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WILLIAMS, M.D. + +IN FIVE VOLUMES +VOLUME II. + + + + +CONTENTS + +BOOK II + +CHAPTER I. SCIENCE IN THE DARK AGE + +CHAPTER II. MEDIAEVAL SCIENCE AMONG THE ARABIANS + +CHAPTER III. MEDIAEVAL SCIENCE IN THE WEST + +CHAPTER IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +CHAPTER V. GALILEO AND THE NEW PHYSICS + +CHAPTER VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +CHAPTER VII. FROM PARACELSUS TO HARVEY + +CHAPTER VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +CHAPTER IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF +LEARNING + +CHAPTER X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +CHAPTER XI. NEWTON AND THE COMPOSITION OF LIGHT + +CHAPTER XII. NEWTON AND THE LAW OF GRAVITATION + +CHAPTER XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON + +CHAPTER XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON +GUERICKE TO FRANKLIN + +CHAPTER XV. NATURAL HISTORY TO THE TIME OF LINNAEUS + +APPENDIX + + + +A HISTORY OF SCIENCE + +BOOK II + +THE BEGINNINGS OF MODERN SCIENCE + +The studies of the present book cover the progress of science +from the close of the Roman period in the fifth century A.D. to +about the middle of the eighteenth century. In tracing the course +of events through so long a period, a difficulty becomes +prominent which everywhere besets the historian in less degree--a +difficulty due to the conflict between the strictly chronological +and the topical method of treatment. We must hold as closely as +possible to the actual sequence of events, since, as already +pointed out, one discovery leads on to another. But, on the other +hand, progressive steps are taken contemporaneously in the +various fields of science, and if we were to attempt to introduce +these in strict chronological order we should lose all sense of +topical continuity. + +Our method has been to adopt a compromise, following the course +of a single science in each great epoch to a convenient +stopping-point, and then turning back to bring forward the story +of another science. Thus, for example, we tell the story of +Copernicus and Galileo, bringing the record of cosmical and +mechanical progress down to about the middle of the seventeenth +century, before turning back to take up the physiological +progress of the fifteenth and sixteenth centuries. Once the +latter stream is entered, however, we follow it without +interruption to the time of Harvey and his contemporaries in the +middle of the seventeenth century, where we leave it to return to +the field of mechanics as exploited by the successors of Galileo, +who were also the predecessors and contemporaries of Newton. + +In general, it will aid the reader to recall that, so far as +possible, we hold always to the same sequences of topical +treatment of contemporary events; as a rule we treat first the +cosmical, then the physical, then the biological sciences. The +same order of treatment will be held to in succeeding volumes. + +Several of the very greatest of scientific generalizations are +developed in the period covered by the present book: for example, +the Copernican theory of the solar system, the true doctrine of +planetary motions, the laws of motion, the theory of the +circulation of the blood, and the Newtonian theory of +gravitation. The labors of the investigators of the early decades +of the eighteenth century, terminating with Franklin's discovery +of the nature of lightning and with the Linnaean classification +of plants and animals, bring us to the close of our second great +epoch; or, to put it otherwise, to the threshold of the modern +period, + + +I. SCIENCE IN THE DARK AGE + +An obvious distinction between the classical and mediaeval epochs +may be found in the fact that the former produced, whereas the +latter failed to produce, a few great thinkers in each generation +who were imbued with that scepticism which is the foundation of +the investigating spirit; who thought for themselves and supplied +more or less rational explanations of observed phenomena. Could +we eliminate the work of some score or so of classical observers +and thinkers, the classical epoch would seem as much a dark age +as does the epoch that succeeded it. + +But immediately we are met with the question: Why do no great +original investigators appear during all these later centuries? +We have already offered a part explanation in the fact that the +borders of civilization, where racial mingling naturally took +place, were peopled with semi-barbarians. But we must not forget +that in the centres of civilization all along there were many men +of powerful intellect. Indeed, it would violate the principle of +historical continuity to suppose that there was any sudden change +in the level of mentality of the Roman world at the close of the +classical period. We must assume, then, that the direction in +which the great minds turned was for some reason changed. Newton +is said to have alleged that he made his discoveries by +"intending" his mind in a certain direction continuously. It is +probable that the same explanation may be given of almost every +great scientific discovery. Anaxagoras could not have thought out +the theory of the moon's phases; Aristarchus could not have found +out the true mechanism of the solar system; Eratosthenes could +not have developed his plan for measuring the earth, had not each +of these investigators "intended" his mind persistently towards +the problems in question. + +Nor can we doubt that men lived in every generation of the dark +age who were capable of creative thought in the field of science, +bad they chosen similarly to "intend" their minds in the right +direction. The difficulty was that they did not so choose. Their +minds had a quite different bent. They were under the spell of +different ideals; all their mental efforts were directed into +different channels. What these different channels were cannot be +in doubt--they were the channels of oriental ecclesiasticism. One +all-significant fact speaks volumes here. It is the fact that, as +Professor Robinson[1] points out, from the time of Boethius (died +524 or 525 A.D.) to that of Dante (1265-1321 A.D.) there was not +a single writer of renown in western Europe who was not a +professional churchman. All the learning of the time, then, +centred in the priesthood. We know that the same condition of +things pertained in Egypt, when science became static there. But, +contrariwise, we have seen that in Greece and early Rome the +scientific workers were largely physicians or professional +teachers; there was scarcely a professional theologian among +them. + +Similarly, as we shall see in the Arabic world, where alone there +was progress in the mediaeval epoch, the learned men were, for +the most part, physicians. Now the meaning of this must be +self-evident. The physician naturally "intends" his mind towards +the practicalities. His professional studies tend to make him an +investigator of the operations of nature. He is usually a +sceptic, with a spontaneous interest in practical science. But +the theologian "intends" his mind away from practicalities and +towards mysticism. He is a professional believer in the +supernatural; he discounts the value of merely "natural" +phenomena. His whole attitude of mind is unscientific; the +fundamental tenets of his faith are based on alleged occurrences +which inductive science cannot admit--namely, miracles. And so +the minds "intended" towards the supernatural achieved only the +hazy mysticism of mediaeval thought. Instead of investigating +natural laws, they paid heed (as, for example, Thomas Aquinas +does in his Summa Theologia) to the "acts of angels," the +"speaking of angels," the "subordination of angels," the "deeds +of guardian angels," and the like. They disputed such important +questions as, How many angels can stand upon the point of a +needle? They argued pro and con as to whether Christ were coeval +with God, or whether he had been merely created "in the +beginning," perhaps ages before the creation of the world. How +could it be expected that science should flourish when the +greatest minds of the age could concern themselves with problems +such as these? + +Despite our preconceptions or prejudices, there can be but one +answer to that question. Oriental superstition cast its blight +upon the fair field of science, whatever compensation it may or +may not have brought in other fields. But we must be on our guard +lest we overestimate or incorrectly estimate this influence. +Posterity, in glancing backward, is always prone to stamp any +given age of the past with one idea, and to desire to +characterize it with a single phrase; whereas in reality all ages +are diversified, and any generalization regarding an epoch is +sure to do that epoch something less or something more than +justice. We may be sure, then, that the ideal of ecclesiasticism +is not solely responsible for the scientific stasis of the dark +age. Indeed, there was another influence of a totally different +character that is too patent to be overlooked--the influence, +namely, of the economic condition of western Europe during this +period. As I have elsewhere pointed out,[2] Italy, the centre of +western civilization, was at this time impoverished, and hence +could not provide the monetary stimulus so essential to artistic +and scientific no less than to material progress. There were no +patrons of science and literature such as the Ptolemies of that +elder Alexandrian day. There were no great libraries; no colleges +to supply opportunities and afford stimuli to the rising +generation. Worst of all, it became increasingly difficult to +secure books. + +This phase of the subject is often overlooked. Yet a moment's +consideration will show its importance. How should we fare to-day +if no new scientific books were being produced, and if the +records of former generations were destroyed? That is what +actually happened in Europe during the Middle Ages. At an earlier +day books were made and distributed much more abundantly than is +sometimes supposed. Bookmaking had, indeed, been an important +profession in Rome, the actual makers of books being slaves who +worked under the direction of a publisher. It was through the +efforts of these workers that the classical works in Greek and +Latin were multiplied and disseminated. Unfortunately the climate +of Europe does not conduce to the indefinite preservation of a +book; hence very few remnants of classical works have come down +to us in the original from a remote period. The rare exceptions +are certain papyrus fragments, found in Egypt, some of which are +Greek manuscripts dating from the third century B.C. Even from +these sources the output is meagre; and the only other repository +of classical books is a single room in the buried city of +Herculaneum, which contained several hundred manuscripts, mostly +in a charred condition, a considerable number of which, however, +have been unrolled and found more or less legible. This library +in the buried city was chiefly made up of philosophical works, +some of which were quite unknown to the modern world until +discovered there. + +But this find, interesting as it was from an archaeological +stand-point, had no very important bearing on our knowledge of +the literature of antiquity. Our chief dependence for our +knowledge of that literature must still be placed in such copies +of books as were made in the successive generations. +Comparatively few of the extant manuscripts are older than the +tenth century of our era. It requires but a momentary +consideration of the conditions under which ancient books were +produced to realize how slow and difficult the process was before +the invention of printing. The taste of the book-buying public +demanded a clearly written text, and in the Middle Ages it became +customary to produce a richly ornamented text as well. The script +employed being the prototype of the modern printed text, it will +be obvious that a scribe could produce but a few pages at best in +a day. A large work would therefore require the labor of a scribe +for many months or even for several years. We may assume, then, +that it would be a very flourishing publisher who could produce a +hundred volumes all told per annum; and probably there were not +many publishers at any given time, even in the period of Rome's +greatest glory, who had anything like this output. + +As there was a large number of authors in every generation of the +classical period, it follows that most of these authors must have +been obliged to content themselves with editions numbering very +few copies; and it goes without saying that the greater number of +books were never reproduced in what might be called a second +edition. Even books that retained their popularity for several +generations would presently fail to arouse sufficient interest to +be copied; and in due course such works would pass out of +existence altogether. Doubtless many hundreds of books were thus +lost before the close of the classical period, the names of their +authors being quite forgotten, or preserved only through a chance +reference; and of course the work of elimination went on much +more rapidly during the Middle Ages, when the interest in +classical literature sank to so low an ebb in the West. Such +collections of references and quotations as the Greek Anthology +and the famous anthologies of Stobaeus and Athanasius and +Eusebius give us glimpses of a host of writers--more than seven +hundred are quoted by Stobaeus--a very large proportion of whom +are quite unknown except through these brief excerpts from their +lost works. + +Quite naturally the scientific works suffered at least as largely +as any others in an age given over to ecclesiastical dreamings. +Yet in some regards there is matter for surprise as to the works +preserved. Thus, as we have seen, the very extensive works of +Aristotle on natural history, and the equally extensive natural +history of Pliny, which were preserved throughout this period, +and are still extant, make up relatively bulky volumes. These +works seem to have interested the monks of the Middle Ages, while +many much more important scientific books were allowed to perish. +A considerable bulk of scientific literature was also preserved +through the curious channels of Arabic and Armenian translations. +Reference has already been made to the Almagest of Ptolemy, +which, as we have seen, was translated into Arabic, and which was +at a later day brought by the Arabs into western Europe and (at +the instance of Frederick II of Sicily) translated out of their +language into mediaeval Latin. + +It remains to inquire, however, through what channels the Greek +works reached the Arabs themselves. To gain an answer to this +question we must follow the stream of history from its Roman +course eastward to the new seat of the Roman empire in Byzantium. +Here civilization centred from about the fifth century A.D., and +here the European came in contact with the civilization of the +Syrians, the Persians, the Armenians, and finally of the Arabs. +The Byzantines themselves, unlike the inhabitants of western +Europe, did not ignore the literature of old Greece; the Greek +language became the regular speech of the Byzantine people, and +their writers made a strenuous effort to perpetuate the idiom and +style of the classical period. Naturally they also made +transcriptions of the classical authors, and thus a great mass of +literature was preserved, while the corresponding works were +quite forgotten in western Europe. + +Meantime many of these works were translated into Syriac, +Armenian, and Persian, and when later on the Byzantine +civilization degenerated, many works that were no longer to be +had in the Greek originals continued to be widely circulated in +Syriac, Persian, Armenian, and, ultimately, in Arabic +translations. When the Arabs started out in their conquests, +which carried them through Egypt and along the southern coast of +the Mediterranean, until they finally invaded Europe from the +west by way of Gibraltar, they carried with them their +translations of many a Greek classical author, who was introduced +anew to the western world through this strange channel. + +We are told, for example, that Averrhoes, the famous commentator +of Aristotle, who lived in Spain in the twelfth century, did not +know a word of Greek and was obliged to gain his knowledge of the +master through a Syriac translation; or, as others alleged +(denying that he knew even Syriac), through an Arabic version +translated from the Syriac. We know, too, that the famous +chronology of Eusebius was preserved through an Armenian +translation; and reference has more than once been made to the +Arabic translation of Ptolemy's great work, to which we still +apply its Arabic title of Almagest. + +The familiar story that when the Arabs invaded Egypt they burned +the Alexandrian library is now regarded as an invention of later +times. It seems much more probable that the library bad been +largely scattered before the coming of the Moslems. Indeed, it +has even been suggested that the Christians of an earlier day +removed the records of pagan thought. Be that as it may, the +famous Alexandrian library had disappeared long before the +revival of interest in classical learning. Meanwhile, as we have +said, the Arabs, far from destroying the western literature, were +its chief preservers. Partly at least because of their regard for +the records of the creative work of earlier generations of alien +peoples, the Arabs were enabled to outstrip their contemporaries. +For it cannot be in doubt that, during that long stretch of time +when the western world was ignoring science altogether or at most +contenting itself with the casual reading of Aristotle and Pliny, +the Arabs had the unique distinction of attempting original +investigations in science. To them were due all important +progressive steps which were made in any scientific field +whatever for about a thousand years after the time of Ptolemy and +Galen. The progress made even by the Arabs during this long +period seems meagre enough, yet it has some significant features. +These will now demand our attention. + + + +II. MEDIAEVAL SCIENCE AMONG THE ARABIANS + +The successors of Mohammed showed themselves curiously receptive +of the ideas of the western people whom they conquered. They came +in contact with the Greeks in western Asia and in Egypt, and, as +has been said, became their virtual successors in carrying +forward the torch of learning. It must not be inferred, however, +that the Arabian scholars, as a class, were comparable to their +predecessors in creative genius. On the contrary, they retained +much of the conservative oriental spirit. They were under the +spell of tradition, and, in the main, what they accepted from the +Greeks they regarded as almost final in its teaching. There were, +however, a few notable exceptions among their men of science, and +to these must be ascribed several discoveries of some importance. + +The chief subjects that excited the interest and exercised the +ingenuity of the Arabian scholars were astronomy, mathematics, +and medicine. The practical phases of all these subjects were +given particular attention. Thus it is well known that our +so-called Arabian numerals date from this period. The +revolutionary effect of these characters, as applied to practical +mathematics, can hardly be overestimated; but it is generally +considered, and in fact was admitted by the Arabs themselves, +that these numerals were really borrowed from the Hindoos, with +whom the Arabs came in contact on the east. Certain of the Hindoo +alphabets, notably that of the Battaks of Sumatra, give us clews +to the originals of the numerals. It does not seem certain, +however, that the Hindoos employed these characters according to +the decimal system, which is the prime element of their +importance. Knowledge is not forthcoming as to just when or by +whom such application was made. If this was an Arabic innovation, +it was perhaps the most important one with which that nation is +to be credited. Another mathematical improvement was the +introduction into trigonometry of the sine--the half-chord of the +double arc--instead of the chord of the arc itself which the +Greek astronomers had employed. This improvement was due to the +famous Albategnius, whose work in other fields we shall examine +in a moment. + +Another evidence of practicality was shown in the Arabian method +of attempting to advance upon Eratosthenes' measurement of the +earth. Instead of trusting to the measurement of angles, the +Arabs decided to measure directly a degree of the earth's +surface--or rather two degrees. Selecting a level plain in +Mesopotamia for the experiment, one party of the surveyors +progressed northward, another party southward, from a given point +to the distance of one degree of arc, as determined by +astronomical observations. The result found was fifty-six miles +for the northern degree, and fifty-six and two-third miles for +the southern. Unfortunately, we do not know the precise length of +the mile in question, and therefore cannot be assured as to the +accuracy of the measurement. It is interesting to note, however, +that the two degrees were found of unequal lengths, suggesting +that the earth is not a perfect sphere--a suggestion the validity +of which was not to be put to the test of conclusive measurements +until about the close of the eighteenth century. The Arab +measurement was made in the time of Caliph Abdallah al-Mamun, the +son of the famous Harun-al-Rashid. Both father and son were +famous for their interest in science. Harun-al-Rashid was, it +will be recalled, the friend of Charlemagne. It is said that he +sent that ruler, as a token of friendship, a marvellous clock +which let fall a metal ball to mark the hours. This mechanism, +which is alleged to have excited great wonder in the West, +furnishes yet another instance of Arabian practicality. + +Perhaps the greatest of the Arabian astronomers was Mohammed ben +Jabir Albategnius, or El-batani, who was born at Batan, in +Mesopotamia, about the year 850 A.D., and died in 929. +Albategnius was a student of the Ptolemaic astronomy, but he was +also a practical observer. He made the important discovery of the +motion of the solar apogee. That is to say, he found that the +position of the sun among the stars, at the time of its greatest +distance from the earth, was not what it had been in the time of +Ptolemy. The Greek astronomer placed the sun in longitude 65 +degrees, but Albategnius found it in longitude 82 degrees, a +distance too great to be accounted for by inaccuracy of +measurement. The modern inference from this observation is that +the solar system is moving through space; but of course this +inference could not well be drawn while the earth was regarded as +the fixed centre of the universe. + +In the eleventh century another Arabian discoverer, Arzachel, +observing the sun to be less advanced than Albategnius had found +it, inferred incorrectly that the sun had receded in the mean +time. The modern explanation of this observation is that the +measurement of Albategnius was somewhat in error, since we know +that the sun's motion is steadily progressive. Arzachel, however, +accepting the measurement of his predecessor, drew the false +inference of an oscillatory motion of the stars, the idea of the +motion of the solar system not being permissible. This assumed +phenomenon, which really has no existence in point of fact, was +named the "trepidation of the fixed stars," and was for centuries +accepted as an actual phenomenon. Arzachel explained this +supposed phenomenon by assuming that the equinoctial points, or +the points of intersection of the equator and the ecliptic, +revolve in circles of eight degrees' radius. The first points of +Aries and Libra were supposed to describe the circumference of +these circles in about eight hundred years. All of which +illustrates how a difficult and false explanation may take the +place of a simple and correct one. The observations of later +generations have shown conclusively that the sun's shift of +position is regularly progressive, hence that there is no +"trepidation" of the stars and no revolution of the equinoctial +points. + +If the Arabs were wrong as regards this supposed motion of the +fixed stars, they made at least one correct observation as to the +inequality of motion of the moon. Two inequalities of the motion +of this body were already known. A third, called the moon's +variation, was discovered by an Arabian astronomer who lived at +Cairo and observed at Bagdad in 975, and who bore the formidable +name of Mohammed Aboul Wefaal-Bouzdjani. The inequality of motion +in question, in virtue of which the moon moves quickest when she +is at new or full, and slowest at the first and third quarter, +was rediscovered by Tycho Brahe six centuries later; a fact which +in itself evidences the neglect of the Arabian astronomer's +discovery by his immediate successors. + +In the ninth and tenth centuries the Arabian city of Cordova, in +Spain, was another important centre of scientific influence. +There was a library of several hundred thousand volumes here, and +a college where mathematics and astronomy were taught. Granada, +Toledo, and Salamanca were also important centres, to which +students flocked from western Europe. It was the proximity of +these Arabian centres that stimulated the scientific interests of +Alfonso X. of Castile, at whose instance the celebrated Alfonsine +tables were constructed. A familiar story records that Alfonso, +pondering the complications of the Ptolemaic cycles and +epicycles, was led to remark that, had he been consulted at the +time of creation, he could have suggested a much better and +simpler plan for the universe. Some centuries were to elapse +before Copernicus was to show that it was not the plan of the +universe, but man's interpretation of it, that was at fault. + +Another royal personage who came under Arabian influence was +Frederick II. of Sicily--the "Wonder of the World," as he was +called by his contemporaries. The Almagest of Ptolemy was +translated into Latin at his instance, being introduced to the +Western world through this curious channel. At this time it +became quite usual for the Italian and Spanish scholars to +understand Arabic although they were totally ignorant of Greek. + +In the field of physical science one of the most important of the +Arabian scientists was Alhazen. His work, published about the +year 1100 A.D., had great celebrity throughout the mediaeval +period. The original investigations of Alhazen had to do largely +with optics. He made particular studies of the eye itself, and +the names given by him to various parts of the eye, as the +vitreous humor, the cornea, and the retina, are still retained by +anatomists. It is known that Ptolemy had studied the refraction +of light, and that he, in common with his immediate predecessors, +was aware that atmospheric refraction affects the apparent +position of stars near the horizon. Alhazen carried forward these +studies, and was led through them to make the first recorded +scientific estimate of the phenomena of twilight and of the +height of the atmosphere. The persistence of a glow in the +atmosphere after the sun has disappeared beneath the horizon is +so familiar a phenomenon that the ancient philosophers seem not +to have thought of it as requiring an explanation. Yet a moment's +consideration makes it clear that, if light travels in straight +lines and the rays of the sun were in no wise deflected, the +complete darkness of night should instantly succeed to day when +the sun passes below the horizon. That this sudden change does +not occur, Alhazen explained as due to the reflection of light by +the earth's atmosphere. + +Alhazen appears to have conceived the atmosphere as a sharply +defined layer, and, assuming that twilight continues only so long +as rays of the sun reflected from the outer surface of this layer +can reach the spectator at any given point, he hit upon a means +of measurement that seemed to solve the hitherto inscrutable +problem as to the atmospheric depth. Like the measurements of +Aristarchus and Eratosthenes, this calculation of Alhazen is +simple enough in theory. Its defect consists largely in the +difficulty of fixing its terms with precision, combined with the +further fact that the rays of the sun, in taking the slanting +course through the earth's atmosphere, are really deflected from +a straight line in virtue of the constantly increasing density of +the air near the earth's surface. Alhazen must have been aware of +this latter fact, since it was known to the later Alexandrian +astronomers, but he takes no account of it in the present +measurement. The diagram will make the method of Alhazen clear. + +His important premises are two: first, the well-recognized fact +that, when light is reflected from any surface, the angle of +incidence is equal to the angle of reflection; and, second, the +much more doubtful observation that twilight continues until such +time as the sun, according to a simple calculation, is nineteen +degrees below the horizon. Referring to the diagram, let the +inner circle represent the earth's surface, the outer circle the +limits of the atmosphere, C being the earth's centre, and RR +radii of the earth. Then the observer at the point A will +continue to receive the reflected rays of the sun until that body +reaches the point S, which is, according to the hypothesis, +nineteen degrees below the horizon line of the observer at A. +This horizon line, being represented by AH, and the sun's ray by +SM, the angle HMS is an angle of nineteen degrees. The +complementary angle SMA is, obviously, an angle of (180-19) one +hundred and sixty-one degrees. But since M is the reflecting +surface and the angle of incidence equals the angle of +reflection, the angle AMC is an angle of one-half of one hundred +and sixty-one degrees, or eighty degrees and thirty minutes. Now +this angle AMC, being known, the right-angled triangle MAC is +easily resolved, since the side AC of that triangle, being the +radius of the earth, is a known dimension. Resolution of this +triangle gives us the length of the hypotenuse MC, and the +difference between this and the radius (AC), or CD, is obviously +the height of the atmosphere (h), which was the measurement +desired. According to the calculation of Alhazen, this h, or the +height of the atmosphere, represents from twenty to thirty miles. +The modern computation extends this to about fifty miles. But, +considering the various ambiguities that necessarily attended the +experiment, the result was a remarkably close approximation to +the truth. + +Turning from physics to chemistry, we find as perhaps the +greatest Arabian name that of Geber, who taught in the College of +Seville in the first half of the eighth century. The most +important researches of this really remarkable experimenter had +to do with the acids. The ancient world had had no knowledge of +any acid more powerful than acetic. Geber, however, vastly +increased the possibilities of chemical experiment by the +discovery of sulphuric, nitric, and nitromuriatic acids. He made +use also of the processes of sublimation and filtration, and his +works describe the water bath and the chemical oven. Among the +important chemicals which he first differentiated is oxide of +mercury, and his studies of sulphur in its various compounds have +peculiar interest. In particular is this true of his observation +that, tinder certain conditions of oxidation, the weight of a +metal was lessened. + +From the record of these studies in the fields of astronomy, +physics, and chemistry, we turn to a somewhat extended survey of +the Arabian advances in the field of medicine. + + +ARABIAN MEDICINE + +The influence of Arabian physicians rested chiefly upon their use +of drugs rather than upon anatomical knowledge. Like the +mediaeval Christians, they looked with horror on dissection of +the human body; yet there were always among them investigators +who turned constantly to nature herself for hidden truths, and +were ready to uphold the superiority of actual observation to +mere reading. Thus the physician Abd el-Letif, while in Egypt, +made careful studies of a mound of bones containing more than +twenty thousand skeletons. While examining these bones he +discovered that the lower jaw consists of a single bone, not of +two, as had been taught by Galen. He also discovered several +other important mistakes in Galenic anatomy, and was so impressed +with his discoveries that he contemplated writing a work on +anatomy which should correct the great classical authority's +mistakes. + +It was the Arabs who invented the apothecary, and their +pharmacopoeia, issued from the hospital at Gondisapor, and +elaborated from time to time, formed the basis for Western +pharmacopoeias. Just how many drugs originated with them, and how +many were borrowed from the Hindoos, Jews, Syrians, and Persians, +cannot be determined. It is certain, however, that through them +various new and useful drugs, such as senna, aconite, rhubarb, +camphor, and mercury, were handed down through the Middle Ages, +and that they are responsible for the introduction of alcohol in +the field of therapeutics. + +In mediaeval Europe, Arabian science came to be regarded with +superstitious awe, and the works of certain Arabian physicians +were exalted to a position above all the ancient writers. In +modern times, however, there has been a reaction and a tendency +to depreciation of their work. By some they are held to be mere +copyists or translators of Greek books, and in no sense original +investigators in medicine. Yet there can be little doubt that +while the Arabians did copy and translate freely, they also +originated and added considerably to medical knowledge. It is +certain that in the time when Christian monarchs in western +Europe were paying little attention to science or education, the +caliphs and vizirs were encouraging physicians and philosophers, +building schools, and erecting libraries and hospitals. They made +at least a creditable effort to uphold and advance upon the +scientific standards of an earlier age. + +The first distinguished Arabian physician was Harets ben Kaladah, +who received his education in the Nestonian school at Gondisapor, +about the beginning of the seventh century. Notwithstanding the +fact that Harets was a Christian, he was chosen by Mohammed as +his chief medical adviser, and recommended as such to his +successor, the Caliph Abu Bekr. Thus, at the very outset, the +science of medicine was divorced from religion among the +Arabians; for if the prophet himself could employ the services of +an unbeliever, surely others might follow his example. And that +this example was followed is shown in the fact that many +Christian physicians were raised to honorable positions by +succeeding generations of Arabian monarchs. This broad-minded +view of medicine taken by the Arabs undoubtedly assisted as much +as any one single factor in upbuilding the science, just as the +narrow and superstitious view taken by Western nations helped to +destroy it. + +The education of the Arabians made it natural for them to +associate medicine with the natural sciences, rather than with +religion. An Arabian savant was supposed to be equally well +educated in philosophy, jurisprudence, theology, mathematics, and +medicine, and to practise law, theology, and medicine with equal +skill upon occasion. It is easy to understand, therefore, why +these religious fanatics were willing to employ unbelieving +physicians, and their physicians themselves to turn to the +scientific works of Hippocrates and Galen for medical +instruction, rather than to religious works. Even Mohammed +himself professed some knowledge of medicine, and often relied +upon this knowledge in treating ailments rather than upon prayers +or incantations. He is said, for example, to have recommended and +applied the cautery in the case of a friend who, when suffering +from angina, had sought his aid. + +The list of eminent Arabian physicians is too long to be given +here, but some of them are of such importance in their influence +upon later medicine that they cannot be entirely ignored. One of +the first of these was Honain ben Isaac (809-873 A.D.), a +Christian Arab of Bagdad. He made translations of the works of +Hippocrates, and practised the art along the lines indicated by +his teachings and those of Galen. He is considered the greatest +translator of the ninth century and one of the greatest +philosophers of that period. + +Another great Arabian physician, whose work was just beginning as +Honain's was drawing to a close, was Rhazes (850-923 A.D.), who +during his life was no less noted as a philosopher and musician +than as a physician. He continued the work of Honain, and +advanced therapeutics by introducing more extensive use of +chemical remedies, such as mercurial ointments, sulphuric acid, +and aqua vitae. He is also credited with being the first +physician to describe small-pox and measles accurately. + +While Rhazes was still alive another Arabian, Haly Abbas (died +about 994), was writing his famous encyclopaedia of medicine, +called The Royal Book. But the names of all these great +physicians have been considerably obscured by the reputation of +Avicenna (980-1037), the Arabian "Prince of Physicians," the +greatest name in Arabic medicine, and one of the most remarkable +men in history. Leclerc says that "he was perhaps never surpassed +by any man in brilliancy of intellect and indefatigable +activity." His career was a most varied one. He was at all times +a boisterous reveller, but whether flaunting gayly among the +guests of an emir or biding in some obscure apothecary cellar, +his work of philosophical writing was carried on steadily. When a +friendly emir was in power, he taught and wrote and caroused at +court; but between times, when some unfriendly ruler was supreme, +he was hiding away obscurely, still pouring out his great mass of +manuscripts. In this way his entire life was spent. + +By his extensive writings he revived and kept alive the best of +the teachings of the Greek physicians, adding to them such +observations as he had made in anatomy, physiology, and materia +medica. Among his discoveries is that of the contagiousness of +pulmonary tuberculosis. His works for several centuries continued +to be looked upon as the highest standard by physicians, and he +should undoubtedly be credited with having at least retarded the +decline of mediaeval medicine. + +But it was not the Eastern Arabs alone who were active in the +field of medicine. Cordova, the capital of the western caliphate, +became also a great centre of learning and produced several great +physicians. One of these, Albucasis (died in 1013 A.D.), is +credited with having published the first illustrated work on +surgery, this book being remarkable in still another way, in that +it was also the first book, since classical times, written from +the practical experience of the physician, and not a mere +compilation of ancient authors. A century after Albucasis came +the great physician Avenzoar (1113-1196), with whom he divides +about equally the medical honors of the western