. With characteristic patience and love of truth, Newton +steadily replied to each such attack. He showed most completely how +utterly his adversaries had misunderstood the subject, and how slight +indeed was their acquaintance with the natural phenomenon in +question. In reply to each point raised, he was ever able to cite +fresh experiments and adduce fresh illustrations, until at last his +opponents retired worsted from the combat. + +It has been often a matter for surprise that Newton, throughout his +whole career, should have taken so much trouble to expose the errors +of those who attacked his views. He used even to do this when it +plainly appeared that his adversaries did not understand the subject +they were discussing. A philosopher might have said, "I know I am +right, and whether others think I am right or not may be a matter of +concern to them, but it is certainly not a matter about which I need +trouble. If after having been told the truth they elect to remain in +error, so much the worse for them; my time can be better employed +than in seeking to put such people right." This, however, was not +Newton's method. He spent much valuable time in overthrowing +objections which were often of a very futile description. Indeed, he +suffered a great deal of annoyance from the persistency, and in some +cases one might almost say from the rancour, of the attacks which +were made upon him. Unfortunately for himself, he did not possess +that capacity for sublime indifference to what men may say, which is +often the happy possession of intellects greatly inferior to his. + +The subject of optics still continuing to engross Newton's attention, +he followed up his researches into the structure of the sunbeam by +many other valuable investigations in connection with light. Every +one has noticed the beautiful colours manifested in a soap-bubble. +Here was a subject which not unnaturally attracted the attention of +one who had expounded the colours of the spectrum with such success. +He perceived that similar hues were produced by other thin plates of +transparent material besides soap-bubbles, and his ingenuity was +sufficient to devise a method by which the thicknesses of the +different films could be measured. We can hardly, indeed, say that a +like success attended his interpretation of these phenomena to that +which had been so conspicuous in his explanation of the spectrum. It +implies no disparagement to the sublime genius of Newton to admit +that the doctrines he put forth as to the causes of the colours in +the soap-bubbles can be no longer accepted. We must remember that +Newton was a pioneer in accounting for the physical properties of +light. The facts that he established are indeed unquestionable, but +the explanations which he was led to offer of some of them are seen +to be untenable in the fuller light of our present knowledge. + +[PLATE: SIR ISAAC NEWTON'S SUN-DIAL.] + +Had Newton done nothing beyond making his wonderful discoveries in +light, his fame would have gone down to posterity as one of the +greatest of Nature's interpreters. But it was reserved for him to +accomplish other discoveries, which have pushed even his analysis of +the sunbeam into the background; it is he who has expounded the +system of the universe by the discovery of the law of universal +gravitation. + +The age had indeed become ripe for the advent of the genius of +Newton. Kepler had discovered with marvellous penetration the laws +which govern the movements of the planets around the sun, and in +various directions it had been more or less vaguely felt that the +explanation of Kepler's laws, as well as of many other phenomena, +must be sought for in connection with the attractive power of +matter. But the mathematical analysis which alone could deal with +this subject was wanting; it had to be created by Newton. + +At Woolsthorpe, in the year 1666, Newton's attention appears to have +been concentrated upon the subject of gravitation. Whatever may be +the extent to which we accept the more or less mythical story as to +how the fall of an apple first directed the attention of the +philosopher to the fact that gravitation must extend through space, +it seems, at all events, certain that this is an excellent +illustration of the line of reasoning which he followed. He argued +in this way. The earth attracts the apple; it would do so, no matter +how high might be the tree from which that apple fell. It would then +seem to follow that this power which resides in the earth by which it +can draw all external bodies towards it, extends far beyond the +altitude of the loftiest tree. Indeed, we seem to find no limit to +it. At the greatest elevation that has ever been attained, the +attractive power of the earth is still exerted, and though we cannot +by any actual experiment reach an altitude more than a few miles +above the earth, yet it is certain that gravitation would extend to +elevations far greater. It is plain, thought Newton, that an apple +let fall from a point a hundred miles above this earth's surface, +would be drawn down by the attraction, and would continually gather +fresh velocity until it reached the ground. From a hundred miles it +was natural to think of what would happen at a thousand miles, or at +hundreds of thousands of miles. No doubt the intensity of the +attraction becomes weaker with every increase in the altitude, but +that action would still exist to some extent, however lofty might be +the elevation which had been attained. + +It then occurred to Newton, that though the moon is at a distance of +two hundred and forty thousand miles from the earth, yet the +attractive power of the earth must extend to the moon. He was +particularly led to think of the moon in this connection, not only +because the moon is so much closer to the earth than are any other +celestial bodies, but also because the moon is an appendage to the +earth, always revolving around it. The moon is certainly attracted +to the earth, and yet the moon does not fall down; how is this to be +accounted for? The explanation was to be found in the character of +the moon's present motion. If the moon were left for a moment at +rest, there can be no doubt that the attraction of the earth would +begin to draw the lunar globe in towards our globe. In the course of +a few days our satellite would come down on the earth with a most +fearful crash. This catastrophe is averted by the circumstance that +the moon has a movement of revolution around the earth. Newton was +able to calculate from the known laws of mechanics, which he had +himself been mainly instrumental in discovering, what the attractive +power of the earth must be, so that the moon shall move precisely as +we find it to move. It then appeared that the very power which makes +an apple fall at the earth's surface is the power which guides the +moon in its orbit. + +[PLATE: SIR ISAAC NEWTON'S TELESCOPE.] + +Once this step had been taken, the whole scheme of the universe might +almost be said to have become unrolled before the eye of the +philosopher. It was natural to suppose that just as the moon was +guided and controlled by the attraction of the earth, so the earth +itself, in the course of its great annual progress, should be guided +and controlled by the supreme attractive power of the sun. If this +were so with regard to the earth, then it would be impossible to +doubt that in the same way the movements of the planets could be +explained to be consequences of solar attraction. + +It was at this point that the great laws of Kepler became especially +significant. Kepler had shown how each of the planets revolves in an +ellipse around the sun, which is situated on one of the foci. This +discovery had been arrived at from the interpretation of +observations. Kepler had himself assigned no reason why the orbit of +a planet should be an ellipse rather than any other of the infinite +number of closed curves which might be traced around the sun. Kepler +had also shown, and here again he was merely deducing the results +from observation, that when the movements of two planets were +compared together, the squares of the periodic times in which each +planet revolved were proportional to the cubes of their mean +distances from the sun. This also Kepler merely knew to be true as a +fact, he gave no demonstration of the reason why nature should have +adopted this particular relation between the distance and the +periodic time rather than any other. Then, too, there was the law by +which Kepler with unparalleled ingenuity, explained the way in which +the velocity of a planet varies at the different points of its track, +when he showed how the line drawn from the sun to the planet +described equal areas around the sun in equal times. These were the +materials with which Newton set to work. He proposed to infer from +these the actual laws regulating the force by which the sun guides +the planets. Here it was that his sublime mathematical genius came +into play. Step by step Newton advanced until he had completely +accounted for all the phenomena. + +In the first place, he showed that as the planet describes equal +areas in equal times about the sun, the attractive force which the +sun exerts upon it must necessarily be directed in a straight line +towards the sun itself. He also demonstrated the converse truth, +that whatever be the nature of the force which emanated from a sun, +yet so long as that force was directed through the sun's centre, any +body which revolved around it must describe equal areas in equal +times, and this it must do, whatever be the actual character of the +law according to which the intensity of the force varies at different +parts of the planet's journey. Thus the first advance was taken in +the exposition of the scheme of the universe. + +The next step was to determine the law according to which the force +thus proved to reside in the sun varied with the distance of the +planet. Newton presently showed by a most superb effort of +mathematical reasoning, that if the orbit of a planet were an ellipse +and if the sun were at one of the foci of that ellipse, the intensity +of the attractive force must vary inversely as the square of the +planet's distance. If the law had any other expression than the +inverse square of the distance, then the orbit which the planet must +follow would not be an ellipse; or if an ellipse, it would, at all +events, not have the sun in the focus. Hence he was able to show +from Kepler's laws alone that the force which guided the planets was +an attractive power emanating from the sun, and that the intensity of +this attractive power varied with the inverse square of the distance +between the two bodies. + +These circumstances being known, it was then easy to show that the +last of Kepler's three laws must necessarily follow. If a number of +planets were revolving around the sun, then supposing the materials +of all these bodies were equally affected by gravitation, it can be +demonstrated that the square of the periodic time in which each +planet completes its orbit is proportional to the cube of the +greatest diameter in that orbit. + +[PLATE: SIR ISAAC NEWTON'S ASTROLABE.] + +These superb discoveries were, however, but the starting point from +which Newton entered on a series of researches, which disclosed many +of the profoundest secrets in the scheme of celestial mechanics. His +natural insight showed that not only large masses like the sun and +the earth, and the moon, attract each other, but that every particle +in the universe must attract every other particle with a force which +varies inversely as the square of the distance between them. If, for +example, the two particles were placed twice as far apart, then the +intensity of the force which sought to bring them together would be +reduced to one-fourth. If two particles, originally ten miles +asunder, attracted each other with a certain force, then, when the +distance was reduced to one mile, the intensity of the attraction +between the two particles would be increased one-hundred-fold. This +fertile principle extends throughout the whole of nature. In some +cases, however, the calculation of its effect upon the actual +problems of nature would be hardly possible, were it not for another +discovery which Newton's genius enabled him to accomplish. In the +case of two globes like the earth and the moon, we must remember that +we are dealing not with particles, but with two mighty masses of +matter, each composed of innumerable myriads of particles. Every +particle in the earth does attract every particle in the moon with a +force which varies inversely as the square of their distance. The +calculation of such attractions is rendered feasible by the following +principle. Assuming that the earth consists of materials +symmetrically arranged in shells of varying densities, we may then, +in calculating its attraction, regard the whole mass of the globe as +concentrated at its centre. Similarly we may regard the moon as +concentrated at the centre of its mass. In this way the earth and +the moon can both be regarded as particles in point of size, each +particle having, however, the entire mass of the corresponding +globe. The attraction of one particle for another is a much more +simple matter to investigate than the attraction of the myriad +different points of the earth upon the myriad different points of the +moon. + +Many great discoveries now crowded in upon Newton. He first of all +gave the explanation of the tides that ebb and flow around our +shores. Even in the earliest times the tides had been shown to be +related to the moon. It was noticed that the tides were specially +high during full moon or during new moon, and this circumstance +obviously pointed to the existence of some connection between the +moon and these movements of the water, though as to what that +connection was no one had any accurate conception until Newton +announced the law of gravitation. Newton then made it plain that the +rise and fall of the water was simply a consequence of the attractive +power which the moon exerted upon the oceans lying upon our globe. He +showed also that to a certain extent the sun produces tides, and he +was able to explain how it was that when the sun and the moon both +conspire, the joint result was to produce especially high tides, +which we call "spring tides"; whereas if the solar tide was low, +while the lunar tide was high, then we had the phenomenon of "neap" +tides. + +But perhaps the most signal of Newton's applications of the law of +gravitation was connected with certain irregularities in the +movements of the moon. In its orbit round the earth our satellite +is, of course, mainly guided by the great attraction of our globe. If +there were no other body in the universe, then the centre of the moon +must necessarily perform an ellipse, and the centre of the earth +would lie in the focus of that ellipse. Nature, however, does not +allow the movements to possess the simplicity which this arrangement +would imply, for the sun is present as a source of disturbance. The +sun attracts the moon, and the sun attracts the earth, but in +different degrees, and the consequence is that the moon's movement +with regard to the earth is seriously affected by the influence of +the sun. It is not allowed to move exactly in an ellipse, nor is the +earth exactly in the focus. How great was Newton's achievement in +the solution of this problem will be appreciated if we realise that +he not only had to determine from the law of gravitation the nature +of the disturbance of the moon, but he had actually to construct the +mathematical tools by which alone such calculations could be +effected. + +The resources of Newton's genius seemed, however, to prove equal to +almost any demand that could be made upon it. He saw that each +planet must disturb the other, and in that way he was able to render +a satisfactory account of certain phenomena which had perplexed all +preceding investigators. That mysterious movement by which the pole +of the earth sways about among the stars had been long an unsolved +enigma, but Newton showed that the moon grasped with its attraction +the protuberant mass at the equatorial regions of the earth, and thus +tilted the earth's axis in a way that accounted for the phenomenon +which had been known but had never been explained for two thousand +years. All these discoveries were brought together in that immortal +work, Newton's "Principia." + +Down to the year 1687, when the "Principia" was published, Newton had +lived the life of a recluse at Cambridge, being entirely occupied +with those transcendent researches to which we have referred. But in +that year he issued from his seclusion under circumstances of +considerable historical interest. King James the Second attempted an +invasion of the rights and privileges of the University of Cambridge +by issuing a command that Father Francis, a Benedictine monk, should +be received as a Master of Arts in the University, without having taken +the oaths of allegiance and supremacy. With this arbitrary command +the University sternly refused to comply. The Vice-Chancellor was +accordingly summoned to answer for an act of contempt to the authority +of the Crown. Newton was one of nine delegates who were chosen to +defend the independence of the University before the High Court. +They were able to show that Charles the Second, who had issued a +MANDAMUS under somewhat similar circumstances, had been induced after +due consideration to withdraw it. This argument appeared satisfactory, +and the University gained their case. Newton's next step in public +life was his election, by a narrow majority, as member for the +University, and during the years 1688 and 1689, he seems to have +attended to his parliamentary duties with considerable regularity. + +An incident which happened in 1692 was apparently the cause of +considerable disturbance in Newton's equanimity, if not in his +health. He had gone to early morning chapel, leaving a lighted +candle among his papers on his desk. Tradition asserts that his +little dog "Diamond" upset the candle; at all events, when Newton +came back he found that many valuable papers had perished in a +conflagration. The loss of these manuscripts seems to have had a +serious effect. Indeed, it has been asserted that the distress +reduced Newton to a state of mental aberration for a considerable +time. This has, apparently, not been confirmed, but there is no +doubt that he experienced considerable disquiet, for in writing on +September 13th, 1693, to Mr. Pepys, he says: + +"I am extremely troubled at the embroilment I am in, and have +neither ate nor slept well this twelve-month, nor have my former +consistency of mind." + +Notwithstanding the fame which Newton had achieved, by the +publication of his, "Principia," and by all his researches, the State +had not as yet taken any notice whatever of the most illustrious man +of science that this or any other country has ever produced. Many of +his friends had exerted themselves to procure him some permanent +appointment, but without success. It happened, however, that Mr. +Montagu, who had sat with Newton in Parliament, was appointed +Chancellor of the Exchequer in 1694. Ambitious of distinction in his +new office, Mr. Montagu addressed himself to the improvement of the +current coin, which was then in a very debased condition. It +fortunately happened that an opportunity occurred of appointing a new +official in the Mint; and Mr. Montagu on the 19th of March, 1695, +wrote to offer Mr. Newton the position of warden. The salary was to +be five or six hundred a year, and the business would not require +more attendance than Newton could spare. The Lucasian professor +accepted this post, and forthwith entered upon his new duties. + +The knowledge of physics which Newton had acquired by his experiments +was of much use in connection with his duties at the Mint. He +carried out the re-coinage with great skill in the course of two +years, and as a reward for his exertions, he was appointed, in 1697, +to the Mastership of the Mint, with a salary between 1,200 Pounds and +1,500 Pounds per annum. In 1701, his duties at the Mint being so +engrossing, he resigned his Lucasian professorship at Cambridge, and +at the same time he had to surrender his fellowship at Trinity +College. This closed his connection with the University of +Cambridge. It should, however, be remarked that at a somewhat +earlier stage in his career he was very nearly being appointed to an +office which might have enabled the University to retain the great +philosopher within its precincts. Some of his friends had almost +succeeded in securing his nomination to the Provostship of King's +College, Cambridge; the appointment, however, fell through, inasmuch +as the statute could not be evaded, which required that the Provost +of King's College should be in holy orders. + +In those days it was often the custom for illustrious mathematicians, +when they had discovered a solution for some new and striking +problem, to publish that problem as a challenge to the world, while +withholding their own solution. A famous instance of this is found +in what is known as the Brachistochrone problem, which was solved by +John Bernouilli. The nature of this problem may be mentioned. It +was to find the shape of the curve along which a body would slide +down from one point (A) to another point (B) in the shortest time. It +might at first be thought that the straight line from A to B, as it +is undoubtedly the shortest distance between the points, would also +be the path of quickest descent; but this is not so. There is a +curved line, down which a bead, let us say, would run on a smooth +wire from A to B in a shorter time than the same bead would require +to run down the straight wire. Bernouilli's problem was to find out +what that curve must be. Newton solved it correctly; he showed that +the curve was a part of what is termed a cycloid--that is to say, a +curve like that which is described by a point on the rim of a +carriage-wheel as the wheel runs along the ground. Such was Newton's +geometrical insight that he was able to transmit a solution of the +problem on the day after he had received it, to the President of the +Royal Society. + +In 1703 Newton, whose world wide fame was now established, was +elected President of the Royal Society. Year after year he was +re-elected to this distinguished position, and his tenure, which +lasted twenty-five years, only terminated with his life. It was in +discharge of his duties as President of the Royal Society that Newton +was brought into contact with Prince George of Denmark. In April, +1705, the Queen paid a visit to Cambridge as the guest of Dr. +Bentley, the then Master of Trinity, and in a court held at Trinity +Lodge on April 15th, 1705, the honour of knighthood was conferred +upon the discoverer of gravitation. + +Urged by illustrious friends, who sought the promotion of knowledge, +Newton gave his attention to the publication of a new edition of the +"Principia." His duties at the Mint, however, added to the supreme +duty of carrying on his original investigations, left him but little +time for the more ordinary task of the revision. He was accordingly +induced to associate with himself for this purpose a distinguished +young mathematician, Roger Coates, a Fellow of Trinity College, +Cambridge, who had recently been appointed Plumian Professor of +Astronomy. On July 27th, 1713, Newton, by this time a favourite at +Court, waited on the Queen, and presented her with a copy of the new +edition of the "Principia." + +Throughout his life Newton appears to have been greatly interested in +theological studies, and he specially devoted his attention to the +subject of prophecy. He left behind him a manuscript on the +prophecies of Daniel and the Apocalypse of St. John, and he also +wrote various theological papers. Many other subjects had from time +to time engaged his attention. He studied the laws of heat; he +experimented in pursuit of the dreams of the Alchymist; while the +philosopher who had revealed the mechanism of the heavens found +occasional relaxation in trying to interpret hieroglyphics. In the +last few years of his life he bore with fortitude a painful ailment, +and on Monday, March 20th, 1727, he died in the eighty-fifth year of +his age. On Tuesday, March 28th, he was buried in Westminster Abbey. + +Though Newton lived long enough to receive the honour that his +astonishing discoveries so justly merited, and though for many years +of his life his renown was much greater than that of any of his +contemporaries, yet it is not too much to say that, in the years +which have since elapsed, Newton's fame has been ever steadily +advancing, so that it never stood higher than it does at this moment. + +We hardly know whether to admire more the sublime discoveries at +which he arrived, or the extraordinary character of the intellectual +processes by which those discoveries were reached. Viewed from +either standpoint, Newton's "Principia" is incomparably the greatest +work on science that has ever yet been produced. + +[PLATE: SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.] + + + + +FLAMSTEED. + + +Among the manuscripts preserved at Greenwich Observatory are certain +documents in which Flamsteed gives an account of his own life. We +may commence our sketch by quoting the following passage from this +autobiography:--"To keep myself from idleness, and to recreate +myself, I have intended here to give some account of my life, in my +youth, before the actions thereof, and the providences of God +therein, be too far passed out of my memory; and to observe the +accidents of all my years, and inclinations of my mind, that +whosoever may light upon these papers may see I was not so wholly +taken up, either with my father's business or my mathematics, but +that I both admitted and found time for other as weighty +considerations." + +The chief interest which attaches to the name of Flamsteed arises +from the fact that he was the first of the illustrious series of +Astronomers Royal who have presided over Greenwich Observatory. In +that capacity Flamsteed was able to render material assistance to +Newton by providing him with the observations which his lunar theory +required. + +John Flamsteed was born at Denby, in Derbyshire, on the 19th of +August, 1646. His mother died when he was three years old, and the +second wife, whom his father took three years later, only lived until +Flamsteed was eight, there being also two younger sisters. In his +boyhood the future astronomer tells us that he was very fond of those +romances which affect boy's imagination, but as he writes, "At twelve +years of age I left all the wild ones and betook myself to read the +better sort of them, which, though they were not probable, yet +carried no seeming impossibility in the picturing." By the time +Flamsteed was fifteen years old he had embarked in still more serious +work, for he had read Plutarch's "Lives," Tacitus' "Roman History," +and many other books of a similar description. In 1661 he became ill +with some serious rheumatic affection, which obliged him to be +withdrawn from school. It was then for the first time that he +received the rudiments of a scientific education. He had, however, +attained his sixteenth year before he made any progress in +arithmetic. He tells us how his father taught him "the doctrine of +fractions," and "the golden rule of three"--lessons which he seemed +to have learned easily and quickly. One of the books which he read +at this time directed his attention to astronomical instruments, and +he was thus led to construct for himself a quadrant, by which he +could take some simple astronomical observations. He further +calculated a table to give the sun's altitudes at different hours, +and thus displayed those tastes for practical astronomy which he +lived to develop so greatly. It appears that these scientific +studies were discountenanced by his father, who designed that his son +should follow a business career. Flamsteed's natural inclination, +however, forced him to prosecute astronomical work, notwithstanding +the impediments that lay in his path. Unfortunately, his +constitutional delicacy seems to have increased, and he had just +completed his eighteenth year, "when," to use his own words, "the +winter came on and thrust me again into the chimney, whence the heat +and the dryness of the preceding summer had happily once before +withdrawn me. But, it not being a fit season for physic, it was +thought fit to let me alone this winter, and try the skill of another +physician on me in the spring." + +It appears that at this time a quack named Valentine Greatrackes, was +reputed to have effected most astonishing cures in Ireland merely by +the stroke of his hands, without the application of any medicine +whatever. Flamsteed's father, despairing of any remedy for his son +from the legitimate branch of the profession, despatched him to +Ireland on August 26th, 1665, he being then, as recorded with +astronomical accuracy, "nineteen years, six days, and eleven hours +old." The young astronomer, accompanied by a friend, arrived on a +Tuesday at Liverpool but the wind not being favourable, they remained +there till the following Friday, when a shift of the wind to the east +took place. They embarked accordingly on a vessel called the SUPPLY +at noon, and on Saturday night came in sight of Dublin. Ere they +could land, however, they were nearly being wrecked on Lambay +Island. This peril safely passed, there was a long delay for +quarantine before they were at last allowed on shore. On Thursday, +September 6th, they set out from Dublin, where they had been +sojourning at the "Ship" Hotel, in Dame Street, towards Assaune, +where Greatrackes received his patients. + +[PLATE: FLAMSTEED'S HOUSE.] + +Flamsteed gives an interesting account of his travels in Ireland. +They dined at Naas on the first day, and on September 8th they +reached Carlow, a town which is described as one of the fairest they +saw on their journey. By Sunday morning, September 10th, having lost +their way several times, they reached Castleton, called commonly Four +Mile Waters. Flamsteed inquired of the host in the inn where they +might find a church, but was told that the minister lived twelve +miles away, and that they had no sermon except when he came to +receive his tithes once a year, and a woman added that "they had +plenty enough of everything necessary except the word of God." The +travellers accordingly went on to Cappoquin, which lies up the river +Blackwater, on the road to Lismore, eight miles from Youghal. Thence +they immediately started on foot to Assaune. About a mile from +Cappoquin, and entering into the house of Mr. Greatrackes, they saw +him touch several patients, "whereof some were nearly cured, others +were on the mending hand, and some on whom his strokes had no +effect." Flamsteed was touched by the famous quack on the afternoon +of September 11th, but we are hardly surprised to hear his remark +that "he found not his disease to stir." Next morning the astronomer +came again to see Mr. Greatrackes, who had "a kind of majestical yet +affable presence, and a composed carriage." Even after the third +touching had been submitted to, no benefit seems to have been +derived. We must, however record, to the credit of Mr. Greatrackes, +that he refused to accept any payment from Flamsteed, because he was +a stranger. + +Finding it useless to protract his stay any longer, Flamsteed and his +friend set out on their return to Dublin. In the course of his +journey he seems to have been much impressed with Clonmel, which he +describes as an "exceedingly pleasantly seated town." But in those +days a journey to Ireland was so serious an enterprise that when +Flamsteed did arrive safely back at Derby after an absence of a +month, he adds, "For God's providence in this journey, His name be +praised, Amen." + +As to the expected benefits to his health from the expedition we may +quote his own words: "In the winter following I was indifferent +hearty, and my disease was not so violent as it used to be at that +time formerly. But whether through God's mercy I received this +through Mr. Greatrackes' touch, or my journey and vomiting at sea, I +am uncertain; but, by some circumstances, I guess that I received a +benefit from both." + +It is evident that by this time Flamsteed's interest in all +astronomical matters had greatly increased. He studied the +construction of sun-dials, he formed a catalogue of seventy of the +fixed stars, with their places on the heavens, and he computed the +circumstances of the solar eclipse which was to happen on June 22nd, +1666. It is interesting to note that even in those days the +doctrines of the astrologers still found a considerable degree of +credence, and Flamsteed spent a good deal of his time in astrological +studies and computations. He investigated the methods of casting a +nativity, but a suspicion, or, indeed, rather more than a suspicion, +seems to have crossed his mind as to the value of these astrological +predictions, for he says in fine, "I found astrology to give +generally strong conjectural hints, not perfect declarations." + +All this time, however, the future Astronomer Royal was steadily +advancing in astronomical inquiries of a recondite nature. He had +investigated the obliquity of the ecliptic with extreme care, so far +as the circumstances of astronomical observation would at that time +permit. He had also sought to discover the sun's distance from the +earth in so far as it could be obtained by determining when the moon +was exactly half illuminated, and he had measured, with much +accuracy, the length of the tropical year. It will thus be seen +that, even at the age of twenty, Flamsteed had made marked progress, +considering how much his time had been interfered with by ill-health. + +Other branches of astronomy began also to claim his attention. We +learn that in 1669 and 1670 he compared the planets Jupiter and Mars +with certain fixed stars near which they passed. His instrumental +means, though very imperfect, were still sufficient to enable him to +measure the intervals on the celestial sphere between the planets and +the stars. As the places of the stars were known, Flamsteed was thus +able to obtain the places of the planets. This is substantially the +way in which astronomers of the present day still proceed when they +desire to determine the places of the planets, inasmuch as, directly +or indirectly those places are always obtained relatively to the +fixed stars. By his observations at this early period, Flamsteed +was, it is true, not able to obtain any great degree of accuracy; he +succeeded, however, in proving that the tables by which the places of +the planets were ordinarily given were not to be relied upon. + +[PLATE: FLAMSTEED.] + +Flamsteed's labours in astronomy and in the allied branches of +science were now becoming generally known, and he gradually came to +correspond with many distinguished men of learning. One of the first +occasions which brought the talents of the young astronomer into fame +was the publication of some calculations concerning certain +astronomical phenomena which were to happen in the year 1670. In the +monthly revolution of the moon its disc passes over those stars which +lie along its track. The disappearance of a star by the +interposition of the moon is called an "occultation." Owing to the +fact that our satellite is comparatively near us, the position which +the moon appears to occupy on the heavens varies from different parts +of the earth, it consequently happens that a star which would be +occulted to an observer in one locality, would often not be occulted +to an observer who was situated elsewhere. Even when an occultation +is visible from both places, the times at which the star disappears +from view will, generally speaking, be different. Much calculation +is therefore necessary to decide the circumstances under which the +occultations of stars may be visible from any particular station. +Having a taste for such computations, Flamsteed calculated the +occultations which were to happen in the year 1670, it being the case +that several remarkable stars would be passed over by the moon during +this year. Of course at the present time, we find such information +duly set forth in the NAUTICAL ALMANAC, but a couple of centuries ago +there was no such source of astronomical knowledge as is now to be +found in that invaluable publication, which astronomers and +navigators know so well. Flamsteed accordingly sent the results of +his work to the President of the Royal Society. The paper which +contained them was received very favourably, and at once brought +Flamsteed into notice among the most eminent members of that +illustrious body, one of whom, Mr. Collins, became through life his +faithful friend and constant correspondent. Flamsteed's father was +naturally gratified with the remarkable notice which his son was +receiving from the great and learned; accordingly he desired him to +go to London, that he might make the personal acquaintance of those +scientific friends whom he had only known by correspondence +previously. Flamsteed was indeed glad to avail himself of this +opportunity. Thus he became acquainted with Dr. Barrow, and +especially with Newton, who was then Lucasian Professor of +Mathematics at Cambridge. It seems to have been in consequence of +this visit to London that Flamsteed entered himself as a member of +Jesus College, Cambridge. We have but little information as to his +University career, but at all events he took his degree of M.A. on +June 5th, 1674. + +Up to this time it would seem that Flamsteed had been engaged, to a +certain extent, in the business carried on by his father. It is true +that he does not give any explicit details, yet there are frequent +references to journeys which he had to take on business matters. But +the time now approached when Flamsteed was to start on an independent +career, and it appears that he took his degree in Cambridge with the +object of entering into holy orders, so that he might settle in a +small living near Derby, which was in the gift of a friend of his +father, and would be at the disposal of the young astronomer. This +scheme was, however, not carried out, but Flamsteed does not tell us +why it failed, his only remark being, that "the good providence of +God that had designed me for another station ordered it otherwise." + +Sir Jonas Moore, one of the influential friends whom Flamsteed's +talents had attracted, seems to have procured for him the position of +king's astronomer, with a salary of 100 pounds per annum. A larger +salary appears to have been designed at first for this office, which +was now being newly created, but as Flamsteed was resolved on taking +holy orders, a lesser salary was in his case deemed sufficient. The +building of the observatory, in which the first Astronomer Royal was +to be installed, seems to have been brought about, or, at all events, +its progress was accelerated, in a somewhat curious manner. + +A Frenchman, named Le Sieur de S. Pierre, came over to London to +promulgate a scheme for discovering longitudes, then a question of +much importance. He brought with him introductions to distinguished +people, and his mission attracted a great deal of attention. The +proposals which he made came under Flamsteed's notice, who pointed +out that the Frenchman's projects were quite inapplicable in the +present state of astronomical science, inasmuch as the places of the +stars were not known with the degree of accuracy which would be +necessary if such methods were to be rendered available. Flamsteed +then goes on to say:--"I heard no more of the Frenchman after this; +but was told that my letters had been shown King Charles. He was +startled at the assertion of the fixed stars' places being false in +the catalogue, and said, with some vehemence, he must have them anew +observed, examined, and corrected, for the use of his seamen." + +The first question to be settled was the site for the new +observatory. Hyde Park and Chelsea College were both mentioned as +suitable localities, but, at Sir Christopher Wren's suggestion, +Greenwich Hill was finally resolved upon. The king made a grant of +five hundred pounds of money. He gave bricks from Tilbury Fort, +while materials, in the shape of wood, iron, and lead, were available +from a gatehouse demolished in the Tower. The king also promised +whatever further material aid might be shown to be necessary. The +first stone of the Royal Observatory was laid on August 10th, 1675, +and within a few years a building was erected in which the art of +modern practical astronomy was to be created. Flamsteed strove with +extraordinary diligence, and in spite of many difficulties, to obtain +a due provision of astronomical instruments, and to arrange for the +carrying on of his observations. Notwithstanding the king's +promises, the astronomer was, however, but scantily provided with +means, and he had no assistants to help him in his work. It follows +that all the observations, as well as the reductions, and, indeed, +all the incidental work of the observatory, had to be carried on by +himself alone. Flamsteed, as we have seen, had, however, many +staunch friends. Sir Jonas Moore in particular at all times rendered +him most valuable assistance, and encouraged him by the warm sympathy +and keen interest which he showed in astronomy. The work of the +first Astronomer Royal was frequently interrupted by recurrent +attacks of the complaints to which we have already referred. He says +himself that "his distempers stick so close that that he cannot +remove them," and he lost much time by prostration from headaches, as +well as from more serious affections. + +The year 1678 found him in the full tide of work in his observatory. +He was specially engaged on the problem of the earth's motion, which +he sought to derive from observations of the sun and of Venus. But +this, as well as many other astronomical researches which he +undertook, were only subsidiary to that which he made the main task +of his life, namely, the formation of a catalogue of fixed stars. At +the time when Flamsteed commenced his career, the only available +catalogue of fixed stars was that of Tycho Brahe. This work had been +published at the commencement of the seventeenth century, and it +contained about a thousand stars. The positions assigned to these +stars, though obtained with wonderful skill, considering the many +difficulties under which Tycho laboured, were quite inaccurate when +judged by our modern standards. Tycho's instruments were necessarily +most rudely divided, and he had, of course, no telescopes to aid him. +Consequently it was merely by a process of sighting that he could +obtain the places of the stars. It must further be remembered that +Tycho had no clocks, and no micrometers. He had, indeed, but little +correct knowledge of the motions of the heavenly bodies to guide +him. To determine the longitudes of a few principal stars he +conceived the ingenious idea of measuring by day the position of +Venus with respect to the sun, an observation which the exceptional +brightness of this planet rendered possible without telescopic aid, +and then by night he observed the position of Venus with regard to +the stars. + +It has been well remarked by Mr. Baily, in his introduction to the +"British Catalogue of Stars," that "Flamsteed's observations, by a +fortunate combination of circumstances, commenced a new and a +brilliant era. It happened that, at that period, the powerful mind +of Newton was directed to this subject; a friendly intercourse then +existed between these two distinguished characters; and thus the +first observations that could lay any claim to accuracy were at once +brought in aid of those deep researches in which our illustrious +geometer was then engaged. The first edition of the 'Principia' +bears testimony to the assistance afforded by Flamsteed to Newton in +these inquiries; although the former considers that the +acknowledgment is not so ample as it ought to have been." + +Although Flamsteed's observations can hardly be said to possess the +accuracy of those made in more recent times, when instruments so much +superior to his have been available, yet they possess an interest of +a special kind from their very antiquity. This circumstance renders +them of particular importance to the astronomer, inasmuch as they are +calculated to throw light on the proper motions of the stars. +Flamsteed's work may, indeed, be regarded as the origin of all +subsequent catalogues, and the nomenclature which he adopted, though +in some respects it can hardly be said to be very defensible, is, +nevertheless, that which has been adopted by all subsequent +astronomers. There were also a great many errors, as might be +expected in a work of such extent, composed almost