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diff --git a/old/44167-8.txt b/old/44167-8.txt new file mode 100644 index 0000000..4bbc497 --- /dev/null +++ b/old/44167-8.txt @@ -0,0 +1,7990 @@ +The Project Gutenberg eBook, The Royal Observatory Greenwich, by E. Walter +(Edwared Walter) Maunder + + +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: The Royal Observatory Greenwich + A Glance at Its History and Work + + +Author: E. Walter (Edwared Walter) Maunder + + + +Release Date: November 12, 2013 [eBook #44167] + +Language: English + +Character set encoding: ISO-8859-1 + + +***START OF THE PROJECT GUTENBERG EBOOK THE ROYAL OBSERVATORY GREENWICH*** + + +E-text prepared by sp1nd, Julia Neufeld, and the Online Distributed +Proofreading Team (http://www.pgdp.net) from page images generously made +available by Internet Archive (https://archive.org) + + + +Note: Project Gutenberg also has an HTML version of this + file which includes the original illustrations. + See 44167-h.htm or 44167-h.zip: + (http://www.gutenberg.org/files/44167/44167-h/44167-h.htm) + or + (http://www.gutenberg.org/files/44167/44167-h.zip) + + + Images of the original pages are available through + Internet Archive. See + https://archive.org/details/royalobservatory00maun + + +Transcriber's note: + + Text enclosed by underscores is in italics (_italics_). + + Small capital text has been replaced with all capitals. + + The carat character (^) indicates that the following + letter is superscripted (example: II^s). If two or more + letters are superscripted they are enclosed in curly + brackets (example: D^{NI}). + + + + + +[Illustration: FLAMSTEED, THE FIRST ASTRONOMER ROYAL. + +(_From the portrait in the 'Historia Coelestis.'_)] + + + + +THE ROYAL OBSERVATORY GREENWICH + +A Glance at Its History and Work + +by + +E. WALTER MAUNDER, F.R.A.S. + +With Many Portraits and Illustrations from +Old Prints and Original Photographs + + + + + + + +London +The Religious Tract Society +56 Paternoster Row, and 65 St. Paul's Churchyard +1900 + +London: +Printed by William Clowes and Sons, Limited, +Stamford Street and Charing Cross. + + + + +PREFACE + + +I was present on one occasion at a popular lecture delivered in +Greenwich, when the lecturer referred to the way in which so many +English people travel to the ends of the earth in order to see +interesting or wonderful places, and yet entirely neglect places +of at least equal importance in their own land. 'Ten minutes' walk +from this hall,' he said, 'is Greenwich Observatory, the most famous +observatory in the world. Most of you see it every day of your +lives, and yet I dare say that not one in a hundred of you has ever +been inside.' + +Whether the lecturer was justified in the general scope of his +stricture or not, the particular instance he selected was certainly +unfortunate. It was not the fault of the majority of his audience +that they had not entered Greenwich Observatory, since the +regulations by which it is governed forbade them doing so. These +rules are none too stringent, for the efficiency of the institution +would certainly suffer if it were made a 'show' place, like a +picture gallery or museum. The work carried on therein is too +continuous and important to allow of interruption by daily streams +of sightseers. + +To those who may at some time or other visit the Observatory it +may be of interest to have at hand a short account of its history, +principal instruments, and work. To the far greater number who +will never be able to enter it, but who yet feel an interest in +it, I would trust that this little book may prove some sort of a +substitute for a personal visit. + +I would wish to take this opportunity of thanking the Astronomer +Royal for his kind permission to reproduce some of the astronomical +photographs taken at the Observatory and to photograph the domes +and instruments. I would also express my thanks to Miss Airy, for +permission to reproduce the photograph of Sir G. B. Airy; to Mr. J. +Nevil Maskelyne, F.R.A.S., for the portrait of Dr. Maskelyne; to Mr. +Bowyer, for procuring the portraits of Bliss and Pond; to Messrs. +Edney and Lacey, for many photographs of the Royal Observatory; +and to the Editor of _Engineering_, for permission to copy two +engravings of the Astrographic telescope. + + E. W. M. + + ROYAL OBSERVATORY, GREENWICH, + _August, 1900_. + + + + +[Illustration: THE NEW BUILDING. + +(_From a photograph by Mr. Lacey._)] + + + + +CONTENTS + + + CHAPTER PAGE + + I. INTRODUCTION 13 + + II. FLAMSTEED 25 + + III. HALLEY AND HIS SUCCESSORS 60 + + IV. AIRY 102 + + V. THE OBSERVATORY BUILDINGS 124 + + VI. THE TIME DEPARTMENT 146 + + VII. THE TRANSIT AND CIRCLE DEPARTMENTS 181 + + VIII. THE ALTAZIMUTH DEPARTMENT 205 + + IX. THE MAGNETIC AND METEOROLOGICAL DEPARTMENTS 228 + + X. THE HELIOGRAPHIC DEPARTMENT 251 + + XI. THE SPECTROSCOPIC DEPARTMENT 266 + + XII. THE ASTROGRAPHIC DEPARTMENT 284 + + XIII. THE DOUBLE-STAR DEPARTMENT 303 + + INDEX 317 + + + + +LIST OF ILLUSTRATIONS + + + PAGE + + FLAMSTEED, THE FIRST ASTRONOMER ROYAL _Frontispiece_ + + THE NEW BUILDING 7 + + GENERAL VIEW OF THE OBSERVATORY BUILDINGS FROM THE + NEW DOME 12 + + FLAMSTEED'S SEXTANT 36 + + THE ROYAL OBSERVATORY IN FLAMSTEED'S TIME 44 + + THE 'CAMERA STELLATA' IN FLAMSTEED'S TIME 52 + + EDMUND HALLEY 61 + + HALLEY'S QUADRANT 69 + + JAMES BRADLEY 72 + + GRAHAM'S ZENITH SECTOR 77 + + NATHANIEL BLISS 83 + + NEVIL MASKELYNE 87 + + HADLEY'S QUADRANT 91 + + JOHN POND 96 + + GEORGE BIDDELL AIRY, ASTRONOMER ROYAL 103 + + THE ASTRONOMER ROYAL'S ROOM 110 + + THE SOUTH-EAST TOWER 115 + + W. H. M. CHRISTIE, ASTRONOMER ROYAL 121 + + THE ASTRONOMER ROYAL'S HOUSE 127 + + THE COURTYARD 130 + + PLAN OF OBSERVATORY AT PRESENT TIME 134 + + THE GREAT CLOCK AND PORTER'S LODGE 147 + + THE CHRONOGRAPH 158 + + THE TIME-DESK 164 + + HARRISON'S CHRONOMETER 165 + + THE CHRONOMETER ROOM 167 + + THE CHRONOMETER OVEN 171 + + THE TRANSIT PAVILION 174 + + 'LOST IN THE BIRKENHEAD' 179 + + THE TRANSIT CIRCLE 189 + + THE MURAL CIRCLE 195 + + AIRY'S ALTAZIMUTH 208 + + NEW ALTAZIMUTH BUILDING 211 + + THE NEW ALTAZIMUTH 213 + + THE NEW OBSERVATORY AS SEEN FROM FLAMSTEED'S OBSERVATORY 219 + + THE SELF-REGISTERING THERMOMETERS 235 + + THE ANEMOMETER ROOM, NORTH-WEST TURRET 240 + + THE ANEMOMETER TRACE 243 + + MAGNETIC PAVILION--EXTERIOR 246 + + MAGNETIC PAVILION--INTERIOR 248 + + THE DALLMEYER PHOTO-HELIOGRAPH 254 + + PHOTOGRAPH OF A GROUP OF SUN-SPOTS 259 + + THE GREAT NEBULA IN ORION 269 + + THE HALF-PRISM SPECTROSCOPE ON THE SOUTH-EAST EQUATORIAL 273 + + THE WORKSHOP 276 + + THE 30-INCH REFLECTOR WITH THE NEW SPECTROSCOPE + ATTACHED 278 + + 'CHART PLATE' OF THE PLEIADES 286 + + THE CONTROL PENDULUM AND THE BASE OF THE THOMPSON + TELESCOPE 289 + + THE ASTROGRAPHIC TELESCOPE 291 + + THE DRIVING CLOCK OF THE ASTROGRAPHIC TELESCOPE 294 + + THE THOMPSON TELESCOPE IN THE NEW DOME 297 + + THE NEBULÆ OF THE PLEIADES 300 + + DOUBLE-STAR OBSERVATION WITH THE SOUTH-EAST EQUATORIAL 308 + + THE SOUTH-EAST DOME WITH THE SHUTTER OPEN 314 + +[Illustration: GENERAL VIEW OF THE OBSERVATORY BUILDINGS FROM THE +NEW DOME. + +(_From a photograph by Mr. Lacey._)] + + + + +THE ROYAL OBSERVATORY + +GREENWICH + + + + +CHAPTER I + +INTRODUCTION + + +I had parted from a friend one day just as he met an acquaintance +of his to whom I was unknown. 'Who is that?' said the newcomer, +referring to me. My friend replied that I was an astronomer from +Greenwich Observatory. + +'Indeed; and what does he do there?' + +This question completely exhausted my friend's information, for as +his tastes did not lead him in the direction of astronomy, he had +at no time ever concerned himself to inquire as to the nature of my +official duties. 'Oh--er--why--he _observes_, don't you know?' and +the answer, vague as it was, completely slaked the inquirer's thirst +for knowledge. + +It is not every one who has such exceedingly nebulous ideas of an +astronomer's duties. More frequently we find that the inquirer has +already formed a vivid and highly-coloured picture of the astronomer +at his 'soul-entrancing work.' Resting on a comfortable couch, +fixed at a luxurious angle, the eye-piece of some great and perfect +instrument brought most conveniently to his eye, there passes +before him, in grand procession, a sight such as the winter nights, +when clear and frosty, give to the ordinary gazer, but increased +ten thousand times in beauty, brilliance, and wonder by the power +of his telescope. For him Jupiter reveals his wind-drifted clouds +and sunset colours; for him Saturn spreads his rings; for him +the snows of Mars fall and melt, and a thousand lunar plains are +ramparted with titanic crags; his are the star-clusters, where suns +in their first warm youth swarm thicker than hiving bees; his the +faint veils of nebulous smoke, the first hint of shape in worlds +about to be, or, perchance, the last relics of worlds for ever +dead. And beside the enjoyment of all this entrancing spectacle of +celestial beauty, the fortunate astronomer sits at his telescope and +_discovers_--always he _discovers_. + +This, or something like it, is a very popular conception of an +astronomer's experiences and duty; and consequently many, when they +are told that 'discoveries' are not made at Greenwich, are inclined +to consider that the Observatory has failed in its purpose. An +astronomer without 'discoveries' to his record is like an angler +who casts all day and comes home without fish--obviously an idle or +incompetent person. + +Again, it is considered that astronomy is a most transcendental +science. It deals with infinite distances, with numbers beyond +all power of human intellect to appreciate, and therefore it is +supposed, on the one hand, that it is a most elevating study, +keeping the mind continually on the stretch of ecstasy, and, on the +other hand, that it is utterly removed from all connection with +practical, everyday, ordinary life. + +These ideas as to the Royal Observatory, or ideas like them, are +very widely current, and they are, in every respect, exactly and +wholly wrong. First of all, Greenwich Observatory was originally +founded, and has been maintained to the present day, for a strictly +practical purpose. Next, instead of leading a life of dreamy ecstasy +or transcendental speculation, the astronomer has, perhaps, more +than any man, to give the keenest attention to minute practical +details. His life, on the one side, approximates to that of the +engineer; on the other, to that of the accountant. Thirdly, the +professional astronomer has hardly anything to do with the show +places of the sky. It is quite possible that there are many people +whose sole opportunity of looking through a telescope is the penny +peep through the instrument of some itinerant showman, who may have +seen more of these than an active astronomer in a lifetime; while as +to 'discoveries,' these lie no more within the scope of our national +observatory than do geographical discoveries within that of the +captain and officers of an ocean liner. + +If it is not to afford the astronomer beautiful spectacles, nor to +enable him to make thrilling discoveries, what is the purpose of +Greenwich Observatory? + +First and foremost, it is to assist navigation. The ease and +certainty with which to-day thousands of miles of ocean are +navigated have ceased to excite any wonder. We do not even think +about it. We go down to the docks and see, it may be, one steamer +bound for Halifax, another for New York, a third for Charleston, +a fourth for the West Indies, a fifth for Rio de Janeiro; and we +unhesitatingly go on board the one bound for our chosen destination, +without the faintest misgiving as to its direction. We have no more +doubt about the matter than we have in choosing our train at a +railway station. Yet, whilst the train is obliged to follow a narrow +track already laid for it, from which it cannot swerve an inch, +the steamer goes forth to traverse for many days an ocean without +a single fixed mark or indication of direction; and it is exposed, +moreover, to the full force of winds and currents, which may turn it +from its desired path. + +But for this facility of navigation, Great Britain could never have +obtained her present commercial position and world-wide empire. + + 'For the Lord our God most High, + He hath made the deep as dry; + He has smote for us a pathway, + To the ends of all the earth.' + +Part of this facility is, of course, due to the invention of the +steam engine, but much less than is generally supposed. Even yet +the clippers, with their roods of white canvas, are not entirely +superseded; and if we could conceive of all steamships being +suddenly annihilated, ere long the sailing vessels would again, as +of yore, prove the + + 'Swift shuttles of an empire's loom, + That weave us main to main.' + +But with the art of navigation thrust back into its condition of a +hundred and fifty years ago, it is doubtful whether a sufficient +tide of commerce could be carried on to keep our home population +supplied, or to maintain a sufficiently close political connection +between these islands and our colonies. + +Navigation was in a most primitive condition even as late as +the middle of last century. Then the method of finding a ship's +longitude at sea was the insufficient one of dead reckoning. In +other words, the direction and speed of the ship were estimated as +closely as possible, and so the position was carried on from day to +day. The uncertainty of the method was very great, and many terrible +stories might be told of the disastrous consequences which might, +and often did, follow in the train of this method by guess-work. +It will be sufficient, however, to cite the instance of Commodore +Anson. He wanted to make the island of Juan Fernandez, where he +hoped to obtain fresh water and provisions, and to recruit his +crew, many of whom were suffering from that scourge of old-time +navigators--scurvy. He got into its latitude easily enough, and +ran eastward, believing himself to be west of the island. He was, +however, really east of it, and therefore made the mainland of +America. He had therefore to turn round and sail westwards, losing +many days, during which the scurvy increased upon his crew, many of +whom died from the terrible disease before he reached the desired +island. + +The necessity for finding out a ship's place when at sea had not +been very keenly felt until the end of the fifteenth century. It +was always possible for the sailor to ascertain his latitude pretty +closely, either by observing the height of the pole-star at night +or the height of the sun at noonday; and so long as voyages were +chiefly confined to the Mediterranean Sea, and the navigators were +content for the most part to coast from point to point, rarely +losing sight of land, the urgency of solving the second problem--the +longitude of the ship--was not so keenly felt. But immediately the +discoveries of the great Portuguese and Spanish navigators brought a +wider, bolder navigation into vogue, it became a matter of the first +necessity. + +To take, for example, the immortal voyage of Christopher Columbus. +His purpose in setting out into the west was to discover a new +way to India. The Venetians and Genoese practically possessed the +overland route across the Isthmus of Suez and down the Red Sea. +Vasco da Gama had opened out the route eastward round the Cape. +Firmly convinced that the world was a globe, Columbus saw that a +third route was possible, namely, one nearly due west; and when, +therefore, he reached the Bahamas, after traversing some 66° of +longitude, he believed that he was in the islands of the China Sea, +some 230° from Spain. Those who followed him still laboured under +the same impression, and when they reached the mainland of America, +believed that they were close to the shores of India, which was +still distant from them by half the circumference of the globe. + +Little by little the intrepid sailors of the sixteenth century +forced their way to a true knowledge of the size of the globe, and +of the relative position of the great continents. But this knowledge +was only attained after many disasters and terrible miseries; and +though a new kind of navigation was established--the navigation of +the open ocean, far away from any possible landmark, a navigation as +different as could be conceived from the old method of coasting--yet +it remained terribly risky and uncertain throughout the sixteenth +century. Therefore many mathematicians endeavoured to solve the +problem of determining the position of a ship when at sea. Their +suggestions, however, remained entirely fruitless at the time, +though in several instances they struck upon principles which are +being employed at the present day. + +The first country to profit by the discovery of America was Spain, +and hence Spain was the first to feel keenly the pinch of the +problem. In 1598, therefore, Philip III. offered a prize of 100,000 +crowns to any one who would devise a method by which a captain of +a vessel could determine his position when out of sight of land. +Holland, which had recently started on its national existence, and +which was challenging the colonial empire of Spain, followed very +shortly after with the offer of a reward of 30,000 florins. Not very +long after the offer of these rewards, a master mind did work out a +simple method for determining the longitude, a method theoretically +complete, though practically it proved inapplicable. This was +Galileo, who, with his newly invented telescope, had discovered that +Jupiter was attended by four satellites. + +At first sight such a discovery, however interesting, would seem to +have not the slightest bearing upon the sailor's craft, or upon the +commercial progress of one nation or another. But Galileo quickly +saw in it the promise of great practical usefulness. The question +of the determination of the place of a ship when in the open ocean +really resolved itself into this: How could the navigator ascertain +at any time what was the true time, say at the port from which he +sailed? As already pointed out, it was possible, by observing the +height of the sun at noon, or of the pole-star at night, to infer +the latitude of the ship. The longitude was the point of difficulty. +Now, the longitude may be expressed as the difference between the +local time of the place of observation and the local time at the +place chosen as the standard meridian. The sailor could, indeed, +obtain his own local time by observations of the height of the sun. +The sun reached its greatest height at local noon, and a number of +observations before and after noon would enable him to determine +this with sufficient nicety. + +But how was he to determine when he, perhaps, was half-way across +the Atlantic, what was the local time at Genoa, Cadiz, Lisbon, +Bristol, or Amsterdam, or whatever was the port from which he +sailed? Galileo thought out a way by which the satellites of Jupiter +could give him this information. + +For as they circle round their primary, they pass in turn into its +shadow, and are eclipsed by it. It needed, then, only that the +satellites should be so carefully watched, that their motions, +and, consequently, the times of their eclipses could be foretold. +It would follow, then, that if the mariner had in his almanac the +local time of the standard city at which a given satellite would +enter into eclipse, and he were able to note from the deck of his +vessel the disappearance of the tiny point, he would ascertain the +difference between the local times of the two places, or, in other +words, the difference of their longitudes. + +The plan was simplicity itself, but there were difficulties +in carrying it out, the greatest being the impossibility of +satisfactorily making telescopic observations from the moving deck +of a ship at sea. Nor were the observations sufficiently sharp to be +of much help. The entry of a satellite into the shadow of Jupiter is +in most cases a somewhat slow process, and the moment of complete +disappearance would vary according to the size of the telescope, the +keenness of the observer's sight, and the transparency of the air. + +As the power and commerce of Spain declined, two other nations +entered into the contest for the sovereignty of the seas, and with +that sovereignty predominance in the New World of America--France +and England. The problem of the longitude at sea, or, as already +pointed out, what amounts to the same thing, the problem how to +determine when at sea the local time at some standard place, became, +in consequence, of greater necessity to them. + +The standard time would be easily known, if a thoroughly good +chronometer which did not change its rate, and which was set to the +standard time before starting, was carried on board the ship. This +plan had been proposed by Gemma Frisius as early as 1526, but at the +time was a mere suggestion, as there were no chronometers or watches +sufficiently good for the purpose. There was, however, another +method of ascertaining the standard time. The moon moves pretty +quickly amongst the stars, and at the present time, when its motions +are well known, it is possible to draw up a table of its distances +from a number of given stars at definite times for long periods in +advance. This is actually done to-day in the _Nautical Almanac_, +the moon's distance from certain stars being given for every three +hours of Greenwich time. It is possible, then, by measuring these +distances, and making, as in the case of the latitude, certain +corrections, to find out the time at Greenwich. In short, the whole +sky may be considered as a vast clock set to Greenwich time, the +stars being the numbers on the dial face, and the moon the hand (for +this clock has only one hand) moving amongst them. + +The local apparent time--that is, the time at the place at which the +ship itself was--is a simpler matter. It is noon at any place when +the sun is due south--or, as we may put it a little differently, +when it culminates--that is, when it reaches its highest point. + +To find the longitude at sea, therefore, it was necessary to be +able to predict precisely the apparent position of the moon in +the sky for any time throughout the entire year, and it was also +necessary that the places of the stars themselves should be very +accurately known. It was therefore to gather the materials for a +better knowledge of the motions of the moon and the position of the +stars that Greenwich Observatory was founded, whilst the _Nautical +Almanac_ was instituted to convey this information to mariners in a +convenient form. + +This proposal was actually made in the reign of Charles II. by +a Frenchman, Le Sieur de Saint-Pierre, who, having secured an +introduction to the Duchess of Portsmouth, endeavoured to obtain a +reward for his scheme. It would appear that he had simply borrowed +the idea from a book which an eminent French mathematician brought +out forty years before, without having himself any real knowledge +of the subject. But when the matter was brought before the king's +notice, he desired some of the leading scientific men of the day to +report upon its practicability, and the Rev. John Flamsteed was the +man selected for the task. He reported that the scheme in itself +was a good one, but impracticable in the then state of science. The +king, who, in spite of the evil reputation which he has earned for +himself, took a real interest in science, was startled when this was +reported to him, and commanded the man who had drawn his attention +to these deficiencies 'to apply himself,' as the king's astronomer, +'with the most exact care and diligence to the Rectifying the Tables +of the Motions of the Heavens and the Places of the Fixed Stars, +in order to find out the so much desired Longitude at Sea, for the +perfecting the Art of Navigation.' + +This man, the Rev. John Flamsteed, was accordingly appointed first +Astronomer Royal at the meagre salary of £100 a year, with full +permission to provide himself with the instruments he might require, +at his own expense. He followed out the task assigned to him with +extreme devotion, amidst many difficulties and annoyances, until his +death in 1719. He has been succeeded by seven Astronomers Royal, +each of whom has made it his first object to carry out the original +scheme of the institution; and the chief purpose of Greenwich +Observatory to-day, as when it was founded in 1675, is to observe +the motions of the sun, moon, and planets, and to issue accurate +star catalogues. + +It will be seen, therefore, that the establishment of Greenwich +Observatory arose from the actual necessity of the nation. It was +an essential step in its progress towards its present position as +the first commercial nation. No thoughts of abstract science were +in the minds of its founders; there was no desire to watch the +cloud-changes on Jupiter, or to find out what Sirius was made of. +The Observatory was founded for the benefit of the Royal Navy and of +the general commerce of the realm; and, in essence, that which was +the sole object of its foundation at the beginning has continued to +be its first object down to the present time. + +It was impossible that the work of the Observatory should be always +confined within the above limits, and it will be my purpose, in the +pages which follow, to describe when and how the chief expansions of +its programme have taken place. But assistance to navigation is now, +and has always been, the dominant note in its management. + + + + +CHAPTER II + +FLAMSTEED + + +For the first century of its existence, the lives of its Astronomers +Royal formed practically the history of the Royal Observatory. +During this period, the Observatory was itself so small that the +Astronomer Royal, with a single assistant, sufficed for the entire +work. Everything, therefore, depended upon the ability, energy, +and character of the actual director. There was no large organized +staff, established routine, or official tradition, to keep the +institution moving on certain lines, irrespective of the personal +qualities of the chief. It was specially fortunate, therefore, that +the first four Astronomers Royal, Flamsteed, Halley, Bradley, and +Maskelyne (for Bliss, the immediate successor of Bradley, reigned +for so short a time that he may be practically left out of the +count), were all men of the most conspicuous ability. + +It will be convenient to divide the history of the first seven +Astronomers Royal into three sections. In the first, we have the +founder, John Flamsteed, a pathetic and interesting figure, whom +we seem to know with especial clearness, from the fulness of the +memorials which he has left to us. He was succeeded by the man +who was, indeed, best fitted to succeed him, but whom he most +hated. The second to the sixth Astronomers Royal formed what we +might almost speak of as a dynasty, each in turn nominating his +successor, who had entered into more or less close connection with +the Observatory during the lifetime of the previous director; and +the lives of these five may well form the second section. The line +was interrupted after the resignation of the sixth Astronomer Royal, +and the third section will be devoted to the seventh director, +Airy, under whom the Observatory entered upon its modern period of +expansion. + + 'God suffers not man to be idle, although he swim in the midst + of delights; for when He had placed His own image (Adam) in a + paradise so replenished (of His goodness) with varieties of all + things, conducing as well to his pleasure as sustenance, that + the earth produced of itself things convenient for both,--He yet + (to keep him out of idleness) commands him to till, prune, and + dress his pleasant, verdant habitation; and to add (if it might + be) some lustre, grace, or conveniency to that place, which, as + well as he, derived its original from his Creator.' + +In these words JOHN FLAMSTEED begins the first of several +autobiographies which he has handed down to us; this particular one +being written before he attained his majority, 'to keep myself from +idleness and to recreate myself.' + + 'I was born,' he goes on, 'at Denby, in Derbyshire, in the year + 1646, on the 19th day of August, at 7 hours 16 minutes after + noon. My father, named Stephen, was the third son of Mr. William + Flamsteed, of Little Hallam; my mother, Mary, was the daughter + of Mr. John Spateman, of Derby, ironmonger. From these two I + derived my beginning, whose parents were of known integrity, + honesty, and fortune, as they [were] of equal extraction and + ingenuity; betwixt whom I [was] tenderly educated (by reason of + my natural weakness, which required more than ordinary care) + till I was aged three years and a fortnight; when my mother + departed, leaving my father a daughter, then not a month old, + with me, then weak, to his fatherly care and provision.' + +The weakly, motherless boy became at an early age a voracious +reader. At first, he says-- + + 'I began to affect the volubility and ranting stories of + romances; and at twelve years of age I first left off 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 fiction. Afterwards, as my reason + increased, I gathered other real histories; and by the time I + was fifteen years old I had read, of the ancients, Plutarch's + _Lives_, Appian's and Tacitus's _Roman Histories_, Holingshed's + _History of the Kings of England_, Davies's _Life of Queen + Elizabeth_, Saunderson's of _King Charles the First_, Heyling's + _Geography_, and many others of the moderns; besides a company + of romances and other stories, of which I scarce remember a + tenth at present.' + +Flamsteed received his education at the free school at Derby, where +he continued until the Whitsuntide of 1662, when he was nearly +sixteen years of age. Two years earlier than this, however, a great +misfortune fell upon him. + + 'At fourteen years of age,' he writes, 'when I was nearly + arrived to be the head of the free-school, [I was] visited with + a fit of sickness, that was followed with a consumption and + other distempers, which yet did not so much hinder me in my + learning, but that I still kept my station till the form broke + up, and some of my fellows went to the Universities; for which, + though I was designed, my father thought it not advisable to + send me, by reason of my distemper.' + +This was a keen disappointment to him, but seems to have really +been the means of determining his career. The sickly, suffering boy +could not be idle, though 'a day's short reading caused so violent +a headache;' and a month or two after he had left school, he had +a book lent to him--Sacrobosco's _De Sphæra_, in Latin--which was +the beginning of his mathematical studies. A partial eclipse of the +sun in September of the same year seems to have first drawn his +attention to astronomical observation, and during the winter his +father, who had himself a strong passion for arithmetic, instructed +him in that science. + +It was astonishing how quickly his appetite for his new subjects +grew. The _Art of Dialling_, the calculation of tables of the sun's +altitudes for all hours of the day, and for different latitudes, +and the construction of a quadrant--'of which I was not meanly +joyful'--were the occupations of this winter of illness. + +In 1664 he made the acquaintanceship of two friends, Mr. George +Linacre and Mr. William Litchford; the former of whom taught him to +recognize many of the fixed stars, whilst the latter was the means +of his introduction to a knowledge of the motions of the planets. + + 'I had now completed eighteen years, when the winter came + on, and thrust me again into the chimney; whence the heat + and dryness of the preceding summer had happily once before + withdrawn me.' + +The following year, 1665, was memorable to him 'for the appearance +of the comet,' and for a journey which he made to Ireland to be +'stroked' for his rheumatic disorder by Valentine Greatrackes, a +kind of mesmerist, who had the repute of effecting wonderful cures. +The journey, of which he gives a full and vivid account, occupied +a month; but though he was a little better, the following winter +brought him no permanent benefit. + +But, ill or well, he pressed on his astronomical studies. A large +partial eclipse of the sun was due the following June; he computed +the particulars of it for Derby, and observed the eclipse itself to +the best of his ability. He argued out for himself 'the equation +of time'; the difference, that is, between time as given by the +actual sun, or 'apparent time,' and that given by a perfect clock, +or 'mean time.' He drew up a catalogue of seventy stars, computing +their right ascensions, declinations, longitudes, and latitudes +for the year 1701; he attempted to determine the inclination of +the ecliptic, the mean length of the tropical year, and the actual +distance of the earth from the sun. And these were the recreations +of a sickly, suffering young man, not yet twenty-one years of age, +and who had only begun the study of arithmetic, such as fractions +and the rule of three, four years previously! + +His next attempt was almanac-making, in the which he improved +considerably upon those current at the time. His almanac for 1670 +was rejected, however, and returned to him, and, not to lose +his whole labour, he sent his calculations of an eclipse of the +sun, and of five occultations of stars by the moon, which he had +undertaken for the almanac, to the Royal Society. He sent the paper +anonymously, or, rather, signed it with an anagram, 'In mathesi a +sole fundes,' for 'Johannes Flamsteedius.' His covering letter ends +thus:-- + + 'Excuse, I pray you, this juvenile heat for the concerns of + science and want of better language, from one who, from the + sixteenth year of his age to this instant, hath only served one + bare apprenticeship in these arts, under the discouragement of + friends, the want of health, and all other instructors except + his better genius.' + +This letter was dated November 4, 1669, and on January 14, Mr. +Oldenburg, the secretary of the Society, replied to him in a letter +which the young man cannot but have felt encouraging and flattering +to the highest degree. + + 'Though you did what you could to hide your name from us,' + he writes, 'yet your ingenious and useful labours for the + advancement of Astronomy addressed to the noble President of the + Royal Society, and some others of that illustrious body, did + soon discover you to us, upon our solicitous inquiries after + their worthy author.' + +And after congratulating him upon his skill, and encouraging him +to furnish further similar papers, he signs himself, 'Your very +affectionate friend and real servant'--no unmeaning phrase, for the +friendship then commenced ceased only with Oldenburg's life. + +The following June, his father, pleased with the notice that some +of the leading scientific men of the day were taking of his son, +sent him up to London, that he might be personally acquainted with +them; and he then was introduced to Sir Jonas Moore, the Surveyor +of the Ordnance, who made him a present of Townley's micrometer, +and promised to furnish him with object-glasses for telescopes at +moderate rates. + +On his return journey he called at Cambridge, where he visited Dr. +Barrow and Newton, and entered his name in Jesus College. + +It was not until the following year, 1671, that he was enabled to +complete his own observatory, as he had had to wait long for the +lenses which Sir Jonas Moore and Collins had promised to procure +for him. He still laboured under several difficulties, in that he +had no good means for measuring time, pendulum clocks not then +being common. He, therefore, with a practical good sense which was +characteristic, refrained from attempting anything which lay out of +his power to do well, and he devoted himself to such observations as +did not require any very accurate knowledge of the time. At the same +time, he was careful to ascertain the time of his observations as +closely as possible, by taking the altitudes of the stars. + +The next four years seem to have passed exceedingly pleasantly to +him. The notes of ill-health are few. He was making rapid progress +in his acquaintanceship with the work of other astronomers, +particularly with those of the three marvellously gifted young +men--Horrox, Crabtree, and Gascoigne--who had passed away shortly +before his own birth. He was making new friends in scientific +circles, and, in particular, Sir Jonas Moore was evidently esteeming +him more and more highly. In 1674 he became more intimate with +Newton, the occasion which led to this acquaintanceship being the +amusing one, that his assistance was asked by Newton, who had +found himself unable to adjust a microscope, having forgotten its +object-glass--not the only instance of the great mathematician's +absent-mindedness. + +The same year he took his degree of A.M. at Cambridge, designing +to enter the Church; but Sir Jonas Moore was extremely anxious to +give him official charge of an observatory, and was urging the Royal +Society to build an astronomical observatory at Chelsea College, +which then belonged to that body. He therefore came up to London, +and resided some months with Sir Jonas Moore at the Tower. But +shortly after his coming up to London, 'an accident happened,' to +use his own expression, that hastened, if it did not occasion, the +building of Greenwich Observatory. + + 'A Frenchman that called himself Le Sieur de St. Pierre, having + some small skill in astronomy, and made an interest with a + French lady, then in favour at Court, proposed no less than + the discovery of the Longitude, and had procured a kind of + Commission from the King to the Lord Brouncker, Dr. Ward (Bishop + of Salisbury), Sir Christopher Wren, Sir Charles Scarborough, + Sir Jonas Moore, Colonel Titus, Dr. Pell, Sir Robert Murray, + Mr. Hook, and some other ingenious gentlemen about the town and + Court, to receive his proposals, with power to elect, and to + receive into their number, any other skilful persons; and having + heard them, to give the King an account of them, with their + opinion whether or no they were practicable, and would show + what he pretended. Sir Jonas Moore carried me with him to one + of their meetings, where I was chosen into their number; and, + after, the Frenchman's proposals were read, which were: + + '(1) To have the year and day of the observations. + + '(2) The height of two stars, and on which side of the meridian + they appeared. + + '(3) The height of the moon's two limbs. + + '(4) The height of the pole--all to degrees and minutes. + + 'It was easy to perceive, from these demands, that the + sieur understood not that the best lunar tables differed + from the heavens; and that, therefore, his demands were not + sufficient for determining the longitude of the place where + such observations were, or should be, made, from that to which + the lunar tables were fitted, which I represented immediately + to the company. But they, considering the interests of his + patroness at Court, desired to have him furnished according to + his demands. I undertook it; and having gained the moon's true + place by observations made at Derby, February 23, 1672, and + November 12, 1673, gave him observations such as he demanded. + The half-skilled man did not think they could have been given + him, and cunningly answered "_They were feigned_." I delivered + them to Dr. Pell, February 19, 1674-5, who, returning me his + answer some time after, I wrote a letter in English to the + commissioners, and another in Latin to the sieur, to assure him + they were not feigned, and to show them that, if they had been, + yet if we had astronomical tables that would give us the two + places of the fixed stars and the moon's true places, both in + longitude and latitude, nearer than to half a minute, we might + hope to find the longitude of places by lunar observations, but + not by such as he demanded. But that we were so far from having + the places of the fixed stars true, that the Tychonic Catalogues + often erred ten minutes or more; that they were uncertain to + three or four minutes, by reason that Tycho assumed a faulty + obliquity of the ecliptic, and had employed only plain sights + in his observations: and that the best lunar tables differ + one-quarter, if not one-third, of a degree from the heavens; + and lastly, that he might have learnt better methods than he + proposed, from his countryman Morin, whom he had best consult + before he made any more demands of this nature.' + +This was in effect to tell St. Pierre that his proposal was neither +original nor practicable. If St. Pierre had but consulted Morin's +writings (Morin himself had died more than eighteen years before), +he would have known that practically the same proposal had been +laid before Cardinal Richelieu in 1634, and had been rejected, as +quite impracticable in the then state of astronomical knowledge. +Possibly Flamsteed meant further to intimate that St. Pierre had +simply stolen his method from Morin, hoping to trade it off upon +the government of another country; in which case he would no doubt +regard Flamsteed's letter as a warning that he had been found out. + +Flamsteed continues:-- + + 'I heard no more of the Frenchman after this; but was told + that, my letters being shown King Charles, he startled at + the assertion of the fixed stars' places being false in the + catalogue; said, with some vehemence, "He must have them anew + observed, examined, and corrected, for the use of his seamen;" + and further (when it was urged to him how necessary it was to + have a good stock of observations taken for correcting the + motions of the moon and planets), with the same earnestness, + "he must have it done." And when he was asked Who could, or who + should do it? "The person (says he) that informs you of them." + Whereupon I was appointed to it, with the incompetent allowance + aforementioned; but with assurances, at the same time, of such + further additions as thereafter should be found requisite for + carrying on the work.' + +[Illustration: FLAMSTEED'S SEXTANT. + +(_From an engraving in the 'Historia Coelestis.'_)] + +Thus, in his twenty-ninth year, John Flamsteed became the first +Astronomer Royal. In many ways he was an ideal man for the post. +In the twelve years which had passed since he left school he had +accomplished an amazing amount of work. Despite his constant +ill-health and severe sufferings, and the circumstance--which may +be inferred from many expressions in his autobiographies--that he +assisted his father in his business, he had made himself master, +perhaps more thoroughly than any of his contemporaries, of the +entire work of a practical astronomer as it was then understood. +He was an indefatigable computer; the calculation of tables of the +motions of the moon and planets, which should as faithfully as +possible represent their observed positions, had had an especial +attraction for him, and, as has been already mentioned, some years +before his appointment he had drawn up a catalogue of stars, +based upon the observations of Tycho Brahe. More than that, he +had not been a merely theoretical worker, he had been a practical +observer of very considerable skill, and, in the dearth of suitable +instruments, had already made one or two for himself, and had +contemplated the making of others. In his first letter to Sir Jonas +Moore he asks for instruction as to the making of object-glasses +for telescopes, for he was quite prepared to set about the task of +making his own. In addition to his tireless industry, which neither +illness nor suffering could abate, he was a man of singularly exact +and business-like habits. The precision with which he preserves and +records the dates of all letters received or sent is an illustration +of this. On the other hand, he had the defects of his circumstances +and character. His numerous autobiographical sketches betray him, +not indeed as a conceited man, in the ordinary sense of the word, +but as an exceedingly self-conscious one. Devout and high-principled +he most assuredly was, but, on the other hand, he shows in almost +every line he wrote that he was one who could not brook anything +like criticism or opposition. + +Such a man, however efficient, was little likely to be happy as the +first incumbent of a new and important government post; but there +was another circumstance which was destined to cause him greater +unhappiness still. + +If we believe, as surely we must, that not only the moral and the +physical progress of mankind is watched over and controlled by +God's good Providence, but its intellectual progress as well, then +there can be no doubt that John Flamsteed was raised up at this +particular time, not merely to found Greenwich Observatory, and to +assist the solution of the problem of the longitude at sea, but +also, and chiefly, to become the auxiliary to a far greater mind, +the journeyman to a true master-builder. But for the founding of +Greenwich Observatory, and for John Flamsteed's observations made +therein, the working out of Newton's grand theory of gravitation +must have been hindered, and its acceptance by the men of science +of his time immensely delayed. We cannot regard as accidental the +combination, so fortunate for us, of Newton, the great world-genius, +to work out the problem, of Flamsteed, the painstaking observer, to +supply him with the materials for his work, and of the newly-founded +institution, Greenwich Observatory, where Flamsteed was able to +gather those materials together. This is the true debt that we owe +to Flamsteed, that, little as he understood the position in which +he had been placed from the standpoint from which we see it to-day, +yet, to the extent of his ability, and as far as he conceived it +in accordance with his duty, he gave Newton such assistance as he +could. + +This is how we see the matter to-day. It wore a very different +aspect in Flamsteed's eyes; and the two following documents, the +one, the warrant founding the Observatory and making him Astronomer +Royal; the other, the warrant granting him a salary, will go far to +explain his position in the matter. He had a high-sounding, official +position, which could not fail to impress him with a sense of +importance; whilst his salary was so insufficient that he naturally +regarded himself as absolute owner of his own work. + + + _'Warrant for the Payment of Mr. Flamsteed's Salary._ + + 'Charles Rex. + + 'Whereas, we have appointed our trusty and well-beloved John + Flamsteed, Master of Arts, our astronomical observator, + forthwith to apply himself with the most exact care and + diligence to the rectifying the tables of the motions of the + heavens, and the places of the fixed stars, so as to find out + the so-much-desired longitude of places for the perfecting the + art of navigation, Our will and pleasure is, and we do hereby + require and authorize you, for the support and maintenance of + the said John Flamsteed, of whose abilities in astronomy we have + very good testimony, and are well satisfied, that from time + to time you pay, or cause to be paid, unto him, the said John + Flamsteed, or his assigns, the yearly salary or allowance of + one hundred pounds per annum; the same to be charged and borne + upon the quarter-books of the Office of the Ordnance, and paid + to him quarterly, by even and equal portions, by the Treasurer + of our said office, the first quarter to begin and be accompted + from the feast of St. Michael the Archangel last past, and so to + continue during our pleasure. And for so doing, this shall be as + well unto you, as to the Auditors of the Exchequer, for allowing + the same, and all other our officers and ministers whom it may + concern, a full and sufficient warrant. + + 'Given at our Court at Whitehall, the 4th day of March, 1674-5. + + 'By his Majesty's Command, + 'J. WILLIAMSON. + + 'To our right-trusty and well-beloved Counsellor, Sir + Thomas Chichely, Knt., Master of our Ordnance, and to the + Lieutenant-General of our Ordnance, and to the rest of the + Officers of our Ordnance, now and for the time being, and to all + and every of them.' + + + _'Warrant for Building the Observatory._ + + 'Charles Rex. + + 'Whereas, in order to the finding out of the longitude of places + for perfecting navigation and astronomy, we have resolved to + build a small observatory within our park at Greenwich, upon + the highest ground, at or near the place where the Castle + stood, with lodging-rooms for our astronomical observator and + assistant, Our will and pleasure is, that according to such plot + and design as shall be given you by our trusty and well-beloved + Sir Christopher Wren, Knight, our surveyor-general of the place + and scite of the said observatory, you cause the same to be + fenced in, built and finished with all convenient speed, by such + artificers and workmen as you shall appoint thereto, and that + you give order unto our Treasurer of the Ordnance for the paying + of such materials and workmen as shall be used and employed + therein, out of such monies as shall come to your hands for old + and decayed powder, which hath or shall be sold by our order of + the 1st of January last, provided that the whole sum, so to be + expended or paid, shall not exceed five hundred pounds; and our + pleasure is, that all our officers and servants belonging to our + said park be assisting to those that you shall appoint, for the + doing thereof, and for so doing, this shall be to you, and to + all others whom it may concern, a sufficient warrant. + + 'Given at our Court at Whitehall, the 22nd day of June, 1675, in + the 27th year of our reign. + + 'By his Majesty's Command, + 'J. WILLIAMSON. + + 'To our right-trusty and well-beloved Counsellor, Sir Thomas + Chichely, Knt., Master-General of our Ordnance.' + +The first question that arose, when it had been determined to found +the new Observatory, was where it was to be placed. Hyde Park was +suggested, and Sir Jonas Moore recommended Chelsea College, where +he had already thought of establishing Flamsteed in a private +observatory. Fortunately, both these localities were set aside in +favour of one recommended by Sir Christopher Wren. There was a small +building on the top of the hill in the Royal Park of Greenwich +belonging to the Crown, and which was now of little or no use. +Visible from the city, and easily accessible by that which was then +the best and most convenient roadway, the river Thames, it was yet +so completely out of town as to be entirely safe from the smoke +of London. In Greenwich Park, too, but on the more easterly hill, +Charles I. had contemplated setting up an observatory, but the +pressure of events had prevented him carrying out his intention. +A further practical advantage was that materials could be easily +transported thither. The management of public affairs under Charles +II. left much to be desired in the matter of efficiency and economy, +and it was not very easy to procure what was wanted for the erection +of a purely scientific building. However, the matter was arranged. +A gate-house demolished in the Tower supplied wood; iron, and +lead, and bricks were supplied from Tilbury Fort, and these could +be easily brought by water to the selected site. The sum of £500, +actually £520, was further allotted from the results of a sale +of spoilt gunpowder; and with these limited resources Greenwich +Observatory was built. + +The foundation-stone was laid August 10, 1675, and Flamsteed +amused himself by drawing the horoscope of the Observatory, a +fact which--in spite of his having written across the face of the +horoscope _Risum teneatis amici?