caliphate. Among +Avenzoar's discoveries was that of the cause of "itch"--a little +parasite, "so small that he is hardly visible." The discovery of +the cause of this common disease seems of minor importance now, +but it is of interest in medical history because, had Avenzoar's +discovery been remembered a hundred years ago, "itch struck in" +could hardly have been considered the cause of three-fourths of +all diseases, as it was by the famous Hahnemann. + +The illustrious pupil of Avenzoar, Averrhoes, who died in 1198 +A.D., was the last of the great Arabian physicians who, by +rational conception of medicine, attempted to stem the flood of +superstition that was overwhelming medicine. For a time he +succeeded; but at last the Moslem theologians prevailed, and he +was degraded and banished to a town inhabited only by the +despised Jews. + + +ARABIAN HOSPITALS + +To early Christians belong the credit of having established the +first charitable institutions for caring for the sick; but their +efforts were soon eclipsed by both Eastern and Western +Mohammedans. As early as the eighth century the Arabs had begun +building hospitals, but the flourishing time of hospital building +seems to have begun early in the tenth century. Lady Seidel, in +918 A.D., opened a hospital at Bagdad, endowed with an amount +corresponding to about three hundred pounds sterling a month. +Other similar hospitals were erected in the years immediately +following, and in 977 the Emir Adad-adaula established an +enormous institution with a staff of twenty-four medical +officers. The great physician Rhazes is said to have selected the +site for one of these hospitals by hanging pieces of meat in +various places about the city, selecting the site near the place +at which putrefaction was slowest in making its appearance. By +the middle of the twelfth century there were something like sixty +medical institutions in Bagdad alone, and these institutions were +free to all patients and supported by official charity. + +The Emir Nureddin, about the year 1160, founded a great hospital +at Damascus, as a thank-offering for his victories over the +Crusaders. This great institution completely overshadowed all the +earlier Moslem hospitals in size and in the completeness of its +equipment. It was furnished with facilities for teaching, and was +conducted for several centuries in a lavish manner, regardless of +expense. But little over a century after its foundation the fame +of its methods of treatment led to the establishment of a larger +and still more luxurious institution--the Mansuri hospital at +Cairo. It seems that a certain sultan, having been cured by +medicines from the Damascene hospital, determined to build one of +his own at Cairo which should eclipse even the great Damascene +institution. + +In a single year (1283-1284) this hospital was begun and +completed. No efforts were spared in hurrying on the good work, +and no one was exempt from performing labor on the building if he +chanced to pass one of the adjoining streets. It was the order of +the sultan that any person passing near could be impressed into +the work, and this order was carried out to the letter, noblemen +and beggars alike being forced to lend a hand. Very naturally, +the adjacent thoroughfares became unpopular and practically +deserted, but still the holy work progressed rapidly and was +shortly completed. + +This immense structure is said to have contained four courts, +each having a fountain in the centre; lecture-halls, wards for +isolating certain diseases, and a department that corresponded to +the modern hospital's "out-patient" department. The yearly +endowment amounted to something like the equivalent of one +hundred and twenty-five thousand dollars. A novel feature was a +hall where musicians played day and night, and another where +story-tellers were employed, so that persons troubled with +insomnia were amused and melancholiacs cheered. Those of a +religious turn of mind could listen to readings of the Koran, +conducted continuously by a staff of some fifty chaplains. Each +patient on leaving the hospital received some gold pieces, that +he need not be obliged to attempt hard labor at once. + +In considering the astonishing tales of these sumptuous Arabian +institutions, it should be borne in mind that our accounts of +them are, for the most part, from Mohammedan sources. +Nevertheless, there can be little question that they were +enormous institutions, far surpassing any similar institutions in +western Europe. The so-called hospitals in the West were, at this +time, branches of monasteries under supervision of the monks, and +did not compare favorably with the Arabian hospitals. + +But while the medical science of the Mohammedans greatly +overshadowed that of the Christians during this period, it did +not completely obliterate it. About the year 1000 A.D. came into +prominence the Christian medical school at Salerno, situated on +the Italian coast, some thirty miles southeast of Naples. Just +how long this school had been in existence, or by whom it was +founded, cannot be determined, but its period of greatest +influence was the eleventh, twelfth, and thirteenth centuries. +The members of this school gradually adopted Arabic medicine, +making use of many drugs from the Arabic pharmacopoeia, and this +formed one of the stepping-stones to the introduction of Arabian +medicine all through western Europe. + +It was not the adoption of Arabian medicines, however, that has +made the school at Salerno famous both in rhyme and prose, but +rather the fact that women there practised the healing art. +Greatest among them was Trotula, who lived in the eleventh +century, and whose learning is reputed to have equalled that of +the greatest physicians of the day. She is accredited with a work +on Diseases of Women, still extant, and many of her writings on +general medical subjects were quoted through two succeeding +centuries. If we may judge from these writings, she seemed to +have had many excellent ideas as to the proper methods of +treating diseases, but it is difficult to determine just which of +the writings credited to her are in reality hers. Indeed, the +uncertainty is even greater than this implies, for, according to +some writers, "Trotula" is merely the title of a book. Such an +authority as Malgaigne, however, believed that such a woman +existed, and that the works accredited to her are authentic. The +truth of the matter may perhaps never be fully established, but +this at least is certain--the tradition in regard to Trotula +could never have arisen had not women held a far different +position among the Arabians of this period from that accorded +them in contemporary Christendom. + + + +III. MEDIAEVAL SCIENCE IN THE WEST + +We have previously referred to the influence of the Byzantine +civilization in transmitting the learning of antiquity across the +abysm of the dark age. It must be admitted, however, that the +importance of that civilization did not extend much beyond the +task of the common carrier. There were no great creative +scientists in the later Roman empire of the East any more than in +the corresponding empire of the West. There was, however, one +field in which the Byzantine made respectable progress and +regarding which their efforts require a few words of special +comment. This was the field of medicine. + +The Byzantines of this time could boast of two great medical men, +Aetius of Amida (about 502-575 A.D.) and Paul of Aegina (about +620-690). The works of Aetius were of value largely because they +recorded the teachings of many of his eminent predecessors, but +he was not entirely lacking in originality, and was perhaps the +first physician to mention diphtheria, with an allusion to some +observations of the paralysis of the palate which sometimes +follows this disease. + +Paul of Aegina, who came from the Alexandrian school about a +century later, was one of those remarkable men whose ideas are +centuries ahead of their time. This was particularly true of Paul +in regard to surgery, and his attitude towards the supernatural +in the causation and treatment of diseases. He was essentially a +surgeon, being particularly familiar with military surgery, and +some of his descriptions of complicated and difficult operations +have been little improved upon even in modern times. In his books +he describes such operations as the removal of foreign bodies +from the nose, ear, and esophagus; and he recognizes foreign +growths such as polypi in the air-passages, and gives the method +of their removal. Such operations as tracheotomy, tonsellotomy, +bronchotomy, staphylotomy, etc., were performed by him, and he +even advocated and described puncture of the abdominal cavity, +giving careful directions as to the location in which such +punctures should be made. He advocated amputation of the breast +for the cure of cancer, and described extirpation of the uterus. +Just how successful this last operation may have been as +performed by him does not appear; but he would hardly have +recommended it if it had not been sometimes, at least, +successful. That he mentions it at all, however, is significant, +as this difficult operation is considered one of the great +triumphs of modern surgery. + +But Paul of Aegina is a striking exception to the rule among +Byzantine surgeons, and as he was their greatest, so he was also +their last important surgeon. The energies of all Byzantium were +so expended in religious controversies that medicine, like the +other sciences, was soon relegated to a place among the other +superstitions, and the influence of the Byzantine school was +presently replaced by that of the conquering Arabians. + + +THIRTEENTH-CENTURY MEDICINE + +The thirteenth century marks the beginning of a gradual change in +medicine, and a tendency to leave the time-worn rut of +superstitious dogmas that so long retarded the progress of +science. It is thought that the great epidemics which raged +during the Middle Ages acted powerfully in diverting the medical +thought of the times into new and entirely different channels. It +will be remembered that the teachings of Galen were handed +through mediaeval times as the highest and best authority on the +subject of all diseases. When, however, the great epidemics made +their appearance, the medical men appealed to the works of Galen +in vain for enlightenment, as these works, having been written +several centuries before the time of the plagues, naturally +contained no information concerning them. It was evident, +therefore, that on this subject, at least, Galen was not +infallible; and it would naturally follow that, one fallible +point having been revealed, others would be sought for. In other +words, scepticism in regard to accepted methods would be aroused, +and would lead naturally, as such scepticism usually does, to +progress. The devastating effects of these plagues, despite +prayers and incantations, would arouse doubt in the minds of many +as to the efficacy of superstitious rites and ceremonies in +curing diseases. They had seen thousands and tens of thousands of +their fellow-beings swept away by these awful scourges. They had +seen the ravages of these epidemics continue for months or even +years, notwithstanding the fact that multitudes of God-fearing +people prayed hourly that such ravages might be checked. And they +must have observed also that when even very simple rules of +cleanliness and hygiene were followed there was a diminution in +the ravages of the plague, even without the aid of incantations. +Such observations as these would have a tendency to awaken a +suspicion in the minds of many of the physicians that disease was +not a manifestation of the supernatural, but a natural +phenomenon, to be treated by natural methods. + +But, be the causes what they may, it is a fact that the +thirteenth century marks a turning-point, or the beginning of an +attitude of mind which resulted in bringing medicine to a much +more rational position. Among the thirteenth-century physicians, +two men are deserving of special mention. These are Arnald of +Villanova (1235-1312) and Peter of Abano (1250-1315). Both these +men suffered persecution for expressing their belief in natural, +as against the supernatural, causes of disease, and at one time +Arnald was obliged to flee from Barcelona for declaring that the +"bulls" of popes were human works, and that "acts of charity were +dearer to God than hecatombs." He was also accused of alchemy. +Fleeing from persecution, he finally perished by shipwreck. + +Arnald was the first great representative of the school of +Montpellier. He devoted much time to the study of chemicals, and +was active in attempting to re-establish the teachings of +Hippocrates and Galen. He was one of the first of a long line of +alchemists who, for several succeeding centuries, expended so +much time and energy in attempting to find the "elixir of life." +The Arab discovery of alcohol first deluded him into the belief +that the "elixir" had at last been found; but later he discarded +it and made extensive experiments with brandy, employing it in +the treatment of certain diseases--the first record of the +administration of this liquor as a medicine. Arnald also revived +the search for some anaesthetic that would produce insensibility +to pain in surgical operations. This idea was not original with +him, for since very early times physicians had attempted to +discover such an anaesthetic, and even so early a writer as +Herodotus tells how the Scythians, by inhalation of the vapors of +some kind of hemp, produced complete insensibility. It may have +been these writings that stimulated Arnald to search for such an +anaesthetic. In a book usually credited to him, medicines are +named and methods of administration described which will make the +patient insensible to pain, so that "he may be cut and feel +nothing, as though he were dead." For this purpose a mixture of +opium, mandragora, and henbane is to be used. This mixture was +held at the patient's nostrils much as ether and chloroform are +administered by the modern surgeon. The method was modified by +Hugo of Lucca (died in 1252 or 1268), who added certain other +narcotics, such as hemlock, to the mixture, and boiled a new +sponge in this decoction. After boiling for a certain time, this +sponge was dried, and when wanted for use was dipped in hot water +and applied to the nostrils. + +Just how frequently patients recovered from the administration of +such a combination of powerful poisons does not appear, but the +percentage of deaths must have been very high, as the practice +was generally condemned. Insensibility could have been produced +only by swallowing large quantities of the liquid, which dripped +into the nose and mouth when the sponge was applied, and a lethal +quantity might thus be swallowed. The method was revived, with +various modifications, from time to time, but as often fell into +disuse. As late as 1782 it was sometimes attempted, and in that +year the King of Poland is said to have been completely +anaesthetized and to have recovered, after a painless amputation +had been performed by the surgeons. + +Peter of Abano was one of the first great men produced by the +University of Padua. His fate would have been even more tragic +than that of the shipwrecked Arnald had he not cheated the +purifying fagots of the church by dying opportunely on the eve of +his execution for heresy. But if his spirit had cheated the +fanatics, his body could not, and his bones were burned for his +heresy. He had dared to deny the existence of a devil, and had +suggested that the case of a patient who lay in a trance for +three days might help to explain some miracles, like the raising +of Lazarus. + +His great work was Conciliator Differentiarum, an attempt to +reconcile physicians and philosophers. But his researches were +not confined to medicine, for he seems to have had an inkling of +the hitherto unknown fact that air possesses weight, and his +calculation of the length of the year at three hundred and +sixty-five days, six hours, and four minutes, is exceptionally +accurate for the age in which he lived. He was probably the first +of the Western writers to teach that the brain is the source of +the nerves, and the heart the source of the vessels. From this it +is seen that he was groping in the direction of an explanation of +the circulation of the blood, as demonstrated by Harvey three +centuries later. + +The work of Arnald and Peter of Abano in "reviving" medicine was +continued actively by Mondino (1276-1326) of Bologna, the +"restorer of anatomy," and by Guy of Chauliac: (born about 1300), +the "restorer of surgery." All through the early Middle Ages +dissections of human bodies had been forbidden, and even +dissection of the lower animals gradually fell into disrepute +because physicians detected in such practices were sometimes +accused of sorcery. Before the close of the thirteenth century, +however, a reaction had begun, physicians were protected, and +dissections were occasionally sanctioned by the ruling monarch. +Thus Emperor Frederick H. (1194-1250 A.D.)--whose services to +science we have already had occasion to mention--ordered that at +least one human body should be dissected by physicians in his +kingdom every five years. By the time of Mondino dissections were +becoming more frequent, and he himself is known to have dissected +and demonstrated several bodies. His writings on anatomy have +been called merely plagiarisms of Galen, but in all probability +be made many discoveries independently, and on the whole, his +work may be taken as more advanced than Galen's. His description +of the heart is particularly accurate, and he seems to have come +nearer to determining the course of the blood in its circulation +than any of his predecessors. In this quest he was greatly +handicapped by the prevailing belief in the idea that +blood-vessels must contain air as well as blood, and this led him +to assume that one of the cavities of the heart contained +"spirits," or air. It is probable, however, that his accurate +observations, so far as they went, were helpful stepping-stones +to Harvey in his discovery of the circulation. + +Guy of Chauliac, whose innovations in surgery reestablished that +science on a firm basis, was not only one of the most cultured, +but also the most practical surgeon of his time. He had great +reverence for the works of Galen, Albucasis, and others of his +noted predecessors; but this reverence did not blind him to their +mistakes nor prevent him from using rational methods of treatment +far in advance of theirs. His practicality is shown in some of +his simple but useful inventions for the sick-room, such as the +device of a rope, suspended from the ceiling over the bed, by +which a patient may move himself about more easily; and in some +of his improvements in surgical dressings, such as stiffening +bandages by dipping them in the white of an egg so that they are +held firmly. He treated broken limbs in the suspended cradle +still in use, and introduced the method of making "traction" on a +broken limb by means of a weight and pulley, to prevent deformity +through shortening of the member. He was one of the first +physicians to recognize the utility of spectacles, and +recommended them in cases not amenable to treatment with lotions +and eye-waters. In some of his surgical operations, such as +trephining for fracture of the skull, his technique has been +little improved upon even in modern times. In one of these +operations he successfully removed a portion of a man's brain. + + +Surgery was undoubtedly stimulated greatly at this period by the +constant wars. Lay physicians, as a class, had been looked down +upon during the Dark Ages; but with the beginning of the return +to rationalism, the services of surgeons on the battle-field, to +remove missiles from wounds, and to care for wounds and apply +dressings, came to be more fully appreciated. In return for his +labors the surgeon was thus afforded better opportunities for +observing wounds and diseases, which led naturally to a gradual +improvement in surgical methods. + + +FIFTEENTH-CENTURY MEDICINE + +The thirteenth and fourteenth centuries had seen some slight +advancement in the science of medicine; at least, certain +surgeons and physicians, if not the generality, had made +advances; but it was not until the fifteenth century that the +general revival of medical learning became assured. In this +movement, naturally, the printing-press played an all-important +part. Medical books, hitherto practically inaccessible to the +great mass of physicians, now became common, and this output of +reprints of Greek and Arabic treatises revealed the fact that +many of the supposed true copies were spurious. These discoveries +very naturally aroused all manner of doubt and criticism, which +in turn helped in the development of independent thought. + +A certain manuscript of the great Cornelius Celsus, the De +Medicine, which had been lost for many centuries, was found in +the church of St. Ambrose, at Milan, in 1443, and was at once put +into print. The effect of the publication of this book, which had +lain in hiding for so many centuries, was a revelation, showing +the medical profession how far most of their supposed true copies +of Celsus had drifted away from the original. The indisputable +authenticity of this manuscript, discovered and vouched for by +the man who shortly after became Pope Nicholas V., made its +publication the more impressive. The output in book form of other +authorities followed rapidly, and the manifest discrepancies +between such teachers as Celsus, Hippocrates, Galen, and Pliny +heightened still more the growing spirit of criticism. + +These doubts resulted in great controversies as to the proper +treatment of certain diseases, some physicians following +Hippocrates, others Galen or Celsus, still others the Arabian +masters. One of the most bitter of these contests was over the +question of "revulsion," and "derivation"--that is, whether in +cases of pleurisy treated by bleeding, the venesection should be +made at a point distant from the seat of the disease, as held by +the "revulsionists," or at a point nearer and on the same side of +the body, as practised by the "derivationists." That any great +point for discussion could be raised in the fifteenth or +sixteenth centuries on so simple a matter as it seems to-day +shows how necessary to the progress of medicine was the discovery +of the circulation of the blood made by Harvey two centuries +later. After Harvey's discovery no such discussion could have +been possible, because this discovery made it evident that as far +as the general effect upon the circulation is concerned, it made +little difference whether the bleeding was done near a diseased +part or remote from it. But in the sixteenth century this +question was the all-absorbing one among the doctors. At one time +the faculty of Paris condemned "derivation"; but the supporters +of this method carried the war still higher, and Emperor Charles +V. himself was appealed to. He reversed the decision of the Paris +faculty, and decided in favor of "derivation." His decision was +further supported by Pope Clement VII., although the discussion +dragged on until cut short by Harvey's discovery. + +But a new form of injury now claimed the attention of the +surgeons, something that could be decided by neither Greek nor +Arabian authors, as the treatment of gun-shot wounds was, for +obvious reasons, not given in their writings. About this time, +also, came the great epidemics, "the sweating sickness" and +scurvy; and upon these subjects, also, the Greeks and Arabians +were silent. John of Vigo, in his book, the Practica Copiosa, +published in 1514, and repeated in many editions, became the +standard authority on all these subjects, and thus supplanted the +works of the ancient writers. + +According to Vigo, gun-shot wounds differed from the wounds made +by ordinary weapons--that is, spear, arrow, sword, or axe--in +that the bullet, being round, bruised rather than cut its way +through the tissues; it burned the flesh; and, worst of all, it +poisoned it. Vigo laid especial stress upon treating this last +condition, recommending the use of the cautery or the oil of +elder, boiling hot. It is little wonder that gun-shot wounds were +so likely to prove fatal. Yet, after all, here was the germ of +the idea of antisepsis. + + +NEW BEGINNINGS IN GENERAL SCIENCE + +We have dwelt thus at length on the subject of medical science, +because it was chiefly in this field that progress was made in +the Western world during the mediaeval period, and because these +studies furnished the point of departure for the revival all +along the line. It will be understood, however, from what was +stated in the preceding chapter, that the Arabian influences in +particular were to some extent making themselves felt along other +lines. The opportunity afforded a portion of the Western +world--notably Spain and Sicily --to gain access to the +scientific ideas of antiquity through Arabic translations could +not fail of influence. Of like character, and perhaps even more +pronounced in degree, was the influence wrought by the Byzantine +refugees, who, when Constantinople began to be threatened by the +Turks, migrated to the West in considerable numbers, bringing +with them a knowledge of Greek literature and a large number of +precious works which for centuries had been quite forgotten or +absolutely ignored in Italy. Now Western scholars began to take +an interest in the Greek language, which had been utterly +neglected since the beginning of the Middle Ages. Interesting +stories are told of the efforts made by such men as Cosmo de' +Medici to gain possession of classical manuscripts. The revival +of learning thus brought about had its first permanent influence +in the fields of literature and art, but its effect on science +could not be long delayed. Quite independently of the Byzantine +influence, however, the striving for better intellectual things +had manifested itself in many ways before the close of the +thirteenth century. An illustration of this is found in the +almost simultaneous development of centres of teaching, which +developed into the universities of Italy, France, England, and, a +little later, of Germany. + +The regular list of studies that came to be adopted everywhere +comprised seven nominal branches, divided into two groups--the +so-called quadrivium, comprising music, arithmetic, geometry, and +astronomy; and the trivium comprising grammar, rhetoric, and +logic. The vagueness of implication of some of these branches +gave opportunity to the teacher for the promulgation of almost +any knowledge of which he might be possessed, but there can be no +doubt that, in general, science had but meagre share in the +curriculum. In so far as it was given representation, its chief +field must have been Ptolemaic astronomy. The utter lack of +scientific thought and scientific method is illustrated most +vividly in the works of the greatest men of that period--such men +as Albertus Magnus, Thomas Aquinas, Bonaventura, and the hosts of +other scholastics of lesser rank. Yet the mental awakening +implied in their efforts was sure to extend to other fields, and +in point of fact there was at least one contemporary of these +great scholastics whose mind was intended towards scientific +subjects, and who produced writings strangely at variance in tone +and in content with the others. This anachronistic thinker was +the English monk, Roger Bacon. + + +ROGER BACON + +Bacon was born in 1214 and died in 1292. By some it is held that +he was not appreciated in his own time because he was really a +modern scientist living in an age two centuries before modern +science or methods of modern scientific thinking were known. Such +an estimate, however, is a manifest exaggeration of the facts, +although there is probably a grain of truth in it withal. His +learning certainly brought him into contact with the great +thinkers of the time, and his writings caused him to be +imprisoned by his fellow-churchmen at different times, from which +circumstances we may gather that he was advanced thinker, even if +not a modern scientist. + +Although Bacon was at various times in durance, or under +surveillance, and forbidden to write, he was nevertheless a +marvellously prolific writer, as is shown by the numerous books +and unpublished manuscripts of his still extant. His +master-production was the Opus Majus. In Part IV. of this work he +attempts to show that all sciences rest ultimately on +mathematics; but Part V., which treats of perspective, is of +particular interest to modern scientists, because in this he +discusses reflection and refraction, and the properties of +mirrors and lenses. In this part, also, it is evident that he is +making use of such Arabian writers as Alkindi and Alhazen, and +this is of especial interest, since it has been used by his +detractors, who accuse him of lack of originality, to prove that +his seeming inventions and discoveries were in reality +adaptations of the Arab scientists. It is difficult to determine +just how fully such criticisms are justified. It is certain, +however, that in this part he describes the anatomy of the eye +with great accuracy, and discusses mirrors and lenses. + +The magnifying power of the segment of a glass sphere had been +noted by Alhazen, who had observed also that the magnification +was increased by increasing the size of the segment used. Bacon +took up the discussion of the comparative advantages of segments, +and in this discussion seems to show that he understood how to +trace the progress of the rays of light through a spherical +transparent body, and how to determine the place of the image. He +also described a method of constructing a telescope, but it is by +no means clear that he had ever actually constructed such an +instrument. It is also a mooted question as to whether his +instructions as to the construction of such an instrument would +have enabled any one to construct one. The vagaries of the names +of terms as he uses them allow such latitude in interpretation +that modern scientists are not agreed as to the practicability of +Bacon's suggestions. For example, he constantly refers to force +under such names as virtus, species, imago, agentis, and a score +of other names, and this naturally gives rise to the great +differences in the interpretations of his writings, with +corresponding differences in estimates of them. + +The claim that Bacon originated the use of lenses, in the form of +spectacles, cannot be proven. Smith has determined that as early +as the opening years of the fourteenth century such lenses were +in use, but this proves nothing as regards Bacon's connection +with their invention. The knowledge of lenses seems to be very +ancient, if we may judge from the convex lens of rock crystal +found by Layard in his excavations at Nimrud. There is nothing to +show, however, that the ancients ever thought of using them to +correct defects of vision. Neither, apparently, is it feasible to +determine whether the idea of such an application originated with +Bacon. + +Another mechanical discovery about which there has been a great +deal of discussion is Bacon's supposed invention of gunpowder. It +appears that in a certain passage of his work he describes the +process of making a substance that is, in effect, ordinary +gunpowder; but it is more than doubtful whether he understood the +properties of the substance he describes. It is fairly well +established, however, that in Bacon's time gunpowder was known to +the Arabs, so that it should not be surprising to find references +made to it in Bacon's work, since there is reason to believe that +he constantly consulted Arabian writings. + +The great merit of Bacon's work, however, depends on the +principles taught as regards experiment and the observation of +nature, rather than on any single invention. He had the +all-important idea of breaking with tradition. He championed +unfettered inquiry in every field of thought. He had the instinct +of a scientific worker--a rare instinct indeed in that age. Nor +need we doubt that to the best of his opportunities he was +himself an original investigator. + + +LEONARDO DA VINCI + +The relative infertility of Bacon's thought is shown by the fact +that he founded no school and left no trace of discipleship. The +entire century after his death shows no single European name that +need claim the attention of the historian of science. In the +latter part of the fifteenth century, however, there is evidence +of a renaissance of science no less than of art. The German +Muller became famous under the latinized named of Regio Montanus +(1437-1472), although his actual scientific attainments would +appear to have been important only in comparison with the utter +ignorance of his contemporaries. The most distinguished worker of +the new era was the famous Italian Leonardo da Vinci--a man who +has been called by Hamerton the most universal genius that ever +lived. Leonardo's position in the history of art is known to +every one. With that, of course, we have no present concern; but +it is worth our while to inquire at some length as to the famous +painter's accomplishments as a scientist. + +From a passage in the works of Leonardo, first brought to light +by Venturi,[1] it would seem that the great painter anticipated +Copernicus in determining the movement of the earth. He made +mathematical calculations to prove this, and appears to have +reached the definite conclusion that the earth does move--or what +amounts to the same thing, that the sun does not move. Muntz is +authority for the statement that in one of his writings he +declares, "Il sole non si mouve"--the sun does not move.