entirely of +numerical detail. Many of these errors have been corrected by Baily +himself, the assiduous editor of "Flamsteed's Life and Works," for +Flamsteed was so harassed from various causes in the latter part of +his life, and was so subject to infirmities all through his career, +that he was unable to revise his computations with the care that +would have been necessary. Indeed, he observed many additional stars +which he never included in the British Catalogue. It is, as Baily +well remarks, "rather a matter of astonishment that he accomplished +so much, considering his slender means, his weak frame, and the +vexations which he constantly experienced." + +Flamsteed had the misfortune, in the latter part of his life, to +become estranged from his most eminent scientific contemporaries. He +had supplied Newton with places of the moon, at the urgent +solicitation of the author of the "Principia," in order that the +lunar theory should be carefully compared with observation. But +Flamsteed appears to have thought that in Newton's further request +for similar information, he appeared to be demanding as a right that +which Flamsteed considered he was only called upon to render as a +favour. A considerable dispute grew out of this matter, and there +are many letters and documents, bearing on the difficulties which +subsequently arose, that are not, perhaps, very creditable to either +party. + +Notwithstanding his feeble constitution, Flamsteed lived to the age +of seventy-three, his death occurring on the last day of the year +1719. + + + + +HALLEY. + + +Isaac Newton was just fourteen years of age when the birth of Edmund +Halley, who was destined in after years to become Newton's warmly +attached friend, and one of his most illustrious scientific +contemporaries, took place. There can be little doubt that the fame +as an astronomer which Halley ultimately acquired, great as it +certainly was, would have been even greater still had it not been +somewhat impaired by the misfortune that he had to shine in the same +sky as that which was illumined by the unparalleled genius of Newton. + +Edmund Halley was born at Haggerston, in the Parish of St. Leonard's, +Shoreditch, on October 29th, 1656. His father, who bore the same +name as his famous son, was a soap-boiler in Winchester Street, +London, and he had conducted his business with such success that he +accumulated an ample fortune. I have been unable to obtain more than +a very few particulars with respect to the early life of the future +astronomer. It would, however, appear that from boyhood he showed +considerable aptitude for the acquisition of various kinds of +learning, and he also had some capacity for mechanical invention. +Halley seems to have received a sound education at St. Paul's School, +then under the care of Dr. Thomas Gale. + +Here, the young philosopher rapidly distanced his competitors in the +various branches of ordinary school instruction. His superiority +was, however, most conspicuous in mathematical studies, and, as a +natural development of such tastes, we learn that by the time he had +left school he had already made good progress in astronomy. At the +age of seventeen he was entered as a commoner at Queen's College, +Oxford, and the reputation that he brought with him to the University +may be inferred from the remark of the writer of "Athenae +Oxonienses," that Halley came to Oxford "with skill in Latin, Greek, +and Hebrew, and such a knowledge of geometry as to make a complete +dial." Though his studies were thus of a somewhat multifarious +nature, yet it is plain that from the first his most favourite +pursuit was astronomy. His earliest efforts in practical observation +were connected with an eclipse which he observed from his father's +house in Winchester Street. It also appears that he had studied +theoretical branches of astronomy so far as to be conversant with the +application of mathematics to somewhat abstruse problems. + +Up to the time of Kepler, philosophers had assumed almost as an axiom +that the heavenly bodies must revolve in circles and that the motion +of the planet around the orbit which it described must be uniform. We +have already seen how that great philosopher, after very persevering +labour, succeeded in proving that the orbits of the planets were not +circles, but that they were ellipses of small eccentricity. Kepler +was, however, unable to shake himself free from the prevailing notion +that the angular motion of the planet ought to be of a uniform +character around some point. He had indeed proved that the motion +round the focus of the ellipse in which the sun lies is not of this +description. One of his most important discoveries even related to +the fact that at some parts of its orbit a planet swings around the +sun with greater angular velocity than at others. But it so happens +that in elliptic tracks which differ but little from circles, as is +the case with all the more important planetary orbits, the motion +round the empty focus of the ellipse is very nearly uniform. It +seemed natural to assume, that this was exactly the case, in which +event each of the two foci of the ellipse would have had a special +significance in relation to the movement of the planet. The youthful +Halley, however, demonstrated that so far as the empty focus was +concerned, the movement of the planet around it, though so nearly +uniform, was still not exactly so, and at the age of nineteen, he +published a treatise on the subject which at once placed him in the +foremost rank amongst theoretical astronomers. + +But Halley had no intention of being merely an astronomer with his +pen. He longed to engage in the practical work of observing. He saw +that the progress of exact astronomy must depend largely on the +determination of the positions of the stars with all attainable +accuracy. He accordingly determined to take up this branch of work, +which had been so successfully initiated by Tycho Brahe. + +At the present day, astronomers of the great national observatories +are assiduously engaged in the determination of the places of the +stars. A knowledge of the exact positions of these bodies is indeed +of the most fundamental importance, not alone for the purposes of +scientific astronomy, but also for navigation and for extensive +operations of surveying in which accuracy is desired. The fact that +Halley determined to concentrate himself on this work shows clearly +the scientific acumen of the young astronomer. + +Halley, however, found that Hevelius, at Dantzig, and Flamsteed, the +Astronomer Royal at Greenwich, were both engaged on work of this +character. He accordingly determined to direct his energies in a way +that he thought would be more useful to science. He resigned to the +two astronomers whom I have named the investigation of the stars in +the northern hemisphere, and he sought for himself a field hitherto +almost entirely unworked. He determined to go to the southern +hemisphere, there to measure and survey those stars which were +invisible in Europe, so that his work should supplement the labours +of the northern astronomers, and that the joint result of his labours +and of theirs might be a complete survey of the most important stars +on the surface of the heavens. + +In these days, after so many ardent students everywhere have devoted +themselves to the study of Nature, it seems difficult for a beginner +to find a virgin territory in which to commence his explorations. +Halley may, however, be said to have enjoyed the privilege of +commencing to work in a magnificent region, the contents of which +were previously almost entirely unknown. Indeed none of the stars +which were so situated as to have been invisible from Tycho Brahe's +observatory at Uraniborg, in Denmark, could be said to have been +properly observed. There was, no doubt, a rumour that a Dutchman had +observed southern stars from the island of Sumatra, and certain stars +were indicated in the southern heavens on a celestial globe. On +examination, however, Halley found that no reliance could be placed +on the results which had been obtained, so that practically the field +before him may be said to have been unworked. + +At the age of twenty, without having even waited to take that degree +at the university which the authorities would have been glad to +confer on so promising an undergraduate, this ardent student of +Nature sought his father's permission to go to the southern +hemisphere for the purpose of studying the stars which lie around the +southern pole. His father possessed the necessary means, and he had +likewise the sagacity to encourage the young astronomer. He was +indeed most anxious to make everything as easy as possible for so +hopeful a son. He provided him with an allowance of 300 pounds a +year, which was regarded as a very munificent provision in those +days. Halley was also furnished with letters of recommendation from +King Charles II., as well as from the directors of the East India +Company. He accordingly set sail with his instruments in the year +1676, in one of the East India Company's ships, for the island of St. +Helena, which he had selected as the scene of his labours. + +[PLATE: HALLEY.] + +After an uneventful voyage of three months, the astronomer landed on +St. Helena, with his sextant of five and a half feet radius, and a +telescope 24 feet long, and forthwith plunged with ardour into his +investigation of the southern skies. He met, however, with one very +considerable disappointment. The climate of this island had been +represented to him as most favourable for astronomical observation; +but instead of the pure blue skies he had been led to expect, he +found that they were almost always more or less clouded, and that +rain was frequent, so that his observations were very much +interrupted. On this account he only remained at St. Helena for a +single year, having, during that time, and in spite of many +difficulties, accomplished a piece of work which earned for him the +title of "our southern Tycho." Thus did Halley establish his fame as +an astronomer on the same lonely rock in mid-Atlantic, which nearly a +century and a-half later became the scene of Napoleon's imprisonment, +when his star, in which he believed so firmly, had irretrievably set. + +On his return to England, Halley prepared a map which showed the +result of his labours, and he presented it to the king, in 1677. +Like his great predecessor Tycho, Halley did not altogether disdain +the arts of the courtier, for he endeavoured to squeeze a new +constellation into the group around the southern pole which he styled +"The Royal Oak," adding a description to the effect that the +incidents of which "The Royal Oak" was a symbol were of sufficient +importance to be inscribed on the surface of the heavens. + +There is reason to think that Charles II. duly appreciated the +scientific renown which one of his subjects had achieved, and it was +probably through the influence of the king that Halley was made a +Master of Arts at Oxford on November 18th, 1678. Special reference +was made on the occasion to his observations at St. Helena, as +evidence of unusual attainments in mathematics and astronomy. This +degree was no small honour to such a young man, who, as we have seen, +quitted his university before he had the opportunity of graduating in +the ordinary manner. + +On November 30th, in the same year, the astronomer received a further +distinction in being elected a Fellow of the Royal Society. From +this time forward he took a most active part in the affairs of the +Society, and the numerous papers which he read before it form a very +valuable part of that notable series of volumes known as the +"Philosophical Transactions." He was subsequently elected to the +important office of secretary to the Royal Society, and he discharged +the duties of his post until his appointment to Greenwich +necessitated his resignation. + +Within a year of Halley's election as a Fellow of the Royal Society, +he was chosen by the Society to represent them in a discussion which +had arisen with Hevelius. The nature of this discussion, or rather +the fact that any discussion should have been necessary, may seem +strange to modern astronomers, for the point is one on which it would +now seem impossible for there to be any difference of opinion. We +must, however, remember that the days of Halley were, comparatively +speaking, the days of infancy as regards the art of astronomical +observation, and issues that now seem obvious were often, in those +early times, the occasions of grave and anxious consideration. The +particular question on which Halley had to represent the Royal +Society may be simply stated. When Tycho Brahe made his memorable +investigations into the places of the stars, he had no telescopes to +help him. The famous instruments at Uraniborg were merely provided +with sights, by which the telescope was pointed to a star on the same +principle as a rifle is sighted for a target. Shortly after Tycho's +time, Galileo invented the telescope. Of course every one admitted +at once the extraordinary advantages which the telescope had to +offer, so far as the mere question of the visibility of objects was +concerned. But the bearing of Galileo's invention upon what we may +describe as the measuring part of astronomy was not so immediately +obvious. If a star be visible to the unaided eye, we can determine +its place by such instruments as those which Tycho used, in which no +telescope is employed. We can, however, also avail ourselves of an +instrument in which we view the star not directly but through the +intervention of the telescope. Can the place of the star be +determined more accurately by the latter method than it can when the +telescope is dispensed with? With our present knowledge, of course, +there is no doubt about the answer; every one conversant with +instruments knows that we can determine the place of a star far more +accurately with the telescope than is possible by any mere sighting +apparatus. In fact an observer would be as likely to make an error +of a minute with the sighting apparatus in Tycho's instrument, as he +would be to make an error of a second with the modern telescope, or, +to express the matter somewhat differently, we may say, speaking +quite generally, that the telescopic method of determining the places +of the stars does not lead to errors more than one-sixtieth part as +great as which are unavoidable when we make use of Tycho's method. + +But though this is so apparent to the modern astronomer, it was not +at all apparent in the days of Halley, and accordingly he was sent +off to discuss the question with the Continental astronomers. +Hevelius, as the representative of the older method, which Tycho had +employed with such success, maintained that an instrument could be +pointed more accurately at a star by the use of sights than by the +use of a telescope, and vigorously disputed the claims put forward by +those who believed that the latter method was the more suitable. On +May 14th, 1679, Halley started for Dantzig, and the energetic +character of the man may be judged from the fact that on the very +night of his arrival he commenced to make the necessary +observations. In those days astronomical telescopes had only +obtained a fractional part of the perfection possessed by the +instruments in our modern observatories, and therefore it may not be +surprising that the results of the trial were not immediately +conclusive. Halley appears to have devoted much time to the +investigation; indeed, he remained at Dantzig for more than a +twelve-month. On his return to England, he spoke highly of the skill +which Hevelius exhibited in the use of his antiquated methods, but +Halley was nevertheless too sagacious an observer to be shaken in his +preference for the telescopic method of observation. + +The next year we find our young astronomer starting for a Continental +tour, and we, who complain if the Channel passage lasts more than an +hour or two, may note Halley's remark in writing to Hooke on June +15th, 1680: "Having fallen in with bad weather we took forty hours in +the journey from Dover to Calais." The scientific distinction which +he had already attained was such that he was received in Paris with +marked attention. A great deal of his time seems to have been passed +in the Paris observatory, where Cassini, the presiding genius, +himself an astronomer of well-deserved repute, had extended a hearty +welcome to his English visitor. They made observations together of +the place of the splendid comet which was then attracting universal +attention, and Halley found the work thus done of much use when he +subsequently came to investigate the path pursued by this body. +Halley was wise enough to spare no pains to derive all possible +advantages from his intercourse with the distinguished savants of the +French capital. In the further progress of his tour he visited the +principal cities of the Continent, leaving behind him everywhere the +memory of an amiable disposition and of a rare intelligence. + +After Halley's return to England, in 1682, he married a young lady +named Mary Tooke, with whom he lived happily, till her death +fifty-five years later. On his marriage, he took up his abode in +Islington, where he erected his instruments and recommenced his +observations. + +It has often been the good fortune of astronomers to render practical +services to humanity by their investigations, and Halley's +achievements in this respect deserve to be noted. A few years after +he had settled in England, he published an important paper on the +variation of the magnetic compass, for so the departure of the needle +from the true north is termed. This subject had indeed early engaged +his attention, and he continued to feel much interest in it up to the +end of his life. With respect to his labours in this direction, Sir +John Herschel says: "To Halley we owe the first appreciation of the +real complexity of the subject of magnetism. It is wonderful indeed, +and a striking proof of the penetration and sagacity of this +extraordinary man, that with his means of information he should have +been able to draw such conclusions, and to take so large and +comprehensive a view of the subject as he appears to have done." In +1692, Halley explained his theory of terrestrial magnetism, and +begged captains of ships to take observations of the variations of +the compass in all parts of the world, and to communicate them to the +Royal Society, "in order that all the facts may be readily available +to those who are hereafter to complete this difficult and complicated +subject." + +The extent to which Halley was in advance of his contemporaries, in +the study of terrestrial magnetism, may be judged from the fact that +the subject was scarcely touched after his time till the year 1811. +The interest which he felt in it was not of a merely theoretical +kind, nor was it one which could be cultivated in an easy-chair. Like +all true investigators, he longed to submit his theory to the test of +experiment, and for that purpose Halley determined to observe the +magnetic variation for himself. He procured from King William III. +the command of a vessel called the "Paramour Pink," with which he +started for the South Seas in 1694. This particular enterprise was +not, however, successful; for, on crossing the line, some of his men +fell sick and one of his lieutenants mutinied, so that he was obliged +to return the following year with his mission unaccomplished. The +government cashiered the lieutenant, and Halley having procured a +second smaller vessel to accompany the "Paramour Pink," started once +more in September, 1699. He traversed the Atlantic to the 52nd +degree of southern latitude, beyond which his further advance was +stopped. "In these latitudes," he writes to say, "we fell in with +great islands of ice of so incredible height and magnitude, that I +scarce dare write my thoughts of it." + +On his return in 1700, Halley published a general chart, showing the +variation of the compass at the different places which he had +visited. On these charts he set down lines connecting those +localities at which the magnetic variation was identical. He thus +set an example of the graphic representation of large masses of +complex facts, in such a manner as to appeal at once to the eye, a +method of which we make many applications in the present day. + +But probably the greatest service which Halley ever rendered to human +knowledge was the share in which he took in bringing Newton's +"Principia" before the world. In fact, as Dr. Glaisher, writing in +1888, has truly remarked, "but for Halley the 'Principia' would not +have existed." + +It was a visit from Halley in the year 1684 which seems to have first +suggested to Newton the idea of publishing the results of his +investigations on gravitation. Halley, and other scientific +contemporaries, had no doubt some faint glimmering of the great truth +which only Newton's genius was able fully to reveal. Halley had +indeed shown how, on the assumptions that the planets move in +circular orbits round the sun, and that the squares of their periodic +times are proportional to the cubes of their mean distances, it may +be proved that the force acting on each planet must vary inversely as +the square of its distance from the sun. Since, however, each of the +planets actually moves in an ellipse, and therefore, at continually +varying distances from the sun, it becomes a much more difficult +matter to account mathematically for the body's motions on the +supposition that the attractive force varies inversely as the square +of the distance. This was the question with which Halley found +himself confronted, but which his mathematical abilities were not +adequate to solve. It would seem that both Hooke and Sir Christopher +Wren were interested in the same problem; in fact, the former claimed +to have arrived at a solution, but declined to make known his +results, giving as an excuse his desire that others having tried and +failed might learn to value his achievements all the more. Halley, +however, confessed that his attempts at the solution were +unsuccessful, and Wren, in order to encourage the other two +philosophers to pursue the inquiry, offered to present a book of +forty shillings value to either of them who should in the space of +two months bring him a convincing proof of it. Such was the value +which Sir Christopher set on the Law of Gravitation, upon which the +whole fabric of modern astronomy may be said to stand. + +Finding himself unequal to the task, Halley went down to Cambridge to +see Newton on the subject, and was delighted to learn that the great +mathematician had already completed the investigation. He showed +Halley that the motions of all the planets could be completely +accounted for on the hypothesis of a force of attraction directed +towards the sun, which varies inversely as the square of the distance +from that body. + +Halley had the genius to perceive the tremendous importance of +Newton's researches, and he ceased not to urge upon the recluse man +of science the necessity for giving his new discoveries publication. +He paid another visit to Cambridge with the object of learning more +with regard to the mathematical methods which had already conducted +Newton to such sublime truths, and he again encouraged the latter +both to pursue his investigations, and to give some account of them +to the world. In December of the same year Halley had the +gratification of announcing to the Royal Society that Newton had +promised to send that body a paper containing his researches on +Gravitation. + +It seems that at this epoch the finances of the Royal Society were at +a very low ebb. This impecuniosity was due to the fact that a book +by Willoughby, entitled "De Historia Piscium," had been recently +printed by the society at great expense. In fact, the coffers were +so low that they had some difficulty in paying the salaries of their +permanent officials. It appears that the public did not care about +the history of fishes, or at all events the volume did not meet with +the ready demand which was expected for it. Indeed, it has been +recorded that when Halley had undertaken to measure the length of a +degree of the earth's surface, at the request of the Royal Society, +it was ordered that his expenses be defrayed either in 50 pounds +sterling, or in fifty books of fishes. Thus it happened that on June +2nd, the Council, after due consideration of ways and means in +connection with the issue of the Principia, "ordered that Halley +should undertake the business of looking after the book and printing +it at his own charge," which he engaged to do. + +It was, as we have elsewhere mentioned, characteristic of Newton that +he detested controversies, and he was, in fact, inclined to suppress +the third book of the "Principia" altogether rather than have any +conflict with Hooke with respect to the discoveries there +enunciated. He also thought of changing the name of the work to De +Motu Corporum Libri Duo, but upon second thoughts, he retained the +original title, remarking, as he wrote to Halley, "It will help the +sale of the book, which I ought not to diminish, now it is yours," a +sentence which shows conclusively, if further proof were necessary, +that Halley had assumed the responsibility of its publication. + +Halley spared no pains in pushing forward the publication of his +illustrious friend's great work, so that in the same year he was in a +position to present a complete copy to King James II., with a proper +discourse of his own. Halley also wrote a set of Latin hexameters in +praise of Newton's genius, which he printed at the beginning of the +work. The last line of this specimen of Halley's poetic muse may be +thus rendered: "Nor mortals nearer may approach the gods." + +The intimate friendship between the two greatest astronomers of the +time continued without interruption till the death of Newton. It +has, indeed, been alleged that some serious cause of estrangement +arose between them. There is, however, no satisfactory ground for +this statement; indeed, it may be regarded as effectually disposed of +by the fact that, in the year 1727, Halley took up the defence of his +friend, and wrote two learned papers in support of Newton's "System +of Chronology," which had been seriously attacked by a certain +ecclesiastic. It is quite evident to any one who has studied these +papers that Halley's friendship for Newton was as ardent as ever. + +The generous zeal with which Halley adopted and defended the +doctrines of Newton with regard to the movements of the celestial +bodies was presently rewarded by a brilliant discovery, which has +more than any of his other researches rendered his name a familiar +one to astronomers. Newton, having explained the movement of the +planets, was naturally led to turn his attention to comets. He +perceived that their journeyings could be completely accounted for as +consequences of the attraction of the sun, and he laid down the +principles by which the orbit of a comet could be determined, +provided that observations of its positions were obtained at three +different dates. The importance of these principles was by no one +more quickly recognised than by Halley, who saw at once that it +provided the means of detecting something like order in the movements +of these strange wanderers. The doctrine of Gravitation seemed to +show that just as the planets revolved around the sun in ellipses, so +also must the comets. The orbit, however, in the case of the comet, +is so extremely elongated that the very small part of the elliptic +path within which the comet is both near enough and bright enough to +be seen from the earth, is indistinguishable from a parabola. +Applying these principles, Halley thought it would be instructive to +study the movements of certain bright comets, concerning which +reliable observations could be obtained. At the expense of much +labour, he laid down the paths pursued by twenty-four of these +bodies, which had appeared between the years 1337 and 1698. Amongst +them he noticed three, which followed tracks so closely resembling +each other, that he was led to conclude the so called three comets +could only have been three different appearances of the same body. +The first of these occurred in 1531, the second was seen by Kepler in +1607, and the third by Halley himself in 1682. These dates suggested +that the observed phenomena might be due to the successive returns of +one and the same comet after intervals of seventy-five or seventy-six +years. On the further examination of ancient records, Halley found +that a comet had been seen in the year 1456, a date, it will be +observed, seventy-five years before 1531. Another had been observed +seventy-six years earlier than 1456, viz., in 1380, and another +seventy-five years before that, in 1305. + +As Halley thus found that a comet had been recorded on several +occasions at intervals of seventy-five or seventy-six years, he was +led to the conclusion that these several apparitions related to one +and the same object, which was an obedient vassal of the sun, +performing an eccentric journey round that luminary in a period of +seventy-five or seventy-six years. To realise the importance of this +discovery, it should be remembered that before Halley's time a comet, +if not regarded merely as a sign of divine displeasure, or as an omen +of intending disaster, had at least been regarded as a chance visitor +to the solar system, arriving no one knew whence, and going no one +knew whither. + +A supreme test remained to be applied to Halley's theory. The +question arose as to the date at which this comet would be seen +again. We must observe that the question was complicated by the fact +that the body, in the course of its voyage around the sun, was +exposed to the incessant disturbing action produced by the attraction +of the several planets. The comet therefore, does not describe a +simple ellipse as it would do if the attraction of the sun were the +only force by which its movement were controlled. Each of the +planets solicits the comet to depart from its track, and though the +amount of these attractions may be insignificant in comparison with +the supreme controlling force of the sun, yet the departure from the +ellipse is quite sufficient to produce appreciable irregularities in +the comet's movement. At the time when Halley lived, no means +existed of calculating with precision the effect of the disturbance a +comet might experience from the action of the different planets. +Halley exhibited his usual astronomical sagacity in deciding that +Jupiter would retard the return of the comet to some extent. Had it +not been for this disturbance the comet would apparently have been +due in 1757 or early in 1758. But the attraction of the great planet +would cause delay, so that Halley assigned, for the date of its +re-appearance, either the end of 1758 or the beginning of 1759. +Halley knew that he could not himself live to witness the fulfilment +of his prediction, but he says: "If it should return, according to +our predictions, about the year 1758, impartial posterity will not +refuse to acknowledge that this was first discovered by an +Englishman." This was, indeed, a remarkable prediction of an event +to occur fifty-three years after it had been uttered. The way in +which it was fulfilled forms one of the most striking episodes in the +history of astronomy. The comet was first seen on Christmas Day, +1758, and passed through its nearest point to the sun on March 13th, +1759. Halley had then been lying in his grave for seventeen years, +yet the verification of his prophecy reflects a glory on his name +which will cause it to live for ever in the annals of astronomy. The +comet paid a subsequent visit in 1835, and its next appearance is due +about 1910. + +Halley next entered upon a labour which, if less striking to the +imagination than his discoveries with regard to comets, is still of +inestimable value in astronomy. He undertook a series of +investigations with the object of improving our knowledge of the +movements of the planets. This task was practically finished in +1719, though the results of it were not published until after his +death in 1749. In the course of it he was led to investigate closely +the motion of Venus, and thus he came to recognise for the first time +the peculiar importance which attaches to the phenomenon of the +transit of this planet across the sun. Halley saw that the transit, +which was to take place in the year 1761, would afford a favourable +opportunity for determining the distance of the sun, and thus +learning the scale of the solar system. He predicted the +circumstances of the phenomenon with an astonishing degree of +accuracy, considering his means of information, and it is +unquestionably to the exertions of Halley in urging the importance of +the matter upon astronomers that we owe the unexampled degree of +interest taken in the event, and the energy which scientific men +exhibited in observing it. The illustrious astronomer had no hope of +being himself a witness of the event, for it could not happen till +many years after his death. This did not, however, diminish his +anxiety to impress upon those who would then be alive, the importance +of the occurrence, nor did it lead him to neglect anything which +might contribute to the success of the observations. As we now know, +Halley rather over-estimated the value of the transit of Venus, as a +means of determining the solar distance. The fact is that the +circumstances are such that the observation of the time of contact +between the edge of the planet and the edge of the sun cannot be made +with the accuracy which he had expected. + +In 1691, Halley became a candidate for the Savilian Professorship of +Astronomy at Oxford. He was not, however, successful, for his +candidature was opposed by Flamsteed, the Astronomer Royal of the +time, and another was appointed. He received some consolation for +this particular disappointment by the fact that, in 1696, owing to +Newton's friendly influence, he was appointed deputy Controller of +the Mint at Chester, an office which he did not retain for long, as +it was abolished two years later. At last, in 1703, he received what +he had before vainly sought, and he was appointed to the Savilian +chair. + +His observations of the eclipse of the sun, which occurred in 1715, +added greatly to Halley's reputation. This phenomenon excited +special attention, inasmuch as it was the first total eclipse of the +sun which had been visible in London since the year 1140. Halley +undertook the necessary calculations, and predicted the various +circumstances with a far higher degree of precision than the official +announcement. He himself observed the phenomenon from the Royal +Society's rooms, and he minutely describes the outer atmosphere of +the sun, now known as the corona; without, however, offering an +opinion as to whether it was a solar or a lunar appendage. + +At last Halley was called to the dignified office which he of all men +was most competent to fill. On February 9th, 1720, he was appointed +Astronomer Royal in succession to Flamsteed. He found things at the +Royal Observatory in a most unsatisfactory state. Indeed, there were +no instruments, nor anything else that was movable; for such things, +being the property of Flamsteed, had been removed by his widow, and +though Halley attempted to purchase from that lady some of the +instruments which his predecessor had employed, the unhappy personal +differences which had existed between him and Flamsteed, and which, +as we have already seen, prevented his election as Savilian Professor +of Astronomy, proved a bar to the negotiation. Greenwich Observatory +wore a very different appearance in those days, from that which the +modern visitor, who is fortunate enough to gain admission, may now +behold. Not only did Halley find it bereft of instruments, we learn +besides that he had no assistants, and was obliged to transact the +whole business of the establishment single-handed. + +In 1721, however, he obtained a grant of 500 pounds from the Board of +Ordnance, and accordingly a transit instrument was erected in the +same year. Some time afterwards he procured an eight-foot quadrant, +and with these instruments, at the age of sixty-four, he commenced a +series of observations on the moon. He intended, if his life was +spared, to continue his observations for a period of eighteen years, +this being, as astronomers know, a very important cycle in connection +with lunar movements. The special object of this vast undertaking +was to improve the theory of the moon's motion, so that it might +serve more accurately to determine longitudes at sea. This +self-imposed task Halley lived to carry to a successful termination, +and the tables deduced from his observations, and published after his +death, were adopted almost universally by astronomers, those of the +French nation being the only exception. + +Throughout his life Halley had been singularly free from illness of +every kind, but in 1737 he had a stroke of paralysis. Notwithstanding +this, however, he worked diligently at his telescope till 1739, after +which his health began rapidly to give way. He died on January 14th, +1742, in the eighty-sixth year of his age, retaining his mental +faculties to the end. He was buried in the cemetery of the church of +Lee in Kent, in the same grave as his wife, who had died five years +previously. We are informed by Admiral Smyth that Pond, a later +Astronomer Royal, was afterwards laid in the same tomb. + +Halley's disposition seems to have been generous and candid, and +wholly free from anything like jealousy or rancour. In person he was +rather above the middle height, and slight in build; his complexion +was fair, and he is said to have always spoken, as well as acted, +with uncommon sprightliness. In the eloge pronounced upon him at the +Paris Academie Des Sciences, of which Halley had been made a member +in 1719 it was said, "he possessed all the qualifications which were +necessary to please princes who were desirous of instruction, with a +great extent of knowledge and a constant presence of mind; his +answers were ready, and at the same time pertinent, judicious, polite +and sincere." + +[PLATE: GREENWICH OBSERVATORY IN HALLEY'S TIME.] + +Thus we find that Peter the Great was one of his most ardent +admirers. He consulted the astronomer on matters connected with +shipbuilding, and invited him to his own table. But Halley possessed +nobler qualifications than the capacity of pleasing Princes. He was +able to excite and to retain the love and admiration of his equals. +This was due to the warmth of his attachments, the unselfishness of +his devotion to his friends, and to a vein of gaiety and good-humour +which pervaded all his conversation. + + + + +BRADLEY. + + +James Bradley was descended from an ancient family in the county of +Durham. He was born in 1692 or 1693, at Sherbourne, in +Gloucestershire, and was educated in the Grammar School at +Northleach. From thence he proceeded in due course to Oxford, where +he was admitted a commoner at Balliol College, on March 15th, 1711. +Much of his time, while an undergraduate, was passed in Essex with +his maternal uncle, the Rev. James Pound, who was a well-known man of +science and a diligent observer of the stars. It was doubtless by +intercourse with his uncle that young Bradley became so expert in the +use of astronomical instruments, but the immortal discoveries he +subsequently made show him to have been a born astronomer. + +The first exhibition of Bradley's practical skill seems to be +contained in two observations which he made in 1717 and 1718. They +have been published by Halley, whose acuteness had led him to +perceive the extraordinary scientific talents of the young +astronomer. Another illustration of the sagacity which Bradley +manifested, even at the very commencement of his astronomical career, +is contained in a remark of Halley's, who says: "Dr. Pound and his +nephew, Mr. Bradley, did, myself being present, in the last +opposition of the sun and Mars this way demonstrate the extreme +minuteness of the sun's parallax, and that it was not more than +twelve seconds nor less than nine seconds." To make the significance +of this plain, it should be observed that the determination of the +sun's parallax is equivalent to the determination of the distance +from the earth to the sun. At the time of which we are now writing, +this very important unit of celestial measurement was only very +imperfectly known, and the observations of Pound and Bradley may be +interpreted to mean that, from their observations, they had come to +the conclusion that the distance from the earth to the sun must be +more than 94 millions of miles, and less than 125 millions. We now, +of course, know that they were not exactly right, for the true +distance of the sun is about 93 millions of miles. We cannot, +however, but think that it was a very remarkable approach for the +veteran astronomer and his brilliant nephew to make towards the +determination of a magnitude which did not become accurately known +till fifty years later. + +Among the earliest parts of astronomical work to which Bradley's +attention was directed, were the eclipses of Jupiter's satellites. +These phenomena are specially attractive inasmuch as they can be so +readily observed, and Bradley found it extremely interesting to +calculate the times at which the eclipses should take place, and then +to compare his observations with the predicted times. From the +success that he met with in this work, and from his other labours, +Bradley's reputation as an astronomer increased so greatly that on +November the 6th, 1718, he was elected a Fellow of the Royal Society. + +Up to this time the astronomical investigations of Bradley had been +more those of an amateur than of a professional astronomer, and as it +did not at first seem likely that scientific work would lead to any +permanent provision, it became necessary for the youthful astronomer +to choose a profession. It had been all along intended that he +should enter the Church, though for some reason which is not told us, +he did not take orders as soon as his age would have entitled him to +do so. In 1719, however, the Bishop of Hereford offered Bradley the +Vicarage of Bridstow, near Ross, in Monmouthshire, and on July 25th, +1720, he having then taken priest's orders, was duly instituted in +his vicarage. In the beginning of the next year, Bradley had some +addition to his income from the proceeds of a Welsh living, which, +being a sinecure, he was able to hold with his appointment at +Bridstow. It appears, however, that his clerical occupations were +not very exacting in their demands upon his time, for he was still +able to pay long and often-repeated visits to his uncle at +Wandsworth, who, being himself a clergyman, seems to have received +occasional assistance in his ministerial duties from his astronomical +nephew. + +The time, however, soon arrived when Bradley was able to make a +choice between continuing to exercise his profession as a divine, or +devoting himself to a scientific career. The Savilian Professorship +of Astronomy in the University of Oxford became vacant by the death +of Dr. John Keill. The statutes forbade that the Savilian Professor +should also hold a clerical appointment, and Mr. Pound would +certainly have been elected to the professorship had he consented to +surrender his preferments in the Church. But Pound was unwilling to +sacrifice his clerical position, and though two or three other +candidates appeared in the field, yet the talents of Bradley were so +conspicuous that he was duly elected, his willingness to resign the +clerical profession having been first ascertained. + +There can be no doubt that, with such influential friends as Bradley +possessed, he would have made great advances had he adhered to his +profession as a divine. Bishop Hoadly, indeed, with other marks of +favour, had already made the astronomer his chaplain. The engrossing +nature of Bradley's interest in astronomy decided him, however, to +sacrifice all other prospects in comparison with the opening afforded +by the Savilian Professorship. It was not that Bradley found himself +devoid of interest in clerical matters, but he felt that the true +scope for such abilities as he possessed would be better found in the +discharge of the scientific duties of the Oxford chair than in the +spiritual charge of a parish. On April the 26th, 1722, Bradley read +his inaugural lecture in that new position on which he was destined +to confer such lustre. + +It must, of course, be remembered that in those early days the art of +constructing the astronomical telescope was very imperfectly +understood. The only known method for getting over the peculiar +difficulties presented in the construction