_ (Can you keep from laughter, my +friends?), and his having two or three years before written very +severely against the imposture of astrology--has led some modern +astrologers to claim him as a believer in their cult. He actually +entered into residence July 10, 1676. + +[Illustration: THE ROYAL OBSERVATORY IN FLAMSTEED'S DAY. + +(_From an engraving in the 'Historia Coelestis.'_)] + +His position was not a bright one. The Government had, indeed, +provided him with a building for his observatory, and a small house +for his own residence, but he had no instrument and no assistant. +The first difficulty was partly overcome for the moment by gifts +or loans from Sir Jonas Moore, and by one or two small loans from +the Royal Society. The death of this great friend and patron, +four years after the founding of the Observatory, and only three +years after his entering into residence, deprived him of several +of these; it was with difficulty that he maintained against Sir +Jonas' heirs his claim to the instruments which Sir Jonas had given +him. There was nothing for him to do but to make his instruments +himself, and in 1683 he built a mural quadrant of fifty inches +radius. His circumstances improved the following year, when Lord +North gave him the living of Burstow, near Horley, Surrey, Flamsteed +having received ordination almost at the time of his appointment +to the Astronomer Royalship. We have little or no account of the +way in which he fulfilled his duties as a clergyman. Evidently he +considered that his position as Astronomer Royal had the first +claim upon him. At the same time, comparatively early in life he +had expressed his desire to fill the clerical office, and he was a +man too conscientious to neglect any duty that lay upon him. That +in spite of his feeble health he often journeyed to and fro between +Burstow and Greenwich we know; and we may take it as certain that at +a time when the standard of clerical efficiency was extremely low, +he was not one of those who + + 'For their bellies' sake, + Creep and intrude and climb into the fold.' + +His chief source of income, however, seems to have been the private +pupils whom he took in mathematics and astronomy. These numbered in +the years 1676 to 1709 no fewer than 140; and as many of them were +of the very first and wealthiest families in the kingdom, the gain +to Flamsteed in money and influence must have been considerable. But +it was most distasteful work. It was in no sense that which he felt +to be his duty, and which he had at heart. It was undertaken from +sheer, hard necessity, and he grudged bitterly the time and strength +which it diverted from his proper calling. + +How faithfully he followed that, one single circumstance will show. +In the thirteen years ending 1689, he made 20,000 observations, and +had revised single-handed the whole of the theories and tables of +the heavenly bodies then in use. + +In 1688 the death of his father brought him a considerable accession +of means, and, far more important, the assistance of Abraham +Sharp,[1] the first and most distinguished of the long list of +Greenwich assistants, men who, though far less well known than the +Astronomers Royal, have contributed scarcely less in their own field +to the high reputation of the Observatory. + + [1] Abraham Sharp had been with Flamsteed earlier than this--in 1684 + and 1685. + +Sharp was not only a most careful and indefatigable calculator, +he was what was even more essential for Flamsteed--a most skilful +instrument-maker; and he divided for him a new mural arc of 140° and +seven feet radius, with which he commenced operations on December +12, 1689. Above all, Sharp became his faithful and devoted friend +and adherent, and no doubt his sympathy strengthened Flamsteed to +endure the trouble which was at hand. + +That trouble began in 1694, when Newton visited the Royal +Observatory. At that time Flamsteed, though he had done so much, +had published nothing, and Newton, who had made his discovery of +the laws of gravitation some few years before, was then employed +in deducing from them a complete theory of the moon's motion. This +work was one of absolutely first importance. In the first place +and chiefly, upon the success with which it could be carried out, +depended undoubtedly the acceptance of the greatest discovery +which has yet been made in physical science. Secondarily--and this +should, and no doubt did, appeal to Flamsteed--the perfecting of +our knowledge of the movements of the moon was a primary part of +the very work which he was commissioned to do as Astronomer Royal. +Newton was, therefore, anxious beyond everything to receive the +best possible observations of the moon's places, and he came to +Flamsteed, as to the man from whom he had a right to expect to +receive a supply of them. At first Flamsteed seems to have given +these as fully as he was able; but it is evident that Newton chafed +at the necessity for these frequent applications to Flamsteed, and +to the constant need of putting pressure upon him. Flamsteed, on the +other hand, as clearly evidently resented this continual demand. +Feeling, as he keenly did, that, though he had been named Astronomer +Royal, he had been left practically entirely without support; his +instruments were entirely his own, either made or purchased by +himself; his nominal salary of £100 was difficult to get, and did +not nearly cover the actual current expenses of his position, he not +unnaturally regarded his observations as his own exclusive property. +He had a most natural dislike for his observations to be published, +except after such reduction as he himself had carried through, +and in the manner which he himself had chosen. The idea which was +ever before him was that of carrying out a single great work that +should not only be a monument to his own industry and skill, but +should also raise the name of England amongst scientific nations. He +complained of it, therefore, both as a personal wrong and an injury +to the country when some observations of Cassini's were combined +with some observations of his own in order to deduce a better orbit +for a comet. + +Unknown to himself, therefore, he was called upon to decide a +question that has proved fundamental to the policy of Greenwich +Observatory, and he decided it wrongly--the question of publication. +Newton had urged upon him as early as 1691 that he should not wait +until he had formed an exhaustive catalogue of all the brighter +stars, but that he should publish at once a catalogue of a few, +which might serve as standards; but Flamsteed would not hear of it. +He failed to see that his office had been created for a definite +practical purpose, not for the execution of some great scheme, +however important to science. All his work of thirty years had done +nothing to forward navigation so long as he published nothing. But +if, year by year, he had published the places of the moon and of a +few standard stars, he would have advanced the art immensely and +yet have not hindered himself from eventually bringing out a great +catalogue. No doubt the little incident of Newton's difficulty +with the microscope, of which he had forgotten the object-glass, +had given Flamsteed a low opinion of Newton's qualifications as a +practical astronomer. If so, he was wrong, for Newton's insight +into practical matters was greater than Flamsteed's own, and his +practical skill was no less, though his absent-mindedness might +occasionally lead him into an absurd mistake. + +The following extract from Flamsteed's own 'brief History of the +Observatory' gives an account of his view of Newton's action towards +him in desiring the publication of his star catalogue, and at the +same time it illustrates Flamsteed's touchy and suspicious nature. + + 'Whilst Mr. Flamsteed was busied in the laborious work of + the catalogue of the fixed stars, and forced often to watch + and labour by night, to fetch the materials for it from the + heavens, that were to be employed by day, he often, on Sir Isaac + Newton's instances, furnished him with observations of the + moon's places, in order to carry on his correction of the lunar + theory. A civil correspondence was carried on between them; only + Mr. Flamsteed could not but take notice that as Sir Isaac was + advanced in place, so he raised himself in his conversation and + became more magisterial. At last, finding that Mr. Flamsteed + had advanced far in his designed catalogue by the help of his + country calculators, that he had made new lunar tables, and + was daily advancing on the other planets, Sir Isaac Newton + came to see him (Tuesday, April 11, 1704); and desiring, after + dinner, to be shown in what forwardness his work was, had so + much of the catalogue of the fixed stars laid before him as was + then finished; together with the maps of the constellations, + both those drawn by T. Weston and P. Van Somer, as also his + collation of the observed places of Saturn and Jupiter, with + the Rudolphine numbers. Having viewed them well, he told Mr. + Flamsteed he would (_i.e._ he was desirous to) recommend them + to the Prince _privately_. Mr. Flamsteed (who had long been + sensible of his partiality, and heard how his two flatterers + cried Sir Isaac's performances up, was sensible of the snare in + the word _privately_) answered that would not do; and (upon Sir + Isaac's demanding "why not?") that then the Prince's attendants + would tell him these were but curiosities of no great use, and + persuade him to save that expense, that there might be the + more for them to beg of him: and that the recommendation must + be made _publicly_, to prevent any such suggestions. Sir Isaac + apprehended right, that he was understood, and his designs + defeated: and so took his leave not well satisfied with the + refusal. + + 'It was November following ere Mr. Flamsteed heard from him any + more: when, considering with himself that what he had done was + not well understood, he set himself to examine how many folio + pages his work when printed would fill; and found upon an easy + computation that they would at least take up 1400. Being amazed + at this, he set himself to consider them more seriously; drew + up an estimate of them; and, to obviate the misrepresentations + of Dr. S[loane] and some others, who had given out that what he + had was inconsiderable, he delivered a copy of the estimate to + Mr. Hodgson, then lately chosen a member of the Royal Society, + with directions to deliver it to a friend, who he knew would do + him justice; and, on this fair account, obviate those unjust + reports which had been studiously spread to his prejudice. It + happened soon after, Mr. Hodgson being at a meeting, spied this + person there, at the other side of the room; and therefore gave + the paper to one that stood in some company betwixt them, to be + handed to him. But the gentleman, mistaking his request, handed + to the Secretary [Dr. Sloane], who, being a Physician, and not + acquainted with astronomical terms, did not read it readily. + Whereupon another in the company took it out of his hands; + and, having read it distinctly, desired that the works therein + mentioned might be recommended to the Prince; the charge of + printing them being too great either for the author or the Royal + Society. Sir Isaac closed in with this.' + +[Illustration: THE 'CAMERA STELLATA' IN FLAMSTEED'S TIME. + +(_From an engraving in the 'Historia Coelestis.'_)] + +The work was in consequence recommended to Prince George of Denmark, +the Queen's Consort; but it was not till November 10, 1705, that +the contract for the printing was signed. Two years later, the +observations which he had made with his sextant in his first +thirteen years of office were printed. Then came the difficulty of +the catalogue. It was not complete to Flamsteed's satisfaction, and +he was most unwilling to let it pass out of his hands. However, +two manuscripts, comprising some three-quarters of the whole, were +deposited with referees, the first of these being sealed up. The +seal was broken with Flamsteed's concurrence; but the fact that it +had been so broken was made by him the subject of bitter complaint +later. At this critical juncture Prince George died, and a stop +was put to the progress of the printing. Two years more elapsed +without any advance being made, and then, in order to check any +further obstruction, a committee of the Royal Society was appointed +as a Board of Visitors to visit and inspect the Observatory, and so +maintain a control over the Astronomer Royal. This was naturally +felt by so sensitive a man as Flamsteed as a most intolerable wrong, +and when he found that the printing of his catalogue had been placed +in the hands of Halley as editor, a man for whom he had conceived +the most violent distrust, he absolutely refused to furnish the +Visitors with any further material. This led to, perhaps, the most +painful scene in the lives either of Newton or Flamsteed. Flamsteed +was summoned to meet the Council of the Royal Society at their rooms +in Crane Court. A quorum was not present, and so the interview was +not official, and no record of it is preserved in the archives. +Flamsteed has himself described it with great particularity in more +than one document, and it is only too easy to understand the scene +that took place. Newton was a man who had an absolutely morbid dread +of anything like controversy, and over and over again would have +preferred to have buried his choicest researches, rather than to +have encountered the smallest conflict of the kind. He was perhaps, +therefore, the worst man to deal with a high-principled, sensitive, +and obstinate man who was in the wrong, and yet who had been so +hardly dealt with that it was most natural for him to think himself +wholly in the right. Flamsteed adhered absolutely to his position, +from which it is clear it would have been extremely difficult for +the greatest tact and consideration to have dislodged him. Newton, +on his part, simply exerted his authority, and, that failing, was +reduced to the miserable extremity of calling names. The scene is +described by Flamsteed himself, in a letter to Abraham Sharp, as +follows:-- + + 'I have had another contest with the President[2] of the + Royal Society, who had formed a plot to make my instruments + theirs; and sent for me to a Committee, where only himself and + two physicians (Dr. Sloane, and another as little skilful as + himself) were present. The President ran himself into a great + heat, and very indecent passion. I had resolved aforehand + his kn--sh talk should not move me; showed him that all the + instruments in the Observatory were my own; the mural arch and + voluble quadrant having been made at my own charge, the rest + purchased with my own money, except the sextant and two clocks, + which were given me by Sir Jonas Moore, with Mr. Towneley's + micrometer, his gift, some years before I came to Greenwich. + This nettled him; for he has got a letter from the Secretary of + State for the Royal Society to be Visitors of the Observatory, + and he said, "_as good have no observatory as no instruments_." + I complained then of my catalogue being printed by Raymer, + without my knowledge, and that I was _robbed of the fruit of my + labours_. At this he fired, and called me all the ill names, + puppy, etc., that he could think of. All I returned was, I put + him in mind of his passion, desired him to govern it, and keep + his temper: this made him rage worse, and he told me how much + I had received from the Government in thirty-six years I had + served. I asked what he had done for the £500 per annum that he + had received ever since he had settled in London. This made him + calmer; but finding him going to burst out again, I only told + him my catalogue, half finished, was delivered into his hands, + on his own request, sealed up. He could not deny it, but said + Dr. Arbuthnott had procured the Queen's order for opening it. + This, I am persuaded, was false; or it was got after it had been + opened. I said nothing to him in return; but, with a little + more spirit than I had hitherto showed, told them that God (who + was seldom spoken of with due reverence in that meeting) had + hitherto prospered all my labours, and I doubted not would do so + to a happy conclusion; took my leave and left them. Dr. Sloane + had said nothing all this while; the other Doctor told me I was + proud, and insulted the President, and ran into the same passion + with the President. At my going out, I called to Dr. Sloane, + told him he had behaved himself civilly, and thanked him for it. + I saw Raymer after, drank a dish of coffee with him, and told + him, still calmly, of the villany of his conduct, and called it + _blockish_. Since then they let me be quiet; but how long they + will do so I know not, nor am I solicitous.' + + [2] Sir Isaac Newton. + +The Visitors continued the printing, Halley being the editor, and +the work appeared in 1712 under the title of _Historia Coelestis_. +This seemed to Flamsteed the greatest wrong of all. The work as it +appeared seemed to him so full of errors, wilfully or accidentally +inserted, as to be the greatest blot upon his fair fame, and he +set himself, though now an old man, to work it out _de novo_ and +at his own expense. To that purpose he devoted the remaining seven +years of his life. Few things can be more pathetic than the letters +which he wrote in that period referring to it. He was subject to +the attacks of one of the cruelest of all diseases--the stone; he +was at all times liable to distracting headaches. He had been, from +his boyhood, a great sufferer from rheumatism, and yet, in spite of +all, he resolutely pushed on his self-appointed task. The following +extract from one of his letters will give a more vivid idea of the +brave old man than much description:-- + + 'I can still, I praise God for it, walk from my door to the + Blackheath gate and back, with a little resting at some benches + I have caused to be set up betwixt them. But I found myself so + tired with getting up the hill when I return from church, that + at last I have bought a sedan, and am carried thither in state + on Sunday mornings and back; I hope I may employ it in the + afternoons, though I have not hitherto, by reason of the weather + is too cold for me.' + +After the death of Queen Anne, a change in the ministry enabled +him to secure that three hundred copies of the total impression of +four hundred of the _Historia Coelestis_ were handed over to him. +These, except the first volume, containing his sextant observations +(which had received his own approval), he burned, 'as a sacrifice +to heavenly truth.' His own great work had advanced so far that the +first volume was printed, and much of the second, when he himself +died, on the last day of 1719. He was buried in the chancel of +Burstow Church. + +The completion of his work took ten years more; a work of piety and +regard on the part of his assistant, Joseph Crosthwait. + +When compared with the catalogues that have gone before, it was +a work of wonderful accuracy. Nevertheless, as Caroline Herschel +showed, nearly a century later, not a few errors had crept into it. +Some of the stars are non-existent, others have been catalogued in +more than one constellation; important stars have been altogether +omitted. Perhaps the most serious fault arises from the neglect of +Flamsteed to accept from Newton a practical hint, namely, to read +the barometer and thermometer at the time of his observations. +Nevertheless, the work accomplished was not only wonderful under the +untoward conditions in which Flamsteed was placed; it was wonderful +in itself, winning from Airy the following high encomium:-- + + 'In regard not only to accuracy of observation, and to detail in + publication of the methods of observing, but also to steadiness + of system followed through many years, and to completeness of + calculation of the useful results deduced from the observations, + this work may shame any other collection of observations in this + or any other country.' + +This catalogue was not Flamsteed's only achievement. He had +determined the latitude of the Observatory, the obliquity of the +ecliptic, and the position of the equinoctial points. He thought out +an original method of obtaining the absolute right ascensions of +stars by differential observations of the places of the stars and +the sun near to both equinoxes. He had revised and improved Horrox's +theory of the lunar motions, which was by far the best existing in +Flamsteed's day. He showed the existence of the long inequality of +Jupiter and Saturn; that is to say, the periodic influence which +they exercise upon each other. He determined the time in which the +sun rotates on its axis, and the position of that axis. He observed +an apparent movement of the stars in the course of a year, which he +ascribed, though erroneously, to the stellar parallax, and which was +explained by the third Astronomer Royal, Bradley. + +Flamsteed not only met with harsh treatment during his lifetime; he +has not yet received, except from a few, anything like the meed of +appreciation which is his just due; but, at least, his successors in +the office have not forgotten him. They have been proud that their +official residence should be known as Flamsteed House, and his name +is inscribed over the main entrance of the latest and finest of +the Observatory buildings, and his bust looks forth from its front +towards the home where he laboured so devotedly for nearly fifty +years. But he has received little honour, save at Greenwich, and--in +spite of the proverb--in his other home, the village of Burstow, in +Surrey, of which he was for many years the rector. Here a stained +glass window representing, appropriately, the Adoration of the Magi, +has been recently set up to his memory, largely through the interest +taken in his history by an amateur astronomer of the neighbourhood, +Mr. W. Tebb, F.R.A.S. + +No instrument of Flamsteed's remains in the Observatory, his wife +removing them after his death. But we may consider his principal +instrument, the mural quadrant made for him by Abraham Sharp, as +represented by the remains of a quadrant by the same artist, which +was presented to the Observatory by the Rev. N. S. Heineken, in +1865, and now hangs over the door of the transit room. + + + + +CHAPTER III + +HALLEY AND HIS SUCCESSORS + + + There is no need to give the lives of the succeeding Astronomers + Royal so fully as that of Flamsteed. Not that they were inferior + men to him; on the contrary, there can be little doubt that + we ought to reckon some of them as his superiors, but, in the + case of several, their best work was done apart from Greenwich + Observatory, and before they came to it. + +This was particularly the case with EDMUND HALLEY. Born on October +29, 1656, he was ten years the junior of Flamsteed. Like Flamsteed, +he came of a Derbyshire family, though he was born at Haggerston, +in the parish of St. Leonard's, Shoreditch. He was educated at St. +Paul's School, where he made very rapid progress, and already showed +the bent of his mind. He learnt to make dials; he made himself so +thoroughly acquainted with the heavens that it is said, 'If a star +were displaced in the globe he would presently find it out,' and +he observed the changes in the direction of the mariner's compass. +In 1673 he went to Queen's College, Oxford, where he observed a +sunspot in July and August, 1676, and an occultation of Mars. This +was not his first astronomical observation, as, in June, 1675, +he had observed an eclipse of the moon from his father's house in +Winchester Street. + +[Illustration: EDMUND HALLEY. + +(_From an old print._)] + +A much wider scheme of work than such merely casual observations +now entered his mind, possibly suggested to him by Flamsteed's +appointment to the direction of the new Royal Observatory. This was +to make a catalogue of the southern stars. Tycho's places for the +northern stars were defective enough, but there was no catalogue at +all of stars below the horizon of Tycho's observatory. Here, then, +was a field entirely unworked, and young Halley was so eager to +enter upon it that he would not wait at Oxford to obtain his degree, +but was anxious to start at once for the southern hemisphere. + +His father, who was wealthy and proud of his gifted son, strongly +supported him in his project. The station he selected was St. +Helena, an unfortunate choice, as the skies there were almost +always more or less clouded, and rain was frequent during his stay. +However, he remained there a year and a half, and succeeded in +making a catalogue of 341 stars. This catalogue was finally reduced +by Sharp, and included in the third volume of Flamsteed's _Historia +Coelestis_. + +In 1678 he was elected Fellow of the Royal Society, and the +following year he was chosen to represent that society in a +discussion with Hevelius. The question at issue was as to whether +more accurate observations of the place of a star could be obtained +by the use of sights without optical assistance, or by the use of +a telescope. The next year he visited the Paris Observatory, and, +later in the same tour, the principal cities of the Continent. + +Not long after his return from this tour, Halley was led to that +undertaking for which we owe him the greatest debt of gratitude, and +which must be regarded as his greatest achievement. + +Some fifty years before, the great Kepler had brought out the third +of his well-known laws of planetary motion. These laws stated +that the planets move round the sun in ellipses, of which the sun +occupies one of the foci; that the straight line joining any planet +with the sun moves over equal areas of space in equal periods of +time; and, lastly, that the squares of the times in which the +several planets complete a revolution round the sun are proportional +to the cubes of their mean distances from it. These three laws were +deduced from actual examination of the movements of the planets. +Kepler did not work out any underlying cause of which these three +laws were the consequence. + +But the desire to find such an underlying cause was keen amongst +astronomers, and had given rise to many researches. Amongst those +at work on the subject was Halley himself. He had seen, and been +able to prove, that if the planets moved in circles round the sun, +with the sun in the centre, then the law of the relation between the +times of revolution and the distances of the planets would show that +the attractive force of the sun varied inversely as the square of +the distance. The actual case, however, of motion in an ellipse was +too hard for him, and he could not deal with it. Halley therefore +went up to Cambridge to consult Newton, and, to his wonder and +delight, found that the latter had already completely solved the +problem, and had proved that Kepler's three laws of planetary motion +were summed up in one, namely, that the sun attracted the planets to +it with a force inversely proportional to the square of the distance. + +Halley was most enthusiastic over this great discovery, and he at +once strongly urged Newton to publish it. Newton's unwillingness to +do so was great, but at length Halley overcame his reluctance; and +the Royal Society not being able at the time to afford the expense, +Halley took the charges upon himself, although his own resources had +been recently seriously damaged by the death of his father. + +The publication of Newton's _Principia_, which, but for him, might +never have seen the light, and most certainly would have been long +delayed, is Halley's highest claim to our gratitude. But, apart +from this, his record of scientific achievement is indeed a noble +one. Always, from boyhood, he had taken a great interest in the +behaviour of the magnetic compass, and he now followed up the study +of its variations with the greatest energy. For this purpose it was +necessary that he should travel, in view of the great importance of +the subject to navigation. King William III. gave him a captain's +commission in the Royal Navy--a curious and interesting illustration +of the close connection between astronomy and the welfare of our +navy--and placed him in command of a 'pink,' that is to say, a small +vessel with pointed stern, named the Paramour, in which he proceeded +to the southern ocean. His first voyage was unfortunate, but the +Paramour was recommissioned in 1699, and he sailed in it as far as +south latitude 52°. + +In 1701 and the succeeding year he made further voyages in the +Paramour, surveying the tides and coasts of the British Channel +and of the Adriatic, and helping in the fortification of Trieste. +He became Savilian Professor of Geometry at Oxford in 1703, having +failed twelve years previously to secure the Savilian Professorship +of Astronomy, mainly through the opposition of Flamsteed, who had +already formed a strong prejudice against him, which some writers +have traced to Halley's detection of several errors in one of +Flamsteed's tide-tables, others to Halley's supposed materialistic +views. Probably the difference was innate in the two men. There was +likely to be but little sympathy between the strong, masterful man +of action and society and the secluded, self-conscious, suffering +invalid. At any rate, in the contest between Newton and Flamsteed, +which has been already described, Halley took warmly the side of the +former, and was appointed to edit the publication of Flamsteed's +results, and, on the death of the latter, to succeed him at the +Royal Observatory. + +The condition of things at Greenwich when Halley succeeded to +the post of Astronomer Royal in 1720 was most discouraging. The +instruments there had all belonged to Flamsteed, and therefore, +most naturally, had been removed by his widow. The Observatory +had practically to be begun _de novo_, and Halley had now almost +attained the age at which in the present day an Astronomer +Royal would have to retire. More fortunate, however, than his +predecessor, he was able to get a grant for instruments, and he +equipped the Observatory as well as the resources of the time +permitted, and his transit instrument and great eight-foot quadrant +still hang upon the Observatory walls. + +As Astronomer Royal his great work was the systematic observation +of the positions of the moon through an entire _saros_. As is well +known, a period of eighteen years and ten or eleven days brings the +sun and moon very nearly into the same positions relatively to the +earth which they occupied at the commencement of the period. This +period was well known to the ancient Chaldeans, who gave it its +name, since they had noticed that eclipses of the sun or eclipses of +the moon recurred at intervals of the above length. It was Halley's +desire to obtain such a set of observations of the moon through an +entire _saros_ period as to be able to deduce therefrom an improved +set of tables of the moon's motion. It was an ambitious scheme for +a man so much over sixty to undertake, nevertheless he carried it +through successfully. + +His desire to complete this scheme, and to found upon it improved +lunar tables, hindered him from publishing his observations, for +he feared that others might make use of them before he was in a +position to complete his work himself. This omission to publish +troubled Newton, who, as President of the Royal Society--the +Greenwich Board of Visitors having lapsed at Queen Anne's +death--drew attention at a meeting of the Royal Society, March 2, +1727, to Halley's disobedience of the order issued under Queen +Anne, for the prompt communication of the Observatory results. That +Newton should thus have put public pressure upon Halley, the man to +whom he was so much indebted, and with whom there was so close an +affection, is sufficient proof that his similar attitude towards +Flamsteed was one of principle and not of arbitrariness. Halley, on +his side, stood firm, as Flamsteed had done, urging the danger that, +by publishing before he had completed his task, he might give an +opportunity to others to forestall his results. It is said--probably +without sufficient ground--that this refusal broke Newton's heart +and caused his death. Certainly Halley's writings in that very year +show his reverence and affection for Newton to have been as keen and +lively as ever. + +Halley's work at the Observatory went on smoothly, on the lines he +had laid down for himself, for ten years after Newton's death; but +in 1737 he had a stroke of paralysis, and his health, which had +been remarkably robust up to that time, began to give way. He died +January 14, 1742, and was buried in the cemetery of Lee Church. + +As an astronomer, his services to the science rank higher than those +of his predecessor; but as Astronomer Royal, as director, that is to +say, of Greenwich Observatory, he by no means accomplished as much +as Flamsteed had done. Professor Grant, in his _History of Physical +Astronomy_, says that he seems to have undervalued those habits of +minute attention which are indispensable to the attainment of a high +degree of excellence in the practice of astronomical observation. He +was far from being sufficiently careful as to the adjustment of his +instruments, the going of his clocks, or the recording of his own +observations. The important feature of his administration was that +under him the Observatory was first supplied with instruments which +belonged to it. + +[Illustration: HALLEY'S QUADRANT. + +(_From an old print._)] + +His astronomical work apart from the Observatory was of the first +importance. He practically inaugurated the study of terrestrial +magnetism, and his map giving the results of his observations during +his voyage in the Paramour introduced a new and most useful style +of recording observations. He joined together by smooth curves +places of equal variation, the result being that the chart shows at +a glance, not merely the general course of the variation over the +earth's surface, but its value at any spot within the limits of the +chart. + +Another work which has justly made his name immortal was the +prediction of the return of the comet which is called by his name, +to which reference will be made later. Another great scheme, and +one destined to bear much fruit, was the working out of a plan to +determine the distance of the sun by observations of the transit of +Venus. + +Of attractive appearance, pleasing manners, and ready wit, loyal, +generous, and free from self-seeking, he probably was one of the +most personally engaging men who ever held the office. + +The salary of the Astronomer Royal remained under Halley at the same +inadequate rate which it had done under Flamsteed--£100, without +provision for an assistant. But in 1729 Queen Caroline, learning +that Halley had actually had a captain's commission in the Royal +Navy, secured for him a post-captain's pay. + +[Illustration: JAMES BRADLEY. + +(_From the painting by Hudson._)] + +Halley's work is represented at the Observatory by two of his +instruments which are still preserved there, and which hang on the +west wall of the present transit room: the Iron Quadrant afterwards +made famous by the observations of Bradley, and 'Halley's Transit,' +the first of the great series of instruments upon which the fame of +Greenwich chiefly rests. This transit instrument seems to have been +set up in a small room at the west end of what is now known as the +North Terrace. His quadrant was mounted on the pier which is now the +base of the pier of the astrographic telescope. This pier was the +first extension which the Observatory received from the original +building. + +On the breakdown of his health Halley nominated as his successor, +James Bradley; indeed, it is stated that he offered to resign +in his favour. He had known him then for over twenty years, and +that keen and generous appreciation of merit in others which was +characteristic of Halley had led him very early to recognize +Bradley's singular ability. + + * * * * * + +JAMES BRADLEY was born in 1692 or 1693, of an old North of England +family. His birthplace was Sherbourne, in Gloucestershire, and he +was educated at North Leach Grammar School and at Baliol College, +Oxford. During the years of his undergraduateship he resided much +with his uncle, the Rev. James Pound, Rector of Wanstead, Essex, an +ardent amateur astronomer, a frequent visitor at the Observatory +in Flamsteed's time, and one of the most accurate observers in the +country. From him, no doubt, he derived his love of the science, +and possibly some of his skill in observation. + +Bradley's earliest observations seem to have been devoted to the +phenomena of Jupiter's satellites and to the measures of double +stars. The accuracy with which he followed up the first drew the +attention of Halley, and so began a friendship which lasted through +life. His observations of double stars, particularly of Castor, only +just failed to show him the orbital movement of the pair, because +his attention was drawn to other subjects before it had become +sufficiently obvious. + +In 1719 Bradley and his uncle made an attempt to determine the +distance of the sun through observations of Mars when in opposition, +observations which were so accurate that they sufficed to show that +the distance of the sun could not be greater than 125 millions +of miles, nor less than about 94 millions. The lower limit which +they thus found has proved to be almost exactly correct, our best +modern determinations giving it as 93 millions. The instrument with +which the observations were made was a novel one, being 'moved by a +machine that made it to keep pace with the stars;' in other words, +it was the first, or nearly the first, example of what we should now +call a clock-driven equatorial. + +That same year he was offered the Vicarage of Bridstow, near Ross, +in Monmouthshire, where, having by that time taken priest's orders, +he was duly installed, July, 1720. To this was added the sinecure +Rectory of Llandewi-Velgry; but he held both livings only a very +short time. In 1721 the death of Dr. John Keill rendered vacant the +Savilian Professorship of Astronomy at Oxford, for which Bradley +became a candidate, and was duly elected, and resigned his livings +in consequence. + +It was whilst he was Savilian Professor that Bradley made that +great discovery which will always be associated with his name. +Though professor at Oxford, he had continued to assist his uncle, +Mr. Pound, at his observations at Wanstead, and after the death of +the latter he still lived there as much as possible, and continued +his astronomical work. But in 1725 he was invited by Mr. Samuel +Molyneux, who had set up a twenty-four-foot telescope made by +Graham as a zenith tube at his house on Kew Green, to verify some +observations which he was making. These were of the star Gamma +Draconis, a star which passes through the zenith of London, and +which, therefore, had been much observed both by Flamsteed and +Hooke, inasmuch as by fixing a telescope in an absolutely vertical +position--a position which could be easily verified--it was easy to +ascertain if there was any minute change in the apparent position +of the star. Dr. Hooke had declared that there was such a change, +a change due to the motion of the earth in its orbit, which would +prove that the star was not an infinite distance from the earth, the +seeming change of its place in the sky corresponding to the change +in the place of the earth from which the observer was viewing it. + +Bradley found at once that there was such a change--a marked one. It +amounted to as much as 1ŽŽ of arc in three days; but it was not in +the direction in which the parallax of the star would have moved +it, but in the opposite. Whether, therefore, the star was near +enough to show any parallax or not, some other cause was giving rise +to an apparent displacement of the star, which entirely masked and +overcame the effect of parallax. + +So far, Bradley had but come to the same point which Flamsteed +had reached. Flamsteed had detected precisely the same apparent +displacement of stars, and, like Hooke, had ascribed it to +parallax. Cassini had shown that this could not be the case, as +the displacement was in the wrong direction; and there the matter +had rested. Bradley now set to follow the question up. Other stars +beside Gamma Draconis were found to show a displacement of the same +general character, but the amount varied with their distance from +the plane of the ecliptic, the earth's orbit. The first explanation +suggested was that the axis of the earth, which moves very nearly +parallel to itself as the earth moves round the sun, underwent a +slight regular 'wobble' in the course of a year. To check this, +a star was observed on the opposite side of the pole from Gamma +Draconis; then Bradley investigated as to whether refraction might +explain the difficulty, but again without success. He now was +most keenly interested in the problem, and he purchased a zenith +telescope of his own, made, like that of Molyneux, by Graham, +and mounted it in his aunt's house at Wanstead, and observed +continuously with it. The solution of the problem came at last to +him as he was boating on the Thames. Watching a vane at the top of +the mast, he saw with surprise that it shifted its direction every +time that the boat was put about. Remarking to the boatmen that it +was very odd that the wind should change just at the same moment +that there was a shift in the boat's course, they replied that there +was no change in the wind at all, and that the apparent change of +the vane was simply due to the change of direction of the motion of +the boat. + +[Illustration: GRAHAM'S ZENITH SECTOR. + +(_From an old print._)] + +This supplied Bradley with a key to the solution of the mystery +that had troubled him so long. It had been discovered long before +this that light does not travel instantaneously from place to +place, but takes an appreciable time to pass from one member of +the solar system to another. This had been discovered by Römer +from observations of the satellites of Jupiter. He had noted that +the eclipses of the satellites always fell late of the computed +time, when Jupiter was at his greatest distance from the earth; +and Bradley's own work in the observation of those satellites had +brought the fact most intimately under his own acquaintance. The +result of the boating incident taught him, then, that he might look +upon light as analogous to the wind blowing on the boat. As the +wind, so long as it was steady, would seem to blow from one fixed +quarter so long as the boat was also in rest, but as it seemed +to shift its direction when the boat was moving and changed its +direction, so he saw that the light coming from a particular star +must seem to slightly change the direction in which it came, or, in +other words, the apparent position of the star, to correspond with +the movement of the earth in its orbit round the sun. + +This was the celebrated discovery of the Aberration of Light, +a triumph of exact observation and of clear insight. As to the +exactness of Bradley's observations, it is sufficient to say that +his determination of the value of the 'Constant of Aberration' gave +it as 20·39ŽŽ; the value adopted to-day is 20·47ŽŽ. + +On the death of Halley, in 1742, Bradley was appointed to succeed +him. He found the Observatory in as utterly disheartening a +condition as his predecessors had done. As already mentioned, Halley +had not the same qualifications as an observer that Flamsteed +had. He was, further, an old man when appointed to the post, he +had no assistant provided for him, and the last five years of his +life his health and strength had entirely given way. Under these +circumstances, it was no wonder that Bradley found the instruments +of the Observatory in a deplorable state. Nevertheless, he set to +work most energetically, and in the year of his appointment he +made 1500 observations in the last five months of the year. He was +particularly earnest in examining the condition and the errors