[2] + +Among his inventions is a dynamometer for determining the +traction power of machines and animals, and his experiments with +steam have led some of his enthusiastic partisans to claim for +him priority to Watt in the invention of the steam-engine. In +these experiments, however, Leonardo seems to have advanced +little beyond Hero of Alexandria and his steam toy. Hero's +steam-engine did nothing but rotate itself by virtue of escaping +jets of steam forced from the bent tubes, while Leonardo's +"steam-engine" "drove a ball weighing one talent over a distance +of six stadia." In a manuscript now in the library of the +Institut de France, Da Vinci describes this engine minutely. The +action of this machine was due to the sudden conversion of small +quantities of water into steam ("smoke," as he called it) by +coming suddenly in contact with a heated surface in a proper +receptacle, the rapidly formed steam acting as a propulsive force +after the manner of an explosive. It is really a steam-gun, +rather than a steam-engine, and it is not unlikely that the study +of the action of gunpowder may have suggested it to Leonardo. + +It is believed that Leonardo is the true discoverer of the +camera-obscura, although the Neapolitan philosopher, Giambattista +Porta, who was not born until some twenty years after the death +of Leonardo, is usually credited with first describing this +device. There is little doubt, however, that Da Vinci understood +the principle of this mechanism, for he describes how such a +camera can be made by cutting a small, round hole through the +shutter of a darkened room, the reversed image of objects outside +being shown on the opposite wall. + +Like other philosophers in all ages, he had observed a great +number of facts which he was unable to explain correctly. But +such accumulations of scientific observations are always +interesting, as showing how many centuries of observation +frequently precede correct explanation. He observed many facts +about sounds, among others that blows struck upon a bell produced +sympathetic sounds in a bell of the same kind; and that striking +the string of a lute produced vibration in corresponding strings +of lutes strung to the same pitch. He knew, also, that sounds +could be heard at a distance at sea by listening at one end of a +tube, the other end of which was placed in the water; and that +the same expedient worked successfully on land, the end of the +tube being placed against the ground. + +The knowledge of this great number of unexplained facts is often +interpreted by the admirers of Da Vinci, as showing an almost +occult insight into science many centuries in advance of his +time. Such interpretations, however, are illusive. The +observation, for example, that a tube placed against the ground +enables one to hear movements on the earth at a distance, is not +in itself evidence of anything more than acute scientific +observation, as a similar method is in use among almost every +race of savages, notably the American Indians. On the other hand, +one is inclined to give credence to almost any story of the +breadth of knowledge of the man who came so near anticipating +Hutton, Lyell, and Darwin in his interpretation of the geological +records as he found them written on the rocks. + +It is in this field of geology that Leonardo is entitled to the +greatest admiration by modern scientists. He had observed the +deposit of fossil shells in various strata of rocks, even on the +tops of mountains, and he rejected once for all the theory that +they had been deposited there by the Deluge. He rightly +interpreted their presence as evidence that they had once been +deposited at the bottom of the sea. This process he assumed bad +taken hundreds and thousands of centuries, thus tacitly rejecting +the biblical tradition as to the date of the creation. + +Notwithstanding the obvious interest that attaches to the +investigations of Leonardo, it must be admitted that his work in +science remained almost as infertile as that of his great +precursor, Bacon. The really stimulative work of this generation +was done by a man of affairs, who knew little of theoretical +science except in one line, but who pursued that one practical +line until he achieved a wonderful result. This man was +Christopher Columbus. It is not necessary here to tell the trite +story of his accomplishment. Suffice it that his practical +demonstration of the rotundity of the earth is regarded by most +modern writers as marking an epoch in history. With the year of +his voyage the epoch of the Middle Ages is usually regarded as +coming to an end. It must not be supposed that any very sudden +change came over the aspect of scholarship of the time, but the +preliminaries of great things had been achieved, and when +Columbus made his famous voyage in 1492, the man was already +alive who was to bring forward the first great vitalizing thought +in the field of pure science that the Western world had +originated for more than a thousand years. This man bore the name +of Kopernik, or in its familiar Anglicized form, Copernicus. His +life work and that of his disciples will claim our attention in +the succeeding chapter. + + + +IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +We have seen that the Ptolemaic astronomy, which was the accepted +doctrine throughout the Middle Ages, taught that the earth is +round. Doubtless there was a popular opinion current which +regarded the earth as flat, but it must be understood that this +opinion had no champions among men of science during the Middle +Ages. When, in the year 1492, Columbus sailed out to the west on +his memorable voyage, his expectation of reaching India had full +scientific warrant, however much it may have been scouted by +certain ecclesiastics and by the average man of the period. +Nevertheless, we may well suppose that the successful voyage of +Columbus, and the still more demonstrative one made about thirty +years later by Magellan, gave the theory of the earth's rotundity +a certainty it could never previously have had. Alexandrian +geographers had measured the size of the earth, and had not +hesitated to assert that by sailing westward one might reach +India. But there is a wide gap between theory and practice, and +it required the voyages of Columbus and his successors to bridge +that gap. + +After the companions of Magellan completed the circumnavigation +of the globe, the general shape of our earth would, obviously, +never again be called in question. But demonstration of the +sphericity of the earth had, of course, no direct bearing upon +the question of the earth's position in the universe. Therefore +the voyage of Magellan served to fortify, rather than to dispute, +the Ptolemaic theory. According to that theory, as we have seen, +the earth was supposed to lie immovable at the centre of the +universe; the various heavenly bodies, including the sun, +revolving about it in eccentric circles. We have seen that +several of the ancient Greeks, notably Aristarchus, disputed this +conception, declaring for the central position of the sun in the +universe, and the motion of the earth and other planets about +that body. But this revolutionary theory seemed so opposed to the +ordinary observation that, having been discountenanced by +Hipparchus and Ptolemy, it did not find a single important +champion for more than a thousand years after the time of the +last great Alexandrian astronomer. + +The first man, seemingly, to hark back to the Aristarchian +conception in the new scientific era that was now dawning was the +noted cardinal, Nikolaus of Cusa, who lived in the first half of +the fifteenth century, and was distinguished as a philosophical +writer and mathematician. His De Docta Ignorantia expressly +propounds the doctrine of the earth's motion. No one, however, +paid the slightest attention to his suggestion, which, therefore, +merely serves to furnish us with another interesting illustration +of the futility of propounding even a correct hypothesis before +the time is ripe to receive it--particularly if the hypothesis is +not fully fortified by reasoning based on experiment or +observation. + +The man who was destined to put forward the theory of the earth's +motion in a way to command attention was born in 1473, at the +village of Thorn, in eastern Prussia. His name was Nicholas +Copernicus. There is no more famous name in the entire annals of +science than this, yet posterity has never been able fully to +establish the lineage of the famous expositor of the true +doctrine of the solar system. The city of Thorn lies in a +province of that border territory which was then under control of +Poland, but which subsequently became a part of Prussia. It is +claimed that the aspects of the city were essentially German, and +it is admitted that the mother of Copernicus belonged to that +race. The nationality of the father is more in doubt, but it is +urged that Copernicus used German as his mother-tongue. His great +work was, of course, written in Latin, according to the custom of +the time; but it is said that, when not employing that language, +he always wrote in German. The disputed nationality of Copernicus +strongly suggests that he came of a mixed racial lineage, and we +are reminded again of the influences of those ethnical minglings +to which we have previously more than once referred. The +acknowledged centres of civilization towards the close of the +fifteenth century were Italy and Spain. Therefore, the birthplace +of Copernicus lay almost at the confines of civilization, +reminding us of that earlier period when Greece was the centre of +culture, but when the great Greek thinkers were born in Asia +Minor and in Italy. + +As a young man, Copernicus made his way to Vienna to study +medicine, and subsequently he journeyed into Italy and remained +there many years, About the year 1500 he held the chair of +mathematics in a college at Rome. Subsequently he returned to his +native land and passed his remaining years there, dying at +Domkerr, in Frauenburg, East Prussia, in the year 1543. + +It would appear that Copernicus conceived the idea of the +heliocentric system of the universe while he was a comparatively +young man, since in the introduction to his great work, which he +addressed to Pope Paul III., he states that he has pondered his +system not merely nine years, in accordance with the maxim of +Horace, but well into the fourth period of nine years. Throughout +a considerable portion of this period the great work of +Copernicus was in manuscript, but it was not published until the +year of his death. The reasons for the delay are not very fully +established. Copernicus undoubtedly taught his system throughout +the later decades of his life. He himself tells us that he had +even questioned whether it were not better for him to confine +himself to such verbal teaching, following thus the example of +Pythagoras. Just as his life was drawing to a close, he decided +to pursue the opposite course, and the first copy of his work is +said to have been placed in his hands as he lay on his deathbed. + +The violent opposition which the new system met from +ecclesiastical sources led subsequent commentators to suppose +that Copernicus had delayed publication of his work through fear +of the church authorities. There seems, however, to be no direct +evidence for this opinion. It has been thought significant that +Copernicus addressed his work to the pope. It is, of course, +quite conceivable that the aged astronomer might wish by this +means to demonstrate that he wrote in no spirit of hostility to +the church. His address to the pope might have been considered as +a desirable shield precisely because the author recognized that +his work must needs meet with ecclesiastical criticism. Be that +as it may, Copernicus was removed by death from the danger of +attack, and it remained for his disciples of a later generation +to run the gauntlet of criticism and suffer the charges of +heresy. + +The work of Copernicus, published thus in the year 1543 at +Nuremberg, bears the title De Orbium Coelestium Revolutionibus. + +It is not necessary to go into details as to the cosmological +system which Copernicus advocated, since it is familiar to every +one. In a word, he supposed the sun to be the centre of all the +planetary motions, the earth taking its place among the other +planets, the list of which, as known at that time, comprised +Mercury, Venus, the Earth, Mars, Jupiter, and Saturn. The fixed +stars were alleged to be stationary, and it was necessary to +suppose that they are almost infinitely distant, inasmuch as they +showed to the observers of that time no parallax; that is to say, +they preserved the same apparent position when viewed from the +opposite points of the earth's orbit. + +But let us allow Copernicus to speak for himself regarding his +system, His exposition is full of interest. We quote first the +introduction just referred to, in which appeal is made directly +to the pope. + +"I can well believe, most holy father, that certain people, when +they hear of my attributing motion to the earth in these books of +mine, will at once declare that such an opinion ought to be +rejected. Now, my own theories do not please me so much as not to +consider what others may judge of them. Accordingly, when I began +to reflect upon what those persons who accept the stability of +the earth, as confirmed by the opinion of many centuries, would +say when I claimed that the earth moves, I hesitated for a long +time as to whether I should publish that which I have written to +demonstrate its motion, or whether it would not be better to +follow the example of the Pythagoreans, who used to hand down the +secrets of philosophy to their relatives and friends only in oral +form. As I well considered all this, I was almost impelled to put +the finished work wholly aside, through the scorn I had reason to +anticipate on account of the newness and apparent contrariness to +reason of my theory. + +"My friends, however, dissuaded me from such a course and +admonished me that I ought to publish my book, which had lain +concealed in my possession not only nine years, but already into +four times the ninth year. Not a few other distinguished and very +learned men asked me to do the same thing, and told me that I +ought not, on account of my anxiety, to delay any longer in +consecrating my work to the general service of mathematicians. + +"But your holiness will perhaps not so much wonder that I have +dared to bring the results of my night labors to the light of +day, after having taken so much care in elaborating them, but is +waiting instead to hear how it entered my mind to imagine that +the earth moved, contrary to the accepted opinion of +mathematicians--nay, almost contrary to ordinary human +understanding. Therefore I will not conceal from your holiness +that what moved me to consider another way of reckoning the +motions of the heavenly bodies was nothing else than the fact +that the mathematicians do not agree with one another in their +investigations. In the first place, they are so uncertain about +the motions of the sun and moon that they cannot find out the +length of a full year. In the second place, they apply neither +the same laws of cause and effect, in determining the motions of +the sun and moon and of the five planets, nor the same proofs. +Some employ only concentric circles, others use eccentric and +epicyclic ones, with which, however, they do not fully attain the +desired end. They could not even discover nor compute the main +thing--namely, the form of the universe and the symmetry of its +parts. It was with them as if some should, from different places, +take hands, feet, head, and other parts of the body, which, +although very beautiful, were not drawn in their proper +relations, and, without making them in any way correspond, should +construct a monster instead of a human being. + +"Accordingly, when I had long reflected on this uncertainty of +mathematical tradition, I took the trouble to read again the +books of all the philosophers I could get hold of, to see if some +one of them had not once believed that there were other motions +of the heavenly bodies. First I found in Cicero that Niceties had +believed in the motion of the earth. Afterwards I found in +Plutarch, likewise, that some others had held the same opinion. +This induced me also to begin to consider the movability of the +earth, and, although the theory appeared contrary to reason, I +did so because I knew that others before me had been allowed to +assume rotary movements at will, in order to explain the +phenomena of these celestial bodies. I was of the opinion that I, +too, might be permitted to see whether, by presupposing motion in +the earth, more reliable conclusions than hitherto reached could +not be discovered for the rotary motions of the spheres. And +thus, acting on the hypothesis of the motion which, in the +following book, I ascribe to the earth, and by long and continued +observations, I have finally discovered that if the motion of the +other planets be carried over to the relation of the earth and +this is made the basis for the rotation of every star, not only +will the phenomena of the planets be explained thereby, but also +the laws and the size of the stars; all their spheres and the +heavens themselves will appear so harmoniously connected that +nothing could be changed in any part of them without confusion in +the remaining parts and in the whole universe. I do not doubt +that clever and learned men will agree with me if they are +willing fully to comprehend and to consider the proofs which I +advance in the book before us. In order, however, that both the +learned and the unlearned may see that I fear no man's judgment, +I wanted to dedicate these, my night labors, to your holiness, +rather than to any one else, because you, even in this remote +corner of the earth where I live, are held to be the greatest in +dignity of station and in love for all sciences and for +mathematics, so that you, through your position and judgment, can +easily suppress the bites of slanderers, although the proverb +says that there is no remedy against the bite of calumny." + + +In chapter X. of book I., "On the Order of the Spheres," occurs a +more detailed presentation of the system, as follows: + +"That which Martianus Capella, and a few other Latins, very well +knew, appears to me extremely noteworthy. He believed that Venus +and Mercury revolve about the sun as their centre and that they +cannot go farther away from it than the circles of their orbits +permit, since they do not revolve about the earth like the other +planets. According to this theory, then, Mercury's orbit would be +included within that of Venus, which is more than twice as great, +and would find room enough within it for its revolution. + +"If, acting upon this supposition, we connect Saturn, Jupiter, +and Mars with the same centre, keeping in mind the greater extent +of their orbits, which include the earth's sphere besides those +of Mercury and Venus, we cannot fail to see the explanation of +the regular order of their motions. He is certain that Saturn, +Jupiter, and Mars are always nearest the earth when they rise in +the evening--that is, when they appear over against the sun, or +the earth stands between them and the sun--but that they are +farthest from the earth when they set in the evening--that is, +when we have the sun between them and the earth. This proves +sufficiently that their centre belongs to the sun and is the same +about which the orbits of Venus and Mercury circle. Since, +however, all have one centre, it is necessary for the space +intervening between the orbits of Venus and Mars to include the +earth with her accompanying moon and all that is beneath the +moon; for the moon, which stands unquestionably nearest the +earth, can in no way be separated from her, especially as there +is sufficient room for the moon in the aforesaid space. Hence we +do not hesitate to claim that the whole system, which includes +the moon with the earth for its centre, makes the round of that +great circle between the planets, in yearly motion about the sun, +and revolves about the centre of the universe, in which the sun +rests motionless, and that all which looks like motion in the sun +is explained by the motion of the earth. The extent of the +universe, however, is so great that, whereas the distance of the +earth from the sun is considerable in comparison with the size of +the other planetary orbits, it disappears when compared with the +sphere of the fixed stars. I hold this to be more easily +comprehensible than when the mind is confused by an almost +endless number of circles, which is necessarily the case with +those who keep the earth in the middle of the universe. Although +this may appear incomprehensible and contrary to the opinion of +many, I shall, if God wills, make it clearer than the sun, at +least to those who are not ignorant of mathematics. + +"The order of the spheres is as follows: The first and lightest +of all the spheres is that of the fixed stars, which includes +itself and all others, and hence is motionless as the place in +the universe to which the motion and position of all other stars +is referred. + +"Then follows the outermost planet, Saturn, which completes its +revolution around the sun in thirty years; next comes Jupiter +with a twelve years' revolution; then Mars, which completes its +course in two years. The fourth one in order is the yearly +revolution which includes the earth with the moon's orbit as an +epicycle. In the fifth place is Venus with a revolution of nine +months. The sixth place is taken by Mercury, which completes its +course in eighty days. In the middle of all stands the sun, and +who could wish to place the lamp of this most beautiful temple in +another or better place. Thus, in fact, the sun, seated upon the +royal throne, controls the family of the stars which circle +around him. We find in their order a harmonious connection which +cannot be found elsewhere. Here the attentive observer can see +why the waxing and waning of Jupiter seems greater than with +Saturn and smaller than with Mars, and again greater with Venus +than with Mercury. Also, why Saturn, Jupiter, and Mars are nearer +to the earth when they rise in the evening than when they +disappear in the rays of the sun. More prominently, however, is +it seen in the case of Mars, which when it appears in the heavens +at night, seems to equal Jupiter in size, but soon afterwards is +found among the stars of second magnitude. All of this results +from the same cause--namely, from the earth's motion. The fact +that nothing of this is to be seen in the case of the fixed stars +is a proof of their immeasurable distance, which makes even the +orbit of yearly motion or its counterpart invisible to us."[1] + + +The fact that the stars show no parallax had been regarded as an +important argument against the motion of the earth, and it was +still so considered by the opponents of the system of Copernicus. +It had, indeed, been necessary for Aristarchus to explain the +fact as due to the extreme distance of the stars; a perfectly +correct explanation, but one that implies distances that are +altogether inconceivable. It remained for nineteenth-century +astronomers to show, with the aid of instruments of greater +precision, that certain of the stars have a parallax. But long +before this demonstration had been brought forward, the system of +Copernicus had been accepted as a part of common knowledge. + +While Copernicus postulated a cosmical scheme that was correct as +to its main features, he did not altogether break away from +certain defects of the Ptolemaic hypothesis. Indeed, he seems to +have retained as much of this as practicable, in deference to the +prejudice of his time. Thus he records the planetary orbits as +circular, and explains their eccentricities by resorting to the +theory of epicycles, quite after the Ptolemaic method. But now, +of course, a much more simple mechanism sufficed to explain the +planetary motions, since the orbits were correctly referred to +the central sun and not to the earth. + +Needless to say, the revolutionary conception of Copernicus did +not meet with immediate acceptance. A number of prominent +astronomers, however, took it up almost at once, among these +being Rhaeticus, who wrote a commentary on the evolutions; +Erasmus Reinhold, the author of the Prutenic tables; Rothmann, +astronomer to the Landgrave of Hesse, and Maestlin, the +instructor of Kepler. The Prutenic tables, just referred to, so +called because of their Prussian origin, were considered an +improvement on the tables of Copernicus, and were highly esteemed +by the astronomers of the time. The commentary of Rhaeticus gives +us the interesting information that it was the observation of the +orbit of Mars and of the very great difference between his +apparent diameters at different times which first led Copernicus +to conceive the heliocentric idea. Of Reinhold it is recorded +that he considered the orbit of Mercury elliptical, and that he +advocated a theory of the moon, according to which her epicycle +revolved on an elliptical orbit, thus in a measure anticipating +one of the great discoveries of Kepler to which we shall refer +presently. The Landgrave of Hesse was a practical astronomer, who +produced a catalogue of fixed stars which has been compared with +that of Tycho Brahe. He was assisted by Rothmann and by Justus +Byrgius. Maestlin, the preceptor of Kepler, is reputed to have +been the first modern observer to give a correct explanation of +the light seen on portions of the moon not directly illumined by +the sun. He explained this as not due to any proper light of the +moon itself, but as light reflected from the earth. Certain of +the Greek philosophers, however, are said to have given the same +explanation, and it is alleged also that Leonardo da Vinci +anticipated Maestlin in this regard.[2] + +While, various astronomers of some eminence thus gave support to +the Copernican system, almost from the beginning, it +unfortunately chanced that by far the most famous of the +immediate successors of Copernicus declined to accept the theory +of the earth's motion. This was Tycho Brahe, one of the greatest +observing astronomers of any age. Tycho Brahe was a Dane, born at +Knudstrup in the year 1546. He died in 1601 at Prague, in +Bohemia. During a considerable portion of his life he found a +patron in Frederick, King of Denmark, who assisted him to build a +splendid observatory on the Island of Huene. On the death of his +patron Tycho moved to Germany, where, as good luck would have it, +he came in contact with the youthful Kepler, and thus, no doubt, +was instrumental in stimulating the ambitions of one who in later +years was to be known as a far greater theorist than himself. As +has been said, Tycho rejected the Copernican theory of the +earth's motion. It should be added, however, that he accepted +that part of the Copernican theory which makes the sun the centre +of all the planetary motions, the earth being excepted. He thus +developed a system of his own, which was in some sort a +compromise between the Ptolemaic and the Copernican systems. As +Tycho conceived it, the sun revolves about the earth, carrying +with it the planets-Mercury, Venus, Mars, Jupiter, and Saturn, +which planets have the sun and not the earth as the centre of +their orbits. This cosmical scheme, it should be added, may be +made to explain the observed motions of the heavenly bodies, but +it involves a much more complex mechanism than is postulated by +the Copernican theory. + +Various explanations have been offered of the conservatism which +held the great Danish astronomer back from full acceptance of the +relatively simple and, as we now know, correct Copernican +doctrine. From our latter-day point of view, it seems so much +more natural to accept than to reject the Copernican system, that +we find it difficult to put ourselves in the place of a +sixteenth-century observer. Yet if we recall that the traditional +view, having warrant of acceptance by nearly all thinkers of +every age, recorded the earth as a fixed, immovable body, we +shall see that our surprise should be excited rather by the +thinker who can break away from this view than by the one who +still tends to cling to it. + +Moreover, it is useless to attempt to disguise the fact that +something more than a mere vague tradition was supposed to +support the idea of the earth's overshadowing importance in the +cosmical scheme. The sixteenth-century mind was overmastered by +the tenets of ecclesiasticism, and it was a dangerous heresy to +doubt that the Hebrew writings, upon which ecclesiasticism based +its claim, contained the last word regarding matters of science. +But the writers of the Hebrew text had been under the influence +of that Babylonian conception of the universe which accepted the +earth as unqualifiedly central--which, indeed, had never so much +as conceived a contradictory hypothesis; and so the Western +world, which had come to accept these writings as actually +supernatural in origin, lay under the spell of Oriental ideas of +a pre-scientific era. In our own day, no one speaking with +authority thinks of these Hebrew writings as having any +scientific weight whatever. Their interest in this regard is +purely antiquarian; hence from our changed point of view it seems +scarcely credible that Tycho Brahe can have been in earnest when +he quotes the Hebrew traditions as proof that the sun revolves +about the earth. Yet we shall see that for almost three centuries +after the time of Tycho, these same dreamings continued to be +cited in opposition to those scientific advances which new +observations made necessary; and this notwithstanding the fact +that the Oriental phrasing is, for the most part, poetically +ambiguous and susceptible of shifting interpretations, as the +criticism of successive generations has amply testified. + +As we have said, Tycho Brahe, great observer as he was, could not +shake himself free from the Oriental incubus. He began his +objections, then, to the Copernican system by quoting the adverse +testimony of a Hebrew prophet who lived more than a thousand +years B.C. All of this shows sufficiently that Tycho Brahe was +not a great theorist. He was essentially an observer, but in this +regard he won a secure place in the very first rank. Indeed, he +was easily the greatest observing astronomer since Hipparchus, +between whom and himself there were many points of resemblance. +Hipparchus, it will be recalled, rejected the Aristarchian +conception of the universe just as Tycho rejected the conception +of Copernicus. + +But if Tycho propounded no great generalizations, the list of +specific advances due to him is a long one, and some of these +were to prove important aids in the hands of later workers to the +secure demonstration of the Copernican idea. One of his most +important series of studies had to do with comets. Regarding +these bodies there had been the greatest uncertainty in the minds +of astronomers. The greatest variety of opinions regarding them +prevailed; they were thought on the one hand to be divine +messengers, and on the other to be merely igneous phenomena of +the earth's atmosphere. Tycho Brahe declared that a comet which +he observed in the year 1577 had no parallax, proving its extreme +distance. The observed course of the comet intersected the +planetary orbits, which fact gave a quietus to the long-mooted +question as to whether the Ptolemaic spheres were transparent +solids or merely imaginary; since the comet was seen to intersect +these alleged spheres, it was obvious that they could not be the +solid substance that they were commonly imagined to be, and this +fact in itself went far towards discrediting the Ptolemaic +system. It should be recalled, however, that this supposition of +tangible spheres for the various planetary and stellar orbits was +a mediaeval interpretation of Ptolemy's theory rather than an +interpretation of Ptolemy himself, there being nothing to show +that the Alexandrian astronomer regarded his cycles and epicycles +as other than theoretical. + +An interesting practical discovery made by Tycho was his method +of determining the latitude of a place by means of two +observations made at an interval of twelve hours. Hitherto it had +been necessary to observe the sun's angle on the equinoctial +days, a period of six months being therefore required. Tycho +measured the angle of elevation of some star situated near the +pole, when on the meridian, and then, twelve hours later, +measured the angle of elevation of the same star when it again +came to the meridian at the opposite point of its apparent circle +about the polestar. Half the sum of these angles gives the +latitude of the place of observation. + +As illustrating the accuracy of Tycho's observations, it may be +noted that he rediscovered a third inequality of the moon's +motion at its variation, he, in common with other European +astronomers, being then quite unaware that this inequality had +been observed by an Arabian astronomer. Tycho proved also that +the angle of inclination of the moon's orbit to the ecliptic is +subject to slight variation. + +The very brilliant new star which shone forth suddenly in the +constellation of Cassiopeia in the year 1572, was made the object +of special studies by Tycho, who proved that the star had no +sensible parallax and consequently was far beyond the planetary +regions. The appearance of a new star was a phenomenon not +unknown to the ancients, since Pliny records that Hipparchus was +led by such an appearance to make his catalogue of the fixed +stars. But the phenomenon is sufficiently uncommon to attract +unusual attention. A similar phenomenon occurred in the year +1604, when the new star--in this case appearing in the +constellation of Serpentarius--was explained by Kepler as +probably proceeding from a vast combustion. This explanation--in +which Kepler is said to have followed. Tycho--is fully in accord +with the most recent theories on the subject, as we shall see in +due course. It is surprising to hear Tycho credited with so +startling a theory, but, on the other hand, such an explanation +is precisely what should be expected from the other astronomer +named. For Johann Kepler, or, as he was originally named, Johann +von Kappel, was one of the most speculative astronomers of any +age. He was forever theorizing, but such was the peculiar quality +of his mind that his theories never satisfied him for long unless +he could put them to the test of observation. Thanks to this +happy combination of qualities, Kepler became the discoverer of +three famous laws of planetary motion which lie at the very +foundation of modern astronomy, and which were to be largely +instrumental in guiding Newton to his still greater +generalization. These laws of planetary motion were vastly +important as corroborating the Copernican theory of the universe, +though their position in this regard was not immediately +recognized by contemporary thinkers. Let us examine with some +detail into their discovery, meantime catching a glimpse of the +life history of the remarkable man whose name they bear. + + +JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION + +Johann Kepler was born the 27th of December, 1571, in the little +town of Weil, in Wurtemburg. He was a weak, sickly child, further +enfeebled by a severe attack of small-pox. It would seem +paradoxical to assert that the parents of such a genius were +mismated, but their home was not a happy one, the mother being of +a nervous temperament, which perhaps in some measure accounted +for the genius of the child. The father led the life of a +soldier, and finally perished in the campaign against the Turks. +Young Kepler's studies were directed with an eye to the ministry. +After a preliminary training he attended the university at +Tubingen, where he came under the influence of the celebrated +Maestlin and became his life-long friend. + +Curiously enough, it is recorded that at first Kepler had no +taste for astronomy or for mathematics. But the doors of the +ministry being presently barred to him, he turned with enthusiasm +to the study of astronomy, being from the first an ardent +advocate of the Copernican system. His teacher, Maestlin, +accepted the same doctrine, though he was obliged, for +theological reasons, to teach the Ptolemaic system, as also to +oppose the Gregorian reform of the calendar. + +The Gregorian calendar, it should be explained, is so called +because it was instituted by Pope Gregory XIII., who put it into +effect in the year 1582, up to which time the so-called Julian +calendar, as introduced by Julius Caesar, had been everywhere +accepted in Christendom. This Julian calendar, as we have seen, +was a great improvement on preceding ones, but still lacked +something of perfection inasmuch as its theoretical day differed +appreciably from the actual day. In the course of fifteen hundred +years, since the time of Caesar, this defect amounted to a +discrepancy of about eleven days. Pope Gregory proposed to +correct this by omitting ten days from the calendar, which was +done in September, 1582. To prevent similar inaccuracies in the +future, the Gregorian calendar provided that once in four +centuries the additional day to make a leap-year should be +omitted, the date selected for such omission being the last year +of every fourth century. Thus the years 1500, 1900, and 2300, +A.D., would not be leap-years. By this arrangement an approximate +rectification of the calendar was effected, though even this does +not make it absolutely exact. + +Such a rectification as this was obviously desirable, but there +was really no necessity for the omission of the ten days from the +calendar. The equinoctial day had shifted so that in the year +1582 it fell on the 10th of March and September. There was no +reason why it should not have remained there. It would greatly +have simplified the task of future historians had Gregory +contented himself with providing for the future stability of the +calendar without making the needless shift in question. We are so +accustomed to think of the 21st of March and 21st of September as +the natural periods of the equinox, that we are likely to forget +that these are purely arbitrary dates for which the 10th might +have been substituted without any inconvenience or inconsistency. + +But the opposition to the new calendar, to which reference has +been made, was not based on any such considerations as these. It +was due, largely at any rate, to the fact that Germany at this +time was under sway of the Lutheran revolt against the papacy. So +effective was the opposition that the Gregorian calendar did not +come into vogue in Germany until the year 1699. It may be added +that England, under stress of the same manner of prejudice, held +out against the new reckoning until the year 1751, while Russia +does not accept it even now. + +As the Protestant leaders thus opposed the papal attitude in a +matter of so practical a character as the calendar, it might +perhaps have been expected that the Lutherans would have had a +leaning towards the Copernican theory of the universe, since this +theory was opposed by the papacy. Such, however, was not the +case. Luther himself pointed out with great strenuousness, as a +final and demonstrative argument, the fact that Joshua commanded +the sun and not the earth to stand still; and his followers were +quite as intolerant towards the new teaching as were their +ultramontane opponents. Kepler himself was, at various times, to +feel the restraint of ecclesiastical opposition, though he was +never subjected to direct persecution, as was his friend and +contemporary, Galileo. At the very outset of Kepler's career +there was, indeed, question as to the publication of a work he +had written, because that work took for granted the truth of the +Copernican doctrine. This work appeared, however, in the year +1596. It bore the title Mysterium Cosmographium, and it attempted +to explain the positions of the various planetary bodies. +Copernicus had devoted much time to observation of the planets +with reference to measuring their distance, and his efforts had +been attended with considerable success. He did not, indeed, know +the actual distance of the sun, and, therefore, was quite unable +to fix the distance of any planet; but, on the other hand, he +determined the relative distance of all the planets then known, +as measured in terms of the sun's distance, with remarkable +accuracy. + +With these measurements as a guide, Kepler was led to a very +fanciful theory, according to which the orbits of the five +principal planets sustain a peculiar relation to the five regular +solids of geometry. His theory was this: "Around the orbit of the +earth describe a dodecahedron--the circle comprising it will be +that of Mars; around Mars describe a tetrahedron--the circle +comprising it will be that of Jupiter; around Jupiter describe a +cube--the circle comprising it will be that of Saturn; now within +the earth's orbit inscribe an icosahedron--the inscribed circle +will be that of Venus; in the orbit of Venus inscribe an +octahedron --the circle inscribed will be that of Mercury."