of the refracting +telescope, was to have it of the most portentous length. In fact, +Bradley made several of his observations with an instrument of two +hundred and twelve feet focus. In such a case, no tube could be +used, and the object glass was merely fixed at the top of a high +pole. Notwithstanding the inconvenience and awkwardness of such an +instrument, Bradley by its means succeeded in making many careful +measurements. He observed, for example, the transit of Mercury over +the sun's disc, on October 9th, 1723; he also observed the dimensions +of the planet Venus, while a comet which Halley discovered on October +the 9th, 1723, was assiduously observed at Wanstead up to the middle +of the ensuing month. The first of Bradley's remarkable +contributions to the "Philosophical Transactions" relates to this +comet, and the extraordinary amount of work that he went through in +connection therewith may be seen from an examination of his book of +Calculations which is still extant. + +The time was now approaching when Bradley was to make the first of +those two great discoveries by which his name has acquired a lustre +that has placed him in the very foremost rank of astronomical +discoverers. As has been often the case in the history of science, +the first of these great successes was attained while he was pursuing +a research intended for a wholly different purpose. It had long been +recognised that as the earth describes a vast orbit, nearly two +hundred million miles in diameter, in its annual journey round the +sun, the apparent places of the stars should alter, to some extent, +in correspondence with the changes in the earth's position. The +nearer the star the greater the shift in its apparent place on the +heavens, which must arise from the fact that it was seen from +different positions in the earth's orbit. It had been pointed out +that these apparent changes in the places of the stars, due to the +movement of the earth, would provide the means of measuring the +distances of the stars. As, however, these distances are enormously +great in comparison with the orbit which the earth describes around +the sun, the attempt to determine the distances of the stars by the +shift in their positions had hitherto proved ineffectual. Bradley +determined to enter on this research once again; he thought that by +using instruments of greater power, and by making measurements of +increased delicacy, he would be able to perceive and to measure +displacements which had proved so small as to elude the skill of the +other astronomers who had previously made efforts in the same +direction. In order to simplify the investigation as much as +possible, Bradley devoted his attention to one particular star, Beta +Draconis, which happened to pass near his zenith. The object of +choosing a star in this position was to avoid the difficulties which +would be introduced by refraction had the star occupied any other +place in the heavens than that directly overhead. + +We are still able to identify the very spot on which the telescope +stood which was used in this memorable research. It was erected at +the house then occupied by Molyneux, on the western extremity of Kew +Green. The focal length was 24 feet 3 inches, and the eye-glass was +3 and a half feet above the ground floor. The instrument was first +set up on November 26th, 1725. If there had been any appreciable +disturbance in the place of Beta Draconis in consequence of the +movement of the earth around the sun, the star must appear to have +the smallest latitude when in conjunction with the sun, and the +greatest when in opposition. The star passed the meridian at noon in +December, and its position was particularly noticed by Molyneux on +the third of that month. Any perceptible displacement by +parallax--for so the apparent change in position, due to the earth's +motion, is called--would would have made the star shift towards the +north. Bradley, however, when observing it on the 17th, was +surprised to find that the apparent place of the star, so far from +shifting towards the north, as they had perhaps hoped it would, was +found to lie a little more to the south than when it was observed +before. He took extreme care to be sure that there was no mistake in +his observation, and, true astronomer as he was, he scrutinized with +the utmost minuteness all the circumstances of the adjustment of his +instruments. Still the star went to the south, and it continued so +advancing in the same direction until the following March, by which +time it had moved no less than twenty seconds south from the place +which it occupied when the first observation was made. After a brief +pause, in which no apparent movement was perceptible, the star by the +middle of April appeared to be returning to the north. Early in June +it reached the same distance from the zenith which it had in +December. By September the star was as much as thirty-nine seconds +more to the north than it had been in March, then it returned towards +the south, regaining in December the same situation which it had +occupied twelve months before. + +This movement of the star being directly opposite to the movements +which would have been the consequence of parallax, seemed to show +that even if the star had any parallax its effects upon the apparent +place were entirely masked by a much larger motion of a totally +different description. Various attempts were made to account for the +phenomenon, but they were not successful. Bradley accordingly +determined to investigate the whole subject in a more thorough +manner. One of his objects was to try whether the same movements +which he had observed in one star were in any similar degree +possessed by other stars. For this purpose he set up a new +instrument at Wanstead, and there he commenced a most diligent +scrutiny of the apparent places of several stars which passed at +different distances from the zenith. He found in the course of this +research that other stars exhibited movements of a similar +description to those which had already proved so perplexing. For a +long time the cause of these apparent movements seemed a mystery. At +last, however, the explanation of these remarkable phenomena dawned +upon him, and his great discovery was made. + +One day when Bradley was out sailing he happened to remark that every +time the boat was laid on a different tack the vane at the top of the +boat's mast shifted a little, as if there had been a slight change in +the direction of the wind. After he had noticed this three or four +times he made a remark to the sailors to the effect that it was very +strange the wind should always happen to change just at the moment +when the boat was going about. The sailors, however, said there had +been no change in the wind, but that the alteration in the vane was +due to the fact that the boat's course had been altered. In fact, +the position of the vane was determined both by the course of the +boat and the direction of the wind, and if either of these were +altered there would be a corresponding change in the direction of the +vane. This meant, of course, that the observer in the boat which was +moving along would feel the wind coming from a point different from +that in which the wind appeared to be blowing when the boat was at +rest, or when it was sailing in some different direction. Bradley's +sagacity saw in this observation the clue to the Difficulty which had +so long troubled him. + +It had been discovered before the time of Bradley that the passage of +light through space is not an instantaneous phenomenon. Light +requires time for its journey. Galileo surmised that the sun may +have reached the horizon before we see it there, and it was indeed +sufficiently obvious that a physical action, like the transmission of +light, could hardly take place without requiring some lapse of time. +The speed with which light actually travelled was, however, so rapid +that its determination eluded all the means of experimenting which +were available in those days. The penetration of Roemer had +previously detected irregularities in the observed times of the +eclipses of Jupiter's satellites, which were undoubtedly due to the +interval which light required for stretching across the +interplanetary spaces. Bradley argued that as light can only travel +with a certain speed, it may in a measure be regarded like the wind, +which he noticed in the boat. If the observer were at rest, that is +to say, if the earth were a stationary object, the direction in which +the light actually does come would be different from that in which it +appears to come when the earth is in motion. It is true that the +earth travels but eighteen miles a second, while the velocity with +which light is borne along attains to as much as 180,000 miles a +second. The velocity of light is thus ten thousand times greater +than the speed of the earth. But even though the wind blew ten +thousand times faster than the speed with which the boat was sailing +there would still be some change, though no doubt a very small +change, in the position of the vane when the boat was in progress +from the position it would have if the boat were at rest. It +therefore occurred to this most acute of astronomers that when the +telescope was pointed towards a star so as to place it apparently in +the centre of the field of view, yet it was not generally the true +position of the star. It was not, in fact, the position in which the +star would have been observed had the earth been at rest. Provided +with this suggestion, he explained the apparent movements of the +stars by the principle known as the "aberration of light." Every +circumstance was accounted for as a consequence of the relative +movements of the earth and of the light from the star. This +beautiful discovery not only established in the most forcible manner +the nature of the movement of light; not only did it illustrate the +truth of the Copernican theory which asserted that the earth revolved +around the sun, but it was also of the utmost importance in the +improvement of practical astronomy. Every observer now knows that, +generally speaking, the position which the star appears to have is +not exactly the position in which the star does actually lie. The +observer is, however, able, by the application of the principles +which Bradley so clearly laid down, to apply to an observation the +correction which is necessary to obtain from it the true place in +which the object is actually situated. This memorable achievement at +once conferred on Bradley the highest astronomical fame. He tested +his discovery in every way, but only to confirm its truth in the most +complete manner. + +Halley, the Astronomer Royal, died on the 14th, January, 1742, and +Bradley was immediately pointed out as his successor. He was +accordingly appointed Astronomer Royal in February, 1742. On first +taking up his abode at Greenwich he was unable to conduct his +observations owing to the wretched condition in which he found the +instruments. He devoted himself, however, assiduously to their +repair, and his first transit observation is recorded on the 25th +July, 1742. He worked with such energy that on one day it appears +that 255 transit observations were taken by himself alone, and in +September, 1747, he had completed the series of observations which +established his second great discovery, the nutation of the earth's +axis. The way in which he was led to the detection of the nutation +is strikingly illustrative of the extreme care with which Bradley +conducted his observations. He found that in the course of a +twelve-month, when the star had completed the movement which was due +to aberration, it did not return exactly to the same position which +it had previously occupied. At first he thought this must be due to +some instrumental error, but after closer examination and repeated +study of the effect as manifested by many different stars, he came to +the conclusion that its origin must be sought in some quite different +source. The fact is that a certain change takes place in the +apparent position of the stars which is not due to the movement of +the star itself, but is rather to be attributed to changes in the +points from which the star's positions are measured. + +We may explain the matter in this way. As the earth is not a sphere, +but has protuberant parts at the equator, the attraction of the moon +exercises on those protuberant parts a pulling effect which +continually changes the direction of the earth's axis, and +consequently the position of the pole must be in a state of incessant +fluctuation. The pole to which the earth's axis points on the sky +is, therefore, slowly changing. At present it happens to lie near +the Pole Star, but it will not always remain there. It describes a +circle around the pole of the Ecliptic, requiring about 25,000 years +for a complete circuit. In the course of its progress the pole will +gradually pass now near one star and now near another, so that many +stars will in the lapse of ages discharge the various functions which +the present Pole Star does for us. In about 12,000 years, for +instance, the pole will have come near the bright star, Vega. This +movement of the pole had been known for ages. But what Bradley +discovered was that the pole, instead of describing an uniform +movement as had been previously supposed, followed a sinuous course +now on one side and now on the other of its mean place. This he +traced to the fluctuations of the moon's orbit, which undergoes a +continuous change in a period of nineteen years. Thus the efficiency +with which the moon acts on the protuberant mass of the earth varies, +and thus the pole is caused to oscillate. + +This subtle discovery, if perhaps in some ways less impressive than +Bradley's earlier achievements of the detection of the aberration of +light, is regarded by astronomers as testifying even in a higher +degree to his astonishing care and skill as an observer, and justly +entitles him to a unique place among the astronomers whose +discoveries have been effected by consummate practical skill in the +use of astronomical instruments. + +Of Bradley's private or domestic life there is but little to tell. In +1744, soon after he became Astronomer Royal, he married a daughter of +Samuel Peach, of Chalford, in Gloucestershire. There was but one +child, a daughter, who became the wife of her cousin, Rev. Samuel +Peach, rector of Compton, Beauchamp, in Berkshire. + +Bradley's last two years of life were clouded by a melancholy +depression of spirits, due to an apprehension that he should survive +his rational faculties. It seems, however, that the ill he dreaded +never came upon him, for he retained his mental powers to the close. +He died on 13th July, 1762, aged seventy, and was buried at +Michinghamton. + + + + +WILLIAM HERSCHEL. + + +William Herschel, one of the greatest astronomers that has ever +lived, was born at Hanover, on the 15th November, 1738. His father, +Isaac Herschel, was a man evidently of considerable ability, whose +life was devoted to the study and practice of music, by which he +earned a somewhat precarious maintenance. He had but few worldly +goods to leave to his children, but he more than compensated for this +by bequeathing to them a splendid inheritance of genius. Touches of +genius were, indeed, liberally scattered among the members of Isaac's +large family, and in the case of his forth child, William, and of a +sister several years younger, it was united with that determined +perseverance and rigid adherence to principle which enabled genius to +fulfil its perfect work. + +A faithful chronicler has given us an interesting account of the way +in which Isaac Herschel educated his sons; the narrative is taken +from the recollections of one who, at the time we are speaking of, +was an unnoticed little girl five or six years old. She writes:-- + +"My brothers were often introduced as solo performers and assistants +in the orchestra at the Court, and I remember that I was frequently +prevented from going to sleep by the lively criticisms on music on +coming from a concert. Often I would keep myself awake that I might +listen to their animating remarks, for it made me so happy to see +them so happy. But generally their conversation would branch out on +philosophical subjects, when my brother William and my father often +argued with such warmth that my mother's interference became +necessary, when the names--Euler, Leibnitz, and Newton--sounded +rather too loud for the repose of her little ones, who had to be at +school by seven in the morning." The child whose reminiscences are +here given became afterwards the famous Caroline Herschel. The +narrative of her life, by Mrs. John Herschel, is a most interesting +book, not only for the account it contains of the remarkable woman +herself, but also because it provides the best picture we have of the +great astronomer to whom Caroline devoted her life. + +This modest family circle was, in a measure, dispersed at the +outbreak of the Seven Years' War in 1756. The French proceeded to +invade Hanover, which, it will be remembered, belonged at this time +to the British dominions. Young William Herschel had already +obtained the position of a regular performer in the regimental band +of the Hanoverian Guards, and it was his fortune to obtain some +experience of actual warfare in the disastrous battle of Hastenbeck. +He was not wounded, but he had to spend the night after the battle in +a ditch, and his meditations on the occasion convinced him that +soldiering was not the profession exactly adapted to his tastes. We +need not attempt to conceal the fact that he left his regiment by the +very simple but somewhat risky process of desertion. He had, it +would seem, to adopt disguises to effect his escape. At all events, +by some means he succeeded in eluding detection and reached England +in safety. It is interesting to have learned on good authority that +many years after this offence was committed it was solemnly +forgiven. When Herschel had become the famous astronomer, and as +such visited King George at Windsor, the King at their first meeting +handed to him his pardon for deserting from the army, written out in +due form by his Majesty himself. + +It seems that the young musician must have had some difficulty in +providing for his maintenance during the first few years of his abode +in England. It was not until he had reached the age of twenty-two +that he succeeded in obtaining any regular appointment. He was then +made Instructor of Music to the Durham Militia. Shortly afterwards, +his talents being more widely recognised, he was appointed as +organist at the parish church at Halifax, and his prospects in life +now being fairly favourable, and the Seven Years' War being over, he +ventured to pay a visit to Hanover to see his father. We can imagine +the delight with which old Isaac Herschel welcomed his promising son, +as well as his parental pride when a concert was given at which some +of William's compositions were performed. If the father was so +intensely gratified on this occasion, what would his feelings have +been could he have lived to witness his son's future career? But +this pleasure was not to be his, for he died many years before +William became an astronomer. + +In 1766, about a couple of years after his return to England from +This visit to his old home, we find that Herschel had received a +further promotion to be organist in the Octagon Chapel, at Bath. +Bath was then, as now, a highly fashionable resort, and many notable +personages patronised the rising musician. Herschel had other points +in his favour besides his professional skill; his appearance was +good, his address was prepossessing, and even his nationality was a +distinct advantage, inasmuch as he was a Hanoverian in the reign of +King George the Third. On Sundays he played the organ, to the great +delight of the congregation, and on week-days he was occupied by +giving lessons to private pupils, and in preparation for public +performances. He thus came to be busily employed, and seems to have +been in the enjoyment of comfortable means. + +[PLATE: 7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.] + +From his earliest youth Herschel had been endowed with that +invaluable characteristic, an eager curiosity for knowledge. He was +naturally desirous of perfecting himself in the theory of music, and +thus he was led to study mathematics. When he had once tasted the +charms of mathematics, he saw vast regions of knowledge unfolded +before him, and in this way he was induced to direct his attention to +astronomy. More and more this pursuit seems to have engrossed his +attention, until at last it had become an absorbing passion. Herschel +was, however, still obliged, by the exigency of procuring a +livelihood, to give up the best part of his time to his profession as +a musician; but his heart was eagerly fixed on another science, and +every spare moment was steadily devoted to astronomy. For many +years, however, he continued to labour at his original calling, nor +was it until he had attained middle age and become the most +celebrated astronomer of the time, that he was enabled to concentrate +his attention exclusively on his favourite pursuit. + +It was with quite a small telescope which had been lent him by a +friend that Herschel commenced his career as an observer. However, +he speedily discovered that to see all he wanted to see, a telescope +of far greater power would be necessary, and he determined to obtain +this more powerful instrument by actually making it with his own +hands. At first it may seem scarcely likely that one whose +occupation had previously been the study and practice of music should +meet with success in so technical an operation as the construction of +a telescope. It may, however, be mentioned that the kind of +instrument which Herschel designed to construct was formed on a very +different principle from the refracting telescopes with which we are +ordinarily familiar. His telescope was to be what is termed a +reflector. In this type of instrument the optical power is obtained +by the use of a mirror at the bottom of the tube, and the astronomer +looks down through the tube TOWARDS HIS MIRROR and views the +reflection of the stars with its aid. Its efficiency as a telescope +depends entirely on the accuracy with which the requisite form has +been imparted to the mirror. The surface has to be hollowed out a +little, and this has to be done so truly that the slightest deviation +from good workmanship in this essential particular would be fatal to +efficient performance of the telescope. + +[PLATE: WILLIAM HERSCHEL.] + +The mirror that Herschel employed was composed of a mixture of two +parts of copper to one of tin; the alloy thus obtained is an +intensely hard material, very difficult to cast into the proper +shape, and very difficult to work afterwards. It possesses, however, +when polished, a lustre hardly inferior to that of silver itself. +Herschel has recorded hardly any particulars as to the actual process +by which he cast and figured his reflectors. We are however, told +that in later years, after his telescopes had become famous, he made +a considerable sum of money by the manufacture and sale of great +instruments. Perhaps this may be the reason why he never found it +expedient to publish any very explicit details as to the means by +which his remarkable successes were obtained. + +[PLATE: CAROLINE HERSCHEL.] + +Since Herschel's time many other astronomers, notably the late Earl +of Rosse, have experimented in the same direction, and succeeded in +making telescopes certainly far greater, and probably more perfect, +than any which Herschel appears to have constructed. The details of +these later methods are now well known, and have been extensively +practised. Many amateurs have thus been able to make telescopes by +following the instructions so clearly laid down by Lord Rosse and the +other authorities. Indeed, it would seem that any one who has a +little mechanical skill and a good deal of patience ought now to +experience no great difficulty in constructing a telescope quite as +powerful as that which first brought Herschel into fame. I should, +however, mention that in these modern days the material generally +used for the mirror is of a more tractable description than the +metallic substance which was employed by Herschel and by Lord Rosse. +A reflecting telescope of the present day would not be fitted with a +mirror composed of that alloy known as speculum metal, whose +composition I have already mentioned. It has been found more +advantageous to employ a glass mirror carefully figured and polished, +just as a metallic mirror would have been, and then to impart to the +polished glass surface a fine coating of silver laid down by a +chemical process. The silver-on-glass mirrors are so much lighter +and so much easier to construct that the more old-fashioned metallic +mirrors may be said to have fallen into almost total disuse. In one +respect however, the metallic mirror may still claim the advantage +that, with reasonable care, its surface will last bright and +untarnished for a much longer period than can the silver film on the +glass. However, the operation of re-silvering a glass has now become +such a simple one that the advantage this indicates is not relatively +so great as might at first be supposed. + +[PLATE: STREET VIEW, HERSCHEL HOUSE, SLOUGH.] + +Some years elapsed after Herschel's attention had been first directed +to astronomy, before he reaped the reward of his exertions in the +possession of a telescope which would adequately reveal some of the +glories of the heavens. It was in 1774, when the astronomer was +thirty-six years old, that he obtained his first glimpse of the stars +with an instrument of his own construction. Night after night, as +soon as his musical labours were ended, his telescopes were brought +out, sometimes into the small back garden of his house at Bath, and +sometimes into the street in front of his hall-door. It was +characteristic of him that he was always endeavouring to improve his +apparatus. He was incessantly making fresh mirrors, or trying new +lenses, or combinations of lenses to act as eye-pieces, or projecting +alterations in the mounting by which the telescope was supported. +Such was his enthusiasm that his house, we are told, was incessantly +littered with the usual indications of the workman's presence, +greatly to the distress of his sister, who, at this time, had come to +take up her abode with him and look after his housekeeping. Indeed, +she complained that in his astronomical ardour he sometimes omitted +to take off, before going into his workshop, the beautiful lace +ruffles which he wore while conducting a concert, and that +consequently they became soiled with the pitch employed in the +polishing of his mirrors. + +This sister, who occupies such a distinct place in scientific history +is the same little girl to whom we have already referred. From her +earliest days she seems to have cherished a passionate admiration for +her brilliant brother William. It was the proudest delight of her +childhood as well as of her mature years to render him whatever +service she could; no man of science was ever provided with a more +capable or energetic helper than William Herschel found in this +remarkable woman. Whatever work had to be done she was willing to +bear her share in it, or even to toil at it unassisted if she could +be allowed to do so. She not only managed all his domestic affairs, +but in the grinding of the lenses and in the polishing of the mirrors +she rendered every assistance that was possible. At one stage of the +very delicate operation of fashioning a reflector, it is necessary +for the workman to remain with his hand on the mirror for many hours +in succession. When such labours were in progress, Caroline used to +sit by her brother, and enliven the time by reading stories aloud, +sometimes pausing to feed him with a spoon while his hands were +engaged on the task from which he could not desist for a moment. + +When mathematical work had to be done Caroline was ready for it; she +had taught herself sufficient to enable her to perform the kind of +calculations, not, perhaps, very difficult ones, that Herschel's work +required; indeed, it is not too much to say that the mighty life-work +which this man was enabled to perform could never have been accomplished +had it not been for the self-sacrifice of this ever-loving and faithful +sister. When Herschel was at the telescope at night, Caroline sat by +him at her desk, pen in hand, ready to write down the notes of the +observations as they fell from her brother's lips. This was no +insignificant toil. The telescope was, of course, in the open air, +and as Herschel not unfrequently continued his observations throughout +the whole of a long winter's night, there were but few women who could +have accomplished the task which Caroline so cheerfully executed. +From dusk till dawn, when the sky was clear, were Herschel's observing +hours, and what this sometimes implied we can realise from the fact +that Caroline assures us she had sometimes to desist because the ink +had actually frozen in her pen. The night's work over, a brief rest +was taken, and while William had his labours for the day to attend to, +Caroline carefully transcribed the observations made during the night +before, reduced all the figures and prepared everything in readiness +for the observations that were to follow on the ensuing evening. + +But we have here been anticipating a little of the future which lay +before the great astronomer; we must now revert to the history of his +early work, at Bath, in 1774, when Herschel's scrutiny of the skies +first commenced with an instrument of his own manufacture. For some +few years he did not attain any result of importance; no doubt he +made a few interesting observations, but the value of the work during +those years is to be found, not in any actual discoveries which were +accomplished, but in the practice which Herschel obtained in the use +of his instruments. It was not until 1782 that the great achievement +took place by which he at once sprang into fame. + +[PLATE: GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.] + +It is sometimes said that discoveries are made by accident, and, no +doubt, to a certain extent, but only, I fancy to a very small extent, +this statement may be true. It is, at all events, certain that such +lucky accidents do not often fall to the lot of people unless those +people have done much to deserve them. This was certainly the case +with Herschel. He appears to have formed a project for making a +close examination of all the stars above a certain magnitude. Perhaps +he intended to confine this research to a limited region of the sky, +but, at all events, he seems to have undertaken the work +energetically and systematically. Star after star was brought to the +centre of the field of view of his telescope, and after being +carefully examined was then displaced, while another star was brought +forward to be submitted to the same process. In the great majority +of cases such observations yield really nothing of importance; no +doubt even the smallest star in the heavens would, if we could find +out all about it, reveal far more than all the astronomers that were +ever on the earth have even conjectured. What we actually learn +about the great majority of stars is only information of the most +meagre description. We see that the star is a little point of light, +and we see nothing more. + +In the great review which Herschel undertook he doubtless examined +hundreds, or perhaps thousands of stars, allowing them to pass away +without note or comment. But on an ever-memorable night in March, +1782, it happened that he was pursuing his task among the stars in +the Constellation of Gemini. Doubtless, on that night, as on so many +other nights, one star after another was looked at only to be +dismissed, as not requiring further attention. On the evening in +question, however, one star was noticed which, to Herschel's acute +vision seemed different from the stars which in so many thousands are +strewn over the sky. A star properly so called appears merely as a +little point of light, which no increase of magnifying power will +ever exhibit with a true disc. But there was something in the +star-like object which Herschel saw that immediately arrested his +attention and made him apply to it a higher magnifying power. This +at once disclosed the fact that the object possessed a disc, that is, +a definite, measurable size, and that it was thus totally different +from any one of the hundreds and thousands of stars which exist +elsewhere in space. Indeed, we may say at once that this little +object was not a star at all; it was a planet. That such was its +true nature was confirmed, after a little further observation, by +perceiving that the body was shifting its place on the heavens +relatively to the stars. The organist at the Octagon Chapel at Bath +had, therefore, discovered a new planet with his home-made telescope. + +I can imagine some one will say, "Oh, there was nothing so wonderful +in that; are not planets always being discovered? Has not M. Palisa, +for instance, discovered about eighty of such objects, and are there +not hundreds of them known nowadays?" This is, to a certain extent, +quite true. I have not the least desire to detract from the credit +of those industrious and sharp-sighted astronomers who have in modern +days brought so many of these little objects within our cognisance. I +think, however, it must be admitted that such discoveries have a +totally different importance in the history of science from that +which belongs to the peerless achievement of Herschel. In the first +place, it must be observed that the minor planets now brought to +light are so minute that if a score of them were rolled to together +into one lump it would not be one-thousandth part of the size of the +grand planet discovered by Herschel. This is, nevertheless, not the +most important point. What marks Herschel's achievement as one of +the great epochs in the history of astronomy is the fact that the +detection of Uranus was the very first recorded occasion of the +discovery of any planet whatever. + +For uncounted ages those who watched the skies had been aware of the +existence of the five old planets--Jupiter, Mercury, Saturn, Venus, +and Mars. It never seems to have occurred to any of the ancient +philosophers that there could be other similar objects as yet +undetected over and above the well-known five. Great then was the +astonishment of the scientific world when the Bath organist announced +his discovery that the five planets which had been known from all +antiquity must now admit the company of a sixth. And this sixth +planet was, indeed, worthy on every ground to be received into the +ranks of the five glorious bodies of antiquity. It was, no doubt, +not so large as Saturn, it was certainly very much less than Jupiter; +on the other hand, the new body was very much larger than Mercury, +than Venus, or than Mars, and the earth itself seemed quite an +insignificant object in comparison with this newly added member of +the Solar System. In one respect, too, Herschel's new planet was a +much more imposing object than any one of the older bodies; it swept +around the sun in a majestic orbit, far outside that of Saturn, which +had previously been regarded as the boundary of the Solar System, and +its stately progress required a period of not less than eighty-one +years. + +King George the Third, hearing of the achievements of the Hanoverian +musician, felt much interest in his discovery, and accordingly +Herschel was bidden to come to Windsor, and to bring with him the +famous telescope, in order to exhibit the new planet to the King, and +to tell his Majesty all about it. The result of the interview was to +give Herschel the opportunity for which he had so long wished, of +being able to devote himself exclusively to science for the rest of +his life. + +[PLATE: VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.] + +The King took so great a fancy to the astronomer that he first, as I +have already mentioned, duly pardoned his desertion from the army, +some twenty-five years previously. As a further mark of his favour +the King proposed to confer on Herschel the title of his Majesty's +own astronomer, to assign to him a residence near Windsor, to provide +him with a salary, and to furnish such funds as might be required for +the erection of great telescopes, and for the conduct of that mighty +scheme of celestial observation on which Herschel was so eager to +enter. Herschel's capacity for work would have been much impaired if +he had been deprived of the aid of his admirable sister, and to her, +therefore, the King also assigned a salary, and she was installed as +Herschel's assistant in his new post. + +With his usually impulsive determination, Herschel immediately cut +himself free from all his musical avocations at Bath, and at once +entered on the task of making and erecting the great telescopes at +Windsor. There, for more than thirty years, he and his faithful +sister prosecuted with unremitting ardour their nightly scrutiny of +the sky. Paper after paper was sent to the Royal Society, describing +the hundreds, indeed the thousands, of objects such as double stars; +nebulae and clusters, which were first revealed to human gaze during +those midnight vigils. To the end of his life he still continued at +every possible opportunity to devote himself to that beloved pursuit +in which he had such unparalleled success. No single discovery of +Herschel's later years was, however, of the same momentous +description as that which first brought him to fame. + +[PLATE: THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL +HOUSE, SLOUGH.] + +Herschel married when considerably advanced in life and he lived to +enjoy the indescribable pleasure of finding that his only son, +afterwards Sir John Herschel, was treading worthily in his footsteps, +and attaining renown as an astronomical observer, second only to that +of his father. The elder Herschel died in 1822, and his illustrious +sister Caroline then returned to Hanover, where she lived for many +years to receive the respect and attention which were so justly +hers. She died at a very advanced age in 1848. + + + + +LAPLACE. + + +The author of the "Mecanique Celeste" was born at Beaumont-en-Auge, +near Honfleur, in 1749, just thirteen years later than his renowned +friend Lagrange. His father was a farmer, but appears to have been +in a position to provide a good education for a son who seemed +promising. Considering the unorthodoxy in religious matters which is +generally said to have characterized Laplace in later years, it is +interesting to note that when he was a boy the subject which first +claimed his attention was theology. He was, however, soon introduced +to the study of mathematics, in which he presently became so +proficient, that while he was still no more than eighteen years old, +he obtained employment as a mathematical teacher in his native town. + +Desiring wider opportunities for study and for the acquisition of +fame than could be obtained in the narrow associations of provincial +life, young Laplace started for Paris, being provided with letters of +introduction to D'Alembert, who then occupied the most prominent +position as a mathematician in France, if not in the whole of +Europe. D'Alembert's fame was indeed so brilliant that Catherine the +Great wrote to ask him to undertake the education of her Son, and +promised the splendid income of a hundred thousand francs. He +preferred, however, a quiet life of research in Paris, although there +was but a modest salary attached to his office. The philosopher +accordingly declined the alluring offer to go to Russia, even though +Catherine wrote again to say: "I know that your refusal arises from +your desire to cultivate your studies and your friendships in quiet. +But this is of no consequence: bring all your friends with you, and I +promise you that both you and they shall have every accommodation in +my power." With equal firmness the illustrious mathematician +resisted the manifold attractions with which Frederick the Great +sought to induce him, to take up his residence at Berlin. In reading +of these invitations we cannot but be struck at the extraordinary +respect which was then paid to scientific distinction. It must be +remembered that the discoveries of such a man as D'Alembert were +utterly incapable of being appreciated except by those who possessed +a high degree of mathematical culture. We nevertheless find the +potentates of Russia and Prussia entreating and, as it happens, +vainly entreating, the most distinguished mathematician in France to +accept the positions that they were proud to offer him. + +It was to D'Alembert, the profound mathematician, that young Laplace, +the son of the country farmer, presented his letters of +introduction. But those letters seem to have elicited no reply, +whereupon Laplace wrote to D'Alembert submitting a discussion on some +point in Dynamics. This letter instantly produced the desired +effect. D'Alembert thought that such mathematical talent as the +young man displayed was in itself the best of introductions to his +favour. It could not be overlooked, and accordingly he invited +Laplace to come and see him. Laplace, of course, presented himself, +and ere long D'Alembert obtained for the rising philosopher a +professorship of mathematics in the Military School in Paris. This +gave the brilliant young mathematician the opening for which he +sought, and he quickly availed himself of it. + +Laplace was twenty-three years old when his first memoir on a +profound mathematical subject appeared in the Memoirs of the Academy +at Turin. From this time onwards we find him publishing one memoir +after another in which he attacks, and in many cases successfully +vanquishes, profound difficulties in the application of the Newtonian +theory of gravitation to the explanation of the solar system. Like +his great contemporary Lagrange, he loftily attempted problems which +demanded consummate analytical skill for their solution. The +attention of the scientific world thus became riveted on the splendid +discoveries which emanated from these two men, each gifted with +extraordinary genius. + +Laplace's most famous work is, of course, the "Mecanique Celeste," in +which he essayed a comprehensive attempt to carry out the principles +which Newton had laid down, into much greater detail than Newton had +found practicable. The fact was that Newton had not only to +construct the theory of gravitation, but he had to invent the +mathematical tools, so to speak, by which his theory could be applied +to the explanation of the movements of the heavenly bodies. In the +course of the century which had elapsed between the time of Newton +and the time of Laplace, mathematics had been extensively developed. +In particular, that potent instrument called the infinitesimal +calculus, which Newton had invented for the investigation of nature, +had become so far perfected that Laplace, when he attempted to +unravel the movements of the heavenly bodies, found himself provided +with a calculus far more efficient than that which had been available +to Newton. The purely geometrical methods which Newton employed, +though they are admirably adapted for demonstrating in a general way +the tendencies of forces and for explaining the more obvious +phenomena by which the movements of the heavenly bodies are +disturbed, are yet quite inadequate for dealing with the more subtle +effects of the Law of Gravitation. The disturbances which one planet +exercises upon the rest can only be fully ascertained by the aid of +long calculation, and for these calculations analytical methods are +required. + +With an armament of mathematical methods which had been perfected +since the days of Newton by the labours of two or three generations +of consummate mathematical inventors, Laplace essayed in the +"Mecanique Celeste" to unravel the mysteries of the heavens. It will +hardly be disputed that the book which he has produced is one of the +most difficult books to understand that has ever been written. In +great part, of course, this difficulty arises from the very nature of +the subject, and is so far unavoidable. No one need attempt to read +the "Mecanique Celeste" who has not been naturally endowed with +considerable mathematical aptitude which he has cultivated by years +of assiduous study. The critic will also note that there are grave +defects in Laplace's method of treatment. The style is often +extremely obscure, and the author frequently leaves great gaps in his +argument, to the sad discomfiture of his reader. Nor does it mend +matters to say, as Laplace often does say, that it is "easy to see" +how