of +his instruments; and as their defects became known to him, he was +more and more anxious for a better equipment. He moved the Royal +Society, therefore, to apply on his behalf for the instruments he +required; and a petition from that body, in 1748, obtained what +in those days must be considered the generous grant of £1000, +the proceeds of the sale of old Admiralty stores. The principal +instruments purchased therewith were a mural quadrant and a transit +instrument, both eight feet in focal length, still preserved on the +walls of the transit-room. It is interesting also to note that, +following in the steps of Halley, and forecasting, as it were, the +magnetic observatory which Airy would found, he devoted £20 of the +grant to purchasing magnetic instruments. + +Meantime he had continued his observations on aberration, and had +discovered that the aberration theory was not sufficient entirely +to account for the apparent changes in places of stars which he had +discovered. A second cause was at work, a movement of the earth's +axis, a 'wobble' in its inclination, technically known as Nutation, +which is due to the action of the moon, and goes through its course +in a period of nineteen years. + +Beside these two great discoveries of aberration and nutation, +Bradley's reputation rests upon his magnificent observations of the +places of more than three thousand stars. This part of his work was +done with such thoroughness, that the star-places deduced from them +form the basis of most of our knowledge as to the actual movements +of individual stars. In particular, he was careful to investigate +and to correct for the errors of his instrument, and to determine +the laws of refraction, introducing corrections for changes in the +readings of thermometer and barometer. His tables of refraction +were used, indeed, for seventy years after his death. Of his other +labours it may be sufficient to refer to his determination of the +longitudes of Lisbon and of New York, and to his effort to ascertain +the parallax of the sun and moon, in combination with La Caille, who +was observing at the Cape of Good Hope. + +As Astronomer Royal, Bradley's great achievement was the high +standard to which he raised the practical work of observation. From +his day onwards, also, there was always at least one assistant. +His first assistant was his own nephew, John Bradley, who received +the munificent salary of ten shillings a week. Still, this was +not out of proportion to the then salary of the Astronomer Royal, +which practically amounted only to £90. However, in 1752, Bradley +was awarded a Crown pension of £250 a year. He refused the living +of Greenwich, which was offered him in order to increase his +emoluments, on the ground that he could not suitably fulfil the +double office. Bradley's later assistants were Charles Mason and +Charles Green. + +Bradley's last work was the preparation for the observations of the +transit of Venus of 1761, according to the lines laid down by his +predecessor, Halley. His health gave way, and he became subject to +melancholia, so that the actual observations were taken by the Rev. +Nathaniel Bliss, who succeeded him in his office after his death, in +1762. He was buried at Minchinhampton. + +So far as we know Bradley's character, he seems to have been a +gentle, modest, unassuming man, entirely free from self-seeking, +and indifferent to personal gain. He was in many ways an ideal +astronomer, exact, methodical, and conscientious to the last degree. +His skill as an observer was his chief characteristic; and though +his abilities were not equal as a mathematician or a mechanician, +yet, on the one hand, he had a very clear insight into the meaning +of his observations, and, on the other, he was skilful enough to +himself adjust, repair, and improve his instruments. + +Of Bradley's instruments, there are still preserved his famous +twelve-and-a-half-foot zenith sector, with which he made his two +great discoveries; his brass quadrant, which in 1750 he substituted +for Halley's iron quadrant; his transit instrument, and equatorial +sector. Bradley added to the buildings of the Observatory that +portion which is now represented by the upper and lower computing +rooms, and the chronometer room, which adjoins the latter. This +room--the chronometer room--was his transit room, and the position +of the shutters is still marked by the window in the roof. + + * * * * * + +The Rev. NATHANIEL BLISS, who succeeded Bradley, only held the +office for a couple of years, and during that time was much at +Oxford. He, therefore, has left no special mark behind him as +Astronomer Royal. + +He was born November 28, 1700. His father, like himself, Nathaniel +Bliss, was a gentleman, of Bisley, Gloucestershire. + +[Illustration: NATHANIEL BLISS. + +(_From an engraving on an old pewter flagon._)] + +Bliss graduated at Pembroke College, Oxford, as B.A. in 1720, +and M.A. in 1723. He became the Rector of St. Ebb's, Oxford, in +1736, and on Halley's death succeeded him as Savilian Professor of +Geometry. He supplied Bradley with his observations of Jupiter's +satellites, and from time to time, at his request, rendered him some +assistance at the Royal Observatory. This was particularly the case, +as has been already mentioned, with respect to the transit of +Venus of 1761, the observations of which were carried out by Bliss, +owing to Bradley's ill-health. It was natural, therefore, that on +Bradley's death he should succeed to the vacant post; but he held +it too short a time to do any distinctive work. Such observations +as he made seem to have been entirely in continuation of Bradley's. +He took a great interest, however, in the improvement of clocks, a +department in which so much was being done at this time by Graham, +Ellicott, and others. + + * * * * * + +NEVIL MASKELYNE, the fifth Astronomer Royal, was, like Bliss, a +close friend of Bradley's. He was the third son of a wealthy country +gentleman, Edmund Maskelyne, of Purton, in Wiltshire. Maskelyne was +born in London, October 6, 1732, and was educated at Westminster +School. Thence he proceeded to Cambridge, where he graduated seventh +Wrangler in 1754. He was ordained to the curacy of Barnet in 1755, +and, twenty years later, was presented by his nephew, Lord Clive, to +the living of Shrawardine, in Shropshire. In 1782 he was presented +by his college to the Rectory of North Runcton, Norfolk. + +The event which turned his thoughts in the direction of astronomy +was the solar eclipse of July 25, 1748; and about the time that he +was appointed to the curacy of Barnet he became acquainted with +Bradley, then the Astronomer Royal, to whom he gave great assistance +in the preparation of his table of refractions. + +Like Halley before him, he made an astronomical expedition to the +island of St. Helena. This was for the special purpose of observing +the transit of Venus of June 6, 1761, Bradley having induced the +Royal Society to send him out for that purpose. Here he stayed +ten months, and made many observations. But though the transit +of Venus was his special object, it was not the chief result of +the expedition: not because clouds hindered his observations, but +because the voyage gave him the especial bent of his life. + +Halley had actually held a captain's commission in the Royal Navy, +and commanded a ship; Maskelyne, more than any of the Astronomers +Royal before or since, made the improvement of the practical +business of navigation his chief aim. None of all the incumbents of +the office kept its original charter--'To find the so much desired +Longitude at Sea, for the perfecting the Art of Navigation,' so +closely before him. + +The solution of the problem was at hand at this time--its solution +in two different ways. On the one hand, the offer by the Government +of a reward of £20,000 for a clock or watch which should go so +perfectly at sea, notwithstanding the tossing of the ship and the +wide changes of temperature to which it might be exposed, that the +navigator might at any moment learn the true Greenwich time from +it, had brought out the invention of Harrison's time-keeper; on the +other hand, the great improvement that had now taken place in the +computation of tables of the moon's motion, and the more accurate +star-catalogues now procurable, had made the method of 'lunars,' +suggested a hundred and thirty years before by the Frenchman, Morin, +and others, a practicable one. + +[Illustration: NEVIL MASKELYNE.] + +In principle, the method of finding the longitude from 'lunars,' +that is to say, from measurements of the distances between the moon +and certain stars, is an exceedingly simple one. In actual practice, +it involves a very toilsome calculation, beside exact and careful +observation. The principle, as already mentioned, is simply this: +The moon travels round the sky, making a complete circuit of the +heavens in between twenty-seven and twenty-eight days. It thus +moves amongst the stars, roughly speaking, its own diameter, in +about an hour. When once its movements were sufficiently well known +to be exactly predicted, almanacs could be drawn up in which the +Greenwich time of its reaching any definite point of the sky could +be predicted long beforehand; or, what comes to the same thing, +its distances from a number of suitable stars could be given for +definite intervals of Greenwich time. It is only necessary, then, to +measure the distances between the moon and some of these stars, and +by comparing them with the distances given in the almanac, the exact +time at Greenwich can be inferred. As has been already pointed out, +the determination of the latitude of the ship and of the local time +at any place where the ship is, is not by any means so difficult +a matter; but the local time being known and the Greenwich time, +the difference between these gives the longitude; and the latitude +having been also ascertained, the exact position of the ship is +known. + +There are, of course, difficulties in the way of working out this +method. One is, that whilst it takes the sun but twenty-four hours +to move round the sky from one noon to the next, and consequently +its movements, from which the local time is inferred, are fairly +rapid, the moon takes nearly twenty-eight days to move amongst the +stars from the neighbourhood of one particular star round to that +particular star again. Consequently, it is much easier to determine +the local time with a given degree of exactness than the Greenwich +time; it is something like the difference of reading a clock from +both hands and from the hour hand alone. + +There are other difficulties in the case which make the computation +a long and laborious one, and difficult in that sense; but they do +not otherwise affect its practicability. + +During this voyage to St. Helena, both when outward bound and when +returning, Maskelyne gave the method of 'lunars' a very thorough +testing, and convinced himself that it was capable of giving the +information required. For by this time the improvement of the +sextant, or quadrant as it then was, by the introduction of a second +mirror, by Hadley, had rendered the actual observation at sea of +lunar distances, and of altitudes generally, a much more exact +operation. + +This conclusion he put at once to practical effect, and, in 1763, +he published the _British Mariner's Guide_, a handbook for the +determination of the longitude at sea by the method of lunars. + +At the same time, the other method, that by the time-keeper or +chronometer, was practically tested by him. The time-keeper +constructed by John Harrison had been tested by a voyage to Jamaica +in 1761, and now, in 1763, another time-keeper was tested in a +voyage to Barbadoes. Charles Green, the assistant at Greenwich +Observatory, was sent in charge of the chronometer, and Maskelyne +went with him to test its performance, in the capacity of chaplain +to his Majesty's ship Louisa. + +[Illustration: HADLEY'S QUADRANT. + +(_From an old print._)] + +The position which Maskelyne had already won for himself as a +practical astronomer, and the intimate relations into which he +had entered with Bradley and Bliss, made his appointment to the +Astronomer Royalship, on the death of the latter, most suitable. +At once he bent his mind to the completion of the revolution +in nautical astronomy which his _British Mariner's Guide_ had +inaugurated, and in the year after his appointment he published +the first number of the _Nautical Almanac_, together with a volume +entitled, _Tables Requisite to be Used with the Nautical Ephemeris_, +the value of which was so instantly appreciated, that 10,000 copies +were sold at once. + +The _Nautical Almanac_ was Maskelyne's greatest work, and it must +be remembered that he carried it on from this time up to the day of +his death--truly a formidable addition to the routine labours of an +Astronomer Royal who had but a single assistant on his staff. The +_Nautical Almanac_ was, however, in the main not computed at the +Observatory; the calculations were effected by computers living in +different parts of the country, the work being done in duplicate, on +the principle which Flamsteed had inaugurated in the preparation of +his _Historia Coelestis_. + +Maskelyne's next service to science was almost as important. +He arranged that the regular and systematic publication of the +observations made at Greenwich should be a distinct part of the +duties of an Astronomer Royal, and he procured an arrangement +by which a special fund was set apart by the Royal Society for +printing them. His observations covering the years 1776 to 1811 +fill four large folio volumes, and though, as already stated, he +had but one assistant, they are 90,000 in number. Thus it was +Maskelyne who first rendered effective the design which Charles +II. had in the establishment of the Observatory. Flamsteed and +Halley had been too jealous of their own observations to publish; +Bradley's observations--though he himself was entirely free from +this jealousy--were made, after his death, the subject of litigation +by his heirs and representatives, who claimed an absolute property +in them, a claim which the Government finally allowed. None of the +three, however much their work ultimately tended to the improvement +of the art of navigation, made that their first object. Whereas +Maskelyne set this most eminently practical object in the forefront, +and so gave to the Royal Observatory, which under his predecessors +somewhat resembled a private observatory, its distinctive +characteristics of a public institution. + +It fell to Maskelyne to have to advise the Government as to the +assignment of their great reward of £20,000 for the discovery of +the longitude at sea. Maskelyne, while reporting favourably of the +behaviour of Harrison's time-keeper, considered that the method +of 'lunars' was far too important to be ignored, and he therefore +recommended that half the sum should be given to Harrison for his +watch, whilst the other half was awarded for the lunar tables +which Mayer, before his death, had sent to the Board of Longitude. +This decision, though there can be no doubt it was the right one, +led to much dissatisfaction on the part of Harrison, who urged +his claim for the whole grant very vigorously; and eventually +the whole £20,000 was paid him. The whole question of rewards to +chronometer-makers must have been one which caused Maskelyne much +vexation. He was made the subject of a bitter and most voluminous +attack by Thomas Mudge, for having preferred the work of Arnold and +Earnshaw to his own. + +Otherwise his reign at the Observatory seems to have been a +singularly peaceful one, and there is little to record about it +beyond the patient prosecution, year by year, of an immense amount +of sober, practical work. To Maskelyne, however, we owe the practice +of taking a transit of a star over five wires instead of over one, +and he provided the transit instrument with a sliding eye-piece, to +get over the difficulty of the displacement which might ensue if the +star were observed askew when out of the centre of the field. To +Maskelyne, too, we owe in a pre-eminent degree the orderly form of +recording, reducing, and printing the observations. Much of the work +in this direction which is generally ascribed to Airy was really +due to Maskelyne. Indeed, without a wonderful gift of organization, +it would have been impossible to plan and to carry the _Nautical +Almanac_. + +Beside the editing of various works intended for use in nautical +astronomy or in general computation, the chief events of his long +reign at Greenwich were the transit of Venus in 1769, which he +himself observed, and for which he issued instructions in the +_Nautical Almanac_; and his expedition in 1774 to Scotland, where he +measured the deviation of the plumb-line from the vertical caused by +the attraction of the mountain Schiehallion, deducing therefrom the +mean density of the earth to be four and a half times that of water. + +[Illustration: JOHN POND. + +(_From an old engraving._)] + +He died at the Observatory, February 9, 1811, aged 79, leaving but +one child, a daughter, who married Mr. Anthony Mervin Story, +to whom she brought the family estates in Wiltshire, inherited by +Maskelyne on the deaths of his elder brothers, and, in consequence, +Mr. Story added the name of Maskelyne to his own. + +Maskelyne's character and policy as Astronomer Royal have been +sufficiently dwelt upon. His private character was mild, amiable, +and generous. 'Every astronomer, every man of learning, found in him +a brother;' and, in particular, when the French Revolution drove +some French astronomers to this country to find a refuge, they +received from the Astronomer Royal the kindest reception and most +delicate assistance. + +Maskelyne added no instrument to the Observatory during his reign, +though he improved Bradley's transit materially. He designed the +mural circle, but it was not completed until after his death. His +additions to the Observatory buildings consisted of three new rooms +in the Astronomer Royal's house, and the present transit circle room. + + * * * * * + +JOHN POND was recommended by Maskelyne as his successor at +Greenwich. At the time of his succession he was forty-four years of +age, having been born in 1767. He was educated at Trinity College, +Cambridge, and then spent some considerable time travelling in +the south of Europe and Egypt. On his return home he settled at +Westbury, where he erected an altazimuth by Troughton, with a +two-and-a-half-foot circle. A born observer, his observations of the +declinations of some of the principal fixed stars showed that the +instrument which Maskelyne was using at Greenwich--the quadrant by +Bird--could no longer be trusted. Maskelyne, in consequence, ordered +a six-foot mural circle from Troughton, but did not live to see it +installed, and in 1816 this was supplemented by Troughton's transit +instrument of five inches aperture and ten feet focal length. + +The introduction of these two important instruments, and of other +new instruments, together with new methods of observation, form one +of the chief characteristics of Pond's administration. Under this +head must be specially mentioned the introduction of the mercury +trough, both for determining the position of the vertical, and for +obtaining a check upon the flexure of the mural circle in different +positions; and the use in combination of a pair of mural circles for +determining the declinations of stars. + +Another characteristic of his reign was that under him there was the +first attempt to give the Astronomer Royal a salary somewhat higher +than that of a mechanic, and to support him with an adequate staff +of assistants. His salary was fixed at £600 a year, and the single +assistant of Maskelyne was increased to six. + +This multiplication of assistants was for the purpose of multiplying +observations, for Pond was the first astronomer to recognize the +importance of greatly increasing the number of all observations upon +which the fundamental data of astronomy were to be based. + +In 1833 he finished his standard catalogue of 1113 stars, at that +time the fullest of any catalogue prepared on the same scale of +accuracy. 'It is not too much to say,' was the verdict of the Royal +Astronomical Society, 'that meridian sidereal observation owes more +to him than to all his countrymen put together since the time of +Bradley.' + +A yet higher testimony to the exactness of his work is given by his +successor, Airy. + + 'The points upon which, in my opinion, Mr. Pond's claims to + the gratitude of astronomers are founded, are principally the + following. _First_ and chief, the accuracy which he introduced + into all the principal observations. This is a thing which, + from its nature, it is extremely difficult to estimate now, so + long after the change has been made; and I can only say that, + so far as I can ascertain from books, the change is one of very + great extent; for certainty and accuracy, astronomy is quite a + different thing from what it was, and this is mainly due to Mr. + Pond.' + +The same authority eulogizes him further for his laborious working +out of every conceivable cause or indication of error in his +declination instruments, for the system which he introduced in +the observation of transits, for the thoroughness with which he +determined all his fundamental data, and for the regularity which he +infused into the Greenwich observations. + +One result of this great increase of accuracy was that Pond was able +at once authoritatively to discard the erroneous stellar parallaxes +that had been announced by Brinkley, Royal Astronomer for Ireland. + +But Pond's administration was open, in several particulars, to +serious censure, and the Board of Visitors, which had been for +many years but a committee of the Royal Society, but which had +recently been reconstituted, proved its value and efficiency by +the remonstrances which it addressed to him, and which eventually +brought about his resignation. His personal skill and insight as an +observer were of the highest order; but either from lack of interest +or failing health, he absented himself almost entirely from the +Observatory in later years, visiting it only every ninth or tenth +day. He had caused the staff of assistants to be increased from one +to six, but had stipulated that the men supplied to him should be +'drudges.' His minute on the subject ran-- + + 'I want indefatigable, hard-working, and, above all, obedient + drudges (for so I must call them, although they are drudges + of a superior order), men who will be contented to pass half + their day in using their hands and eyes in the mechanical act + of observing, and the remainder of it in the dull process of + calculation.' + +This was a fatal mistake, and one which it is very hard to +understand how any one with a real interest in the science could +have made. Men who had the spirit of 'drudges,' to whom observation +was a mere 'mechanical act,' and calculation a 'dull process,' were +not likely to maintain the honour of the Observatory, particularly +under an absentee Astronomer Royal. Pond tried to overcome the +difficulty by devising rules for their guidance of iron rigidity. +The result was that after his resignation, in 1835, the First Lord +and the Secretary of the Admiralty expressed their feeling to Airy, +Pond's successor, 'that the Observatory had fallen into such a state +of disrepute that the whole establishment should be cleared out.' A +further evil was the excessive development of chronometer business, +so as practically to swamp the real work of the Observatory, whilst +the prices paid for the chronometers at this time were often much +larger than would have been the case under a more business-like +administration. + +With all his merits, therefore, as an observer, the administration +of Pond was, in some respects, the least satisfactory of all that +the Observatory has known, and he alone of all the Astronomers Royal +retired under pressure. He did not long survive his resignation, +dying in September, 1836. He was buried by the side of Halley, in +the churchyard at Lee. + +Of Pond's instruments, the Observatory retains the fine transit +instrument which was constructed by Troughton at his direction, and +the mural circle, designed by Maskelyne, but which Pond was the +first to use. Both of these have, of course, long been obsolete, and +now hang on the walls of the transit room. The small equatorial, +called, after its donor, the Shuckburgh equatorial, was also added +in Pond's day, and though practically never used, still remains +mounted in its special dome. + + + + +CHAPTER IV + +AIRY + + + One hundred and sixty years from the day when Flamsteed laid the + foundation stone of the Observatory, the Royal Warrant under the + sign manual was issued, appointing the seventh and strongest of + the Astronomers Royal, August 11, 1835. He actually entered on + his office in the following October, but did not remove to the + Observatory until the end of the year. + +GEORGE BIDDELL AIRY was born at Alnwick, in Northumberland, on +July 27, 1801. His father was William Airy, of Luddington, in +Lincolnshire, a collector of excise; his mother was the daughter +of George Biddell, a well-to-do farmer, of Playford, near Ipswich. +He was educated at the Grammar School, Colchester, and so +distinguished himself there that although his father was at this +time very straitened in his circumstances, it was resolved that +young Airy should go to Cambridge. Here he was entered as sizar +at Trinity College, and his robust, self-reliant character was +seen in the promptness with which he rendered himself independent +of all pecuniary help from his relatives. In 1823 he graduated as +Bachelor of Arts, being Senior Wrangler and Smith's prizeman, +entirely distancing all other men of his year. He had already begun +to pay attention to astronomy, at first from the side of optics, +to the study of which he had been very early attracted; a paper of +his on the achromatism of eye-pieces and microscopes, written in +1824, being one of especial value. In 1826 he attempted to determine +'the diminution of gravity in a deep mine'--that of Dolcoath, in +Cornwall. In the winter of 1823-24 he was invited to London by Mr. +(afterwards Sir) James South, who took him, amongst other places, +to Greenwich Observatory, and gave him his first introduction to +practical astronomy. In 1826 he was appointed Lucasian Professor at +Cambridge, and in 1828, Plumian Professor, with the charge of the +new University Observatory. Prior to his election he had definitely +told the electors that the salary proposed was not sufficient for +him to undertake the responsibility of the Observatory. He followed +this up by a formal application for an increase, which created not a +little commotion at the time, the action being so unprecedented; and +after a delay of a little over a year he obtained what he had asked +for. The delay gave rise, however, to the remark of a local wit, +that the University had given 'to Airy, nothing, a local habitation +and a name.' + +[Illustration: GEORGE BIDDELL AIRY.] + +The seven years which he spent in the Cambridge Observatory were +the best possible preparation for that greater charge which he was +to assume later. When he entered on his duties the Observatory had +been completed four years, but no observations had been published; +there was no assistant, and the only instruments were a couple of +good clocks and a transit instrument. But Airy set to work at once +with so much energy that the observations for 1828 were published +early in the following year, and he had very quickly worked out +the best methods for correcting and reducing his observations. In +1829 an assistant was granted to him, in 1833 a second, and in the +latter year Mr. Baldrey, the senior assistant, observed about 5000 +transits, and Mr. Glaisher, the junior, about the same number of +zenith distances. + +A syndicate had been appointed at Cambridge for the purpose of +visiting the Observatory once in each term, and making an annual +report to the senate. A smaller-minded and less acute man than +Airy might have resented such an arrangement. He, on the contrary, +threw himself heartily into it, and made such formal written +reports to the syndicate as best helped them in the performance +of their duty, and at the same time secured for the Observatory +the support and assistance which from time to time it required. +On his appointment to Greenwich, he at once entered into the same +relations to the Board of Visitors of that Observatory, and from +that time forth the friction that had occasionally existed between +the Board and the Astronomer Royal in the past entirely ceased. The +Board was henceforth no longer a body whose chief function was to +reprove, to check, or to quicken the Astronomer Royal, but rather a +company of experts, before whom he might lay the necessities of the +Observatory, that they in turn might present them to the Government. + +Such representations were not likely to be in vain. For, as Mr. +Sheepshanks has left on record-- + + 'When Mr. Airy wants to carry anything into effect by Government + assistance, he states, clearly and briefly, why he wants it; + what advantages he expects from it; and what is the probable + expense. He also engages to direct and superintend the + execution, making himself personally responsible, and giving + his labour gratis. When he has obtained permission (which is + very seldom refused), he arranges everything with extraordinary + promptitude and foresight, conquers his difficulties by storm, + and presents his results and his accounts in perfect order, + before men like ... or myself would have made up our minds + about the preliminaries. Now, men in office naturally like + persons of this stamp. There is no trouble, no responsibility, + no delay, no inquiries in the House; the matter is done, paid + for, and published, before the seekers of a grievance can find + an opportunity to be heard. This mode of proceeding is better + relished by busy statesmen than recommendations from influential + noblemen or fashionable ladies.' + +His first action towards the Board was, however, a very bold and +independent one. He made strong representations on the subject of +the growth of the chronometer business, which proved displeasing +to the Hydrographer, Captain Beaufort, who was one of the official +visitors, and by his influence the report was not printed. Airy +'kept it, and succeeding reports, safe for three years, and then +the Board of Visitors agreed to print them, and four reports were +printed together, and bound with the Greenwich Observations of 1838.' + +With the completion of arrangements which put the chronometer +business in proper subordination to the scientific charge of the +Observatory, Airy was free to push forward its development on the +lines which he had already marked out for himself. To go through +these in detail is simply to describe the Observatory as he left +it. Little by little he entirely renovated the equipment. Greatly +as Pond had improved the instruments of the Observatory, Airy +carried that work much further still. Though he did not observe +much himself, and was not Pond's equal in the actual handling of a +telescope, he had a great mechanical gift, and the detail in its +minutest degree of every telescope set up during his long reign was +his own design. + +In the work of reduction he introduced the use of printed skeleton +forms, to which Pond had been a stranger. The publication of the +Greenwich results was carried on with the utmost regularity; and, +in striking contrast to the reluctance of Flamsteed and Halley, he +was always most prompt in communicating any observations to every +applicant who could show cause for his request for them. + +It is most difficult to give any adequate impression of his +far-reaching ability and measureless activity. Perhaps the best +idea of these qualities may be obtained from a study of his +autobiography, edited and published some four years after his death +by his son. The book, to any one who was not personally acquainted +with Airy, is heavy and monotonous, chiefly for the reason that +its 400 pages are little but a mere catalogue of the works which +he undertook and carried through; and catalogues, except to the +specialist, are the dullest of reading. To enter into the details of +his work might fill a library. + +[Illustration: THE ASTRONOMER ROYAL'S ROOM.] + +As Astronomer Royal he seems to have inherited and summed up all +the great qualities of his predecessors: Flamsteed's methodical +habits and unflagging industry; Halley's interest in the lunar +theory; Bradley's devotion to star observation and catalogue +making; Maskelyne's promptitude in publishing, and keen interest +in practical navigation; Pond's refinement of observation. Nor did +he allow this inheritance to be merely metaphorical; he made it +an actual reality. He discussed, reduced, and published, in forms +suitable for use and comparison to-day, the whole vast mass of +planetary and lunar observations made at the Royal Observatory from +the year 1760 to his own accession, a work of prodigious labour, +but of proportionate importance. Airy has been accused--and with +some reason--of being a strong, selfish, aggressive man; yet nothing +can show more clearly than this great work how thoroughly he placed +the fame and usefulness of the Observatory before all personal +considerations. With far less labour he could have carried on a +dozen investigations that would have brought him more fame than this +great enterprise, the purpose of which was to render the work of +his predecessors of the highest possible use. The light in which he +regarded his office may best be expressed in his own words:-- + + 'The Observatory was expressly built for the aid of astronomy + and navigation, for promoting methods of determining longitude + at sea, and (as the circumstances that led to its foundation + show) more especially for determination of the moon's motions. + All these imply, as their first step, the formation of accurate + catalogues of stars, and the determination of the fundamental + elements of the solar system. These objects have been steadily + pursued from the foundation of the Observatory; in one way by + Flamsteed; in another way by Halley, and by Bradley in the + earlier part of his career; in a third form by Bradley in his + later years; by Maskelyne (who contributed most powerfully both + to lunar and to chronometric nautical astronomy), and for a time + by Pond; then with improved instruments by Pond, and by myself + for some years; and subsequently, with the instruments now in + use. It has been invariably my own intention to maintain the + principles of the long-established system in perfect integrity; + varying the instruments, the modes of employing them, and + the modes of utilizing the observations of calculation and + publication, as the progress of science might seem to require.' + +The result of this keen appreciation of the essential continuity +of the Astronomer Royalship has been that it is to Airy, more than +to any of his predecessors, or than to all of them put together, +that the high reputation of Greenwich Observatory is due. Professor +Newcomb, the greatest living authority on the subject outside our +own land--and other great foreign astronomers have independently +pronounced the same verdict--has said:-- + + 'The most useful branch of astronomy has hitherto been that + which, treating of the positions and motions of the heavenly + bodies, is practically applied to the determination of + geographical positions on land and at sea. The Greenwich + Observatory has, during the past century, been so far the + largest contributor in this direction as to give rise to the + remark that, if this branch of astronomy were entirely lost, it + could be reconstructed from the Greenwich observations alone.' + +Early in 1836 Airy proposed to the Board of Visitors the creation +of the Magnetic and Meteorological department of the Observatory, +and in 1840 a system of regular two-hourly observations was set +on foot. This was the first great enlargement of programme for +the Observatory beyond the original one expressed in Flamsteed's +warrant. It was followed in 1873 with the formation of the Solar +Photographic department, to which the Spectroscope was added a +little later. + +Though he had objected strongly on his first coming to the +Observatory to the excessive time devoted to the merely commercial +side of the care of chronometers, yet the perfecting of these +instruments was one that he had much at heart, and many recent +appliances are either of his own invention or are due to suggestions +which he threw out. + +Much work lying outside the Observatory, and yet intimately +connected with it, was carried out either by him or in accordance +with his directions. The transit of Venus expeditions of 1874, the +delimitation of the boundary line between Canada and the United +States, and, later, that of the Oregon boundary; the determination +of the longitudes of Valencia, Cambridge, Edinburgh, Brussels, +and Paris; assistance in the determination of the longitude of +Altona--all came under Airy's direction. Nor did he neglect +expeditions in connection with what we would now call the physical +side of astronomy. On three occasions, 1842, 1851, and 1860, he +himself personally took part in successful eclipse expeditions. The +determination of the increase of gravity observable in the descent +of a deep mine was also the subject of another expedition, to the +Harton Colliery, near South Shields. + +But with all these, and many other inquiries--for he was the +confidential adviser of the Government in a vast number of subjects: +lighthouses, railways, standard weights and measures, drainage, +bridges--he yet always kept the original objects of the Observatory +in the very first place. It was in order to get more frequent +observations of the moon that he had the altazimuth erected, which +was completed in May, 1847. This was followed, in 1851, by the +transit circle, as he had long felt the need for more powerful +light grasp in the fundamental instrument of the Observatory. The +transit circle took the place both of the old transit instrument and +of the mural circle. Above all, he arranged for the observations +of moon and stars to be carried out with practical continuity. The +observations were made and reduced at once, and published in such a +way that any one wishing to discuss them afresh could for himself go +over every step of the reduction from the commencement, and could +see precisely what had been done. + +The greatest addition made to the equipment of the Observatory in +Airy's day was the erection of the 12-3/4-inch Merz equatorial, +which proved of great service when spectroscopy became a department +of the Observatory. + +[Illustration: THE SOUTH-EAST TOWER. + +(_From a photograph by Mr. Lacey._)] + +So strong and gifted a man as Airy was bound to make enemies, and +at different times of his life bitter attacks were made on him from +one quarter or another. One of these, curiously enough, was from +Sir James South, the man who, as he said, first introduced him to +practical astronomy. Later came the discovery of Neptune, and Airy +was subjected to much bitter criticism, since, as it appeared on the +surface, it was owing to his supineness that Adams missed being +held the sole discoverer of the new planet, and narrowly missed +all credit for it altogether. Last of all was the vehement attack +made upon him by Richard Anthony Proctor, in connection with his +preparations for the transit of Venus. All such attacks, however, +simply realized the old fable of the viper and the file. Attacks +which would have agonized Flamsteed's every nerve, and have called +forth full and dignified rejoinders from Maskelyne, were absolutely +and entirely disregarded by Airy. He had done his duty, and in +his own estimation--and, it should be added, in the estimation of +those best qualified to judge--had done it well. He was perfectly +satisfied with himself, and what other people thought or said about +him influenced him no more than the opinions of the inhabitants of +Saturn. + +But great as Airy was, he had the defects of his qualities, and +some of these were serious. His love of method and order was often +carried to an absurd extreme, and much of the time of one of the +greatest intellects of the century was often devoted to doing what +a boy at fifteen shillings a week could have done as well, or +better. The story has often been told, and it is exactly typical +of him, that on one occasion he devoted an entire afternoon to +himself labelling a number of wooden cases 'empty,' it so happening +that the routine of the establishment kept every one else engaged +at the time. His friend Dr. Morgan jocularly said that if Airy +wiped his pen on a piece of blotting-paper he would duly endorse +the blotting-paper with the date and particulars of its use, and +file it away amongst his papers. His mind had that consummate grasp +of detail which is characteristic of great organizers, but the +details acquired for him an importance almost equal to the great +principles, and the statement that he had put a new pane of glass +into a window would figure as prominently in his annual report to +the Board of Visitors as the construction of the new transit circle. +His son remarks of him that 'in his last days he seemed to be more +anxious to put letters which he received into their proper place for +reference than even to master their contents,' his system having +grown with him from being a means to an end, to becoming the end +itself. + +So, too, his regulation of his subordinates was, especially in his +earlier days, despotic in the extreme--despotic to an extent which +would scarcely be tolerated in the present day, and which was the +cause of not a little serious suffering to some of his staff, whom, +at that time, he looked upon in the true spirit of Pond, as mere +mechanical 'drudges.' For thirty-five years of his administration +the salaries of his assistants remained discreditably low, and +his treatment of the supernumerary members of his staff would now +probably be characterized as 'remorseless sweating.' The unfortunate +boys who carried out the computations of the great lunar reductions +were kept at their desks from eight in the morning till eight +at night, without the slightest intermission, except an hour at +midday. As an example of the extreme detail of the oversight which +he exercised over his assistants, it may be mentioned that he drew +up for each one of those who took part in the Harton Colliery +experiment, instructions, telling them by what trains to travel, +where to change, and so forth, with the same minuteness that one +might for a child who was taking his first journey alone; and he +himself packed up soap and towels with the instruments, lest his +astronomers should find themselves, in Co. Durham, out of reach of +these necessaries of civilization. + +A regime so essentially personal may indeed have been necessary +after Pond's administration, and to give the Observatory a +fresh start. But it would not have been to the advantage of +the Observatory, had it become a permanent feature of its +administration, as it militated--was almost avowedly intended to +militate--against the growth of real zeal and intelligence in the +staff, and necessarily occasioned labour and discomfort out of +proportion to the results obtained. Fortunately, in Airy's later +years, the extension of the work of the Observatory, a slight +failing in his own powers, and the efforts he was devoting to the +working out of the lunar theory, compelled him to relax something +of that microscopic imperiousness which had been the chief +characteristic of his rule for so long. + +Airy had, in the fullest degree, the true spirit of the public +servant; his sense of duty to the State was very high. He was +always ready to undertake any duty which he felt to be of public +usefulness, and many of these he discharged without fee or reward. + +So great an astronomer was necessarily most highly esteemed by +astronomers. He was President of the Royal Society for two years; +he was five times President of the Royal Astronomical Society, +and twice received its gold medal, beside a special testimonial +for his reduction of the Greenwich lunar observations. From the +Royal Society he received the Copley medal and the Royal medal, +beside honorary titles from the Universities of Oxford, Cambridge, +and Edinburgh. So invaluable a public servant, he received the +distinction of a Knight Commandership of the Bath in 1872. He had +been repeatedly offered knighthood before, but had not thought it +well to receive it. He was in the receipt of decorations also from +a great number of foreign countries; for, for many years, he was +looked up to, not only by English astronomers, but by scientific men +in all countries, as the very head and representative of his science. + +And he also received a more popular appreciation--and most justly +so. For whilst no one could have less of the arts of the ordinary +popularizer about him, no one has ever given popular lectures on +astronomy which more fully corresponded to the ideal of what such +should be than Airy's six lectures to working men, delivered at +Ipswich. And we may count the bestowal upon him of the honorary +freedom of the City of London, in 1875, as one of the tokens that +his services in this direction had not been unappreciated. + +During the last seven years of his official career he undertook +the working out of a lunar theory, and, to allow himself more +leisure for its completion, he resigned his position August 15, +1881, after forty-six years of office. He was now eighty years of +age, and he took up his residence at the White House, just outside +Greenwich Park. He resided there till his death, more than ten years +later--January 2, 1892. + + * * * * * + +Airy was succeeded in the Astronomer Royalship by the present and +eighth holder of the office, W. H. M. CHRISTIE. He was born at +Woolwich, in 1845, his father having been Professor Samuel Hunter +Christie, F.R.S. He was educated at King's College, London, and +Trinity College, Cambridge, graduating as fourth Wrangler in 1868. +In 1870 he was appointed chief assistant at Greenwich, in succession +to Mr. Stone, who had become her Majesty's astronomer at the Cape, +and in 1881 he succeeded Airy as Astronomer Royal. + +[Illustration: W. H. M. CHRISTIE, ASTRONOMER ROYAL. + +(_From a photograph by Elliott and Fry._)] + +During Mr. Christie's office, the two new departments of the +Astrographic Chart and Double-star observations have come into +being. The following buildings have been erected under his +administration: the great New Observatory in the south ground, +the New Altazimuth, the New Library, nearly opposite to it, the +Transit Pavilion, the porter's lodge, and the Magnetic Pavilion +out in the Park. Whilst in the old buildings the Astrographic dome +has been added, and the Upper and Lower Computing rooms have been +rebuilt and enlarged. As to the instruments, the 28-inch refractor, +the astrographic twin telescope, the new altazimuth, the 26-inch +and 9-inch Thompson photographic refractors, and the 30-inch +reflector are all additions during the present reign. Roughly +speaking, therefore, we may say that three-fourths of the present +Observatory has been added during the nineteen years of the present +Astronomer Royal. One exceedingly important improvement should not +be overlooked. Airy observed little himself whilst at Greenwich, +and had an inadequate idea of the necessity for room in a dome and +breadth in a shutter-opening. With the sole exception, perhaps, of +the transit circle, every instrument set up by Airy was crammed into +too small a dome or looked out through too narrow an opening. The +increase of shutter-opening of the newer domes may be well seen by +contrasting, say, the old altazimuth or the Sheepshanks dome with +that of the astrographic. This reform has had much to do with the +success of later work. + + + + +CHAPTER V + +THE OBSERVATORY BUILDINGS + + +Like a living organism, Greenwich Observatory bears the record of +its life-history in its structure. It was not one of those favoured +institutions that have sprung complete and fully equipped from the +liberality of some great king or private millionaire. As we have +seen, it was originally established on the most modest--not to say +meagre--scale, and has been enlarged just as it has been absolutely +necessary. To quote again from Professor Newcomb-- + + 'Whenever any part of it was found insufficient for its purpose, + new rooms were built for the special object in view, and thus + it has been growing from the beginning by a process as natural + and simple as that of the growth of a tree. Even now the very + value of its structure is less than that of several other public + observatories, though it eclipses them all in the results of its + work.' + +Entering the courtyard--an enclosure some eighty feet deep by +ninety feet in extreme breadth--by the great gate, we see before +us Flamsteed House, the original building of the Observatory. +Flamsteed's little domain was only some twenty-seven yards wide +by fifty deep, and for buildings comprised little beyond a small +dwelling-house on the ground floor, and one fine room above it. This +room--the original Greenwich Observatory--still remains, and is +used as a council room by the official Board of Visitors, who come +down to the Observatory on the first Saturday in June, to examine +into its condition and to receive the Astronomer Royal's report. The +room is called, from its shape, the Octagon Room, and is well known +to Londoners from the great north window which looks out straight +over the river between the twin domes of the Hospital. + +In Bradley's time, about 1749, the first extension of the domains +of the Observatory took place to the south and east of the original +building, the direction in which, on the whole, all subsequent +extensions have taken place, owing to the fact that the original +building was constructed at the extremity of what Sir George Airy +was accustomed to call a 'peninsula'--a projecting spur of the +Blackheath plateau, from which the ground falls away very sharply on +three sides and on part of the fourth. + +The Observatory domain at present is fully two hundred yards in +greatest length, with an average breadth of about sixty. Nearly the +whole of this accession took place under the directorates of Pond +and Airy. The present instruments are, therefore, as a rule, the +more modern in direct proportion to their distance from the Octagon +Room--the old original Observatory. There is one notable exception. +The very first extension of the Observatory buildings, made in +the time of Halley, the second Astronomer Royal, consisted in the +setting up of a strong pier, to carry two quadrant telescopes. The +pier still remains, but now forms the base of the support of the +twin telescopes devoted to the photographic survey of the heavens +for the International Chart. + +Standing just within the gate of the courtyard, and looking +westward, that is toward Flamsteed House, we have immediately on +our right hand the porter's lodge; a little farther forward, also +on the right, the Transit Pavilion, a small building sheltering +a portable transit instrument; and farther forward, still on the +right, the entrance to the Chronograph Room. Above the Chronograph +Room is a little, inconveniently-placed dome, containing a small +equatorially-mounted telescope, known as the Shuckburgh. Beyond the +Chronograph Room a door opens on to the North Terrace, over which +is seen the great north window of the Octagon Room. Close by the +door of the Chronograph Room a great wooden staircase rises to the +roof of the main building. It is not an attractive-looking ascent, +as the steps overlap inconveniently. Still, there is no record of +an accident upon them, and those who venture on the climb to the +roof, where are placed the anemometers and the turret carrying the +time-ball, which is dropped daily at 1 p.m., will be well repaid by +the splendid view of the river which is there afforded to them. + +Passing under this staircase, on the wall by its side is seen the +following inscription:-- + + CAROLUS II^S REX OPTIMUS + ASTRONOMIÆ ET NAUTICÆ ARTIS + PATRONUS MAXIMUS + SPECULAM HANC IN UTRIUSQUE COMMODUM + FECIT + ANNO D^{NI} MDCLXXVI. REGNI SUI XXVIII. + + Curante Iona Moore milite + R. T. S. G. + +[Illustration: THE ASTRONOMER ROYAL'S HOUSE. + +(_From a photograph by Mr. Lacey._)] + +In the extreme angle of the courtyard is the entrance to the mean +solar clock cupboard, and to the staircase leading up to the Octagon +Room. At the head of this staircase in a small closet is the winch +for winding up the time-ball. + +Coming back into the courtyard, and crossing the face of the +Astronomer Royal's private house, the range of buildings is reached +which form the left hand or south side of the enclosure. Entering +the first of these, we find ourselves in the Lower Computing Room, +which is devoted to the 'Time Department.' The next room which opens +out of it, as we turn eastwards, was Bradley's Transit Room, but is +now used for the storage of chronometers. Passing through Bradley's +Transit Room, we come to the present Transit Room, which brings +us close to the great gate. The range of buildings is, however, +continued somewhat farther, containing on the ground floor some +small sitting-rooms and a fire-proof room for records. + +[Illustration: THE COURTYARD. + +(_From a photograph by Mr. Lacey._)] + +Turning back to the Lower Computing Room, we notice in it the stone +pier, already alluded to, which was set up by Halley, and formed +the first addition to the original Observatory of Flamsteed. The +Lower Computing Room itself and Bradley's Transit Room were due +to the Astronomer after which the latter is named. An iron spiral +staircase in the middle of the Lower Computing Room leads up to the +Upper Computing Room, and above that to the Astrographic dome, so +called because the twin telescope housed therein is devoted to the +work of the Astrographic Chart--a chart of the entire sky to be made +by eighteen co-operating observatories by means of photography. In +this way it is intended to secure a record of the places of far +more stars than could be done by the ordinary methods, and in this +project Greenwich has necessarily taken a premier place. This is +a work which, whilst it is the legitimate and natural outcome of +the original purpose of the Observatory, is yet pushed beyond what +is necessary for any mere utilitarian assistance to navigation. For +the sailor it will always be sufficient to know the places of a +mere handful of the brightest stars, and the vast majority of those +in the great photographic map will never be visible in the little +portable telescope of the sailor's sextant. But it will be freely +admitted that in the case of an enterprise of this nature, in which +the observatories of so many different nations were uniting, and +which was so precisely on the lines of its original charter, though +an extension of it, it was impossible for Greenwich to hold back on +the plea that the work was not entirely utilitarian. + +Descending again to the Lower Computing Room, and passing through +it, not to the east, into Bradley's Transit Room, but through a +little lobby to the south, we come upon an inconvenient wooden +staircase winding round a great stone pillar with three rays. This +pillar is the support of Airy's altazimuth, and very nearly marks +the place where Flamsteed set up his original sextant. + +Returning again to the Lower Computing Room, and passing out to the +east, just in front of the Time Superintendent's desk, we enter a +small passage running along the back of Bradley's Transit Room, and +from this passage enter the present Transit Room near its south end. +Just before reaching the Transit Room, however, we pass the Reflex +Zenith Tube, a telescope of a very special kind. + +Immediately outside the Transit Room is a staircase leading on the +first floor to two rooms long used as libraries, and to the leads +above them, on which is a small dome containing the Sheepshanks +equatorial. These libraries are over the small sitting-rooms already +referred to. The fire-proof Record Rooms, two stories in height, +terminate this range of buildings. + +Beyond the Record Rooms the boundary turns sharply south, where +stands a large octagonal building surmounted by a dome of oriental +appearance, a 'circular versatile roof,' as the Visitors would have +called it a hundred years ago. This dome--which has been likened, +according to the school of æsthetics in which its critics have been +severally trained, to the Taj at Agra, a collapsed balloon, or a +mammoth Spanish onion--houses the largest refractor in England, the +'South-east Equatorial' of twenty-eight inches aperture. But, though +the largest that England possesses, it would appear but as a pigmy +beside some of the great telescopes for which America is famous. + +Beyond this dome the hollow devoted to the Astronomer Royal's +private garden reduces the Observatory ground to a mere 'wasp's +waist,' a narrow, inconvenient passage from the old and north +observatory to the younger southern one. + +The first building, as the grounds begin to widen out to the south, +contains the New Altazimuth, a transit instrument which can be +turned into any meridian. A library of white brick and a low wooden +cruciform building--the Magnetic Observatory--follow it closely. + +This latter building houses the Magnetic Department, a department +which, though it lies aside from the original purposes of the +Observatory, as defined in the warrant given to Flamsteed, is yet +intimately connected with navigation, and was founded by Airy very +early in his period of office. This deals with the observation of +the changes in the force and direction of the earth's magnetism, an +inquiry which the greater delicacy of modern compasses, and, in more +recent times, the use of iron instead of wood in the construction of +ships, has rendered imperative. + +Closely associated with the Magnetic Department is the +Meteorological. Weather forecasts, so necessary for the safety +of shipping round our coasts, are not issued from Greenwich +Observatory, any more than the _Nautical Almanac_ is now issued from +it. But just as the Observatory furnishes the astronomical data upon +which the almanac is based, so also a considerable department is set +apart for furnishing observations to be used by the Meteorological +Office at Westminster for their daily predictions. + +So far, the development of the Observatory had been along the +central line of assistance to navigation. But the 'Magnetic +Department' led on to a new one, which had but a secondary +connection with it. It had been discovered that the extent of +the daily range of the magnetic needle, and the amount of the +disturbances to which it was subjected, were in close connection +with the numbers and size of the spots on the sun's surface. This +led to the institution of a daily photographic record of the state +of the sun's surface, a record of which Greenwich has now the +complete monopoly. + +[Illustration: PLAN OF OBSERVATORY AT PRESENT TIME. + +(For key to plan, see p. 135.)] + +KEY TO THE PLAN OF THE OBSERVATORY ON PAGE 134. + + 1. Chronograph Room. + 2. Old Altazimuth Dome. + 3. Safe Room. + 4. Computing Room. + 5. Bradley's Transit Room. + 6. Transit Circle Room. + 7. Assistants' Room. + 8. Chief Assistant's Room. + 9. Computers' Room. + 10. Record Rooms. + 11. Chronometer Rooms and South-east Dome. + 12. Greenhouse and Outbuildings. + 14. New Library. + 15. Magnetic Observatory. + 16. Offices. + 19. Sheds. + 23. Winch Room for Time-ball. + 24. Porter's Lodge. + 25. New Transit Pavilion. + 26. New Altazimuth Pavilion. + 27. Museum: New Building. + 28. South Wing " + 29. North Wing " + 30. West Wing " + 31. East Wing " + + F. Rooms built for Flamsteed. + H. Added by Halley. + B. " Bradley. + M. " Maskelyne. + A. " Airy. + F'F'. Flamsteed's boundaries. + M'M'. Maskelyne's " 1790. + P'P'. Pond's " 1814. + A'A'. Airy's " 1837. + A"A". Airy's " 1868. + +Beyond the Magnetic Observatory the ground widens out into an area +about equal to that of the northern part, and the new building +just completed, and which is now emphatically 'The Observatory,' +stands clear before us. The transfer to this stately building of the +computing rooms, libraries, and store rooms has been aptly described +as a shift in the latitude of Greenwich Observatory, which still +preserves its longitude. It may be noted that the only two buildings +of any architectural pretensions in the whole range are--Flamsteed's +original observatory, built by Sir Christopher Wren, and containing +little beyond the octagon room, in the extreme north; and this +newest building in the extreme south. + +This 'New Observatory,' like the old, and like the great +South-eastern tower, is an octagon in its central portion. But +whilst the two other great buildings are simply octagonal, here the +octagon serves only as the centre from which radiate four great +wings to the four points of the compass. The building is by far the +largest on the ground, but in little accord with the popular idea of +an astronomer as perpetually looking through a telescope, carries +but a single dome; its best rooms being set apart as 'computing +rooms,' for the use of those members of the staff who are employed +in the calculations and other clerical work, which form, after all, +much the greater portion of the Observatory routine. + +An observer with the transit instrument, for instance, will take +only three or four minutes to make a complete determination of the +place of a single star. But that observation will furnish work to +the computers for many hours afterwards. Or, to take a photograph of +the sun will occupy about five minutes in setting the instrument, +whilst the actual exposure will take but the one-thousandth part of +a second. But the plate, once exposed, will have to be developed, +fixed, and washed; then measured, and the measures reduced, and, _on +the average_, will provide one person with work for four days before +the final results have been printed and published. + +It is easy to see, then, that observing, though the first duty of +the Observatory, makes the smallest demand on its time. The visitor +who comes to the Observatory by day (and none are permitted to do +so by night) finds the official rooms not unlike those of Somerset +House or Whitehall, and its occupants for the most part similarly +engaged in what is, apparently, merely clerical work. An examination +of the big folios would of course show that instead of being ledgers +of sales of stamps, or income-tax schedules, they referred to stars, +planets, and sun-spots; but for one person actively engaged at a +telescope, the visitor would see a dozen writing or computing at a +desk. + +The staff, like the building, is the result of a gradual +development, and bears traces of its life history in its +composition. First comes the Astronomer Royal, the representative +and successor of the original 'King's Astronomer,' the Rev. John +Flamsteed. But the 'single surly and clumsy labourer,' which was +all that the 'Merry Monarch' could grant for his assistance, is now +represented by a large and complex body of workers; each varied +class and rank of which is a relic of some stage in the progress of +the Observatory to its present condition. + +The following extract from the Annual Report of the Astronomer +Royal to the Board of Visitors, June, 1900, describes the present +_personnel_ of the establishment:-- + + 'The staff at the present time is thus constituted, the names in + each class being arranged in alphabetical order:-- + + 'Chief assistants--Mr. Cowell, Mr. Dyson. + + 'Assistants--Mr. Hollis, Mr. Lewis, Mr. Maunder, Mr. Nash, Mr. + Thackeray. + + 'Second-class assistants--Mr. Bryant, Mr. Crommelin. + + 'Clerical assistant--Mr. Outhwaite. + + 'Established computers--Mr. Bowyer, Mr. Davidson, Mr. Edney, Mr. + Furner, Mr. Rendell, and one vacancy. + + 'The two second-class assistants will be replaced by higher + grade established computers as vacancies occur. + + 'Mr. Dyson and Mr. Cowell have the general superintendence of + all the work of the Observatory. Mr. Maunder is charged with + the heliographic photography and reductions, and with the + preparation of the Library Catalogue. Mr. Lewis has charge + of the time-signals and chronometers, and of the 28-inch + equatorial. Mr. Thackeray superintends the miscellaneous + astronomical computations, including the preparation of + the new Ten-Year Catalogue. Mr. Hollis has charge of the + photographic mapping of the heavens, the measurement of the + plates, and the computations for the Astrographic Catalogue. Mr. + Crommelin undertakes the altazimuth and Sheepshanks equatorial + reductions, and Mr. Bryant the transit and meridian zenith + distance reductions and time-determinations. In the magnetic and + meteorological branch, Mr. Nash has charge of the whole of the + work. Mr. Outhwaite acts as responsible accountant officer; has + charge of the library, records, manuscripts, and stores, and + conducts the official correspondence. As regards the established + computers, Mr. Bowyer, Mr. Furner, Mr. Davidson, and Mr. Rendell + assist Mr. Lewis, Mr. Thackeray, Mr. Hollis, and Mr. Bryant + respectively, and Mr. Edney assists Mr. Nash. + + 'There are at the present time twenty-four supernumerary + computers employed at the Observatory, ten being attached to + the astronomical branch, two the chronometer branch, six to the + astrographic, one to the heliographic, four to the magnetic and + meteorological, and one to the clerical. + + 'A foreman of works, with two carpenters, and two labourers; + a skilled mechanic with an assistant; a gate porter, two + messengers, a watchman, a gardener, and a charwoman, are also + attached to the Observatory. + + 'The whole number of persons regularly employed at the + Observatory is fifty-three.' + +The day work, as said before, is by far the greatest in amount, +the 'office hours' being from nine till half-past four, with an +hour's interval. The arrangements for the night watches present some +complications. + +For many years the instruments in regular use were two only, the +transit circle and the altazimuth. The arrangements for observing +were simple. Four assistants divided the work between them thus: an +assistant was on duty with the transit circle one day, his watch +beginning about six a.m. or a little later, and ending about three +the following morning; a watch of twenty-one hours in maximum +length. The second day his duties were entirely computational, and +were only two or three hours in length. The third day he had a full +day's work on the calculations, followed by a night duty with the +altazimuth. The latter instrument might give him a very easy watch +or a terribly severe one. If the moon were a young one it was easy, +especially if the night was clear, as in that case an hour was +enough to secure the observations required. + +Very different was the case with a full moon, especially in the +long, often cloudy, nights of winter. Then a vigilant watch had to +be kept from sunset to sunrise, so that in case of a short break +in the clouds the moon might yet be observed. Such a watch was the +severest (with one exception) that an assistant had to undergo. + +His fourth day would then resemble his second, and with the fifth +day a second cycle of his quartan fever would commence, the symptoms +following each other in the same sequence as before. + +Such a routine carried on with iron inflexibility was exceedingly +trying, as it was absolutely impossible for an observer to keep any +regularity in his hours of rest or times for meals. + +This routine has been considerably modified by the present +Astronomer Royal, partly because the instruments now in regular +daily use are five instead of two, and partly because a less +stringent system has proved not merely far less wearing to the +observers, but also much more prolific of results. It was impossible +for a man to be at his best for long under the old _régime_, and +from forty-six to forty-seven has been an ordinary age for an +assistant to break down under the strain. + +One point in which the observing work has been lightened has been in +the discontinuance of the altazimuth observations at the full of the +moon, another in the shortening of the hours of the transit circle +watch; and a further and most important one in the arrangement that +the observers with the larger instruments should have help at their +work. The net result of these changes has been a most striking +increase in the amount of work achieved. Thus, whilst in the year +ending May 20, 1875, 3780 transits were taken with the transit +circle, and 3636 determinations of north polar distance; in that +ending May 10, 1895, the numbers had risen to 11,240 and 11,006 +respectively, the telescope remaining precisely the same. + +One principle of Airy's rule still remains. So far as possible no +observer is on duty for two consecutive days, but a long day of desk +work and observing is followed by a short day of desk work without +observing. + +It will be readily understood that with five principal telescopes +in constant work and one or two minor ones, some demanding two +observers, others only one, each telescope having its special +programme and its special hours of work, whilst by no means every +member of the staff is authorized to observe with all instruments +indifferently, it becomes a somewhat intricate matter to arrange the +weekly _rota_ in strict accordance with the foregoing principle, and +with the further one, that whilst a considerable amount of Sunday +observing is inevitable, the average duty of an observer should be +three days a week, not seven days a fortnight. There is a story, +received with much reserve at Cambridge, that there was once a man +at that university who had mastered all the colours and combinations +of shades and colours of the various colleges and clubs. If so +gifted a being ever existed, he may be paralleled by the Greenwich +assistant who can predict for any future epoch the sequence of +duties throughout the entire establishment. At any rate, one of the +first items in the week's programme is the preparation of the _rota_ +for the week, or rather, to use an ecclesiastical term, for the +'octave,' _i.e._ from the Monday to the Monday following. + +The special work to be carried out on any telescope is likewise +a matter of programme. For the transit circle a list of the most +important objects to be observed is supplied for the observer's +use, and the general lines upon which the other stars are to be +selected from a huge 'Working Catalogue' are well understood. +With some of the other telescopes the principles upon which the +objects are to be selected are laid down, but the actual choice +is left to the discretion of the observer at the time. There +is no time for the watcher to spend in what the outsider would +regard as 'discovery'; such as sweeping for comets or asteroids, +hunting for variable stars, sketching planets, and so forth. +Indeed, there is a story current in the Observatory that some fifty +years ago, when the tide of asteroid discovery first set in, Airy +found an assistant, since famous, working with a telescope on his +'off-duty' night. That stern disciplinarian asked what business the +assistant had to be there on his free night, and on being told he +was 'searching for new planets,' he was severely reprimanded and +ordered to discontinue at once. A similar energy would not meet +so gruff a discouragement to-day; but the routine work so fully +occupies both staff and telescopes that an assistant may be most +thoroughly devoted to his science, and yet pass a decade at the +Observatory without ever seeing those 'show places' of the sky which +an amateur would have run over in the first week after receiving his +telescope. For example, there is no refractor in the British Isles +so competent to bring out the vivid green light of the great Orion +nebula--that marvellous mass of glowing, curdling, emerald cloud--or +the indescribable magnificence of the myriad suns that cluster +like swarming bees or the grapes of Eshcol in the constellation of +Hercules; yet probably most of the staff have never seen either +spectacle through it. The professional astronomer who is worth his +salt will find abundance of charm and interest in his work, but he +will not, + + 'Like a girl, + Valuing the giddy pleasures of the eyes,' + +consider the charm to lie mainly in the occasional sight of +wonderful beauty which his work may bring to him, nor the interest +in some chance phenomenon which may make his name known. + +It is not every field of astronomy that is cultivated at Greenwich. +The search for comets and for 'pocket planets' forms no part of +its programme; and the occupation so fascinating to those who take +it up, of drawing the details on the surfaces of the moon, Mars, +Jupiter, or Saturn, has been but little followed. Such work is here +incidental, not fundamental, and the same may be said of certain +spectroscopic observations of new or variable stars, and of many +similar subjects. Work such as this is most interesting to the +general public, and is followed with much devotion by many amateur +astronomers. For that very reason it does not form an integral +part of the programme of our State observatory. But work which +is necessary for the general good, or for the advancement of the +science, and which demands observations carried on continuously for +many years, and strict unity of instruments and methods, cannot +possibly be left to chance individual zeal, and is therefore rightly +made the first object at Greenwich. + +Those striking discoveries which from time to time appeal strongly +to the popular imagination, and which have rendered so justly +famous some of the great observatories of the sister continent, have +not often been made here. + +Its work has, none the less, been not only useful but essential. A +century ago, when we were engaged in the hand-to-hand struggle with +Napoleon, by far the most brilliant part of that naval war which we +waged against the French, and the most productive of prize-money, +was carried on by our cruisers, who captured valuable prizes in +every sea. But a much greater service, indeed an absolutely vital +one, was rendered to the State by those line-of-battle ships which +were told off to watch the harbours wherein the French fleet was +taking refuge. This was a work void of the excitement, interest, +and profit of cruising. It was monotonous, wearing, and almost +inglorious, but absolutely necessary to the very existence of +England. So the continuance for more than two centuries of daily +observations of places of moon, stars, and planets is likewise +'monotonous, wearing, and almost inglorious;' the one compensation +is that it is essential to the life of astronomy. + +The eight Astronomers Royal have, as already said, kept the +Observatory strictly on the lines originally laid down for it, +subject, of course, to that enlargement which the growth of +the science has inevitably brought. But had they been inclined +to change its course, the Board of Visitors has been specially +appointed to bring them back to the right way. As already mentioned +in the account of Flamsteed, the Board dates from 1710, when it +practically consisted of the President and Council of the Royal +Society. Its Royal warrant lapsed on the death of Queen Anne, and +was not renewed at the accession of the two following sovereigns; +but in the reign of George III. a new warrant was issued under date +February 22, 1765; and this was renewed at the accession of George +IV. When William IV. came to the throne, the constitution of the +Board was extended, so as to give a representation to the new Royal +Astronomical Society, founded in 1820. The President of the Royal +Society is still chairman of the Board, but the Admiralty, of which +the Observatory is a department, the two Universities of Oxford and +Cambridge, and the Royal Astronomical Society are all represented on +it by _ex officio_ members, and twelve other members are contributed +by the Royal and Royal Astronomical Societies respectively, six +by each. The first Saturday in June is the appointed day for the +annual inspection by the Board, and for the presentation to it +of the Astronomer Royal's Report. To this all-important business +meeting has been added something of a social function, by the +invitation of many well-known astronomers and the leading men of the +allied sciences to inspect the results of the year, and to partake +of the chocolate and cracknels, which have been the traditional +refreshments offered on these occasions for a period 'whereof the +memory of man runneth not to the contrary.' + + + + +CHAPTER VI + +THE TIME DEPARTMENT + + +One day two Scotchmen stood just outside the main entrance +of Greenwich Observatory, looking intently at the great +twenty-four-hour clock, which is such an object of attention to the +passers through the Park. 'Jock,' said one of them to the other, +'d'ye ken whaur ye are?' Jock admitted his ignorance. 'Ye are at the +vara ceentre of the airth.' + +Geographers tell us that there is a sense in which this statement as +it stands may be accepted as true. For if the surface of the globe +be divided into two hemispheres, so related to each other that the +one contains as much land as possible, and the other as little, then +London will occupy the centre or thereabouts of the hemisphere with +most land. + +This was not, however, what the Scotchman meant. He meant to tell +his companion that he was standing on the prime meridian of the +world, the imaginary base line from which all distances, east or +west, are reckoned; in short, that he was on 'Longitude Nought.' + +He was not absolutely correct, however, for the great +twenty-four-hour clock does not mark the exact meridian of +Greenwich. To find the instrument which marks it out and defines it +we must step inside the Observatory precincts, and just within the +gate we see before us on the left hand a door which leads through +a little lobby straight into the most important room of the whole +Observatory--the Transit Room. + +[Illustration: THE GREAT CLOCK AND PORTER'S LODGE. + +(_From a photograph by Mr. Lacey._)] + +This room is not well adapted for representation by artist or +photographer. Four broad stone pillars occupy the greater part of +the space, and leave little more than mere passage room beside. Two +of these pillars are tall, as well as broad and massive, and stand +east and west of the centre of the room, carrying between them the +fundamental instrument of the Observatory, the transit circle. The +optical axis of this telescope marks 'Longitude Nought,' which is +further continued by a pair of telescopes, one to the north of it, +the other to the south, mounted on the third and fourth of the +pillars alluded to above. + +This room has not always marked the meridian of Greenwich, for it +stands outside the original boundary of the Observatory. But it is +only a few feet to the east of the first transit instrument which +was set up by Halley, the second Astronomer Royal, in the extreme +N.-W. corner of the Observatory domain, a distance equivalent to +very much less than one-tenth of a second of time, an utterly +insensible quantity with the instruments of two hundred years ago. + +It would be a long story to tell in detail how the Greenwich transit +room has come to define one of the two fundamental lines that +encircle the earth. The other, the equator, is fixed for us by the +earth itself, and is independent of any political considerations, +or of any effort or enterprise of man. But of all the infinite +number of great circles which could be drawn at right angles to the +equator, and passing through the north and south poles, it was not +easy to select one with such an overwhelming amount of argument in +its favour as to obtain a practically universal acceptance. The +meridians of Jerusalem and of Rome have both been urged, upon what +we may call religious or sentimental grounds; that of the Great +Pyramid at Ghizeh has been pressed in accordance with the fantastic +delusion that the Pyramid was erected under Divine inspiration and +direction; that of Ferro, in the Canaries, as being an oceanic +station, well to the west of the Old World, and as giving a base +line without preference or distinction for one nation rather than +another. + +The actual decision has been made upon no such grounds as these. +It has been one of pure practical convenience, and has resulted +from the amazing growth of Great Britain as a naval and commercial +power. Like Tyre of old, she is 'situate at the entry of the sea, +a merchant of the people for many isles,' and 'her merchants are +the great men of the earth.' To tell in full, therefore, the +steps by which the Greenwich meridian has overcome all others is +practically to tell again, from a different standpoint, the story +of the 'expansion of England.' The need for a supreme navy, the +development of our empire beyond the seven seas, the vast increase +of our carrying trade--these have made it necessary that Englishmen +should be well supplied with maps and charts. The hydrographic and +geographic surveys carried on, either officially by this country, or +by Englishmen in their own private capacity, have been so numerous, +complete, and far-reaching as not only to outweigh those of all +other countries put together, but to induce the surveyors and +explorers of not a few other countries to adopt in their work the +same prime meridian as that which they found in the British charts +of regions bordering on those which they were themselves studying. +Naturally, the meridian of Greenwich has not only been adopted +for Great Britain, but also for the British possessions over-sea, +and, from these, for a large number of foreign countries; whilst +our American cousins retain it, an historic relic of their former +political connection with us. The victories of Clive at Arcot and +Plassy, of Nelson at the Nile and Trafalgar, the voyages and surveys +of Cook and Flinders, and many more; the explorations of Bruce, +Park, Livingstone, Speke, Cameron, and Stanley; these are some of +the agencies which have tended to fix 'Longitude Nought' in the +Greenwich Transit Room. + +There are two somewhat different senses in which the meridian of +Greenwich is the standard meridian for nearly the entire world. The +first is the sense about which we have already been speaking; it +constitutes the fundamental line whence distances east and west are +measured, just as distances north and south are measured from the +equator. But there is another, though related sense, in which it has +become the standard. _It gives the time to the world._ + +There are few questions more frequently put than, 'What time is +it?' 'Can you tell me the true time?' A stickler for exactitude +might reply, 'What kind of time do you mean?' 'Do you mean solar +or sidereal time?' 'Apparent time or mean time?' 'Local time or +standard time?' There are all these six kinds of time, but it is +only within the last two generations, within, indeed, the reign of +our Sovereign, Queen Victoria, that the subject of the differences +of most of these kinds of time has become of pressing importance to +any but theorists. + +In one of the public gardens of Paris a little cannon is set up +with a burning-glass attached to it in such a manner that the +sun itself fires the cannon as it reaches the meridian. This, of +course, is the time of Paris noon--apparent noon--but it would be +exceedingly imprudent of any traveller through Paris who wished, +say, to catch the one o'clock express, to set his watch by the gun. +For if it happened to be in February, he would find when he reached +the railway station that the station clock was faster than the sun +by nearly a full quarter of an hour, and that his train had gone; +whilst towards the end of October or the beginning of November, he +would find himself as much too soon. + +Until machines for accurately measuring time were invented, apparent +time--time, that is to say, given by the sun itself, as by a +sun-dial--was the only time about which men knew or cared. But when +reasonably good clocks and watches were made, it was very soon seen +that at different times in the year there was a marked difference +between sun-dial time and that shown by the clock, the reason being +simply that the apparent rate of motion of the sun across the sky +was not always quite the same, whilst the movement of the clock was, +of course, as regular as it could be made. + +This difference between time as shown by the actual sun and by a +perfect clock is known as the 'equation of time.' It is least about +April 15, June 15, August 31, and December 25. It is greatest, +the sun being after the clock, about February 11; and the sun +being before the clock, about November 2. Flamsteed, before he +became Astronomer Royal, investigated the question, and so clearly +demonstrated the existence, cause, and amount of the equation of +time as entirely to put an end to controversy on the subject. + +We had thus, early in the century, the two kinds of time in common +use, apparent time and mean time, or clock time. But as the sun can +only be on one particular meridian at any given instant, the time +as shown by the clocks in one particular town will differ from that +of another town several miles to the east or west of it. It is thus +noon at Moscow 1 hr. 36 min. before it is noon at Berlin, and noon +at Berlin 54 min. before it is noon in London. + +This was all well enough known, but occasioned no inconvenience +until the introduction of railway travelling; then a curious +difficulty arose. Suppose an express train was running at the rate +of sixty miles an hour from London to Bristol. The guard of the +train sets his watch to London time before he leaves Paddington, +but if the various towns through which the train passes, Reading, +Swindon, etc., each keep their own local time, he will find his +watch apparently fast at each place he reaches; but on his return +journey, if he sets to Bristol time before starting, he will in a +similar way find it apparently slow by the Swindon, Reading, and +Paddington clocks as he reaches them in succession. + +It became at once necessary to settle upon one uniform system of +time for use in the railway guides. Apart from this, a passenger +taking train, say, at Swindon, might have been very troubled to +know whether the advertised time of his train was that of Exeter, +the place whence it started, or Swindon, the station where he was +getting in, or London, its destination. 'Railway time,' therefore, +was very early fixed for the whole of Great Britain to be the same +as London time, which is, of course, time as determined at Greenwich +Observatory. At first it was the custom to keep at the various +stations two clocks, one showing local time, the other 'railway,' or +Greenwich time, or else the clocks would be provided with a double +minute hand, one branch of which pointed to the time of the place, +the other to the time of Greenwich. + +It was soon found, however, that there was no sufficient reason +for keeping up local time. Even in the extreme West of England the +difference between the two only amounted to twenty-three minutes, +and it was found that no practical inconvenience resulted from +saying that the sun rose at twenty-three minutes past six on March +22, rather than at six o'clock. The hours of work and business were +practically put twenty-three minutes earlier in the day, a change of +which very few people took any notice. + +Other countries besides England felt the same difficulty, and solved +it in the same way, each country as a rule taking as its standard +time the time of its own chief city. + +There were two countries for which this expedient was not +sufficient--the United States and Canada. The question was of no +importance until the iron road had linked the Atlantic to the +Pacific in both countries. Then it became pressing. No fewer than +seventy different standards prevailed in the United States only some +twenty years ago. The case was a very different one here from that +of England, where east and west differed in local time by only a +little over twenty minutes. In North America, in the extreme case, +the difference amounted to four hours, and it seemed asking too much +of men to call eight o'clock in their morning, or it might be four +o'clock in their afternoon, their noonday. + +The device was therefore adopted of keeping the minutes and seconds +the same for all places right across the continent, but of changing +the hour at every 15° of longitude. The question then arose what +longitude should be adopted as the standard. The Americans might +very naturally have taken their standard time from their great +national observatory at Washington, or from that of their chief +city, New York, or of their principal central city, Chicago. But, +guided partly no doubt by a desire to have their standard times +correspond directly to the longitudes of their maps, and partly +from a desire to fall in, if possible, with some universal time +scheme, if such could be brought forward, they fixed upon the +meridian of Greenwich as their ultimate reference line, and defined +their various hour standards as being exactly so many hours slow of +Greenwich mean time. + +The decision of the United States and of Canada brought with it +later a similar decision on the part of all the principal States +of Europe; and Greenwich is not only 'Longitude Nought' for the +bulk of the civilized world, but Greenwich mean time, increased or +decreased by an exact number of hours or half-hours, is the standard +time all over the planet. + +No; the statement requires correction. Two countries hold out, both +close to our own doors. France, instead of adopting Greenwich time +as such, adopts _Paris time less_ 9 m. 21 s. (that being the precise +difference in longitude between the two national observatories). +Ireland disdains even such a veiled surrender, and Dublin time is +the only one recognized from the Hill of Howth to far Valentia. So +the distressful country preserves her old grievance, that she does +not even get her time until after England has been served. + +The alteration in national habits following on the adoption of +this European system has had a very perceptible effect in some +cases. Thus, Switzerland has adopted Mid-European time, one hour +fast of Greenwich; the true local time for Berne being just half +an hour later. The result of putting the working hours this thirty +minutes earlier in the day has had such a noticeable effect on +the consumption of gas, as to lead the gas company to contemplate +agitating for a return to the old system. + +Thus, Greenwich time, as well as the Greenwich meridian, has +practically been adopted the world over. + +It follows, then, that the determination of time is the most +important duty of the Royal Observatory; and the Time Department, +the one to which is entrusted the duty of determining, keeping, and +distributing the time, calls for the first attention. + +Entering the transit room, the first thing that strikes the +visitor is the extreme solidity with which the great telescope is +mounted. It turns but in one plane, that of 'longitude nought,' +and its pivots are supported by the pair of great stone pillars +which we have already spoken of as occupying the principal part of +the transit-room area, and the foundations of which go deep down +under the surface of the hill. On the west side of the telescope, +and rigidly connected with it, is a large wheel some six feet in +diameter, and with a number of wooden handles attached to it, +resembling the steering-wheel of a large steamer. This wheel carries +the setting circle, which is engraved upon a band of silver let +into its face near its circumference, a similar circle being at the +back of the wheel nearer the pillar. Eleven microscopes, of which +only seven are ordinarily used, penetrate through the pier, and are +directed on to this second circle. + +The present transit is the fourth which the Observatory has +possessed, and its three predecessors, known as Halley's, Bradley's, +and Troughton's, respectively, are still preserved and hang on +the walls of the transit room, affording by their comparison an +interesting object-lesson in the evolution of a modern astronomical +instrument. + +The watcher who wishes to observe the passing of a star must note +two things: he must know in what direction to point his telescope, +and at what time to look for the star. Then, about two minutes +before the appointed time, he takes his place at the eyepiece. As +he looks in he sees a number of vertical lines across his field +of view. These are spider-threads placed in the focus of the +eye-piece. Presently, as he looks, a bright point of silver light, +often surrounded by little flashing, vibrating rays of colour, comes +moving quickly, steadily onward--'swims into his ken,' as the poet +has it. The watcher's hand seeks the side of the telescope till his +finger finds a little button, over which it poises itself to strike. +On comes the star, 'without haste, without rest,' till it reaches +one of the gleaming threads. Tap! The watcher's finger falls sharply +on the button. Some three or four seconds later and the star has +reached another 'wire,' as the spider-threads are commonly called. +Tap! Again the button is struck. Another brief interval and the +third wire is reached, and so on, until ten wires have been passed, +and the transit is over. The intervals are not, however, all the +same, the ten wires being grouped into three sets, two of three +apiece, and the third of four. + +[Illustration: THE CHRONOGRAPH.] + +Each tap of the observer's finger completed for an instant an +electric circuit, and recorded a mark on the 'chronograph.' This +is a large metal cylinder covered with paper, and turned by a +carefully-regulated clock once in every two minutes. Once in every +two seconds a similar mark was made by a current sent by means of +the standard sidereal clock of the Observatory. The paper cover of +the chronograph after an hour's work shows a spiral trace of little +dots encircling it some thirty times. These dots are at regular +intervals, about an inch apart, and are the marks made by the clock. +Interspersed between them are certain other dots, in sets of ten; +and these are the signals sent from the telescope by the transit +observer. If, then, one of the clock dots and one of the observer's +dots come exactly side by side, we know that the star was on one +of the wires at a given precise second. If the observer's dot comes +between two clock dots, it is easy, by measuring its distance from +them with a divided scale, to tell the instant the star was on +the wire to the tenth of a second, or even to a smaller fraction. +Whilst, since the transit was taken over ten wires, and the distance +of each wire from the centre of the field of view is known, we have +practically ten separate observations, and the average of these +will give a much better determination of the time of transit than a +single one would. + +But let the watcher be ever so little too slow in setting his +telescope, or ever so little late in placing himself at his +eye-piece, and the star will have passed the wire, and as it +smoothly, resistlessly moves on its inexorable way, will tell the +tardy watcher in a language there is no mistaking, 'Lost moments can +never be recalled.' The opportunity let slip, not until twenty-four +hours have gone by will another chance come of observing that same +star. + +It is the stars that are chiefly used in this determination, partly +because the stars are so many, whilst there is but one sun. If, +therefore, clouds cover the sun at the important moment of transit, +the astronomer may well exclaim, so far as this observation is +concerned, 'I have lost a day!' The chance will not be offered him +again until the following noon. But if one star is lost by cloud, +there are many others, and the chance is by no means utterly gone. +Beside, the sun enables us to tell the time only at noon; the stars +enable us to find it at various times throughout the entire night; +indeed, throughout both day and night, since the brighter stars can +be observed in a large telescope even during the day. + +There are two great standard clocks at the Observatory: the mean +solar clock and the sidereal clock. The latter registers twenty-four +hours in the precise time that the earth rotates on its axis. A +'day' in our ordinary use of the term is somewhat longer than this; +it is the average time from one noon to the next, and as the earth +whilst turning round on its axis is also travelling round the sun, +it has to rather more than complete a rotation in order to bring the +sun again on to the same meridian. A solar day is therefore some +four minutes longer than an actual rotation of the earth, _i.e._ a +sidereal day, as it is called, since such rotation brings a star +back again to the same meridian. + +The sidereal clock can therefore be readily checked by the +observation of star transits, for the time when the star ought to +be on the meridian is known. If, therefore, the comparison of the +transit taps on the chronograph with the taps of the sidereal clock +show that the clock was not indicating this time at the instant +of the transit, we know the clock must be so much fast or slow. +Similarly, the difference which should be shown between the sidereal +and solar clocks at any moment is known; and hence when the error of +the sidereal clock is known, that of the solar can be readily found. + +It is often quite sufficient to know how much a clock is wrong +without actually setting its hands right; but it is not possible +to treat the Greenwich clock so, for it controls a number of other +clocks continually, and sends hourly signals out over the whole +country, by which the clocks and watches all over the kingdom are +set right. + +In the lower computing room, below the south window, we find the +Time-Desk, the head-quarters of the Time Department. This is a very +convenient place for the department, since one of the chronometer +rooms, formerly Bradley's transit room, opens out of the lower +computing room; the transit instrument is just beyond; it is +close to the main gate of the Observatory, and so convenient for +chronometer makers or naval officers bringing chronometers or coming +for them, whilst just across the courtyard is the chronograph room, +with the Battery Basement, in which the batteries for the electric +currents are kept, and the Mean Solar Clock lobby, with the winch +for the winding of the time-ball at the head of the stairs above it. +These rooms do not exhaust the territory of the department, since it +owns two other chronometer rooms on the ground floor and first floor +respectively of the S.