[3] + +Though this arrangement was a fanciful one, which no one would +now recall had not the theorizer obtained subsequent fame on more +substantial grounds, yet it evidenced a philosophical spirit on +the part of the astronomer which, misdirected as it was in this +instance, promised well for the future. Tycho Brahe, to whom a +copy of the work was sent, had the acumen to recognize it as a +work of genius. He summoned the young astronomer to be his +assistant at Prague, and no doubt the association thus begun was +instrumental in determining the character of Kepler's future +work. It was precisely the training in minute observation that +could avail most for a mind which, like Kepler's, tended +instinctively to the formulation of theories. When Tycho Brahe +died, in 1601, Kepler became his successor. In due time he +secured access to all the unpublished observations of his great +predecessor, and these were of inestimable value to him in the +progress of his own studies. + +Kepler was not only an ardent worker and an enthusiastic +theorizer, but he was an indefatigable writer, and it pleased him +to take the public fully into his confidence, not merely as to +his successes, but as to his failures. Thus his works elaborate +false theories as well as correct ones, and detail the +observations through which the incorrect guesses were refuted by +their originator. Some of these accounts are highly interesting, +but they must not detain us here. For our present purpose it must +suffice to point out the three important theories, which, as +culled from among a score or so of incorrect ones, Kepler was +able to demonstrate to his own satisfaction and to that of +subsequent observers. Stated in a few words, these theories, +which have come to bear the name of Kepler's Laws, are the +following: + +1. That the planetary orbits are not circular, but elliptical, +the sun occupying one focus of the ellipses. + +2. That the speed of planetary motion varies in different parts +of the orbit in such a way that an imaginary line drawn from the +sun to the planet--that is to say, the radius vector of the +planet's orbit--always sweeps the same area in a given time. + + +These two laws Kepler published as early as 1609. Many years more +of patient investigation were required before he found out the +secret of the relation between planetary distances and times of +revolution which his third law expresses. In 1618, however, he +was able to formulate this relation also, as follows: + +3. The squares of the distance of the various planets from the +sun are proportional to the cubes of their periods of revolution +about the sun. + + +All these laws, it will be observed, take for granted the fact +that the sun is the centre of the planetary orbits. It must be +understood, too, that the earth is constantly regarded, in +accordance with the Copernican system, as being itself a member +of the planetary system, subject to precisely the same laws as +the other planets. Long familiarity has made these wonderful laws +of Kepler seem such a matter of course that it is difficult now +to appreciate them at their full value. Yet, as has been already +pointed out, it was the knowledge of these marvellously simple +relations between the planetary orbits that laid the foundation +for the Newtonian law of universal gravitation. Contemporary +judgment could not, of course, anticipate this culmination of a +later generation. What it could understand was that the first law +of Kepler attacked one of the most time-honored of metaphysical +conceptions--namely, the Aristotelian idea that the circle is the +perfect figure, and hence that the planetary orbits must be +circular. Not even Copernicus had doubted the validity of this +assumption. That Kepler dared dispute so firmly fixed a belief, +and one that seemingly had so sound a philosophical basis, +evidenced the iconoclastic nature of his genius. That he did not +rest content until he had demonstrated the validity of his +revolutionary assumption shows how truly this great theorizer +made his hypotheses subservient to the most rigid inductions. + + +GALILEO GALILEI + +While Kepler was solving these riddles of planetary motion, there +was an even more famous man in Italy whose championship of the +Copernican doctrine was destined to give the greatest possible +publicity to the new ideas. This was Galileo Galilei, one of the +most extraordinary scientific observers of any age. Galileo was +born at Pisa, on the 18th of February (old style), 1564. The day +of his birth is doubly memorable, since on the same day the +greatest Italian of the preceding epoch, Michael Angelo, breathed +his last. Persons fond of symbolism have found in the coincidence +a forecast of the transit from the artistic to the scientific +epoch of the later Renaissance. Galileo came of an impoverished +noble family. He was educated for the profession of medicine, but +did not progress far before his natural proclivities directed him +towards the physical sciences. Meeting with opposition in Pisa, +he early accepted a call to the chair of natural philosophy in +the University of Padua, and later in life he made his home at +Florence. The mechanical and physical discoveries of Galileo will +claim our attention in another chapter. Our present concern is +with his contribution to the Copernican theory. + +Galileo himself records in a letter to Kepler that he became a +convert to this theory at an early day. He was not enabled, +however, to make any marked contribution to the subject, beyond +the influence of his general teachings, until about the year +1610. The brilliant contributions which he made were due largely +to a single discovery--namely, that of the telescope. Hitherto +the astronomical observations had been made with the unaided eye. +Glass lenses had been known since the thirteenth century, but, +until now, no one had thought of their possible use as aids to +distant vision. The question of priority of discovery has never +been settled. It is admitted, however, that the chief honors +belong to the opticians of the Netherlands. + +As early as the year 1590 the Dutch optician Zacharias Jensen +placed a concave and a convex lens respectively at the ends of a +tube about eighteen inches long, and used this instrument for the +purpose of magnifying small objects--producing, in short, a crude +microscope. Some years later, Johannes Lippershey, of whom not +much is known except that he died in 1619, experimented with a +somewhat similar combination of lenses, and made the startling +observation that the weather-vane on a distant church-steeple +seemed to be brought much nearer when viewed through the lens. +The combination of lenses he employed is that still used in the +construction of opera-glasses; the Germans still call such a +combination a Dutch telescope. + +Doubtless a large number of experimenters took the matter up and +the fame of the new instrument spread rapidly abroad. Galileo, +down in Italy, heard rumors of this remarkable contrivance, +through the use of which it was said "distant objects might be +seen as clearly as those near at hand." He at once set to work to +construct for himself a similar instrument, and his efforts were +so far successful that at first he "saw objects three times as +near and nine times enlarged." Continuing his efforts, he +presently so improved his glass that objects were enlarged almost +a thousand times and made to appear thirty times nearer than when +seen with the naked eye. Naturally enough, Galileo turned this +fascinating instrument towards the skies, and he was almost +immediately rewarded by several startling discoveries. At the +very outset, his magnifying-glass brought to view a vast number +of stars that are invisible to the naked eye, and enabled the +observer to reach the conclusion that the hazy light of the Milky +Way is merely due to the aggregation of a vast number of tiny +stars. + +Turning his telescope towards the moon, Galileo found that body +rough and earth-like in contour, its surface covered with +mountains, whose height could be approximately measured through +study of their shadows. This was disquieting, because the current +Aristotelian doctrine supposed the moon, in common with the +planets, to be a perfectly spherical, smooth body. The +metaphysical idea of a perfect universe was sure to be disturbed +by this seemingly rough workmanship of the moon. Thus far, +however, there was nothing in the observations of Galileo to bear +directly upon the Copernican theory; but when an inspection was +made of the planets the case was quite different. With the aid of +his telescope, Galileo saw that Venus, for example, passes +through phases precisely similar to those of the moon, due, of +course, to the same cause. Here, then, was demonstrative evidence +that the planets are dark bodies reflecting the light of the sun, +and an explanation was given of the fact, hitherto urged in +opposition to the Copernican theory, that the inferior planets do +not seem many times brighter when nearer the earth than when in +the most distant parts of their orbits; the explanation being, of +course, that when the planets are between the earth and the sun +only a small portion of their illumined surfaces is visible from +the earth. + +On inspecting the planet Jupiter, a still more striking +revelation was made, as four tiny stars were observed to occupy +an equatorial position near that planet, and were seen, when +watched night after night, to be circling about the planet, +precisely as the moon circles about the earth. Here, obviously, +was a miniature solar system--a tangible object-lesson in the +Copernican theory. In honor of the ruling Florentine house of the +period, Galileo named these moons of Jupiter, Medicean stars. + +Turning attention to the sun itself, Galileo observed on the +surface of that luminary a spot or blemish which gradually +changed its shape, suggesting that changes were taking place in +the substance of the sun--changes obviously incompatible with the +perfect condition demanded by the metaphysical theorists. But +however disquieting for the conservative, the sun's spots served +a most useful purpose in enabling Galileo to demonstrate that the +sun itself revolves on its axis, since a given spot was seen to +pass across the disk and after disappearing to reappear in due +course. The period of rotation was found to be about twenty-four +days. + +It must be added that various observers disputed priority of +discovery of the sun's spots with Galileo. Unquestionably a +sun-spot had been seen by earlier observers, and by them mistaken +for the transit of an inferior planet. Kepler himself had made +this mistake. Before the day of the telescope, he had viewed the +image of the sun as thrown on a screen in a camera-obscura, and +had observed a spot on the disk which be interpreted as +representing the planet Mercury, but which, as is now known, must +have been a sun-spot, since the planetary disk is too small to +have been revealed by this method. Such observations as these, +however interesting, cannot be claimed as discoveries of the +sun-spots. It is probable, however, that several discoverers +(notably Johann Fabricius) made the telescopic observation of the +spots, and recognized them as having to do with the sun's +surface, almost simultaneously with Galileo. One of these +claimants was a Jesuit named Scheiner, and the jealousy of this +man is said to have had a share in bringing about that +persecution to which we must now refer. + +There is no more famous incident in the history of science than +the heresy trial through which Galileo was led to the nominal +renunciation of his cherished doctrines. There is scarcely +another incident that has been commented upon so variously. Each +succeeding generation has put its own interpretation on it. The +facts, however, have been but little questioned. It appears that +in the year 1616 the church became at last aroused to the +implications of the heliocentric doctrine of the universe. +Apparently it seemed clear to the church authorities that the +authors of the Bible believed the world to be immovably fixed at +the centre of the universe. Such, indeed, would seem to be the +natural inference from various familiar phrases of the Hebrew +text, and what we now know of the status of Oriental science in +antiquity gives full warrant to this interpretation. There is no +reason to suppose that the conception of the subordinate place of +the world in the solar system had ever so much as occurred, even +as a vague speculation, to the authors of Genesis. In common with +their contemporaries, they believed the earth to be the +all-important body in the universe, and the sun a luminary placed +in the sky for the sole purpose of giving light to the earth. +There is nothing strange, nothing anomalous, in this view; it +merely reflects the current notions of Oriental peoples in +antiquity. What is strange and anomalous is the fact that the +Oriental dreamings thus expressed could have been supposed to +represent the acme of scientific knowledge. Yet such a hold had +these writings taken upon the Western world that not even a +Galileo dared contradict them openly; and when the church fathers +gravely declared the heliocentric theory necessarily false, +because contradictory to Scripture, there were probably few +people in Christendom whose mental attitude would permit them +justly to appreciate the humor of such a pronouncement. And, +indeed, if here and there a man might have risen to such an +appreciation, there were abundant reasons for the repression of +the impulse, for there was nothing humorous about the response +with which the authorities of the time were wont to meet the +expression of iconoclastic opinions. The burning at the stake of +Giordano Bruno, in the year 1600, was, for example, an +object-lesson well calculated to restrain the enthusiasm of other +similarly minded teachers. + +Doubtless it was such considerations that explained the relative +silence of the champions of the Copernican theory, accounting for +the otherwise inexplicable fact that about eighty years elapsed +after the death of Copernicus himself before a single text-book +expounded his theory. The text-book which then appeared, under +date of 1622, was written by the famous Kepler, who perhaps was +shielded in a measure from the papal consequences of such +hardihood by the fact of residence in a Protestant country. Not +that the Protestants of the time favored the heliocentric +doctrine--we have already quoted Luther in an adverse sense--but +of course it was characteristic of the Reformation temper to +oppose any papal pronouncement, hence the ultramontane +declaration of 1616 may indirectly have aided the doctrine which +it attacked, by making that doctrine less obnoxious to Lutheran +eyes. Be that as it may, the work of Kepler brought its author +into no direct conflict with the authorities. But the result was +quite different when, in 1632, Galileo at last broke silence and +gave the world, under cover of the form of dialogue, an elaborate +exposition of the Copernican theory. Galileo, it must be +explained, had previously been warned to keep silent on the +subject, hence his publication doubly offended the authorities. +To be sure, he could reply that his dialogue introduced a +champion of the Ptolemaic system to dispute with the upholder of +the opposite view, and that, both views being presented with full +array of argument, the reader was left to reach a verdict for +himself, the author having nowhere pointedly expressed an +opinion. But such an argument, of course, was specious, for no +one who read the dialogue could be in doubt as to the opinion of +the author. Moreover, it was hinted that Simplicio, the character +who upheld the Ptolemaic doctrine and who was everywhere worsted +in the argument, was intended to represent the pope himself--a +suggestion which probably did no good to Galileo's cause. + +The character of Galileo's artistic presentation may best be +judged from an example, illustrating the vigorous assault of +Salviati, the champion of the new theory, and the feeble retorts +of his conservative antagonist: + +"Salviati. Let us then begin our discussion with the +consideration that, whatever motion may be attributed to the +earth, yet we, as dwellers upon it, and hence as participators in +its motion, cannot possibly perceive anything of it, presupposing +that we are to consider only earthly things. On the other hand, +it is just as necessary that this same motion belong apparently +to all other bodies and visible objects, which, being separated +from the earth, do not take part in its motion. The correct +method to discover whether one can ascribe motion to the earth, +and what kind of motion, is, therefore, to investigate and +observe whether in bodies outside the earth a perceptible motion +may be discovered which belongs to all alike. Because a movement +which is perceptible only in the moon, for instance, and has +nothing to do with Venus or Jupiter or other stars, cannot +possibly be peculiar to the earth, nor can its seat be anywhere +else than in the moon. Now there is one such universal movement +which controls all others--namely, that which the sun, moon, the +other planets, the fixed stars--in short, the whole universe, +with the single exception of the earth--appears to execute from +east to west in the space of twenty-four hours. This now, as it +appears at the first glance anyway, might just as well be a +motion of the earth alone as of all the rest of the universe with +the exception of the earth, for the same phenomena would result +from either hypothesis. Beginning with the most general, I will +enumerate the reasons which seem to speak in favor of the earth's +motion. When we merely consider the immensity of the starry +sphere in comparison with the smallness of the terrestrial ball, +which is contained many million times in the former, and then +think of the rapidity of the motion which completes a whole +rotation in one day and night, I cannot persuade myself how any +one can hold it to be more reasonable and credible that it is the +heavenly sphere which rotates, while the earth stands still. + +"Simplicio. I do not well understand how that powerful motion may +be said to as good as not exist for the sun, the moon, the other +planets, and the innumerable host of fixed stars. Do you call +that nothing when the sun goes from one meridian to another, +rises up over this horizon and sinks behind that one, brings now +day, and now night; when the moon goes through similar changes, +and the other planets and fixed stars in the same way? + +"Salviati. All the changes you mention are such only in respect +to the earth. To convince yourself of it, only imagine the earth +out of existence. There would then be no rising and setting of +the sun or of the moon, no horizon, no meridian, no day, no +night--in short, the said motion causes no change of any sort in +the relation of the sun to the moon or to any of the other +heavenly bodies, be they planets or fixed stars. All changes are +rather in respect to the earth; they may all be reduced to the +simple fact that the sun is first visible in China, then in +Persia, afterwards in Egypt, Greece, France, Spain, America, +etc., and that the same thing happens with the moon and the other +heavenly bodies. Exactly the same thing happens and in exactly +the same way if, instead of disturbing so large a part of the +universe, you let the earth revolve about itself. The difficulty +is, however, doubled, inasmuch as a second very important problem +presents itself. If, namely, that powerful motion is ascribed to +the heavens, it is absolutely necessary to regard it as opposed +to the individual motion of all the planets, every one of which +indubitably has its own very leisurely and moderate movement from +west to east. If, on the other hand, you let the earth move about +itself, this opposition of motion disappears. + +"The improbability is tripled by the complete overthrow of that +order which rules all the heavenly bodies in which the revolving +motion is definitely established. The greater the sphere is in +such a case, so much longer is the time required for its +revolution; the smaller the sphere the shorter the time. Saturn, +whose orbit surpasses those of all the planets in size, traverses +it in thirty years. Jupiter[4] completes its smaller course in +twelve years, Mars in two; the moon performs its much smaller +revolution within a month. Just as clearly in the Medicean stars, +we see that the one nearest Jupiter completes its revolution in a +very short time--about forty-two hours; the next in about three +and one-half days, the third in seven, and the most distant one +in sixteen days. This rule, which is followed throughout, will +still remain if we ascribe the twenty-four-hourly motion to a +rotation of the earth. If, however, the earth is left motionless, +we must go first from the very short rule of the moon to ever +greater ones--to the two-yearly rule of Mars, from that to the +twelve-yearly one of Jupiter, from here to the thirty-yearly one +of Saturn, and then suddenly to an incomparably greater sphere, +to which also we must ascribe a complete rotation in twenty-four +hours. If, however, we assume a motion of the earth, the rapidity +of the periods is very well preserved; from the slowest sphere of +Saturn we come to the wholly motionless fixed stars. We also +escape thereby a fourth difficulty, which arises as soon as we +assume that there is motion in the sphere of the stars. I mean +the great unevenness in the movement of these very stars, some of +which would have to revolve with extraordinary rapidity in +immense circles, while others moved very slowly in small circles, +since some of them are at a greater, others at a less, distance +from the pole. That is likewise an inconvenience, for, on the one +hand, we see all those stars, the motion of which is indubitable, +revolve in great circles, while, on the other hand, there seems +to be little object in placing bodies, which are to move in +circles, at an enormous distance from the centre and then let +them move in very small circles. And not only are the size of the +different circles and therewith the rapidity of the movement very +different in the different fixed stars, but the same stars also +change their orbits and their rapidity of motion. Therein +consists the fifth inconvenience. Those stars, namely, which were +at the equator two thousand years ago, and hence described great +circles in their revolutions, must to-day move more slowly and in +smaller circles, because they are many degrees removed from it. +It will even happen, after not so very long a time, that one of +those which have hitherto been continually in motion will finally +coincide with the pole and stand still, but after a period of +repose will again begin to move. The other stars in the mean +while, which unquestionably move, all have, as was said, a great +circle for an orbit and keep this unchangeably. + +"The improbability is further increased--this may be considered +the sixth inconvenience--by the fact that it is impossible to +conceive what degree of solidity those immense spheres must have, +in the depths of which so many stars are fixed so enduringly that +they are kept revolving evenly in spite of such difference of +motion without changing their respective positions. Or if, +according to the much more probable theory, the heavens are +fluid, and every star describes an orbit of its own, according to +what law then, or for what reason, are their orbits so arranged +that, when looked at from the earth, they appear to be contained +in one single sphere? To attain this it seems to me much easier +and more convenient to make them motionless instead of moving, +just as the paving-stones on the market-place, for instance, +remain in order more easily than the swarms of children running +about on them. + +"Finally, the seventh difficulty: If we attribute the daily +rotation to the higher region of the heavens, we should have to +endow it with force and power sufficient to carry with it the +innumerable host of the fixed stars --every one a body of very +great compass and much larger than the earth--and all the +planets, although the latter, like the earth, move naturally in +an opposite direction. In the midst of all this the little earth, +single and alone, would obstinately and wilfully withstand such +force--a supposition which, it appears to me, has much against +it. I could also not explain why the earth, a freely poised body, +balancing itself about its centre, and surrounded on all sides by +a fluid medium, should not be affected by the universal rotation. +Such difficulties, however, do not confront us if we attribute +motion to the earth--such a small, insignificant body in +comparison with the whole universe, and which for that very +reason cannot exercise any power over the latter. + +"Simplicio. You support your arguments throughout, it seems to +me, on the greater ease and simplicity with which the said +effects are produced. You mean that as a cause the motion of the +earth alone is just as satisfactory as the motion of all the rest +of the universe with the exception of the earth; you hold the +actual event to be much easier in the former case than in the +latter. For the ruler of the universe, however, whose might is +infinite, it is no less easy to move the universe than the earth +or a straw balm. But if his power is infinite, why should not a +greater, rather than a very small, part of it be revealed to me? + +"Salviati. If I had said that the universe does not move on +account of the impotence of its ruler, I should have been wrong +and your rebuke would have been in order. I admit that it is just +as easy for an infinite power to move a hundred thousand as to +move one. What I said, however, does not refer to him who causes +the motion, but to that which is moved. In answer to your remark +that it is more fitting for an infinite power to reveal a large +part of itself rather than a little, I answer that, in relation +to the infinite, one part is not greater than another, if both +are finite. Hence it is unallowable to say that a hundred +thousand is a larger part of an infinite number than two, +although the former is fifty thousand times greater than the +latter. If, therefore, we consider the moving bodies, we must +unquestionably regard the motion of the earth as a much simpler +process than that of the universe; if, furthermore, we direct our +attention to so many other simplifications which may be reached +only by this theory, the daily movement of the earth must appear +much more probable than the motion of the universe without the +earth, for, according to Aristotle's just axiom, 'Frustra fit per +plura, quod potest fieri per p auciora' (It is vain to expend +many means where a few are sufficient)."[2] + + +The work was widely circulated, and it was received with an +interest which bespeaks a wide-spread undercurrent of belief in +the Copernican doctrine. Naturally enough, it attracted immediate +attention from the church authorities. Galileo was summoned to +appear at Rome to defend his conduct. The philosopher, who was +now in his seventieth year, pleaded age and infirmity. He had no +desire for personal experience of the tribunal of the +Inquisition; but the mandate was repeated, and Galileo went to +Rome. There, as every one knows, he disavowed any intention to +oppose the teachings of Scripture, and formally renounced the +heretical doctrine of the earth's motion. According to a tale +which so long passed current that every historian must still +repeat it though no one now believes it authentic, Galileo +qualified his renunciation by muttering to himself, "E pur si +muove" (It does move, none the less), as he rose to his feet and +retired from the presence of his persecutors. The tale is one of +those fictions which the dramatic sense of humanity is wont to +impose upon history, but, like most such fictions, it expresses +the spirit if not the letter of truth; for just as no one +believes that Galileo's lips uttered the phrase, so no one doubts +that the rebellious words were in his mind. + +After his formal renunciation, Galileo was allowed to depart, but +with the injunction that he abstain in future from heretical +teaching. The remaining ten years of his life were devoted +chiefly to mechanics, where his experiments fortunately opposed +the Aristotelian rather than the Hebrew teachings. Galileo's +death occurred in 1642, a hundred years after the death of +Copernicus. Kepler had died thirteen years before, and there +remained no astronomer in the field who is conspicuous in the +history of science as a champion of the Copernican doctrine. But +in truth it might be said that the theory no longer needed a +champion. The researches of Kepler and Galileo had produced a +mass of evidence for the Copernican theory which amounted to +demonstration. A generation or two might be required for this +evidence to make itself everywhere known among men of science, +and of course the ecclesiastical authorities must be expected to +stand by their guns for a somewhat longer period. In point of +fact, the ecclesiastical ban was not technically removed by the +striking of the Copernican books from the list of the Index +Expurgatorius until the year 1822, almost two hundred years after +the date of Galileo's dialogue. But this, of course, is in no +sense a guide to the state of general opinion regarding the +theory. We shall gain a true gauge as to this if we assume that +the greater number of important thinkers had accepted the +heliocentric doctrine before the middle of the seventeenth +century, and that before the close of that century the old +Ptolemaic idea had been quite abandoned. A wonderful revolution +in man's estimate of the universe had thus been effected within +about two centuries after the birth of Copernicus. + + + +V. GALILEO AND THE NEW PHYSICS + +After Galileo had felt the strong hand of the Inquisition, in +1632, he was careful to confine his researches, or at least his +publications, to topics that seemed free from theological +implications. In doing so he reverted to the field of his +earliest studies --namely, the field of mechanics; and the +Dialoghi delle Nuove Scienze, which he finished in 1636, and +which was printed two years later, attained a celebrity no less +than that of the heretical dialogue that had preceded it. The +later work was free from all apparent heresies, yet perhaps it +did more towards the establishment of the Copernican doctrine, +through the teaching of correct mechanical principles, than the +other work had accomplished by a more direct method. + +Galileo's astronomical discoveries were, as we have seen, in a +sense accidental; at least, they received their inception through +the inventive genius of another. His mechanical discoveries, on +the other hand, were the natural output of his own creative +genius. At the very beginning of his career, while yet a very +young man, though a professor of mathematics at Pisa, he had +begun that onslaught upon the old Aristotelian ideas which he was +to continue throughout his life. At the famous leaning tower in +Pisa, the young iconoclast performed, in the year 1590, one of +the most theatrical demonstrations in the history of science. +Assembling a multitude of champions of the old ideas, he proposed +to demonstrate the falsity of the Aristotelian doctrine that the +velocity of falling bodies is proportionate to their weight. +There is perhaps no fact more strongly illustrative of the temper +of the Middle Ages than the fact that this doctrine, as taught by +the Aristotelian philosopher, should so long have gone +unchallenged. Now, however, it was put to the test; Galileo +released a half-pound weight and a hundred-pound cannon-ball from +near the top of the tower, and, needless to say, they reached the +ground together. Of course, the spectators were but little +pleased with what they saw. They could not doubt the evidence of +their own senses as to the particular experiment in question; +they could suggest, however, that the experiment involved a +violation of the laws of nature through the practice of magic. To +controvert so firmly established an idea savored of heresy. The +young man guilty of such iconoclasm was naturally looked at +askance by the scholarship of his time. Instead of being +applauded, he was hissed, and he found it expedient presently to +retire from Pisa. + +Fortunately, however, the new spirit of progress had made itself +felt more effectively in some other portions of Italy, and so +Galileo found a refuge and a following in Padua, and afterwards +in Florence; and while, as we have seen, he was obliged to curb +his enthusiasm regarding the subject that was perhaps nearest his +heart--the promulgation of the Copernican theory--yet he was +permitted in the main to carry on his experimental observations +unrestrained. These experiments gave him a place of unquestioned +authority among his contemporaries, and they have transmitted his +name to posterity as that of one of the greatest of experimenters +and the virtual founder of modern mechanical science. The +experiments in question range over a wide field; but for the most +part they have to do with moving bodies and with questions of +force, or, as we should now say, of energy. The experiment at the +leaning tower showed that the velocity of falling bodies is +independent of the weight of the bodies, provided the weight is +sufficient to overcome the resistance of the atmosphere. Later +experiments with falling bodies led to the discovery of laws +regarding the accelerated velocity of fall. Such velocities were +found to bear a simple relation to the period of time from the +beginning of the fall. Other experiments, in which balls were +allowed to roll down inclined planes, corroborated the +observation that the pull of gravitation gave a velocity +proportionate to the length of fall, whether such fall were +direct or in a slanting direction. + +These studies were associated with observations on projectiles, +regarding which Galileo was the first to entertain correct +notions. According to the current idea, a projectile fired, for +example, from a cannon, moved in a straight horizontal line until +the propulsive force was exhausted, and then fell to the ground +in a perpendicular line. Galileo taught that the projectile +begins to fall at once on leaving the mouth of the cannon and +traverses a parabolic course. According to his idea, which is now +familiar to every one, a cannon-ball dropped from the level of +the cannon's muzzle will strike the ground simultaneously with a +ball fired horizontally from the cannon. As to the paraboloid +course pursued by the projectile, the resistance of the air is a +factor which Galileo could not accurately compute, and which +interferes with the practical realization of his theory. But this +is a minor consideration. The great importance of his idea +consists in the recognition that such a force as that of +gravitation acts in precisely the same way upon all unsupported +bodies, whether or not such bodies be at the same time acted upon +by a force of translation. + +Out of these studies of moving bodies was gradually developed a +correct notion of several important general laws of +mechanics--laws a knowledge of which was absolutely essential to +the progress of physical science. The belief in the rotation of +the earth made necessary a clear conception that all bodies at +the surface of the earth partake of that motion quite +independently of their various observed motions in relation to +one another. This idea was hard to grasp, as an oft-repeated +argument shows. It was asserted again and again that, if the +earth rotates, a stone dropped from the top of a tower could not +fall at the foot of the tower, since the earth's motion would +sweep the tower far away from its original position while the +stone is in transit. + +This was one of the stock arguments against the earth's motion, +yet it was one that could be refuted with the greatest ease by +reasoning from strictly analogous experiments. It might readily +be observed, for example, that a stone dropped from a moving cart +does not strike the ground directly below the point from which it +is dropped, but partakes of the forward motion of the cart. If +any one doubt this he has but to jump from a moving cart to be +given a practical demonstration of the fact that his entire body +was in some way influenced by the motion of translation. +Similarly, the simple experiment of tossing a ball from the deck +of a moving ship will convince any one that the ball partakes of +the motion of the ship, so that it can be manipulated precisely +as if the manipulator were standing on the earth. In short, +every-day experience gives us illustrations of what might be +called compound motion, which makes it seem altogether plausible +that, if the earth is in motion, objects at its surface will +partake of that motion in a way that does not interfere with any +other movements to which they may be subjected. As the Copernican +doctrine made its way, this idea of compound motion naturally +received more and more attention, and such experiments as those +of Galileo prepared the way for a new interpretation of the +mechanical principles involved. + +The great difficulty was that the subject of moving bodies had +all along been contemplated from a wrong point of view. Since +force must be applied to an object to put it in motion, it was +perhaps not unnaturally assumed that similar force must continue +to be applied to keep the object in motion. When, for example, a +stone is thrown from the hand, the direct force applied +necessarily ceases as soon as the projectile leaves the hand. The +stone, nevertheless, flies on for a certain distance and then +falls to the ground. How is this flight of the stone to be +explained? The ancient philosophers puzzled more than a little +over this problem, and the Aristotelians reached the conclusion +that the motion of the hand had imparted a propulsive motion to +the air, and that this propulsive motion was transmitted to the +stone, pushing it on. Just how the air took on this propulsive +property was not explained, and the vagueness of thought that +characterized the time did not demand an explanation. Possibly +the dying away of ripples in water may have furnished, by +analogy, an explanation of the gradual dying out of the impulse +which propels the stone. + +All of this was, of course, an unfortunate maladjustment of the +point of view. As every one nowadays knows, the air retards the +progress of the stone, enabling the pull of gravitation to drag +it to the earth earlier than it otherwise could. Were the +resistance of the air and the pull of gravitation removed, the +stone as projected from the hand would fly on in a straight line, +at an unchanged velocity, forever. But this fact, which is +expressed in what we now term the first law of motion, was +extremely difficult to grasp. The first important step towards it +was perhaps implied in Galileo's study of falling bodies. These +studies, as we have seen, demonstrated that a half-pound weight +and a hundred-pound weight fall with the same velocity. It is, +however, matter of common experience that certain bodies, as, for +example, feathers, do not fall at the same rate of speed with +these heavier bodies. This anomaly demands an explanation, and +the explanation is found in the resistance offered the relatively +light object by the air. Once the idea that the air may thus act +as an impeding force was grasped, the investigator of mechanical +principles had entered on a new and promising course. + +Galileo could not demonstrate the retarding influence of air in +the way which became familiar a generation or two later; he could +not put a feather and a coin in a vacuum tube and prove that the +two would there fall with equal velocity, because, in his day, +the air-pump had not yet been invented. The experiment was made +only a generation after the time of Galileo, as we shall see; +but, meantime, the great Italian had fully grasped the idea that +atmospheric resistance plays a most important part in regard to +the motion of falling and projected bodies. Thanks largely to his +own experiments, but partly also to the efforts of others, he had +come, before the end of his life, pretty definitely to realize +that the motion of a projectile, for example, must be thought of +as inherent in the projectile itself, and that the retardation or +ultimate cessation of that motion is due to the action of +antagonistic forces. In other words, he had come to grasp the +meaning of the first law of motion. It remained, however, for the +great Frenchman Descartes to give precise expression to this law +two years after Galileo's death. As Descartes expressed it in his +Principia Philosophiae, published in 1644, any body once in +motion tends to go on in a straight line, at a uniform rate of +speed, forever. Contrariwise, a stationary body will remain +forever at rest unless acted on by some disturbing force. + +This all-important law, which lies at the very foundation of all +true conceptions of mechanics, was thus worked out during the +first half of the seventeenth century, as the outcome of +numberless experiments for which Galileo's experiments with +failing bodies furnished the foundation. So numerous and so +gradual were the steps by which the reversal of view regarding +moving bodies was effected that it is impossible to trace them in +detail. We must be content to reflect that at the beginning of +the Galilean epoch utterly false notions regarding the subject +were entertained by the very greatest philosophers--by Galileo +himself, for example, and by Kepler--whereas at the close of that +epoch the correct and highly illuminative view had been attained. + +We must now consider some other experiments of Galileo which led +to scarcely less-important results. The experiments in question +had to do with the movements of bodies passing down an inclined +plane, and with the allied subject of the motion of a pendulum. +The elaborate experiments of Galileo regarding the former subject +were made by measuring the velocity of a ball rolling down a +plane inclined at various angles. He found that the velocity +acquired by a ball was proportional to the height from which the +ball descended regardless of the steepness of the incline. +Experiments were made also with a ball rolling down a curved +gutter, the curve representing the are of a circle. These +experiments led to the study of the curvilinear motions of a +weight suspended by a cord; in other words, of the pendulum. + +Regarding the motion of the pendulum, some very curious facts +were soon ascertained. Galileo found, for example, that a +pendulum of a given length performs its oscillations with the +same frequency though the arc described by the pendulum be varied +greatly.