one step follows from another. Such inferences often present +great difficulties even to excellent mathematicians. Tradition +indeed tells us that when Laplace had occasion to refer to his own +book, it sometimes happened that an argument which he had dismissed +with his usual formula, "Il est facile a voir," cost the illustrious +author himself an hour or two of hard thinking before he could +recover the train of reasoning which had been omitted. But there are +certain parts of this great work which have always received the +enthusiastic admiration of mathematicians. Laplace has, in fact, +created whole tracts of science, some of which have been subsequently +developed with much advantage in the prosecution of the study of +Nature. + +Judged by a modern code the gravest defect of Laplace's great work is +rather of a moral than of a mathematical nature. Lagrange and he +advanced together in their study of the mechanics of the heavens, at +one time perhaps along parallel lines, while at other times they +pursued the same problem by almost identical methods. Sometimes the +important result was first reached by Lagrange, sometimes it was +Laplace who had the good fortune to make the discovery. It would +doubtless be a difficult matter to draw the line which should exactly +separate the contributions to astronomy made by one of these +illustrious mathematicians, and the contributions made by the other. +But in his great work Laplace in the loftiest manner disdained to +accord more than the very barest recognition to Lagrange, or to any +of the other mathematicians, Newton alone excepted, who had advanced +our knowledge of the mechanism of the heavens. It would be quite +impossible for a student who confined his reading to the "Mecanique +Celeste" to gather from any indications that it contains whether the +discoveries about which he was reading had been really made by +Laplace himself or whether they had not been made by Lagrange, or by +Euler, or by Clairaut. With our present standard of morality in such +matters, any scientific man who now brought forth a work in which he +presumed to ignore in this wholesale fashion the contributions of +others to the subject on which he was writing, would be justly +censured and bitter controversies would undoubtedly arise. Perhaps +we ought not to judge Laplace by the standard of our own time, and in +any case I do not doubt that Laplace might have made a plausible +defence. It is well known that when two investigators are working at +the same subjects, and constantly publishing their results, it +sometimes becomes difficult for each investigator himself to +distinguish exactly between what he has accomplished and that which +must be credited to his rival. Laplace may probably have said to +himself that he was going to devote his energies to a great work on +the interpretation of Nature, that it would take all his time and all +his faculties, and all the resources of knowledge that he could +command, to deal justly with the mighty problems before him. He +would not allow himself to be distracted by any side issue. He could +not tolerate that pages should be wasted in merely discussing to whom +we owe each formula, and to whom each deduction from such formula is +due. He would rather endeavour to produce as complete a picture as +he possibly could of the celestial mechanics, and whether it were by +means of his mathematics alone, or whether the discoveries of others +may have contributed in any degree to the result, is a matter so +infinitesimally insignificant in comparison with the grandeur of his +subject that he would altogether neglect it. "If Lagrange should +think," Laplace might say, "that his discoveries had been unduly +appropriated, the proper course would be for him to do exactly what I +have done. Let him also write a "Mecanique Celeste," let him employ +those consummate talents which he possesses in developing his noble +subject to the utmost. Let him utilise every result that I or any +other mathematician have arrived at, but not trouble himself unduly +with unimportant historical details as to who discovered this, and +who discovered that; let him produce such a work as he could write, +and I shall heartily welcome it as a splendid contribution to our +science." Certain it is that Laplace and Lagrange continued the best +of friends, and on the death of the latter it was Laplace who was +summoned to deliver the funeral oration at the grave of his great +rival. + +The investigations of Laplace are, generally speaking, of too +technical a character to make it possible to set forth any account of +them in such a work as the present. He did publish, however, one +treatise, called the "Systeme du Monde," in which, without +introducing mathematical symbols, he was able to give a general +account of the theories of the celestial movements, and of the +discoveries to which he and others had been led. In this work the +great French astronomer sketched for the first time that remarkable +doctrine by which his name is probably most generally known to those +readers of astronomical books who are not specially mathematicians. +It is in the "Systeme du Monde" that Laplace laid down the principles +of the Nebular Theory which, in modern days, has been generally +accepted by those philosophers who are competent to judge, as +substantially a correct expression of a great historical fact. + +[PLATE: LAPLACE.] + +The Nebular Theory gives a physical account of the origin of the +solar system, consisting of the sun in the centre, with the planets +and their attendant satellites. Laplace perceived the significance +of the fact that all the planets revolved in the same direction +around the sun; he noticed also that the movements of rotation of the +planets on their axes were performed in the same direction as that in +which a planet revolves around the sun; he saw that the orbits of the +satellites, so far at least as he knew them, revolved around their +primaries also in the same direction. Nor did it escape his +attention that the sun itself rotated on its axis in the same sense. +His philosophical mind was led to reflect that such a remarkable +unanimity in the direction of the movements in the solar system +demanded some special explanation. It would have been in the highest +degree improbable that there should have been this unanimity unless +there had been some physical reason to account for it. To appreciate +the argument let us first concentrate our attention on three +particular bodies, namely the earth, the sun, and the moon. First +the earth revolves around the sun in a certain direction, and the +earth also rotates on its axis. The direction in which the earth +turns in accordance with this latter movement might have been that in +which it revolves around the sun, or it might of course have been +opposite thereto. As a matter of fact the two agree. The moon in +its monthly revolution around the earth follows also the same +direction, and our satellite rotates on its axis in the same period +as its monthly revolution, but in doing so is again observing this +same law. We have therefore in the earth and moon four movements, +all taking place in the same direction, and this is also identical +with that in which the sun rotates once every twenty-five days. Such +a coincidence would be very unlikely unless there were some physical +reason for it. Just as unlikely would it be that in tossing a coin +five heads or five tails should follow each other consecutively. If +we toss a coin five times the chances that it will turn up all heads +or all tails is but a small one. The probability of such an event is +only one-sixteenth. + +There are, however, in the solar system many other bodies besides the +three just mentioned which are animated by this common movement. +Among them are, of course, the great planets, Jupiter, Saturn, Mars, +Venus, and Mercury, and the satellites which attend on these +planets. All these planets rotate on their axes in the same +direction as they revolve around the sun, and all their satellites +revolve also in the same way. Confining our attention merely to the +earth, the sun, and the five great planets with which Laplace was +acquainted, we have no fewer than six motions of revolution and seven +motions of rotation, for in the latter we include the rotation of the +sun. We have also sixteen satellites of the planets mentioned whose +revolutions round their primaries are in the same direction. The +rotation of the moon on its axis may also be reckoned, but as to the +rotations of the satellites of the other planets we cannot speak with +any confidence, as they are too far off to be observed with the +necessary accuracy. We have thus thirty circular movements in the +solar system connected with the sun and moon and those great planets +than which no others were known in the days of Laplace. The +significant fact is that all these thirty movements take place in the +same direction. That this should be the case without some physical +reason would be just as unlikely as that in tossing a coin thirty +times it should turn up all heads or all tails every time without +exception. + +We can express the argument numerically. Calculation proves that +such an event would not generally happen oftener than once out of +five hundred millions of trials. To a philosopher of Laplace's +penetration, who had made a special study of the theory of +probabilities, it seemed well-nigh inconceivable that there should +have been such unanimity in the celestial movements, unless there had +been some adequate reason to account for it. We might, indeed, add +that if we were to include all the objects which are now known to +belong to the solar system, the argument from probability might be +enormously increased in strength. To Laplace the argument appeared +so conclusive that he sought for some physical cause of the +remarkable phenomenon which the solar system presented. Thus it was +that the famous Nebular Hypothesis took its rise. Laplace devised a +scheme for the origin of the sun and the planetary system, in which +it would be a necessary consequence that all the movements should +take place in the same direction as they are actually observed to do. + +Let us suppose that in the beginning there was a gigantic mass of +nebulous material, so highly heated that the iron and other +substances which now enter into the composition of the earth and +planets were then suspended in a state of vapour. There is nothing +unreasonable in such a supposition indeed, we know as a matter of +fact that there are thousands of such nebulae to be discerned at +present through our telescopes. It would be extremely unlikely that +any object could exist without possessing some motion of rotation; we +may in fact assert that for rotation to be entirety absent from the +great primeval nebula would be almost infinitely improbable. As ages +rolled on, the nebula gradually dispersed away by radiation its +original stores of heat, and, in accordance with well-known physical +principles, the materials of which it was formed would tend to +coalesce. The greater part of those materials would become +concentrated in a mighty mass surrounded by outlying uncondensed +vapours. There would, however, also be regions throughout the extent +of the nebula, in which subsidiary centres of condensation would be +found. In its long course of cooling, the nebula would, therefore, +tend ultimately to form a mighty central body with a number of +smaller bodies disposed around it. As the nebula was initially +endowed with a movement of rotation, the central mass into which it +had chiefly condensed would also revolve, and the subsidiary bodies +would be animated by movements of revolution around the central +body. These movements would be all pursued in one common direction, +and it follows, from well-known mechanical principles, that each of +the subsidiary masses, besides participating in the general +revolution around the central body, would also possess a rotation +around its axis, which must likewise be performed in the same +direction. Around the subsidiary bodies other objects still smaller +would be formed, just as they themselves were formed relatively to +the great central mass. + +As the ages sped by, and the heat of these bodies became gradually +dissipated, the various objects would coalesce, first into molten +liquid masses, and thence, at a further stage of cooling, they would +assume the appearance of solid masses, thus producing the planetary +bodies such as we now know them. The great central mass, on account +of its preponderating dimensions, would still retain, for further +uncounted ages, a large quantity of its primeval heat, and would thus +display the splendours of a glowing sun. In this way Laplace was +able to account for the remarkable phenomena presented in the +movements of the bodies of the solar system. There are many other +points also in which the nebular theory is known to tally with the +facts of observation. In fact, each advance in science only seems to +make it more certain that the Nebular Hypothesis substantially +represents the way in which our solar system has grown to its present +form. + +Not satisfied with a career which should be merely scientific, +Laplace sought to connect himself with public affairs. Napoleon +appreciated his genius, and desired to enlist him in the service of +the State. Accordingly he appointed Laplace to be Minister of the +Interior. The experiment was not successful, for he was not by +nature a statesman. Napoleon was much disappointed at the ineptitude +which the great mathematician showed for official life, and, in +despair of Laplace's capacity as an administrator, declared that he +carried the spirit of his infinitesimal calculus into the management +of business. Indeed, Laplace's political conduct hardly admits of +much defence. While he accepted the honours which Napoleon showered +on him in the time of his prosperity, he seems to have forgotten all +this when Napoleon could no longer render him service. Laplace was +made a Marquis by Louis XVIII., a rank which he transmitted to his +son, who was born in 1789. During the latter part of his life the +philosopher lived in a retired country place at Arcueile. Here he +pursued his studies, and by strict abstemiousness, preserved himself +from many of the infirmities of old age. He died on March the 5th, +1827, in his seventy-eighth year, his last words being, "What we know +is but little, what we do not know is immense." + + + + +BRINKLEY. + + +Provost Baldwin held absolute sway in the University of Dublin for +forty-one years. His memory is well preserved there. The Bursar +still dispenses the satisfactory revenues which Baldwin left to the +College. None of us ever can forget the marble angels round the +figure of the dying Provost on which we used to gaze during the pangs +of the Examination Hall. + +Baldwin died in 1785, and was succeeded by Francis Andrews, a Fellow +of seventeen years' standing. As to the scholastic acquirements of +Andrews, all I can find is a statement that he was complimented by +the polite Professors of Padua on the elegance and purity with which +he discoursed to them in Latin. Andrews was also reputed to be a +skilful lawyer. He was certainly a Privy Councillor and a prominent +member of the Irish House of Commons, and his social qualities were +excellent. Perhaps it was Baldwin's example that stimulated a desire +in Andrews to become a benefactor to his college. He accordingly +bequeathed a sum of 3,000 pounds and an annual income of 250 pounds +wherewith to build and endow an astronomical Observatory in the +University. The figures just stated ought to be qualified by the +words of cautious Ussher (afterwards the first Professor of +Astronomy), that "this money was to arise from an accumulation of a +part of his property, to commence upon a particular contingency +happening to his family." The astronomical endowment was soon in +jeopardy by litigation. Andrews thought he had provided for his +relations by leaving to them certain leasehold interests connected +with the Provost's estate. The law courts, however, held that these +interests were not at the disposal of the testator, and handed them +over to Hely Hutchinson, the next Provost. The disappointed +relations then petitioned the Irish Parliament to redress this +grievance by transferring to them the moneys designed by Andrews for +the Observatory. It would not be right, they contended, that the +kindly intentions of the late Provost towards his kindred should be +frustrated for the sake of maintaining what they described as "a +purely ornamental institution." The authorities of the College +protested against this claim. Counsel were heard, and a Committee of +the House made a report declaring the situation of the relations to +be a hard one. Accordingly, a compromise was made, and the dispute +terminated. + +The selection of a site for the new astronomical Observatory was made +by the Board of Trinity College. The beautiful neighbourhood of +Dublin offered a choice of excellent localities. On the north side +of the Liffey an Observatory could have been admirably placed, either +on the remarkable promontory of Howth or on the elevation of which +Dunsink is the summit. On the south side of Dublin there are several +eminences that would have been suitable: the breezy heaths at +Foxrock combine all necessary conditions; the obelisk hill at +Killiney would have given one of the most picturesque sites for an +Observatory in the world; while near Delgany two or three other good +situations could be mentioned. But the Board of those pre-railway +days was naturally guided by the question of proximity. Dunsink was +accordingly chosen as the most suitable site within the distance of a +reasonable walk from Trinity College. + +The northern boundary of the Phoenix Park approaches the little river +Tolka, which winds through a succession of delightful bits of sylvan +scenery, such as may be found in the wide demesne of Abbotstown and +the classic shades of Glasnevin. From the banks of the Tolka, on the +opposite side of the park, the pastures ascend in a gentle slope to +culminate at Dunsink, where at a distance of half a mile from the +stream, of four miles from Dublin, and at a height of 300 feet above +the sea, now stands the Observatory. From the commanding position of +Dunsink a magnificent view is obtained. To the east the sea is +visible, while the southern prospect over the valley of the Liffey is +bounded by a range of hills and mountains extending from Killiney to +Bray Head, thence to the little Sugar Loaf, the Two Rock and the +Three Rock Mountains, over the flank of which the summit of the Great +Sugar Loaf is just perceptible. Directly in front opens the fine +valley of Glenasmole, with Kippure Mountain, while the range can be +followed to its western extremity at Lyons. The climate of Dunsink +is well suited for astronomical observation. No doubt here, as +elsewhere in Ireland, clouds are abundant, but mists or haze are +comparatively unusual, and fogs are almost unknown. + +The legal formalities to be observed in assuming occupation exacted a +delay of many months; accordingly, it was not until the 10th +December, 1782, that a contract could be made with Mr. Graham Moyers +for the erection of a meridian-room and a dome for an equatorial, in +conjunction with a becoming residence for the astronomer. Before the +work was commenced at Dunsink, the Board thought it expedient to +appoint the first Professor of Astronomy. They met for this purpose +on the 22nd January, 1783, and chose the Rev. Henry Ussher, a Senior +Fellow of Trinity College, Dublin. The wisdom of the appointment was +immediately shown by the assiduity with which Ussher engaged in +founding the observatory. In three years he had erected the +buildings and equipped them with instruments, several of which were +of his own invention. On the 19th of February, 1785, a special grant +of 200 pounds was made by the Board to Dr. Ussher as some recompense +for his labours. It happened that the observatory was not the only +scientific institution which came into being in Ireland at this +period; the newly-kindled ardour for the pursuit of knowledge led, at +the same time, to the foundation of the Royal Irish Academy. By a +fitting coincidence, the first memoir published in the "Transactions +Of The Royal Irish Academy," was by the first Andrews, Professor of +Astronomy. It was read on the 13th of June, 1785, and bore the +title, "Account of the Observatory belonging to Trinity College," by +the Rev. H. Ussher, D.D., M.R.I.A., F.R.S. This communication shows +the extensive design that had been originally intended for Dunsink, +only a part of which was, however, carried out. For instance, two +long corridors, running north and south from the central edifice, +which are figured in the paper, never developed into bricks and +mortar. We are not told why the original scheme had to be +contracted; but perhaps the reason may be not unconnected with a +remark of Ussher's, that the College had already advanced from its +own funds a sum considerably exceeding the original bequest. The +picture of the building shows also the dome for the South equatorial, +which was erected many years later. + +Ussher died in 1790. During his brief career at the observatory, he +observed eclipses, and is stated to have done other scientific work. +The minutes of the Board declare that the infant institution had +already obtained celebrity by his labours, and they urge the claims +of his widow to a pension, on the ground that the disease from which +he died had been contracted by his nightly vigils. The Board also +promised a grant of fifty guineas as a help to bring out Dr. Ussher's +sermons. They advanced twenty guineas to his widow towards the +publication of his astronomical papers. They ordered his bust to be +executed for the observatory, and offered "The Death of Ussher" as +the subject of a prize essay; but, so far as I can find, neither the +sermons nor the papers, neither the bust nor the prize essay, ever +came into being. + +There was keen competition for the chair of Astronomy which the death +of Ussher vacated. The two candidates were Rev. John Brinkley, of +Caius College, Cambridge, a Senior Wrangler (born at Woodbridge, +Suffolk, in 1763), and Mr. Stack, Fellow of Trinity College, Dublin, +and author of a book on Optics. A majority of the Board at first +supported Stack, while Provost Hely Hutchinson and one or two others +supported Brinkley. In those days the Provost had a veto at +elections, so that ultimately Stack was withdrawn and Brinkley was +elected. This took place on the 11th December, 1790. The national +press of the day commented on the preference shown to the young +Englishman, Brinkley, over his Irish rival. An animated controversy +ensued. The Provost himself condescended to enter the lists and to +vindicate his policy by a long letter in the "Public Register" or +"Freeman's Journal," of 21st December, 1790. This letter was +anonymous, but its authorship is obvious. It gives the +correspondence with Maskelyne and other eminent astronomers, whose +advice and guidance had been sought by the Provost. It also contends +that "the transactions of the Board ought not to be canvassed in the +newspapers." For this reference, as well as for much other +information, I am indebted to my friend, the Rev. John Stubbs, D.D. + +[PLATE: THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence, +Upper Sackville Street, Dublin.] + +The next event in the history of the Observatory was the issue of +Letters Patent (32 Geo. III., A.D. 1792), in which it is recited that +"We grant and ordain that there shall be forever hereafter a +Professor of Astronomy, on the foundation of Dr. Andrews, to be +called and known by the name of the Royal Astronomer of Ireland." The +letters prescribe the various duties of the astronomer and the mode +of his election. They lay down regulations as to the conduct of the +astronomical work, and as to the choice of an assistant. They direct +that the Provost and the Senior Fellows shall make a thorough +inspection of the observatory once every year in June or July; and +this duty was first undertaken on the 5th of July, 1792. It may be +noted that the date on which the celebration of the tercentenary of +the University was held happens to coincide with the centenary of the +first visitation of the observatory. The visitors on the first +occasion were A. Murray, Matthew Young, George Hall, and John +Barrett. They record that they find the buildings, books and +instruments in good condition; but the chief feature in this report, +as well as in many which followed it, related to a circumstance to +which we have not yet referred. + +In the original equipment of the observatory, Ussher, with the +natural ambition of a founder, desired to place in it a telescope of +more magnificent proportions than could be found anywhere else. The +Board gave a spirited support to this enterprise, and negotiations +were entered into with the most eminent instrument-maker of those +days. This was Jesse Ramsden (1735-1800), famous as the improver of +the sextant, as the constructor of the great theodolite used by +General Roy in the English Survey, and as the inventor of the +dividing engine for graduating astronomical instruments. Ramsden had +built for Sir George Schuckburgh the largest and most perfect +equatorial ever attempted. He had constructed mural quadrants for +Padua and Verona, which elicited the wonder of astronomers when Dr. +Maskelyne declared he could detect no error in their graduation so +large as two seconds and a half. But Ramsden maintained that even +better results would be obtained by superseding the entire quadrant +by the circle. He obtained the means of testing this prediction when +he completed a superb circle for Palermo of five feet diameter. +Finding his anticipations were realised, he desired to apply the same +principles on a still grander scale. Ramsden was in this mood when +he met with Dr. Ussher. The enthusiasm of the astronomer and the +instrument-maker communicated itself to the Board, and a tremendous +circle, to be ten feet in diameter, was forthwith projected. + +Projected, but never carried out. After Ramsden had to some extent +completed a 10-foot circle, he found such difficulties that he tried +a 9-foot, and this again he discarded for an 8-foot, which was +ultimately accomplished, though not entirely by himself. +Notwithstanding the contraction from the vast proportions originally +designed, the completed instrument must still be regarded as a +colossal piece of astronomical workmanship. Even at this day I do +not know that any other observatory can show a circle eight feet in +diameter graduated all round. + +I think it is Professor Piazzi Smith who tells us how grateful he was +to find a large telescope he had ordered finished by the opticians on +the very day they had promised it. The day was perfectly correct; it +was only the year that was wrong. A somewhat remarkable experience +in this direction is chronicled by the early reports of the visitors +to Dunsink Observatory. I cannot find the date on which the great +circle was ordered from Ramsden, but it is fixed with sufficient +precision by an allusion in Ussher's paper to the Royal Irish +Academy, which shows that by the 13th June, 1785, the order had been +given, but that the abandonment of the 10-foot scale had not then +been contemplated. It was reasonable that the board should allow +Ramsden ample time for the completion of a work at once so elaborate +and so novel. It could not have been finished in a year, nor would +there have been much reason for complaint if the maker had found he +required two or even three years more. + +Seven years gone, and still no telescope, was the condition in which +the Board found matters at their first visitation in 1792. They had, +however, assurances from Ramsden that the instrument would be +completed within the year; but, alas for such promises, another seven +years rolled on, and in 1799 the place for the great circle was still +vacant at Dunsink. Ramsden had fallen into bad health, and the Board +considerately directed that "inquiries should be made." Next year +there was still no progress, so the Board were roused to threaten +Ramsden with a suit at law; but the menace was never executed, for +the malady of the great optician grew worse, and he died that year. + +Affairs had now assumed a critical aspect, for the college had +advanced much money to Ramsden during these fifteen years, and the +instrument was still unfinished. An appeal was made by the Provost +to Dr. Maskelyne, the Astronomer Royal of England, for his advice and +kindly offices in this emergency. Maskelyne responds--in terms +calculated to allay the anxiety of the Bursar--"Mr. Ramsden has left +property behind him, and the College can be in no danger of losing +both their money and the instrument." The business of Ramsden was +then undertaken by Berge, who proceeded to finish the circle quite as +deliberately as his predecessor. After four years Berge promised the +instrument in the following August, but it did not come. Two years +later (1806) the professor complains that he can get no answer from +Berge. In 1807, it is stated that Berge will send the telescope in a +month. He did not; but in the next year (1808), about twenty-three +years after the great circle was ordered, it was erected at Dunsink, +where it is still to be seen. + +The following circumstances have been authenticated by the signatures +of Provosts, Proctors, Bursars, and other College dignitaries:--In +1793 the Board ordered two of the clocks at the observatory to be +sent to Mr. Crosthwaite for repairs. Seven years later, in 1800, Mr. +Crosthwaite was asked if the clocks were ready. This impatience was +clearly unreasonable, for even in four more years, 1804, we find the +two clocks were still in hand. Two years later, in 1806, the Board +determined to take vigorous action by asking the Bursar to call upon +Crosthwaite. This evidently produced some effect, for in the +following year, 1807, the Professor had no doubt that the clocks +would be speedily returned. After eight years more, in 1815, one of +the clocks was still being repaired, and so it was in 1816, which is +the last record we have of these interesting time-pieces. Astronomers +are, however, accustomed to deal with such stupendous periods in +their calculations, that even the time taken to repair a clock seems +but small in comparison. + +The long tenure of the chair of Astronomy by Brinkley is divided into +two nearly equal periods by the year in which the great circle was +erected. Brinkley was eighteen years waiting for his telescope, and +he had eighteen years more in which to use it. During the first of +these periods Brinkley devoted himself to mathematical research; +during the latter he became a celebrated astronomer. Brinkley's +mathematical labours procured for their author some reputation as a +mathematician. They appear to be works of considerable mathematical +elegance, but not indicating any great power of original thought. +Perhaps it has been prejudicial to Brinkley's fame in this direction, +that he was immediately followed in his chair by so mighty a genius +as William Rowan Hamilton. + +After the great circle had been at last erected, Brinkley was able to +begin his astronomical work in earnest. Nor was there much time to +lose. He was already forty-five years old, a year older than was +Herschel when he commenced his immortal career at Slough. Stimulated +by the consciousness of having the command of an instrument of unique +perfection, Brinkley loftily attempted the very highest class of +astronomical research. He resolved to measure anew with his own eye +and with his own hand the constants of aberration and of nutation. He +also strove to solve that great problem of the universe, the +discovery of the distance of a fixed star. + +These were noble problems, and they were nobly attacked. But to +appraise with justice this work of Brinkley, done seventy years ago, +we must not apply to it the same criterion as we would think right to +apply to similar work were it done now. We do not any longer use +Brinkley's constant of aberration, nor do we now think that +Brinkley's determinations of the star distances were reliable. But, +nevertheless, his investigations exercised a marked influence on the +progress of science; they stimulated the study of the principles on +which exact measurements were to be conducted. + +Brinkley had another profession in addition to that of an +astronomer. He was a divine. When a man endeavours to pursue two +distinct occupations concurrently, it will be equally easy to explain +why his career should be successful, or why it should be the +reverse. If he succeeds, he will, of course, exemplify the wisdom of +having two strings to his bow. Should he fail, it is, of course, +because he has attempted to sit on two stools at once. In Brinkley's +case, his two professions must be likened to the two strings rather +than to the two stools. It is true that his practical experience of +his clerical life was very slender. He had made no attempt to +combine the routine of a parish with his labours in the observatory. +Nor do we associate a special eminence in any department of religious +work with his name. If, however, we are to measure Brinkley's merits +as a divine by the ecclesiastical preferment which he received, his +services to theology must have rivalled his services to astronomy. +Having been raised step by step in the Church, he was at last +appointed to the See of Cloyne, in 1826, as the successor of Bishop +Berkeley. + +Now, though it was permissible for the Archdeacon to be also the +Andrews Professor, yet when the Archdeacon became a Bishop, it was +understood that he should transfer his residence from the observatory +to the palace. The chair of Astronomy accordingly became vacant. +Brinkley's subsequent career seems to have been devoted entirely to +ecclesiastical matters, and for the last ten years of his life he did +not contribute a paper to any scientific society. Arago, after a +characteristic lament that Brinkley should have forsaken the pursuit +of science for the temporal and spiritual attractions of a bishopric, +pays a tribute to the conscientiousness of the quondam astronomer, +who would not even allow a telescope to be brought into the palace +lest his mind should be distracted from his sacred duties. + +The good bishop died on the 13th September, 1835. He was buried in +the chapel of Trinity College, and a fine monument to his memory is a +familiar object at the foot of the noble old staircase of the library. +The best memorial of Brinkley is his admirable book on the "Elements +of Plane Astronomy." It passed through many editions in his lifetime, +and even at the present day the same work, revised first by Dr. Luby, +and more recently by the Rev. Dr. Stubbs and Dr. Brunnow, has a large +and well-merited circulation. + + + + +JOHN HERSCHEL. + + +This illustrious son of an illustrious father was born at Slough, +near Windsor, on the 7th March, 1792. He was the only child of Sir +William Herschel, who had married somewhat late in life, as we have +already mentioned. + +[PLATE: ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light +of certain stars by the intervention of the moon.] + +The surroundings among which the young astronomer was reared afforded +him an excellent training for that career on which he was to enter, +and in which he was destined to attain a fame only less brilliant +than that of his father. The circumstances of his youth permitted +him to enjoy one great advantage which was denied to the elder +Herschel. He was able, from his childhood, to devote himself almost +exclusively to intellectual pursuits. William Herschel, in the early +part of his career, had only been able to snatch occasional hours for +study from his busy life as a professional musician. But the son, +having been born with a taste for the student's life, was fortunate +enough to have been endowed with the leisure and the means to enjoy +it from the commencement. His early years have been so well +described by the late Professor Pritchard in the "Report of the +Council of the Royal Astronomical Society for 1872," that I venture +to make an extract here:-- + +"A few traits of John Herschel's boyhood, mentioned by himself in his +maturer life, have been treasured up by those who were dear to him, +and the record of some of them may satisfy a curiosity as pardonable +as inevitable, which craves to learn through what early steps great +men or great nations become illustrious. His home was singular, and +singularly calculated to nurture into greatness any child born as +John Herschel was with natural gifts, capable of wide development. At +the head of the house there was the aged, observant, reticent +philosopher, and rarely far away his devoted sister, Caroline +Herschel, whose labours and whose fame are still cognisable as a +beneficent satellite to the brighter light of her illustrious +brother. It was in the companionship of these remarkable persons, +and under the shadow of his father's wonderful telescope, that John +Herschel passed his boyish years. He saw them, in silent but +ceaseless industry, busied about things which had no apparent concern +with the world outside the walls of that well-known house, but which, +at a later period of his life, he, with an unrivalled eloquence, +taught his countrymen to appreciate as foremost among those living +influences which but satisfy and elevate the noblest instincts of our +nature. What sort of intercourse passed between the father and the +boy may be gathered from an incident or two which he narrated as +having impressed themselves permanently on the memory of his youth. +He once asked his father what he thought was the oldest of all +things. The father replied, after the Socratic method, by putting +another question: 'And what do you yourself suppose is the oldest of +all things?' The boy was not successful in his answers, thereon the +old astronomer took up a small stone from the garden walk: 'There, my +child, there is the oldest of all the things that I certainly know.' +On another occasion his father is said to have asked the boy, 'What +sort of things, do you think, are most alike?' The delicate, +blue-eyed boy, after a short pause, replied, 'The leaves of the same +tree are most like each other.' 