-E. tower. + +At the time-desk means are provided for setting the clock right very +easily and exactly. Just above the desk are a range of little dials +and bright brass knobs, that almost suggest the stops of a great +organ. + +Two of these little dials are clock faces, electrically connected +with the solar and sidereal standard clocks, so that, though these +clocks are themselves a good way off, in entirely different parts +of the Observatory, the time superintendent, seated here at the +time-desk, can see at once what they are indicating. Between the +two is a dial labelled 'Commutator.' From this dial a little handle +usually hangs vertically downwards, but it can be turned either +to the right or to the left, and when thus switched hard over, an +electric current is sent through to the mean solar clock. If now +we leave the computing room and cross the courtyard to the extreme +north-west corner, we find the Mean Solar Clock in a little lobby, +carefully guarded by double doors and double windows against rapid +changes of temperature. Opening the door of the clock case, we +see that the pendulum carries on its side a long steel bar, and +that this bar as the pendulum swings passes just over the upper +end of an electro-magnet. When the current is switched on at the +commutator, this electro-magnet attracts or repels the steel bar +according to the direction of the current, and the action of the +clock is accordingly quickened or retarded. To put the commutator +in action for one minute will alter the clock by the tenth of a +second. As the error of the clock is determined twice a day, shortly +before ten o'clock in the morning, and shortly before one o'clock in +the afternoon, its error is always small, usually only one or two +tenths. These two times are chosen because, though time-signals are +sent over the metropolitan area every hour from the Greenwich clock +through the medium of the Post Office, at ten and at one o'clock +signals are also sent to all the great provincial centres. Further, +at one o'clock the time balls at Greenwich and at Deal are dropped, +so that the captains of ships in the docks, on the river, or in the +Downs may check their chronometers. + +The Time-Ball is dropped directly by the mean solar clock itself. +It is raised by means of a windlass turned by hand-power to the top +of its mast just before one o'clock. Connected with it is a piston +working in a stout cylinder. When the ball has reached the top of +the mast, the piston is lightly supported by a pair of catches. +These catches are pulled back by the hourly signal current, and +the piston at once falls sharply, bringing the ball with it. But +after a fall of a few feet, the air compressed by the piston acts +as a cushion and checks the fall, the ball then gently and slowly +finishing its descent. The instant of the beginning of the fall is, +of course, the true moment to be noted. + +The other dials on the time-desk are for various purposes connected +with the signals. One little needle in a continual state of +agitation shows that the electric current connecting the various +sympathetic clocks of the Observatory is in full action. Another +receives a return signal from various places after the despatch +of the time-signal from Greenwich, and shows that the signal has +been properly received at the distant station, whilst all the many +electric wires within the Observatory or radiating from it are made +to pass through the great key-board, where they can be at once +tested, disconnected, or joined up, as may be required. + +[Illustration: THE TIME-DESK.] + +The distribution of Greenwich time over the island in this way is +thus a simple matter. The far more important one of the distribution +of Greenwich time to ships at sea is more difficult. The difficulty +lay in the construction of a clock or watch, the rate of which +would not be altered by the uneasy motion of a ship, or by the +changes of temperature which are inevitable on a voyage. Two hundred +years ago it was not deemed possible to construct a watch of +anything like sufficient accuracy. They would not even keep going +whilst they were being wound, and would lose or gain as much as a +minute in the day for a fall or rise of 10° in temperature. This +was owing to the extreme sensitiveness of the balance spring--which +takes the place in a watch of a pendulum in a clock--to the effects +of temperature. The British Government, therefore, in 1714 offered +a prize of the amount of £20,000 for a means of finding the +longitude at sea within half a degree, or, in other words, for a +watch that would keep Greenwich time correct to two minutes in a +voyage across the Atlantic. In 1735, James Harrison, the son of a +Yorkshire carpenter, succeeded in solving the problem. His method +was to attach a sort of automatic regulator to the spring which +should push the regulator over in one direction as the temperature +rose, and bring it back as it fell. This he effected by fastening +together two strips of brass and steel. The brass expanded with heat +more rapidly than the steel, and hence with a rise of temperature +the strip bent over on the steel side. This was the first germ of +the idea of making watches 'compensated for temperature;' watches, +that is, which maintain practically the same rate whether they are +in heat or cold, an idea now brought to great perfection in the +modern chronometer. + +[Illustration: HARRISON'S CHRONOMETER.] + +The great reward the Government had offered stimulated many men to +endeavour to solve the problem. Of these, Dr. Halley, the second +Astronomer Royal, and Graham, the inventor of the astronomical +clock, were the most celebrated. But when Harrison, then poor and +unknown, came to London in 1735, and laid his invention before them, +with an utter absence of self-seeking, and in the true scientific +spirit, they gave him every assistance. + +Harrison's first four time-keepers are still preserved at the +Royal Observatory. He did not, however, receive his reward until +a facsimile of the fourth had been made by his apprentice, Larcum +Kendall. The latter is preserved at the Royal Observatory. There is +a Larcum Kendall at the Royal Institution which is said to have been +used by Captain Cook. Harrison's chronometer was sent on a trial +voyage to Jamaica in 1761, and on its return to Portsmouth in the +following year it was found that its complete variation was under +the two minutes for which the Government had stipulated. + +Since Harrison's day the improvement of the chronometer has been +carried on almost to perfection, and now the care and rating of +chronometers for the Royal Navy is one of the most important duties +of the Observatory. + +[Illustration: THE CHRONOMETER ROOM.] + +A visitor who should make the attempt to compare a single +chronometer with a standard clock would probably feel very +disheartened when, after many minutes of comparison, he had got out +its error to the nearest second, were he told that it was his duty +to compare the entire army here collected, some five hundred or +more, and to do it not to the second, but to the nearest tenth of a +second. Practice and system make, however, the impossible easy, and +one assistant will quietly walk round the room calling out the error +of each chronometer as he passes it, as fast as a second assistant +seated at the table can enter it at his dictation in the chronometer +ledgers. The seconds beat of a clock sympathetic with the solar +standard, rings out loud and clear above the insect-like chatter +of the ticking of the hundreds of chronometers, and wherever the +assistant stands, he has but to lift his eyes to see straight before +him, if not a complete clock-face, at least a seconds dial moving in +exact accordance with the solar standard. + +The test to which chronometers are subjected is not merely one of +rate, but one of rate under carefully altered conditions. Thus +they may be tried with the XII pointing in succession to the four +points of the compass, or, in the case of chronometer watches, +they may be laid flat down on the table or hung from the ring or +pendant, or with the ring right or left, as it would be likely to +be when carried in the waistcoat pocket. But the chief test is the +performance of a chronometer when subjected to considerable heat +for a long period. This is a matter of great consequence, since +a chronometer travelling from England to India, Australia, or the +Cape, would necessarily be subjected to very different conditions +of temperature from those to which it would be exposed in England. +They are therefore kept for eight weeks in a closed stove at a +temperature of about 85° or 90°. At one time a cold test was also +applied, and Sir George Airy, the late Astronomer Royal, in one of +his popular lectures, drew a humorous comparison between the unhappy +chronometers thus doomed to trial, now in heat and now in frost, +and the lost spirits whom Dante describes as alternately plunged +in flame and ice. The cold test has, however, been done away with. +It is perfectly easy on the modern ship to keep the chronometer +comfortably warm even on an Arctic expedition. The elaborate cold +testing applied to Sir George Nares' chronometers before he started +on his polar journey was found to have been practically quite +superfluous; the chronometers were, if anything, kept rather too +warm. The exposure of the chronometer in the cooling box, moreover, +was found to be attended with a risk of rusting its springs. + +[Illustration: THE CHRONOMETER OVEN.] + +Once the determination of the longitude at sea became possible, +it was clearly the next duty to fix with precision the position +of the principal places, cities, ports, capes, islands, the world +over. Of all the work done in this department none has ever been +done better, in proportion to the means at command, than that +accomplished by Captain Cook in his celebrated three voyages. As has +already been pointed out, it is the extent and thoroughness of the +hydrographic surveys of the British Admiralty which have largely +contributed to the honour done to England by the international +selection of the English meridian, and of English standard time, as +in principle those for the whole civilized world. The generosity and +public spirit therefore which led the second Astronomer Royal to +help forward and support his rival, has almost directly led to this +great distinction accruing to the Observatory of which he was the +head. + +Three different methods have successively been used in the +determination of longitudes of distant places. In each case the +problem required was to ascertain the time at the standard place, +say Greenwich, at the same time that it was being determined in +the ordinary way at the given station. One method of ascertaining +Greenwich time when at a distance from it was, as stated in Chapter +I., to use the moon, as it were, as the hand of a vast clock, of +which the sky was the face and the stars the dial figures. This is +the method of 'lunar distances,' the distances of the moon from a +certain number of bright stars being given in the _Nautical Almanac_ +for every three hours of Greenwich time. + +As chronometers were brought to a greater point of perfection, it +was found easier and better in many cases to use 'chronometer runs,' +that is, to carry backwards and forwards between the two stations +a number of good chronometers, and by constant comparison and +re-comparison to get over the errors which might attach to any one +of them. + +[Illustration: THE TRANSIT PAVILION. + +(_From a photograph by Mr. Lacey._)] + +But of late years another method has proved available. Distant +nations are now woven together across thousands of miles of ocean +by the submarine telegraph. The American reads in his morning +paper a summary of the debates of the previous night in the House +of Commons at Westminster. The Londoner watches with interest +the scores of the English cricket team in Australia. It is now +therefore possible for an astronomer in England to record, should +he so desire, the time of the transit of a star across the wires +of his instrument, not only on his own chronograph, but upon that +of another observatory, it may be 2000 miles away. Or, much more +conveniently, each observer may independently determine the error of +his own clock, and then bring his clock into the current, so that +it may send a signal to the chronograph of the other station. + +In one way or another this work of the determination of geographical +longitudes has been an important part of the extra-routine work +at Greenwich, part of the work which has built up and sustained +its claim to define 'longitude nought'; and many distinguished +astronomers, especially from the leading observatories of the +Continent, have come here from time to time to obtain more +accurately the longitude of their own cities. The traces of their +visits may be seen here and there about the Observatory grounds in +flat stones which lie level with the surface, and bear a name and +date like the gravestones in some old country churchyard. These are +not, as one might suppose, to mark the burial-places of deceased +astronomers, but record the sites where, on their visits for +longitude purposes, different foreign astronomers have set up their +transit instruments. Now, however, a permanent pier has been erected +in the courtyard, and a neat house--the Transit Pavilion--built over +it, so that in all probability no fresh additions will be made to +these sepulchral-looking little monuments. + +It might be asked, What reason is there for a foreign observer to +come over to England for such a purpose? Would it not be sufficient +for the clock signals to be exchanged? But a curious little fact +has come out with the increase of accuracy of transit observation, +and that is, that each observer has his own particular habit or +method of observation. A hundred years ago, Maskelyne, the fifth +Astronomer Royal, was greatly disturbed to find that his assistant, +David Kinnebrook, constantly and regularly observed a star-transit +a little later than he did himself. The offender was scolded, +warned, exhorted, and finally, when all proved useless to bring +his observations into exact agreement with the Astronomer Royal's, +dismissed as an incompetent observer. As a matter of fact, poor +Kinnebrook has a right to be regarded as one of the martyrs of +science, and Maskelyne, by this most natural but mistaken judgment, +missed the chance of making an important discovery, which was not +made until some thirty years later. Astronomers now would be more +cautious of concluding that observations were bad simply because +they differed from what had been expected. They have learnt by +experience that these unexpected differences are the most likely +hunting-ground in which to look for new discoveries. + +In a modern transit observation with the use of the chronograph +it will be seen at once that before the observer can register a +star-transit on the chronograph, he has to perceive with his eye +that the star has reached the wire, he has to mentally recognize +the fact, and consciously or unconsciously to exert the effort of +will necessary to bring his finger down on the button. A very slight +knowledge of character will show that this will require different +periods of time for different people. It will be but a fraction +of a second in any case, but there will be a distinct difference, +a constant difference, between the eager, quick, impulsive man +who habitually anticipates, as it were, the instant when he sees +star and wire together, and the phlegmatic, slow-and-sure man +who carefully waits till he is quite sure that the contact has +taken place, and then deliberately and firmly records it. These +differences are so truly personal to the observer that it is quite +possible to correct for them, and after a given observer's habit has +become known, to reduce his transit times to those of some standard +observer. It must, of course, be remembered that this 'personal +equation' is an exceedingly minute quantity, and in most cases is +rather a question of hundredths of seconds than of tenths. + +It will be seen from the foregoing description how little of what +may be termed the picturesque or sensational side of astronomy +enters into the routine of the Time Department, the most important +of all the departments of the Observatory. The daily observation of +sun and of many stars--selected from a carefully chosen list of some +hundreds, and known as 'clock stars'--the determination of the error +of the standard clock to the hundredth of a second if possible, and +its correction twice a day, the sending out of time signals to the +General Post Office and other places, whence they are distributed +all over the country; the care, winding, and rating of hundreds of +chronometers and chronometer watches, and from time to time the +determination of the longitude of foreign or colonial cities, make +up a heavy, ceaseless routine in which there is little opportunity +for the realization of an astronomer's life as it is apt to be +popularly conceived. + +Yet there is interest enough in the work. There is the charm +which always attaches to work of precision, the delight of using +delicate and exact instruments, and of obtaining results of steadily +increasing perfection. It may be akin to the sporting passion for +record-breaking, but surely it is a noble form of it which has led +the assistants, in recent years, to steadily increase the number of +observations in a normal night's work up to the very limit, taking +care the while that their accuracy has in no degree suffered. In +longitude work also 'the better is the enemy of the good,' and there +is the ambition that each fresh determination shall be markedly +more precise than all that have preceded it. The constant care of +chronometers soon reveals a kind of individuality in them which +forms a fresh source of interest, whilst if a man has but a spark +of imagination, how easily he will wrap them round with a halo of +romance! + +Glance through the ledgers, and you will see how some of them have +heard the guns at the siege of Alexandria, others have been carried +far into the frozen north, others have wandered with Livingstone or +Cameron in the trackless forests of equatorial Africa. + +More striking still are those pages across which the closing line +has been drawn; never again will the time-keeper there scheduled +return to the kindly inquisition of Flamsteed Hill. This sailed away +in the Wasp, and was swallowed up in the eastern typhoon; that went +down in the sudden squall that smote the Eurydice off the Isle of +Wight; these foundered with the Captain. The last fatal journey of +Sir John Franklin to find the North-West Passage leaves its record +here; the chronometers of the Erebus and Terror will never again +appear on the Greenwich muster roll. Land exploration claims its +victims too. Sturt's ill-fated expedition across Australia, and +Livingstone's last wandering, are represented. + +[Illustration: 'LOST IN THE BIRKENHEAD.'] + +Sometimes an amusing entry interrupts the silent pathos of these +closed pages. 'Lost by Mr. Smith on the coast of Africa,' reads at +first sight like a rather thin attempt of some one to shift the +responsibility of his own carelessness on to the broad shoulders of +Mr. Nobody. In reality it probably gives a hint of the necessary, +dangerous, and exciting work of slave-dhow chasing which gives +employment to our ships on the African coast. 'Mr. Smith' was no +doubt a petty officer who was told off to carry the chronometer for +a boat's crew sent to search for a slave-dhow up some equatorial +estuary. Probably the dhow was found, and the Arabs who manned it +gave so stout a resistance that 'Mr. Smith' and his men had other +things to do than take care of chronometers before they could +overcome them. We may take it that the real story outlined here was +one of courage and hard fighting, not of carelessness and shirking. + +Stories of higher valour and nobler courage yet are also hinted: +the calm discipline of the crew of the Victoria as she sank from +the ram of the Camperdown, the yet nobler devotion of the men of +the Birkenhead, as they formed up in line on deck and cheered the +boats that bore away the women and children to safety, whilst they +themselves went down with the ship into the shark-crowded sea. + + 'There rose no murmur from the ranks, no thought + By shameful strength, unhonoured life to seek; + Our post to quit we were not trained, nor taught + To trample down the weak. + + 'What followed, why recall? The brave who died + Died without flinching in that bloody surf. + They sleep as well beneath that purple tide + As others under turf.' + + + + +CHAPTER VII + +THE TRANSIT AND CIRCLE DEPARTMENTS + + +The determination of time is a duty the importance of which readily +commends itself to the general public. It is easy to see that in any +civilized country it is very necessary to have an accurate standard +of time. Our railways and telegraphs make it quite impossible for +us to be content with the rough-and-ready sun-dial which satisfied +our forefathers. But it should be remembered that it was neither to +establish a 'longitude nought,' nor to create a system of standard +time, that Greenwich Observatory was founded in 1675. It was for +'The Rectifying the Tables of the Motions of the Heavens and the +Places of the Fixed Stars, in order to find out the so-much-desired +Longitude at Sea for the perfecting the Art of Navigation.' + +The two related departments, therefore, those of the Transit and the +Circle, which are concerned in the work of making star-catalogues, +come next in order to the Time Department. Though both departments +deal with the same instrument, the transit circle, they are at +present placed at opposite ends of the Observatory domain; the +Circle Department being lodged in the upper computing room of the +old building; the Transit Department in the south wing of the New +Observatory in the south ground. + +It may be asked why, if this were the purpose of the Observatory +at its foundation, two and a quarter centuries ago; if, as was +the case, the work was set on foot from the beginning and was +carried out with every possible care, how comes it that it is still +the fundamental work of the Observatory, and, instead of being +completed, has assumed greater proportions at the present day than +ever before? + +The answer to this inquiry may be found in a special application of +the old proverb, originally directed against the discontent of man: +'The more he has, the more he wants.' For, however paradoxical it +may seem, it is true that the fuller a star-catalogue is, and the +more accurate the places of the stars that it contains, the greater +is the need for a yet fuller catalogue, with places more accurate +still. + +It is worth while following up this paradox in some detail, as +it affords a very instructive example of the way in which a work +started on purely utilitarian grounds extends itself till it crosses +the undefined boundary and enters the region of pure science. + +We have no idea who made the earliest census of the sky. It is +written for us in no book; it is not even engraved on any monument. +And yet no small portion of it is in our hands to-day, and, +strangest of all, we are able to fix fairly closely the time at +which it was made, and the latitude in which its compiler lived. The +catalogue is very unlike our star-catalogues of to-day. The places +of the stars are very roughly indicated; and yet this catalogue has +left a more enduring mark than all those that have succeeded it. The +catalogue simply consists of the star names. + +An old lady who had attended a University Extension lecture +on astronomy was heard to exclaim: 'What wonderful men these +astronomers are! I can understand how they can find out how far +off the stars are, how big they are, and what they weigh--that is +all easy enough; and I think I can see how they find out what they +are made of. But there is one thing that I can't understand--I +don't know how they can find out what are their names!' This same +difficulty, though with a much deeper meaning than the old lady in +her simplicity was able to grasp, has occurred to many students of +astronomy. Many have wished to know what was the meaning of, and +whence were derived, the sonorous names which are found attached to +all the brighter stars on our celestial globes: Adhara, Alderamin, +Betelgeuse, Denebola, Schedar, Zubeneschamal, and many more. The +explanation lies here. Some 5000 years ago, a man, or college of +men, living in latitude 40° north, in order that they might better +remember the stars, associated certain groups of them with certain +fancied figures, and the individual star names are simply Arabic +words designed to indicate whereabouts in its peculiar figure or +constellation that special star was situated. Thus Adhara means +'back,' and is the name of the bright star in the back of the great +Dog. Alderamin means 'right arm,' and is the brightest star in the +right arm of Cepheus, the king. Betelgeuse is 'giant's shoulder,' +the giant being Orion; Denebola is 'lion's tail.' Schedar is the +star on the 'breast' of Cassiopeia, and Zubeneschamal is 'northern +claw,' that is, of the Scorpion. So far is clear enough. The names +of the stars for the most part explain themselves; but whence the +constellations derived their names, how it was that so many snakes +and fishes and centaurs were pictured out in the sky, is a much more +difficult problem, and one which does not concern us here. + +One point, however, these old constellations do tell us, and tell +us plainly. They show that the axis of the earth, which, as the +earth travels round the sun, moves parallel with itself, yet, in +the course of ages, itself rotates so as in a period of some 26,000 +years to trace out a circle amongst the stars. This is the cause of +what is called 'precession,' and explains how it is that the star +we call the pole-star to-day was not always the pole-star, nor will +always remain so. We learn this fact from the circumstance that +the old constellations do not cover the entire celestial sphere. +They leave a great circular space of 40° radius unmapped in the +southern heavens. This simply means that the originators of the +constellations lived in 40° north latitude, and stars within 40° of +their south pole never rose above their horizon, and consequently +were never seen, and could not be mapped, by them. In like manner, +the star census taken at Greenwich Observatory does not include +the whole sky, but leaves a space some 52° in radius round our +south pole. Since the latitude of Greenwich is nearly 52° north, +stars within that distance of the south pole do not rise above our +horizon, and are never seen here. But if we compare the vacant space +left by the old original constellations with the vacant space left +by a Greenwich catalogue of to-day, we see that the centre of the +first space, which must have been the south pole of that time, is +a long way from the centre of the second space--our south pole of +to-day. The difference tells us how far the pole has moved since +those old forgotten astronomers did their work. We know the rate +at which the pole appears to move, by comparing our more modern +catalogues one with another; and so we are able to fix pretty nearly +the time when lived those old first census-takers of the stars, +whose names have perished so completely, but whose work has proved +so immortal. + +These old workers gave us the constellation groupings and names +which still remain to us, and are still in common, every-day use. +Their work affords us the most striking illustration of the result +of precession, but precession itself was not recognized till nearly +3000 years after their day, when a marvellous genius, Hipparchus, +established the fact, and 'built himself an everlasting name' by +the creation of a catalogue of over 1000 stars prepared on modern +principles. That catalogue formed the basis of one which survives to +us at the present time, and was made some 1750 years ago by Claudius +Ptolemy, the great astronomer of Alexandria, whose work, which still +bears the proud name of _Almagest_, 'The Greatest,' remained for +fourteen centuries the one universal astronomical text-book. + +A modern catalogue contains, like that of Ptolemy, four columns +of entry. The first gives the star's designation; the second +an indication of its brightness; the third and fourth the +determinations of its place. These are expressed in two directions, +which, in modern catalogues, not in Ptolemy's, correspond on the +celestial sphere to longitude and latitude on the terrestrial. +Distance north or south of the celestial equator is termed +'declination,' corresponding to terrestrial latitude. Distance in +a direction parallel to the equator is termed 'right ascension,' +corresponding to terrestrial longitude. For geographical purposes +we conceive the earth to be encircled by two imaginary lines at +right angles to each other--the one, the equator, marked out for us +by the earth itself; the other, 'longitude nought,' the meridian +of Greenwich, fixed for us by general consent, after the lapse of +centuries, by a kind of historical evolution. On the celestial globe +in like manner we have two fundamental lines--one, the celestial +equator, marked out for us by nature; the other at right angles to +it, and passing through the poles of the sky, adopted as a matter +of convenience. But a difficulty at once confronts us--Where can +we fix our 'right ascension nought'? What star has the right to be +considered the Greenwich of the sky? + +The difficulty is met in the following manner: For six months of +the year, the summer months, the sun is north of the celestial +equator; for the other six months of the year, the months of winter, +it is south of it. It crosses the equator, therefore, twice in +the year--once when moving northward at the spring equinox; once +when moving southward at the equinox of autumn. The point where it +crosses the equator at the first of these times is taken as the +fundamental point of the heavens, and the first sign of the zodiac, +Aries the Ram, is said to begin here, and it is called, therefore, +'the first point of Aries.' + +One of the very first facts noticed in the very early days of +astronomy was that, as the stars seemed to move across the sky night +by night, they seemed to move in one solid piece, as if they were +lamps rigidly fixed in one and the same solid vault. Of course it +has long been perfectly understood that this apparent movement was +not in the least due to any motion of the stars, but simply to the +rotation of the earth on its axis. This rotation is the smoothest, +most constant, and regular movement of which we know. It follows, +therefore, that the interval of time between the passage of one star +across the meridian of Greenwich and that of any other given star +is always the same. This interval of time is simply the difference +of their right ascension. If we are able, then, to turn our transit +instrument to the sun, and to a number of stars, each in its proper +turn, and by pressing the tapping-piece on the instrument as the +sun or star comes up to each of the ten wires in succession, to +record the times of its transit on the chronograph, we shall have +practically determined their right ascensions--one of the two +elements of their places. + +The other element, that of declination, is found in a different +manner. The celestial equator, like the terrestrial, is 90° from the +pole. The bright star Polaris is not exactly at the north pole, but +describes a small circle round it. Twice in the twenty-four hours +it transits across the meridian--once when going from east to west +it passes above the pole, once when going from west to east below +the pole. The mean between these two altitudes of Polaris above the +horizon gives the position of the true pole. + +[Illustration: THE TRANSIT CIRCLE.] + +A complete transit observation of a star consists therefore of two +operations. The observer, as we have already described, sees a +star entering the field of the telescope, and as it swims forward, +he presses the galvanic button, which sends a signal to the +chronograph as the star comes up to each of the ten vertical wires +in succession. But, beside the ten wires, there are others. Two +vertical wires lie outside the ten of which we have already spoken, +and there is also a horizontal wire. The latter can be moved by a +graduated screw-head just above the eye-piece, and as the star comes +in succession to these two vertical wires, this horizontal wire is +moved by the screw-head, so as to meet the star at the moment it +is crossing the vertical wire, and the observer presses a second +little button, which records the position of the horizontal wire on +a small paper-covered drum. Then, the transit over, the observer +leaves the telescope and comes round to the outside of the west +pier. Here he finds seven large microscopes, which pierce the whole +thickness of the pier, and are directed towards the circumference +of a large wheel which is rigidly attached to the telescope and +revolves with it. This wheel is six feet in diameter, and has a +silver circle upon both faces. Each circle is divided extremely +carefully into 4320 divisions--these divisions, therefore, being +about the one-twentieth of an inch apart. There are, therefore, +twelve divisions to every degree (12 × 360 = 4320), and each +division equals five minutes of arc. The lowest microscope is the +least powerful, and shows a large part of the circle, enabling the +observer to see at once to what degree and division of a degree +the microscope is pointing. The other six microscopes are very +carefully placed 60° apart--as equally placed as they possibly can +be. These microscopes are all fitted with movable wires--wires moved +by a very fine and delicate screw; the screw-head having divisions +upon it so that the exact amount of its movement can be told. Each +of the six screw-heads will read to the one five-thousandth part +of a division of the circle; in other words, to the one hundred +thousandth part of an inch. Using all six microscopes, and taking +their mean, we are able to _read_ to the one-hundredth of a second +of arc. If, therefore, the observations could be made with perfect +certainty down to the extremest nicety of reading which the +instrument supplies, we should be able to read the declination of a +star to this degree of refinement. It may be added that a halfpenny, +at a distance of three miles, appears to be one second of arc in +diameter; at three hundred miles it would be one-hundredth of a +second. It need scarcely be said that we cannot observe with quite +such refinement of exactness as this would indicate. Nevertheless, +this exactness is one after which the observer is constantly +striving, and tenths, even hundredths, of seconds of arc are +quantities which the astronomer cannot now neglect. + +The observer has then to read the heads of all these seven +microscopes on the pier side, and also two positions of the +horizontal wire on the screw-head at the eye-piece. The following +morning he will also read off from the chronograph-sheet the times +when he made the ten taps as the star passed each of the ten +vertical wires. There are, therefore, nine entries to make for one +position of a star in declination, and ten for one position of a +star in right ascension. The observer will also have to read the +barometer to get the pressure of the air at the time of observation, +and one thermometer inside the transit room, and another outside, +to get the temperature of the air. In some cases thermometers at +different heights in the room are also read. A complete observation +of a single star means, therefore, the entry of two-and-twenty +different numbers. + +It may be asked, What is the use of reading the barometer and +thermometer? The answer to the question can only be given by +contradicting a statement made above, that the true pole lay midway +between the position of the telescope when pointing to the pole-star +at its upper transit, and its position when pointing to it at its +lower transit. The pole being very high in the heavens in this +country, there are a great number of stars that, like the pole-star, +cross the meridian twice in the twenty-four hours--once when they +pass above the pole, moving from east to west, once when they pass +below it, moving from west to east As the real distance of a star +from the true pole does not alter, it follows that we ought to get +the position of the pole from the mean of the two transits of any of +these stars, and they ought all to exactly agree with each other. +But they do not. So, too, I said that the stars all appeared to move +as in a single piece. If, then, we constructed an instrument with +its axis parallel to the axis of the earth, and fixed a telescope to +it, pointing to any particular star, if we turn the telescope round +as fast from east to west as the earth itself is turning from west +to east--if we built an equatorial, that is to say--we ought to find +that the star once in the centre of the field would remain there. As +a matter of fact, when the star got near the horizon it would soon +be a long way from the centre of the field. + +Sir George Airy, the seventh Astronomer Royal, makes, with reference +to this very point, the following remarks: + + 'Perhaps you may be surprised to hear me say the rule is + established as true, and yet there is a departure from it. + This is the way we go on in science, as in everything else; + we have to make out that something is true, then we find out + under certain circumstances that it is not quite true; and + then we have to consider and find out how the departure can be + explained.' + +In this particular case, the disturbing cause is found in the +action of our own atmosphere. The rays of light from the star are +bent out of a perfectly straight course as they pass through the +various layers of that atmosphere, layers which necessarily become +denser the closer we get to the actual surface of the earth. Every +celestial body therefore appears to be a little higher in the sky +than it really is. This action is most noticeable at the horizon, +where it amounts to about half a degree. As both sun and moon are +about half a degree in diameter, it follows that when they have +really just entirely sunk below the horizon they appear to be just +entirely above it. It happens, in consequence, on rare occasions, +that an eclipse of the moon will take place when both sun and moon +are together seen above the horizon. + +It was a great matter to discover this effect of refraction. It +was soon seen that it was not constant, that it varied with both +temperature and pressure. It is, indeed, the most troublesome of all +the hindrances to exact observation with which the astronomer has +to contend; partly because of its large amount--half a degree, as +has been already said, in the extreme case--and partly because it is +difficult in many cases to determine its exact effect. + +The double observation with the transit circle gives us, then, the +place in the sky where the star _appeared_ to be at the moment of +observation, not its true place; to find that true place we have +to calculate how much refraction had displaced the star at the +particular height in the sky, and at the particular temperature and +atmospheric pressure at which the observation was made. + +[Illustration: THE MURAL CIRCLE.] + +The transit circle is a comparatively recent instrument. In earlier +times the two observations of right ascension and declination were +entrusted to perfectly separate instruments. The transit instrument +was mounted as the transit circle is, between two solid stone piers, +and moved in precisely the same way. But the great six-foot wheel, +which was made as stiff as it possibly could be, was mounted on +the face of a great stone pier or wall, from which circumstance it +was called the 'mural circle,' and a light telescope was attached +to it which turned about its centre. This arrangement had a double +disadvantage--that the two observations had to be made separately, +and the mural circle, not being a symmetrical instrument, was +liable to small errors which it was difficult to detect. Thus, being +supported on one side only, a flexure or bending outwards of either +telescope or circle, or both, might be feared. + +It was for this reason that Pond set up a pair of mural circles, +one on the east side of its supporting pier and the other on +the west.