[1] He found, also, that the rate of oscillation for +pendulums of different lengths varies according to a simple law. +In order that one pendulum shall oscillate one-half as fast as +another, the length of the pendulums must be as four to one. +Similarly, by lengthening the pendulums nine times, the +oscillation is reduced to one-third, In other words, the rate of +oscillation of pendulums varies inversely as the square of their +length. Here, then, is a simple relation between the motions of +swinging bodies which suggests the relation which Kepler bad +discovered between the relative motions of the planets. Every +such discovery coming in this age of the rejuvenation of +experimental science had a peculiar force in teaching men the +all-important lesson that simple laws lie back of most of the +diverse phenomena of nature, if only these laws can be +discovered. + +Galileo further observed that his pendulum might be constructed +of any weight sufficiently heavy readily to overcome the +atmospheric resistance, and that, with this qualification, +neither the weight nor the material had any influence upon the +time of oscillation, this being solely determined by the length +of the cord. Naturally, the practical utility of these +discoveries was not overlooked by Galileo. Since a pendulum of a +given length oscillates with unvarying rapidity, here is an +obvious means of measuring time. Galileo, however, appears not to +have met with any great measure of success in putting this idea +into practice. It remained for the mechanical ingenuity of +Huyghens to construct a satisfactory pendulum clock. + +As a theoretical result of the studies of rolling and oscillating +bodies, there was developed what is usually spoken of as the +third law of motion--namely, the law that a given force operates +upon a moving body with an effect proportionate to its effect +upon the same body when at rest. Or, as Whewell states the law: +"The dynamical effect of force is as the statical effect; that +is, the velocity which any force generates in a given time, when +it puts the body in motion, is proportional to the pressure which +this same force produces in a body at rest."[2] According to the +second law of motion, each one of the different forces, operating +at the same time upon a moving body, produces the same effect as +if it operated upon the body while at rest. + + +STEVINUS AND THE LAW OF EQUILIBRIUM + +It appears, then, that the mechanical studies of Galileo, taken +as a whole, were nothing less than revolutionary. They +constituted the first great advance upon the dynamic studies of +Archimedes, and then led to the secure foundation for one of the +most important of modern sciences. We shall see that an important +company of students entered the field immediately after the time +of Galileo, and carried forward the work he had so well begun. +But before passing on to the consideration of their labors, we +must consider work in allied fields of two men who were +contemporaries of Galileo and whose original labors were in some +respects scarcely less important than his own. These men are the +Dutchman Stevinus, who must always be remembered as a co-laborer +with Galileo in the foundation of the science of dynamics, and +the Englishman Gilbert, to whom is due the unqualified praise of +first subjecting the phenomenon of magnetism to a strictly +scientific investigation. + +Stevinus was born in the year 1548, and died in 1620. He was a +man of a practical genius, and he attracted the attention of his +non-scientific contemporaries, among other ways, by the +construction of a curious land-craft, which, mounted on wheels, +was to be propelled by sails like a boat. Not only did he write a +book on this curious horseless carriage, but he put his idea into +practical application, producing a vehicle which actually +traversed the distance between Scheveningen and Petton, with no +fewer than twenty-seven passengers, one of them being Prince +Maurice of Orange. This demonstration was made about the year +1600. It does not appear, however, that any important use was +made of the strange vehicle; but the man who invented it put his +mechanical ingenuity to other use with better effect. It was he +who solved the problem of oblique forces, and who discovered the +important hydrostatic principle that the pressure of fluids is +proportionate to their depth, without regard to the shape of the +including vessel. + +The study of oblique forces was made by Stevinus with the aid of +inclined planes. His most demonstrative experiment was a very +simple one, in which a chain of balls of equal weight was hung +from a triangle; the triangle being so constructed as to rest on +a horizontal base, the oblique sides bearing the relation to each +other of two to one. Stevinus found that his chain of balls just +balanced when four balls were on the longer side and two on the +shorter and steeper side. The balancing of force thus brought +about constituted a stable equilibrium, Stevinus being the first +to discriminate between such a condition and the unbalanced +condition called unstable equilibrium. By this simple experiment +was laid the foundation of the science of statics. Stevinus had a +full grasp of the principle which his experiment involved, and he +applied it to the solution of oblique forces in all directions. +Earlier investigations of Stevinus were published in 1608. His +collected works were published at Leyden in 1634. + +This study of the equilibrium of pressure of bodies at rest led +Stevinus, not unnaturally, to consider the allied subject of the +pressure of liquids. He is to be credited with the explanation of +the so-called hydrostatic paradox. The familiar modern experiment +which illustrates this paradox is made by inserting a long +perpendicular tube of small caliber into the top of a tight +barrel. On filling the barrel and tube with water, it is possible +to produce a pressure which will burst the barrel, though it be a +strong one, and though the actual weight of water in the tube is +comparatively insignificant. This illustrates the fact that the +pressure at the bottom of a column of liquid is proportionate to +the height of the column, and not to its bulk, this being the +hydrostatic paradox in question. The explanation is that an +enclosed fluid under pressure exerts an equal force upon all +parts of the circumscribing wall; the aggregate pressure may, +therefore, be increased indefinitely by increasing the surface. +It is this principle, of course, which is utilized in the +familiar hydrostatic press. Theoretical explanations of the +pressure of liquids were supplied a generation or two later by +numerous investigators, including Newton, but the practical +refoundation of the science of hydrostatics in modern times dates +from the experiments of Stevinus. + + +GALILEO AND THE EQUILIBRIUM OF FLUIDS + +Experiments of an allied character, having to do with the +equilibrium of fluids, exercised the ingenuity of Galileo. Some +of his most interesting experiments have to do with the subject +of floating bodies. It will be recalled that Archimedes, away +back in the Alexandrian epoch, had solved the most important +problems of hydrostatic equilibrium. Now, however, his +experiments were overlooked or forgotten, and Galileo was obliged +to make experiments anew, and to combat fallacious views that +ought long since to have been abandoned. Perhaps the most +illuminative view of the spirit of the times can be gained by +quoting at length a paper of Galileo's, in which he details his +own experiments with floating bodies and controverts the views of +his opponents. The paper has further value as illustrating +Galileo's methods both as experimenter and as speculative +reasoner. + +The current view, which Galileo here undertakes to refute, +asserts that water offers resistance to penetration, and that +this resistance is instrumental in determining whether a body +placed in water will float or sink. Galileo contends that water +is non-resistant, and that bodies float or sink in virtue of +their respective weights. This, of course, is merely a +restatement of the law of Archimedes. But it remains to explain +the fact that bodies of a certain shape will float, while bodies +of the same material and weight, but of a different shape, will +sink. We shall see what explanation Galileo finds of this anomaly +as we proceed. + +In the first place, Galileo makes a cone of wood or of wax, and +shows that when it floats with either its point or its base in +the water, it displaces exactly the same amount of fluid, +although the apex is by its shape better adapted to overcome the +resistance of the water, if that were the cause of buoyancy. +Again, the experiment may be varied by tempering the wax with +filings of lead till it sinks in the water, when it will be found +that in any figure the same quantity of cork must be added to it +to raise the surface. + +"But," says Galileo, "this silences not my antagonists; they say +that all the discourse hitherto made by me imports little to +them, and that it serves their turn; that they have demonstrated +in one instance, and in such manner and figure as pleases them +best --namely, in a board and in a ball of ebony--that one when +put into the water sinks to the bottom, and that the other stays +to swim on the top; and the matter being the same, and the two +bodies differing in nothing but in figure, they affirm that with +all perspicuity they have demonstrated and sensibly manifested +what they undertook. Nevertheless, I believe, and think I can +prove, that this very experiment proves nothing against my +theory. And first, it is false that the ball sinks and the board +not; for the board will sink, too, if you do to both the figures +as the words of our question require; that is, if you put them +both in the water; for to be in the water implies to be placed in +the water, and by Aristotle's own definition of place, to be +placed imports to be environed by the surface of the ambient +body; but when my antagonists show the floating board of ebony, +they put it not into the water, but upon the water; where, being +detained by a certain impediment (of which more anon), it is +surrounded, partly with water, partly with air, which is contrary +to our agreement, for that was that bodies should be in the +water, and not part in the water, part in the air. + +"I will not omit another reason, founded also upon experience, +and, if I deceive not myself, conclusive against the notion that +figure, and the resistance of the water to penetration, have +anything to do with the buoyancy of bodies. Choose a piece of +wood or other matter, as, for instance, walnut-wood, of which a +ball rises from the bottom of the water to the surface more +slowly than a ball of ebony of the same size sinks, so that, +clearly, the ball of ebony divides the water more readily in +sinking than the ball of wood does in rising. Then take a board +of walnut-tree equal to and like the floating one of my +antagonists; and if it be true that this latter floats by reason +of the figure being unable to penetrate the water, the other of +walnut-tree, without a question, if thrust to the bottom, ought +to stay there, as having the same impeding figure, and being less +apt to overcome the said resistance of the water. But if we find +by experience that not only the thin board, but every other +figure of the same walnut-tree, will return to float, as +unquestionably we shall, then I must desire my opponents to +forbear to attribute the floating of the ebony to the figure of +the board, since the resistance of the water is the same in +rising as in sinking, and the force of ascension of the +walnut-tree is less than the ebony's force for going to the +bottom. + +"Now let us return to the thin plate of gold or silver, or the +thin board of ebony, and let us lay it lightly upon the water, so +that it may stay there without sinking, and carefully observe the +effect. It will appear clearly that the plates are a considerable +matter lower than the surface of the water, which rises up and +makes a kind of rampart round them on every side. But if it has +already penetrated and overcome the continuity of the water, and +is of its own nature heavier than the water, why does it not +continue to sink, but stop and suspend itself in that little +dimple that its weight has made in the water? My answer is, +because in sinking till its surface is below the water, which +rises up in a bank round it, it draws after and carries along +with it the air above it, so that that which, in this case, +descends in the water is not only the board of ebony or the plate +of iron, but a compound of ebony and air, from which composition +results a solid no longer specifically heavier than the water, as +was the ebony or gold alone. But, gentlemen, we want the same +matter; you are to alter nothing but the shape, and, therefore, +have the goodness to remove this air, which may be done simply by +washing the surface of the board, for the water having once got +between the board and the air will run together, and the ebony +will go to the bottom; and if it does not, you have won the day. + +"But methinks I hear some of my antagonists cunningly opposing +this, and telling me that they will not on any account allow +their boards to be wetted, because the weight of the water so +added, by making it heavier than it was before, draws it to the +bottom, and that the addition of new weight is contrary to our +agreement, which was that the matter should be the same. + +"To this I answer, first, that nobody can suppose bodies to be +put into the water without their being wet, nor do I wish to do +more to the board than you may do to the ball. Moreover, it is +not true that the board sinks on account of the weight of the +water added in the washing; for I will put ten or twenty drops on +the floating board, and so long as they stand separate it shall +not sink; but if the board be taken out and all that water wiped +off, and the whole surface bathed with one single drop, and put +it again upon the water, there is no question but it will sink, +the other water running to cover it, being no longer hindered by +the air. In the next place, it is altogether false that water can +in any way increase the weight of bodies immersed in it, for +water has no weight in water, since it does not sink. Now just as +he who should say that brass by its own nature sinks, but that +when formed into the shape of a kettle it acquires from that +figure the virtue of lying in water without sinking, would say +what is false, because that is not purely brass which then is put +into the water, but a compound of brass and air; so is it neither +more nor less false that a thin plate of brass or ebony swims by +virtue of its dilated and broad figure. Also, I cannot omit to +tell my opponents that this conceit of refusing to bathe the +surface of the board might beget an opinion in a third person of +a poverty of argument on their side, especially as the +conversation began about flakes of ice, in which it would be +simple to require that the surfaces should be kept dry; not to +mention that such pieces of ice, whether wet or dry, always +float, and so my antagonists say, because of their shape. + +"Some may wonder that I affirm this power to be in the air of +keeping plate of brass or silver above water, as if in a certain +sense I would attribute to the air a kind of magnetic virtue for +sustaining heavy bodies with which it is in contact. To satisfy +all these doubts I have contrived the following experiment to +demonstrate how truly the air does support these bodies; for I +have found, when one of these bodies which floats when placed +lightly on the water is thoroughly bathed and sunk to the bottom, +that by carrying down to it a little air without otherwise +touching it in the least, I am able to raise and carry it back to +the top, where it floats as before. To this effect, I take a ball +of wax, and with a little lead make it just heavy enough to sink +very slowly to the bottom, taking care that its surface be quite +smooth and even. This, if put gently into the water, submerges +almost entirely, there remaining visible only a little of the +very top, which, so long as it is joined to the air, keeps the +ball afloat; but if we take away the contact of the air by +wetting this top, the ball sinks to the bottom and remains there. +Now to make it return to the surface by virtue of the air which +before sustained it, thrust into the water a glass with the mouth +downward, which will carry with it the air it contains, and move +this down towards the ball until you see, by the transparency of +the glass, that the air has reached the top of it; then gently +draw the glass upward, and you will see the ball rise, and +afterwards stay on the top of the water, if you carefully part +the glass and water without too much disturbing it."[3] + +It will be seen that Galileo, while holding in the main to a +correct thesis, yet mingles with it some false ideas. At the very +outset, of course, it is not true that water has no resistance to +penetration; it is true, however, in the sense in which Galileo +uses the term--that is to say, the resistance of the water to +penetration is not the determining factor ordinarily in deciding +whether a body sinks or floats. Yet in the case of the flat body +it is not altogether inappropriate to say that the water resists +penetration and thus supports the body. The modern physicist +explains the phenomenon as due to surface-tension of the fluid. +Of course, Galileo's disquisition on the mixing of air with the +floating body is utterly fanciful. His experiments were +beautifully exact; his theorizing from them was, in this +instance, altogether fallacious. Thus, as already intimated, his +paper is admirably adapted to convey a double lesson to the +student of science. + + +WILLIAM GILBERT AND THE STUDY OF MAGNETISM + +It will be observed that the studies of Galileo and Stevinus were +chiefly concerned with the force of gravitation. Meanwhile, there +was an English philosopher of corresponding genius, whose +attention was directed towards investigation of the equally +mysterious force of terrestrial magnetism. With the doubtful +exception of Bacon, Gilbert was the most distinguished man of +science in England during the reign of Queen Elizabeth. He was +for many years court physician, and Queen Elizabeth ultimately +settled upon him a pension that enabled him to continue his +researches in pure science. + +His investigations in chemistry, although supposed to be of great +importance, are mostly lost; but his great work, De Magnete, on +which he labored for upwards of eighteen years, is a work of +sufficient importance, as Hallam says, "to raise a lasting +reputation for its author." From its first appearance it created +a profound impression upon the learned men of the continent, +although in England Gilbert's theories seem to have been somewhat +less favorably received. Galileo freely expressed his admiration +for the work and its author; Bacon, who admired the author, did +not express the same admiration for his theories; but Dr. +Priestley, later, declared him to be "the father of modern +electricity." + +Strangely enough, Gilbert's book had never been translated into +English, or apparently into any other language, until recent +years, although at the time of its publication certain learned +men, unable to read the book in the original, had asked that it +should be. By this neglect, or oversight, a great number of +general readers as well as many scientists, through succeeding +centuries, have been deprived of the benefit of writings that +contained a good share of the fundamental facts about magnetism +as known to-day. + +Gilbert was the first to discover that the earth is a great +magnet, and he not only gave the name of "pole" to the +extremities of the magnetic needle, but also spoke of these +"poles" as north and south pole, although he used these names in +the opposite sense from that in which we now use them, his south +pole being the extremity which pointed towards the north, and +vice versa. He was also first to make use of the terms "electric +force," "electric emanations," and "electric attractions." + +It is hardly necessary to say that some of the views taken by +Gilbert, many of his theories, and the accuracy of some of his +experiments have in recent times been found to be erroneous. As a +pioneer in an unexplored field of science, however, his work is +remarkably accurate. "On the whole," says Dr. John Robinson, +"this performance contains more real information than any writing +of the age in which he lived, and is scarcely exceeded by any +that has appeared since."[4] + +In the preface to his work Gilbert says: "Since in the discovery +of secret things, and in the investigation of hidden causes, +stronger reasons are obtained from sure experiments and +demonstrated arguments than from probable conjectures and the +opinions of philosophical speculators of the common sort, +therefore, to the end of that noble substance of that great +loadstone, our common mother (the earth), still quite unknown, +and also that the forces extraordinary and exalted of this globe +may the better be understood, we have decided, first, to begin +with the common stony and ferruginous matter, and magnetic +bodies, and the part of the earth that we may handle and may +perceive with senses, and then to proceed with plain magnetic +experiments, and to penetrate to the inner parts of the +earth."[5] + +Before taking up the demonstration that the earth is simply a +giant loadstone, Gilbert demonstrated in an ingenious way that +every loadstone, of whatever size, has definite and fixed poles. +He did this by placing the stone in a metal lathe and converting +it into a sphere, and upon this sphere demonstrated how the poles +can be found. To this round loadstone he gave the name of +terrella--that is, little earth. + +"To find, then, poles answering to the earth," he says, "take in +your hand the round stone, and lay on it a needle or a piece of +iron wire: the ends of the wire move round their middle point, +and suddenly come to a standstill. Now, with ochre or with chalk, +mark where the wire lies still and sticks. Then move the middle +or centre of the wire to another spot, and so to a third and +fourth, always marking the stone along the length of the wire +where it stands still; the lines so marked will exhibit meridian +circles, or circles like meridians, on the stone or terrella; and +manifestly they will all come together at the poles of the stone. +The circle being continued in this way, the poles appear, both +the north and the south, and betwixt these, midway, we may draw a +large circle for an equator, as is done by the astronomer in the +heavens and on his spheres, and by the geographer on the +terrestrial globe."[6] + +Gilbert had tried the familiar experiment of placing the +loadstone on a float in water, and observed that the poles always +revolved until they pointed north and south, which he explained +as due to the earth's magnetic attraction. In this same +connection he noticed that a piece of wrought iron mounted on a +cork float was attracted by other metals to a slight degree, and +he observed also that an ordinary iron bar, if suspended +horizontally by a thread, assumes invariably a north and south +direction. These, with many other experiments of a similar +nature, convinced him that the earth "is a magnet and a +loadstone," which he says is a "new and till now unheard-of view +of the earth." + +Fully to appreciate Gilbert's revolutionary views concerning the +earth as a magnet, it should be remembered that numberless +theories to explain the action of the electric needle had been +advanced. Columbus and Paracelsus, for example, believed that the +magnet was attracted by some point in the heavens, such as a +magnetic star. Gilbert himself tells of some of the beliefs that +had been held by his predecessors, many of whom he declares +"wilfully falsify." One of his first steps was to refute by +experiment such assertions as that of Cardan, that "a wound by a +magnetized needle was painless"; and also the assertion of +Fracastoni that loadstone attracts silver; or that of Scalinger, +that the diamond will attract iron; and the statement of +Matthiolus that "iron rubbed with garlic is no longer attracted +to the loadstone." + +Gilbert made extensive experiments to explain the dipping of the +needle, which had been first noticed by William Norman. His +deduction as to this phenomenon led him to believe that this was +also explained by the magnetic attraction of the earth, and to +predict where the vertical dip would be found. These deductions +seem the more wonderful because at the time he made them the dip +had just been discovered, and had not been studied except at +London. His theory of the dip was, therefore, a scientific +prediction, based on a preconceived hypothesis. Gilbert found the +dip to be 72 degrees at London; eight years later Hudson found +the dip at 75 degrees 22' north latitude to be 89 degrees 30'; +but it was not until over two hundred years later, in 1831, that +the vertical dip was first observed by Sir James Ross at about 70 +degrees 5' north latitude, and 96 degrees 43' west longitude. +This was not the exact point assumed by Gilbert, and his +scientific predictions, therefore, were not quite correct; but +such comparatively slight and excusable errors mar but little the +excellence of his work as a whole. + +A brief epitome of some of his other important discoveries +suffices to show that the exalted position in science accorded +him by contemporaries, as well as succeeding generations of +scientists, was well merited. He was first to distinguish between +magnetism and electricity, giving the latter its name. He +discovered also the "electrical charge," and pointed the way to +the discovery of insulation by showing that the charge could be +retained some time in the excited body by covering it with some +non-conducting substance, such as silk; although, of course, +electrical conduction can hardly be said to have been more than +vaguely surmised, if understood at all by him. The first +electrical instrument ever made, and known as such, was invented +by him, as was also the first magnetometer, and the first +electrical indicating device. Although three centuries have +elapsed since his death, the method of magnetizing iron first +introduced by him is in common use to-day. + +He made exhaustive experiments with a needle balanced on a pivot +to see how many substances he could find which, like amber, on +being rubbed affected the needle. In this way he discovered that +light substances were attracted by alum, mica, arsenic, +sealing-wax, lac sulphur, slags, beryl, amethyst, rock-crystal, +sapphire, jet, carbuncle, diamond, opal, Bristol stone, glass, +glass of antimony, gum-mastic, hard resin, rock-salt, and, of +course, amber. He discovered also that atmospheric conditions +affected the production of electricity, dryness being unfavorable +and moisture favorable. + +Galileo's estimate of this first electrician is the verdict of +succeeding generations. "I extremely admire and envy this +author," he said. "I think him worthy of the greatest praise for +the many new and true observations which he has made, to the +disgrace of so many vain and fabling authors." + + +STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE + +We have seen that Gilbert was by no means lacking in versatility, +yet the investigations upon which his fame is founded were all +pursued along one line, so that the father of magnetism may be +considered one of the earliest of specialists in physical +science. Most workers of the time, on the other band, extended +their investigations in many directions. The sum total of +scientific knowledge of that day had not bulked so large as to +exclude the possibility that one man might master it all. So we +find a Galileo, for example, making revolutionary discoveries in +astronomy, and performing fundamental experiments in various +fields of physics. Galileo's great contemporary, Kepler, was +almost equally versatile, though his astronomical studies were of +such pre-eminent importance that his other investigations sink +into relative insignificance. Yet he performed some notable +experiments in at least one department of physics. These +experiments had to do with the refraction of light, a subject +which Kepler was led to investigate, in part at least, through +his interest in the telescope. + +We have seen that Ptolemy in the Alexandrian time, and Alhazen, +the Arab, made studies of refraction. Kepler repeated their +experiments, and, striving as always to generalize his +observations, he attempted to find the law that governed the +observed change of direction which a ray of light assumes in +passing from one medium to another. Kepler measured the angle of +refraction by means of a simple yet ingenious trough-like +apparatus which enabled him to compare readily the direct and +refracted rays. He discovered that when a ray of light passes +through a glass plate, if it strikes the farther surface of the +glass at an angle greater than 45 degrees it will be totally +refracted instead of passing through into the air. He could not +well fail to know that different mediums refract light +differently, and that for the same medium the amount of light +valies with the change in the angle of incidence. He was not +able, however, to generalize his observations as he desired, and +to the last the law that governs refraction escaped him. It +remained for Willebrord Snell, a Dutchman, about the year 1621, +to discover the law in question, and for Descartes, a little +later, to formulate it. Descartes, indeed, has sometimes been +supposed to be the discoverer of the law. There is reason to +believe that he based his generalizations on the experiment of +Snell, though he did not openly acknowledge his indebtedness. The +law, as Descartes expressed it, states that the sine of the angle +of incidence bears a fixed ratio to the sine of the angle of +refraction for any given medium. Here, then, was another +illustration of the fact that almost infinitely varied phenomena +may be brought within the scope of a simple law. Once the law had +been expressed, it could be tested and verified with the greatest +ease; and, as usual, the discovery being made, it seems +surprising that earlier investigators--in particular so sagacious +a guesser as Kepler--should have missed it. + +Galileo himself must have been to some extent a student of light, +since, as we have seen, he made such notable contributions to +practical optics through perfecting the telescope; but he seems +not to have added anything to the theory of light. The subject of +heat, however, attracted his attention in a somewhat different +way, and he was led to the invention of the first contrivance for +measuring temperatures. His thermometer was based on the +afterwards familiar principle of the expansion of a liquid under +the influence of heat; but as a practical means of measuring +temperature it was a very crude affair, because the tube that +contained the measuring liquid was exposed to the air, hence +barometric changes of pressure vitiated the experiment. It +remained for Galileo's Italian successors of the Accademia del +Cimento of Florence to improve upon the apparatus, after the +experiments of Torricelli--to which we shall refer in a +moment--had thrown new light on the question of atmospheric +pressure. Still later the celebrated Huygens hit upon the idea of +using the melting and the boiling point of water as fixed points +in a scale of measurements, which first gave definiteness to +thermometric tests. + + +TORRICELLI + +In the closing years of his life Galileo took into his family, as +his adopted disciple in science, a young man, Evangelista +Torricelli (1608-1647), who proved himself, during his short +lifetime, to be a worthy follower of his great master. Not only +worthy on account of his great scientific discoveries, but +grateful as well, for when he had made the great discovery that +the "suction" made by a vacuum was really nothing but air +pressure, and not suction at all, he regretted that so important +a step in science might not have been made by his great teacher, +Galileo, instead of by himself. "This generosity of Torricelli," +says Playfair, "was, perhaps, rarer than his genius: there are +more who might have discovered the suspension of mercury in the +barometer than who would have been willing to part with the honor +of the discovery to a master or a friend." + +Torricelli's discovery was made in 1643, less than two years +after the death of his master. Galileo had observed that water +will not rise in an exhausted tube, such as a pump, to a height +greater than thirty-three feet, but he was never able to offer a +satisfactory explanation of the principle. Torricelli was able to +demonstrate that the height at which the water stood depended +upon nothing but its weight as compared with the weight of air. +If this be true, it is evident that any fluid will be supported +at a definite height, according to its relative weight as +compared with air. Thus mercury, which is about thirteen times +more dense than water, should only rise to one-thirteenth the +height of a column of water--that is, about thirty inches. +Reasoning in this way, Torricelli proceeded to prove that his +theory was correct. Filling a long tube, closed at one end, with +mercury, he inverted the tube with its open orifice in a vessel +of mercury. The column of mercury fell at once, but at a height +of about thirty inches it stopped and remained stationary, the +pressure of the air on the mercury in the vessel maintaining it +at that height. This discovery was a shattering blow to the old +theory that had dominated that field of physics for so many +centuries. It was completely revolutionary to prove that, instead +of a mysterious something within the tube being responsible for +the suspension of liquids at certain heights, it was simply the +ordinary atmospheric pressure mysterious enough, it is +true--pushing upon them from without. The pressure exerted by the +atmosphere was but little understood at that time, but +Torricelli's discovery aided materially in solving the mystery. +The whole class of similar phenomena of air pressure, which had +been held in the trammel of long-established but false doctrines, +was now reduced to one simple law, and the door to a solution of +a host of unsolved problems thrown open. + +It had long been suspected and believed that the density of the +atmosphere varies at certain times. That the air is sometimes +"heavy" and at other times "light" is apparent to the senses +without scientific apparatus for demonstration. It is evident, +then, that Torricelli's column of mercury should rise and fall +just in proportion to the lightness or heaviness of the air. A +short series of observations proved that it did so, and with +those observations went naturally the observations as to changes +in the weather. It was only necessary, therefore, to scratch a +scale on the glass tube, indicating relative atmospheric +pressures, and the Torricellian barometer was complete. + +Such a revolutionary theory and such an important discovery were, +of course, not to be accepted without controversy, but the feeble +arguments of the opponents showed how untenable the old theory +had become. In 1648 Pascal suggested that if the theory of the +pressure of air upon the mercury was correct, it could be +demonstrated by ascending a mountain with the mercury tube. As +the air was known to get progressively lighter from base to +summit, the height of the column should be progressively lessened +as the ascent was made, and increase again on the descent into +the denser air. The experiment was made on the mountain called +the Puy-de-Dome, in Auvergne, and the column of mercury fell and +rose progressively through a space of about three inches as the +ascent and descent were made. + +This experiment practically sealed the verdict on the new theory, +but it also suggested something more. If the mercury descended to +a certain mark on the scale on a mountain-top whose height was +known, why was not this a means of measuring the heights of all +other elevations? And so the beginning was made which, with +certain modifications and corrections in details, is now the +basis of barometrical measurements of heights. + +In hydraulics, also, Torricelli seems to have taken one of the +first steps. He did this by showing that the water which issues +from a hole in the side or bottom of a vessel does so at the same +velocity as that which a body would acquire by falling from the +level of the surface of the water to that of the orifice. This +discovery was of the greatest importance to a correct +understanding of the science of the motions of fluids. He also +discovered the valuable mechanical principle that if any number +of bodies be connected so that by their motion there is neither +ascent nor descent of their centre of gravity, these bodies are +in equilibrium. + +Besides making these discoveries, he greatly improved the +microscope and the telescope, and invented a simple microscope +made of a globule of glass. In 1644 he published a tract on the +properties of the cycloid in which he suggested a solution of the +problem of its quadrature. As soon as this pamphlet appeared its +author was accused by Gilles Roberval (1602-1675) of having +appropriated a solution already offered by him. This led to a +long debate, during which Torricelli was seized with a fever, +from the effects of which he died, in Florence, October 25, 1647. +There is reason to believe, however, that while Roberval's +discovery was made before Torricelli's, the latter reached his +conclusions independently. + + + +VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +In recent chapters we have seen science come forward with +tremendous strides. A new era is obviously at hand. But we shall +misconceive the spirit of the times if we fail to understand that +in the midst of all this progress there was still room for +mediaeval superstition and for the pursuit of fallacious ideals. +Two forms of pseudo-science were peculiarly prevalent --alchemy +and astrology. Neither of these can with full propriety be called +a science, yet both were pursued by many of the greatest +scientific workers of the period. Moreover, the studies of the +alchemist may with some propriety be said to have laid the +foundation for the latter-day science of chemistry; while +astrology was closely allied to astronomy, though its relations +to that science are not as intimate as has sometimes been +supposed. + +Just when the study of alchemy began is undetermined. It was +certainly of very ancient origin, perhaps Egyptian, but its most +flourishing time was from about the eighth century A.D. to the +eighteenth century. The stories of the Old Testament formed a +basis for some of the strange beliefs regarding the properties of +the magic "elixir," or "philosopher's stone." Alchemists believed +that most of the antediluvians, perhaps all of them, possessed a +knowledge of this stone. How, otherwise, could they have +prolonged their lives to nine and a half centuries? And Moses was +surely a first-rate alchemist, as is proved by the story of the +Golden Calf.