'Gather, then, a handful of leaves of +that tree,' rejoined the philosopher, 'and choose two that are +alike.' The boy failed; but he hid the lesson in his heart, and his +thoughts were revealed after many days. These incidents may be +trifles; nor should we record them here had not John Herschel +himself, though singularly reticent about his personal emotions, +recorded them as having made a strong impression on his mind. Beyond +all doubt we can trace therein, first, that grasp and grouping of +many things in one, implied in the stone as the oldest of things; +and, secondly, that fine and subtle discrimination of each thing out +of many like things as forming the main features which characterized +the habit of our venerated friend's philosophy." + +John Herschel entered St. John's College, Cambridge, when he was +seventeen years of age. His university career abundantly fulfilled +his father's eager desire, that his only son should develop a +capacity for the pursuit of science. After obtaining many lesser +distinctions, he finally came out as Senior Wrangler in 1813. It +was, indeed, a notable year in the mathematical annals of the +University. Second on that list, in which Herschel's name was first, +appeared that of the illustrious Peacock, afterwards Dean of Ely, who +remained throughout life one of Herschel's most intimate friends. + +Almost immediately after taking his degree, Herschel gave evidence of +possessing a special aptitude for original scientific investigation. +He sent to the Royal Society a mathematical paper which was published +in the PHILOSOPHICAL TRANSACTIONS. Doubtless the splendour that +attached to the name he bore assisted him in procuring early +recognition of his own great powers. Certain it is that he was made +a Fellow of the Royal Society at the unprecedentedly early age of +twenty-one. Even after this remarkable encouragement to adopt a +scientific career as the business of his life, it does not seem that +John Herschel at first contemplated devoting himself exclusively to +science. He commenced to prepare for the profession of the Law by +entering as a student at the Middle Temple, and reading with a +practising barrister. + +But a lawyer John Herschel was not destined to become. Circumstances +brought him into association with some leading scientific men. He +presently discovered that his inclinations tended more and more in +the direction of purely scientific pursuits. Thus it came to pass +that the original intention as to the calling which he should follow +was gradually abandoned. Fortunately for science Herschel found its +pursuit so attractive that he was led, as his father had been before +him, to give up his whole life to the advancement of knowledge. Nor +was it unnatural that a Senior Wrangler, who had once tasted the +delights of mathematical research, should have been tempted to devote +much time to this fascinating pursuit. By the time John Herschel was +twenty-nine he had published so much mathematical work, and his +researches were considered to possess so much merit, that the Royal +Society awarded him the Copley Medal, which was the highest +distinction it was capable of conferring. + +At the death of his father in 1822, John Herschel, with his tastes +already formed for a scientific career, found himself in the +possession of ample means. To him also passed all his father's great +telescopes and apparatus. These material aids, together with a +dutiful sense of filial obligation, decided him to make practical +astronomy the main work of his life. He decided to continue to its +completion that great survey of the heavens which had already been +inaugurated, and, indeed, to a large extent accomplished, by his +father. + +The first systematic piece of practical astronomical work which John +Herschel undertook was connected with the measurement of what are +known as "Double Stars." It should be observed, that there are in +the heavens a number of instances in which two stars are seen in very +close association. In the case of those objects to which the +expression "Double Stars" is generally applied, the two luminous +points are so close together that even though they might each be +quite bright enough to be visible to the unaided eye, yet their +proximity is such that they cannot be distinguished as two separate +objects without optical aid. The two stars seem fused together into +one. In the telescope, however, the bodies may be discerned +separately, though they are frequently so close together that it +taxes the utmost power of the instrument to indicate the division +between them. + +The appearance presented by a double star might arise from the +circumstance that the two stars, though really separated from each +other by prodigious distances, happened to lie nearly in the same +line of vision, as seen from our point of view. No doubt, many of +the so-called double stars could be accounted for on this +supposition. Indeed, in the early days when but few double stars +were known, and when telescopes were not powerful enough to exhibit +the numerous close doubles which have since been brought to light, +there seems to have been a tendency to regard all double stars as +merely such perspective effects. It was not at first suggested that +there could be any physical connection between the components of each +pair. The appearance presented was regarded as merely due to the +circumstance that the line joining the two bodies happened to pass +near the earth. + +[PLATE: SIR JOHN HERSCHEL.] + +In the early part of his career, Sir William Herschel seems to have +entertained the view then generally held by other astronomers with +regard to the nature of these stellar pairs. The great observer +thought that the double stars could therefore be made to afford a +means of solving that problem in which so many of the observers of +the skies had been engaged, namely, the determination of the +distances of the stars from the earth. Herschel saw that the +displacement of the earth in its annual movement round the sun would +produce an apparent shift in the place of the nearer of the two stars +relatively to the other, supposed to be much more remote. If this +shift could be measured, then the distance of the nearer of the stars +could be estimated with some degree of precision. + +As has not unfrequently happened in the history of science, an effect +was perceived of a very different nature from that which had been +anticipated. If the relative places of the two stars had been +apparently deranged merely in consequence of the motion of the earth, +then the phenomenon would be an annual one. After the lapse of a +year the two stars would have regained their original relative +positions. This was the effect for which William Herschel was +looking. In certain of the so called double stars, he, no doubt, did +find a movement. He detected the remarkable fact that both the +apparent distance and the relative positions of the two bodies were +changing. But what was his surprise to observe that these +alterations were not of an annually periodic character. It became +evident then that in some cases one of the component stars was +actually revolving around the other, in an orbit which required many +years for its completion. Here was indeed a remarkable discovery. It +was clearly impossible to suppose that movements of this kind could +be mere apparent displacements, arising from the annual shift in our +point of view, in consequence of the revolution of the earth. +Herschel's discovery established the interesting fact that, in +certain of these double stars, or binary stars, as these particular +objects are more expressively designated, there is an actual orbital +revolution of a character similar to that which the earth performs +around the sun. Thus it was demonstrated that in these particular +double stars the nearness of the two components was not merely +apparent. The objects must actually lie close together at a distance +which is small in comparison with the distance at which either of +them is separated from the earth. The fact that the heavens contain +pairs of twin suns in mutual revolution was thus brought to light. + +In consequence of this beautiful discovery, the attention of +astronomers was directed to the subject of double stars with a degree +of interest which these objects had never before excited. It was +therefore not unnatural that John Herschel should have been attracted +to this branch of astronomical work. Admiration for his father's +discovery alone might have suggested that the son should strive to +develop this territory newly opened up to research. But it also +happened that the mathematical talents of the younger Herschel +inclined his inquiries in the same direction. He saw clearly that, +when sufficient observations of any particular binary star had been +accumulated, it would then be within the power of the mathematician +to elicit from those observations the shape and the position in space +of the path which each of the revolving stars described around the +other. Indeed, in some cases he would be able to perform the +astonishing feat of determining from his calculations the weight of +these distant suns, and thus be enabled to compare them with the mass +of our own sun. + +[PLATE: NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel.] + +But this work must follow the observations, it could not precede +them. The first step was therefore to observe and to measure with +the utmost care the positions and distances of those particular +double stars which appear to offer the greatest promise in this +particular research. In 1821, Herschel and a friend of his, Mr. +James South, agreed to work together with this object. South was a +medical man with an ardent devotion to science, and possessed of +considerable wealth. He procured the best astronomical instruments +that money could obtain, and became a most enthusiastic astronomer +and a practical observer of tremendous energy. + +South and John Herschel worked together for two years in the +observation and measurement of the double stars discovered by Sir +William Herschel. In the course of this time their assiduity was +rewarded by the accumulation of so great a mass of careful +measurements that when published, they formed quite a volume in the +"Philosophical Transactions." The value and accuracy of the work, +when estimated by standards which form proper criteria for that +period, is universally recognised. It greatly promoted the progress +of sidereal astronomy, and the authors were in consequence awarded +medals from the Royal Society, and the Royal Astronomical Society, +as well as similar testimonials from various foreign institutions. + +This work must, however, be regarded as merely introductory to the +main labours of John Herschel's life. His father devoted the greater +part of his years as an observer to what he called his "sweeps" of +the heavens. The great reflecting telescope, twenty feet long, was +moved slowly up and down through an arc of about two degrees towards +and from the pole, while the celestial panorama passed slowly in the +course of the diurnal motion before the keenly watching eye of the +astronomer. Whenever a double star traversed the field Herschel +described it to his sister Caroline, who, as we have already +mentioned, was his invariable assistant in his midnight watches. When +a nebula appeared, then he estimated its size and its brightness, he +noticed whether it had a nucleus, or whether it had stars disposed in +any significant manner with regard to it. He also dictated any other +circumstance which he deemed worthy of record. These observations +were duly committed to writing by the same faithful and indefatigable +scribe, whose business it also was to take a memorandum of the exact +position of the object as indicated by a dial placed in front of her +desk, and connected with the telescope. + +John Herschel undertook the important task of re-observing the +various double stars and nebulae which had been discovered during +these memorable vigils. The son, however, lacked one inestimable +advantage which had been possessed by the father. John Herschel had +no assistant to discharge all those duties which Caroline had so +efficiently accomplished. He had, therefore, to modify the system of +sweeping previously adopted in order to enable all the work both of +observing and of recording to be done by himself. This, in many +ways, was a great drawback to the work of the younger astronomer. The +division of labour between the observer and the scribe enables a +greatly increased quantity of work to be got through. It is also +distinctly disadvantageous to an observer to have to use his eye at +the telescope directly after he has been employing it for reading the +graduations on a circle, by the light of a lamp, or for entering +memoranda in a note book. Nebulae, especially, are often so +excessively faint that they can only be properly observed by an eye +which is in that highly sensitive condition which is obtained by long +continuance in darkness. The frequent withdrawal of the eye from the +dark field of the telescope, and the application of it to reading by +artificial light, is very prejudicial to its use for the more +delicate purpose. John Herschel, no doubt, availed himself of every +precaution to mitigate the ill effects of this inconvenience as much +as possible, but it must have told upon his labours as compared with +those of his father. + +But nevertheless John Herschel did great work during his "sweeps." He +was specially particular to note all the double stars which presented +themselves to his observation. Of course some little discretion must +be allowed in deciding as to what degree of proximity in adjacent +stars does actually bring them within the category of "double +stars." Sir John set down all such objects as seemed to him likely +to be of interest, and the results of his discoveries in this branch +of astronomy amount to some thousands. Six or seven great memoirs in +the TRANSACTIONS of the Royal Astronomical Society have been devoted +to giving an account of his labours in this department of astronomy. + +[PLATE: THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.] + +One of the achievements by which Sir John Herschel is best known is +his invention of a method by which the orbits of binary stars could +be determined. It will be observed that when one star revolves +around another in consequence of the law of gravitation, the orbit +described must be an ellipse. This ellipse, however, generally +speaking, appears to us more or less foreshortened, for it is easily +seen that only under highly exceptional circumstances would the plane +in which the stars move happen to be directly square to the line of +view. It therefore follows that what we observe is not exactly the +track of one star around the other; it is rather the projection of +that track as seen on the surface of the sky. Now it is remarkable +that this apparent path is still an ellipse. Herschel contrived a +very ingenious and simple method by which he could discover from the +observations the size and position of the ellipse in which the +revolution actually takes place. He showed how, from the study of +the apparent orbit of the star, and from certain measurements which +could easily be effected upon it, the determination of the true +ellipse in which the movement is performed could be arrived at. In +other words, Herschel solved in a beautiful manner the problem of +finding the true orbits of double stars. The importance of this work +may be inferred from the fact that it has served as the basis on +which scores of other investigators have studied the fascinating +subject of the movement of binary stars. + +The labours, both in the discovery and measurement of the double +stars, and in the discussion of the observations with the object of +finding the orbits of such stars as are in actual revolution, +received due recognition in yet another gold medal awarded by the +Royal Society. An address was delivered on the occasion by the Duke +of Sussex (30th November, 1833), in the course of which, after +stating that the medal had been conferred on Sir John Herschel, he +remarks:-- + +"It has been said that distance of place confers the same privilege +as distance of time, and I should gladly avail myself of the +privilege which is thus afforded me by Sir John Herschel's separation +from his country and friends, to express my admiration of his +character in stronger terms than I should otherwise venture to use; +for the language of panegyric, however sincerely it may flow from the +heart, might be mistaken for that of flattery, if it could not thus +claim somewhat of an historical character; but his great attainments +in almost every department of human knowledge, his fine powers as a +philosophical writer, his great services and his distinguished +devotion to science, the high principles which have regulated his +conduct in every relation of life, and, above all, his engaging +modesty, which is the crown of all his other virtues, presenting such +a model of an accomplished philosopher as can rarely be found beyond +the regions of fiction, demand abler pens than mine to describe them +in adequate terms, however much inclined I might feel to undertake +the task." + +The first few lines of the eulogium just quoted allude to Herschel's +absence from England. This was not merely an episode of interest in +the career of Herschel, it was the occasion of one of the greatest +scientific expeditions in the whole history of astronomy. + +Herschel had, as we have seen, undertaken a revision of his father's +"sweeps" for new objects, in those skies which are visible from our +latitudes in the northern hemisphere. He had well-nigh completed +this task. Zone by zone the whole of the heavens which could be +observed from Windsor had passed under his review. He had added +hundreds to the list of nebulae discovered by his father. He had +announced thousands of double stars. At last, however, the great +survey was accomplished. The contents of the northern hemisphere, so +far at least as they could be disclosed by his telescope of twenty +feet focal length, had been revealed. + +[PLATE: SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN, +Cape of Good Hope.] + +But Herschel felt that this mighty task had to be supplemented by +another of almost equal proportions, before it could be said that the +twenty-foot telescope had done its work. It was only the northern +half of the celestial sphere which had been fully explored. The +southern half was almost virgin territory, for no other astronomer +was possessed of a telescope of such power as those which the +Herschels had used. It is true, of course, that as a certain margin +of the southern hemisphere was visible from these latitudes, it had +been more or less scrutinized by observers in northern skies. And +the glimpses which had thus been obtained of the celestial objects in +the southern sky, were such as to make an eager astronomer long for a +closer acquaintance with the celestial wonders of the south. The +most glorious object in the sidereal heavens, the Great Nebula in +Orion, lies indeed in that southern hemisphere to which the younger +Herschel's attention now became directed. It fortunately happens, +however, for votaries of astronomy all the world over, that Nature +has kindly placed her most astounding object, the great Nebula in +Orion, in such a favoured position, near the equator, that from a +considerable range of latitudes, both north and south, the wonders of +the Nebula can be explored. There are grounds for thinking that the +southern heavens contain noteworthy objects which, on the whole, are +nearer to the solar system than are the noteworthy objects in the +northern skies. The nearest star whose distance is known, Alpha +Centauri, lies in the southern hemisphere, and so also does the most +splendid cluster of stars. + +Influenced by the desire to examine these objects, Sir John Herschel +determined to take his great telescope to a station in the southern +hemisphere, and thus complete his survey of the sidereal heavens. The +latitude of the Cape of Good Hope is such that a suitable site could +be there found for his purpose. The purity of the skies in South +Africa promised to provide for the astronomer those clear nights +which his delicate task of surveying the nebulae would require. + +On November 13, 1833, Sir John Herschel, who had by this time +received the honour of knighthood from William IV., sailed from +Portsmouth for the Cape of Good Hope, taking with him his gigantic +instruments. After a voyage of two months, which was considered to +be a fair passage in those days, he landed in Table Bay, and having +duly reconnoitred various localities, he decided to place his +observatory at a place called Feldhausen, about six miles from Cape +Town, near the base of the Table Mountain. A commodious residence +was there available, and in it he settled with his family. A +temporary building was erected to contain the equatorial, but the +great twenty-foot telescope was accommodated with no more shelter +than is provided by the open canopy of heaven. + +As in his earlier researches at home, the attention of the great +astronomer at the Cape of Good Hope was chiefly directed to the +measurement of the relative positions and distances apart of the +double stars, and to the close examination of the nebulae. In the +delineation of the form of these latter objects Herschel found ample +employment for his skilful pencil. Many of the drawings he has made +of the celestial wonders in the southern sky are admirable examples +of celestial portraiture. + +The number of the nebulae and of those kindred objects, the star +clusters, which Herschel studied in the southern heavens, during four +years of delightful labour, amount in all to one thousand seven +hundred and seven. His notes on their appearance, and the +determinations of their positions, as well as his measurements of +double stars, and much other valuable astronomical research, were +published in a splendid volume, brought out at the cost of the Duke +of Northumberland. This is, indeed, a monumental work, full of +interesting and instructive reading for any one who has a taste for +astronomy. + +Herschel had the good fortune to be at the Cape on the occasion of +the periodical return of Halley's great comet in 1833. To the study +of this body he gave assiduous attention, and the records of his +observations form one of the most interesting chapters in that +remarkable volume to which we have just referred. + +[PLATE: COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John +Herschel's survey of the Southern Heavens.] + +Early in 1838 Sir John Herschel returned to England. He had made +many friends at the Cape, who deeply sympathised with his self- +imposed labours while he was resident among them. They desired to +preserve the recollection of this visit, which would always, they +considered, be a source of gratification in the colony. Accordingly, +a number of scientific friends in that part of the world raised a +monument with a suitable inscription, on the spot which had been +occupied by the great twenty-foot reflector at Feldhausen. + +His return to England after five years of absence was naturally an +occasion for much rejoicing among the lovers of astronomy. He was +entertained at a memorable banquet, and the Queen, at her coronation, +made him a baronet. His famous aunt Caroline, at that time aged +eighty, was still in the enjoyment of her faculties, and was able to +estimate at its true value the further lustre which was added to the +name she bore. But there is reason to believe that her satisfaction +was not quite unmixed with other feelings. With whatever favour she +might regard her nephew, he was still not the brother to whom her +life had been devoted. So jealous was this vigorous old lady of the +fame of the great brother William, that she could hardly hear with +patience of the achievements of any other astronomer, and this +failing existed in some degree even when that other astronomer +happened to be her illustrious nephew. + +With Sir John Herschel's survey of the Southern Hemisphere it may be +said that his career as an observing astronomer came to a close. He +did not again engage in any systematic telescopic research. But it +must not be inferred from this statement that he desisted from active +astronomical work. It has been well observed that Sir John Herschel +was perhaps the only astronomer who has studied with success, and +advanced by original research, every department of the great science +with which his name is associated. It was to some other branches of +astronomy besides those concerned with looking through telescopes, +that the rest of the astronomer's life was to be devoted. + +To the general student Sir John Herschel is best known by the volume +which he published under the title of "Outlines of Astronomy." This +is, indeed, a masterly work, in which the characteristic difficulties +of the subject are resolutely faced and expounded with as much +simplicity as their nature will admit. As a literary effort this +work is admirable, both on account of its picturesque language and +the ennobling conceptions of the universe which it unfolds. The +student who desires to become acquainted with those recondite +departments of astronomy, in which the effects of the disturbing +action of one planet upon the motions of another planet are +considered, will turn to the chapters in Herschel's famous work on +the subject. There he will find this complex matter elucidated, +without resort to difficult mathematics. Edition after edition of +this valuable work has appeared, and though the advances of modern +astronomy have left it somewhat out of date in certain departments, +yet the expositions it contains of the fundamental parts of the +science still remain unrivalled. + +Another great work which Sir John undertook after his return from the +Cape, was a natural climax to those labours on which his father and +he had been occupied for so many years. We have already explained +how the work of both these observers had been mainly devoted to the +study of the nebulae and the star clusters. The results of their +discoveries had been announced to the world in numerous isolated +memoirs. The disjointed nature of these publications made their use +very inconvenient. But still it was necessary for those who desired +to study the marvellous objects discovered by the Herschels, to have +frequent recourse to the original works. To incorporate all the +several observations of nebular into one great systematic catalogue, +seemed, therefore, to be an indispensable condition of progress in +this branch of knowledge. No one could have been so fitted for this +task as Sir John Herschel. He, therefore, attacked and carried +through the great undertaking. Thus at last a grand catalogue of +nebulae and clusters was produced. Never before was there so +majestic an inventory. If we remember that each of the nebulae is an +object so vast, that the whole of the solar system would form an +inconsiderable speck by comparison, what are we to think of a +collection in which these objects are enumerated in thousands? In +this great catalogue we find arranged in systematic order all the +nebulae and all the clusters which had been revealed by the diligence +of the Herschels, father and son, in the Northern Hemisphere, and of +the son alone in the Southern Hemisphere. Nor should we omit to +mention that the labours of other astronomers were likewise +incorporated. It was unavoidable that the descriptions given to each +of the objects should be very slight. Abbreviations are used, which +indicate that a nebula is bright, or very bright, or extremely +bright, or faint, or very faint, or extremely faint. Such phrases +have certainly but a relative and technical meaning in such a +catalogue. The nebulae entered as extremely bright by the +experienced astronomer are only so described by way of contrast to +the great majority of these delicate telescopic objects. Most of the +nebulae, indeed, are so difficult to see, that they admit of but very +slight description. It should be observed that Herschel's catalogue +augmented the number of known nebulous objects to more than ten times +that collected into any catalogue which had ever been compiled before +the days of William Herschel's observing began. But the study of +these objects still advances, and the great telescopes now in use +could probably show at least twice as many of these objects as are +contained in the list of Herschel, of which a new and enlarged +edition has since been brought out by Dr. Dreyer. + +One of the best illustrations of Sir John Herschel's literary powers +is to be found in the address which he delivered at the Royal +Astronomical Society, on the occasion of presenting a medal to Mr. +Francis Baily, in recognition of his catalogue of stars. The passage +I shall here cite places in its proper aspect the true merit of the +laborious duty involved in such a task as that which Mr. Baily had +carried through with such success:-- + +"If we ask to what end magnificent establishments are maintained by +states and sovereigns, furnished with masterpieces of art, and placed +under the direction of men of first-rate talent and high-minded +enthusiasm, sought out for those qualities among the foremost in the +ranks of science, if we demand QUI BONO? for what good a Bradley has +toiled, or a Maskelyne or a Piazzi has worn out his venerable age in +watching, the answer is--not to settle mere speculative points in the +doctrine of the universe; not to cater for the pride of man by +refined inquiries into the remoter mysteries of nature; not to trace +the path of our system through space, or its history through past and +future eternities. These, indeed, are noble ends and which I am far +from any thought of depreciating; the mind swells in their +contemplation, and attains in their pursuit an expansion and a +hardihood which fit it for the boldest enterprise. But the direct +practical utility of such labours is fully worthy of their +speculative grandeur. The stars are the landmarks of the universe; +and, amidst the endless and complicated fluctuations of our system, +seem placed by its Creator as guides and records, not merely to +elevate our minds by the contemplation of what is vast, but to teach +us to direct our actions by reference to what is immutable in His +works. It is, indeed, hardly possible to over-appreciate their value +in this point of view. Every well-determined star, from the moment +its place is registered, becomes to the astronomer, the geographer, +the navigator, the surveyor, a point of departure which can never +deceive or fail him, the same for ever and in all places, of a +delicacy so extreme as to be a test for every instrument yet invented +by man, yet equally adapted for the most ordinary purposes; as +available for regulating a town clock as for conducting a navy to the +Indies; as effective for mapping down the intricacies of a petty +barony as for adjusting the boundaries of Transatlantic empires. When +once its place has been thoroughly ascertained and carefully +recorded, the brazen circle with which that useful work was done may +moulder, the marble pillar may totter on its base, and the astronomer +himself survive only in the gratitude of posterity; but the record +remains, and transfuses all its own exactness into every +determination which takes it for a groundwork, giving to inferior +instruments--nay, even to temporary contrivances, and to the +observations of a few weeks or days--all the precision attained +originally at the cost of so much time, labour, and expense." + +Sir John Herschel wrote many other works besides those we have +mentioned. His "Treatise on Meteorology" is, indeed, a standard work +on this subject, and numerous articles from the same pen on +miscellaneous subjects, which have been collected and reprinted, +seemed as a relaxation from his severe scientific studies. Like +certain other great mathematicians Herschel was also a poet, and he +published a translation of the Iliad into blank verse. + +In his later years Sir John Herschel lived a retired life. For a +brief period he had, indeed, been induced to accept the office of +Master of the Mint. It was, however, evident that the routine of +such an occupation was not in accordance with his tastes, and he +gladly resigned it, to return to the seclusion of his study in his +beautiful home at Collingwood, in Kent. + +His health having gradually failed, he died on the 11th May, 1871, in +the seventy-ninth year of his age. + + + + +THE EARL OF ROSSE. + + +The subject of our present sketch occupies quite a distinct position +in scientific history. Unlike many others who have risen by their +scientific discoveries from obscurity to fame, the great Earl of +Rosse was himself born in the purple. His father, who, under the +title of Sir Lawrence Parsons, had occupied a distinguished position +in the Irish Parliament, succeeded on the death of his father to the +Earldom which had been recently created. The subject of our present +memoir was, therefore, the third of the Earls of Rosse, and he was +born in York on June 17, 1800. Prior to his father's death in 1841, +he was known as Lord Oxmantown. + +The University education of the illustrious astronomer was begun in +Dublin and completed at Oxford. We do not hear in his case of any +very remarkable University career. Lord Rosse was, however, a +diligent student, and obtained a first-class in mathematics. He +always took a great deal of interest in social questions, and was a +profound student of political economy. He had a seat in the House of +Commons, as member for King's County, from 1821 to 1834, his +ancestral estate being situated in this part of Ireland. + +[PLATE: THE EARL OF ROSSE.] + +Lord Rosse was endowed by nature with a special taste for mechanical +pursuits. Not only had he the qualifications of a scientific +engineer, but he had the manual dexterity which qualified him +personally to carry out many practical arts. Lord Rosse was, in +fact, a skilful mechanic, an experienced founder, and an ingenious +optician. His acquaintances were largely among those who were +interested in mechanical pursuits, and it was his delight to visit +the works or engineering establishments where refined processes in +the arts were being carried on. It has often been stated--and as I +have been told by members of his family, truly stated--that on one +occasion, after he had been shown over some large works in the north +of England, the proprietor bluntly said that he was greatly in want +of a foreman, and would indeed be pleased if his visitor, who had +evinced such extraordinary capacity for mechanical operations, would +accept the post. Lord Rosse produced his card, and gently explained +that he was not exactly the right man, but he appreciated the +compliment, and this led to a pleasant dinner, and was the basis of a +long friendship. + +I remember on one occasion hearing Lord Rosse explain how it was that +he came to devote his attention to astronomy. It appears that when +he found himself in the possession of leisure and of means, he +deliberately cast around to think how that means and that leisure +could be most usefully employed. Nor was it surprising that he +should search for a direction which would offer special scope for his +mechanical tastes. He came to the conclusion that the building of +great telescopes was an art which had received no substantial advance +since the great days of William Herschel. He saw that to construct +mighty instruments for studying the heavens required at once the +command of time and the command of wealth, while he also felt that +this was a subject the inherent difficulties of which would tax to +the uttermost whatever mechanical skill he might possess. Thus it +was he decided that the construction of great telescopes should +become the business of his life. + +[PLATE: BIRR CASTLE. + +PLATE: THE MALL, PARSONSTOWN.] + +In the centre of Ireland, seventy miles from Dublin, on the border +between King's County and Tipperary, is a little town whereof we must +be cautious before writing the name. The inhabitants of that town +frequently insist that its name is Birr, * while the official +designation is Parsonstown, and to this day for every six people who +apply one name to the town, there will be half a dozen who use the +other. But whichever it may be, Birr or Parsonstown--and I shall +generally call it by the latter name--it is a favourable specimen of +an Irish county town. The widest street is called the Oxmantown +Mall. It is bordered by the dwelling-houses of the chief residents, +and adorned with rows of stately trees. At one end of this +distinctly good feature in the town is the Parish Church, while at +the opposite end are the gates leading into Birr Castle, the +ancestral home of the house of Parsons. Passing through the gates +the visitor enters a spacious demesne, possessing much beauty of wood +and water, one of the most pleasing features being the junction of +the two rivers, which unite at a spot ornamented by beautiful +timber. At various points illustrations of the engineering skill of +the great Earl will be observed. The beauty of the park has been +greatly enhanced by the construction of an ample lake, designed with +the consummate art by which art is concealed. Even in mid-summer it +is enlivened by troops of wild ducks preening themselves in that +confidence which they enjoy in those happy localities where the sound +of a gun is seldom heard. The water is led into the lake by a tube +which passes under one of the two rivers just mentioned, while the +overflow from the lake turns a water-wheel, which works a pair of +elevators ingeniously constructed for draining the low-lying parts of +the estate. + + * Considering the fame acquired by Parsonstown from Lord Rosse's + mirrors, it may be interesting to note the following extract from + "The Natural History of Ireland," by Dr. Gerard Boate, Thomas + Molyneux M.D., F.R.S., and others, which shows that 150 years ago + Parsonstown was famous for its glass:-- + + "We shall conclude this chapter with the glass, there having been + several glasshouses set up by the English in Ireland, none in Dublin + or other cities, but all of them in the country; amongst which the + principal was that of Birre, a market town, otherwise called + Parsonstown, after one Sir Lawrence Parsons, who, having purchased + that lordship, built a goodly house upon it; his son William Parsons + having succeeded him in the possession of it; which town is situate + in Queen's County, about fifty miles (Irish) to the southwest of + Dublin, upon the borders of the two provinces of Leinster and Munster; + from this place Dublin was furnished with all sorts of window and + drinking glasses, and such other as commonly are in use. One part of + the materials, viz., the sand, they had out of England; the other, + to wit the ashes, they made in the place of ash-tree, and used no + other. The chiefest difficulty was to get the clay for the pots to + melt the materials in; this they had out of the north."--Chap. XXI., + Sect. VIII. "Of the Glass made in Ireland." + +Birr Castle itself is a noble mansion with reminiscences from the +time of Cromwell. It is surrounded by a moat and a drawbridge of +modern construction, and from its windows beautiful views can be had +over the varied features of the park. But while the visitors to +Parsonstown will look with great interest on this residence of an +Irish landlord, whose delight it was to dwell in his own country, and +among his own people, yet the feature which they have specially come +to observe is not to be found in the castle itself. On an extensive +lawn, sweeping down from the moat towards the lake, stand two noble +masonry walls. They are turreted and clad with ivy, and considerably +loftier than any ordinary house. As the visitor approaches, he will +see between those walls what may at first sight appear to him to be +the funnel of a steamer lying down horizontally. On closer approach +he will find that it is an immense wooden tube, sixty feet long, and +upwards of six feet in diameter. It is in fact large enough to admit +of a tall man entering into it and walking erect right through from +one end to the other. This is indeed the most gigantic instrument +which has ever been constructed for the purpose of exploring the +heavens. Closely adjoining the walls between which the great tube +swings, is a little building called "The Observatory." In this the +smaller instruments are contained, and there are kept the books which +are necessary for reference. The observatory also offers shelter to +the observers, and provides the bright fire and the cup of warm tea, +which are so acceptable in the occasional intervals of a night's +observation passed on the top of the walls with no canopy but the +winter sky. + +Almost the first point which would strike the visitor to Lord Rosse's +telescope is that the instrument at which he is looking is not only +enormously greater than anything of the kind that he has ever seen +before, but also that it is something of a totally different nature. +In an ordinary telescope he is accustomed to find a tube with lenses +of glass at either end, while the large telescopes that we see in our +observatories are also in general constructed on the same principle. +At one end there is the object-glass, and at the other end the +eye-piece, and of course it is obvious that with an instrument of +this construction it is to the lower end of the tube that the eye of +the observer must be placed when the telescope is pointed to the +skies. But in Lord Rosse's telescope you would look in vain for +these glasses, and it is not at the lower end of the instrument that +you are to take your station when you are going to make your +observations. The astronomer at Parsonstown has rather to avail +himself of the ingenious system of staircases and galleries, by which +he is enabled to obtain access to the mouth of the great tube. The +colossal telescope which swings between the great walls, like +Herschel's great telescope already mentioned, is a reflector, the +original invention of which is due of course to Newton. The optical +work which is accomplished by the lenses in the ordinary telescope is +effected in the type of instrument constructed by Lord Rosse by a +reflecting mirror which is placed at the lower end of the vast tube. +The mirror in this instrument is made of a metal consisting of two +parts of copper to one of tin. As we have already seen, this mixture +forms an alloy of a very peculiar nature. The copper and the tin +both surrender their distinctive qualities, and unite to form a +material of a very different physical character. The copper is tough +and brown, the tin is no doubt silvery in hue, but soft and almost +fibrous in texture. When the two metals are mixed together in the +proportions I have stated, the alloy obtained is intensely hard and +quite brittle being in both these respects utterly unlike either of +the two ingredients of which it is composed. It does, however, +resemble the tin in its whiteness, but it acquires a lustre far +brighter than tin; in fact, this alloy hardly falls short of silver +itself in its brilliance when polished. + +[PLATE: LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence, +Upper Sackville Street, Dublin.] + +The first duty that Lord Rosse had to undertake was the construction +of this tremendous mirror, six feet across, and about four or five +inches thick. The dimensions were far in excess of those which had +been contemplated in any previous attempt of the same kind. Herschel +had no doubt fashioned one mirror of four feet in diameter, and many +others of smaller dimensions, but the processes which he employed had +never been fully published, and it was obvious that, with a large +increase in dimensions, great additional difficulties had to be +encountered. Difficulties began at the very commencement of the +process, and were experienced in one form or another at every +subsequent stage. In the first place, the mere casting of a great +disc of this mixture of tin and copper, weighing something like three +or four tons, involved very troublesome problems. No doubt a casting +of this size, if the material had been, for example, iron, would have +offered no difficulties beyond those with which every practical +founder is well acquainted, and which he has to encounter daily in +the course of his ordinary work. But speculum metal is a material of +a very intractable description. There is, of course, no practical +difficulty in melting the copper, nor in adding the proper proportion +of tin when the copper has been melted. There may be no great +difficulty in arranging an organization by which several crucibles, +filled with the molten material, shall be poured simultaneously so as +to obtain the requisite mass of metal, but from this point the +difficulties begin. For speculum metal when cold is excessively +brittle, and were the casting permitted to cool like an ordinary +copper or iron casting, the mirror would inevitably fly into pieces. +Lord Rosse, therefore, found it necessary to anneal the casting with +extreme care by allowing it to cool very slowly. This was +accomplished by drawing the disc of metal as soon as it had entered +into the solid state, though still glowing red, into an annealing +oven. There the temperature was allowed to subside so gradually, +that six weeks elapsed before the mirror had reached the temperature +of the external air. The necessity for extreme precaution in the +operation of annealing will be manifest if we reflect on one of the +accidents which happened. On a certain occasion, after the cooling +of a great casting had been completed, it was found, on withdrawing +the speculum, that it was cracked into two pieces. This mishap was +eventually traced to the fact that one of the walls of the oven had +only a single brick in its thickness, and that therefore the heat had +escaped more easily through that side than through the other sides +which were built of double thickness. The speculum had, +consequently, not cooled uniformly, and hence the fracture had +resulted. Undeterred, however, by this failure, as well as by not a +few other difficulties, into a description of which we cannot now +enter, Lord Rosse steadily adhered to his self-imposed task, and at +last succeeded in casting two perfect discs on which to commence the +tedious processes of grinding and polishing. The magnitude of the +operations involved may perhaps be appreciated if I mention that the +value of the mere copper and tin entering into the composition of +each of the mirrors was about 500 pounds. + +In no part of his undertaking was Lord Rosse's mechanical ingenuity +more taxed than in the devising of the mechanism for carrying out the +delicate operations of grinding and polishing the mirrors, whose +casting we have just mentioned. In the ordinary operations of the +telescope-maker, such processes had hitherto been generally effected +by hand, but, of course, such methods became impossible when dealing +with mirrors which were as large as a good-sized dinner table, and +whose weight was measured by tons. The rough grinding was effected +by means of a tool of cast iron about the same size as the mirror, +which was moved by suitable machinery both backwards and forwards, +and round and round, plenty of sand and water being supplied between +the mirror and the tool to produce the necessary attrition. As the +process proceeded and as the surface became smooth, emery was used +instead of sand; and when this stage was complete, the grinding tool +was removed and the polishing tool was substituted. The essential +part of this was a surface of pitch, which, having been temporarily +softened by heat, was then placed on the mirror, and accepted from +the mirror the proper form. Rouge was then introduced as the +polishing powder, and the operation was continued about nine hours, +by which time the great mirror had acquired the appearance of highly +polished silver. When completed, the disc of speculum metal was +about six feet across and four inches thick. The depression in the +centre was about half an inch. Mounted on a little truck, the great +speculum was then conveyed to the instrument, to be placed in its +receptacle at the bottom of the tube, the length of which was sixty +feet, this being the focal distance of the mirror. Another small +reflector was inserted in the great tube sideways, so as to direct +the gaze of the observer down upon the great reflector. Thus was +completed the most colossal instrument for the exploration of the +heavens which the art of man has ever constructed. + +[PLATE: ROMAN CATHOLIC CHURCH AT PARSONSTOWN.] + +It was once my privilege to be one of those to whom the illustrious +builder of the great telescope entrusted its use. For two seasons in +1865 and 1866 I had the honour of being Lord Rosse's astronomer. +During that time I passed many a fine night in the observer's +gallery, examining different objects in the heavens with the aid of +this remarkable instrument. At the time I was there, the objects +principally studied were the nebulae, those faint stains of light +which lie on the background of the sky. Lord Rosse's telescope was +specially suited for the scrutiny of these objects, inasmuch as their +delicacy required all the light-grasping power which could be +provided. + +One of the greatest discoveries made by Lord Rosse, when his huge +instrument was first turned towards the heavens, consisted in the +detection of the spiral character of some of the nebulous forms. +When the extraordinary structure of these objects was first +announced, the discovery was received with some degree of +incredulity. Other astronomers looked at the same objects, and when +they failed to discern--and they frequently did fail to discern--the +spiral structure which Lord Rosse had indicated, they drew the +conclusion that this spiral structure did not exist. They thought it +must be due possibly to some instrumental defect or to the +imagination of the observer. It was, however, hardly possible for +any one who was both willing and competent to examine into the +evidence, to doubt the reality of Lord Rosse's discoveries. It +happens, however, that they have been recently placed beyond all +doubt by testimony which it is impossible to gainsay. A witness +never influenced by imagination has now come forward, and the +infallible photographic plate has justified Lord Rosse. Among the +remarkable discoveries which Dr. Isaac Roberts has recently made in +the application of his photographic apparatus to the heavens, there +is none more striking than that which declares, not only that the +nebulae which Lord Rosse described as spirals, actually do possess +the character so indicated, but that there are many others of the +same description. He has even brought to light the astonishingly +interesting fact that there are invisible objects of this class which +have never been seen by human eye, but whose spiral character is +visible to the peculiar delicacy of the photographic telescope. + +In his earlier years, Lord Rosse himself used to be a diligent +observer of the heavenly bodies with the great telescope which was +completed in the year 1845. But I think that those who knew Lord +Rosse well, will agree that it was more the mechanical processes +incidental to the making of the telescope which engaged his interest +than the actual observations with the telescope when it was +completed. Indeed one who was well acquainted with him believed Lord +Rosse's special interest in the great telescope ceased when the last +nail had been driven into it. But the telescope was never allowed to +lie idle, for Lord Rosse always had associated with him some ardent +young astronomer, whose delight it was to employ to the uttermost the +advantages of his position in exploring the wonders of the sky. Among +those who were in this capacity in the early days of the great +telescope, I may mention my esteemed friend Dr. Johnston Stoney. + +Such was the renown of Lord Rosse himself, brought about by his +consummate mechanical genius and his astronomical discoveries, and +such the interest which gathered around the marvellous workshops at +Birr castle, wherein his monumental exhibitions of optical skill were +constructed, that visitors thronged to see him from all parts of the +world. His home at Parsonstown became one of the most remarkable +scientific centres in Great Britain; thither assembled from time to +time all the leading men of science in the country, as well as many +illustrious foreigners. For many years Lord Rosse filled with marked +distinction the exalted position of President of the Royal Society, +and his advice and experience in practical mechanical matters were +always at the disposal of those who sought his assistance. Personally +and socially Lord Rosse endeared himself to all with whom he came in +contact. I remember one of the attendants telling me that on one +occasion he had the misfortune to let fall and break one of the small +mirrors on which Lord Rosse had himself expended many hours of hard +personal labour. The only remark of his lordship was that "accidents +will happen." + +The latter years of his life Lord Rosse passed in comparative +seclusion; he occasionally went to London for a brief sojourn during +the season, and he occasionally went for a cruise in his yacht; but +the greater part of the year he spent at Birr Castle, devoting +himself largely to the study of political and social questions, and +rarely going outside the walls of his demesne, except to church on +Sunday mornings. He died on October 31, 1867. + +He was succeeded by his eldest son, the present Earl of Rosse, who +has inherited his father's scientific abilities, and done much +notable work with the great telescope. + + + + +AIRY. + + +In our sketch of the life of Flamsteed, we have referred to the +circumstances under which the famous Observatory that crowns +Greenwich Hill was founded. We have also had occasion to mention +that among the illustrious successors of Flamsteed both Halley and +Bradley are to be included. But a remarkable development of +Greenwich Observatory from the modest establishment of early days +took place under the direction of the distinguished astronomer whose +name is at the head of this chapter. By his labours this temple of +science was organised to such a degree of perfection that it has +served in many respects as a model for other astronomical +establishments in various parts of the world. An excellent account +of Airy's career has been given by Professor H. H. Turner, in the +obituary notice published by the Royal Astronomical Society. To this +I am indebted for many of the particulars here to be set down +concerning the life of the illustrious Astronomer Royal. + +The family from which Airy took his origin came from Kentmere, in +Westmoreland. His father, William Airy, belonged to a Lincolnshire +branch of the same stock. His mother's maiden name was Ann Biddell, +and her family resided at Playford, near Ipswich. William Airy held +some small government post which necessitated an occasional change of +residence to different parts of the country, and thus it was that his +son, George Biddell, came to be born at Alnwick, on 27th July, 1801. +The boy's education, so far as his school life was concerned was +partly conducted at Hereford and partly at Colchester. He does not, +however, seem to have derived much benefit from the hours which he +passed in the schoolroom. But it was delightful to him to spend his +holidays on the farm at Playford, where his uncle, Arthur Biddell, +showed him much kindness. The scenes of his early youth remained +dear to Airy throughout his life, and in subsequent years he himself +owned a house at Playford, to which it was his special delight to +resort for relaxation during the course of his arduous career. In +spite of the defects of his school training he seems to have +manifested such remarkable abilities that his uncle decided to enter +him in Cambridge University. He accordingly joined Trinity College +as a sizar in 1819, and after a brilliant career in mathematical and +physical science he graduated as Senior Wrangler in 1823. It may be +noted as an exceptional circumstance that, notwithstanding the +demands on his time in studying for his tripos, he was able, after +his second term of residence, to support himself entirely by taking +private pupils. In the year after he had taken his degree he was +elected to a Fellowship at Trinity College. + +Having thus gained an independent position, Airy immediately entered +upon that career of scientific work which he prosecuted without +intermission almost to the very close of his life. One of his most +interesting researches in these early days is on the subject of +Astigmatism, which defect he had discovered in his own eyes. His +investigations led him to suggest a means of correcting this defect +by using a pair of spectacles with lenses so shaped as to counteract +the derangement which the astigmatic eye impressed upon the rays of +light. His researches on this subject were of a very complete +character, and the principles he laid down are to the present day +practically employed by oculists in the treatment of this +malformation. + +On the 7th of December, 1826, Airy was elected to the Lucasian +Professorship of Mathematics in the University of Cambridge, the +chair which Newton's occupancy had rendered so illustrious. His +tenure of this office only lasted for two years, when he exchanged it +for the Plumian Professorship. The attraction which led him to +desire this change is doubtless to be found in the circumstance that +the Plumian Professorship of Astronomy carried with it at that time +the appointment of director of the new astronomical observatory, the +origin of which must now be described. + +Those most interested in the scientific side of University life +decided in 1820 that it would be proper to found an astronomical +observatory at Cambridge. Donations were accordingly sought for this +purpose, and upwards of 6,000 pounds were contributed by members of +the University and the public. To this sum 5,000 pounds were added +by a grant from the University chest, and in 1824 further sums +amounting altogether to 7,115 pounds were given by the University for +the same object. The regulations as to the administration of the new +observatory placed it under the management of the Plumian Professor, +who was to be provided with two assistants. Their duties were to +consist in making meridian observations of the sun, moon, and the +stars, and the observations made each year were to be printed and +published. The observatory was also to be used in the educational +work of the University, for it was arranged that smaller instruments +were to be provided by which students could be instructed in the +practical art of making astronomical observations. + +The building of the Cambridge Astronomical Observatory was completed +in 1824, but in 1828, when Airy entered on the discharge of his +duties as Director, the establishment was still far from completion, +in so far as its organisation was concerned. Airy commenced his work +so energetically that in the next year after his appointment he was +able to publish the first volume of "Cambridge Astronomical +Observations," notwithstanding that every part of the work, from the +making of observations to the revising of the proof-sheets, had to be +done by himself. + +It may here be remarked that these early volumes of the publications +of the Cambridge Observatory contained the first exposition of those +systematic methods of astronomical work which Airy afterwards +developed to such a great extent at Greenwich, and which have been +subsequently adopted in many other places. No more profitable +instruction for the astronomical beginner can be found than that +which can be had by the study of these volumes, in which the Plumian +Professor has laid down with admirable clearness the true principles +on which meridian work should be conducted. + +[PLATE: SIR GEORGE AIRY. +From a Photograph by Mr. E.P. Adams, Greenwich.] + +Airy gradually added to the instruments with which the observatory +was originally equipped. A mural circle was mounted in 1832, and in +the same year a small equatorial was erected by Jones. This was made +use of by Airy in a well-known series of observations of Jupiter's +fourth satellite for the determination of the mass of the great +planet. His memoir on this subject fully ex pounds the method of +finding the weight of a planet from observations of the movements of +a satellite by which the planet is attended. This is, indeed, a +valuable investigation which no student of astronomy can afford to +neglect. The ardour with which Airy devoted himself to astronomical +studies may be gathered from a remarkable report on the progress of +astronomy during the present century, which he communicated to the +British Association at its second meeting in 1832. In the early +years of his life at Cambridge his most famous achievement was +connected with a research in theoretical astronomy for which +consummate mathematical power was required. We can only give a brief +account of the Subject, for to enter into any full detail with regard +to it would be quite out of the question. + +Venus is a planet of about the same size and the same weight as the +earth, revolving in an orbit which lies within that described by our +globe. Venus, consequently, takes less time than the earth to +accomplish one revolution round the sun, and it happens that the +relative movements of Venus and the earth are so proportioned that in +the time in which our earth accomplishes eight of her revolutions the +other planet will have accomplished almost exactly thirteen. It, +therefore, follows that if the earth and Venus are in line with the +sun at one date, then in eight years later both planets will again be +found at the same points in their orbits. In those eight years the +earth has gone round eight times, and has, therefore, regained its +original position, while in the same period Venus has accomplished +thirteen complete revolutions, and, therefore, this planet also has +reached the same spot where it was at first. Venus and the earth, of +course, attract each other, and in consequence of these mutual +attractions the earth is swayed from the elliptic track which it +would otherwise pursue. In like manner Venus is also forced by the +attraction of the earth to revolve in a track which deviates from +that which it would otherwise follow. Owing to the fact that the sun +is of such preponderating magnitude (being, in fact, upwards of +300,000 times as heavy as either Venus or the earth), the +disturbances induced in the motion of either planet, in consequence +of the attraction of the other, are relatively insignificant to the +main controlling agency by which each of the movements is governed. +It is, however, possible under certain circumstances that the +disturbing effects produced upon one planet by the other can become +so multiplied as to produce peculiar effects which attain measurable +dimensions. Suppose that the periodic times in which the earth and +Venus revolved had no simple relation to each other, then the points +of their tracks in which the two planets came into line with the sun +would be found at different parts of the orbits, and consequently the +disturbances would to a great extent neutralise each other, and +produce but little appreciable effect. As, however, Venus and the +earth come back every eight years to nearly the same positions at the +same points of their track, an accumulative effect is produced. For +the disturbance of one planet upon the other will, of course, be +greatest when those two planets are nearest, that is, when they lie +in line with the sun and on the same side of it. Every eight years a +certain part of the orbit of the earth is, therefore, disturbed by +the attraction of Venus with peculiar vigour. The consequence is +that, owing to the numerical relation between the movements of the +planets to which I have referred, disturbing effects become +appreciable which would otherwise be too small to permit of +recognition. Airy proposed to himself to compute the effects which +Venus would have on the movement of the earth in consequence of the +circumstance that eight revolutions of the one planet required almost +the same time as thirteen revolutions of the other. This is a +mathematical inquiry of the most arduous description, but the Plumian +Professor succeeded in working it out, and he had, accordingly, the +gratification of announcing to the Royal Society that he had detected +the influence which Venus was thus able to assert on the movement of +our earth around the sun. This remarkable investigation gained for +its author the gold medal of the Royal Astronomical Society in the +year 1832. + +In consequence of his numerous discoveries, Airy's scientific fame +had become so well recognised that the Government awarded him a +special pension, and in 1835, when Pond, who was then Astronomer +Royal, resigned, Airy was offered the post at Greenwich. There was +in truth, no scientific inducement to the Plumian Professor to leave +the comparatively easy post he held at Cambridge, in which he had +ample leisure to devote himself to those researches which specially +interested him, and accept that of the much more arduous observatory +at Greenwich. There were not even pecuniary inducements to make the +change; however, he felt it to be his duty to accede to the request +which the Government had made that he would take up the position +which Pond had vacated, and accordingly Airy went to Greenwich as +Astronomer Royal on October 1st, 1835. + +He immediately began with his usual energy to organise the systematic +conduct of the business of the National Observatory. To realise one +of the main characteristics of Airy's great work at Greenwich, it is +necessary to explain a point that might not perhaps be understood +without a little explanation by those who have no practical +experience in an observatory. In the work of an establishment such +as Greenwich, an observation almost always consists of a measurement +of some kind. The observer may, for instance, be making a +measurement of the time at which a star passes across a spider line +stretched through the field of view; on another occasion his object +may be the measurement of an angle which is read off by examining +through a microscope the lines of division on a graduated circle when +the telescope is so pointed that the star is placed on a certain mark +in the field of view. In either case the immediate result of the +astronomical observation is a purely numerical one, but it rarely +happens, indeed we may say it never happens, that the immediate +numerical result which the observation gives expresses directly the +quantity which we are really seeking for. No doubt the observation +has been so designed that the quantity we want to find can be +obtained from the figures which the measurement gives, but the object +sought is not those figures, for there are always a multitude of +other influences by which those figures are affected. For example, +if an observation were to be perfect, then the telescope with which +the observation is made should be perfectly placed in the exact +position which it ought to occupy; this is, however, never the case, +for no mechanic can ever construct or adjust a telescope so perfectly +as the wants of the astronomer demand. The clock also by which we +determine the time of the observation should be correct, but this is +rarely if ever the case. We have to correct our observations for +such errors, that is to say, we have to determine the errors in the +positions of our telescopes and the errors in the going of our +clocks, and then we have to determine what the observations would +have been had our telescopes been absolutely perfect, and had our +clocks been absolutely correct. There are also many other matters +which have to be attended to in order to reduce our observations so +as to obtain from the figures as yielded to the observer at the +telescope the actual quantities which it is his object to determine. + +The work of effecting these reductions is generally a very intricate +and laborious matter, so that it has not unfrequently happened that +while observations have accumulated in an observatory, yet the +tedious duty of reducing these observations has been allowed to fall +into arrear. When Airy entered on his duties at Greenwich he found +there an enormous mass of observations which, though implicitly +containing materials of the greatest value to astronomers, were, in +their unreduced form, entirely unavailable for any useful purpose. +He, therefore, devoted himself to coping with the reduction of the +observations of his predecessors. He framed systematic methods by +which the reductions were to be effected, and he so arranged the work +that little more than careful attention to numerical accuracy would +be required for the conduct of the operations. Encouraged by the +Admiralty, for it is under this department that Greenwich Observatory +is placed, the Astronomer Royal employed a large force of computers +to deal with the work. BY his energy and admirable organisation he +managed to reduce an extremely valuable series of planetary +observations, and to publish the results, which have been of the +greatest importance to astronomical investigation. + +The Astronomer Royal was a capable, practical engineer as well as an +optician, and he presently occupied himself by designing astronomical +instruments of improved pattern, which should replace the antiquated +instruments he found in the observatory. In the course of years the +entire equipment underwent a total transformation. He ordered a +great meridian circle, every part of which may be said to have been +formed from his own designs. He also designed the mounting for a +fine equatorial telescope worked by a driving clock, which he had +himself invented. Gradually the establishment at Greenwich waxed +great under his incessant care. It was the custom for the +observatory to be inspected every year by a board of visitors, whose +chairman was the President of the Royal Society. At each annual +visitation, held on the first Saturday in June, the visitors received +a report from the Astronomer Royal, in which he set forth the +business which had been accomplished during the past year. It was on +these occasions that applications were made to the Admiralty, either +for new instruments or for developing the work of the observatory in +some other way. After the more official business of the inspection +was over, the observatory was thrown open to visitors, and hundreds +of people enjoyed on that day the privilege of seeing the national +observatory. These annual gatherings are happily still continued, +and the first Saturday in June is known to be the occasion of one of +the most interesting reunions of scientific men which takes place in +the course of the year. + +Airy's scientific work was, however, by no means confined to the +observatory. He interested himself largely in expeditions for the +observation of eclipses and in projects for the measurement of arcs +on the earth. He devoted much attention to the collection of magnetic +observations from various parts of the world. Especially will it be +remembered that the circumstances of the transits of Venus, which +occurred in 1874 and in 1882, were investigated by him, and under his +guidance expeditions were sent forth to observe the transits from +those localities in remote parts of the earth where observations most +suitable for the determination of the sun's distance from the earth +could be obtained. The Astronomer Royal also studied tidal +phenomena, and he rendered great service to the country in the +restoration of the standards of length and weight which had been +destroyed in the great fire at the House of Parliament in October, +1834. In the most practical scientific matters his advice was often +sought, and was as cheerfully rendered. Now we find him engaged in +an investigation of the irregularities of the compass in iron ships, +with a view to remedying its defects; now we find him reporting on +the best gauge for railways. Among the most generally useful +developments of the observatory must be mentioned the telegraphic +method for the distribution of exact time. By arrangement with the +Post Office, the astronomers at Greenwich despatch each morning a +signal from the observatory to London at ten o'clock precisely. By +special apparatus, this signal is thence distributed automatically +over the country, so as to enable the time to be known everywhere +accurately to a single second. It was part of the same system that a +time ball should be dropped daily at one o'clock at Deal, as well as +at other places, for the purpose of enabling ship's chronometers to +be regulated. + +Airy's writings were most voluminous, and no fewer than forty-eight +memoirs by him are mentioned in the "Catalogue of Scientific +Memoirs," published by the Royal Society up to the year 1873, and +this only included ten years out of an entire life of most +extraordinary activity. Many other subjects besides those of a +purely scientific character from time to time engaged his attention. +He wrote, for instance, a very interesting treatise on the Roman +invasion of Britain, especially with a view of determining the port +from which Caesar set forth from Gaul, and the point at which he +landed on the British coast. Airy was doubtless led to this +investigation by his study of the tidal phenomena in the Straits of +Dover. Perhaps the Astronomer Royal is best known to the general +reading public by his excellent lectures on astronomy, delivered at +the Ipswich Museum in 1848. This book has passed through many +editions, and it gives a most admirable account of the manner in +which the fundamental problems in astronomy have to be attacked. + +As years rolled by almost every honour and distinction that could be +conferred upon a scientific man was awarded to Sir George Airy. He +was, indeed, the recipient of other honours not often awarded for +scientific distinction. Among these we may mention that in 1875 he +received the freedom of the City of London, "as a recognition of his +indefatigable labours in astronomy, and of his eminent services in +the advancement of practical science, whereby he has so materially +benefited the cause of commerce and civilisation." + +Until his eightieth year Airy continued to discharge his labours at +Greenwich with unflagging energy. At last, on August 15th, 1881, he +resigned the office which he had held so long with such distinction +to himself and such benefit to his country. He had married in 1830 +the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died +in 1875, and three sons and three daughters survived him. One +daughter is the wife of Dr. Routh, of Cambridge, and his other +daughters were the constant companions of their father during the +declining years of his life. Up to the age of ninety he enjoyed +perfect physical health, but an accidental fall which then occurred +was attended with serious results. He died on Saturday, January 2nd, +1892, and was buried in the churchyard at Playford. + + + + +HAMILTON. + + +William Rowan Hamilton was born at midnight between the 3rd and 4th +of August, 1805, at Dublin, in the house which was then 29, but +subsequently 36, Dominick Street. His father, Archibald Hamilton, +was a solicitor, and William was the fourth of a family of nine. With +reference to his descent, it may be sufficient to notice that his +ancestors appear to have been chiefly of gentle Irish families, but +that his maternal grandmother was of Scottish birth. When he was +about a year old, his father and mother decided to hand over the +education of the child to his uncle, James Hamilton, a clergyman of +Trim, in County Meath. James Hamilton's sister, Sydney, resided with +him, and it was in their home that the days of William's childhood +were passed. + +In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of +letters will be found, in which Aunt Sydney details the progress of +the boy to his mother in Dublin. Probably there is no record of an +infant prodigy more extraordinary than that which these letters +contain. At three years old his aunt assured the mother that William +is "a hopeful blade," but at that time it was his physical vigour to +which she apparently referred; for the proofs of his capacity, which +she adduces, related to his prowess in making boys older than himself +fly before him. In the second letter, a month later, we hear that +William is brought in to read the Bible for the purpose of putting to +shame other boys double his age who could not read nearly so well. +Uncle James appears to have taken much pains with William's +schooling, but his aunt said that "how he picks up everything is +astonishing, for he never stops playing and jumping about." When he +was four years and three months old, we hear that he went out to dine +at the vicar's, and amused the company by reading for them equally +well whether the book was turned upside down or held in any other +fashion. His aunt assures the mother that "Willie is a most sensible +little creature, but at the same time has a great deal of roguery." +At four years and five months old he came up to pay his mother a +visit in town, and she writes to her sister a description of the +boy;-- + +"His reciting is astonishing, and his clear and accurate knowledge of +geography is beyond belief; he even draws the countries with a pencil +on paper, and will cut them out, though not perfectly accurate, yet +so well that a anybody knowing the countries could not mistake them; +but, you will think this nothing when I tell you that he reads Latin, +Greek, and Hebrew." + +Aunt Sydney recorded that the moment Willie got back to Trim he was +desirous of at once resuming his former pursuits. He would not eat +his breakfast till his uncle had heard him his Hebrew, and he +comments on the importance of proper pronunciation. At five he was +taken to see a friend, to whom he repeated long passages from +Dryden. A gentleman present, who was not unnaturally sceptical about +Willie's attainments, desired to test him in Greek, and took down a +copy of Homer which happened to have the contracted type, and to his +amazement Willie went on with the greatest ease. At six years and +nine months he was translating Homer and Virgil; a year later his +uncle tells us that William finds so little difficulty in learning +French and Italian, that he wishes to read Homer in French. He is +enraptured with the Iliad, and carries it about with him, repeating +from it whatever particularly pleases him. At eight years and one +month the boy was one of a party who visited the Scalp in the Dublin +mountains, and he was so delighted with the scenery that he forthwith +delivered an oration in Latin. At nine years and six months he is +not satisfied until he learns Sanscrit; three months later his thirst +for the Oriental languages is unabated, and at ten years and four +months he is studying Arabic and Persian. When nearly twelve he +prepared a manuscript ready for publication. It was a "Syriac +Grammar," in Syriac letters and characters compiled from that of +Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was +fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a +visit to Dublin, and, as a practical exercise in his Oriental +languages, the young scholar addressed to his Excellency a letter in +Persian; a translation of which production is given by Mr. Graves. +When William was fourteen he had the misfortune to lose his father; +and he had lost his mother two years previously. The boy and his +three sisters were kindly provided for by different members of the +family on both sides. + +It was when William was about fifteen that his attention began to be +turned towards scientific subjects. These were at first regarded +rather as a relaxation from the linguistic studies with which he had +been so largely occupied. On November 22nd, 1820, he notes in his +journal that he had begun Newton's "Principia": he commenced also the +study of astronomy by observing eclipses, occultations, and similar +phenomena. When he was sixteen we learn that he had read conic +sections, and that he was engaged in the study of pendulums. After +an attack of illness, he was moved for change to Dublin, and in May, +1822, we find him reading the differential calculus and Laplace's +"Mecanique Celeste." He criticises an important part of Laplace's +work relative to the demonstration of the parallelogram of forces. In +this same year appeared the first gushes of those poems which +afterwards flowed in torrents. + +His somewhat discursive studies had, however, now to give place to a +more definite course of reading in preparation for entrance to the +University of Dublin. The tutor under whom he entered, Charles +Boyton, was himself a distinguished man, but he frankly told the +young William that he could be of little use to him as a tutor, for +his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom +this is recorded, adds, "But there is one thing which Boyton would +promise to be to him, and that was a FRIEND; and that one proof he +would give of this should be that, if ever he saw William beginning +to be UPSET by the sensation he would excite, and the notice he would +attract, he would tell him of it." At the beginning of his college +career he distanced all his competitors in every intellectual +pursuit. At his first term examination in the University he was +first in Classics and first in Mathematics, while he received the +Chancellor's prize for a poem on the Ionian Islands, and another for +his poem on Eustace de St. Pierre. + +There is abundant testimony that Hamilton had "a heart for friendship +formed." Among the warmest of the friends whom he made in these +early days was the gifted Maria Edgeworth, who writes to her sister +about "young Mr. Hamilton, an admirable Crichton of eighteen, a real +prodigy of talents, who Dr. Brinkley says may be a second Newton, +quiet, gentle, and simple." His sister Eliza, to whom he was +affectionately attached, writes to him in 1824:-- + +"I had been drawing pictures of you in my mind in your study at +Cumberland Street with 'Xenophon,' &c., on the table, and you, with +your most awfully sublime face of thought, now sitting down, and now +walking about, at times rubbing your hands with an air of +satisfaction, and at times bursting forth into some very heroical +strain of poetry in an unknown language, and in your own internal +solemn ventriloquist-like voice, when you address yourself to the +silence and solitude of your own room, and indeed, at times, even +when your mysterious poetical addresses are not quite unheard." + +This letter is quoted because it refers to a circumstance which all +who ever met with Hamilton, even in his latest years, will remember. +He was endowed with two distinct voices, one a high treble, the other +a deep bass, and he alternately employed these voices not only in +ordinary conversation, but when he was delivering an address on the +profundities of Quaternions to the Royal Irish Academy, or on +similar occasions. His friends had long grown so familiar with this +peculiarity that they were sometimes rather surprised to find how +ludicrous it appeared to strangers. + +Hamilton was fortunate in finding, while still at a very early age, a +career open before him which was worthy of his talents. He had not +ceased to be an undergraduate before he was called to fill an +illustrious chair in his university. The circumstances are briefly +as follows. + +We have already mentioned that, in 1826, Brinkley was appointed +Bishop of Cloyne, and the professorship of astronomy thereupon became +vacant. Such was Hamilton's conspicuous eminence that, +notwithstanding he was still an undergraduate, and had only just +completed his twenty-first year, he was immediately thought of as a +suitable successor to the chair. Indeed, so remarkable were his +talents in almost every direction that had the vacancy been in the +professorship of classics or of mathematics, of English literature or +of metaphysics, of modern or of Oriental languages, it seems +difficult to suppose that he would not have occurred to every one as +a possible successor. The chief ground, however, on which the +friends of Hamilton urged his appointment was the earnest of original +power which he had already shown in a research on the theory of +Systems of Rays. This profound work created a new branch of optics, +and led a few years later to a superb discovery, by which the fame of +its author became world-wide. + +At first Hamilton thought it would be presumption for him to apply +for so exalted a position; he accordingly retired to the country, and +resumed his studies for his degree. Other eminent candidates came +forward, among them some from Cambridge, and a few of the Fellows +from Trinity College, Dublin, also sent in their claims. It was not +until Hamilton received an urgent letter from his tutor Boyton, in +which he was assured of the favourable disposition of the Board +towards his candidature, that he consented to come forward, and on +June 16th, 1827, he was unanimously chosen to succeed the Bishop of +Cloyne as Professor of Astronomy in the University. The appointment +met with almost universal approval. It should, however, be noted +that Brinkley, whom Hamilton succeeded, did not concur in the general +sentiment. No one could have formed a higher opinion than he had +done of Hamilton's transcendent powers; indeed, it was on that very +ground that he seemed to view the appointment with disapprobation. +He considered that it would have been wiser for Hamilton to have +obtained a Fellowship, in which capacity he would have been able to +exercise a greater freedom in his choice of intellectual pursuits. +The bishop seems to have thought, and not without reason, that +Hamilton's genius would rather recoil from much of the routine work +of an astronomical establishment. Now that Hamilton's whole life is +before us, it is easy to see that the bishop was entirely wrong. It +is quite true that Hamilton never became a skilled astronomical +observer; but the seclusion of the observatory was eminently +favourable to those gigantic labours to which his life was devoted, +and which have shed so much lustre, not only on Hamilton himself, but +also on his University and his country. + +In his early years at Dunsink, Hamilton did make some attempts at a +practical use of the telescopes, but he possessed no natural aptitude +for such work, while exposure which it involved seems to have acted +injuriously on his health. He, therefore, gradually allowed his +attention to be devoted to those mathematical researches in which he +had already given such promise of distinction. Although it was in +pure mathematics that he ultimately won his greatest fame, yet he +always maintained and maintained with justice, that he had ample +claims to the title of an astronomer. In his later years he set +forth this position himself in a rather striking manner. De Morgan +had written commending to Hamilton's notice Grant's "History of +Physical Astronomy." After becoming acquainted with the book, +Hamilton writes to his friend as follows:-- + +"The book is very valuable, and very creditable to its composer. But +your humble servant may be pardoned if he finds himself somewhat +amused at the title, 'History of Physical Astronomy from the Earliest +Ages to the Middle of the Nineteenth Century,' when he fails to +observe any notice of the discoveries of Sir W. R. Hamilton in the +theory of the 'Dynamics of the Heavens.'" + +The intimacy between the two correspondents will account for the tone +of this letter; and, indeed, Hamilton supplies in the lines which +follow ample grounds for his complaint. He tells how Jacobi spoke of +him in Manchester in 1842 as "le Lagrange de votre pays," and how +Donkin had said that, "The Analytical Theory of Dynamics as it exists +at present is due mainly to the labours of La Grange Poisson, +Sir W. R. Hamilton, and Jacobi, whose researches on this subject +present a series of discoveries hardly paralleled for their elegance +and importance in any other branch of mathematics." In the same +letter Hamilton also alludes to the success which had attended the +applications of his methods in other hands than his own to the +elucidation of the difficult subject of Planetary Perturbations. +Even had his contributions to science amounted to no more than these +discoveries, his tenure of the chair would have been an illustrious +one. It happens, however, that in the gigantic mass of his +intellectual work these researches, though intrinsically of such +importance, assume what might almost be described as a relative +insignificance. + +The most famous achievement of Hamilton's earlier years at the +observatory was the discovery of conical refraction. This was one of +those rare events in the history of science, in which a sagacious +calculation has predicted a result of an almost startling character, +subsequently confirmed by observation. At once this conferred on the +young professor a world-wide renown. Indeed, though he was still +only twenty-seven, he had already lived through an amount of +intellectual activity which would have been remarkable for a man of +threescore and ten. + +Simultaneously with his growth in fame came the growth of his several +friendships. There were, in the first place, his scientific +friendships with Herschel, Robinson, and many others with whom he had +copious correspondence. In the excellent biography to which I have +referred, Hamilton's correspondence with Coleridge may be read, as +can also the letters to his lady correspondents, among them being +Maria Edgeworth, Lady Dunraven, and Lady Campbell. Many of these +sheets relate to literary matters, but they are largely intermingled +With genial pleasantry, and serve at all events to show the affection +and esteem with which he was regarded by all who had the privilege of +knowing him. There are also the letters to the sisters whom he +adored, letters brimming over with such exalted sentiment, that most +ordinary sisters would be tempted to receive them with a smile in the +excessively improbable event of their still more ordinary brothers +attempting to pen such effusions. There are also indications of +letters to and from other young ladies who from time to time were the +objects of Hamilton's tender admiration. We use the plural +advisedly, for, as Mr. Graves has set forth, Hamilton's love affairs +pursued a rather troubled course. The attention which he lavished on +one or two fair ones was not reciprocated, and even the intense +charms of mathematical discovery could not assuage the pangs which +the disappointed lover experienced. At last he reached the haven of +matrimony in 1833, when he was married to Miss Bayly. Of his married +life Hamilton said, many years later to De Morgan, that it was as +happy as he expected, and happier than he deserved. He had two sons, +William and Archibald, and one daughter, Helen, who became the wife +of Archdeacon O'Regan. + +[PLATE: SIR W. ROWAN HAMILTON.] + +The most remarkable of Hamilton's friendships in his early years was +unquestionably that with Wordsworth. It commenced with Hamilton's +visit to Keswick; and on the first evening, when the poet met the +young mathematician, an incident occurred which showed the mutual +interest that was aroused. Hamilton thus describes it in a letter to +his sister Eliza:-- + +"He (Wordsworth) walked back with our party as far as their lodge, +and then, on our bidding Mrs. Harrison good-night, I offered to walk +back with him while my party proceeded to the hotel. This offer he +accepted, and our conversation had become so interesting that when we +had arrived at his home, a distance of about a mile, he proposed to +walk back with me on my way to Ambleside, a proposal which you may be +sure I did not reject; so far from it that when he came to turn once +more towards his home I also turned once more along with him. It was +very late when I reached the hotel after all this walking." + +Hamilton also submitted to Wordsworth an original poem, entitled +"It Haunts me Yet." The reply of Wordsworth is worth repeating:-- + +"With a safe conscience I can assure you that, in my judgment, your +verses are animated with the poetic spirit, as they are evidently the +product of strong feeling. The sixth and seventh stanzas affected me +much, even to the dimming of my eyes and faltering of my voice while +I was reading them aloud. Having said this, I have said enough. Now +for the per contra. You will not, I am sure, be hurt when I tell you +that the workmanship (what else could be expected from so young a +writer?) is not what it ought to be. . . + +"My household desire to be remembered to you in no formal way. +Seldom have I parted--never, I was going to say--with one whom after +so short an acquaintance I lost sight of with more regret. I trust +we shall meet again." + +The further affectionate intercourse between Hamilton and Wordsworth +is fully set forth, and to Hamilton's latest years a recollection of +his "Rydal hours" was carefully treasured and frequently referred +to. Wordsworth visited Hamilton at the observatory, where a +beautiful shady path in the garden is to the present day spoken of as +"Wordsworth's Walk." + +It was the practice of Hamilton to produce a sonnet on almost every +occasion which admitted of poetical treatment, and it was his delight +to communicate his verses to his friends all round. When Whewell was +producing his "Bridgewater Treatises," he writes to Hamilton in +1833:-- + +"Your sonnet which you showed me expressed much better than I could +express it the feeling with which I tried to write this book, and I +once intended to ask your permission to prefix the sonnet to my book, +but my friends persuaded me that I ought to tell my story in my own +prose, however much better your verse might be." + +The first epoch-marking contribution to Theoretical Dynamics after +the time of Newton was undoubtedly made by Lagrange, in his discovery +of the general equations of Motion. The next great step in the same +direction was that taken by Hamilton in his discovery of a still more +comprehensive method. Of this contribution Hamilton writes to +Whewell, March 31st, 1834:-- + +"As to my late paper, a day or two ago sent off to London, it is +merely mathematical and deductive. I ventured, indeed, to call it +the 'Mecanique Analytique' of Lagrange, 'a scientific poem'; and +spoke of Dynamics, or the Science of Force, as treating of 'Power +acting by Law in Space and Time.' In other respects it is as +unpoetical and unmetaphysical as my gravest friends could desire." + +It may well be doubted whether there is a more beautiful chapter in +the whole of mathematical philosophy than that which contains +Hamilton's dynamical theory. It is disfigured by no tedious +complexity of symbols; it condescends not to any particular problems; +it is an all embracing theory, which gives an intellectual grasp of +the most appropriate method for discovering the result of the +application of force to matter. It is the very generality of this +doctrine which has somewhat impeded the applications of which it is +susceptible. The exigencies of examinations are partly responsible +for the fact that the method has not become more familiar to students +of the higher mathematics. An eminent professor has complained that +Hamilton's essay on dynamics was of such an extremely abstract +character, that he found himself unable to extract from it problems +suitable for his examination papers. + +The following extract is from a letter of Professor Sylvester to +Hamilton, dated 20th of September, 1841. It will show how his works +were appreciated by so consummate a mathematician as the writer:-- + +"Believe me, sir, it is not the least of my regrets in quitting this +empire to feel that I forego the casual occasion of meeting those +masters of my art, yourself chief amongst the number, whose +acquaintance, whose conversation, or even