[3] His plan was not only to have each star observed +simultaneously in the two instruments, a plan by which, at the cost +of some additional labour, he would have got rid, to a large extent, +of the individual errors of the two separate instruments, inasmuch +as, on the whole, it might have been expected that the errors of +the two instruments would have been very nearly equal in amount, +but of opposite character. The differences, too, between the two +instruments would have afforded the means for tracing these small +errors to their respective causes, and so ascertaining the laws to +which they were subject. + + [3] The second circle was intended for the Cape Observatory, but + Pond obtained leave to retain it. In 1851 it was transferred to the + Observatory of Queen's College, Belfast. + +Pond went further still. He added to the mural circle a simple +instrument, the extreme value of which every astronomer recognizes +to-day--the mercury trough. Not only was the star to be observed by +both circles when the two telescopes were pointing directly to it, +it was also to be observed by reflection; the telescopes were to +be pointed down towards a basin of mercury, in which the image of +the star would be seen reflected. The mercury being a liquid, its +surface is perfectly horizontal; and, since the law of reflection +is that the angle of incidence is equal to the angle of reflection, +it follows that the telescope, when pointed down toward the mercury +trough, points just at as great an angle below the horizon as, when +it is set directly on the star, it points above it. If the circle, +therefore, be carefully read at both settings, half the difference +between the two readings will give the angular elevation of the +star above the horizon. A combination, therefore, of all four +observations, that is to say, one reflection and one direct with +each of the telescopes, would give an exceedingly exact value for +the star's altitude. The conception of this method gives a striking +idea of Pond's thoroughness and skill as a practical observer, and +it is a distinct blot upon Airy's justly high reputation in the same +line that he discontinued the system upon his accession to office. + +However, in 1851, as already mentioned, Airy substituted for the +two separate instruments--the transit and mural circle--the transit +circle, which, unlike the mural circle, is equally supported on both +sides. This, however, does not free it from the liability to some +minute flexure in the direction of its length, from the weight of +its two ends, and the mercury trough is used for the detection of +such bending, should it exist. The present practice is to observe +a star both by reflection and directly in the course of the same +transit. The observer sets the telescope carefully before ever the +star comes into the field of view, and reads his seven microscopes. +Then he climbs up a narrow wooden staircase and watches the star +transit nearly half across the field. Then comes a rush, the +observer swings himself down the ladder, unclamps the telescope, +turns it rapidly up to the star itself, clamps it again, flings +himself on his back on a bench below the telescope, and does it so +quickly that he is able to observe the star across the second half +of the field. There is no time for dawdling, no room for making any +mistakes; the stars never forgive; 'they haste not, they rest not;' +and if the unfortunate observer is too slow, or makes some slip in +his second setting, the star, cold and inexorable, takes no pity, +and moves regardless on. + +It will be seen that a considerable amount of work is involved +in taking a single observation of a star-place. But in making a +star-catalogue it is always deemed necessary to obtain at least +three observations of each star; and many are observed much more +frequently. + +A modern star-catalogue contains, like Ptolemy's, four columns. It +contains also several more. Of these the principal are devoted to +the effect of precession. As precession is caused by a movement +of the earth's axis making the pole of the sky seem to describe a +circle in the heavens, it follows that the celestial poles, and the +celestial equator with them are slowly, but continually, changing +their place with respect to the stars, and therefore that the +declinations of the stars are always undergoing change, and as the +equator changes, the point where the sun crosses it in spring--the +first point of Aries--changes also, and with it the stars' right +ascensions. + +To make one determination of a star's place comparable with +another made at another time, it is clear that we must correct for +the effects of precession in the interval of time between the two +observations, and for the effects of refraction. But observations +made with the transit circle must also be corrected for errors +in the instrument itself. The astronomer will see to it that his +instrument is made and is set up as perfectly as possible. The +pivots on which it turns must be exactly on the same level; they +must point exactly east and west, and the axis of the telescope +must be exactly at right angles to the line joining the pivots +in all positions of the instrument. These conditions are very +nearly fulfilled, but never absolutely. Day by day, therefore, the +astronomer has to ascertain just how much his instrument is in error +in each of these three matters. Were his instrument absolutely +without error to-day, he could not assume that it would remain so, +nor, if he had measured the amount of its errors yesterday, would it +be safe to assume that those errors would not change to-day. + +In the examination of these sources of error the mercury trough +comes again into use. The transit circle is turned directly +downwards, and the mercury trough brought below it. A light is +so arranged as to illuminate the field of the telescope, and the +observer, looking in, sees the ten transit wires and the one +declination wire, and also sees their images reflected from the +surface of the mercury. If the telescope be pointing _exactly_ +down towards the surface of the mercury, then the image of the +declination wire will fall exactly on the declination wire +itself, and by reading the circle we can tell where the zenith +point of the circle is. Similarly, if the pivots of the telescope +are precisely on the same level, the centre wire of the right +ascension series would coincide with its reflected image. A third +point is determined by looking through the eye-piece of the north +collimator telescope--that is to say, the telescope mounted in a +horizontal position at the north end of the room--at the spider +lines in the focus of the south collimator. In order to get this +view, the transit telescope has either to be lifted up out of its +usual position, or else the middle of the tube has to be opened. +The spider lines in the north collimator are then made to coincide +with the image of the wires of the south collimator. The transit +telescope is then turned first to one collimator, then to the other, +and the central wire of the right ascension series is turned till it +coincides with the wire of the collimator; the amount by which it +has to be moved giving an index of the error of collimation; that is +to say, of the deviation of the optical axis of the telescope from +perpendicularity to the line joining the pivots. + +I have said enough to show that the making of an observation is +a small matter as compared with those corrections which have to +be made to it afterwards, before it is available for use. But I +have only mentioned some of the reductions and corrections which +have to be made. There are several more, and it is a just pride of +Greenwich that her third ruler, Bradley, as has been already told +in the notice of his life, discovered two of the most important. +The one, aberration, is due to the fact that light, though it moves +so swiftly--186,000 miles per second--yet does not move with an +infinitely greater velocity than that of the earth. The other, +nutation, might be called a correction to precession, inasmuch as, +moved by the moon's attraction, the earth's axis does not swing +round smoothly, but with a slight nodding or staggering motion. + +But when these observations of the places of a star have been made, +and have been properly 'reduced,' even then we do not find an +exact correspondence between two different determinations. Little +differences still remain. Some of these are to be accounted for by +changes in the actual crust of the earth, which, solid and stable as +we think it, is yet always in motion. Professor Milne, our greatest +authority on earth movements, says, 'The earth is so elastic that +a comparatively small impetus will set it vibrating; why, even two +hills tip together when there is a heavy load of moisture in the +valley between them. And then, when the moisture evaporates in a +hot sun, they tip away from each other.' So there is a perceptible +rocking to and fro even of the huge stone piers of a transit +circle, as seasons of rain and drought, heat and cold, follow each +other. More than that, the earth is so sensitive to pressure that +it was found, at the Oxford University Observatory, that there was +a distinct swaying shown by a horizontal pendulum when the whole +of a party of seventy-six undergraduates stood on one side of the +instrument and close up to it, from the position it had when the +party stood ninety feet away. More wonderful still, a comparison of +the star-places, obtained at a number of observatories, including +Greenwich, has shown that the earth is continually changing her axis +of rotation. And so the star-places determined at Greenwich have +shown that the north pole of the earth, 2600 miles away, moves about +in an irregular curve about thirty feet in radius. + +Nothing is stable, nothing is immovable, nothing is constant. The +astronomer even finds that his own presence near the instrument is +sufficient to disturb it. + +The great interest attaching to transit-circle work is this +striving after ever greater and greater precision, with the result +of bringing out fresh little discordances, which, at first sight, +appear purely accidental, but which, under further scrutiny, show +themselves to be subject to some law. Then comes the hunt for this +new unknown law. Its discovery follows. It explains much, but when +it is allowed for, though the observations now come much closer +together, little deviations still remain, to form the subject of a +fresh inquiry. Astronomy has well been called the exact science, and +yet exactitude ever eludes its pursuer. + +If it be asked, 'What is the use of this ever-increasing refinement +of observation?' no better answer can be given than the words of +Sir John Herschel in one of his Presidential addresses to the Royal +Astronomical Society:-- + + '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, _cui 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.' + +But for these strictly utilitarian purposes a comparatively small +number of stars would meet our every requisite. In the narrow sense +of which Sir John Herschel is here speaking, we have no use for +anything beyond the smallest of catalogues; and if the question +before us is, 'Why are we continually extending our catalogues?' the +following words of a more recent writer[4] on the subject will set +forth the real explanation:-- + + 'A word in conclusion, suggested by the history of + star-catalogues. We have no difficulty in understanding that it + is necessary to study the planets, and a reasonable number of + the brighter stars, for the purpose of determining the figure + of the earth, and the positions of points upon its surface; but + the use for a catalogue of ten thousand stars, such as La Caille + compiled, is not just so apparent. Nay, what did Ptolemy want + with a thousand stars, or Tamerlane's grandson, born, reared, + and destined to die amidst a horde of savages, however splendid + in their trappings? There is not, and there never was, any + real, practical use for the great volumes of star-catalogues + that weigh down the shelves of our libraries. The navigator + and explorer need never see them at all. Why, then, were these + pages compiled? Why have astronomers, from Hipparchus's time + to the present, spent their lives in the weary routine-work of + observing the places of tiny points in the stellar depths? Does + it not seem that there is something in the mind of man that + impels him to seek after knowledge--truly--for its own sake? + something heaven-born, heaven-nurtured, God-given ... that there + is something in man common to him and his Creator, and therefore + eternal ... in beautiful accord with the plain statement that + "God made man in His own image?"' + + [4] Mr. Thomas Lindsay, _Transactions of the Astronomical and + Physical Society of Toronto_, 1899, p. 17. + + + + +CHAPTER VIII + +THE ALTAZIMUTH DEPARTMENT + + +The determining of the places of the fixed stars which Flamsteed +carried out so efficiently in his _British Catalogue of Stars_--the +first 'Census of the Sky' made with the aid of a telescope--was but +half of the work imposed upon him. The other half, equally necessary +for the solution of the problem of the longitude at sea, was the +'Rectifying the Tables of the Motions of the Heavens.' + +This second duty was not less necessary than the other, for, if we +may again use the old simile of the clock-face, the fixed stars +may be taken to represent the figures on the vast dial of the sky, +whilst the moon, as it moves amongst them, corresponds to the moving +hand of the timepiece. To know the places of the stars, then, +without being able to predict the place of the moon, would be much +like having a clock without its hands. But if not less necessary, +it was certainly more difficult. The secret of the movements of the +moon and planets had not then been grasped, and the only tables +which had been calculated were based upon observations made before +the days of telescopes. + +It is one of the most fortunate and remarkable coincidences in the +whole history of science, that at the very time that Greenwich +Observatory was being called into existence, the greatest of +all astronomers was working out his demonstration of the great +fundamental law of the material universe--the law that every +particle of matter attracts every other particle with a force which +varies directly with the mass and inversely with the square of the +distance. + +Several other of the great minds of that time, in particular +Dr. Hooke, the Gresham Professor of Astronomy, had seen that +it was possible that some such law might supply the secret of +planetary motion; but it is one thing to make a suggestion, and +a very different matter indeed to be able to demonstrate it; and +the latter was in Newton's power alone. He did much more than +demonstrate it--he brought out a whole series of most important and +far-reaching consequences. He showed that the ebb and flow of the +tides was due to the attraction of both sun and moon, especially +the latter, upon the waters of our oceans. He pointed out certain +irregularities which must take place in the motion of our moon, due +to the influence of the sun upon it. He showed, too, what was the +cause of that swinging of the axis of the earth which gives rise to +precession. He deduced the relative weights of the earth, the sun, +and of Jupiter and Saturn, the planets with satellites. He proved +also that comets, which had seemed hitherto to men as perfectly +lawless wanderers, obeyed in their orbits the self-same law which +governed the moon and planets. The whole vast system of celestial +movements, which had long seemed to men irregular and uncontrolled, +now fell, every one of them, into its place, as but the necessary +manifestations of one grand, simple order. + +This great discovery gave a new and additional importance to the +regular observation of the moon and planets. They were needed now, +not only to assist in the practical work of navigation, but for +the development of questions of pure science. Halley, the second +Astronomer Royal, and Maskelyne, the fifth, devoted themselves +chiefly to this department of work, to the partial neglect of the +observation of the places of stars. Airy, the seventh, whilst making +catalogue-work a part of the regular routine of the Observatory, +developed the observation of the members of the solar system, and +especially of the moon, in a most marked degree, and collected and +completely reduced the vast mass of material which the industry of +his predecessors had gathered. It is pre-eminently of the work of +Airy that the memorable words quoted before of Professor Newcomb, +the great American mathematician and astronomer, are applicable: +'that if this branch of astronomy were entirely lost, it could be +reconstructed from the Greenwich observations alone.' + +A most important step taken by Airy was the construction of an +altazimuth. An altazimuth is practically a theodolite on a large +scale. Its purpose is to determine, not the declination and right +ascension of some celestial body, as is the case with the transit +circle, but its altitude, _i.e._ its height above the horizon, and +its azimuth, _i.e._ the angle measured on the horizontal plane from +the north point. The altazimuth, then, like the transit circle, +consists of a telescope revolving on a horizontal axis, but, unlike +the transit circle, both the telescope and the piers which carry its +pivots can be rotated so as to point not merely due north and south, +but in any direction whatsoever. + +[Illustration: AIRY'S ALTAZIMUTH.] + +The observations with the altazimuth are rather more complicated +than those with the transit circle. Looking in the telescope, the +observer sees a double set of spider threads or 'wires'; and when a +star or other heavenly body enters the field, it will generally be +observed to move obliquely across both sets of wires. The observer +usually determines to make an observation either in altitude or +azimuth. In the former case he presses the little contact button, +which, as in the transit circle, is provided close to the eyepiece, +as the star reaches each of the horizontal wires in succession. If +in azimuth, it is the times of crossing the vertical wires that are +in like manner telegraphed to the chronograph. The transit over, +the appropriate circle is read; for the telescope itself is rigidly +attached to a vertical wheel having a carefully engraved circle on +its face and read by four microscopes, whilst the entire instrument +carries another set of microscopes, pointing to a fixed horizontal +circle, and upon which the azimuth can be read. A complete +observation involves four such transits and sets of circle readings, +two of altitude, and two of azimuth; for after one of altitude +and one of azimuth the telescope is turned round, and a second +observation is taken in each element. + +The observation gives us the altitude and azimuth of the star. These +particulars are of no direct value to us. But it is a mere matter +of computation, though a long and laborious one, to convert these +elements into right ascension and declination. + +The usefulness of the altazimuth will be seen at once. It will be +remembered that with the transit circle any particular object can +only be observed as it crosses the meridian. If the weather should +be cloudy, or the observer late, the chance of observation is +lost for four and twenty hours, and in the case of the moon, for +which the altazimuth is specially used, it is on the meridian only +in broad daylight during that part of the month which immediately +precedes and follows new moon. At such times it is practically +impossible to observe it with the transit circle; with the +altazimuth it may be caught in the twilight before sunrise or after +sunset; and at other times in the month, if lost on the meridian in +the transit circle, the altazimuth still gives the observer a chance +of catching it any time before it sets. But for this instrument, our +observations of the moon would have been practically impossible over +at least one-fourth of its orbit. + +Airy's altazimuth was but a small instrument of three and +three-quarter inches aperture, mounted in a high tower built on +the site of Flamsteed's mural arc; and, after a life history of +about half a century, has been succeeded by a far more powerful +instrument. The 'New Altazimuth' has an aperture of eight inches, +and is housed in a very solidly constructed building of striking +appearance, the connection of the Observatory with navigation being +suggested by a row of circular lights which strongly recall a ship's +portholes. This building is at the southern end of the narrow +passage, 'the wasp's waist,' which connects the older Observatory +domain with the newer. It is the first building we come to in the +south ground. The computations of the department are carried on in +the south wing of the new Observatory. + +It will be seen from the photograph that the instrument is much +larger, heavier, and less easy to move in azimuth than the old +altazimuth. It is, therefore, not often moved in azimuth, but is set +in some particular direction, not necessarily north and south, in +which it is used practically as a transit circle. + +[Illustration: NEW ALTAZIMUTH BUILDING.] + +There is quite another way of determining the place of the moon, +which is sometimes available, and which offers one of the prettiest +of observations to the astronomer. As the moon travels across the +sky, moving amongst the stars from west to east, it necessarily +passes in front of some of them, and hides them from us for a time. +Such a passage, or 'occultation,' offers two observations: the +'disappearance,' as the moon comes up to the star and covers it; the +'reappearance,' as it leaves it again, and so discloses it. + +[Illustration: THE NEW ALTAZIMUTH. + +(_From a photograph by Mr. Lacey._)] + +Except at the exact time of full moon, we do not see the entire face +of our satellite; one edge or 'limb' is in darkness. As the moon +therefore passes over the star, either the limb at which the star +disappears, or that at which it reappears, is invisible to us. To +watch an occultation at the bright limb is pretty; the moon, with +its shining craters and black hollows, its mountain ranges in bright +relief, like a model in frosted silver, slowly, surely, inevitably +comes nearer and nearer to the little brilliant which it is going to +eclipse. The movement is most regular, most smooth, yet not rapid. +The observer glances at his clock, and marks the minute as the two +heavenly bodies come closer and closer to each other. Then he counts +the clock beats: 'five, six, seven,' it may be, as the star has +been all but reached by the advancing moon. 'Eight,' it is still +clear; ere the beat of the clock rings to the 'nine,' perhaps the +little diamond point has been touched by the wide arch of the moon's +limb, and has gone! Less easy to exactly time is a reappearance at +the bright limb. In this case the observer must ascertain from the +_Nautical Almanac_ precisely where the star will reappear; then +a little before the predicted time he takes his place at the +telescope, watches intently the moon's circumference at the point +indicated, and, listening for the clock-beats, counts the seconds as +they fly. Suddenly, without warning, a pin-point of light flashes +out at the edge of the moon, and at once draws away from it. The +star has 'reappeared.' + +Far more striking is a disappearance or reappearance at the 'dark +limb.' In this case the limb of the moon is absolutely invisible, +and it may be that no part of the moon is visible in the field +of the telescope. In this case the observer sees a star shining +brightly and alone in the middle of the field of his telescope. He +takes the time from his faithful clock, counting beat after beat, +when suddenly the star is gone! So sudden is the disappearance that +the novice feels almost as astonished as if he had received a slap +in the face, and not unfrequently he loses all count or recollection +of the clock beats. The reappearance at the dark limb is quite as +startling; with a bright star it is almost as if a shell had burst +in his very face, and it would require no very great imagination to +make him think that he had heard the explosion. One moment nothing +was visible; now a great star is shining down serenely on the +watcher. A little practice soon enables the observer to accustom +himself to these effects, and an old hand finds no more difficulty +in observing an occultation of any kind than in taking a transit. + +Such an observation is useful for more purposes than one. If the +position of the star occulted is known--and it can be determined at +leisure afterwards--we necessarily know where the limb of the moon +was at the time of the observation. Then the time which the moon +took to pass over the star enables us to calculate the diameter of +our satellite; the different positions of the moon relative to the +star, as seen from different observatories, enable us to calculate +its distance. + +But if the disappearance takes place at the bright limb, the +reappearance usually takes place at the dark, and _vice versâ_; +and the two observations are not quite comparable. There is one +occasion, however, when both observations are made under similar +circumstances, namely, at the full. And if the moon happens also +to be totally eclipsed, the occultations of quite faint stars can +be successfully observed, much fainter than can ordinarily be +seen close up to the moon. Total eclipses of the moon, therefore, +have recently come to be looked upon as important events for the +astronomer, and observatories the world over usually co-operate in +watching them. October 4, 1884, was the first occasion when such an +organised observation was made; there have been several since, and +on these nights every available telescope and observer at Greenwich +is called into action. + +It may be asked why these different modes of observing the moon +are still kept up, year in and year out. 'Do we not know the +moon's orbit sufficiently well, especially since the discovery of +gravitation?' No; we do not. This simple and beautiful law--simple +enough in itself, gives rise to the most amazing complexity of +calculation. If the earth and moon were the only two bodies in the +universe, the problem would be a simple one. But the earth, sun, +and moon are members of a triple system, each of which is always +acting on both of the others. More, the planets, too, have an +appreciable influence, and the net result is a problem so intricate +that our very greatest mathematicians have not thoroughly worked it +out. Our calculations of the moon's motions need, therefore, to be +continually compared with observation, need even to be continually +corrected by it. + +There is a further reason for this continual observation, not only +in the case of the sun, which is our great standard star, since +from it we derive the right ascensions of the stars, and it is also +our great timekeeper; not only in that of the moon, but also in the +case of the planets. Their places as computed need continually to +be compared with their places as observed, and the discordances, +if any, inquired into. The great triumph which resulted to science +from following this course--to pure science, since Uranus is too +faint a planet to be any help to the sailor in navigation--is well +known. The observed movements of Uranus proved not to be in accord +with computation, and from the discordances between calculation and +observation Adams and Leverrier were able to predicate the existence +of a hitherto unseen planet beyond-- + + 'To see it, as Columbus saw America from Spain. Its movements + were felt by them trembling along the far-reaching line of their + analysis, with a certainty hardly inferior to that of ocular + demonstration.'[5] + + [5] From Sir John Herschel's address to the British Association, + September 10, 1846, thirteen days before Galle's first observation + of the planet. + +The discovery of Neptune was not made at Greenwich, and Airy has +been often and bitterly attacked because he did not start on the +search for the predicted planet the moment Adams addressed his +first communication to him, and so allowed the French astronomer +to engross so much of the honour of the exploit. The controversy +has been argued over and over again, and we may be content to leave +it alone here. There is one point, however, which is hardly ever +mentioned, which must have had much effect in determining Airy's +conduct. In 1845, the year in which Adams sent his provisional +elements of the unseen disturbing planet to Airy, the largest +telescope available for the search at Greenwich was an equatorial of +only six and three-quarter inches aperture, provided with small and +insufficient circles for determining positions, and housed in a very +small and inconvenient dome; whilst at Cambridge, within a mile or +so of Adams' own college, was the 'Northumberland' equatorial, of +nearly twelve inches aperture, under the charge of the University +Professor of Astronomy, Professor Challis, and which was then much +the largest, best mounted and housed equatorial in the entire +country. The 'Northumberland' had been begun from Airy's designs and +under his own superintendence, when he was Professor of Astronomy at +Cambridge. Naturally, then, knowing how much superior the Cambridge +telescope was to any which he had under his care, he thought the +search should be made with it. He had no reason to believe that his +own instrument was competent for the work. + +[Illustration: THE NEW OBSERVATORY AS SEEN FROM FLAMSTEED'S +OBSERVATORY.] + +On the other hand, it is hard for the ordinary man to understand +how it was that Adams not only left unnoticed and unanswered for +three-quarters of a year, an inquiry of Airy's with respect to his +calculations, but also never took the trouble to visit Challis, +whom he knew well, and who was so near at hand, to stir him up +to the search. But, in truth, the whole interest of the matter +for Adams rested in the mathematical problem. The irregularities +in the motion of Uranus were interesting to him simply for the +splendid opportunity which they gave him for their analysis. A +purely imaginary case would have served his purpose nearly as well. +The actuality of the planet which he predicted was of very little +moment; the _éclat_ and popular reputation of the discovery was less +than nothing; the problem itself and the mental exercise in its +solution, were what he prized. + +But it was not creditable to the nation that the Royal Observatory +should have been so ill-provided with powerful telescopes; and a +few years later Airy obtained the sanction of the Government for +the erection of an equatorial larger than the 'Northumberland,' +but on the same general plan and in a much more ample dome. This +was for thirty-four years the 'Great' or 'South-East' equatorial, +and the mounting still remains and bears the old name, though the +original telescope has been removed elsewhere. The object-glass had +an aperture of twelve and three-quarter inches and a focal length of +eighteen feet, and was made by Merz of Munich, the engineering work +by Ransomes and Sims of Ipswich, and the graduations and general +optical work by Simms, now of Charlton, Kent. The mounting was so +massive and stable that the present Astronomer Royal has found it +quite practicable and safe to place upon it a telescope (with its +counterpoises) of many times the weight, one made by Sir Howard +Grubb, of Dublin, of twenty-eight inches aperture and twenty-eight +feet focal length, the largest refractor in the British Empire, +though surpassed by several American and Continental instruments. + +The stability of the mounting was intended to render the telescope +suitable for a special work. This was the observation of 'minor +planets.' On the first day of the present century the first of these +little bodies was discovered by Piazzi at Palermo. Three more were +discovered at no great interval afterwards, and then there was an +interval of thirty-eight years without any addition to their number. +But from December 8, 1845, up to the present time, the work of +picking up fresh individuals of these 'pocket planets' has gone on +without interruption, until now more than 400 are known. Most of +these are of no interest to us, but a few come sufficiently near to +the earth for their distance to be very accurately determined; and +when the distance of one member of the solar system is determined, +those of all the others can be calculated from the relations which +the law of gravitation reveals to us. It is a matter of importance, +therefore, to continue the work of discovery, since we may at any +time come across an interesting or useful member of the family; and +that we may be able to distinguish between minor planets already +discovered and new ones, their orbits must be determined as they +are discovered, and some sort of watch kept on their movements. + +A striking example of the scientific prizes which we may light upon +in the process of the rather dreary and most laborious work which +the minor planets cause, has been recently supplied by the discovery +of Eros. On August 13, 1898, Herr Witt, of the Urania Observatory, +Berlin, discovered a very small planet that was moving much faster +in the sky than is common with these small bodies. The great +majority are very much farther from the sun than the planet Mars, +many of them twice as far, and hence, since the time of a planet's +revolution round the sun increases, in accordance with Kepler's law, +more rapidly than does its distance, it follows that they move much +more slowly than Mars. But this new object was moving at almost the +same speed as Mars; it must, therefore, be most unusually near to +us. Further observations soon proved that this was the case, and +Eros, as the little stranger has been called, comes nearer to us +than any other body of which we are aware except the moon. Venus +when in transit is 24-1/2 millions of miles from us, Mars at its +nearest is 34-1/2 millions, Eros at its nearest approach is but +little over 13 millions. + +The use of such a body to us is, of course, quite apart from any +purpose of navigation, except very indirectly. But it promises to +be of the greatest value in the solution of a question in which +astronomers must always feel an interest, the determination of +the distance of the earth from the sun. We know the _relative_ +distances of the different planets, and, consequently if we could +determine the absolute distance of any one, we should know the +distances of all. As it is practically impossible to measure our +distance from the sun directly, several attempts have been made +to determine the distances of Venus, Mars, or such of the minor +planets as come the nearest to us. Three of these in particular, the +little planets Iris, Victoria, and Sappho, have given us the most +accurate determinations of the sun's distance (92,874,000 miles) +which we have yet obtained; but Eros at its nearest approach will +be six times as near to us as either of the three mentioned above, +and therefore should give us a value with only one-sixth of the +uncertainty attaching to that just mentioned. + +The discovery of minor planets has lain outside the scope of +Greenwich work, but their observation has formed an integral part of +it. The general public is apt to lay stress rather on the first than +on the second, and to think it rather a reproach to Greenwich that +it has taken no part in such explorations. Experience has, however, +shown that they may be safely left to amateur activity, whilst the +monotonous drudgery of the observation of minor planets can only be +properly carried out in a permanent institution. + +The observation of these minute bodies with the transit circle +and altazimuth is attended with some difficulties; but precise +observations of various objects may be made with an equatorial; +indeed, comets are usually observed by its means. + +The most ordinary way of observing a comet with an equatorial is as +follows: Two bars are placed in the eye-piece of the telescope, at +right angles to each other, and at an angle of forty-five degrees +to the direction of the apparent daily motion of the stars. The +telescope is turned to the neighbourhood of the comet, and moved +about until it is detected. The telescope is then put a little in +front of the comet, and very firmly fixed. The observer soon sees +the comet entering his field, and by pressing the contact button he +telegraphs to the chronograph the time when the comet is exactly +bisected by each of the bars successively. He then waits until a +bright star, or it may be two or three, have entered the telescope +and been observed in like manner. The telescope is then unclamped, +and moved forward until it is again ahead of the comet, and the +observations are repeated; and this is done as often as is thought +desirable. The places of the stars have, of course, to be found out +from catalogues, or have to be observed with the transit circle, but +when they are known the position of the comet or minor planet can +easily be inferred. + +Next to the glory of having been the means of bringing about the +publication of Newton's _Principia_, the greatest achievement of +Halley, the second Astronomer Royal, was that he was the first to +predict the return of a comet. Newton had shown that comets were +no lawless wanderers, but were as obedient to gravitation as were +the planets themselves, and he also showed how the orbit of a comet +could be determined from observations on three different dates. +Following these principles, Halley computed the orbits of no fewer +than twenty-four comets, and found that three of them, visible at +intervals of about seventy-five years, pursued practically the same +path. He concluded, therefore, that these were really different +appearances of the same object, and, searching old records, he +found reason to believe that it had been observed frequently +earlier still. It seems, in fact, to have been the comet which is +recorded to have been seen in 1066 in England at the time of the +Norman invasion; in A.D. 66, shortly before the commencement of +that war which ended in the destruction of Jerusalem by Titus; +and earlier still, so far back as B.C. 12. Halley, however, +experienced a difficulty in his investigation. The period of the +comet's revolution was not always the same. This, he concluded, +must be due to the attraction of the planets near which the comet +might chance to travel. In the summer of 1681 it had passed very +close to Jupiter, for instance, and in consequence he expected +that instead of returning in August 1757, seventy-five years after +its last appearance, it would not return until the end of 1758 or +the beginning of 1759. It has returned twice since Halley's day, +a triumphant verification of the law of gravitation; and we are +looking for it now for a third return some ten years hence, in 1910. + +Halley's comet, therefore, is an integral member of our solar +system, as much so as the earth or Neptune, though it is utterly +unlike them in appearance and constitution, and though its path is +so utterly unlike theirs that it approaches the sun nearer than our +earth, and recedes farther than Neptune. But there are other comets, +which are not permanent members of our system, but only passing +visitors. From the unfathomed depths of space they come, to those +depths they go. They obey the law of gravitation so far as our sight +can follow them, but what happens to them beyond? Do they come under +some other law, or, perchance, in outermost space is there still a +region reserved to primeval Chaos, the 'Anarch old,' where no law +at all prevails? Gravitation is the bond of the solar system; is it +also the bond of the Universe? + + + + +CHAPTER IX + +THE MAGNETIC AND METEOROLOGICAL DEPARTMENTS + + +Passing out of the south door of the new altazimuth building, we +come to a white cruciform erection, constructed entirely of wood. +This is the Magnet House or Magnetic Observatory, the home of a +double Department, the Magnetic and Meteorological. + +This department does not, indeed, lie within the original purpose +of the Observatory as that was defined in the warrant given to +Flamsteed, and yet is so intimately connected with it, through its +bearing on navigation, that there can be no question as to its +suitability at Greenwich. Indeed, its creation is a striking example +of the thorough grasp which Airy had upon the essential principles +which should govern the great national observatory of an essentially +naval race, and of the keen insight with which he watched the new +development of science. The Magnetic Observatory, therefore, the +purpose of which was to deal with the observation of the changes in +the force and direction of the earth's magnetism--an inquiry which +the greater delicacy of modern compasses, and, in more recent times, +the use of iron instead of wood in the construction of ships has +rendered imperative--was suggested by Airy on the first possible +occasion after he entered on his office, and was sanctioned in 1837. +The Meteorological Department has a double bearing on the purpose of +the Observatory. On the one side, a knowledge of the temperature and +pressure of the atmosphere is, as we have already seen, necessary +in order to correct astronomical observations for the effect of +refraction. On the other hand, meteorology proper, the study of +the movements of the atmosphere, the elucidation of the laws which +regulate those movements, leading to accurate forecasts of storms, +are of the very first necessity for the safety of our shipping. +It is true that weather forecasts are not issued from Greenwich +Observatory, any more than the _Nautical Almanac_ is now issued from +it; but just as the Observatory furnishes the astronomical data upon +which the Almanac is based, so also it takes its part in furnishing +observations to be used by the Meteorological Office at Westminster +for its daily predictions. + +Those predictions are often made the subject of much cheap ridicule; +but, however far short they may fall of the exact and accurate +predictions which we would like to have, yet they mark an enormous +advance upon the weather-lore of our immediate forefathers. + + 'He that is weather wise + Is seldom other wise,' + +says the proverb, and the saying is not without a shrewd amount of +truth. For perhaps nowhere can we find a more striking combination +of imperfect observation and inconsequent deduction than in the +saws which form the stock-in-trade of the ordinary would-be weather +prophet. How common it is to find men full of the conviction that +the weather must change at the co-called 'changes of the moon,' +forgetful that + + 'If we'd no moon at all-- + And that may seem strange-- + We still should have weather + That's subject to change.' + +They will say, truly enough, no doubt, that they have known the +weather to change at 'new' or 'full,' as the case may be, and they +argue that it, therefore, must always do so. But, in fact, they have +only noted a few chance coincidences, and have let the great number +of discordances pass by unnoticed. + +But observations of this kind seem scientific and respectable +compared with those numerous weather proverbs which are based upon +the mere jingle of a rhyme, as + + 'If the ash is out before the oak, + You may expect a thorough soak'-- + +a proverb which is deftly inverted in some districts by making 'oak' +rhyme to 'choke.' + +Others, again, are based upon a mere childish fancy, as, for +example, when the young moon 'lying on her back' is supposed to bode +a spell of dry weather, because it looks like a cup, and so might be +thought of as able to hold the water. + +During the present reign, however, a very different method of +weather study has come into action, and the foundations of a +true weather wisdom have been laid. These have been based, not +on fancied analogies or old wives' rhymes, or a few forechosen +coincidences, but upon observations carried on for long periods of +time and over wide areas of country, and discussed in their entirety +without selection and bias. Above all, mathematical analysis has +been applied to the motions of the air, and ideas, ever gaining +in precision and exactness, have been formulated of the general +circulation of the atmosphere. + +As compared with its sister science, astronomy, meteorology appears +to be still in a very undeveloped state. There is such a difference +between the power of the astronomer to foretell the precise position +of sun, moon, and planets for years, even for centuries, beforehand, +and the failure of the meteorologist to predict the weather for a +single season ahead, that the impression has been widely spread that +there is yet no true meteorological science at all. It is forgotten +that astronomy offered us, in the movements of the heavenly bodies, +the very simplest and easiest problem of related motion. Yet for how +many thousands of years did men watch the planets, and speculate +concerning their motions, before the labours of Tycho, Kepler, and +Newton culminated in the revelation of their meaning? For countless +generations it was supposed that their movements regulated the +lives, characters, and private fortunes of individual men; just as +quite recently it was fancied that a new moon falling on a Saturday, +or two full moons coming within the same calendar month, brought bad +weather! + +It is still impossible to foresee the course of weather change for +long ahead; but the difference between the modern navigator, surely +and confidently making a 'bee-line' across thousands of miles of +ocean to his destination, and the timid sailor of old, creeping from +point to point of land, is hardly greater than the contrast between +the same two men, the one watching his barometer, the other trusting +in the old wives' rhymes which afforded him his only indication as +to coming storms. + +It is still impossible to foresee the weather change for long ahead, +but in our own and in many other countries, especially the United +States, it has been found possible to predict the weather of the +coming four-and-twenty hours with very considerable exactness, and +often to forecast the coming of a great storm several days ahead. +This is the chief purpose of the two great observatories of the +storm-swept Indian and Chinese seas, Hong Kong and Mauritius; and +the value of the work which they have done in preventing the loss +of ships, and the consequent loss of lives and property, has been +beyond all estimate. + +The Royal Observatory, Greenwich, is a meteorological as well as an +astronomical observatory, but, as remarked above, it does not itself +issue any weather forecasts. Just as the Greenwich observations +of the places of the moon and stars are sent to the _Nautical +Almanac_ Office, for use in the preparation of that ephemeris; just +as the Greenwich determinations of time are used for the issue of +signals to the Post Office, whence they are distributed over the +kingdom, so the Greenwich observations of weather are sent to the +Meteorological Office, there to be combined with similar records +from every part of the British Isles, to form the basis of the +daily forecasts which the latter office publishes. To each of these +three offices, therefore, the Royal Observatory, Greenwich, stands +in the relation of purveyor. It supplies them with the original +observations more or less in reduced and corrected form, without +which they could not carry on most important portions of their work. + +Let it be noted how closely these three several departments, +the _Nautical Almanac_ Office, the Time Department, and the +Meteorological Office, are related to practical navigation. Whatever +questions of pure science--of knowledge, that is, apart from its +useful applications--may arise out of the following up of these +several inquiries, yet the first thought, the first principle of +each, is to render navigation more sure and more safe. + +The first of all meteorological instruments is the barometer, which, +under its two chief forms of mercurial and aneroid, is simply a +means of measuring the pressure exerted by the atmosphere. + +There are two important corrections to which its readings are +subject. The first is for the height of the station above the +level of the sea; the second is for the effect of temperature upon +the mercury in the barometer itself, lengthening the column. To +overcome these, the height of the standard barometer at Greenwich +above sea-level has been most carefully ascertained, and the +heights relative to it of the other barometers of the Observatory, +particularly those in rooms occupied by fundamental telescopes, +have also been determined, whilst the self-recording barometer is +mounted in a basement, where it is almost completely protected from +changes of temperature. + +Next in importance to the barometer as a meteorological instrument +comes the thermometer. The great difficulty in the Observatory +use of the thermometer is to secure a perfectly unexceptionable +exposure, so that the thermometer may be in free and perfect contact +with the air, and yet completely sheltered from any direct ray from +the sun. This is secured in the great thermometer shed at Greenwich +by a double series of 'louvre' boards, on the east, south, and west +sides of the shed, the north side being open. The shed itself is +made a very roomy one, in order to give access to a greater body of +air. + +A most important use of the thermometer is in the measurement +of the amount of moisture in the air. To obtain this, a pair of +thermometers are mounted close together, the bulb of one being +covered by damp muslin, and the other being freely exposed. If +the air is completely saturated with moisture, no evaporation +can take place from the damp muslin, and consequently the two +thermometers will read the same. But if the air be comparatively +dry, more or less evaporation will take place from the wet bulb, +and its temperature will sink to that at which the air would be +fully saturated with the moisture which it already contained. For +the higher the temperature, the greater is its power of containing +moisture. The difference of the reading of the two thermometers is, +therefore, an index of humidity. The greater the difference, the +greater the power of absorbing moisture, or, in other words, the +dryness of the air. The great shed already alluded to is devoted to +these companion thermometers. + +[Illustration: THE SELF-REGISTERING THERMOMETERS.] + +Very closely connected with atmospheric pressure, as shown us by the +barometer, is the study of the direction of winds. If we take a map +of the British Isles and the neighbouring countries, and put down +upon them the barometer readings from a great number of observing +stations, and then join together the different places which show the +same barometric pressure, we shall find that these lines of equal +pressure--technically called 'isobars'--are apt to run much nearer +together in some places than in others. Clearly, where the isobars +are close together it means that in a very short distance of country +we have a great difference of atmospheric pressure. In this case +we are likely to get a very strong wind blowing from the region of +high pressure to the region of low pressure, in order to restore the +balance. + +If, further, we had information from these various observing +stations of the direction in which the wind was blowing, we should +soon perceive other