[1] After Aaron had made the calf of gold, Moses +performed the much more difficult task of grinding it to powder +and "strewing it upon the waters," thus showing that he had +transmuted it into some lighter substance. + +But antediluvians and Biblical characters were not the only +persons who were thought to have discovered the coveted. +"elixir." Hundreds of aged mediaeval chemists were credited with +having made the discovery, and were thought to be living on +through the centuries by its means. Alaies de Lisle, for example, +who died in 1298, at the age of 110, was alleged to have been at +the point of death at the age of fifty, but just at this time he +made the fortunate discovery of the magic stone, and so continued +to live in health and affluence for sixty years more. And De +Lisle was but one case among hundreds. + +An aged and wealthy alchemist could claim with seeming +plausibility that he was prolonging his life by his magic; +whereas a younger man might assert that, knowing the great +secret, he was keeping himself young through the centuries. In +either case such a statement, or rumor, about a learned and +wealthy alchemist was likely to be believed, particularly among +strangers; and as such a man would, of course, be the object of +much attention, the claim was frequently made by persons seeking +notoriety. One of the most celebrated of these impostors was a +certain Count de Saint-Germain, who was connected with the court +of Louis XV. His statements carried the more weight because, +having apparently no means of maintenance, he continued to live +in affluence year after year--for two thousand years, as he +himself admitted--by means of the magic stone. If at any time his +statements were doubted, he was in the habit of referring to his +valet for confirmation, this valet being also under the influence +of the elixir of life. + +"Upon one occasion his master was telling a party of ladies and +gentlemen, at dinner, some conversation he had had in Palestine, +with King Richard I., of England, whom he described as a very +particular friend of his. Signs of astonishment and incredulity +were visible on the faces of the company, upon which +Saint-Germain very coolly turned to his servant, who stood behind +his chair, and asked him if he had not spoken the truth. 'I +really cannot say,' replied the man, without moving a muscle; +'you forget, sir, I have been only five hundred years in your +service.' 'Ah, true,' said his master, 'I remember now; it was a +little before your time!' "[2] + +In the time of Saint-Germain, only a little over a century ago, +belief in alchemy had almost disappeared, and his extraordinary +tales were probably regarded in the light of amusing stories. +Still there was undoubtedly a lingering suspicion in the minds of +many that this man possessed some peculiar secret. A few +centuries earlier his tales would hardly have been questioned, +for at that time the belief in the existence of this magic +something was so strong that the search for it became almost a +form of mania; and once a man was seized with it, lie gambled +away health, position, and life itself in pursuing the coveted +stake. An example of this is seen in Albertus Magnus, one of the +most learned men of his time, who it is said resigned his +position as bishop of Ratisbon in order that he might pursue his +researches in alchemy. + +If self-sacrifice was not sufficient to secure the prize, crime +would naturally follow, for there could be no limit to the price +of the stakes in this game. The notorious Marechal de Reys, +failing to find the coveted stone by ordinary methods of +laboratory research, was persuaded by an impostor that if he +would propitiate the friendship of the devil the secret would be +revealed. To this end De Reys began secretly capturing young +children as they passed his castle and murdering them. When he +was at last brought to justice it was proved that he had murdered +something like a hundred children within a period of three years. +So, at least, runs one version of the story of this perverted +being. + +Naturally monarchs, constantly in need of funds, were interested +in these alchemists. Even sober England did not escape, and +Raymond Lully, one of the most famous of the thirteenth and +fourteenth century alchemists, is said to have been secretly +invited by King Edward I. (or II.) to leave Milan and settle in +England. According to some accounts, apartments were assigned to +his use in the Tower of London, where he is alleged to have made +some six million pounds sterling for the monarch, out of iron, +mercury, lead, and pewter. + +Pope John XXII., a friend and pupil of the alchemist Arnold de +Villeneuve, is reported to have learned the secrets of alchemy +from his master. Later he issued two bulls against "pretenders" +in the art, which, far from showing his disbelief, were cited by +alchemists as proving that he recognized pretenders as distinct +from true masters of magic. + +To moderns the attitude of mind of the alchemist is difficult to +comprehend. It is, perhaps, possible to conceive of animals or +plants possessing souls, but the early alchemist attributed the +same thing--or something kin to it--to metals also. Furthermore, +just as plants germinated from seeds, so metals were supposed to +germinate also, and hence a constant growth of metals in the +ground. To prove this the alchemist cited cases where previously +exhausted gold-mines were found, after a lapse of time, to +contain fresh quantities of gold. The "seed" of the remaining +particles of gold had multiplied and increased. But this +germinating process could only take place under favorable +conditions, just as the seed of a plant must have its proper +surroundings before germinating; and it was believed that the +action of the philosopher's stone was to hasten this process, as +man may hasten the growth of plants by artificial means. Gold was +looked upon as the most perfect metal, and all other metals +imperfect, because not yet "purified." By some alchemists they +were regarded as lepers, who, when cured of their leprosy, would +become gold. And since nature intended that all things should be +perfect, it was the aim of the alchemist to assist her in this +purifying process, and incidentally to gain wealth and prolong +his life. + +By other alchemists the process of transition from baser metals +into gold was conceived to be like a process of ripening fruit. +The ripened product was gold, while the green fruit, in various +stages of maturity, was represented by the base metals. Silver, +for example, was more nearly ripe than lead; but the difference +was only one of "digestion," and it was thought that by further +"digestion" lead might first become silver and eventually gold. +In other words, Nature had not completed her work, and was +wofully slow at it at best; but man, with his superior faculties, +was to hasten the process in his laboratories--if he could but +hit upon the right method of doing so. + +It should not be inferred that the alchemist set about his task +of assisting nature in a haphazard way, and without training in +the various alchemic laboratory methods. On the contrary, he +usually served a long apprenticeship in the rudiments of his +calling. He was obliged to learn, in a general way, many of the +same things that must be understood in either chemical or +alchemical laboratories. The general knowledge that certain +liquids vaporize at lower temperatures than others, and that the +melting-points of metals differ greatly, for example, was just as +necessary to alchemy as to chemistry. The knowledge of the gross +structure, or nature, of materials was much the same to the +alchemist as to the chemist, and, for that matter, many of the +experiments in calcining, distilling, etc., were practically +identical. + +To the alchemist there were three principles--salt, sulphur, and +mercury--and the sources of these principles were the four +elements--earth, water, fire, and air. These four elements were +accountable for every substance in nature. Some of the +experiments to prove this were so illusive, and yet apparently so +simple, that one is not surprised that it took centuries to +disprove them. That water was composed of earth and air seemed +easily proven by the simple process of boiling it in a +tea-kettle, for the residue left was obviously an earthy +substance, whereas the steam driven off was supposed to be air. +The fact that pure water leaves no residue was not demonstrated +until after alchemy had practically ceased to exist. It was +possible also to demonstrate that water could be turned into fire +by thrusting a red-hot poker under a bellglass containing a dish +of water. Not only did the quantity of water diminish, but, if a +lighted candle was thrust under the glass, the contents ignited +and burned, proving, apparently, that water had been converted +into fire. These, and scores of other similar experiments, seemed +so easily explained, and to accord so well with the "four +elements" theory, that they were seldom questioned until a later +age of inductive science. + +But there was one experiment to which the alchemist pinned his +faith in showing that metals could be "killed" and "revived," +when proper means were employed. It had been known for many +centuries that if any metal, other than gold or silver, were +calcined in an open crucible, it turned, after a time, into a +peculiar kind of ash. This ash was thought by the alchemist to +represent the death of the metal. But if to this same ash a few +grains of wheat were added and heat again applied to the +crucible, the metal was seen to "rise from its ashes" and resume +its original form--a well-known phenomenon of reducing metals +from oxides by the use of carbon, in the form of wheat, or, for +that matter, any other carbonaceous substance. Wheat was, +therefore, made the symbol of the resurrection of the life +eternal. Oats, corn, or a piece of charcoal would have "revived" +the metals from the ashes equally well, but the mediaeval +alchemist seems not to have known this. However, in this +experiment the metal seemed actually to be destroyed and +revivified, and, as science had not as yet explained this +striking phenomenon, it is little wonder that it deceived the +alchemist. + +Since the alchemists pursued their search of the magic stone in +such a methodical way, it would seem that they must have some +idea of the appearance of the substance they sought. Probably +they did, each according to his own mental bias; but, if so, they +seldom committed themselves to writing, confining their +discourses largely to speculations as to the properties of this +illusive substance. Furthermore, the desire for secrecy would +prevent them from expressing so important a piece of information. +But on the subject of the properties, if not on the appearance of +the "essence," they were voluminous writers. It was supposed to +be the only perfect substance in existence, and to be confined in +various substances, in quantities proportionate to the state of +perfection of the substance. Thus, gold being most nearly perfect +would contain more, silver less, lead still less, and so on. The +"essence" contained in the more nearly perfect metals was thought +to be more potent, a very small quantity of it being capable of +creating large quantities of gold and of prolonging life +indefinitely. + +It would appear from many of the writings of the alchemists that +their conception of nature and the supernatural was so confused +and entangled in an inexplicable philosophy that they themselves +did not really understand the meaning of what they were +attempting to convey. But it should not be forgotten that alchemy +was kept as much as possible from the ignorant general public, +and the alchemists themselves had knowledge of secret words and +expressions which conveyed a definite meaning to one of their +number, but which would appear a meaningless jumble to an +outsider. Some of these writers declared openly that their +writings were intended to convey an entirely erroneous +impression, and were sent out only for that purpose. + +However, while it may have been true that the vagaries of their +writings were made purposely, the case is probably more correctly +explained by saying that the very nature of the art made definite +statements impossible. They were dealing with something that did +not exist--could not exist. Their attempted descriptions became, +therefore, the language of romance rather than the language of +science. + +But if the alchemists themselves were usually silent as to the +appearance of the actual substance of the philosopher's stone, +there were numberless other writers who were less reticent. By +some it was supposed to be a stone, by others a liquid or elixir, +but more commonly it was described as a black powder. It also +possessed different degrees of efficiency according to its +degrees of purity, certain forms only possessing the power of +turning base metals into gold, while others gave eternal youth +and life or different degrees of health. Thus an alchemist, who +had made a partial discovery of this substance, could prolong +life a certain number of years only, or, possessing only a small +and inadequate amount of the magic powder, he was obliged to give +up the ghost when the effect of this small quantity had passed +away. + +This belief in the supernatural power of the philosopher's stone +to prolong life and heal diseases was probably a later phase of +alchemy, possibly developed by attempts to connect the power of +the mysterious essence with Biblical teachings. The early Roman +alchemists, who claimed to be able to transmute metals, seem not +to have made other claims for their magic stone. + +By the fifteenth century the belief in the philosopher's stone +had become so fixed that governments began to be alarmed lest +some lucky possessor of the secret should flood the country with +gold, thus rendering the existing coin of little value. Some +little consolation was found in the thought that in case all the +baser metals were converted into gold iron would then become the +"precious metal," and would remain so until some new +philosopher's stone was found to convert gold back into iron--a +much more difficult feat, it was thought. However, to be on the +safe side, the English Parliament, in 1404, saw fit to pass an +act declaring the making of gold and silver to be a felony. +Nevertheless, in 1455, King Henry VI. granted permission to +several "knights, citizens of London, chemists, and monks" to +find the philosopher's stone, or elixir, that the crown might +thus be enabled to pay off its debts. The monks and ecclesiastics +were supposed to be most likely to discover the secret process, +since "they were such good artists in transubstantiating bread +and wine." + +In Germany the emperors Maximilian I., Rudolf II., and Frederick +II. gave considerable attention to the search, and the example +they set was followed by thousands of their subjects. It is said +that some noblemen developed the unpleasant custom of inviting to +their courts men who were reputed to have found the stone, and +then imprisoning the poor alchemists until they had made a +certain quantity of gold, stimulating their activity with +tortures of the most atrocious kinds. Thus this danger of being +imprisoned and held for ransom until some fabulous amount of gold +should be made became the constant menace of the alchemist. It +was useless for an alchemist to plead poverty once it was noised +about that he had learned the secret. For how could such a man be +poor when, with a piece of metal and a few grains of magic +powder, he was able to provide himself with gold? It was, +therefore, a reckless alchemist indeed who dared boast that he +had made the coveted discovery. + +The fate of a certain indiscreet alchemist, supposed by many to +have been Seton, a Scotchman, was not an uncommon one. Word +having been brought to the elector of Saxony that this alchemist +was in Dresden and boasting of his powers, the elector caused him +to be arrested and imprisoned. Forty guards were stationed to see +that he did not escape and that no one visited him save the +elector himself. For some time the elector tried by argument and +persuasion to penetrate his secret or to induce him to make a +certain quantity of gold; but as Seton steadily refused, the rack +was tried, and for several months he suffered torture, until +finally, reduced to a mere skeleton, be was rescued by a rival +candidate of the elector, a Pole named Michael Sendivogins, who +drugged the guards. However, before Seton could be "persuaded" by +his new captor, he died of his injuries. + +But Sendivogins was also ambitious in alchemy, and, since Seton +was beyond his reach, he took the next best step and married his +widow. From her, as the story goes, he received an ounce of black +powder--the veritable philosopher's stone. With this he +manufactured great quantities of gold, even inviting Emperor +Rudolf II. to see him work the miracle. That monarch was so +impressed that he caused a tablet to be inserted in the wall of +the room in which he had seen the gold made. + +Sendivogins had learned discretion from the misfortune of Seton, +so that he took the precaution of concealing most of the precious +powder in a secret chamber of his carriage when he travelled, +having only a small quantity carried by his steward in a gold +box. In particularly dangerous places, he is said to have +exchanged clothes with his coachman, making the servant take his +place in the carriage while he mounted the box. + + +About the middle of the seventeenth century alchemy took such +firm root in the religious field that it became the basis of the +sect known as the Rosicrucians. The name was derived from the +teaching of a German philosopher, Rosenkreutz, who, having been +healed of a dangerous illness by an Arabian supposed to possess +the philosopher's stone, returned home and gathered about him a +chosen band of friends, to whom he imparted the secret. This sect +came rapidly into prominence, and for a short time at least +created a sensation in Europe, and at the time were credited with +having "refined and spiritualized" alchemy. But by the end of the +seventeenth century their number had dwindled to a mere handful, +and henceforth they exerted little influence. + +Another and earlier religious sect was the Aureacrucians, founded +by Jacob Bohme, a shoemaker, born in Prussia in 1575. According +to his teachings the philosopher's stone could be discovered by a +diligent search of the Old and the New Testaments, and more +particularly the Apocalypse, which contained all the secrets of +alchemy. This sect found quite a number of followers during the +life of Bohme, but gradually died out after his death; not, +however, until many of its members had been tortured for heresy, +and one at least, Kuhlmann, of Moscow, burned as a sorcerer. + +The names of the different substances that at various times were +thought to contain the large quantities of the "essence" during +the many centuries of searching for it, form a list of +practically all substances that were known, discovered, or +invented during the period. Some believed that acids contained +the substance; others sought it in minerals or in animal or +vegetable products; while still others looked to find it among +the distilled "spirits"--the alcoholic liquors and distilled +products. On the introduction of alcohol by the Arabs that +substance became of all-absorbing interest, and for a long time +allured the alchemist into believing that through it they were +soon to be rewarded. They rectified and refined it until +"sometimes it was so strong that it broke the vessels containing +it," but still it failed in its magic power. Later, brandy was +substituted for it, and this in turn discarded for more recent +discoveries. + +There were always, of course, two classes of alchemists: serious +investigators whose honesty could not be questioned, and clever +impostors whose legerdemain was probably largely responsible for +the extended belief in the existence of the philosopher's stone. +Sometimes an alchemist practised both, using the profits of his +sleight-of-hand to procure the means of carrying on his serious +alchemical researches. The impostures of some of these jugglers +deceived even the most intelligent and learned men of the time, +and so kept the flame of hope constantly burning. The age of cold +investigation had not arrived, and it is easy to understand how +an unscrupulous mediaeval Hermann or Kellar might completely +deceive even the most intelligent and thoughtful scholars. In +scoffing at the credulity of such an age, it should not be +forgotten that the "Keely motor" was a late nineteenth-century +illusion. + +But long before the belief in the philosopher's stone had died +out, the methods of the legerdemain alchemist had been +investigated and reported upon officially by bodies of men +appointed to make such investigations, although it took several +generations completely to overthrow a superstition that had been +handed down through several thousand years. In April of 1772 +Monsieur Geoffroy made a report to the Royal Academy of Sciences, +at Paris, on the alchemic cheats principally of the sixteenth and +seventeenth centuries. In this report he explains many of the +seemingly marvellous feats of the unscrupulous alchemists. A very +common form of deception was the use of a double-bottomed +crucible. A copper or brass crucible was covered on the inside +with a layer of wax, cleverly painted so as to resemble the +ordinary metal. Between this layer of wax and the bottom of the +crucible, however, was a layer of gold dust or silver. When the +alchemist wished to demonstrate his power, he had but to place +some mercury or whatever substance he chose in the crucible, heat +it, throw in a grain or two of some mysterious powder, pronounce +a few equally mysterious phrases to impress his audience, and, +behold, a lump of precious metal would be found in the bottom of +his pot. This was the favorite method of mediocre performers, but +was, of course, easily detected. + +An equally successful but more difficult way was to insert +surreptitiously a lump of metal into the mixture, using an +ordinary crucible. This required great dexterity, but was +facilitated by the use of many mysterious ceremonies on the part +of the operator while performing, just as the modern vaudeville +performer diverts the attention of the audience to his right hand +while his left is engaged in the trick. Such ceremonies were not +questioned, for it was the common belief that the whole process +"lay in the spirit as much as in the substance," many, as we have +seen, regarding the whole process as a divine manifestation. + +Sometimes a hollow rod was used for stirring the mixture in the +crucible, this rod containing gold dust, and having the end +plugged either with wax or soft metal that was easily melted. +Again, pieces of lead were used which had been plugged with lumps +of gold carefully covered over; and a very simple and impressive +demonstration was making use of a nugget of gold that had been +coated over with quicksilver and tarnished so as to resemble lead +or some base metal. When this was thrown into acid the coating +was removed by chemical action, leaving the shining metal in the +bottom of the vessel. In order to perform some of these tricks, +it is obvious that the alchemist must have been well supplied +with gold, as some of them, when performing before a royal +audience, gave the products to their visitors. But it was always +a paying investment, for once his reputation was established the +gold-maker found an endless variety of ways of turning his +alleged knowledge to account, frequently amassing great wealth. + +Some of the cleverest of the charlatans often invited royal or +other distinguished guests to bring with them iron nails to be +turned into gold ones. They were transmuted in the alchemist's +crucible before the eyes of the visitors, the juggler adroitly +extracting the iron nail and inserting a gold one without +detection. It mattered little if the converted gold nail differed +in size and shape from the original, for this change in shape +could be laid to the process of transmutation; and even the very +critical were hardly likely to find fault with the exchange thus +made. Furthermore, it was believed that gold possessed the +property of changing its bulk under certain conditions, some of +the more conservative alchemists maintaining that gold was only +increased in bulk, not necessarily created, by certain forms of +the magic stone. Thus a very proficient operator was thought to +be able to increase a grain of gold into a pound of pure metal, +while one less expert could only double, or possibly treble, its +original weight. + +The actual number of useful discoveries resulting from the +efforts of the alchemists is considerable, some of them of +incalculable value. Roger Bacon, who lived in the thirteenth +century, while devoting much of his time to alchemy, made such +valuable discoveries as the theory, at least, of the telescope, +and probably gunpowder. Of this latter we cannot be sure that the +discovery was his own and that he had not learned of it through +the source of old manuscripts. But it is not impossible nor +improbable that he may have hit upon the mixture that makes the +explosives while searching for the philosopher's stone in his +laboratory. "Von Helmont, in the same pursuit, discoverd the +properties of gas," says Mackay; "Geber made discoveries in +chemistry, which were equally important; and Paracelsus, amid his +perpetual visions of the transmutation of metals, found that +mercury was a remedy for one of the most odious and excruciating +of all the diseases that afflict humanity."' As we shall see a +little farther on, alchemy finally evolved into modern chemistry, +but not until it had passed through several important +transitional stages. + + +ASTROLOGY + +In a general way modern astronomy may be considered as the +outgrowth of astrology, just as modern chemistry is the result of +alchemy. It is quite possible, however, that astronomy is the +older of the two; but astrology must have developed very shortly +after. The primitive astronomer, having acquired enough knowledge +from his observations of the heavenly bodies to make correct +predictions, such as the time of the coming of the new moon, +would be led, naturally, to believe that certain predictions +other than purely astronomical ones could be made by studying the +heavens. Even if the astronomer himself did not believe this, +some of his superstitious admirers would; for to the unscientific +mind predictions of earthly events would surely seem no more +miraculous than correct predictions as to the future movements of +the sun, moon, and stars. When astronomy had reached a stage of +development so that such things as eclipses could be predicted +with anything like accuracy, the occult knowledge of the +astronomer would be unquestioned. Turning this apparently occult +knowledge to account in a mercenary way would then be the +inevitable result, although it cannot be doubted that many of the +astrologers, in all ages, were sincere in their beliefs. + +Later, as the business of astrology became a profitable one, +sincere astronomers would find it expedient to practise astrology +as a means of gaining a livelihood. Such a philosopher as Kepler +freely admitted that he practised astrology "to keep from +starving," although he confessed no faith in such predictions. +"Ye otherwise philosophers," he said, "ye censure this daughter +of astronomy beyond her deserts; know ye not that she must +support her mother by her charms." + +Once astrology had become an established practice, any +considerable knowledge of astronomy was unnecessary, for as it +was at best but a system of good guessing as to future events, +clever impostors could thrive equally well without troubling to +study astronomy. The celebrated astrologers, however, were +usually astronomers as well, and undoubtedly based many of their +predictions on the position and movements of the heavenly bodies. +Thus, the casting of a horoscope that is, the methods by which +the astrologers ascertained the relative position of the heavenly +bodies at the time of a birth--was a simple but fairly exact +procedure. Its basis was the zodiac, or the path traced by the +sun in his yearly course through certain constellations. At the +moment of the birth of a child, the first care of the astrologer +was to note the particular part of the zodiac that appeared on +the horizon. The zodiac was then divided into "houses"--that is, +into twelve spaces--on a chart. In these houses were inserted the +places of the planets, sun, and moon, with reference to the +zodiac. When this chart was completed it made a fairly correct +diagram of the heavens and the position of the heavenly bodies as +they would appear to a person standing at the place of birth at a +certain time. + +Up to this point the process was a simple one of astronomy. But +the next step--the really important one--that of interpreting +this chart, was the one which called forth the skill and +imagination of the astrologer. In this interpretation, not in his +mere observations, lay the secret of his success. Nor did his +task cease with simply foretelling future events that were to +happen in the life of the newly born infant. He must not only +point out the dangers, but show the means whereby they could be +averted, and his prophylactic measures, like his predictions, +were alleged to be based on his reading of the stars. + +But casting a horoscope at the time of births was, of course, +only a small part of the astrologer's duty. His offices were +sought by persons of all ages for predictions as to their +futures, the movements of an enemy, where to find stolen goods, +and a host of everyday occurrences. In such cases it is more than +probable that the astrologers did very little consulting of the +stars in making their predictions. They became expert +physiognomists and excellent judges of human nature, and were +thus able to foretell futures with the same shrewdness and by the +same methods as the modern "mediums," palmists, and +fortune-tellers. To strengthen belief in their powers, it became +a common thing for some supposedly lost document of the +astrologer to be mysteriously discovered after an important +event, this document purporting to foretell this very event. It +was also a common practice with astrologers to retain, or have +access to, their original charts, cleverly altering them from +time to time to fit conditions. + +The dangers attendant upon astrology were of such a nature that +the lot of the astrologer was likely to prove anything but an +enviable one. As in the case of the alchemist, the greater the +reputation of an astrologer the greater dangers he was likely to +fall into. If he became so famous that he was employed by kings +or noblemen, his too true or too false prophecies were likely to +bring him into disrepute--even to endanger his life. + +Throughout the dark age the astrologers flourished, but the +sixteenth and seventeenth centuries were the golden age of these +impostors. A skilful astrologer was as much an essential to the +government as the highest official, and it would have been a bold +monarch, indeed, who would undertake any expedition of importance +unless sanctioned by the governing stars as interpreted by these +officials. + +It should not be understood, however, that belief in astrology +died with the advent of the Copernican doctrine. It did become +separated from astronomy very shortly after, to be sure, and +undoubtedly among the scientists it lost much of its prestige. +But it cannot be considered as entirely passed away, even to-day, +and even if we leave out of consideration street-corner +"astrologers" and fortune-tellers, whose signs may be seen in +every large city, there still remains quite a large class of +relatively intelligent people who believe in what they call "the +science of astrology." Needless to say, such people are not found +among the scientific thinkers; but it is significant that +scarcely a year passes that some book or pamphlet is not +published by some ardent believer in astrology, attempting to +prove by the illogical dogmas characteristic of unscientific +thinkers that astrology is a science. The arguments contained in +these pamphlets are very much the same as those of the +astrologers three hundred years ago, except that they lack the +quaint form of wording which is one of the features that lends +interest to the older documents. These pamphlets need not be +taken seriously, but they are interesting as exemplifying how +difficult it is, even in an age of science, to entirely stamp out +firmly established superstitions. Here are some of the arguments +advanced in defence of astrology, taken from a little brochure +entitled "Astrology Vindicated," published in 1898: It will be +found that a person born when the Sun is in twenty degrees +Scorpio has the left ear as his exceptional feature and the nose +(Sagittarius) bent towards the left ear. A person born when the +Sun is in any of the latter degrees of Taurus, say the +twenty-fifth degree, will have a small, sharp, weak chin, curved +up towards Gemini, the two vertical lines on the upper lip."[4] +The time was when science went out of its way to prove that such +statements were untrue; but that time is past, and such writers +are usually classed among those energetic but misguided persons +who are unable to distinguish between logic and sophistry. + + +In England, from the time of Elizabeth to the reign of William +and Mary, judicial astrology was at its height. After the great +London fire, in 1666, a committee of the House of Commons +publicly summoned the famous astrologer, Lilly, to come before +Parliament and report to them on his alleged prediction of the +calamity that had befallen the city. Lilly, for some reason best +known to himself, denied having made such a prediction, being, as +he explained, "more interested in determining affairs of much +more importance to the future welfare of the country." Some of +the explanations of his interpretations will suffice to show +their absurdities, which, however, were by no means regarded as +absurdities at that time, for Lilly was one of the greatest +astrologers of his day. He said that in 1588 a prophecy had been +printed in Greek characters which foretold exactly the troubles +of England between the years 1641. and 1660. "And after him shall +come a dreadful dead man," ran the prophecy, "and with him a +royal G of the best blood in the world, and he shall have the +crown and shall set England on the right way and put out all +heresies. His interpretation of this was that, "Monkery being +extinguished above eighty or ninety years, and the Lord General's +name being Monk, is the dead man. The royal G or C (it is gamma +in the Greek, intending C in the Latin, being the third letter in +the alphabet) is Charles II., who, for his extraction, may be +said to be of the best blood of the world."[5] + +This may be taken as a fair sample of Lilly's interpretations of +astrological prophesies, but many of his own writings, while +somewhat more definite and direct, are still left sufficiently +vague to allow his skilful interpretations to set right an +apparent mistake. One of his famous documents was "The Starry +Messenger," a little pamphlet purporting to explain the +phenomenon of a "strange apparition of three suns" that were seen +in London on November 19, 1644---the anniversary of the birth of +Charles I., then the reigning monarch. This phenomenon caused a +great stir among the English astrologers, coming, as it did, at a +time of great political disturbance. Prophecies were numerous, +and Lilly's brochure is only one of many that appeared at that +time, most of which, however, have been lost. Lilly, in his +preface, says: "If there be any of so prevaricate a judgment as +to think that the apparition of these three Suns doth intimate no +Novelle thing to happen in our own Climate, where they were +manifestly visible, I shall lament their indisposition, and +conceive their brains to be shallow, and voyde of understanding +humanity, or notice of common History." + +Having thus forgiven his few doubting readers, who were by no +means in the majority in his day, he takes up in review the +records of the various appearances of three suns as they have +occurred during the Christian era, showing how such phenomena +have governed certain human events in a very definite manner. +Some of these are worth recording. + +"Anno 66. A comet was seen, and also three Suns: In which yeer, +Florus President of the Jews was by them slain. Paul writes to +Timothy. The Christians are warned by a divine Oracle, and depart +out of Jerusalem. Boadice a British Queen, killeth seventy +thousand Romans. The Nazareni, a scurvie Sect, begun, that +boasted much of Revelations and Visions. About a year after Nero +was proclaimed enemy to the State of Rome." + +Again, "Anno 1157, in September, there were seen three Suns +together, in as clear weather as could be: And a few days after, +in the same month, three Moons, and, in the Moon that stood in +the middle, a white Crosse. Sueno, King of Denmark, at a great +Feast, killeth Canutus: Sueno is himself slain, in pursuit of +Waldemar. The Order of Eremites, according to the rule of Saint +Augustine, begun this year; and in the next, the Pope submits to +the Emperour: (was not this miraculous?) Lombardy was also +adjudged to the Emperour." + +Continuing this list of peculiar phenomena he comes down to +within a few years of his own time. + +"Anno 1622, three Suns appeared at Heidelberg. The woful +Calamities that have ever since fallen upon the Palatinate, we +are all sensible of, and of the loss of it, for any thing I see, +for ever, from the right Heir. Osman the great Turk is strangled +that year; and Spinola besiegeth Bergen up Zoom, etc." + +Fortified by the enumeration of these past events, he then +proceeds to make his deductions. "Only this I must tell thee," he +writes, "that the interpretation I write is, I conceive, grounded +upon probable foundations; and who lives to see a few years over +his head, will easily perceive I have unfolded as much as was fit +to discover, and that my judgment was not a mile and a half from +truth." + +There is a great significance in this "as much as was fit to +discover"--a mysterious something that Lilly thinks it expedient +not to divulge. But, nevertheless, one would imagine that he was +about to make some definite prediction about Charles I., since +these three suns appeared upon his birthday and surely must +portend something concerning him. But after rambling on through +many pages of dissertations upon planets and prophecies, he +finally makes his own indefinite prediction. + +"O all you Emperors, Kings, Princes, Rulers and Magistrates of +Europe, this unaccustomed Apparition is like the Handwriting in +Daniel to some of you; it premonisheth you, above all other +people, to make your peace with God in time. You shall every one +of you smart, and every one of you taste (none excepted) the +heavie hand of God, who will strengthen your subjects with +invincible courage to suppress your misgovernments and +Oppressions in Church or Common-wealth; . . . Those words are +general: a word for my own country of England. . . . Look to +yourselves; here's some monstrous death towards you. But to whom? +wilt thou say. Herein we consider the Signe, Lord thereof, and +the House; The Sun signifies in that Royal Signe, great ones; the +House signifies captivity, poison, Treachery: From which is +derived thus much, That some very great man, what King, Prince, +Duke, or the like, I really affirm I perfectly know not, shall, I +say, come to some such untimely end."