notice, have in themselves +the power to inspire, and almost to impart fresh vigour to the +understanding, and the courage and faith without which the efforts of +invention are in vain. The golden moments I enjoyed under your +hospitable roof at Dunsink, or moments such as they were, may +probably never again fall to my lot. + +"At a vast distance, and in an humble eminence, I still promise myself +the calm satisfaction of observing your blazing course in the +elevated regions of discovery. Such national honour as you are able +to confer on your country is, perhaps, the only species of that +luxury for the rich (I mean what is termed one's glory) which is not +bought at the expense of the comforts of the million." + +The study of metaphysics was always a favourite recreation when +Hamilton sought for a change from the pursuit of mathematics. In the +year 1834 we find him a diligent student of Kant; and, to show the +views of the author of Quaternions and of Algebra as the Science of +Pure Time on the "Critique of the Pure Reason," we quote the +following letter, dated 18th of July, 1834, from Hamilton to Viscount +Adare:-- + +"I have read a large part of the 'Critique of the Pure Reason,' and +find it wonderfully clear, and generally quite convincing. +Notwithstanding some previous preparation from Berkeley, and from my +own thoughts, I seem to have learned much from Kant's own statement +of his views of 'Space and Time.' Yet, on the whole, a large part of +my pleasure consists in recognising through Kant's works, opinions, +or rather views, which have been long familiar to myself, although +far more clearly and systematically expressed and combined by him. +. . . Kant is, I think, much more indebted than he owns, or, perhaps +knows, to Berkeley, whom he calls by a sneer, 'GUTEM Berkeley'. . . +as it were, 'good soul, well meaning man,' who was able for all that +to shake to its centre the world of human thought, and to effect a +revolution among the early consequences of which was the growth of +Kant himself." + +At several meetings of the British Association Hamilton was a very +conspicuous figure. Especially was this the case in 1835, when the +Association met in Dublin, and when Hamilton, though then but thirty +years old, had attained such celebrity that even among a very +brilliant gathering his name was perhaps the most renowned. A +banquet was given at Trinity College in honour of the meeting. The +distinguished visitors assembled in the Library of the University. +The Earl of Mulgrave, then Lord Lieutenant of Ireland, made this the +opportunity of conferring on Hamilton the honour of knighthood, +gracefully adding, as he did so: "I but set the royal, and therefore +the national mark, on a distinction already acquired by your genius +and labours." + +The banquet followed, writes Mr. Graves. "It was no little addition +to the honour Hamilton had already received that, when Professor +Whewell returned thanks for the toast of the University of Cambridge, +he thought it appropriate to add the words, 'There was one point +which strongly pressed upon him at that moment: it was now one +hundred and thirty years since a great man in another Trinity College +knelt down before his sovereign, and rose up Sir Isaac Newton.' The +compliment was welcomed by immense applause." + +A more substantial recognition of the labours of Hamilton took place +subsequently. He thus describes it in a letter to Mr. Graves of 14th +of November, 1843:-- + +"The Queen has been pleased--and you will not doubt that it was +entirely unsolicited, and even unexpected, on my part--'to express +her entire approbation of the grant of a pension of two hundred +pounds per annum from the Civil List' to me for scientific services. +The letters from Sir Robert Peel and from the Lord Lieutenant of +Ireland in which this grant has been communicated or referred to have +been really more gratifying to my feelings than the addition to my +income, however useful, and almost necessary, that may have been." + +The circumstances we have mentioned might lead to the supposition +that Hamilton was then at the zenith of his fame but this was not +so. It might more truly be said, that his achievements up to this +point were rather the preliminary exercises which fitted him for the +gigantic task of his life. The name of Hamilton is now chiefly +associated with his memorable invention of the calculus of +Quaternions. It was to the creation of this branch of mathematics +that the maturer powers of his life were devoted; in fact he gives us +himself an illustration of how completely habituated he became to the +new modes of thought which Quaternions originated. In one of his +later years he happened to take up a copy of his famous paper on +Dynamics, a paper which at the time created such a sensation among +mathematicians, and which is at this moment regarded as one of the +classics of dynamical literature. He read, he tells us, his paper +with considerable interest, and expressed his feelings of +gratification that he found himself still able to follow its +reasoning without undue effort. But it seemed to him all the time as +a work belonging to an age of analysis now entirely superseded. + +In order to realise the magnitude of the revolution which Hamilton +has wrought in the application of symbols to mathematical +investigation, it is necessary to think of what Hamilton did beside +the mighty advance made by Descartes. To describe the character of +the quaternion calculus would be unsuited to the pages of this work, +but we may quote an interesting letter, written by Hamilton from his +death-bed, twenty-two years later, to his son Archibald, in which he +has recorded the circumstances of the discovery:-- + +"Indeed, I happen to be able to put the finger of memory upon the year +and month--October, 1843--when having recently returned from visits +to Cork and Parsonstown, connected with a meeting of the British +Association, the desire to discover the laws of multiplication +referred to, regained with me a certain strength and earnestness +which had for years been dormant, but was then on the point of being +gratified, and was occasionally talked of with you. Every morning in +the early part of the above-cited month, on my coming down to +breakfast, your (then) little brother William Edwin, and yourself, +used to ask me, 'Well papa, can you multiply triplets?' Whereto I +was always obliged to reply, with a sad shake of the head: 'No, I +can only ADD and subtract them,' + +"But on the 16th day of the same month--which happened to be Monday, +and a Council day of the Royal Irish Academy--I was walking in to +attend and preside, and your mother was walking with me along the +Royal Canal, to which she had perhaps driven; and although she talked +with me now and then, yet an UNDERCURRENT of thought was going on in +my mind which gave at last a RESULT, whereof it is not too much to +say that I felt AT ONCE the importance. An ELECTRIC circuit seemed +to CLOSE; and a spark flashed forth the herald (as I FORESAW +IMMEDIATELY) of many long years to come of definitely directed +thought and work by MYSELF, if spared, and, at all events, on the +part of OTHERS if I should even be allowed to live long enough +distinctly to communicate the discovery. Nor could I resist the +impulse--unphilosophical as it may have been--to cut with a knife on +a stone of Brougham Bridge as we passed it, the fundamental formula +which contains the SOLUTION of the PROBLEM, but, of course, the +inscription has long since mouldered away. A more durable notice +remains, however, on the Council Books of the Academy for that day +(October 16, 1843), which records the fact that I then asked for and +obtained leave to read a Paper on 'Quaternions,' at the First General +Meeting of the Session; which reading took place accordingly, on +Monday, the 13th of November following." + +Writing to Professor Tait, Hamilton gives further particulars of the +same event. And again in a letter to the Rev. J. W. Stubbs:-- + +"To-morrow will be the fifteenth birthday of the Quaternions. They +started into life full-grown on the 16th October, 1843, as I was +walking with Lady Hamilton to Dublin, and came up to Brougham +Bridge--which my boys have since called Quaternion Bridge. I pulled +out a pocketbook which still exists, and made entry, on which at the +very moment I felt that it might be worth my while to expend the +labour of at least ten or fifteen years to come. But then it is fair +to say that this was because I felt a problem to have been at that +moment solved, an intellectual want relieved which had haunted me for +at least fifteen years before. + +"But did the thought of establishing such a system, in which +geometrically opposite facts--namely, two lines (or areas) which are +opposite IN SPACE give ALWAYS a positive product--ever come into +anybody's head till I was led to it in October, 1843, by trying to +extend my old theory of algebraic couples, and of algebra as the +science of pure time? As to my regarding geometrical addition of +lines as equivalent to composition of motions (and as performed by +the same rules), that is indeed essential in my theory but not +peculiar to it; on the contrary, I am only one of many who have been +led to this view of addition." + +Pilgrims in future ages will doubtless visit the spot commemorated by +the invention of Quaternions. Perhaps as they look at that by no +means graceful structure Quaternion Bridge, they will regret that the +hand of some Old Mortality had not been occasionally employed in +cutting the memorable inscription afresh. It is now irrecoverably +lost. + +It was ten years after the discovery that the great volume appeared +under the title of "Lectures on Quaternions," Dublin, 1853. The +reception of this work by the scientific world was such as might have +been expected from the extraordinary reputation of its author, and +the novelty and importance of the new calculus. His valued friend, +Sir John Herschel, writes to him in that style of which he was a +master:-- + +"Now, most heartily let me congratulate you on getting out your +book--on having found utterance, ore rotundo, for all that labouring +and seething mass of thought which has been from time to time sending +out sparks, and gleams, and smokes, and shaking the soil about you; +but now breaks into a good honest eruption, with a lava stream and a +shower of fertilizing ashes. + +"Metaphor and simile apart, there is work for a twelve-month to any +man to read such a book, and for half a lifetime to digest it, and I +am glad to see it brought to a conclusion." + +We may also record Hamilton's own opinion expressed to Humphrey +Lloyd:-- + +"In general, although in one sense I hope that I am actually growing +modest about the quaternions, from my seeing so many peeps and vistas +into future expansions of their principles, I still must assert that +this discovery appears to me to be as important for the middle of the +nineteenth century as the discovery of fluxions was for the close of +the seventeenth." + +Bartholomew Lloyd died in 1837. He had been the Provost of Trinity +College, and the President of the Royal Irish Academy. Three +candidates were put forward by their respective friends for the +vacant Presidency. One was Humphrey Lloyd, the son of the late +Provost, and the two others were Hamilton and Archbishop Whately. +Lloyd from the first urged strongly the claims of Hamilton, and +deprecated the putting forward of his own name. Hamilton in like +manner desired to withdraw in favour of Lloyd. The wish was strongly +felt by many of the Fellows of the College that Lloyd should be +elected, in consequence of his having a more intimate association +with collegiate life than Hamilton; while his scientific eminence was +world-wide. The election ultimately gave Hamilton a considerable +majority over Lloyd, behind whom the Archbishop followed at a +considerable distance. All concluded happily, for both Lloyd and the +Archbishop expressed, and no doubt felt, the pre-eminent claims of +Hamilton, and both of them cordially accepted the office of a +Vice-President, to which, according to the constitution of the +Academy, it is the privilege of the incoming President to nominate. + +In another chapter I have mentioned as a memorable episode in +astronomical history, that Sir J. Herschel went for a prolonged +sojourn to the Cape of Good Hope, for the purpose of submitting the +southern skies to the same scrutiny with the great telescope that his +father had given to the northern skies. The occasion of Herschel's +return after the brilliant success of his enterprise, was celebrated +by a banquet. On June 15th, 1838, Hamilton was assigned the high +honour of proposing the health of Herschel. This banquet is +otherwise memorable in Hamilton's career as being one of the two +occasions in which he was in the company of his intimate friend De +Morgan. + +In the year 1838 a scheme was adopted by the Royal Irish Academy for +the award of medals to the authors of papers which appeared to +possess exceptionally high merit. At the institution of the medal +two papers were named in competition for the prize. One was +Hamilton's "Memoir on Algebra, as the Science of Pure Time." The +other was Macullagh's paper on the "Laws of Crystalline Reflection +and Refraction." Hamilton expresses his gratification that, mainly +in consequence of his own exertions, he succeeded in having the medal +awarded to Macullagh rather than to himself. Indeed, it would almost +appear as if Hamilton had procured a letter from Sir J. Herschel, +which indicated the importance of Macullagh's memoir in such a way as +to decide the issue. It then became Hamilton's duty to award the +medal from the chair, and to deliver an address in which he expressed +his own sense of the excellence of Macullagh's scientific work. It +is the more necessary to allude to these points, because in the whole +of his scientific career it would seem that Macullagh was the only +man with whom Hamilton had ever even an approach to a dispute about +priority. The incident referred to took place in connection with the +discovery of conical refraction, the fame of which Macullagh made a +preposterous attempt to wrest from Hamilton. This is evidently +alluded to in Hamilton's letter to the Marquis of Northampton, dated +June 28th, 1838, in which we read:-- + +"And though some former circumstances prevented me from applying to +the person thus distinguished the sacred name of FRIEND, I had the +pleasure of doing justice...to his high intellectual merits... I +believe he was not only gratified but touched, and may, perhaps, +regard me in future with feelings more like those which I long to +entertain towards him." + +Hamilton was in the habit, from time to time, of commencing the +keeping of a journal, but it does not appear to have been +systematically conducted. Whatever difficulties the biographer may +have experienced from its imperfections and irregularities, seem to +be amply compensated for by the practice which Hamilton had of +preserving copies of his letters, and even of comparatively +insignificant memoranda. In fact, the minuteness with which +apparently trivial matters were often noted down appears almost +whimsical. He frequently made a memorandum of the name of the person +who carried a letter to the post, and of the hour in which it was +despatched. On the other hand, the letters which he received were +also carefully preserved in a mighty mass of manuscripts, with which +his study was encumbered, and with which many other parts of the +house were not unfrequently invaded. If a letter was laid aside for +a few hours, it would become lost to view amid the seething mass of +papers, though occasionally, to use his own expression, it might be +seen "eddying" to the surface in some later disturbance. + +The great volume of "Lectures on Quaternions" had been issued, and +the author had received the honours which the completion of such a +task would rightfully bring him. The publication of an immortal work +does not, however, necessarily provide the means for paying the +printer's bill. The printing of so robust a volume was necessarily +costly; and even if all the copies could be sold, which at the time +did not seem very likely, they would hardly have met the inevitable +expenses. The provision of the necessary funds was, therefore, a +matter for consideration. The Board of Trinity College had already +contributed 200 pounds to the printing, but yet another hundred was +required. Even the discoverer of Quaternions found this a source of +much anxiety. However, the board, urged by the representation of +Humphrey Lloyd, now one of its members, and, as we have already seen, +one of Hamilton's staunchest friends, relieved him of all liability. +We may here note that, notwithstanding the pension which Hamilton +enjoyed in addition to the salary of his chair, he seems always to +have been in some what straitened circumstances, or, to use his own +words in one of his letters to De Morgan, "Though not an embarrassed +man, I am anything rather than a rich one." It appears that, +notwithstanding the world-wide fame of Hamilton's discoveries, the +only profit in a pecuniary sense that he ever obtained from any of +his works was by the sale of what he called his Icosian Game. Some +enterprising publisher, on the urgent representations of one of +Hamilton's friends in London, bought the copyright of the Icosian +Game for 25 pounds. Even this little speculation proved unfortunate +for the purchaser, as the public could not be induced to take the +necessary interest in the matter. + +After the completion of his great book, Hamilton appeared for awhile +to permit himself a greater indulgence than usual in literary +relaxations. He had copious correspondence with his intimate friend, +Aubrey de Vere, and there were multitudes of letters from those +troops of friends whom it was Hamilton's privilege to possess. He +had been greatly affected by the death of his beloved sister Eliza, a +poetess of much taste and feeling. She left to him her many papers +to preserve or to destroy, but he said it was only after the +expiration of four years of mourning that he took courage to open her +pet box of letters. + +The religious side of Hamilton's character is frequently illustrated +in these letters; especially is this brought out in the +correspondence with De Vere, who had seceded to the Church of Rome. +Hamilton writes, August 4, 1855:-- + +"If, then, it be painfully evident to both, that under such +circumstances there CANNOT (whatever we may both DESIRE) be NOW in +the nature of things, or of minds, the same degree of INTIMACY +between us as of old; since we could no longer TALK with the same +degree of unreserve on every subject which happened to present +itself, but MUST, from the simplest instincts of courtesy, be each on +his guard not to say what might be offensive, or, at least, painful +to the other; yet WE were ONCE so intimate, and retain still, and, as +I trust, shall always retain, so much of regard and esteem and +appreciation for each other, made tender by so many associations of +my early youth and your boyhood, which can never be forgotten by +either of us, that (as times go) TWO OR THREE VERY RESPECTABLE +FRIENDSHIPS might easily be carved out from the fragments of our +former and ever-to-be-remembered INTIMACY. It would be no +exaggeration to quote the words: 'Heu! quanto minus est cum reliquis +versari, quam tui meminisse!'" + +In 1858 a correspondence on the subject of Quaternions commenced +between Professor Tait and Sir William Hamilton. It was particularly +gratifying to the discoverer that so competent a mathematician as +Professor Tait should have made himself acquainted with the new +calculus. It is, of course, well known that Professor Tait +subsequently brought out a most valuable elementary treatise on +Quaternions, to which those who are anxious to become acquainted with +the subject will often turn in preference to the tremendous work of +Hamilton. + +In the year 1861 gratifying information came to hand of the progress +which the study of Quaternions was making abroad. Especially did the +subject attract the attention of that accomplished mathematician, +Moebius, who had already in his "Barycentrische Calculus" been led to +conceptions which bore more affinity to Quaternions than could be +found in the writings of any other mathematician. Such notices of +his work were always pleasing to Hamilton, and they served, perhaps, +as incentives to that still closer and more engrossing labour by +which he became more and more absorbed. During the last few years of +his life he was observed to be even more of a recluse than he had +hitherto been. His powers of long and continuous study seemed to +grow with advancing years, and his intervals of relaxation, such as +they were, became more brief and more infrequent. + +It was not unusual for him to work for twelve hours at a stretch. +The dawn would frequently surprise him as he looked up to snuff his +candles after a night of fascinating labour at original research. +Regularity in habits was impossible to a student who had prolonged +fits of what he called his mathematical trances. Hours for rest and +hours for meals could only be snatched in the occasional the lucid +intervals between one attack of Quaternions and the next. When +hungry, he would go to see whether anything could be found on the +sideboard; when thirsty, he would visit the locker, and the one +blemish in the man's personal character is that these latter visits +were sometimes paid too often. + +As an example of one of Hamilton's rare diversions from the all- +absorbing pursuit of Quaternions, we find that he was seized with +curiosity to calculate back to the date of the Hegira, which he found +on the 15th July, 622. He speaks of the satisfaction with which he +ascertained subsequently that Herschel had assigned precisely the +same date. Metaphysics remained also, as it had ever been, a +favourite subject of Hamilton's readings and meditations and of +correspondence with his friends. He wrote a very long letter to Dr. +Ingleby on the subject of his "Introduction to Metaphysics." In it +Hamilton alludes, as he has done also in other places, to a +peculiarity of his own vision. It was habitual to him, by some +defect in the correlation of his eyes, to see always a distinct image +with each; in fact, he speaks of the remarkable effect which the use +of a good stereoscope had on his sensations of vision. It was then, +for the first time, that he realised how the two images which he had +always seen hitherto would, under normal circumstances, be blended +into one. He cites this fact as bearing on the phenomena of +binocular vision, and he draws from it the inference that the +necessity of binocular vision for the correct appreciation of +distance is unfounded. "I am quite sure," he says, "that I SEE +DISTANCE with EACH EYE SEPARATELY." + +The commencement of 1865, the last year of his life saw Hamilton as +diligent as ever, and corresponding with Salmon and Cayley. On April +26th he writes to a friend to say, that his health has not been good +for years past, and that so much work has injured his constitution; +and he adds, that it is not conducive to good spirits to find that he +is accumulating another heavy bill with the printer for the +publication of the "Elements." This was, indeed, up to the day of +his death, a cause for serious anxiety. It may, however, be +mentioned that the whole cost, which amounted to nearly 500 pounds, +was, like that of the previous volume, ultimately borne by the +College. Contrary to anticipation, the enterprise, even in a +pecuniary sense, cannot have been a very unprofitable one. The whole +edition has long been out of print, and as much as 5 pounds has since +been paid for a single copy. + +It was on the 9th of May, 1865, that Hamilton was in Dublin for the +last time. A few days later he had a violent attack of gout, and on +the 4th of June he became alarmingly ill, and on the next day had an +attack of epileptic convulsions. However, he slightly rallied, so +that before the end of the month he was again at work at the +"Elements." A gratifying incident brightened some of the last days +of his life. The National Academy of Science in America had then +been just formed. A list of foreign Associates had to be chosen from +the whole world, and a discussion took place as to what name should +be placed first on the list. Hamilton was informed by private +communication that this great distinction was awarded to him by a +majority of two-thirds. + +In August he was still at work on the table of contents of the +"Elements," and one of his very latest efforts was his letter to Mr. +Gould, in America, communicating his acknowledgements of the honour +which had been just conferred upon him by the National Academy. On +the 2nd of September Mr. Graves went to the observatory, in response +to a summons, and the great mathematician at once admitted to his +friend that he felt the end was approaching. He mentioned that he +had found in the 145th Psalm a wonderfully suitable expression of his +thoughts and feelings, and he wished to testify his faith and +thankfulness as a Christian by partaking of the Lord's Supper. He +died at half-past two on the afternoon of the 2nd of September, 1865, +aged sixty years and one month. He was buried in Mount Jerome +Cemetery on the 7th of September. + +Many were the letters and other more public manifestations of the +feelings awakened by Hamilton's death. Sir John Herschel wrote to +the widow:-- + +"Permit me only to add that among the many scientific friends whom +time has deprived me of, there has been none whom I more deeply +lament, not only for his splendid talents, but for the excellence of +his disposition and the perfect simplicity of his manners--so great, +and yet devoid of pretensions." + +De Morgan, his old mathematical crony, as Hamilton affectionately +styled him, also wrote to Lady Hamilton:-- + +"I have called him one of my dearest friends, and most truly; for I +know not how much longer than twenty-five years we have been in +intimate correspondence, of most friendly agreement or disagreement, +of most cordial interest in each other. And yet we did not know each +other's faces. I met him about 1830 at Babbage's breakfast table, +and there for the only time in our lives we conversed. I saw him, a +long way off, at the dinner given to Herschel (about 1838) on his +return from the Cape and there we were not near enough, nor on that +crowded day could we get near enough, to exchange a word. And this +is all I ever saw, and, so it has pleased God, all I shall see in +this world of a man whose friendly communications were among my +greatest social enjoyments, and greatest intellectual treats." + +There is a very interesting memoir of Hamilton written by De Morgan, +in the "Gentleman's Magazine" for 1866, in which he produces an +excellent sketch of his friend, illustrated by personal reminiscences +and anecdotes. He alludes, among other things, to the picturesque +confusion of the papers in his study. There was some sort of order +in the mass, discernible however, by Hamilton alone, and any invasion +of the domestics, with a view to tidying up, would throw the +mathematician as we are informed, into "a good honest thundering +passion." + +Hardly any two men, who were both powerful mathematicians, could have +been more dissimilar in every other respect than were Hamilton and De +Morgan. The highly poetical temperament of Hamilton was remarkably +contrasted with the practical realism of De Morgan. Hamilton sends +sonnets to his friend, who replies by giving the poet advice about +making his will. The metaphysical subtleties, with which Hamilton +often filled his sheets, did not seem to have the same attraction for +De Morgan that he found in battles about the quantification of the +Predicate. De Morgan was exquisitely witty, and though his jokes +were always appreciated by his correspondent, yet Hamilton seldom +ventured on anything of the same kind in reply; indeed his rare +attempts at humour only produced results of the most ponderous +description. But never were two scientific correspondents more +perfectly in sympathy with each other. Hamilton's work on +Quaternions, his labours in Dynamics, his literary tastes, his +metaphysics, and his poetry, were all heartily welcomed by his +friend, whose letters in reply invariably evince the kindliest +interest in all Hamilton's concerns. In a similar way De Morgan's +letters to Hamilton always met with a heartfelt response. + +Alike for the memory of Hamilton, for the credit of his University, +and for the benefit of science, let us hope that a collected edition +of his works will ere long appear--a collection which shall show +those early achievements in splendid optical theory, those +achievements of his more mature powers which made him the Lagrange of +his country, and finally those creations of the Quaternion Calculus +by which new capabilities have been bestowed on the human intellect. + + + + +LE VERRIER. + + +The name of Le Verrier is one that goes down to fame on account of +very different discoveries from those which have given renown to +several of the other astronomers whom we have mentioned. We are +sometimes apt to identify the idea of an astronomer with that of a +man who looks through a telescope at the stars; but the word +astronomer has really much wider significance. No man who ever lived +has been more entitled to be designated an astronomer than Le +Verrier, and yet it is certain that he never made a telescopic +discovery of any kind. Indeed, so far as his scientific achievements +have been concerned, he might never have looked through a telescope +at all. + +For the full interpretation of the movements of the heavenly bodies, +mathematical knowledge of the most advanced character is demanded. +The mathematician at the outset calls upon the astronomer who uses +the instruments in the observatory, to ascertain for him at various +times the exact positions occupied by the sun, the moon, and the +planets. These observations, obtained with the greatest care, and +purified as far as possible from the errors by which they may be +affected form, as it were, the raw material on which the +mathematician exercises his skill. It is for him to elicit from the +observed places the true laws which govern the movements of the +heavenly bodies. Here is indeed a task in which the highest powers +of the human intellect may be worthily employed. + +Among those who have laboured with the greatest success in the +interpretation of the observations made with instruments of +precision, Le Verrier holds a highly honoured place. To him it has +been given to provide a superb illustration of the success with which +the mind of man can penetrate the deep things of Nature. + +The illustrious Frenchman, Urban Jean Joseph Le Verrier, was born on +the 11th March, 1811, at St. Lo, in the department of Manche. He +received his education in that famous school for education in the +higher branches of science, the Ecole Polytechnique, and acquired +there considerable fame as a mathematician. On leaving the school Le +Verrier at first purposed to devote himself to the public service, in +the department of civil engineering; and it is worthy of note that +his earliest scientific work was not in those mathematical researches +in which he was ultimately to become so famous. His duties in the +engineering department involved practical chemical research in the +laboratory. In this he seems to have become very expert, and +probably fame as a chemist would have been thus attained, had not +destiny led him into another direction. As it was, he did engage in +some original chemical research. His first contributions to science +were the fruits of his laboratory work; one of his papers was on the +combination of phosphorus and hydrogen, and another on the +combination of phosphorus and oxygen. + +His mathematical labours at the Ecole Polytechnique had, however, +revealed to Le Verrier that he was endowed with the powers requisite +for dealing with the subtlest instruments of mathematical analysis. +When he was twenty-eight years old, his first great astronomical +investigation was brought forth. It will be necessary to enter into +some explanation as to the nature of this, inasmuch as it was the +commencement of the life-work which he was to pursue. + +If but a single planet revolved around the sun, then the orbit of +that planet would be an ellipse, and the shape and size, as well as +the position of the ellipse, would never alter. One revolution after +another would be traced out, exactly in the same manner, in +compliance with the force continuously exerted by the sun. Suppose, +however, that a second planet be introduced into the system. The sun +will exert its attraction on this second planet also, and it will +likewise describe an orbit round the central globe. We can, however, +no longer assert that the orbit in which either of the planets moves +remains exactly an ellipse. We may, indeed, assume that the mass of +the sun is enormously greater than that of either of the planets. In +this case the attraction of the sun is a force of such preponderating +magnitude, that the actual path of each planet remains nearly the +same as if the other planet were absent. But it is impossible for +the orbit of each planet not to be affected in some degree by the +attraction of the other planet. The general law of nature asserts +that every body in space attracts every other body. So long as there +is only a single planet, it is the single attraction between the sun +and that planet which is the sole controlling principle of the +movement, and in consequence of it the ellipse is described. But +when a second planet is introduced, each of the two bodies is not +only subject to the attraction of the sun, but each one of the +planets attracts the other. It is true that this mutual attraction +is but small, but, nevertheless, it produces some effect. It +"disturbs," as the astronomer says, the elliptic orbit which would +otherwise have been pursued. Hence it follows that in the actual +planetary system where there are several planets disturbing each +other, it is not true to say that the orbits are absolutely elliptic. + +At the same time in any single revolution a planet may for most +practical purposes be said to be actually moving in an ellipse. As, +however, time goes on, the ellipse gradually varies. It alters its +shape, it alters its plane, and it alters its position in that +plane. If, therefore, we want to study the movements of the planets, +when great intervals of time are concerned, it is necessary to have +the means of learning the nature of the movement of the orbit in +consequence of the disturbances it has experienced. + +We may illustrate the matter by supposing the planet to be running +like a railway engine on a track which has been laid in a long +elliptic path. We may suppose that while the planet is coursing +along, the shape of the track is gradually altering. But this +alteration may be so slow, that it does not appreciably affect the +movement of the engine in a single revolution. We can also suppose +that the plane in which the rails have been laid has a slow +oscillation in level, and that the whole orbit is with more or less +uniformity moved slowly about in the plane. + +In short periods of time the changes in the shapes and positions of +the planetary orbits, in consequence of their mutual attractions, are +of no great consequence. When, however, we bring thousands of years +into consideration, then the displacements of the planetary orbits +attain considerable dimensions, and have, in fact, produced a +profound effect on the system. + +It is of the utmost interest to investigate the extent to which one +planet can affect another in virtue of their mutual attractions. Such +investigations demand the exercise of the highest mathematical +gifts. But not alone is intellectual ability necessary for success +in such inquiries. It must be united with a patient capacity for +calculations of an arduous type, protracted, as they frequently have +to be, through many years of labour. Le Verrier soon found in these +profound inquiries adequate scope for the exercise of his peculiar +gifts. His first important astronomical publication contained an +investigation of the changes which the orbits of several of the +planets, including the earth, have undergone in times past, and which +they will undergo in times to come. + +As an illustration of these researches, we may take the case of the +planet in which we are, of course, especially interested, namely, the +earth, and we can investigate the changes which, in the lapse of +time, the earth's orbit has undergone, in consequence of the +disturbance to which it has been subjected by the other planets. In +a century, or even in a thousand years, there is but little +recognisable difference in the shape of the track pursued by the +earth. Vast periods of time are required for the development of the +large consequences of planetary perturbation. Le Verrier has, +however, given us the particulars of what the earth's journey through +space has been at intervals of 20,000 years back from the present +date. His furthest calculation throws our glance back to the state +of the earth's track 100,000 years ago, while, with a bound forward, +he shows us what the earth's orbit is to be in the future, at +successive intervals of 20,000 years, till a date is reached which is +100,000 years in advance of A.D. 1800. + +The talent which these researches displayed brought Le Verrier into +notice. At that time the Paris Observatory was presided over by +Arago, a SAVANT who occupies a distinguished position in French +scientific annals. Arago at once perceived that Le Verrier was just +the man who possessed the qualifications suitable for undertaking a +problem of great importance and difficulty that had begun to force +itself on the attention of astronomers. What this great problem was, +and how astonishing was the solution it received, must now be +considered. + +Ever since Herschel brought himself into fame by his superb discovery +of the great planet Uranus, the movements of this new addition to the +solar system were scrutinized with care and attention. The position +of Uranus was thus accurately determined from time to time. At +length, when sufficient observations of this remote planet had been +brought together, the route which the newly-discovered body pursued +through the heavens was ascertained by those calculations with which +astronomers are familiar. It happens, however, that Uranus possesses +a superficial resemblance to a star. Indeed the resemblance is so +often deceptive that long ere its detection as a planet by Herschel, +it had been observed time after time by skilful astronomers, who +little thought that the star-like point at which they looked was +anything but a star. From these early observations it was possible +to determine the track of Uranus, and it was found that the great +planet takes a period of no less than eighty-four years to accomplish +a circuit. Calculations were made of the shape of the orbit in which +it revolved before its discovery by Herschel, and these were compared +with the orbit which observations showed the same body to pursue in +those later years when its planetary character was known. It could +not, of course, be expected that the orbit should remain unaltered; +the fact that the great planets Jupiter and Saturn revolve in the +vicinity of Uranus must necessarily imply that the orbit of the +latter undergoes considerable changes. When, however, due allowance +has been made for whatever influence the attraction of Jupiter and +Saturn, and we may add of the earth and all the other Planets, could +possibly produce, the movements of Uranus were still inexplicable. It +was perfectly obvious that there must be some other influence at work +besides that which could be attributed to the planets already known. + +Astronomers could only recognise one solution of such a difficulty. +It was impossible to doubt that there must be some other planet in +addition to the bodies at that time known, and that the perturbations +of Uranus hitherto unaccounted for, were due to the disturbances +caused by the action of this unknown planet. Arago urged Le Verrier +to undertake the great problem of searching for this body, whose +theoretical existence seemed demonstrated. But the conditions of the +search were such that it must needs be conducted on principles wholly +different from any search which had ever before been undertaken for a +celestial object. For this was not a case in which mere survey with +a telescope might be expected to lead to the discovery. + +Certain facts might be immediately presumed with reference to the +unknown object. There could be no doubt that the unknown disturber +of Uranus must be a large body with a mass far exceeding that of the +earth. It was certain, however, that it must be so distant that it +could only appear from our point of view as a very small object. +Uranus itself lay beyond the range, or almost beyond the range, of +unassisted vision. It could be shown that the planet by which the +disturbance was produced revolved in an orbit which must lie outside +that of Uranus. It seemed thus certain that the planet could not be +a body visible to the unaided eye. Indeed, had it been at all +conspicuous its planetary character would doubtless have been +detected ages ago. The unknown body must therefore be a planet which +would have to be sought for by telescopic aid. + +There is, of course, a profound physical difference between a planet +and a star, for the star is a luminous sun, and the planet is merely +a dark body, rendered visible by the sunlight which falls upon it. +Notwithstanding that a star is a sun thousands of times larger than +the planet and millions of times more remote, yet it is a singular +fact that telescopic planets possess an illusory resemblance to the +stars among which their course happens to lie. So far as actual +appearance goes, there is indeed only one criterion by which a planet +of this kind can be discriminated from a star. If the planet be +large enough the telescope will show that it possesses a disc, and +has a visible and measurable circular outline. This feature a star +does not exhibit. The stars are indeed so remote that no matter how +large they may be intrinsically, they only exhibit radiant points of +light, which the utmost powers of the telescope fail to magnify into +objects with an appreciable diameter. The older and well-known +planets, such as Jupiter and Mars, possess discs, which, though not +visible to the unaided eye, were clearly enough discernible with the +slightest telescopic power. But a very remote planet like Uranus, +though it possessed a disc large enough to be quickly appreciated by +the consummate observing skill of Herschel, was nevertheless so +stellar in its appearance, that it had been observed no fewer than +seventeen times by experienced astronomers prior to Herschel. In +each case the planetary nature of the object had been overlooked, and +it had been taken for granted that it was a star. It presented no +difference which was sufficient to arrest attention. + +As the unknown body by which Uranus was disturbed was certainly much +more remote than Uranus, it seemed to be certain that though it might +show a disc perceptible to very close inspection, yet that the disc +must be so minute as not to be detected except with extreme care. In +other words, it seemed probable that the body which was to be sought +for could not readily be discriminated from a small star, to which +class of object it bore a superficial resemblance, though, as a +matter of fact, there was the profoundest difference between the two +bodies. + +There are on the heavens many hundreds of thousands of stars, and the +problem of identifying the planet, if indeed it should lie among +these stars, seemed a very complex matter. Of course it is the +abundant presence of the stars which causes the difficulty. If the +stars could have been got rid of, a sweep over the heavens would at +once disclose all the planets which are bright enough to be visible +with the telescopic power employed. It is the fortuitous resemblance +of the planet to the stars which enables it to escape detection. To +discriminate the planet among stars everywhere in the sky would be +almost impossible. If, however, some method could be devised for +localizing that precise region in which the planet's existence might +be presumed, then the search could be undertaken with some prospect +of success. + +To a certain extent the problem of localizing the region on the sky +in which the planet might be expected admitted of an immediate +limitation. It is known that all the planets, or perhaps I ought +rather to say, all the great planets, confine their