relationships. For instance, if we found that +the barometer read about the same in a line across the country from +east to west, but that it was higher in the north of the islands +than in the south, we should then have a general set of winds from +the east, and a similar relation would hold good if the barometer +were highest in some other quarter; that is, the prevailing wind +will come from a quarter at right angles to the region of highest +barometer, or, as it is expressed in what is known as 'Buys Ballot's +law,' 'stand with your back to the wind, and the barometer will be +lower on your left hand than on your right.' This law holds good for +the northern hemisphere generally, except near to the equator; in +the southern hemisphere the right hand is the side of low barometer. + +The instruments for wind observation are of two classes: vanes +to show its direction, and anemometers to show its speed and its +pressure. These may be regarded as two different modes in which the +strength of the wind manifests itself. Pressure anemometers are +usually of two forms: one in which a heavy plate is allowed to swing +by its upper edge in a position fronting the wind, the amount of its +deviation from the vertical being measured; and the other in which +the plate is supported by springs, the degree of compression of the +springs being the quantity registered in that case. Of the speed +anemometers, the best known form is the 'Robinson,' in which four +hemispherical cups are carried at the extremities of a couple of +cross bars. + +For the mounting of these wind instruments the old original +Observatory, known as the Octagon Room, has proved an excellent +site, with its flat roof surmounted by two turrets in the north-east +and north-west corners, and raised some two hundred feet above +high-water mark. + +[Illustration: THE ANEMOMETER ROOM, NORTH-WEST TURRET.] + +The two chief remaining instruments are those for measuring the +amount of rainfall and of full sunshine. The rain gauge consists +essentially of a funnel to collect the rain, and a graduated glass +to measure it. The sunshine recorder usually consists of a large +glass globe arranged to throw an image of the sun on a piece of +specially prepared paper. This image, as the sun moves in the sky, +moves along the paper, charring it as it moves, and at the end of +the day it is easy to see, from the broken, burnt trace, at what +hours the sun was shining clear, and when it was hidden by cloud. + +An amusing difficulty was encountered in an attempt to set on +foot another inquiry. The Superintendent of the Meteorological +Department at the time wished to have a measure of the rate at which +evaporation took place, and therefore exposed carefully measured +quantities of water in the open air in a shallow vessel. For a few +days the record seemed quite satisfactory. Then the evaporation +showed a sudden increase, and developed in the most erratic +and inexplicable manner, until it was found that some sparrows +had come to the conclusion that the saucer full of water was a +kindly provision for their morning 'tub,' and had made use of it +accordingly. + +A large proportion of the meteorological instruments at +Greenwich and other first-class observatories are arranged to be +self-recording. It was early felt that it was necessary that the +records of the barometer and thermometer should be as nearly as +possible continuous; and at one time, within the memory of members +of the staff still living, it was the duty of the observer to read +a certain set of instruments at regular two-hour intervals during +the whole of the day and night--a work probably the most monotonous, +trying, and distasteful of any that the Observatory had to show. + +The two-hour record was no doubt practically equivalent to a +continuous one, but it entailed a heavy amount of labour. Automatic +registers were, therefore, introduced whenever they were available. +The earliest of these were mechanical, and several still make their +records in this manner. + +On the roof of the Octagon Room we find, beside the two turrets +already referred to, a small wooden cabin built on a platform +several feet above the roof level. This cabin and the north-western +turret contain the wind-registering instruments. Opening the turret +door, we find ourselves in a tiny room which is nearly filled by +a small table. Upon this table lies a graduated sheet of paper in +a metal frame, and as we look at it, we see that a clock set up +close to the table is slowly drawing the paper across it. Three +little pencils rest lightly on the face of the paper at different +points. One of these, and usually the most restless, is connected +with a spindle which comes down into the turret from the roof, and +which is, in fact, the spindle of the wind vane. The gearing is so +contrived that the motion on a pivot of the vane is turned into +motion in a straight line at right angles to the direction in which +the paper is drawn by the clock. A second pencil is connected with +the wind-pressure anemometer. The third pencil indicates the amount +of rain that has fallen since the last setting, the pencil being +moved by a float in the receiver of the rain gauge. + +[Illustration: THE ANEMOMETER TRACE.] + +An objection to all the mechanical methods of continuous +registration is that, however carefully the gearing between the +instrument itself and the pencil is contrived, however lightly +the pencil moves over the paper, yet some friction enters in +and affects the record: this is of no great moment in wind +registration, when we are dealing with so powerful an agent as +the wind, but it becomes a serious matter when the barometer is +considered, since its variations require to be registered with the +greatest minuteness. When photography, therefore, was invented, +meteorologists were very prompt to take advantage of this new ally. +A beam of light passing over the head of the column of mercury in a +thermometer or barometer could easily be made to fall upon a drum +revolving once in the twenty-four hours, and covered with a sheet +of photographic paper. In this case, when the sensitive paper is +developed, we find its upper half blackened, the lower edge of the +blackened part showing an irregular curve according as the mercury +in the thermometer or barometer rose or fell, and admitted less or +more light through the space above it. + +Here we have a very perfect means of registration: the passage of +the light exercises no friction or check on the free motion of the +mercury in the tube, or on the turning of the cylinder covered by +the sensitive paper, whilst it is easy to obtain a time scale on the +register by cutting off the light for an instant--say at each hour. +In this way the wet and dry bulb thermometers in the great shed make +their registers. + +The supply of material to the Meteorological Office is not the only +use of the Greenwich meteorological observations. Two elements of +meteorology, the temperature and the pressure of the atmosphere, +have the very directest bearing upon astronomical work. And this +in two ways. An instrument is sensible to heat and cold, and +undergoes changes of form, size, or scale, which, however absolutely +minute, yet become, with the increased delicacy of modern work, not +merely appreciable, but important. So too with the density of the +atmosphere: the light from a distant star, entering our atmosphere, +suffers refraction; and being thus bent out of its path, the star +appears higher in the heavens than it really is. The amount of this +bending varies with the density of the layers of air through which +the light has to pass. The two great meteorological instruments, the +thermometer and barometer, are therefore astronomical instruments as +well. + +In the arrangements at Greenwich the Magnetic Department is closely +connected with the Meteorological, and it is because the two +departments have been associated together that the building devoted +to both is constructed of wood, not brick, since ordinary bricks are +made of clay which is apt to be more or less ferruginous. Copper +nails have alone been employed in the construction of the buildings. +The fire-grates, coal-scuttles, and fire-irons are all of the same +metal. + +The growth of the Observatory has, however, made it necessary to +set up some of the new telescopes, into the mounting of which much +iron enters, very close to the magnetic building. The present +Astronomer-Royal has therefore erected a Magnetic Pavilion right out +in the park at an ample distance from these disturbing causes. + +The double department is, therefore, the most widely scattered in +the whole Observatory. It is located for computing purposes in the +west wing of the New Observatory; many of its magnetic instruments +are in the old Magnet House, others are across the park in the new +Magnetic Pavilion; the anemometers are on the roof of the Octagon +Room, Flamsteed's original observatory, and the self-registering +thermometers are in the south ground between the old Magnet House +and the New Observatory. + +[Illustration: MAGNETIC PAVILION--EXTERIOR. + +(_From a photograph by Mr. Lacey._)] + +The object of the Magnetic Observatory is to study the movements of +the magnetic needle. The quaintest answer that I ever received in an +examination was in reply to the question, 'What is meant by magnetic +inclination and declination?' The examinee replied: + + 'To make a magnet, you take a needle, and rub it on a lodestone. + If it refuses or _declines_ to become a magnet, that is magnetic + declination; if it is easily made a magnet, or is _inclined_ to + become one, that is magnetic inclination.' + +One greatly regretted that it was necessary to mark the reply +according to its ignorance, and not, as one would have wished, in +proportion to its ingenuity. Magnetic declination, however, as +everybody knows, measures the deviation of the 'needle' from the +true geographical north and south direction; the inclination or dip +is the angle which a 'needle' makes with the horizon. + +At one time the only method of watching the movements of the +magnetic needles was by direct observation, just precisely as it was +wont to be in the case of the barometer and thermometer. But the +same agent that has been called in to help in their case has enabled +the magnets also to give us a direct and continuous record of their +movements. In principle the arrangement is as follows: A small light +mirror is attached to the magnetic needle, and a beam of light is +arranged to fall upon the mirror, and is reflected away from it to a +drum covered with sensitive paper. If, then, the needle is perfectly +at rest, a spot of light falls on the drum and blackens the paper at +one particular point. The drum is made to revolve by clockwork once +in twenty-four hours, and the black dot is therefore lengthened out +into a straight line encircling the drum. If, however, the needle +moves, then the spot of light travels up or down, as the case may +be. + +Now, if we look at one of these sheets of photographic paper after +it has been taken from the drum, we shall see that the north pole of +the magnet has moved a little, a very little, towards the west in +the early part of the day, say from sunrise to 2 p.m., and has swung +backwards from that hour till about 10 p.m., remaining fairly quiet +during the night. The extent of this daily swing is but small, but +it is greater in summer than in winter, and it varies also from year +to year. + +[Illustration: MAGNETIC PAVILION--INTERIOR. + +(_From a photograph by Mr. Lacey._)] + +Besides this daily swing, there occasionally happen what are called +'magnetic storms;' great convulsive twitchings of the needle, as +if some unseen operator were endeavouring, whilst in a state of +intense excitement, to telegraph a message of vast importance, so +rapid and so sharp are the movements of the needle to and fro. These +great storms are felt, so far as we know, simultaneously over the +whole earth, and the more characteristic begin with a single sharp +twitch of the needle towards the east. + +Besides the movements of the magnetic needle, the intensity of the +currents of electricity which are always passing through the crust +of the earth are also determined at Greenwich; but this work has +been rendered practically useless for the last few years by the +construction of the electric railway from Stockwell to the City. +Since it was opened, the photographic register of earth currents +has shown a broad blurring from the moment of the starting of the +first train in the morning to the stopping of the last train at +night. As an indication of the delicacy of modern instruments, it +may be mentioned that distinct indications of the current from this +railway have been detected as far off as North Walsham, in Norfolk, +a distance of more than a hundred miles. A further illustration of +the delicacy of the magnetic needles was afforded shortly after +the opening of the railway referred to. On one occasion the then +Superintendent of the Magnetic Department visited the Generating +Station at Stockwell, and on his return it was noticed day after day +that the traces from the magnets showed a curious deflection from 9 +a.m. to 3 p.m., the hours of his attendance. This gave rise to some +speculation, as it did not seem possible that the gentleman could +himself have become magnetized. Eventually, the happy accident +of a fine day solved the mystery. That morning the Superintendent +left his umbrella at home, and the magnets were undisturbed. The +secret was out. The umbrella had become a permanent magnet, and its +presence in the lobby of the magnetic house had been sufficient to +influence the needles. + + + + +CHAPTER X + +THE HELIOGRAPHIC DEPARTMENT + + +So far the development of the Observatory had been along the central +line of assistance to navigation. But the Magnetic Department led on +to one which had but a very secondary connection with it. + +A greatly enhanced interest was given to the observations of earth +magnetism, when it was found that the intensity and frequency of +its disturbances were in close accord with changes that were in +progress many millions of miles away. That the surface of the sun +was occasionally diversified by the presence of dark spots, had been +known almost from the first invention of the telescope; but it was +not until the middle of the present century that any connection was +established between these solar changes and the changes which took +place in the magnetism of the earth. Then two observers, the one +interesting himself entirely with the spots on the sun, the other as +wholly devoted to the study of the movements of the magnetic needle, +independently found that the particular phenomenon which each was +watching was one which varied in a more or less regular cycle. And +further, when the cycles were compared, they proved to be the same. +Whatever the secret of the connection, it is now beyond dispute that +as the spots on the sun become more and more numerous, so the daily +swing of the magnetic needle becomes stronger; and, on the other +hand, as the spots diminish, so the magnetic needle moves more and +more feebly. + +This discovery has given a greatly increased significance to the +study of the earth's magnetism. The daily swing, the occasional +'storms,' are seen to be something more than matters of merely local +interest; they have the closest connection with changes going on in +the vast universe beyond; they have an astronomical importance. + +And it was soon felt to be necessary to supplement the Magnetic +Observatory at Greenwich by one devoted to the direct study of the +solar surface; and here again that invaluable servant of modern +science, photography, was ready to lend its help. Just as, by the +means of photography, the magnets recorded their own movements, so +even more directly the sun himself makes register of his changes by +the same agency, and gives us at once his portrait and his autograph. + +This new department was again due to Airy, and in 1873 the 'Kew' +photo-heliograph, which had been designed by De la Rue for this +work, was installed at Greenwich. + +[Illustration: THE DALLMEYER PHOTO-HELIOGRAPH.] + +In order to photograph so bright a body as the sun, it is not in +the least necessary to have a very large telescope. The one in +common use at Greenwich from 1875 to 1897, is only four inches in +aperture and even that is usually diminished by a cap to three +inches, and its focal length is but five feet. This is not very much +larger than what is commonly called a 'student's telescope,' but it +is amply sufficient for its work. + +This 'Dallmeyer' telescope, so called from the name of its maker, +is one of five identical instruments which were made for use +in the observation of the transit of Venus of 1874, and which, +since they are designed for photographing the sun, are called +'photo-heliographs.' + +The image of the sun in the principal focus of this telescope is +about six-tenths of an inch in diameter; but a magnifying lens +is used, so that the photograph actually obtained is about eight +inches. Even with this great enlargement, the light of the sun is +so intense that with the slowest photographic plates that are made +the exposure has to be for only a very small fraction of a second. +This is managed by arranging a very narrow slit in a strip of brass. +The strip is made to run in a groove across the principal focus. +Before the exposure, it is fastened up so as to cut off all light +from entering the camera part of the telescope. When all is ready, +it is released and drawn down very rapidly by a powerful spring, and +the slit, flying across the image of the sun, gives exposure to the +plate for a very minute fraction of a second--in midsummer for less +than a thousandth of a second. + +Two of these photographs are taken every fine day at Greenwich; +occasionally more, if anything specially interesting appears to +be going on. But in our cloudy climate at least one day in three +gives no good opportunity for taking photographs of the sun, +and in the winter time long weeks may pass without a chance. The +present Astronomer-Royal, Mr. Christie, has therefore arranged that +photographs with precisely similar instruments should be taken in +India and in the Mauritius, and these are sent over to Greenwich as +they are required, to fill up the gaps in the Greenwich series. We +have therefore at Greenwich, from one source or another, practically +a daily record of the state of the sun's surface. + +More recently the 'Dallmeyer' photo-heliograph, though still +retained for occasional use, has been superseded generally by the +'Thompson'; a photographic refractor of nine inches aperture, and +nearly nine feet focal length, presented to the Observatory by Sir +Henry Thompson. The image of the sun obtained after enlargement in +the telescope, with this instrument, is seven and a half inches in +diameter. The 'Thompson' is mounted below the great twenty-six-inch +photographic refractor,--also presented to the Observatory by Sir +Henry Thompson,--in the dome which crowns the centre of the New +Observatory. + +A photograph of the sun taken, it has next to be measured, the four +following particulars being determined for each spot: First, its +distance from the centre of the image of the sun; next, the angle +between it and the north point; thirdly, the size of the spot; and +fourthly, the size of the umbra of the spot, that is to say, of +its dark central portion. The size or area of the spot is measured +by placing a thin piece of glass, on which a number of cross-lines +have been ruled one-hundredth of an inch apart, in contact with the +photograph. These cross-lines make up a number of small squares, +each the ten-thousandth (1/10000 in.) part of a square inch in +area. When the photograph and the little engraved glass plate are +nearly in contact, the photograph is examined with a magnifying +glass, and the number of little squares covered by a given spot are +counted. It will give some idea of the vast scale of the sun when +it is stated that a tiny spot, so small that it only just covers +one of these little squares, and which is only one-millionth of the +visible hemisphere of the sun in area, yet covers in actual extent +considerably more than one million of square miles. + +The dark spots are not the only objects on the sun's surface. Here +and there, and especially near the edge of the sun, are bright +marks, generally in long branching lines, so bright as to appear +bright even against the dazzling background of the sun itself. These +are called 'faculæ,' and they, like the spots, have their times of +great abundance and of scarcity, changing on the whole at the same +time as the spots. + +After the solar photographs have been measured, the measures must be +'reduced,' and the positions of the spots as expressed in longitude +and latitude on the sun computed. There is no difficulty in doing +this, for the position of the sun's equator and poles have long been +known approximately, the sun revolving on its axis in a little more +than twenty-five days, and carrying of course the spots and faculæ +round with him. + +There are few studies in astronomy more engrossing than the watch on +the growth and changes of the solar spots. Their strange shapes, +their rapid movements, and striking alterations afford an unfailing +interest. For example, the amazing spectacle is continually being +afforded of a spot, some two, three, or four hundred millions of +square miles in area, moving over the solar surface at a speed +of three hundred miles an hour, whilst other spots in the same +group are remaining stationary. But a higher interest attaches to +the behaviour of the sun as a whole than to the changes of any +particular single spot; and the curious fact has been brought +to light, that not only do the spots increase and diminish in a +regular cycle of about eleven years in length, but they also affect +different regions of the sun at different points of the cycle. +At the time when spots are most numerous and largest, they are +found occupying two broad belts, the one with its centre about 15° +north of the equator, the other about as far south, the equator +itself being very nearly free from them. But as the spots begin to +diminish, so they appear continually in lower and lower latitudes, +until instead of having two zones of spots there is only one, and +this one lies along the equator. By this time the spots have become +both few and small. The next stage is that a very few small spots +are seen from time to time in one hemisphere or the other at a great +distance from the equator, much farther than any were seen at the +time of greatest activity. There are then for a little time three +sun-spot belts, but the equatorial one soon dies out. The two belts +in high latitude, on the other hand, continually increase; but as +they increase, so do they move downwards in latitude, until at +length they are again found in about latitude 15° north or south, +when the spots have attained their greatest development. + +[Illustration: PHOTOGRAPH OF A GROUP OF SUN-SPOTS. + +(_From a photograph taken at the Royal Observatory, Greenwich, +April, 1882, 20 d. 10 h. 6 m._)] + +The clearest connection between the magnetic movements and the +sun-spot changes is seen when we take the mean values of either for +considerable periods of time, as, for instance, year by year. But +occasionally we have much more special instances of this connection. +Some three or four times within the last twenty years an enormous +spot has broken out on the sun, a spot so vast that worlds as great +as our own could lie in it like peas in a breakfast saucer, and in +each case there has been an immediate and a threefold answer from +the earth. One of the most remarkable of these occurred in November, +1882. A great spot was then seen covering an area of more than three +thousand millions of square miles. The weather in London happened +to be somewhat foggy, and the sun loomed, a dull red ball, through +the haze, a ball it was perfectly easy to look at without specially +shading the eyes. So large a spot under such circumstances was quite +visible to the naked eye, and it caught the attention of a great +number of people, many of whom knew nothing about the existence of +spots on the sun. + +This great disturbance, evidently something of the nature of a storm +in the solar atmosphere, stretched over one hundred thousand miles +on the surface of the sun. The disturbance extended farther still, +even to nearly one hundred millions of miles. For simultaneously +with the appearance of the spot the magnetic needles at Greenwich +began to suffer from a strange excitement, an excitement which grew +from day to day until it had passed half-way across the sun's disc. +As the twitchings of the magnetic needle increased in frequency and +violence, other symptoms were noticed throughout the length of the +British Isles. Telegraphic communication was greatly interfered +with. The telegraph lines had other messages to carry more urgent +than those of men. The needles in the telegraph instruments +twitched to and fro. The signal bells on many of the railway lines +were rung, and some of the operators received shocks from their +instruments. Lastly, on November 17, a superb aurora was witnessed, +the culminating feature of which was the appearance, at about six +o'clock in the evening, of a mysterious beam of greenish light, in +shape something like a cigar, and many degrees in length, which rose +in the east and crossed the sky at a pace much quicker than but +nearly as even as that of sun, moon, or stars, till it set in the +west two minutes after its rising. + +So far we have been dealing only with effects. Their causes still +rest hidden from us. There is clearly a connection between the solar +activity as shown by the spots and the agitation of the magnetic +needles. But many great spots find no answer in any magnetic +vibration, and not a few considerable magnetic storms occur when we +can detect no great solar changes to correspond. + +Thus even in the simplest case before us we have still very much +to explain. Two far more difficult problems are still offered us +for solution. What is the cause of these mysterious solar spots? +and have they any traceable connection with the fitful vagaries of +earthly weather? It was early suggested that probably the first +problem might find an answer in the ever-varying combinations and +configurations of the various planets, and that the sun-spots in +their turn might hold the key of our meteorology. Both ideas were +eagerly followed up--not that there was much to support either, +but because they seemed to offer the only possible hope of our +being able to foretell the general current of weather change for +any long period in advance. So far, however, the first idea may be +considered as completely discredited. As to the second, there would +appear to be, in the case of certain great tropical and continental +countries like India, some slight but by no means conclusive +evidence of a connection between the changes in the annual rainfall +and the changes in the spotted surface of the sun. Dr. Meldrum, the +late veteran Director of the great Meteorological Observatory in +Mauritius, has expressed himself as confident that the years of most +spots are the years of most violent cyclones in the Indian Ocean. +But this is about as far as real progress has been made, and it may +be taken as certain that many years more of observation will be +required, and the labours of many skilful investigators, before we +can hope to carry much farther our knowledge as to any connection +between storm and sun. + +A further relation of great interest has come to light within the +last few years. The year 1868 opened a new epoch in the study of +eclipses of the sun. These, perhaps, scarcely lie within the scope +of a book on the Royal Observatory, since Greenwich has seen but +one in all its history. That fell in the year 1715; for the next +it must wait many centuries. Yet, as the late Astronomer Royal +conducted three expeditions to see total eclipses, and as the +present Astronomer Royal has undertaken a like number, and members +of the staff have been sent on other occasions, it may not be deemed +quite a digression to refer to one feature which they have brought +to light. + +When the dark body of the moon has entirely hidden the sun, +we have revealed to us, there and then only, that strange and +beautiful surrounding of the sun which we call the corona. The +earlier observations of the corona seem to reveal it as a body of +the most weird and intricate form, a form which seemed to change +quite lawlessly from one eclipse to another. But latterly it has +been abundantly clear that the forms which it assumes may be +grouped under a few well-defined types. In 1878 the corona was of +a particularly simple and striking character. Two great wings shot +out east and west in the direction of the sun's equator; round +either pole was a cluster of beautiful radiating 'plumes.' It was +then recollected that the corona of 1867 had been of precisely the +same character, both years being years when sun-spots were at their +fewest. The coronæ, on the other hand, seen at times when sun-spots +are more abundant, were of an altogether different character, the +streamers being irregularly distributed all round the sun. Other +types also have been recognized, and it is perfectly apparent +that the corona changes its shape in close accordance with the +eleven-year period. The eclipses of 1889 and 1900, for example, +showed coronæ that bore the very closest resemblance to those of +1878 and 1866, the interval of eleven years bringing a return to the +same form. + +The further problem, therefore, now confronts us: Does the corona +produce the sun-spots, or do the sun-spots produce the corona, or +are both the result of some mysterious magnetic action of the sun, +an action powerful enough on occasion to thrill through and through +this world of ours, ninety-three millions of miles away? + + + + +CHAPTER XI + +THE SPECTROSCOPIC DEPARTMENT + + +Another department was set on foot by Airy at the same time as +the Heliographic Department, and in connection with it; and it is +the department which has the greatest of interest for the general +public. This deals with astronomical physics, or astrophysics, as +it is sometimes more shortly called; the astronomy, that is, which +treats of the constitution and condition of the heavenly bodies, not +with their movements. + +The older astronomy, on the other hand, confined itself to the +movements of the heavens so entirely that Bessel, the man whose +practical genius revolutionized the science of observation, +and whose influence may be traced throughout in Airy's great +reconstitution of Greenwich Observatory, denied that anything but +the study of the celestial movements had a right to the title of +astronomy at all. Hardly more than sixty years ago he wrote: + + 'What astronomy is expected to accomplish is evidently at all + times the same. It may lay down rules by which the movements + of the celestial bodies, as they appear to us upon the earth, + can be computed. All else which we may learn respecting these + bodies, as, for example, their appearance, and the character of + their surfaces, is, indeed, not undeserving of attention, but + possesses no proper astronomical interest. Whether the mountains + of the moon are arranged in this way or in that is no further + an object of interest to astronomers than is a knowledge of the + mountains of the earth to others. Whether Jupiter appears with + dark stripes upon its surface, or is uniformly illuminated, + pertains as little to the inquiries of the astronomer; and its + four moons are interesting to him only for the motions they + have. To learn so perfectly the motions of the celestial bodies + that for any specified time an accurate computation of these can + be given--that was, and is, the problem which astronomy has to + solve.' + +There is a curious irony of progress which seems to delight in +falsifying the predictions of even master minds as to the limits +beyond which it cannot advance. Bessel laid down his dictum as to +the true subjects of astronomical inquiry, Comte declared that +we could never learn what were the elements of which the stars +were composed, at the very time that the first steps were being +taken towards the creation of a research which should begin by +demonstrating the existence in the heavenly bodies of the elements +with which we are familiar on the earth, and should go on to prove +itself a true astronomy, even in Bessel's restricted sense, by +supplying the means for determining motion in a direction which he +would have thought impossible--that is to say, directly to or from +us. + +The years that followed Kirchhoff's application of the spectroscope +to the study of the sun, and his demonstration that sodium and iron +existed in the solar atmosphere, were crowded with a succession +of brilliant discoveries in the same field. Kirchhoff, Bunsen, +Angström, Thalèn, added element after element to the list of those +recognized in the sun. Huggins and Miller carried the same research +into a far more difficult field, and showed us the same elements +in the stars. Rutherfurd and Secchi grouped the stars according to +the types of their spectra, and so laid the foundations of what +may be termed stellar comparative anatomy. Huggins discovered true +gaseous nebulæ, and so revived the nebular theory, which had been +supposed crushed when the great telescope of Lord Rosse appeared to +have resolved several portions of the Orion nebula into separate +stars. The great riddle of 'new stars'--which still remains a +riddle--was at least attacked, and glowing hydrogen was seen to be a +feature in their constitution. Glowing hydrogen, again, was, in the +observation of total eclipses, seen to be a principal constituent +of those surroundings of our own sun which we now call prominences +and chromosphere. Then the method was discovered of observing the +prominences without an eclipse, and they were found to wax and wane +in more or less sympathy with the solar spots. Sun-spots, planets, +comets, meteors, variable stars, all were studied with the new +instrument, and all yielded to it fresh and valuable, and often +unexpected, information. + +[Illustration: THE GREAT NEBULA IN ORION. + +(_From a photograph taken at the Royal Observatory Greenwich, +December 1, 1899, with an exposure of 2-1/4 hours._)] + +In this activity Greenwich Observatory practically took no part. +Airy, ever mindful of the original purpose of the Observatory, and +deeply imbued with views similar to those which we have quoted from +Bessel, considered that the new science lay outside the scope of his +duties, until in Mr., now Sir William, Huggins's skilful hands +the spectroscope showed itself not only as a means for determining +the condition and constitution of the stars, but also their +movements--until, in short, it had shown itself as an astronomical +instrument even within Bessel's narrow definition. + +The principle of this inquiry is as follows: If a source of light +is approaching us very rapidly, then the waves of light coming from +it necessarily appear a little shorter than they really are, or, in +other words, that light appears to be slightly more blue--the blue +waves being shorter than the red--than it really is. A similar thing +with regard to the waves of sound is often noticed in connection +with a railway train. If an express train, the whistle of which is +blowing the whole time, dashes past us at full speed, there is a +perceptible drop in the note of the whistle after it has gone by. +The sound waves as it was coming were a little shortened, and the +whistle therefore appeared to have a sharper note than it had in +reality. And in the same way, when it had gone by, the sound waves +were a little lengthened, making the note of the whistle appear a +very little flatter. + +Such a change of colour in a star could never have been detected +without the spectroscope; but since when light passes through a +prism the shorter waves are refracted more strongly, that is to +say, are more turned out of their course than the longer, the +spectroscope affords us the means of detecting and measuring this +change. Let us suppose that the lines of hydrogen are recognized +in a given star. If we compare the spectrum of this star with the +spectrum of a tube containing hydrogen and through which the +electric spark is passing, we shall be able to see whether any +particular hydrogen line occupies the same place as shown by the two +spectra. If the line from the star is a little to the red of the +line from the tube, the star must be receding from us; if to the +blue, approaching us. The amount of displacement may be measured by +a delicate micrometer, and the rate of motion concluded from it. + +[Illustration: THE HALF-PRISM SPECTROSCOPE ON THE SOUTH-EAST +EQUATORIAL.] + +The principle is clear enough. The actual working out of the +observation was one of very great difficulty. The movements of the +stars towards us, or away from us, are, in general, extremely slow +as compared with the speed of light itself; and hence the apparent +shift in the position of a line is only perceptible when a very +powerful spectroscope is used. This means that the feeble light of +a star has to be spread out into a great length of spectrum, and +a very powerful telescope is necessary. The work of observing the +motions of stars in the line of sight was started at Greenwich in +1875, the 'Great Equatorial' being devoted to it. This telescope, of +12-3/4 inches aperture, was not powerful enough to do much more than +afford a general indication of the direction in which the principal +stars were moving, and to confirm in a general way the inference +which various astronomers had found, from discussing the proper +motions of stars, that the sun and the solar system were moving +towards that part of the heavens where the constellations Hercules +and Lyra are placed. In 1891, therefore, the work was discontinued, +and as already mentioned, the 12-3/4 telescope by Merz was removed +to make room for the present much larger instrument by Sir Howard +Grubb, upon the same mounting. The new telescope being much larger +than the one for which mounting and observing room were originally +built, it was not possible to put the spectroscope in the usual +position, in the same straight line as the great telescope. It was +therefore mounted under it, and parallel to it, and the light of +the star was brought into it after two reflections. The observer +therefore stood with his back to the object and looked down into +the spectroscope. It had, however, become apparent by this time +that this most delicate field of work was one for which photography +possessed several advantages, and as Sir Henry Thompson had made +the munificent gift to the Observatory of a great photographic +equatorial, it was resolved to devote the 28-inch telescope chiefly +to double-star work, and to transfer the spectroscope to the 'New +Building.' + +The 'New Observatory' in the south ground is crowned indeed with +the dome devoted to the great Thompson photographic refractor, but +this is not its chief purpose. Its principal floor contains four +fine rooms which are used as 'computing rooms'--for the office +work, that is to say, of the Observatory. Of these the principal +is in the north wing, where the main entrance is placed, and is +occupied by the Astronomer Royal and the two chief assistants. The +basement contains the libraries and the workshops of the mechanics +and carpenters. The upper floor will eventually be used for the +storage of photographs and manuscripts, and the terrace roofs of +the four wings will be exceedingly convenient for occasional +observations, as, for example, of meteor showers. The central dome, +which rises high above the level of the terraces, is the only room +in the building devoted to telescopic work. As in the New Altazimuth +building, a ring of circular lights just below the coping of the +wall recalls the portholes of a ship, and again reminds us of the +connection of the Observatory with navigation. + +[Illustration: THE WORKSHOP.] + +Here the spectroscope is now placed, but not, as it happens, on +the Thompson refractor. The equatorial mounting in this new dome +is a modification of what is usually called the 'German' form of +mounting--that is to say, there is but one pier to support the +telescope, and the telescope rides on one side of the pier and a +counterpoise balances it on the other The 'Great Equatorial,' on +the other hand, is an example of the English mounting, and has two +piers, one north and the other south, whilst the telescope swings +in a frame between them. In the new dome three telescopes are found +rigidly connected with each other on one side of the pier, the +telescopes being (1) the great Thompson photographic telescope, +double the aperture and double the focal length of the standard +astrographic telescope used for the International Photographic +Survey; (2) the 12-3/4 telescope by Merz, that used to be in the +great South-East dome, but which is now rigidly connected with the +Thompson refractor as a guide telescope; and (3) a photographic +telescope of 9 inches aperture, already described as the 'Thompson' +photo-heliograph, and used for photographing the sun or in eclipse +expeditions. The counterpoise to this collection of instruments is +not a mere mass of lead, but a powerful reflector of 30 inches' +aperture, and it is to this telescope that the spectroscope is now +attached. At the present time, however (August, 1900), regular work +has not been commenced with it. + +[Illustration: THE 30-INCH REFLECTOR WITH THE NEW SPECTROSCOPE +ATTACHED.] + +Beside this attempt to determine the motions of the stars as they +approach us or retreat from us, on rare occasions the spectroscope +has been turned on the planets. As these shine by reflected light, +their spectra are normally the same as that of the sun. Mars +appeared to the writer, as to Huggins and others, to show some +slight indication of the presence of water vapour in its atmosphere. +Jupiter and Saturn show that their atmospheres contain some +absorbing vapour unknown to ours. And Uranus and Neptune, faint and +distant as they are, not only show the same dark band given by the +two nearer planets, but several others. More attractive has been +the examination of the spectra of the brighter comets that have +visited us. The years 1881 and 1882 were especially rich in these. +The two principal comets of 1881 were called after their respective +discoverers, Tebbutt's and Schaeberle's. They were not bright +enough to attract popular attention, though they could be seen with +the naked eye, and both gave clear indications of the presence of +carbon, their spectra closely resembling that of the blue part of a +gas or candle flame. There was nothing particularly novel in these +observations, since comets usually show this carbon spectrum, though +why they should is still a matter for inquiry; but the two comets of +the following year were much more interesting. Both comets came very +near indeed to the sun. The earlier one, called from its discoverer +Comet Wells, as it drew near to the sun, began to grow more and more +yellow, until in the first week of June it looked as full an orange +as even the so-called red planet, Mars. The spectroscope showed the +reason of this at a glance. The comet had been rich in sodium. So +long as it was far from the sun the sodium made no sign, but as it +came close to it the sodium was turned into glowing vapour under the +fierce solar heat. And as the writer saw it in the early dawn of +June 7, the comet itself was a disc of much the same colour as Mars, +whilst its spectrum resembled that of a spirit lamp that has been +plentifully fed with carbonate of soda or common salt. The 'Great +Comet' of the autumn of the same year, and which was so brilliant +an object in the early morning, came yet nearer to the sun, and the +heating process went on further. The sodium lines blazed up as they +had done with Comet Wells, but under the fiercer stress of heat to +which the Great Comet was subjected, the lines of iron also flashed +out, a significant indication of the tremendous temperature to which +it was exposed. + +There are two other departments of spectroscopic work which it was +attempted for a time to carry on as part of the Greenwich routine. +These were the daily mapping of the prominences round the sun, and +the detailed examination of the spectra of sun-spots. Both are +almost necessary complements of the work done in the heliographic +department--that is to say, the work of photographing the appearance +of the sun day by day, and of measuring the positions and areas of +the spots. For the spots afford but one index out of several, of +the changes in the sun's activity. The prominences afford another, +nor can we at the present moment say authoritatively which is the +more significant. Then again, with regard to the spots themselves, +it is not certain that either their extent or their changes of +appearance are the features which it is most important for us to +study. We want, if possible, to get down to the soul of the spot, +to find out what makes one spot differ from another; and here the +spectroscope can help us. Great sun-spots are often connected with +violent agitation of the magnetic needles, and with displays of +auroræ. But they are not always so, and the inquiry, 'What makes +them to differ?' has been made again and again, without as yet +receiving any unmistakable answer. The great spot of November, 1882, +which was connected with so remarkable an aurora and so violent a +magnetic storm, was as singular in its spectrum as in its earthly +effects. The sun was only seen through much fog, and the spectrum +was therefore very faint, but shooting up from almost every part of +its area, except the very darkest, were great masses of intensely +brilliant hydrogen, evidently under great pressure. The sodium +lines were extremely broadened, and on November 20 a broad bright +flame of hydrogen was seen shooting up at an immense speed from one +edge of the nucleus. A similar effect--an outburst of intensely +luminous hydrogen--has often been observed in spots which have +been accompanied by great magnetic storms; and it may even be that +it is this violent eruption of intensely heated gas which has the +directest connection with the magnetic and auroral disturbances here +upon earth. + +This sun-spot work was not carried on for very long, as only one +assistant could be spared for the entire solar work of whatever +character. Yet in that time an interesting discovery was made by the +writer--namely, that in the green part of the spectrum of certain +spots a number of broad diffused lines or narrow bands made their +appearance from time to time, and especially when sun-spots were +increasing in number, or were at their greatest development. + +The prominence work had also to be dropped, partly for the same +reason, but chiefly because the atmospheric conditions at Greenwich +are not suitable for these delicate astrophysical researches. When +the Observatory was founded 'in the golden days' of Charles II., +Greenwich was a little country town far enough removed from the +great capital, and no interference from its smoke and dust had to be +feared or was dreamt of. Now the 'great wen,' as Cobbett called it, +has spread far around and beyond it, and the days when the sky is +sufficiently pure round the sun for successful spectrum work on the +spots or prominences are few indeed. + +Whether in the future it will be thought advisable for the Royal +Observatory to enter into serious competition in inquiries of +this description with the great 'astrophysical' observatories