[6] + +Here is shown a typical example of astrological prophecy, which +seems to tell something or nothing, according to the point of +view of the reader. According to a believer in astrology, after +the execution of Charles I., five years later, this could be made +to seem a direct and exact prophecy. For example, he says: "You +Kings, Princes, etc., ... it premonisheth you ... to make your +peace with God.... Look to yourselves; here's some monstrous +death towards you. ... That some very great man, what King, +Prince, . shall, I say, come to such untimely end." + +But by the doubter the complete prophecy could be shown to be +absolutely indefinite, and applicable as much to the king of +France or Spain as to Charles I., or to any king in the future, +since no definite time is stated. Furthermore, Lilly distinctly +states, "What King, Prince, Duke, or the like, I really affirm I +perfectly know not"--which last, at least, was a most truthful +statement. The same ingenuity that made "Gen. Monk" the "dreadful +dead man," could easily make such a prediction apply to the +execution of Charles I. Such a definite statement that, on such +and such a day a certain number of years in the future, the +monarch of England would be beheaded--such an exact statement can +scarcely be found in any of the works on astrology. It should be +borne in mind, also, that Lilly was of the Cromwell party and +opposed to the king. + +After the death of Charles I., Lilly admitted that the monarch +had given him a thousand pounds to cast his horoscope. "I advised +him," says Lilly, "to proceed eastwards; he went west, and all +the world knows the result." It is an unfortunate thing for the +cause of astrology that Lilly failed to mention this until after +the downfall of the monarch. In fact, the sudden death, or +decline in power, of any monarch, even to-day, brings out the +perennial post-mortem predictions of astrologers. + +We see how Lilly, an opponent of the king, made his so-called +prophecy of the disaster of the king and his army. At the same +time another celebrated astrologer and rival of Lilly, George +Wharton, also made some predictions about the outcome of the +eventful march from Oxford. Wharton, unlike Lilly, was a follower +of the king's party, but that, of course, should have had no +influence in his "scientific" reading of the stars. Wharton's +predictions are much less verbose than Lilly's, much more +explicit, and, incidentally, much more incorrect in this +particular instance. "The Moon Lady of the 12," he wrote, "and +moving betwixt the 8 degree, 34 min., and 21 degree, 26 min. of +Aquarius, gives us to understand that His Majesty shall receive +much contentment by certain Messages brought him from foreign +parts; and that he shall receive some sudden and unexpected +supply of . . . by the means of some that assimilate the +condition of his Enemies: And withal this comfort; that His +Majesty shall be exceeding successful in Besieging Towns, +Castles, or Forts, and in persuing the enemy. + +"Mars his Sextile to the Sun, Lord of the Ascendant (which +happeneth the 18 day of May) will encourage our Soldiers to +advance with much alacrity and cheerfulness of spirit; to show +themselves gallant in the most dangerous attempt.... And now to +sum up all: It is most apparent to every impartial and ingenuous +judgment; That although His Majesty cannot expect to be secured +from every trivial disaster that may befall his army, either by +the too much Presumption, Ignorance, or Negligence of some +particular Persons (which is frequently incident and unavoidable +in the best of Armies), yet the several positions of the Heavens +duly considered and compared among themselves, as well in the +prefixed Scheme as at the Quarterly Ingresses, do generally +render His Majesty and his whole Army unexpectedly victorious and +successful in all his designs; Believe it (London), thy Miseries +approach, they are like to be many, great, and grievous, and not +to be diverted, unless thou seasonably crave Pardon of God for +being Nurse to this present Rebellion, and speedily submit to thy +Prince's Mercy; Which shall be the daily Prayer of Geo. +Wharton."[7] + +In the light of after events, it is probable that Wharton's stock +as an astrologer was not greatly enhanced by this document, at +least among members of the Royal family. Lilly's book, on the +other hand, became a favorite with the Parliamentary army. + +After the downfall and death of Napoleon there were unearthed +many alleged authentic astrological documents foretelling his +ruin. And on the death of George IV., in 1830, there appeared a +document (unknown, as usual, until that time) purporting to +foretell the death of the monarch to the day, and this without +the astrologer knowing that his horoscope was being cast for a +monarch. A full account of this prophecy is told, with full +belief, by Roback, a nineteenth-century astrologer. He says: + +"In the year 1828, a stranger of noble mien, advanced in life, +but possessing the most bland manners, arrived at the abode of a +celebrated astrologer in London," asking that the learned man +foretell his future. "The astrologer complied with the request of +the mysterious visitor, drew forth his tables, consulted his +ephemeris, and cast the horoscope or celestial map for the hour +and the moment of the inquiry, according to the established rules +of his art. + +"The elements of his calculation were adverse, and a feeling of +gloom cast a shade of serious thought, if not dejection, over his +countenance. + +" 'You are of high rank,' said the astrologer, as he calculated +and looked on the stranger, 'and of illustrious title.' The +stranger made a graceful inclination of the head in token of +acknowledgment of the complimentary remarks, and the astrologer +proceeded with his mission. + +"The celestial signs were ominous of calamity to the stranger, +who, probably observing a sudden change in the countenance of the +astrologer, eagerly inquired what evil or good fortune had been +assigned him by the celestial orbs. + +'To the first part of your inquiry,' said the astrologer, 'I can +readily reply. You have been a favorite of fortune; her smiles on +you have been abundant, her frowns but few; you have had, perhaps +now possess, wealth and power; the impossibility of their +accomplishment is the only limit to the fulfilment of your +desires.' " + +" 'You have spoken truly of the past,' said the stranger. 'I have +full faith in your revelations of the future: what say you of my +pilgrimage in this life--is it short or long?' + +" 'I regret,' replied the astrologer, in answer to this inquiry, +'to be the herald of ill, though TRUE, fortune; your sojourn on +earth will be short.' + +" 'How short?' eagerly inquired the excited and anxious stranger. + +" 'Give me a momentary truce,' said the astrologer; 'I will +consult the horoscope, and may possibly find some mitigating +circumstances.' + +"Having cast his eyes over the celestial map, and paused for some +moments, he surveyed the countenance of the stranger with great +sympathy, and said, 'I am sorry that I can find no planetary +influences that oppose your destiny--your death will take place +in two years.' + +"The event justified the astrologic prediction: George IV. died +on May 18, 1830, exactly two years from the day on which he had +visited the astrologer."[8] + +This makes a very pretty story, but it hardly seems like occult +insight that an astrologer should have been able to predict an +early death of a man nearly seventy years old, or to have guessed +that his well-groomed visitor "had, perhaps now possesses, wealth +and power." Here again, however, the point of view of each +individual plays the governing part in determining the importance +of such a document. To the scientist it proves nothing; to the +believer in astrology, everything. The significant thing is that +it appeared shortly AFTER the death of the monarch. + + +On the Continent astrologers were even more in favor than in +England. Charlemagne, and some of his immediate successors, to be +sure, attempted to exterminate them, but such rulers as Louis XI. +and Catherine de' Medici patronized and encouraged them, and it +was many years after the time of Copernicus before their +influence was entirely stamped out even in official life. There +can be no question that what gave the color of truth to many of +the predictions was the fact that so many of the prophecies of +sudden deaths and great conflagrations were known to have come +true--in many instances were made to come true by the astrologer +himself. And so it happened that when the prediction of a great +conflagration at a certain time culminated in such a +conflagration, many times a second but less-important burning +took place, in which the ambitious astrologer, or his followers, +took a central part about a stake, being convicted of +incendiarism, which they had committed in order that their +prophecies might be fulfilled. + +But, on the other hand, these predictions were sometimes turned +to account by interested friends to warn certain persons of +approaching dangers. + +For example, a certain astrologer foretold the death of Prince +Alexander de' Medici. He not only foretold the death, but +described so minutely the circumstances that would attend it, and +gave such a correct description of the assassin who should murder +the prince, that he was at once suspected of having a hand in the +assassination. It developed later, however, that such was +probably not the case; but that some friend of Prince Alexander, +knowing of the plot to take his life, had induced the astrologer +to foretell the event in order that the prince might have timely +warning and so elude the conspirators. + +The cause of the decline of astrology was the growing prevalence +of the new spirit of experimental science. Doubtless the most +direct blow was dealt by the Copernican theory. So soon as this +was established, the recognition of the earth's subordinate place +in the universe must have made it difficult for astronomers to be +longer deceived by such coincidences as had sufficed to convince +the observers of a more credulous generation. Tycho Brahe was, +perhaps, the last astronomer of prominence who was a +conscientious practiser of the art of the astrologer. + + + +VII. FROM PARACELSUS TO HARVEY + +PARACELSUS + +In the year 1526 there appeared a new lecturer on the platform at +the University at Basel--a small, beardless, effeminate-looking +person--who had already inflamed all Christendom with his +peculiar philosophy, his revolutionary methods of treating +diseases, and his unparalleled success in curing them. A man who +was to be remembered in after-time by some as the father of +modern chemistry and the founder of modern medicine; by others as +madman, charlatan, impostor; and by still others as a combination +of all these. This soft-cheeked, effeminate, woman-hating man, +whose very sex has been questioned, was Theophrastus von +Hohenheim, better known as Paracelsus (1493-1541). + +To appreciate his work, something must be known of the life of +the man. He was born near Maria-Einsiedeln, in Switzerland, the +son of a poor physician of the place. He began the study of +medicine under the instruction of his father, and later on came +under the instruction of several learned churchmen. At the age of +sixteen he entered the University of Basel, but, soon becoming +disgusted with the philosophical teachings of the time, he +quitted the scholarly world of dogmas and theories and went to +live among the miners in the Tyrol, in order that he might study +nature and men at first hand. Ordinary methods of study were +thrown aside, and he devoted his time to personal +observation--the only true means of gaining useful knowledge, as +he preached and practised ever after. Here he became familiar +with the art of mining, learned the physical properties of +minerals, ores, and metals, and acquired some knowledge of +mineral waters. More important still, he came in contact with +such diseases, wounds, and injuries as miners are subject to, and +he tried his hand at the practical treatment of these conditions, +untrammelled by the traditions of a profession in which his +training had been so scant. + +Having acquired some empirical skill in treating diseases, +Paracelsus set out wandering from place to place all over Europe, +gathering practical information as he went, and learning more and +more of the medicinal virtues of plants and minerals. His +wanderings covered a period of about ten years, at the end of +which time he returned to Basel, where he was soon invited to +give a course of lectures in the university. + +These lectures were revolutionary in two respects--they were +given in German instead of time-honored Latin, and they were +based upon personal experience rather than upon the works of such +writers as Galen and Avicenna. Indeed, the iconoclastic teacher +spoke with open disparagement of these revered masters, and +openly upbraided his fellow-practitioners for following their +tenets. Naturally such teaching raised a storm of opposition +among the older physicians, but for a time the unparalleled +success of Paracelsus in curing diseases more than offset his +unpopularity. Gradually, however, his bitter tongue and his +coarse personality rendered him so unpopular, even among his +patients, that, finally, his liberty and life being jeopardized, +he was obliged to flee from Basel, and became a wanderer. He +lived for brief periods in Colmar, Nuremberg, Appenzell, Zurich, +Pfeffers, Augsburg, and several other cities, until finally at +Salzburg his eventful life came to a close in 1541. His enemies +said that he had died in a tavern from the effects of a +protracted debauch; his supporters maintained that he had been +murdered at the instigation of rival physicians and apothecaries. + +But the effects of his teachings had taken firm root, and +continued to spread after his death. He had shown the fallibility +of many of the teachings of the hitherto standard methods of +treating diseases, and had demonstrated the advantages of +independent reasoning based on observation. In his Magicum he +gives his reasons for breaking with tradition. "I did," he says, +"embrace at the beginning these doctrines, as my adversaries +(followers of Galen) have done, but since I saw that from their +procedures nothing resulted but death, murder, stranglings, +anchylosed limbs, paralysis, and so forth, that they held most +diseases incurable. . . . therefore have I quitted this wretched +art, and sought for truth in any other direction. I asked myself +if there were no such thing as a teacher in medicine, where could +I learn this art best? Nowhere better than the open book of +nature, written with God's own finger." We shall see, however, +that this "book of nature" taught Paracelsus some very strange +lessons. Modesty was not one of these. "Now at this time," he +declares, "I, Theophrastus Paracelsus, Bombast, Monarch of the +Arcana, was endowed by God with special gifts for this end, that +every searcher after this supreme philosopher's work may be +forced to imitate and to follow me, be he Italian, Pole, Gaul, +German, or whatsoever or whosoever he be. Come hither after me, +all ye philosophers, astronomers, and spagirists. . . . I will +show and open to you ... this corporeal regeneration."[1] + +Paracelsus based his medical teachings on four "pillars" +--philosophy, astronomy, alchemy, and virtue of the physician--a +strange-enough equipment surely, and yet, properly interpreted, +not quite so anomalous as it seems at first blush. Philosophy was +the "gate of medicine," whereby the physician entered rightly +upon the true course of learning; astronomy, the study of the +stars, was all-important because "they (the stars) caused disease +by their exhalations, as, for instance, the sun by excessive +heat"; alchemy, as he interpreted it, meant the improvement of +natural substances for man's benefit; while virtue in the +physician was necessary since "only the virtuous are permitted to +penetrate into the innermost nature of man and the universe." + +All his writings aim to promote progress in medicine, and to hold +before the physician a grand ideal of his profession. In this his +views are wide and far-reaching, based on the relationship which +man bears to nature as a whole; but in his sweeping condemnations +he not only rejected Galenic therapeutics and Galenic anatomy, +but condemned dissections of any kind. He laid the cause of all +diseases at the door of the three mystic elements--salt, sulphur, +and mercury. In health he supposed these to be mingled in the +body so as to be indistinguishable; a slight separation of them +produced disease; and death he supposed to be the result of their +complete separation. The spiritual agencies of diseases, he said, +had nothing to do with either angels or devils, but were the +spirits of human beings. + +He believed that all food contained poisons, and that the +function of digestion was to separate the poisonous from the +nutritious. In the stomach was an archaeus, or alchemist, whose +duty was to make this separation. In digestive disorders the +archaeus failed to do this, and the poisons thus gaining access +to the system were "coagulated" and deposited in the joints and +various other parts of the body. Thus the deposits in the kidneys +and tartar on the teeth were formed; and the stony deposits of +gout were particularly familiar examples of this. All this is +visionary enough, yet it shows at least a groping after rational +explanations of vital phenomena. + +Like most others of his time, Paracelsus believed firmly in the +doctrine of "signatures"--a belief that every organ and part of +the body had a corresponding form in nature, whose function was +to heal diseases of the organ it resembled. The vagaries of this +peculiar doctrine are too numerous and complicated for lengthy +discussion, and varied greatly from generation to generation. In +general, however, the theory may be summed up in the words of +Paracelsus: "As a woman is known by her shape, so are the +medicines." Hence the physicians were constantly searching for +some object of corresponding shape to an organ of the body. The +most natural application of this doctrine would be the use of the +organs of the lower animals for the treatment of the +corresponding diseased organs in man. Thus diseases of the heart +were to be treated with the hearts of animals, liver disorders +with livers, and so on. But this apparently simple form of +treatment had endless modifications and restrictions, for not all +animals were useful. For example, it was useless to give the +stomach of an ox in gastric diseases when the indication in such +cases was really for the stomach of a rat. Nor were the organs of +animals the only "signatures" in nature. Plants also played a +very important role, and the herb-doctors devoted endless labor +to searching for such plants. Thus the blood-root, with its red +juice, was supposed to be useful in blood diseases, in stopping +hemorrhage, or in subduing the redness of an inflammation. + +Paracelsus's system of signatures, however, was so complicated by +his theories of astronomy and alchemy that it is practically +beyond comprehension. It is possible that he himself may have +understood it, but it is improbable that any one else did--as +shown by the endless discussions that have taken place about it. +But with all the vagaries of his theories he was still rational +in his applications, and he attacked to good purpose the +complicated "shot-gun" prescriptions of his contemporaries, +advocating more simple methods of treatment. + +The ever-fascinating subject of electricity, or, more +specifically, "magnetism," found great favor with him, and with +properly adjusted magnets he claimed to be able to cure many +diseases. In epilepsy and lockjaw, for example, one had but to +fasten magnets to the four extremities of the body, and then, +"when the proper medicines were given," the cure would be +effected. The easy loop-hole for excusing failure on the ground +of improper medicines is obvious, but Paracelsus declares that +this one prescription is of more value than "all the humoralists +have ever written or taught." + +Since Paracelsus condemned the study of anatomy as useless, he +quite naturally regarded surgery in the same light. In this he +would have done far better to have studied some of his +predecessors, such as Galen, Paul of Aegina, and Avicenna. But +instead of "cutting men to pieces," he taught that surgeons would +gain more by devoting their time to searching for the universal +panacea which would cure all diseases, surgical as well as +medical. In this we detect a taint of the popular belief in the +philosopher's stone and the magic elixir of life, his belief in +which have been stoutly denied by some of his followers. He did +admit, however, that one operation alone was perhaps +permissible--lithotomy, or the "cutting for stone." + +His influence upon medicine rests undoubtedly upon his +revolutionary attitude, rather than on any great or new +discoveries made by him. It is claimed by many that he brought +prominently into use opium and mercury, and if this were +indisputably proven his services to medicine could hardly be +overestimated. Unfortunately, however, there are good grounds for +doubting that he was particularly influential in reintroducing +these medicines. His chief influence may perhaps be summed up in +a single phrase--he overthrew old traditions. + +To Paracelsus's endeavors, however, if not to the actual products +of his work, is due the credit of setting in motion the chain of +thought that developed finally into scientific chemistry. Nor can +the ultimate aim of the modern chemist seek a higher object than +that of this sixteenth-century alchemist, who taught that "true +alchemy has but one aim and object, to extract the quintessence +of things, and to prepare arcana, tinctures, and elixirs which +may restore to man the health and soundness he has lost." + + +THE GREAT ANATOMISTS + +About the beginning of the sixteenth century, while Paracelsus +was scoffing at the study of anatomy as useless, and using his +influence against it, there had already come upon the scene the +first of the great anatomists whose work was to make the century +conspicuous in that branch of medicine. + +The young anatomist Charles etienne (1503-1564) made one of the +first noteworthy discoveries, pointing out for the first time +that the spinal cord contains a canal, continuous throughout its +length. He also made other minor discoveries of some importance, +but his researches were completely overshadowed and obscured by +the work of a young Fleming who came upon the scene a few years +later, and who shone with such brilliancy in the medical world +that he obscured completely the work of his contemporary until +many years later. This young physician, who was destined to lead +such an eventful career and meet such an untimely end as a martyr +to science, was Andrew Vesalius (1514-1564), who is called the +"greatest of anatomists." At the time he came into the field +medicine was struggling against the dominating Galenic teachings +and the theories of Paracelsus, but perhaps most of all against +the superstitions of the time. In France human dissections were +attended with such dangers that the young Vesalius transferred +his field of labors to Italy, where such investigations were +covertly permitted, if not openly countenanced. + +From the very start the young Fleming looked askance at the +accepted teachings of the day, and began a series of independent +investigations based upon his own observations. The results of +these investigations he gave in a treatise on the subject which +is regarded as the first comprehensive and systematic work on +human anatomy. This remarkable work was published in the author's +twenty-eighth or twenty-ninth year. Soon after this Vesalius was +invited as imperial physician to the court of Emperor Charles V. +He continued to act in the same capacity at the court of Philip +II., after the abdication of his patron. But in spite of this +royal favor there was at work a factor more powerful than the +influence of the monarch himself--an instrument that did so much +to retard scientific progress, and by which so many lives were +brought to a premature close. + +Vesalius had received permission from the kinsmen of a certain +grandee to perform an autopsy. While making his observations the +heart of the outraged body was seen to palpitate--so at least it +was reported. This was brought immediately to the attention of +the Inquisition, and it was only by the intervention of the king +himself that the anatomist escaped the usual fate of those +accused by that tribunal. As it was, he was obliged to perform a +pilgrimage to the Holy Land. While returning from this he was +shipwrecked, and perished from hunger and exposure on the island +of Zante. + +At the very time when the anatomical writings of Vesalius were +startling the medical world, there was living and working +contemporaneously another great anatomist, Eustachius (died +1574), whose records of his anatomical investigations were ready +for publication only nine years after the publication of the work +of Vesalius. Owing to the unfortunate circumstances of the +anatomist, however, they were never published during his +lifetime--not, in fact, until 1714. When at last they were given +to the world as Anatomical Engravings, they showed conclusively +that Eustachius was equal, if not superior to Vesalius in his +knowledge of anatomy. It has been said of this remarkable +collection of engravings that if they had been published when +they were made in the sixteenth century, anatomy would have been +advanced by at least two centuries. But be this as it may, they +certainly show that their author was a most careful dissector and +observer. + +Eustachius described accurately for the first time certain +structures of the middle ear, and rediscovered the tube leading +from the ear to the throat that bears his name. He also made +careful studies of the teeth and the phenomena of first and +second dentition. He was not baffled by the minuteness of +structures and where he was unable to study them with the naked +eye he used glasses for the purpose, and resorted to macerations +and injections for the study of certain complicated structures. +But while the fruit of his pen and pencil were lost for more than +a century after his death, the effects of his teachings were not; +and his two pupils, Fallopius and Columbus, are almost as well +known to-day as their illustrious teacher. Columbus (1490-1559) +did much in correcting the mistakes made in the anatomy of the +bones as described by Vesalius. He also added much to the science +by giving correct accounts of the shape and cavities of the +heart, and made many other discoveries of minor importance. +Fallopius (1523-1562) added considerably to the general knowledge +of anatomy, made several discoveries in the anatomy of the ear, +and also several organs in the abdominal cavity. + +At this time a most vitally important controversy was in progress +as to whether or not the veins of the bodies were supplied with +valves, many anatomists being unable to find them. etienne had +first described these structures, and Vesalius had confirmed his +observations. It would seem as if there could be no difficulty in +settling the question as to the fact of such valves being present +in the vessels, for the demonstration is so simple that it is now +made daily by medical students in all physiological laboratories +and dissecting-rooms. But many of the great anatomists of the +sixteenth century were unable to make this demonstration, even +when it had been brought to their attention by such an authority +as Vesalius. Fallopius, writing to Vesalius on the subject in +1562, declared that he was unable to find such valves. Others, +however, such as Eustachius and Fabricius (1537-1619), were more +successful, and found and described these structures. But the +purpose served by these valves was entirely misinterpreted. That +they act in preventing the backward flow of the blood in the +veins on its way to the heart, just as the valves of the heart +itself prevent regurgitation, has been known since the time of +Harvey; but the best interpretation that could be given at that +time, even by such a man as Fabricius, was that they acted in +retarding the flow of the blood as it comes from the heart, and +thus prevent its too rapid distribution throughout the body. The +fact that the blood might have been going towards the heart, +instead of coming from it, seems never to have been considered +seriously until demonstrated so conclusively by Harvey. + +Of this important and remarkable controversy over the valves in +veins, Withington has this to say: "This is truly a marvellous +story. A great Galenic anatomist is first to give a full and +correct description of the valves and their function, but fails +to see that any modification of the old view as to the motion of +the blood is required. Two able dissectors carefully test their +action by experiment, and come to a result. the exact reverse of +the truth. Urged by them, the two foremost anatomists of the age +make a special search for valves and fail to find them. Finally, +passing over lesser peculiarities, an aged and honorable +professor, who has lived through all this, calmly asserts that no +anatomist, ancient or modern, has ever mentioned valves in veins +till he discovered them in 1574!"[2] + +Among the anatomists who probably discovered these valves was +Michael Servetus (1511-1553); but if this is somewhat in doubt, +it is certain that he discovered and described the pulmonary +circulation, and had a very clear idea of the process of +respiration as carried on in the lungs. The description was +contained in a famous document sent to Calvin in 1545--a document +which the reformer carefully kept for seven years in order that +he might make use of some of the heretical statements it +contained to accomplish his desire of bringing its writer to the +stake. The awful fate of Servetus, the interesting character of +the man, and the fact that he came so near to anticipating the +discoveries of Harvey make him one of the most interesting +figures in medical history. + +In this document which was sent to Calvin, Servetus rejected the +doctrine of natural, vital, and animal spirits, as contained in +the veins, arteries, and nerves respectively, and made the +all-important statement that the fluids contained in veins and +arteries are the same. He showed also that the blood is "purged +from fume" and purified by respiration in the lungs, and declared +that there is a new vessel in the lungs, "formed out of vein and +artery." Even at the present day there is little to add to or +change in this description of Servetus's. + +By keeping this document, pregnant with advanced scientific +views, from the world, and in the end only using it as a means of +destroying its author, the great reformer showed the same +jealousy in retarding scientific progress as had his arch-enemies +of the Inquisition, at whose dictates Vesalius became a martyr to +science, and in whose dungeons etienne perished. + + +THE COMING OF HARVEY + +The time was ripe for the culminating discovery of the +circulation of the blood; but as yet no one had determined the +all-important fact that there are two currents of blood in the +body, one going to the heart, one coming from it. The valves in +the veins would seem to show conclusively that the venous current +did not come from the heart, and surgeons must have observed +thousands of times the every-day phenomenon of congested veins at +the distal extremity of a limb around which a ligature or +constriction of any kind had been placed, and the simultaneous +depletion of the vessels at the proximal points above the +ligature. But it should be remembered that inductive science was +in its infancy. This was the sixteenth, not the nineteenth +century, and few men had learned to put implicit confidence in +their observations and convictions when opposed to existing +doctrines. The time was at hand, however, when such a man was to +make his appearance, and, as in the case of so many revolutionary +doctrines in science, this man was an Englishman. It remained for +William Harvey (1578-1657) to solve the great mystery which had +puzzled the medical world since the beginning of history; not +only to solve it, but to prove his case so conclusively and so +simply that for all time his little booklet must he handed down +as one of the great masterpieces of lucid and almost faultless +demonstration. + +Harvey, the son of a prosperous Kentish yeoman, was born at +Folkestone. His education was begun at the grammar-school of +Canterbury, and later he became a pensioner of Caius College, +Cambridge. Soon after taking his degree of B.A., at the age of +nineteen, he decided upon the profession of medicine, and went to +Padua as a pupil of Fabricius and Casserius. Returning to England +at the age of twenty-four, he soon after (1609) obtained the +reversion of the post of physician to St. Bartholomew's Hospital, +his application being supported by James I. himself. Even at this +time he was a popular physician, counting among his patients such +men as Francis Bacon. In 1618 he was appointed physician +extraordinary to the king, and, a little later, physician in +ordinary. He was in attendance upon Charles I. at the battle of +Edgehill, in 1642, where, with the young Prince of Wales and the +Duke of York, after seeking shelter under a hedge, he drew a book +out of his pocket and, forgetful of the battle, became absorbed +in study, until finally the cannon-balls from the enemy's +artillery made him seek a more sheltered position. + +On the fall of Charles I. he retired from practice, and lived in +retirement with his brother. He was then well along in years, but +still pursued his scientific researches with the same vigor as +before, directing his attention chiefly to the study of +embryology. On June 3, 1657, he was attacked by paralysis and +died, in his eightieth year. He had lived to see his theory of +the circulation accepted, several years before, by all the +eminent anatomists of the civilized world. + +A keenness in the observation of facts, characteristic of the +mind of the man, had led Harvey to doubt the truth of existing +doctrines as to the phenomena of the circulation. Galen had +taught that "the arteries are filled, like bellows, because they +are expanded," but Harvey thought that the action of spurting +blood from a severed vessel disproved this. For the spurting was +remittant, "now with greater, now with less impetus," and its +greater force always corresponded to the expansion (diastole), +not the contraction (systole) of the vessel. Furthermore, it was +evident that contraction of the heart and the arteries was not +simultaneous, as was commonly taught, because in that case there +would be no marked propulsion of the blood in any direction; and +there was no gainsaying the fact that the blood was forcibly +propelled in a definite direction, and that direction away from +the heart. + +Harvey's investigations led him to doubt also the accepted theory +that there was a porosity in the septum of tissue that divides +the two ventricles of the heart. It seemed unreasonable to +suppose that a thick fluid like the blood could find its way +through pores so small that they could not be demonstrated by any +means devised by man. In evidence that there could be no such +openings he pointed out that, since the two ventricles contract +at the same time, this process would impede rather than +facilitate such an intra-ventricular passage of blood. But what +seemed the most conclusive proof of all was the fact that in the +foetus there existed a demonstrable opening between the two +ventricles, and yet this is closed in the fully developed heart. +Why should Nature, if she intended that blood should pass between +the two cavities, choose to close this opening and substitute +microscopic openings in place of it? It would surely seem more +reasonable to have the small perforations in the thin, easily +permeable membrane of the foetus, and the opening in the adult +heart, rather than the reverse. From all this Harvey drew his +correct conclusions, declaring earnestly, "By Hercules, there ARE +no such porosities, and they cannot be demonstrated." + +Having convinced himself that no intra-ventricular opening +existed, he proceeded to study the action of the heart itself, +untrammelled by too much faith in established theories, and, as +yet, with no theory of his own. He soon discovered that the +commonly accepted theory of the heart striking against the +chest-wall during the period of relaxation was entirely wrong, +and that its action was exactly the reverse of this, the heart +striking the chest-wall during contraction. Having thus disproved +the accepted theory concerning the heart's action, he took up the +subject of the action of arteries, and soon was able to +demonstrate by vivisection that the contraction of the arteries +was not simultaneous with contractions of the heart. His +experiments demonstrated that these vessels were simply elastic +tubes whose pulsations were "nothing else than the impulse of the +blood within them." The reason that the arterial pulsation was +not simultaneous with the heart-beat he found to be because of +the time required to carry the impulse along the tube, + +By a series of further careful examinations and experiments, +which are too extended to be given here, he was soon able further +to demonstrate the action and course of the blood during the +contractions of the heart. His explanations were practically the +same as those given to-day--first the contraction of the auricle, +sending blood into the ventricle; then ventricular contraction, +making the pulse, and sending the blood into the arteries. He had +thus demonstrated what had not been generally accepted before, +that the heart was an organ for the propulsion of blood. To make +such a statement to-day seems not unlike the sober announcement +that the earth is round or that the sun does not revolve about +it. Before Harvey's time, however, it was considered as an organ +that was "in some mysterious way the source of vitality and +warmth, as an animated crucible for the concoction of blood and +the generation of vital spirits."