movements to a +certain zone around the heavens. This zone extends some way on +either side of that line called the ecliptic in which the earth +pursues its journey around the sun. It was therefore to be inferred +that the new planet need not be sought for outside this zone. It is +obvious that this consideration at once reduces the area to be +scrutinized to a small fraction of the entire heavens. But even +within the zone thus defined there are many thousands of stars. It +would seem a hopeless task to detect the new planet unless some +further limitation to its position could be assigned. + +It was accordingly suggested to Le Verrier that he should endeavour +to discover in what particular part of the strip of the celestial +sphere which we have indicated the search for the unknown planet +should be instituted. The materials available to the mathematician +for the solution of this problem were to be derived solely from the +discrepancies between the calculated places in which Uranus should be +found, taking into account the known causes of disturbance, and the +actual places in which observation had shown the planet to exist. +Here was indeed an unprecedented problem, and one of extraordinary +difficulty. Le Verrier, however, faced it, and, to the astonishment +of the world, succeeded in carrying it through to a brilliant +solution. We cannot here attempt to enter into any account of the +mathematical investigations that were necessary. All that we can do +is to give a general indication of the method which had to be +adopted. + +Let us suppose that a planet is revolving outside Uranus, at a +distance which is suggested by the several distances at which the +other planets are dispersed around the sun. Let us assume that this +outer planet has started on its course, in a prescribed path, and +that it has a certain mass. It will, of course, disturb the motion +of Uranus, and in consequence of that disturbance Uranus will follow +a path the nature of which can be determined by calculation. It +will, however, generally be found that the path so ascertained does +not tally with the actual path which observations have indicated for +Uranus. This demonstrates that the assumed circumstances of the +unknown planet must be in some respects erroneous, and the astronomer +commences afresh with an amended orbit. At last after many trials, +Le Verrier ascertained that, by assuming a certain size, shape, and +position for the unknown Planet's orbit, and a certain value for the +mass of the hypothetical body, it would be possible to account for +the observed disturbances of Uranus. Gradually it became clear to +the perception of this consummate mathematician, not only that the +difficulties in the movements of Uranus could be thus explained, but +that no other explanation need be sought for. It accordingly +appeared that a planet possessing the mass which he had assigned, and +moving in the orbit which his calculations had indicated, must indeed +exist, though no eye had ever beheld any such body. Here was, +indeed, an astonishing result. The mathematician sitting at his +desk, by studying the observations which had been supplied to him of +one planet, is able to discover the existence of another planet, and +even to assign the very position which it must occupy, ere ever the +telescope is invoked for its discovery. + +Thus it was that the calculations of Le Verrier narrowed greatly the +area to be scrutinised in the telescopic search which was presently +to be instituted. It was already known, as we have just pointed out, +that the planet must lie somewhere on the ecliptic. The French +mathematician had now further indicated the spot on the ecliptic at +which, according to his calculations, the planet must actually be +found. And now for an episode in this history which will be +celebrated so long as science shall endure. It is nothing less than +the telescopic confirmation of the existence of this new planet, +which had previously been indicated only by mathematical +calculation. Le Verrier had not himself the instruments necessary +for studying the heavens, nor did he possess the skill of the +practical astronomer. He, therefore, wrote to Dr. Galle, of the +Observatory at Berlin, requesting him to undertake a telescopic +search for the new planet in the vicinity which the mathematical +calculation had indicated for the whereabouts of the planet at that +particular time. Le Verrier added that he thought the planet ought +to admit of being recognised by the possession of a disc sufficiently +definite to mark the distinction between it and the surrounding +stars. + +It was the 23rd September, 1846, when the request from Le Verrier +reached the Berlin Observatory, and the night was clear, so that the +memorable search was made on the same evening. The investigation was +facilitated by the circumstance that a diligent observer had recently +compiled elaborate star maps for certain tracts of the heavens lying +in a sufficiently wide zone on both sides of the equator. These maps +were as yet only partially complete, but it happened that Hora. XXI., +which included the very spot which Le Verrier's results referred to, +had been just issued. Dr. Galle had thus before his, eyes a chart of +all the stars which were visible in that part of the heavens at the +time when the map was made. The advantage of such an assistance to +the search could hardly be over-estimated. It at once gave the +astronomer another method of recognising the planet besides that +afforded by its possible possession of a disc. For as the planet was +a moving body, it would not have been in the same place relatively to +the stars at the time when the map was constructed, as it occupied +some years later when the search was being made. If the body should +be situated in the spot which Le Verrier's calculations indicated in +the autumn of 1846, then it might be regarded as certain that it +would not be found in that same place on a map drawn some years +previously. + +The search to be undertaken consisted in a comparison made point by +point between the bodies shown on the map, and those stars in the sky +which Dr. Galle's telescope revealed. In the course of this +comparison it presently appeared that a star-like object of the +eighth magnitude, which was quite a conspicuous body in the +telescope, was not represented in the map. This at once attracted +the earnest attention of the astronomer, and raised his hopes that +here was indeed the planet. Nor were these hopes destined to be +disappointed. It could not be supposed that a star of the eighth +magnitude would have been overlooked in the preparation of a chart +whereon stars of many lower degrees of brightness were set down. One +other supposition was of course conceivable. It might have been that +this suspicious object belonged to the class of variables, for there +are many such stars whose brightness fluctuates, and if it had +happened that the map was constructed at a time when the star in +question had but feeble brilliance, it might have escaped notice. It +is also well known that sometimes new stars suddenly develop, so that +the possibility that what Dr. Galle saw should have been a variable +star or should have been a totally new star had to be provided +against. + +Fortunately a test was immediately available to decide whether the +new object was indeed the long sought for planet, or whether it was a +star of one of the two classes to which I have just referred. A star +remains fixed, but a planet is in motion. No doubt when a planet +lies at the distance at which this new planet was believed to be +situated, its apparent motion would be so slow that it would not be +easy to detect any change in the course of a single night's +observation. Dr. Galle, however, addressed himself with much skill +to the examination of the place of the new body. Even in the course +of the night he thought he detected slight movements, and he awaited +with much anxiety the renewal of his observations on the subsequent +evenings. His suspicions as to the movement of the body were then +amply confirmed, and the planetary nature of the new object was thus +unmistakably detected. + +Great indeed was the admiration of the scientific world at this +superb triumph. Here was a mighty planet whose very existence was +revealed by the indications afforded by refined mathematical +calculation. At once the name of Le Verrier, already known to those +conversant with the more profound branches of astronomy, became +everywhere celebrated. It soon, however, appeared, that the fame +belonging to this great achievement had to be shared between Le +Verrier and another astronomer, J. C. Adams, of Cambridge. In our +chapter on this great English mathematician we shall describe the +manner in which he was independently led to the same discovery. + +Directly the planetary nature of the newly-discovered body had been +established, the great observatories naturally included this +additional member of the solar system in their working lists, so that +day after day its place was carefully determined. When sufficient +time had elapsed the shape and position of the orbit of the body +became known. Of course, it need hardly be said that observations +applied to the planet itself must necessarily provide a far more +accurate method of determining the path which it follows, than would +be possible to Le Verrier, when all he had to base his calculations +upon was the influence of the planet reflected, so to speak, from +Uranus. It may be noted that the true elements of the planet, when +revealed by direct observation, showed that there was a considerable +discrepancy between the track of the planet which Le Verrier had +announced, and that which the planet was actually found to pursue. + +The name of the newly-discovered body had next to be considered. As +the older members of the system were already known by the same names +as great heathen divinities, it was obvious that some similar source +should be invoked for a suggestion as to a name for the most recent +planet. The fact that this body was so remote in the depths of +space, not unnaturally suggested the name "Neptune." Such is +accordingly the accepted designation of that mighty globe which +revolves in the track that at present seems to trace out the +frontiers of our system. + +Le Verrier attained so much fame by this discovery, that when, in +1854, Arago's place had to be filled at the head of the great Paris +Observatory, it was universally felt that the discoverer of Neptune +was the suitable man to assume the office which corresponds in France +to that of the Astronomer Royal in England. It was true that the +work of the astronomical mathematician had hitherto been of an +abstract character. His discoveries had been made at his desk and +not in the observatory, and he had no practical acquaintance with the +use of astronomical instruments. However, he threw himself into the +technical duties of the observatory with vigour and determination. He +endeavoured to inspire the officers of the establishment with +enthusiasm for that systematic work which is so necessary for the +accomplishment of useful astronomical research. It must, however, be +admitted that Le Verrier was not gifted with those natural qualities +which would make him adapted for the successful administration of +such an establishment. Unfortunately disputes arose between the +Director and his staff. At last the difficulties of the situation +became so great that the only possible solution was to supersede Le +Verrier, and he was accordingly obliged to retire. He was succeeded +in his high office by another eminent mathematician, M. Delaunay, +only less distinguished than Le Verrier himself. + +Relieved of his official duties, Le Verrier returned to the +mathematics he loved. In his non-official capacity he continued to +work with the greatest ardour at his researches on the movements of +the planets. After the death of M. Delaunay, who was accidentally +drowned in 1873, Le Verrier was restored to the directorship of the +observatory, and he continued to hold the office until his death. + +The nature of the researches to which the life of Le Verrier was +subsequently devoted are not such as admit of description in a +general sketch like this, where the language, and still less the +symbols, of mathematics could not be suitably introduced. It may, +however, be said in general that he was particularly engaged with the +study of the effects produced on the movements of the planets by +their mutual attractions. The importance of this work to astronomy +consists, to a considerable extent, in the fact that by such +calculations we are enabled to prepare tables by which the places of +the different heavenly bodies can be predicted for our almanacs. To +this task Le Verrier devoted himself, and the amount of work he has +accomplished would perhaps have been deemed impossible had it not +been actually done. + +The superb success which had attended Le Verrier's efforts to explain +the cause of the perturbations of Uranus, naturally led this +wonderful computer to look for a similar explanation of certain other +irregularities in planetary movements. To a large extent he +succeeded in showing how the movements of each of the great planets +could be satisfactorily accounted for by the influence of the +attractions of the other bodies of the same class. One circumstance +in connection with these investigations is sufficiently noteworthy to +require a few words here. Just as at the opening of his career, Le +Verrier had discovered that Uranus, the outermost planet of the then +known system, exhibited the influence of an unknown external body, so +now it appeared to him that Mercury, the innermost body of our +system, was also subjected to some disturbances, which could not be +satisfactorily accounted for as consequences of any known agents of +attraction. The ellipse in which Mercury revolved was animated by a +slow movement, which caused it to revolve in its plane. It appeared +to Le Verrier that this displacement was incapable of explanation by +the action of any of the known bodies of our system. He was, +therefore, induced to try whether he could not determine from the +disturbances of Mercury the existence of some other planet, at +present unknown, which revolved inside the orbit of the known +planet. Theory seemed to indicate that the observed alteration in +the track of the planet could be thus accounted for. He naturally +desired to obtain telescopic confirmation which might verify the +existence of such a body in the same way as Dr. Galle verified the +existence of Neptune. If there were, indeed, an intramercurial +planet, then it must occasionally cross between the earth and the +sun, and might now and then be expected to be witnessed in the actual +act of transit. So confident did Le Verrier feel in the existence of +such a body that an observation of a dark object in transit, by +Lescarbault on 26th March, 1859, was believed by the mathematician to +be the object which his theory indicated. Le Verrier also thought it +likely that another transit of the same object would be seen in +March, 1877. Nothing of the kind was, however, witnessed, +notwithstanding that an assiduous watch was kept, and the explanation +of the change in Mercury's orbit must, therefore, be regarded as +still to be sought for. + +Le Verrier naturally received every honour that could be bestowed +upon a man of science. The latter part of his life was passed during +the most troubled period of modern French history. He was a +supporter of the Imperial Dynasty, and during the Commune he +experienced much anxiety; indeed, at one time grave fears were +entertained for his personal safety. + +Early in 1877 his health, which had been gradually failing for some +years, began to give way. He appeared to rally somewhat in the +summer, but in September he sank rapidly, and died on Sunday, the +23rd of that month. + +His remains were borne to the cemetery on Mont Parnasse in a public +funeral. Among his pallbearers were leading men of science, from +other countries as well as France, and the memorial discourses +pronounced at the grave expressed their admiration of his talents and +of the greatness of the services he had rendered to science. + + + + +ADAMS. + + +The illustrious mathematician who, among Englishmen, at all events, +was second only to Newton by his discoveries in theoretical +astronomy, was born on June the 5th, 1819, at the farmhouse of +Lidcot, seven miles from Launceston, in Cornwall. His early +education was imparted under the guidance of the Rev. John Couch +Grylls, a first cousin of his mother. He appears to have received an +education of the ordinary school type in classics and mathematics, +but his leisure hours were largely devoted to studying what +astronomical books he could find in the library of the Mechanics' +Institute at Devonport. He was twenty years old when he entered St. +John's College, Cambridge. His career in the University was one of +almost unparalleled distinction, and it is recorded that his +answering at the Wranglership examination, where he came out at the +head of the list in 1843, was so high that he received more than +double the marks awarded to the Second Wrangler. + +Among the papers found after his death was the following memorandum, +dated July the 3rd, 1841: "Formed a design at the beginning of this +week of investigating, as soon as possible after taking my degree, +the irregularities in the motion of Uranus, which are as yet +unaccounted for, in order to find whether they may be attributed to +the action of an undiscovered planet beyond it; and, if possible, +thence to determine the elements of its orbit approximately, which +would lead probably to its discovery." + +After he had taken his degree, and had thus obtained a little +relaxation from the lines within which his studies had previously +been necessarily confined, Adams devoted himself to the study of the +perturbations of Uranus, in accordance with the resolve which we have +just seen that he formed while he was still an undergraduate. As a +first attempt he made the supposition that there might be a planet +exterior to Uranus, at a distance which was double that of Uranus +from the sun. Having completed his calculation as to the effect +which such a hypothetical planet might exercise upon the movement of +Uranus, he came to the conclusion that it would be quite possible to +account completely for the unexplained difficulties by the action of +an exterior planet, if only that planet were of adequate size and had +its orbit properly placed. It was necessary, however, to follow up +the problem more precisely, and accordingly an application was made +through Professor Challis, the Director of the Cambridge Observatory, +to the Astronomer Royal, with the object of obtaining from the +observations made at Greenwich Observatory more accurate values for +the disturbances suffered by Uranus. Basing his work on the more +precise materials thus available, Adams undertook his calculations +anew, and at last, with his completed results, he called at Greenwich +Observatory on October the 21st, 1845. He there left for the +Astronomer Royal a paper which contained the results at which he had +arrived for the mass and the mean distance of the hypothetical planet +as well as the other elements necessary for calculating its exact +position. + +[PLATE: JOHN COUCH ADAMS.] + +As we have seen in the preceding chapter, Le Verrier had been also +investigating the same problem. The place which Le Verrier assigned +to the hypothetical disturbing planet for the beginning of the year +1847, was within a degree of that to which Adams's computations +pointed, and which he had communicated to the Astronomer Royal seven +months before Le Verrier's work appeared. On July the 29th, 1846, +Professor Challis commenced to search for the unknown object with the +Northumberland telescope belonging to the Cambridge Observatory. He +confined his attention to a limited region in the heavens, extending +around that point to which Mr. Adams' calculations pointed. The +relative places of all the stars, or rather star-like objects within +this area, were to be carefully measured. When the same observations +were repeated a week or two later, then the distances of the several +pairs of stars from each other would be found unaltered, but any +planet which happened to lie among the objects measured would +disclose its existence by the alterations in distance due to its +motion in the interval. This method of search, though no doubt it +must ultimately have proved successful, was necessarily a very +tedious one, but to Professor Challis, unfortunately, no other method +was available. Thus it happened that, though Challis commenced his +search at Cambridge two months earlier than Galle at Berlin, yet, as +we have already explained, the possession of accurate star-maps by +Dr. Galle enabled him to discover the planet on the very first night +that he looked for it. + +The rival claims of Adams and Le Verrier to the discovery of Neptune, +or rather, we should say, the claims put forward by their respective +champions, for neither of the illustrious investigators themselves +condescended to enter into the personal aspect of the question, need +not be further discussed here. The main points of the controversy +have been long since settled, and we cannot do better than quote the +words of Sir John Herschel when he addressed the Royal Astronomical +Society in 1848:-- + +"As genius and destiny have joined the names of Le Verrier and Adams, +I shall by no means put them asunder; nor will they ever be +pronounced apart so long as language shall celebrate the triumphs of +science in her sublimest walks. On the great discovery of Neptune, +which may be said to have surpassed, by intelligible and legitimate +means, the wildest pretensions of clairvoyance, it Would now be quite +superfluous for me to dilate. That glorious event and the steps +which led to it, and the various lights in which it has been placed, +are already familiar to every one having the least tincture of +science. I will only add that as there is not, nor henceforth ever +can be, the slightest rivalry on the subject between these two +illustrious men--as they have met as brothers, and as such will, I +trust, ever regard each other--we have made, we could make, no +distinction between then, on this occasion. May they both long adorn +and augment our science, and add to their own fame already so high +and pure, by fresh achievements." + +Adams was elected a Fellow of St. John's College, Cambridge, in 1843; +but as he did not take holy orders, his Fellowship, in accordance +with the rules then existing came to an end in 1852. In the +following year he was, however, elected to a Fellowship at Pembroke +College, which he retained until the end of his life. In 1858 he was +appointed Professor of Mathematics in the University of St. Andrews, +but his residence in the north was only a brief one, for in the same +year he was recalled to Cambridge as Lowndean Professor of Astronomy +and Geometry, in succession to Peacock. In 1861 Challis retired from +the Directorship of the Cambridge Observatory, and Adams was +appointed to succeed him. + +The discovery of Neptune was a brilliant inauguration of the +astronomical career of Adams. He worked at, and wrote upon, the +theory of the motions of Biela's comet; he made important corrections +to the theory of Saturn; he investigated the mass of Uranus, a +subject in which he was naturally interested from its importance in +the theory of Neptune; he also improved the methods of computing the +orbits of double stars. But all these must be regarded as his minor +labours, for next to the discovery of Neptune the fame of Adams +mainly rests on his researches upon certain movements of the moon, +and upon the November meteors. + +The periodic time of the moon is the interval required for one +circuit of its orbit. This interval is known with accuracy at the +present day, and by means of the ancient eclipses the period of the +moon's revolution two thousand years ago can be also ascertained. It +had been discovered by Halley that the period which the moon requires +to accomplish each of its revolutions around the earth has been +steadily, though no doubt slowly, diminishing. The change thus +produced is not appreciable when only small intervals of time are +considered, but it becomes appreciable when we have to deal with +intervals of thousands of years. The actual effect which is produced +by the lunar acceleration, for so this phenomenon is called, may be +thus estimated. If we suppose that the moon had, throughout the +ages, revolved around the earth in precisely the same periodic time +which it has at present, and if from this assumption we calculate +back to find where the moon must have been about two thousand years +ago, we obtain a position which the ancient eclipses show to be +different from that in which the moon was actually situated. The +interval between the position in which the moon would have been found +two thousand years ago if there had been no acceleration, and the +position in which the moon was actually placed, amounts to about a +degree, that is to say, to an arc on the heavens which is twice the +moon's apparent diameter. + +If no other bodies save the earth and the moon were present in the +universe, it seems certain that the motion of the moon would never +have exhibited this acceleration. In such a simple case as that +which I have supposed the orbit of the moon would have remained for +ever absolutely unchanged. It is, however, well known that the +presence of the sun exerts a disturbing influence upon the movements +of the moon. In each revolution our satellite is continually drawn +aside by the action of the sun from the place which it would +otherwise have occupied. These irregularities are known as the +perturbations of the lunar orbit, they have long been studied, and +the majority of them have been satisfactorily accounted for. It +seems, however, to those who first investigated the question that the +phenomenon of the lunar acceleration could not be explained as a +consequence of solar perturbation, and, as no other agent competent +to produce such effects was recognised by astronomers, the lunar +acceleration presented an unsolved enigma. + +At the end of the last century the illustrious French mathematician +Laplace undertook a new investigation of the famous problem, and was +rewarded with a success which for a long time appeared to be quite +complete. Let us suppose that the moon lies directly between the +earth and the sun, then both earth and moon are pulled towards the +sun by the solar attraction; as, however, the moon is the nearer of +the two bodies to the attracting centre it is pulled the more +energetically, and consequently there is an increase in the distance +between the earth and the moon. Similarly when the moon happens to +lie on the other side of the earth, so that the earth is interposed +directly between the moon and the sun, the solar attraction exerted +upon the earth is more powerful than the same influence upon the +moon. Consequently in this case, also, the distance of the moon from +the earth is increased by the solar disturbance. These instances +will illustrate the general truth, that, as one of the consequences +of the disturbing influence exerted by the sun upon the earth-moon +system, there is an increase in the dimensions of the average orbit +which the moon describes around the earth. As the time required by +the moon to accomplish a journey round the earth depends upon its +distance from the earth, it follows that among the influences of the +sun upon the moon there must be an enlargement of the periodic time, +from what it would have been had there been no solar disturbing +action. + +This was known long before the time of Laplace, but it did not +directly convey any explanation of the lunar acceleration. It no +doubt amounted to the assertion that the moon's periodic time was +slightly augmented by the disturbance, but it did not give any +grounds for suspecting that there was a continuous change in +progress. It was, however, apparent that the periodic time was +connected with the solar disturbance, so that, if there were any +alteration in the amount of the sun's disturbing effect, there must +be a corresponding alteration in the moon's periodic time. Laplace, +therefore, perceived that, if he could discover any continuous change +in the ability of the sun for disturbing the moon, he would then have +accounted for a continuous change in the moon's periodic time, and +that thus an explanation of the long-vexed question of the lunar +acceleration might be forthcoming. + +The capability of the sun for disturbing the earth-moon system is +obviously connected with the distance of the earth from the sun. If +the earth moved in an orbit which underwent no change whatever, then +the efficiency of the sun as a disturbing agent would not undergo any +change of the kind which was sought for. But if there were any +alteration in the shape or size of the earth's orbit, then that might +involve such changes in the distance between the earth and the sun as +would possibly afford the desired agent for producing the observed +lunar effect. It is known that the earth revolves in an orbit which, +though nearly circular, is strictly an ellipse. If the earth were +the only planet revolving around the sun then that ellipse would +remain unaltered from age to age. The earth is, however, only one of +a large number of planets which circulate around the great luminary, +and are guided and controlled by his supreme attracting power. These +planets mutually attract each other, and in consequence of their +mutual attractions the orbits of the planets are disturbed from the +simple elliptic form which they would otherwise possess. The +movement of the earth, for instance, is not, strictly speaking, +performed in an elliptical orbit. We may, however, regard it as +revolving in an ellipse provided we admit that the ellipse is itself +in slow motion. + +It is a remarkable characteristic of the disturbing effects of the +planets that the ellipse in which the earth is at any moment moving +always retains the same length; that is to say, its longest diameter +is invariable. In all other respects the ellipse is continually +changing. It alters its position, it changes its plane, and, most +important of all, it changes its eccentricity. Thus, from age to age +the shape of the track which the earth describes may at one time be +growing more nearly a circle, or at another time may be departing +more widely from a circle. These alterations are very small in +amount, and they take place with extreme slowness, but they are in +incessant progress, and their amount admits of being accurately +calculated. At the present time, and for thousands of years past, as +well as for thousands of years to come, the eccentricity of the +earth's orbit is diminishing, and consequently the orbit described by +the earth each year is becoming more nearly circular. We must, +however, remember that under all circumstances the length of the +longest axis of the ellipse is unaltered, and consequently the size +of the track which the earth describes around the sun is gradually +increasing. In other words, it may be said that during the present +ages the average distance between the earth and the sun is waxing +greater in consequence of the perturbations which the earth +experiences from the attraction of the other planets. We have, +however, already seen that the efficiency of the solar attraction for +disturbing the moon's movement depends on the distance between the +earth and the sun. As therefore the average distance between the +earth and the sun is increasing, at all events during the thousands +of years over which our observations extend, it follows that the +ability of the sun for disturbing the moon must be gradually +diminishing. + +[PLATE: CAMBRIDGE OBSERVATORY.] + +It has been pointed out that, in consequence of the solar +disturbance, the orbit of the moon must be some what enlarged. As it +now appears that the solar disturbance is on the whole declining, it +follows that the orbit of the moon, which has to be adjusted +relatively to the average value of the solar disturbance, must also +be gradually declining. In other words, the moon must be approaching +nearer to the earth in consequence of the alterations in the +eccentricity of the earth's orbit produced by the attraction of the +other planets. It is true that the change in the moon's position +thus arising is an extremely small one, and the consequent effect in +accelerating the moon's motion is but very slight. It is in fact +almost imperceptible, except when great periods of time are +involved. Laplace undertook a calculation on this subject. He knew +what the efficiency of the planets in altering the dimensions of the +earth's orbit amounted to; from this he was able to determine the +changes that would be propagated into the motion of the moon. Thus +he ascertained, or at all events thought he had ascertained, that the +acceleration of the moon's motion, as it had been inferred from the +observations of the ancient eclipses which have been handed down to +us, could be completely accounted for as a consequence of planetary +perturbation. This was regarded as a great scientific triumph. Our +belief in the universality of the law of gravitation would, in fact, +have been seriously challenged unless some explanation of the lunar +acceleration had been forthcoming. For about fifty years no one +questioned the truth of Laplace's investigation. When a +mathematician of his eminence had rendered an explanation of the +remarkable facts of observation which seemed so complete, it is not +surprising that there should have been but little temptation to doubt +it. On undertaking a new calculation of the same question, Professor +Adams found that Laplace had not pursued this approximation +sufficiently far, and that consequently there was a considerable +error in the result of his analysis. Adams, it must be observed, did +not impugn the value of the lunar acceleration which Halley had +deduced from the observations, but what he did show was, that the +calculation by which Laplace thought he had provided an explanation +of this acceleration was erroneous. Adams, in fact, proved that the +planetary influence which Laplace had detected only possessed about +half the efficiency which the great French mathematician had +attributed to it. There were not wanting illustrious mathematicians +who came forward to defend the calculations of Laplace. They +computed the question anew and arrived at results practically +coincident with those he had given. On the other hand certain +distinguished mathematicians at home and abroad verified the results +of Adams. The issue was merely a mathematical one. It had only one +correct solution. Gradually it appeared that those who opposed Adams +presented a number of different solutions, all of them discordant +with his, and, usually, discordant with each other. Adams showed +distinctly where each of these investigators had fallen into error, +and at last it became universally admitted that the Cambridge +Professor had corrected Laplace in a very fundamental point of +astronomical theory. + +Though it was desirable to have learned the truth, yet the breach +between observation and calculation which Laplace was believed to +have closed thus became reopened. Laplace's investigation, had it +been correct, would have exactly explained the observed facts. It +was, however, now shown that his solution was not correct, and that +the lunar acceleration, when strictly calculated as a consequence of +solar perturbations, only produced about half the effect which was +wanted to explain the ancient eclipses completely. It now seems +certain that there is no means of accounting for the lunar +acceleration as a direct consequence of the laws of gravitation, if +we suppose, as we have been in the habit of supposing, that the +members of the solar system concerned may be regarded as rigid +particles. It has, however, been suggested that another explanation +of a very interesting kind may be forthcoming, and this we must +endeavour to set forth. + +It will be remembered that we have to explain why the period of +revolution of the moon is now shorter than it used to be. If we +imagine the length of the period to be expressed in terms of days and +fractions of a day, that is to say, in terms of the rotations of the +earth around its axis, then the difficulty encountered is, that the +moon now requires for each of its revolutions around the earth rather +a smaller number of rotations of the earth around its axis than used +formerly to be the case. Of course this may be explained by the fact +that the moon is now moving more swiftly than of yore, but it is +obvious that an explanation of quite a different kind might be +conceivable. The moon may be moving just at the same pace as ever, +but the length of the day may be increasing. If the length of the +day is increasing, then, of course, a smaller number of days will be +required for the moon to perform each revolution even though the +moon's period was itself really unchanged. It would, therefore, seem +as if the phenomenon known as the lunar acceleration is the result of +the two causes. The first of these is that discovered by Laplace, +though its value was over-estimated by him, in which the perturbations +of the earth by the planets indirectly affect the motion of the +moon. The remaining part of the acceleration of our satellite is +apparent rather than real, it is not that the moon is moving more +quickly, but that our time-piece, the earth, is revolving more +slowly, and is thus actually losing time. It is interesting to note +that we can detect a physical explanation for the apparent checking +of the earth's motion which is thus manifested. The tides which ebb +and flow on the earth exert a brake-like action on the revolving +globe, and there can be no doubt that they are gradually reducing its +speed, and thus lengthening the day. It has accordingly been +suggested that it is this action of the tides which produces the +supplementary effect necessary to complete the physical explanation +of the lunar acceleration, though it would perhaps be a little +premature to assert that this has been fully demonstrated. + +The third of Professor Adams' most notable achievements was connected +with the great shower of November meteors which astonished the world +in 1866. This splendid display concentrated the attention of +astronomers on the theory of the movements of the little objects by +which the display was produced. For the definite discovery of the +track in which these bodies revolve, we are indebted to the labours +of Professor Adams, who, by a brilliant piece of mathematical work, +completed the edifice whose foundations had been laid by Professor +Newton, of Yale, and other astronomers. + +Meteors revolve around the sun in a vast swarm, every individual +member of which pursues an orbit in accordance with the well-known +laws of Kepler. In order to understand the movements of these +objects, to account satisfactorily for their periodic recurrence, and +to predict the times of their appearance, it became necessary to +learn the size and the shape of the track which the swarm followed, +as well as the position which it occupied. Certain features of the +track could no doubt be readily assigned. The fact that the shower +recurs on one particular day of the year, viz., November 13th, +defines one point through which the orbit must pass. The position on +the heavens of the radiant point from which the meteors appear to +diverge, gives another element in the track. The sun must of course +be situated at the focus, so that only one further piece of +information, namely, the periodic time, will be necessary to complete +our knowledge of the movements of the system. Professor H. Newton, +of Yale, had shown that the choice of possible orbits for the +meteoric swarm is limited to five. There is, first, the great +ellipse in which we now know the meteors revolve once every thirty +three and one quarter years. There is next an orbit of a nearly +circular kind in which the periodic time would be a little more than +a year. There is a similar track in which the periodic time would be +a few days short of a year, while two other smaller orbits would also +be conceivable. Professor Newton had pointed out a test by which it +would be possible to select the true orbit, which we know must be one +or other of these five. The mathematical difficulties which attended +the application of this test were no doubt great, but they did not +baffle Professor Adams. + +There is a continuous advance in the date of this meteoric shower. +The meteors now cross our track at the point occupied by the earth on +November 13th, but this point is gradually altering. The only +influence known to us which could account for the continuous change +in the plane of the meteor's orbit arises from the attraction of the +various planets. The problem to be solved may therefore be attacked +in this manner. A specified amount of change in the plane of the +orbit of the meteors is known to arise, and the changes which ought +to result from the attraction of the planets can be computed for each +of the five possible orbits, in one of which it is certain that the +meteors must revolve. Professor Adams undertook the work. Its +difficulty principally arises from the high eccentricity of the +largest of the orbits, which renders the more ordinary methods of +calculation inapplicable. After some months of arduous labour the +work was completed, and in April, 1867, Adams announced his solution +of the problem. He showed that if the meteors revolved in the +largest of the five orbits, with the periodic time of thirty three +and one quarter years, the perturbations of Jupiter would account for +a change to the extent of twenty minutes of arc in the point in which +the orbit crosses the earth's track. The attraction of Saturn would +augment this by seven minutes, and Uranus would add one minute more, +while the influence of the Earth and of the other planets would be +inappreciable. The accumulated effect is thus twenty-eight minutes, +which is practically coincident with the observed value as determined +by Professor Newton from an examination of all the showers of which +there is any historical record. Having thus showed that the great +orbit was a possible path for the meteors, Adams next proved that no +one of the other four orbits would be disturbed in the same manner. +Indeed, it appeared that not half the observed amount of change could +arise in any orbit except in that one with the long period. Thus was +brought to completion the interesting research which demonstrated the +true relation of the meteor swarm to the solar system. + +Besides those memorable scientific labours with which his attention +was so largely engaged, Professor Adams found time for much other +study. He occasionally allowed himself to undertake as a relaxation +some pieces of numerical calculation, so tremendously long that we +can only look on them with astonishment. He has calculated certain +important mathematical constants accurately to more than two hundred +places of decimals. He was a diligent reader of works on history, +geology, and botany, and his arduous labours were often beguiled by +novels, of which, like many other great men, he was very fond. He +had also the taste of a collector, and he brought together about +eight hundred volumes of early printed works, many of considerable +rarity and value. As to his personal character, I may quote the +words of Dr. Glaisher when he says, "Strangers who first met him were +invariably struck by his simple and unaffected manner. He was a +delightful companion, always cheerful and genial, showing in society +but few traces of his really shy and retiring disposition. His +nature was sympathetic and generous, and in few men have the moral +and intellectual qualities been more perfectly balanced." + +In 1863 he married the daughter of Haliday Bruce, Esq., of Dublin and +up to the close of his life he lived at the Cambridge Observatory, +pursuing his mathematical work and enjoying the society of his +friends. + +He died, after a long illness, on 21st January, 1892, and was +interred in St. Giles's Cemetery, on the Huntingdon Road, Cambridge. + + + + + + + +End of the Project Gutenberg EBook of Great Astronomers, by R. S. Ball + +*** END OF THIS PROJECT GUTENBERG EBOOK GREAT ASTRONOMERS *** + +***** This file should be named 2298.txt or 2298.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/2/9/2298/ + +Produced by Chris Brennen cbrennen@freenet.co.uk +Jill R. Diffendal, Barb Grow pebareka@iexpress.net.au +Christine L. Hall Goleta, CA. USA +Pamela L. 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