of +the Continent and of America--Potsdam, Meudon, the Lick, and the +Yerkes--we cannot say. That would involve a very considerable +departure from its original programme, and probably also a departure +from its original site. For the conditions at Greenwich tend to +become steadily less favourable for such work, and it would most +probably be found that full efficiency could only be secured by +setting up a branch or branches far from the monster town. + +With the older work it is otherwise. So long as Greenwich Park +and Blackheath are kept--as it is to be hoped they always will +be--sacred from the invasion of the builder; so long as no +new railways burrow their tunnels in the neighbourhood of the +Observatory, so long the fundamental duties laid upon Flamsteed, +'of Rectifying the Tables of the Motions of the Heavens and the +Places of the Fixed Stars,' will be carried out by his successors on +Flamsteed Hill. + + + + +CHAPTER XII + +THE ASTROGRAPHIC DEPARTMENT + + +The two last departments mentioned, the heliographic and +spectroscopic, lie clearly and unmistakably outside the terms of +the original warrant of the Observatory, though the progress of +science has led naturally and inevitably to their being included in +the Greenwich programme. But the Astrographic Department, though +it could no more have been conceived in the days of Charles II. +than the spectroscopic, does come within the terms of the warrant, +and is but an expansion of that work of 'Rectifying the Places of +the Fixed Stars,' which formed part of the programme enjoined upon +Flamsteed, the first Astronomer Royal, at the first foundation of +the Observatory, and which was so diligently carried out by him, the +first Greenwich catalogue, containing about 3000 stars, being due to +his labours. + +[Illustration: 'CHART PLATE' OF THE PLEIADES. + +(_From a photograph taken at the Royal Observatory, Greenwich, with +an exposure of forty minutes._)] + +His immediate successors did much less in this field, though +Bradley's observations were published, long after his death, as a +catalogue of 3222 stars, in some aspects the most important ever +issued. Pond, the sixth Astronomer Royal, restored catalogue-making +to a prominent place in the Greenwich routine, and his precedent +is sedulously followed to-day. But each of these was confined to +about 3000 stars. The necessity has long been felt for a much +ampler census, and Argelander, at the Bonn Observatory, brought +out a catalogue of 324,000 stars north of South declination 2°, a +work which has been completed by Schönfeld, who carried the census +down to South declination 23°, and by the two great astronomers of +Cordoba, South America, Dr. Gould and Dr. Thome, by whom it was +extended to the South Pole. + +These last three catalogues embrace stars of all magnitudes down to +the 9th or 10th; but certain astronomers had endeavoured to go much +lower, and to make charts of limited portions of the sky down to +even the 14th magnitude. + +From the very earliest days that men observed the stars, they +could not help noticing that 'one star differeth from another star +in glory,' and consequently they divided them into six classes, +according to their brightness--classes which are commonly spoken +of now as magnitudes. The ordinary 6th magnitude star is one which +can be clearly seen by average sight on a good night, and it gives +us about one-hundredth the light of an average 1st magnitude star. +Sirius, the brightest of all the fixed stars, is called a 1st +magnitude star, but is really some six or seven times as bright as +the average. It would take, therefore, more than two and a half +million stars of the 14th magnitude to give as much light as Sirius. + +It is evident that so searching a census as to embrace stars of the +14th magnitude would involve a most gigantic chart. But the work +went on in more than one Observatory for a considerable time, until +at last the observers entered on to the region of the Milky Way. +Here the numbers of the stars presented to them were so great as to +baffle all ordinary means of observation. What could be done? + +Just at this time immense interest was caused in the astronomical +world by the appearance of the great comet of 1882. It was watched +and observed and sketched by countless admirers, but more important +still, it was photographed, and some of its photographs, taken at +the Royal Observatory, Cape of Good Hope, showed not only the comet +with marvellous beauty of detail, but also thousands of stars, +and the success of these photographs suggested to her Majesty's +Astronomer at the Cape, Dr. Gill, that in photography we possessed +the means for making a complete sky census even to the 14th +magnitude. + +The project was thought over in all its bearings, and in 1887 +a great conference of astronomers at Paris resolved upon an +international scheme for photographing the entire heavens. The +work was to be divided between eighteen Observatories of different +nationalities. It was to result in a photographic chart extending to +the 14th magnitude, and probably embracing some forty million stars, +and a catalogue made from measures of the photographs down to the +11th magnitude, which would probably include between two and three +million stars. + +[Illustration: THE CONTROL PENDULUM AND THE BASE OF THE THOMPSON +TELESCOPE.] + +The eighteen Observatories all undertook to use instruments of the +same capacity. This was to be a photographic refractor, with an +object-glass of 13 inches aperture and 11 feet focus. At Greenwich +this telescope is mounted equatorially--that is, so as to follow the +stars in their courses--and is mounted on the top of the pier that +once supported Halley's quadrant. The telescope is driven by a most +efficient clock, whose motive power is a heavy weight. The rate of +the weight in falling is regulated by an ingenious governor, which +brings its speed very nearly indeed to that of the star, and any +little irregularities in its motion are corrected by the following +device. A seconds pendulum is mounted in a glass case on the wall +of the Observatory, and a needle at the lower end of the pendulum +passes at each swing through a globule of mercury. On one of the +wheels of the clock are arranged a number of little brass points, +at such intervals apart that the wheel, when going at the proper +rate, takes exactly one second to move through the distance between +any pair. A little spring is arranged above the wheel, so that +these points touch it as they pass. If this occurs exactly as the +pendulum point passes through the mercury nothing happens, but if +the clock is ever so little late or early, the electric current from +the pendulum brings into action a second wheel, which accelerates +or retards the driving of the clock, as the case may be. The total +motion, therefore, is most beautifully even. + +[Illustration: THE ASTROGRAPHIC TELESCOPE. + +(_Reproduced from 'Engineering' by permission._)] + +But even this is not quite sufficient, especially as the plates +for the great chart have to be exposed for at least forty minutes. +Rigidly united with the 13-inch refractor, so that the two look +like the two barrels of a huge double-barrelled gun, is a second +telescope for the use of the observer. In its eyepiece are fixed +two pairs of cross spider lines, commonly called wires, and a +bright star, as near as possible to the centre of the field to be +photographed, is brought to the junction of two wires. Should the +star appear to move away from the wire, the observer has but to +press one of two buttons on a little plate which he carries in his +hand, and which is connected by an electric wire with the driving +clock, to bring it back to its position. + +The photographs taken with this instrument are of two kinds. Those +for the great chart have but a single exposure, but this lasts for +forty minutes. Those for the great catalogue have three exposures on +them, the three images of a star being some 20 seconds of arc apart. +These exposures are of six minutes', three minutes', and twenty +seconds' duration, and the last exposure is given as a test, since, +if stars of the 9th magnitude are visible with an exposure of twenty +seconds, stars of the 11th magnitude should be visible with three +minutes' exposure. + +Thus it will be seen that in three minutes an impression is got of +many scores of stars, whose places it would require many hours to +determine at the transit instrument. But the positions of these +stars on the plate still remain to be measured. For this purpose a +net-work of lines, at right angles to each other, is printed on the +photograph before its development, and, after it has been developed, +washed and dried, the distances of the stars from their nearest +cross-lines are measured in the measuring machine. + +[Illustration: THE DRIVING CLOCK OF THE ASTROGRAPHIC TELESCOPE. + +(_Reproduced from 'Engineering' by permission._)] + +The measuring machine is constructed to hold two plates, one half +its breadth higher than the other. In fact, in each of the two +series of photographs the whole sky is taken twice, but the two +photographs of any region are not simply duplicates of each other. +The centre of each plate is at a corner of four other plates, and +in the micrometer the stars on the quarter common to two plates are +measured simultaneously. + +In this way will be carried out a great census of the sky that will +exceed Flamsteed's ten thousand fold. And just as Flamsteed's was +but the first of many similar catalogues, so, no doubt, will this be +followed by others--not superseded, for its value will increase with +its age and the number of those that follow it, by comparison with +which it will prove an inexhaustible mine of information concerning +the motions of the stars and the structure of the universe. + +There is a great difference between the work of the observer with +the 'Astrographic Telescope,' as this great twin photographic +instrument is called, and the work of the transit observer. The +latter sees the star gliding past him, and telegraphs the instant +that the star threads itself on each of the ten vertical wires in +succession. The astrographic observer, on the other hand, sees his +star shining almost immovably in the centre of his field, threaded +on the two cross wires placed there, for the driving-clock moves +the telescope so as to almost exactly compensate for the rotation +movement of the earth. The observer's duty in this case is to +telegraph to his driving-clock, when it has in the least come short +of or exceeded its duty, and so to bring back the 'guiding star' to +its exact proper place on the cross wires. + +So far, the work of the Astrographic Department has been, as +mentioned above, a development on an extraordinary scale, but a +development still, of the original programme of the Observatory. +But the munificent gift of Sir Henry Thompson has put it within +the power of the Astronomer Royal to push this work of sidereal +photography a stage further. Sir Henry Thompson gave to the +Observatory, not merely the photographic refractor of 9 inches' +aperture, now used for solar photography, and known as the 'Thompson +photo-heliograph,' but also one of 26 inches' aperture and 22-1/2 +feet focal length. This instrument was specially designed of exactly +double the dimensions of the standard astrographic telescope used +for the International Photographic Survey, the idea being that, +in the case of a field of special interest and importance, a +photograph could be obtained with the larger instrument on exactly +double the scale given by the smaller. It has rather, however, +found its usefulness in a slightly different field. The observation +of the satellites of Jupiter was suggested by Galileo as a means +of determining the longitude at sea. As already pointed out, the +suggestion did not prove to be a practical one for that purpose, but +observations of the satellites have been made none the less with +a view simply to improving our knowledge of their movements, and +of the mass of Jupiter. The utilitarian motive for the work having +fallen through, it has been carried on as a matter of pure science. + +And the work has not stopped with the satellites of Jupiter; eight +satellites were in due time discovered to Saturn, four to Uranus, +and two to Mars; and though these could give not the remotest +assistance to navigation, they too have been made the subjects of +observation for precisely the same reason as those of Jupiter have +been. + +[Illustration: THE THOMPSON TELESCOPE IN THE NEW DOME.] + +In just the same way, when the discovery of Neptune was followed by +that of a solitary companion to it, this also had to be followed. +The difficulties in the way of observing the fainter of all these +satellites were considerable, and the work has been mostly confined +to two or three observatories possessing very large telescopes. As +the largest telescope at Greenwich was only 7 inches in aperture up +to 1859, and only 12-3/4 inches up to 1893, it is only very recently +that it has been able to take any very substantial part in satellite +measures. But since the Thompson photographic telescope was set up, +it has been found that a photograph of Neptune and its satellite can +be taken in considerably less time than a complete set of direct +measures can be made, whilst the photograph, which can be measured +at leisure during the day, gives distinctly the more accurate +results. + +So, too, the places of the minor planets can be got more accurately +and quickly by means of photographs with this great telescope than +by direct observation, and photographs of the most interesting +of them all, the little planet Eros, have been very successfully +obtained. So that, though doing nothing directly to improve the +art of navigation, or to find the longitude at sea, the great +photographic refractor takes its share in the work of 'Rectifying +the Tables of the Planets.' + +[Illustration: THE NEBULÆ OF THE PLEIADES. + +(_From a photograph taken at the Royal Observatory, Greenwich, +December 3, 1899, with an exposure of three hours._)] + +The reflector of 30 inches' aperture, which acts as a counterpoise +to the sheaf of telescopes of the Thompson, is intended for use with +the spectroscope, the quality which mirrors possess of bringing +all rays, whatever their colour, to the same focus being of great +importance for spectroscopic work. But the experiments which have +been made with it in celestial photography have proved so extremely +successful as to cause the postponement of the recommencement of +the spectroscopic researches. Chief amongst these photographs are +some good ones of the moon, and more recently some exceedingly fine +photographs of the principal nebulæ. + +In no department of astronomy has photography brought us such +striking results as in regard to the nebulæ. Dr. Roberts' photograph +of the great nebula in Andromeda converted the two or three +meaningless rifts--which some of the best drawings had shown--into +the divisions between concentric rings; and what had appeared a +mere shapeless cloud was seen to be a vast symmetrical structure, a +great sidereal system in the making. The great nebula in Orion has +grown in successive photographs in detail and extent, until we have +a large part of the constellation bound together in the convolutions +of a single nebula of the most exquisite detail and most amazing +complexity. The group of the Pleiades has had a more wonderful +record still. Manifestly a single system even to the naked eye, +and showing some faint indications of nebulosity in the telescope, +the photographs have revealed its principal stars shining out from +nebulous masses, in appearance like carded wool, and have shown +smaller stars threaded on nebulous lines like pearls upon a string. + +Such photographs are, of course, of no utilitarian value, and at +present they lead us to no definite scientific conclusions. They +lie, therefore, doubly outside the limits of the purely practical, +but they attract us by their extreme beauty, and by the amazing +difficulty of the problems they suggest. How are these weird masses +of gas retained in such complex form over distances which must +be reckoned by millions of millions of miles? By what agency are +they made to glow so as to be visible to us here? What conceivable +condition threads together suns on a line of nebula? What universes +are here in the making, or perhaps it may be falling into ruin and +decay? + + + + +CHAPTER XIII + +THE DOUBLE-STAR DEPARTMENT + + +The foregoing chapters will have shown that though the original +purpose of the Observatory has always been kept in view, yet the +progress of science has caused many researches to be undertaken +which overstep its boundaries. Thus in the present transit room, +beside the successive transit instruments we find upon the wall two +long thin tubes, labelled respectively Alpha Aquilæ and Alpha Cygni. +These were two telescopes set up by Pond for a special purpose. +Dr. Brinkley, Royal Astronomer for Ireland, had announced that he +had found that several stars shifted their apparent place in the +sky in the course of a year, due to the change in the position of +the earth from which we view them, by an amount which would show +that they were only about six to nine billions of miles distant +from us; or, in other words, they showed a parallax of from two to +three seconds of arc. Pond was not able to confirm these parallaxes +from his observations, and to decide the point he set up these two +telescopes, the Alpha Aquilæ telescope being rigidly fixed on the +west side of the pier of Troughton's mural circles; the Alpha Cygni +telescope on another pier, the one which now forms the base of the +pier of the astrographic telescope. Pond's method was to compare +the position of these two stars with that of a star almost exactly +the same distance from the pole, but at a great distance from it in +time of crossing the meridian; in other words, of almost the same +declination, but widely different right ascension. The result proved +that Brinkley was wrong, and vindicated the delicacy and accuracy of +Pond's observations. + +These two telescopes, therefore, had their day and ceased to be. +Others have followed them. An ingenious telescope was set up by +Sir George Airy in order to ascertain if the speed of light were +different when passing through water than when passing through +air. Or, in other words, if the aberration of light would give the +same value as at present if we observed through water. The water +telescope, as it was called, is kept on the ground floor of the +central octagon of the new observatory. The observations obtained +with it were hardly quite satisfactory, but gave on the whole a +negative result. + +Turning back to the transit room, and leaving it by the south-west +door, we come into the little passage which leads at the back of +Bradley's transit room into the lower computing room. Just inside +this passage, on the left-hand side, there is a little room of +a most curious shape, the 'reflex zenith room.' Here is fixed a +telescope pointing straight upwards, the eye-piece being fixed +by the side of the object-glass. The light from a star--the star +Gamma Draconis--which passes exactly over the zenith of Greenwich, +enters the object-glass, passes downwards to a basin of mercury, and +is reflected upwards from the surface of the mercury to a little +prism placed over the centre of the object-glass, from which it +is reflected again into the eye-piece. By means of this telescope +the distance of the star Gamma Draconis from the zenith could +be measured very exactly, and, consequently, the changes in the +apparent position of the star due to aberration, parallax, and other +causes could be very exactly followed, and the corrections to be +applied on account of these causes precisely determined. + +This particular telescope was devised by Airy, and the observations +with it were continued to the end of his reign. The germ of the idea +may be traced back, however, to the time of Flamsteed, who would +seem to have occasionally observed Gamma Draconis from the bottom +of a deep well; the precise position of the well is not, however, +now known. Later, Bradley set up his celebrated 12-1/2-foot zenith +sector, still preserved in the transit room, first at Wanstead +and then at Greenwich, for the determination of the amount of +aberration. Later, a zenith tube by Troughton, of 25 feet focus, was +used by Pond in conjunction with the mural circle for observations +of Gamma Draconis in order to determine the zenith point of the +latter instrument. + +These telescopes for special purposes have passed out of use. +Observations with the spectroscope have been suspended for some +years. The work of the Astrographic Department will come to an end, +in the ordinary course of events, when the programme assigned to +Greenwich in the International Scheme is completed. + +Within the last few years a new department has come into being at +Greenwich--a department which has been steadily worked at many +foreign public observatories, but only recently here. + +This is the Department of Double-Star Observation. The first double +star, Zeta Ursæ Majoris, was discovered 250 years ago. Bradley +discovered two exceedingly famous double stars whilst still a young +man observing with his uncle at Wanstead--Gamma Virginis and Castor. +Bradley made also other discoveries of double stars after his +appointment to Greenwich, and Maskelyne succeeded him in the same +line, but the great foundation of double-star astronomy was laid by +Sir William Herschel. + +At first it was supposed that double stars were double only in +appearance; one star comparatively near us 'happened' to lie in +almost exactly the same direction as another star much further +off. It was, indeed, in the very expectation that this would +prove to be the case, that the elder Herschel first took up their +study. But he was soon convinced that many of the objects were +true double stars--members of the same system of which the smaller +revolved round the larger--not merely apparently double, one star +appearing by chance to be close to another with which it had no +connection--but real double stars. The discovery of these has led to +the establishment of a new department of astronomy, again scientific +rather than utilitarian. + +[Illustration: DOUBLE-STAR OBSERVATION WITH THE SOUTH-EAST +EQUATORIAL. + +(_From a photograph by Mr. Edney._)] + +As mentioned above, it is only recently that Greenwich has +taken any appreciable part in this work. Under Airy, the largest +equatorial of the time had been furnished with a good micrometer, +and observations of one or two double stars been made now and +again; but Airy's programme of work was far too rigid, and kept the +staff too closely engaged for such observations to be anything but +extremely rare. And, indeed, when the micrometers of the equatorials +were brought into use, they were far more generally devoted to the +satellites of Saturn than to the companions of stars. In the main, +double-star astronomy has been in the hands of amateurs, at least +in England. But the discovery in recent years of many pairs so +close that a telescope of the largest size is required for their +successful observation, has put an important section of double stars +beyond the reach of most private observers, and therefore the great +telescope at Greenwich is now mainly devoted to their study. The +Astronomer Royal, therefore, soon after the completion of the great +equatorial of 28-inches aperture placed in the south-east dome, +added this work to the Observatory programme. + +The 28-inch equatorial is a remarkable-looking instrument, its +mounting being of an entirely different kind to that of the other +equatorials in the Observatory, with the solitary exception of the +Shuckburgh, which is set up in a little dome over the chronograph +room. The Shuckburgh was presented to the Observatory in the year +1811, by Sir G. Shuckburgh. It was first intended to be mounted as +an altazimuth, but proved to be unsteady in that position, and was +then converted into an equatorial without clockwork, and mounted in +its present position. The position is about as hopelessly bad a one +as a telescope could well have, completely overshadowed as it is by +the trees and buildings close at hand. The dome is a small one, and +the arrangements for the shutters and for turning the dome are as +bad as they could possibly be. It has practically been useless for +the last forty years. + +Its only interest is that the method of mounting employed is a small +scale model of that of the great telescope in the S.-E. dome. In the +German or Fraunhofer form of mounting for an equatorial there is but +a single pillar, which carries a comparatively short polar axis. At +the upper end of the polar axis we find the declination axis, and +at one end of the declination axis is the telescope, whilst at the +other end is a heavy weight to counterpoise it. The German mounting +has the advantage that the telescope can easily point to the pole +of the heavens; its drawbacks are that, except in certain special +forms, the telescope cannot travel very far when it is on the +same side of the meridian as the star to which it is pointed, the +end of the telescope coming into contact under such circumstances +with the central pier, whilst the introduction of mere deadweight +as the necessary counterpoise, is not economical. It has been +already pointed out that the present Astronomer Royal has not only +considerably modified the German mounting in the great collection of +telescopes in the Thompson dome, but has used a powerful reflector +as a counterpoise to the sheaf of refractors at the other end of the +declination axis. + +The English equatorial requires two piers. Between these two piers +is a long polar axis. Both in the little Shuckburgh and in the +great 28-inch equatorial the frame of the polar axis consists of +six parallel rods disposed in two equilateral triangles, with their +bases parallel to each other, the telescope swinging in the space +between the two bases. The construction of this form of equatorial, +therefore, is expensive, as it requires two piers. It takes much +more room than the German form, and the telescope cannot be directed +precisely to the pole. But the instrument is symmetrical, there is +no deadweight, and the telescope can follow a star from rising to +setting without having to be reversed on crossing the meridian. + +The great stability of the English form of mounting, therefore, +commended it very highly to Airy, and he designed the great +Northumberland equatorial of the Cambridge Observatory on that plan, +as well as one for the Liverpool Observatory at Bidston, and in 1858 +the S.-E. equatorial at Greenwich. + +The telescope at first mounted upon it had an object-glass of 12-3/4 +inches' aperture, and 18 feet focal length. That was dismounted +in 1891, and is now used as the guiding telescope of the Thompson +26-inch photographic refractor. Its place was taken by an immensely +heavier instrument, the present refractor of 28 inches' aperture, +and 28 feet focal length; and that this change was effected safely +was an eloquent testimony to the solidity of the original mounting. + +The clock that drives this great instrument, so that it can follow +a star or other celestial object in its apparent daily motion +across the sky, is in the basement of the S.-E. tower. It is a very +simple looking instrument, a conical pendulum in a glass case. The +pendulum makes a complete revolution once in two seconds. Below +it in a closed case is a water turbine. A cistern on the roof of +the staircase supplies this turbine with water, having a fall of +about thirty feet. The water rushing out of the arms of the turbine +forces it backward, and the turbine spins rapidly round, driving a +spindle which runs up into the dome, and gears through one or two +intermediate wheels with the great circle of the telescope; the +extremely rapid rotation of the spindle, four times in a second, +being converted by these intermediate wheels into the exceedingly +slow one of once in twenty-four hours. Just above the centre of +motion of the turbine is a set of three small wheels, all of exactly +the same size, and of the same number of teeth. Of these the bottom +wheel is horizontal, and is turned by the turbine. The top wheel +is also horizontal, and is turned by the pendulum. The third wheel +gears into both these, and is vertical. If the top and bottom wheels +are moving exactly at the same rate, the intermediate wheel simply +turns on its axis, but does not travel; but if the turbine and +pendulum are moving at different rates, then the vertical wheel is +forced to run in one direction or the other, and, doing so, it opens +or closes a throttle valve, which controls the supply of water to +the turbine, and so speedily brings the turbine into accord with +the pendulum. The control of the motion of the great telescope is +therefore almost as perfect as that of the astrographic and Thompson +equatorials, though the principle employed is very different. And +the control needs to be perfect, for, as said above, the great +telescope is mostly devoted to the observation of double stars, and +there can be no greater hindrance to this work than a telescope +which does not move accurately with the star. + +There is a striking contrast between the great telescope and all the +massive machinery for its direction and movement, and the objects +on which it is directed--two little points of light separated by a +delicate hair of darkness. + +The observation is very unlike those of which we have hitherto +spoken. The object is not to ascertain the actual position in the +sky of the two stars, but their relative position to each other. +A spider's thread of the finest strands is moved from one star to +the other by turning an exquisitely fine screw; this enables us +to measure their distance apart. Another spider thread at right +angles to the first is laid through the centres of both stars, and +a divided circle enables us to read the angle which this line makes +to the true east and west direction. Such observations repeated +year after year on many stars have enabled the orbits of not a few +to be laid down with remarkable precision; and we find that their +movements are completely consistent with the law of gravitation. +Further, just as Neptune was pre-recognized and discovered +from noting the irregularities in the motion of Uranus, so the +discordances in the place of Sirius led to the belief that it was +attracted by a then unseen companion, whose position with respect to +the brighter star was predicted and afterwards seen. + +[Illustration: THE SOUTH-EAST DOME WITH THE SHUTTER OPEN.] + +Gravitation thus appears, indeed, to be the Bond of the Universe, +yet it leaves us with several weighty problems. The observation of +the positions of stars shows that though we call them fixed they +really have motions of their own. Of these motions, a great part +consists of a drift away from one portion of the heavens towards a +point diametrically opposite to it, a drift such as must be due, not +to a true motion of the individual stars, but to a motion through +space of our sun and its attendant system. The elder Herschel was +the first to discover this mysterious solar motion. Sir George Airy +and Mr. Edwin Dunkin, for forty-six years a member of the Greenwich +staff, and from 1881-1884 the Chief Assistant, contributed important +determinations of its direction. + +What is the cause of this motion, what is the law of this motion, +is at present beyond our power to find out. Many years ago a +German astronomer made the random suggestion that possibly we were +revolving in an orbit round the Pleiades as a centre. The suggestion +was entirely baseless, but unfortunately has found its way into many +popular works, and still sometimes is brought forward as if it were +one of the established truths of astronomy. We can at present only +say that this solar motion is a mystery. + +There is a greater mystery still. The stars have their own +individual motions, and in the case of a few these are of the most +amazing swiftness. The earth in its motion round the sun travels +nearly nineteen miles in a second, say one thousand times faster +than the quickest rush of an express train. The sun's rate of motion +is probably not quite so swift, but Arcturus, a sun far larger than +our own, has a pace some twenty times as swift as the orbital motion +of the earth. This is not a motion that we can conceive of as being +brought about by gravitation, for if there were some unseen body so +vast as to draw Arcturus with this swiftness, other stars too would +be hurtling across the sky as quickly. Such 'runaway stars' afford a +problem to which we have as yet no key, and, like Job of old, we are +speechless when the question comes to us from heaven, 'Canst thou +guide Arcturus and his sons?' + +It will be seen then that, fundamentally, Greenwich Observatory was +founded and has been maintained for distinctly practical purposes, +chiefly for the improvement of the eminently practical science +of navigation. Other inquiries relating to navigation, as, for +instance, terrestrial magnetism and meteorology, have been added +since. The pursuit of these objects has of necessity meant that the +Observatory was equipped with powerful and accurate instruments, and +the possession of these again has led to their use in fields which +lay outside the domain of the purely utilitarian, fields from which +the only harvest that could be reaped was that of the increase of +our knowledge. So we have been led step by step from the mere desire +to help the mariner to find his way across the trackless ocean, to +the establishment of the secret law which rules the movements of +every body of the universe, till at length we stand face to face +with the mysteries of vast systems in the making, with the intimate +structure of the stellar universe, with the apparently aimless, +causeless wanderings of vast suns in lightning flight; with problems +that we cannot solve, nor hope to solve, yet cannot cease from +attempting, problems to which the only answer we can give is the +confession of the magicians of Egypt--'This is the finger of God.' + + + + +INDEX + + + Aberration of light, 79 + + Adams, John C., his discovery of Neptune, 217 + + Adhara, 183 + + Airy, George Biddell, seventh Astronomer Royal, his early + life, 102; + his work at Cambridge, 105; + comes to Greenwich, 105; + his relations with the Visitors, 106; + his autobiography, 108; + his character, 111; + his labours, 113; + attacks on, 114; + his distinctions, 118; + his resignation, 119; + his death, 120; + anecdote of, 142; + his conduct _re_ Adams, 217; + his water telescope, 304 + + Alderamin, 183 + + _Almagest_, 185 + + Almanac making, 29 + + Alpha Aquilæ, telescope for, 303 + + ---- Cygni, telescope for, 303 + + Altazimuth the, 114; + description and work of, 207, _et seq._ + + Altazimuth Department, 205, _et seq._ + + American time, 153 + + Andromeda nebula, 301 + + Anemometer, use of, 238; + trace of, 242 + + Angström, 268 + + Anson, Commodore, 17 + + Apparent time, 152 + + Arcturus, motion of, 315 + + Argelander, star catalogue of, 287 + + _Art of Dialling_, the, 28 + + Assistants, position of the, 98, 100, 117, 137 + + Astrographic chart, 128 + + ---- Department, 284, _et seq._ + + ---- dome, 128 + + ---- telescope, 289, _et seq._ + + Astronomers Royal, the, 25 + + Astrophysical researches, 282 + + Auroræ, 281 + + Automatic register, 241 + + Axis of the earth, precession of, 184 + + + Ball, Time, 162 + + Barometer, use of the, 192, 233 + + Battery basement, 161 + + Beaufort, Captain, 107 + + Bessel quoted, 266 + + Betelgeuse, 184 + + Birkenhead, wreck of the, 180 + + Bliss, Nathaniel, fourth Astronomer Royal, history of, 82 + + Bradley, James, third Astronomer Royal, his life, 73; + his ordination, 74; + Vicar of Bridstow, 74; + Savilian Professor of Astronomy, 75; + discovers Aberration of Light, 75, _et seq._; + becomes Astronomer Royal, 79; + labours of, 80; + character of, 81 + + Bradley's transit room, 128 + + Brinkley, Dr., 303 + + _British Mariner's Guide_, the, 90 + + Bunsen, 268 + + Buys Ballot's law, 237 + + + Canadian time, 153 + + Castor, 74, 306 + + Catalogues, star, 182, 185, _et seq._, 198, 284 + + Cepheus, 183 + + Charles II., warrants of, 39, 40 + + Christie, W. H. M., eighth Astronomer Royal, work of, 120 + + Chromosphere of the sun, 268 + + Chronograph, the, 157 + + ---- room, 126 + + Chronometer business, 101, 107 + + Chronometers, Harrison's improvements in, 165, _et seq._; + tests of, 169; + 'runs' of, 173; + romance of, 178 + + Circle Department, 181, _et seq._ + + Clock, Astrographic driving, 290; + driving 28-inch telescope, 312 + + Clocks, standard, 160 + + Columbus, aim of voyage of, 18 + + Comet, appearance of a, 28 + + ---- Wells, 280 + + Comets, observation of, 224; + spectra of, 280 + + Commutator, the, 162 + + Comte, assertion of, 267 + + Constant of Aberration, 79 + + Cook, Captain, work of, 170 + + Copper, use of in Observatory, 245 + + Corona of the sun, 264 + + Crabtree, James, 31 + + Crosthwait, Joseph, 57 + + + Dallmeyer telescope, 252 + + Declination, 186, _et seq._ + + Denebola, 184 + + Distances of planets, 223; + of sun, 224 + + Double-Star Department, 303, _et seq._ + + Double Stars, 306 + + Dublin time, 155 + + Dunkin, Edwin, 315 + + + Earth, the, movements of, 201 + + Eclipses of the moon, 216; + of the sun, July 25, 1748...85; + other eclipses of the sun, 263, _et seq._ + + Electric Railway, influence of, 249 + + Equation of Time, the, 29, 151 + + Equatorial, Shuckburgh's, 101 + + ----, the great 28-inch, 221 + + ----, the Merz, 12-3/4-inch, 114 + + ----, 28-inch, driving clock of, 309; + use of, 313 + + ----, clock-driven, 74 + + Eros, discovery of, 223; + photographs of, 298 + + Errors in observations, noting of, 199, _et seq._ + + Evaporation, 241 + + + Faculæ of the sun, 257 + + Flamsteed, John, his report on Saint-Pierre's proposal, 23, 32; + appointed first Astronomer Royal, 23, 34; + his autobiography, 26; + his studies, 29; + his almanac, 29; + sent to London, 30; + enters Jesus College, Cambridge, 31; + completes his observatory, 31; + acquaintance with Newton, 31; + takes his degree, 32; + his work, 34; + warrant for his salary, 39; + position of, 42; + his ordination, 45; + his pupils, 45; + his trouble with Newton, 46, _et seq._; + his catalogue, 53; + his letter to Sharp, 54; + his death, 56; + his labours, 57 + + Flamsteed House, 126 + + Fraunhofer mounting, 310 + + French time, 155 + + + Galileo, his discovery of Jupiter's satellites, 19 + + Gamma Draconis, 75, 304 + + ---- Virginis, 306 + + Gascoigne, William, 31 + + Gemma Frisius, plan of, 22 + + George of Denmark, Prince, 50 + + German mounting, 276, 310 + + Gould, Dr., 287 + + Graham, 166 + + Gravitation, the bond of the universe, 313 + + Great comet of 1882, the, 280, 288 + + Greatrackes, Valentine, 29 + + Green, Charles, 91 + + Greenwich time, 153; + distribution of, 163 + + + Halley, Edmund, his life, 60; + his early work, 60; + his catalogue of stars, 63; + elected F.R.S., 63; + his work on Kepler's laws, 64; + becomes captain, 65; + Savilian Professor of Geometry, 66; + Astronomer Royal, 66; + observations on saros of the moon, 67; + pressed by Newton, 68; + his death, 68; + his services to science, 68; + his pay, 70; + nominates his successor, 73; + his transit instrument, 73 + + Halley's comet, 225 + + Harrison, James, timekeepers of, 86, 91, 93, 165 + + Heineken, Rev. N. S., 59 + + Heineken quadrant, 59 + + Heliographic Department, 251, _et seq._ + + Herschel, Caroline, 57 + + Hipparchus, catalogue of, 185 + + Hodgson, Mr., 50 + + Hooke, Robert, 75, 206 + + Horrox, Jeremiah, 31 + + Huggins, Sir W., his use of spectroscope, 268 + + + Inscription, an, 126 + + International Photographic Survey, 296 + + Ireis, 224 + + Iron quadrant, 73 + + Isobars, 237 + + + Jupiter, satellites of, 19, 296; + atmosphere of, 279 + + + Keill, John, 74 + + Kendall, Larcum, 166 + + Kepler, laws of, 64 + + Kew, photo-heliograph, the, 252 + + Kinnebrook, David, 176 + + Kirchhoff's use of spectroscope, 267 + + + Latitude, finding the, 18 + + Ledgers, chronometer, romance of, 176 + + Leverrier, his discovery of Neptune, 217 + + Libraries, 132 + + Linacre, G., 28 + + Lindsay, Thomas, quoted, 204 + + Litchford, W., 28 + + Local apparent time, 22 + + Longitude, finding the, 18; + at sea, problem of, 86; + determination of, 173 + + Longitude nought, 148 + + Lower computing room, 128 + + Lunars, method of, 86 + + + Magnetic Department, work of, 133; + description of, 228, _et seq._ + + Magnetic inclination and declination, 246 + + ---- needles, movements of, 247, 262 + + ---- observatory, 132 + + ---- pavilion, 245 + + ---- storms, 248, 262 + + Mars, distance of, 223; + atmosphere of, 279; + satellites of, 296 + + Maskelyne, Nevil, fifth Astronomer Royal, 85; + practical work of, 86; + Astronomer Royal, 91; + his work, 92; + his publications, 92; + his observations and work, 92, _et seq._; + his death, 94; + his character, 97; + recommends his successor, 97; + his mural circle, 101 + + Mean solar clock, 160 + + Mean time, 152 + + Meldrum, Dr., on sun spots, 263 + + Meridian, the, 149 + + Merz telescope, 279 + + Meteorological Department, work of, 133; + description of, 228, _et seq._ + + Micrometers, use of, 309 + + Microscopes, use of, 188 + + Milky Way, 288 + + Miller, Professor, 268 + + Milne, Professor, on earth movements, 201 + + Minor planets, 222 + + Molyneux, Samuel, 75 + + Moon, observation of the, 212, _et seq._; + eclipses of, 266 + + Moore, Sir Jonas, 30; + death of, 42 + + Morin, 33 + + Mounting telescopes, modes of, 310 + + Mudge, Thomas, 94 + + Mural arc, 7-feet, 46 + + Mural circles, 101, 196 + + + Names of stars, origin of, 183 + + Nares, Sir George, 170 + + _Nautical Almanac_, the, 22, 23, 92 + + Navigation, state of primitive, 17 + + Neptune, discovery of, 217; + atmosphere of, 280; + satellite of, 298 + + New altazimuth, the, 132, 210 + + New Observatory, the, 136, 275 + + New stars, 268 + + Newcomb, Professor, on growth of Observatory, 124; + on Greenwich observations, 207 + + Newton, Sir I., his absent-mindedness, 31; + his trouble with Flamsteed, 46, _et seq._; + on Kepler's laws, 65; + his _Principia_, 65; + his pressure on Halley, 68; + his discovery of gravitation, 206 + + North terrace, the, 126 + + Northumberland equatorial, 218 + + Nutation of the earth, 80 + + + Observation, modes of, 156, 176, 188; + by reflection, 196; + of comets, 224 + + Observatory, Greenwich, work of, 13; + foundation of, 23; + warrant for building, 40; + position of, 41; + foundation stone laid, 42; + condition of, 79; + enlargement of, 112; + recent extensions of, 120; + description of, 124, _et seq._; + staff of, 137; + work of, 139, _et seq._; + visitors to, 175; + new altazimuth building, 211; + magnet house, 228; + magnetic pavilion, 245; + new Observatory, 275; + future of, 283; + reflex zenith room, 304; + objects of, 316 + + Occultations by the moon, 212, _et seq._ + + Octagon room, 125, 238, 242 + + Oldenburg, Mr., 30 + + Orion nebula, 268, 301 + + + Parallax of stars, 303 + + Paramour, the, 65 + + Paris, conference at, 288 + + ----, noon at, 151 + + Philip III., offer of, 19 + + Photographic registration, 244, 247, 252, 255; + refractors, 288 + + Photographs, star, 290 + + Photo-heliographs, 252, _et seq._, 279 + + Piazzi, discovery of, 222 + + Pleiades, the, 301 + + Polar plumes of the corona, 264 + + Polaris, 188 + + Pole-star, variation of, 184 + + Pond, John, sixth Astronomer Royal, his life, 97; + his reign, 98; + his salary, 98; + his assistants, 98; + his observations, 99; + censured by Visitors, 99; + his observations of stars, 303 + + Pound, James, 73 + + Precession of earth's axis, 184 + + _Principia_, publication of, 65 + + Proctor, R. A., attack of, 116 + + Ptolemy, Claudius, catalogue of, 185 + + Publication, the problem of, 48, 92 + + + Quadrant, Heineken, 59 + + ----, the iron, 73 + + + Railway time, 152 + + Rain gauge, 238 + + Record rooms, 132 + + Reflection, observation by, 196 + + Reflex zenith room, 304 + + ---- ---- tube, 131 + + Refraction, effects of, 194 + + Right ascension, 186, _et seq._ + + Roberts, Dr. Isaac, 301 + + Römer, discovery of, 78 + + Rosse, Lord, 268 + + Royal Society and Flamsteed, 46, _et seq._ + + + Saint-Pierre, Le Sieur de, proposal of, 23, 32 + + Sappho, 224 + + Saros of the moon, 67 + + Satellites, discovery of, 296 + + Saturn, atmosphere of, 279; + satellites of, 296 + + Schaeberle's comet, 280 + + Schedar, 184 + + Schiehallion, attraction of, 94 + + Schönfeld, 287 + + Scotchmen, anecdote of, 146 + + Sharp, Abraham, 46 + + Sheepshanks, Rev. James, on Airy, 107 + + Shuckburgh equatorial, 309 + + Sidereal clock, 160 + + Sirius, 287 + + Sloane, Dr., 50 + + 'Smith, Mr.,' his chronometer, 179 + + Solar photographs, 257 + + ---- storms, 261, 282 + + Sound waves, 271 + + South, Sir James, 105, 114 + + South-east equatorial, the, 132, 221 + + Spectroscope, use of, 267 + + Spectroscopic Department, 266, _et seq._ + + Spots, sun, 251, _et seq._, 281 + + Staff of Observatory, 137; + work of, 139, _et seq._ + + Standard time, 21 + + Stars, observations of, 156, 176, 188; + origin of names of, 183; + movements of, 187; + catalogues of, 198, 284, _et seq._; + composition of, 268, _et seq._; + colour of, 271; + classes of, 287; + census of, 287; + photographs of, 288, _et seq._; + motions of, 303, 315 + + Story, Mr. A. M., 97 + + Sun, distance of the, 74, 224; + spots on, 251, _et seq._, 281; + eclipses of, 263, _et seq._; + chromosphere of, 268; + motions of, 315 + + Sunshine recorder, 238 + + Swiss time, 155 + + + Tebb, Mr. W., 58 + + Tebbutt's comet, 280 + + Telescope, the great transit, 156 + + ----, 28-inch, 275 + + ----, astrographic, 289 + + ----, Shuckburgh, 309 + + ----, Thompson, 256, 279, 296 + + Thalèn, 268 + + Thermometer, use of, 192, 234 + + Thome, Dr., 287 + + Thompson photo-heliograph, 256, 279, 296 + + Time ball, 162 + + ---- Department, the, 146, _et seq._ + + ---- desk, 161 + + ----, foreign, 153 + + ---- signals, 162 + + ---- standard, 21 + + Transit, Halley's, 73 + + Transit circle, the, 114; + mode of observation with, 188, _et seq._ + + Transit circle, Troughton's, 98 + + ---- Department, 181, _et seq._ + + ---- observations, number of, 140 + + ---- pavilion, 126, 175 + + ---- room, 128, 147 + + Troughton's transit circle, 98 + + + Uranus, discovery of, 217; + atmosphere of, 279; + satellites of, 296 + + + Vanes, use of, 238 + + Venus, distance of, 223 + + Victoria, 224 + + Visitors, the Board of, 53; + censures Pond, 99; + work of, 106; + constitution of, 144 + + Visitors to Observatory, 175 + + + Warrant for Flamsteed's salary, 39 + + Water telescope, 304 + + Weather predictions, 229, _et seq._ + + Winds, study of, 237 + + Witt, Herr, discovery of, 223 + + Working Catalogue, the, 142 + + + Zenith sector, 82, 305 + + ---- tube, 75, 305 + + Zeta Ursæ Majoris, 306 + + Zubeneschamal, 184 + + +THE END + + + LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, + STAMFORD STREET AND CHARING CROSS. + + + + + * * * * * + + + + +Transcriber's note: + +Minor typographical errors have been corrected without note. +Irregularities and inconsistencies in the text have been retained as +printed. + +The illustrations have been moved so that they do not break up +paragraphs. + +Mismatched quotation marks were not corrected if it was not clear +where the missing quotation mark should be placed. + + + +***END OF THE PROJECT GUTENBERG EBOOK THE ROYAL OBSERVATORY GREENWICH*** + + +******* This file should be named 44167-8.txt or 44167-8.zip ******* + + +This and all associated files of various formats will be found in: +http://www.gutenberg.org/dirs/4/4/1/6/44167 + + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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