[3] + +In watching the rapid and ceaseless contractions of the heart, +Harvey was impressed with the fact that, even if a very small +amount of blood was sent out at each pulsation, an enormous +quantity must pass through the organ in a day, or even in an +hour. Estimating the size of the cavities of the heart, and +noting that at least a drachm must be sent out with each +pulsation, it was evident that the two thousand beats given by a +very slow human heart in an hour must send out some forty pounds +of blood--more than twice the amount in the entire body. The +question was, what became of it all? For it should be remembered +that the return of the blood by the veins was unknown, and +nothing like a "circulation" more than vaguely conceived even by +Harvey himself. Once it could be shown that the veins were +constantly returning blood to the heart, the discovery that the +blood in some way passes from the arteries to the veins was only +a short step. Harvey, by resorting to vivisections of lower +animals and reptiles, soon demonstrated beyond question the fact +that the veins do carry the return blood. "But this, in +particular, can be shown clearer than daylight," says Harvey. +"The vena cava enters the heart at an inferior portion, while the +artery passes out above. Now if the vena cava be taken up with +forceps or the thumb and finger, and the course of the blood +intercepted for some distance below the heart, you will at once +see it almost emptied between the fingers and the heart, the +blood being exhausted by the heart's pulsation, the heart at the +same time becoming much paler even in its dilatation, smaller in +size, owing to the deficiency of blood, and at length languid in +pulsation, as if about to die. On the other hand, when you +release the vein the heart immediately regains its color and +dimensions. After that, if you leave the vein free and tie and +compress the arteries at some distance from the heart, you will +see, on the contrary, their included portion grow excessively +turgid, the heart becoming so beyond measure, assuming a dark-red +color, even to lividity, and at length so overloaded with blood +as to seem in danger of suffocation; but when the obstruction is +removed it returns to its normal condition, in size, color, and +movement."[4] + +This conclusive demonstration that the veins return the blood to +the heart must have been most impressive to Harvey, who had been +taught to believe that the blood current in the veins pursued an +opposite course, and must have tended to shake his faith in all +existing doctrines of the day. + +His next step was the natural one of demonstrating that the blood +passes from the arteries to the veins. He demonstrated +conclusively that this did occur, but for once his rejection of +the ancient writers and one modern one was a mistake. For Galen +had taught, and had attempted to demonstrate, that there are sets +of minute vessels connecting the arteries and the veins; and +Servetus had shown that there must be such vessels, at least in +the lungs. + +However, the little flaw in the otherwise complete demonstration +of Harvey detracts nothing from the main issue at stake. It was +for others who followed to show just how these small vessels +acted in effecting the transfer of the blood from artery to vein, +and the grand general statement that such a transfer does take +place was, after all, the all-important one, and the exact method +of how it takes place a detail. Harvey's experiments to +demonstrate that the blood passes from the arteries to the veins +are so simply and concisely stated that they may best be given in +his own words. + +"I have here to cite certain experiments," he wrote, "from which +it seems obvious that the blood enters a limb by the arteries, +and returns from it by the veins; that the arteries are the +vessels carrying the blood from the heart, and the veins the +returning channels of the blood to the heart; that in the limbs +and extreme parts of the body the blood passes either by +anastomosis from the arteries into the veins, or immediately by +the pores of the flesh, or in both ways, as has already been said +in speaking of the passage of the blood through the lungs; whence +it appears manifest that in the circuit the blood moves from +thence hither, and hence thither; from the centre to the +extremities, to wit, and from the extreme parts back again to the +centre. Finally, upon grounds of circulation, with the same +elements as before, it will be obvious that the quantity can +neither be accounted for by the ingesta, nor yet be held +necessary to nutrition. + +"Now let any one make an experiment on the arm of a man, either +using such a fillet as is employed in blood-letting or grasping +the limb tightly with his hand, the best subject for it being one +who is lean, and who has large veins, and the best time after +exercise, when the body is warm, the pulse is full, and the blood +carried in large quantities to the extremities, for all then is +more conspicuous; under such circumstances let a ligature be +thrown about the extremity and drawn as tightly as can be borne: +it will first be perceived that beyond the ligature neither in +the wrist nor anywhere else do the arteries pulsate, that at the +same time immediately above the ligature the artery begins to +rise higher at each diastole, to throb more violently, and to +swell in its vicinity with a kind of tide, as if it strove to +break through and overcome the obstacle to its current; the +artery here, in short, appears as if it were permanently full. +The hand under such circumstances retains its natural color and +appearances; in the course of time it begins to fall somewhat in +temperature, indeed, but nothing is DRAWN into it. + +"After the bandage has been kept on some short time in this way, +let it be slackened a little, brought to the state or term of +middling tightness which is used in bleeding, and it will be seen +that the whole hand and arm will instantly become deeply suffused +and distended, injected, gorged with blood, DRAWN, as it is said, +by this middling ligature, without pain, or heat, or any horror +of a vacuum, or any other cause yet indicated. + +"As we have noted, in connection with the tight ligature, that +the artery above the bandage was distended and pulsated, not +below it, so, in the case of the moderately tight bandage, on the +contrary, do we find that the veins below, never above, the +fillet swell and become dilated, while the arteries shrink; and +such is the degree of distention of the veins here that it is +only very strong pressure that will force the blood beyond the +fillet and cause any of the veins in the upper part of the arm to +rise. + +"From these facts it is easy for any careful observer to learn +that the blood enters an extremity by the arteries; for when they +are effectively compressed nothing is DRAWN to the member; the +hand preserves its color; nothing flows into it, neither is it +distended; but when the pressure is diminished, as it is with the +bleeding fillet, it is manifest that the blood is instantly +thrown in with force, for then the hand begins to swell; which is +as much as to say that when the arteries pulsate the blood is +flowing through them, as it is when the moderately tight ligature +is applied; but when they do not pulsate, or when a tight +ligature is used, they cease from transmitting anything; they are +only distended above the part where the ligature is applied. The +veins again being compressed, nothing can flow through them; the +certain indication of which is that below the ligature they are +much more tumid than above it, and than they usually appear when +there is no bandage upon the arm. + +"It therefore plainly appears that the ligature prevents the +return of the blood through the veins to the parts above it, and +maintains those beneath it in a state of permanent distention. +But the arteries, in spite of the pressure, and under the force +and impulse of the heart, send on the blood from the internal +parts of the body to the parts beyond the bandage."[5] + + +This use of ligatures is very significant, because, as shown, a +very tight ligature stops circulation in both arteries and veins, +while a loose one, while checking the circulation in the veins, +which lie nearer the surface and are not so directly influenced +by the force of the heart, does not stop the passage of blood in +the arteries, which are usually deeply imbedded in the tissues, +and not so easily influenced by pressure from without. + +The last step of Harvey's demonstration was to prove that the +blood does flow along the veins to the heart, aided by the valves +that had been the cause of so much discussion and dispute between +the great sixteenth-century anatomists. Harvey not only +demonstrated the presence of these valves, but showed +conclusively, by simple experiments, what their function was, +thus completing his demonstration of the phenomena of the +circulation. + +The final ocular demonstration of the passage of the blood from +the arteries to the veins was not to be made until four years +after Harvey's death. This process, which can be observed easily +in the web of a frog's foot by the aid of a low-power lens, was +first demonstrated by Marcello Malpighi (1628-1694) in 1661. By +the aid of a lens he first saw the small "capillary" vessels +connecting the veins and arteries in a piece of dried lung. +Taking his cue from this, he examined the lung of a turtle, and +was able to see in it the passage of the corpuscles through these +minute vessels, making their way along these previously unknown +channels from the arteries into the veins on their journey back +to the heart. Thus the work of Harvey, all but complete, was made +absolutely entire by the great Italian. And all this in a single +generation. + + +LEEUWENHOEK DISCOVERS BACTERIA + +The seventeenth century was not to close, however, without +another discovery in science, which, when applied to the +causation of disease almost two centuries later, revolutionized +therapeutics more completely than any one discovery. This was the +discovery of microbes, by Antonius von Leeuwenhoek (1632-1723), +in 1683. Von Leeuwenhoek discovered that "in the white matter +between his teeth" there were millions of microscopic +"animals"--more, in fact, than "there were human beings in the +united Netherlands," and all "moving in the most delightful +manner." There can be no question that he saw them, for we can +recognize in his descriptions of these various forms of little +"animals" the four principal forms of microbes--the long and +short rods of bacilli and bacteria, the spheres of micrococci, +and the corkscrew spirillum. + +The presence of these microbes in his mouth greatly annoyed +Antonius, and he tried various methods of getting rid of them, +such as using vinegar and hot coffee. In doing this he little +suspected that he was anticipating modern antiseptic surgery by a +century and three-quarters, and to be attempting what antiseptic +surgery is now able to accomplish. For the fundamental principle +of antisepsis is the use of medicines for ridding wounds of +similar microscopic organisms. Von Leenwenhoek was only +temporarily successful in his attempts, however, and took +occasion to communicate his discovery to the Royal Society of +England, hoping that they would be "interested in this novelty." +Probably they were, but not sufficiently so for any member to +pursue any protracted investigations or reach any satisfactory +conclusions, and the whole matter was practically forgotten until +the middle of the nineteenth century. + + + +VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +Of the half-dozen surgeons who were prominent in the sixteenth +century, Ambroise Pare (1517-1590), called the father of French +surgery, is perhaps the most widely known. He rose from the +position of a common barber to that of surgeon to three French +monarchs, Henry II., Francis II., and Charles IX. Some of his +mottoes are still first principles of the medical man. Among +others are: "He who becomes a surgeon for the sake of money, and +not for the sake of knowledge, will accomplish nothing"; and "A +tried remedy is better than a newly invented." On his statue is +his modest estimate of his work in caring for the wounded, "Je le +pansay, Dieu le guarit"--I dressed him, God cured him. + +It was in this dressing of wounds on the battlefield that he +accidentally discovered how useless and harmful was the terribly +painful treatment of applying boiling oil to gunshot wounds as +advocated by John of Vigo. It happened that after a certain +battle, where there was an unusually large number of casualties, +Pare found, to his horror, that no more boiling oil was available +for the surgeons, and that he should be obliged to dress the +wounded by other simpler methods. To his amazement the results +proved entirely satisfactory, and from that day he discarded the +hot-oil treatment. + +As Pare did not understand Latin he wrote his treatises in +French, thus inaugurating a custom in France that was begun by +Paracelsus in Germany half a century before. He reintroduced the +use of the ligature in controlling hemorrhage, introduced the +"figure of eight" suture in the operation for hare-lip, improved +many of the medico-legal doctrines, and advanced the practice of +surgery generally. He is credited with having successfully +performed the operation for strangulated hernia, but he probably +borrowed it from Peter Franco (1505-1570), who published an +account of this operation in 1556. As this operation is +considered by some the most important operation in surgery, its +discoverer is entitled to more than passing notice, although he +was despised and ignored by the surgeons of his time. + +Franco was an illiterate travelling lithotomist--a class of +itinerant physicians who were very generally frowned down by the +regular practitioners of medicine. But Franco possessed such +skill as an operator, and appears to have been so earnest in the +pursuit of what he considered a legitimate calling, that he +finally overcame the popular prejudice and became one of the +salaried surgeons of the republic of Bern. He was the first +surgeon to perform the suprapubic lithotomy operation--the +removal of stone through the abdomen instead of through the +perineum. His works, while written in an illiterate style, give +the clearest descriptions of any of the early modern writers. + +As the fame of Franco rests upon his operation for prolonging +human life, so the fame of his Italian contemporary, Gaspar +Tagliacozzi (1545-1599), rests upon his operation for increasing +human comfort and happiness by restoring amputated noses. At the +time in which he lived amputation of the nose was very common, +partly from disease, but also because a certain pope had fixed +the amputation of that member as the penalty for larceny. +Tagliacozzi probably borrowed his operation from the East; but he +was the first Western surgeon to perform it and describe it. So +great was the fame of his operations that patients flocked to him +from all over Europe, and each "went away with as many noses as +he liked." Naturally, the man who directed his efforts to +restoring structures that bad been removed by order of the Church +was regarded in the light of a heretic by many theologians; and +though he succeeded in cheating the stake or dungeon, and died a +natural death, his body was finally cast out of the church in +which it had been buried. + +In the sixteenth century Germany produced a surgeon, Fabricius +Hildanes (1560-1639), whose work compares favorably with that of +Pare, and whose name would undoubtedly have been much better +known had not the circumstances of the time in which he lived +tended to obscure his merits. The blind followers of Paracelsus +could see nothing outside the pale of their master's teachings, +and the disastrous Thirty Years' War tended to obscure and retard +all scientific advances in Germany. Unlike many of his +fellow-surgeons, Hildanes was well versed in Latin and Greek; +and, contrary to the teachings of Paracelsus, he laid particular +stress upon the necessity of the surgeon having a thorough +knowledge of anatomy. He had a helpmate in his wife, who was also +something of a surgeon, and she is credited with having first +made use of the magnet in removing particles of metal from the +eye. Hildanes tells of a certain man who had been injured by a +small piece of steel in the cornea, which resisted all his +efforts to remove it. After observing Hildanes' fruitless efforts +for a time, it suddenly occurred to his wife to attempt to make +the extraction with a piece of loadstone. While the physician +held open the two lids, his wife attempted to withdraw the steel +with the magnet held close to the cornea, and after several +efforts she was successful--which Hildanes enumerates as one of +the advantages of being a married man. + +Hildanes was particularly happy in his inventions of surgical +instruments, many of which were designed for locating and +removing the various missiles recently introduced in warfare. + + +The seventeenth century, which was such a flourishing one for +anatomy and physiology, was not as productive of great surgeons +or advances in surgery as the sixteenth had been or the +eighteenth was to be. There was a gradual improvement all along +the line, however, and much of the work begun by such surgeons as +Pare and Hildanes was perfected or improved. Perhaps the most +progressive surgeon of the century was an Englishman, Richard +Wiseman (1625-1686), who, like Harvey, enjoyed royal favor, being +in the service of all the Stuart kings. He was the first surgeon +to advocate primary amputation, in gunshot wounds, of the limbs, +and also to introduce the treatment of aneurisms by compression; +but he is generally rated as a conservative operator, who favored +medication rather than radical operations, where possible. + +In Italy, Marcus Aurelius Severinus (1580-1656) and Peter +Marchettis (1589-1675) were the leading surgeons of their nation. +Like many of his predecessors in Europe, Severinus ran amuck with +the Holy Inquisition and fled from Naples. But the waning of the +powerful arm of the Church is shown by the fact that he was +brought back by the unanimous voice of the grateful citizens, and +lived in safety despite the frowns of the theologians. + + +The sixteenth century cannot be said to have added much of +importance in the field of practical medicine, and, as in the +preceding and succeeding centuries, was at best only struggling +along in the wake of anatomy, physiology, and surgery. In the +seventeenth century, however, at least one discovery in +therapeutics was made that has been an inestimable boon to +humanity ever since. This was the introduction of cinchona bark +(from which quinine is obtained) in 1640. But this century was +productive of many medical SYSTEMS, and could boast of many great +names among the medical profession, and, on the whole, made +considerably more progress than the preceding century. + +Of the founders of medical systems, one of the most widely known +is Jan Baptista van Helmont (1578-1644), an eccentric genius who +constructed a system of medicine of his own and for a time +exerted considerable influence. But in the end his system was +destined to pass out of existence, not very long after the death +of its author. Van Helmont was not only a physician, but was +master of all the other branches of learning of the time, taking +up the study of medicine and chemistry as an after-thought, but +devoting himself to them with the greatest enthusiasm once he had +begun his investigations. His attitude towards existing doctrines +was as revolutionary as that of Paracelsus, and he rejected the +teachings of Galen and all the ancient writers, although +retaining some of the views of Paracelsus. He modified the +archaeus of Paracelsus, and added many complications to it. He +believed the whole body to be controlled by an archaeus influus, +the soul by the archaei insiti, and these in turn controlled by +the central archeus. His system is too elaborate and complicated +for full explanation, but its chief service to medicine was in +introducing new chemical methods in the preparation of drugs. In +this way he was indirectly connected with the establishment of +the Iatrochemical school. It was he who first used the word +"gas"--a word coined by him, along with many others that soon +fell into disuse. + +The principles of the Iatrochemical school were the use of +chemical medicines, and a theory of pathology different from the +prevailing "humoral" pathology. The founder of this school was +Sylvius (Franz de le Boe, 1614-1672), professor of medicine at +Leyden. He attempted to establish a permanent system of medicine +based on the newly discovered theory of the circulation and the +new chemistry, but his name is remembered by medical men because +of the fissure in the brain (fissure of Sylvius) that bears it. +He laid great stress on the cause of fevers and other diseases as +originating in the disturbances of the process of fermentation in +the stomach. The doctrines of Sylvius spread widely over the +continent, but were not generally accepted in England until +modified by Thomas Willis (1622-1675), whose name, like that of +Sylvius, is perpetuated by a structure in the brain named after +him, the circle of Willis. Willis's descriptions of certain +nervous diseases, and an account of diabetes, are the first +recorded, and added materially to scientific medicine. These +schools of medicine lasted until the end of the seventeenth +century, when they were finally overthrown by Sydenham. + +The Iatrophysical school (also called iatromathematical, +iatromechanical, or physiatric) was founded on theories of +physiology, probably by Borelli, of Naples (1608-1679), although +Sanctorius; Sanctorius, a professor at Padua, was a precursor, if +not directly interested in establishing it. Sanctorius discovered +the fact that an "insensible perspiration" is being given off by +the body continually, and was amazed to find that loss of weight +in this way far exceeded the loss of weight by all other +excretions of the body combined. He made this discovery by means +of a peculiar weighing-machine to which a chair was attached, and +in which he spent most of his time. Very naturally he +overestimated the importance of this discovery, but it was, +nevertheless, of great value in pointing out the hygienic +importance of the care of the skin. He also introduced a +thermometer which he advocated as valuable in cases of fever, but +the instrument was probably not his own invention, but borrowed +from his friend Galileo. + +Harvey's discovery of the circulation of the blood laid the +foundation of the Iatrophysical school by showing that this vital +process was comparable to a hydraulic system. In his On the +Motive of Animals, Borelli first attempted to account for the +phenomena of life and diseases on these principles. The +iatromechanics held that the great cause of disease is due to +different states of elasticity of the solids of the body +interfering with the movements of the fluids, which are +themselves subject to changes in density, one or both of these +conditions continuing to cause stagnation or congestion. The +school thus founded by Borelli was the outcome of the unbounded +enthusiasm, with its accompanying exaggeration of certain +phenomena with the corresponding belittling of others that +naturally follows such a revolutionary discovery as that of +Harvey. Having such a founder as the brilliant Italian Borelli, +it was given a sufficient impetus by his writings to carry it +some distance before it finally collapsed. Some of the +exaggerated mathematical calculations of Borelli himself are +worth noting. Each heart-beat, as he calculated it, overcomes a +resistance equal to one hundred and eighty thousand pounds;--the +modern physiologist estimates its force at from five to nine +ounces! + + +THOMAS SYDENHAM + +But while the Continent was struggling with these illusive +"systems," and dabbling in mystic theories that were to scarcely +outlive the men who conceived + +them, there appeared in England--the "land of common-sense," as a +German scientist has called it--"a cool, clear, and unprejudiced +spirit," who in the golden age of systems declined "to be like +the man who builds the chambers of the upper story of his house +before he had laid securely the foundation walls."[1] This man +was Thomas Sydenham (1624-1689), who, while the great Harvey was +serving the king as surgeon, was fighting as a captain in the +parliamentary army. Sydenham took for his guide the teachings of +Hippocrates, modified to suit the advances that had been made in +scientific knowledge since the days of the great Greek, and +established, as a standard, observation and experience. He cared +little for theory unless confirmed by practice, but took the +Hippocratic view that nature cured diseases, assisted by the +physician. He gave due credit, however, to the importance of the +part played by the assistant. As he saw it, medicine could be +advanced in three ways: (1) "By accurate descriptions or natural +histories of diseases; (2) by establishing a fixed principle or +method of treatment, founded upon experience; (3) by searching +for specific remedies, which he believes must exist in +considerable numbers, though he admits that the only one yet +discovered is Peruvian bark."[2] As it happened, another equally +specific remedy, mercury, when used in certain diseases, was +already known to him, but he evidently did not recognize it as +such. + +The influence on future medicine of Sydenham's teachings was most +pronounced, due mostly to his teaching of careful observation. To +most physicians, however, he is now remembered chiefly for his +introduction of the use of laudanum, still considered one of the +most valuable remedies of modern pharmacopoeias. The German gives +the honor of introducing this preparation to Paracelsus, but the +English-speaking world will always believe that the credit should +be given to Sydenham. + + + +IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + +We saw that in the old Greek days there was no sharp line of +demarcation between the field of the philosopher and that of the +scientist. In the Hellenistic epoch, however, knowledge became +more specialized, and our recent chapters have shown us +scientific investigators whose efforts were far enough removed +from the intangibilities of the philosopher. It must not be +overlooked, however, that even in the present epoch there were +men whose intellectual efforts were primarily directed towards +the subtleties of philosophy, yet who had also a penchant for +strictly scientific imaginings, if not indeed for practical +scientific experiments. At least three of these men were of +sufficient importance in the history of the development of +science to demand more than passing notice. These three are the +Englishman Francis Bacon (1561-1626), the Frenchman Rene +Descartes (1596-1650); and the German Gottfried Leibnitz +(1646-1716). Bacon, as the earliest path-breaker, showed the way, +theoretically at least, in which the sciences should be studied; +Descartes, pursuing the methods pointed out by Bacon, carried the +same line of abstract reason into practice as well; while +Leibnitz, coming some years later, and having the advantage of +the wisdom of his two great predecessors, was naturally +influenced by both in his views of abstract scientific +principles. + +Bacon's career as a statesman and his faults and misfortunes as a +man do not concern us here. Our interest in him begins with his +entrance into Trinity College, Cambridge, where he took up the +study of all the sciences taught there at that time. During the +three years he became more and more convinced that science was +not being studied in a profitable manner, until at last, at the +end of his college course, he made ready to renounce the old +Aristotelian methods of study and advance his theory of inductive +study. For although he was a great admirer of Aristotle's work, +he became convinced that his methods of approaching study were +entirely wrong. + +"The opinion of Aristotle," he says, in his De Argumentum +Scientiarum, "seemeth to me a negligent opinion, that of those +things which exist by nature nothing can be changed by custom; +using for example, that if a stone be thrown ten thousand times +up it will not learn to ascend; and that by often seeing or +hearing we do not learn to see or hear better. For though this +principle be true in things wherein nature is peremptory (the +reason whereof we cannot now stand to discuss), yet it is +otherwise in things wherein nature admitteth a latitude. For he +might see that a straight glove will come more easily on with +use; and that a wand will by use bend otherwise than it grew; and +that by use of the voice we speak louder and stronger; and that +by use of enduring heat or cold we endure it the better, and the +like; which latter sort have a nearer resemblance unto that +subject of manners he handleth than those instances which he +allegeth."[1] + +These were his opinions, formed while a young man in college, +repeated at intervals through his maturer years, and reiterated +and emphasized in his old age. Masses of facts were to be +obtained by observing nature at first hand, and from such +accumulations of facts deductions were to be made. In short, +reasoning was to be from the specific to the general, and not +vice versa. + +It was by his teachings alone that Bacon thus contributed to the +foundation of modern science; and, while he was constantly +thinking and writing on scientific subjects, he contributed +little in the way of actual discoveries. "I only sound the +clarion," he said, "but I enter not the battle." + +The case of Descartes, however, is different. He both sounded the +clarion and entered into the fight. He himself freely +acknowledges his debt to Bacon for his teachings of inductive +methods of study, but modern criticism places his work on the +same plane as that of the great Englishman. "If you lay hold of +any characteristic product of modern ways of thinking," says +Huxley, "either in the region of philosophy or in that of +science, you find the spirit of that thought, if not its form, +has been present in the mind of the great Frenchman."[2] + +Descartes, the son of a noble family of France, was educated by +Jesuit teachers. Like Bacon, he very early conceived the idea +that the methods of teaching and studying science were wrong, but +be pondered the matter well into middle life before putting into +writing his ideas of philosophy and science. Then, in his +Discourse Touching the Method of Using One's Reason Rightly and +of Seeking Scientific Truth, he pointed out the way of seeking +after truth. His central idea in this was to emphasize the +importance of DOUBT, and avoidance of accepting as truth anything +that does not admit of absolute and unqualified proof. In +reaching these conclusions he had before him the striking +examples of scientific deductions by Galileo, and more recently +the discovery of the circulation of the blood by Harvey. This +last came as a revelation to scientists, reducing this seemingly +occult process, as it did, to the field of mechanical phenomena. +The same mechanical laws that governed the heavenly bodies, as +shown by Galileo, governed the action of the human heart, and, +for aught any one knew, every part of the body, and even the mind +itself. + +Having once conceived this idea, Descartes began a series of +dissections and experiments upon the lower animals, to find, if +possible, further proof of this general law. To him the human +body was simply a machine, a complicated mechanism, whose +functions were controlled just as any other piece of machinery. +He compared the human body to complicated machinery run by +water-falls and complicated pipes. "The nerves of the machine +which I am describing," he says, "may very well be compared to +the pipes of these waterworks; its muscles and its tendons to the +other various engines and springs which seem to move them; its +animal spirits to the water which impels them, of which the heart +is the fountain; while the cavities of the brain are the central +office. Moreover, respiration and other such actions as are +natural and usual in the body, and which depend on the course of +the spirits, are like the movements of a clock, or a mill, which +may be kept up by the ordinary flow of water."[3] + +In such passages as these Descartes anticipates the ideas of +physiology of the present time. He believed that the functions +are performed by the various organs of the bodies of animals and +men as a mechanism, to which in man was added the soul. This soul +he located in the pineal gland, a degenerate and presumably +functionless little organ in the brain. For years Descartes's +idea of the function of this gland was held by many +physiologists, and it was only the introduction of modern +high-power microscopy that reduced this also to a mere mechanism, +and showed that it is apparently the remains of a Cyclopean eye +once common to man's remote ancestors. + +Descartes was the originator of a theory of the movements of the +universe by a mechanical process--the Cartesian theory of +vortices--which for several decades after its promulgation +reigned supreme in science. It is the ingenuity of this theory, +not the truth of its assertions, that still excites admiration, +for it has long since been supplanted. It was certainly the best +hitherto advanced--the best "that the observations of the age +admitted," according to D'Alembert. + +According to this theory the infinite universe is full of matter, +there being no such thing as a vacuum. Matter, as Descartes +believed, is uniform in character throughout the entire universe, +and since motion cannot take place in any part of a space +completely filled, without simultaneous movement in all other +parts, there are constant more or less circular movements, +vortices, or whirlpools of particles, varying, of course, in size +and velocity. As a result of this circular movement the particles +of matter tend to become globular from contact with one another. +Two species of matter are thus formed, one larger and globular, +which continue their circular motion with a constant tendency to +fly from the centre of the axis of rotation, the other composed +of the clippings resulting from the grinding process. These +smaller "filings" from the main bodies, becoming smaller and +smaller, gradually lose their velocity and accumulate in the +centre of the vortex. This collection of the smaller matter in +the centre of the vortex constitutes the sun or star, while the +spherical particles propelled in straight lines from the centre +towards the circumference of the vortex produce the phenomenon of +light radiating from the central star. Thus this matter becomes +the atmosphere revolving around the accumulation at the centre. +But the small particles being constantly worn away from the +revolving spherical particles in the vortex, become entangled in +their passage, and when they reach the edge of the inner strata +of solar dust they settle upon it and form what we call +sun-spots. These are constantly dissolved and reformed, until +sometimes they form a crust round the central nucleus. + +As the expansive force of the star diminishes in the course of +time, it is encroached upon by neighboring vortices. If the part +of the encroaching star be of a less velocity than the star which +it has swept up, it will presently lose its hold, and the smaller +star pass out of range, becoming a comet. But if the velocity of +the vortex into which the incrusted star settles be equivalent to +that of the surrounded vortex, it will hold it as a captive, +still revolving and "wrapt in its own firmament." Thus the +several planets of our solar system have been captured and held +by the sun-vortex, as have the moon and other satellites. + +But although these new theories at first created great enthusiasm +among all classes of philosophers and scientists, they soon came +under the ban of the Church. While no actual harm came to +Descartes himself, his writings were condemned by the Catholic +and Protestant churches alike. The spirit of philosophical +inquiry he had engendered, however, lived on, and is largely +responsible for modern philosophy. + +In many ways the life and works of Leibnitz remind us of Bacon +rather than Descartes. His life was spent in filling high +political positions, and his philosophical and scientific +writings were by-paths of his fertile mind. He was a theoretical +rather than a practical scientist, his contributions to science +being in the nature of philosophical reasonings rather than +practical demonstrations. Had he been able to withdraw from +public life and devote himself to science alone, as Descartes +did, he would undoubtedly have proved himself equally great as a +practical worker. But during the time of his greatest activity in +philosophical fields, between the years 1690 and 1716, he was all +the time performing extraordinary active duties in entirely +foreign fields. His work may be regarded, perhaps, as doing for +Germany in particular what Bacon's did for England and the rest +of the world in general. + +Only a comparatively small part of his philosophical writings +concern us here. According to his theory of the ultimate elements +of the universe, the entire universe is composed of individual +centres, or monads. To these monads he ascribed numberless +qualities by which every phase of nature may be accounted. They +were supposed by him to be percipient, self-acting beings, not +under arbitrary control of the deity, and yet God himself was the +original monad from which all the rest are generated. With this +conception as a basis, Leibnitz deduced his doctrine of +pre-established harmony, whereby the numerous independent +substances composing the world are made to form one universe. He +believed that by virtue of an inward energy monads develop +themselves spontaneously, each being independent of every other. +In short, each monad is a kind of deity in itself--a microcosm +representing all the great features of the macrocosm. + +It would be impossible clearly to estimate the precise value of +the stimulative influence of these philosophers upon the +scientific thought of their time. There was one way, however, in +which their influence was made very tangible--namely, in the +incentive they gave to the foundation of scientific societies. + + +SCIENTIFIC SOCIETIES + +At the present time, when the elements of time and distance are +practically eliminated in the propagation of news, and when cheap +printing has minimized the difficulties of publishing scientific +discoveries, it is difficult to understand the isolated position +of the scientific investigation of the ages that preceded steam +and electricity. Shut off from the world and completely out of +touch with fellow-laborers perhaps only a few miles away, the +investigators were naturally seriously handicapped; and +inventions and discoveries were not made with the same rapidity +that they would undoubtedly have been had the same men been +receiving daily, weekly, or monthly communications from +fellow-laborers all over the world, as they do to-day. Neither +did they have the advantage of public or semi-public +laboratories, where they were brought into contact with other +men, from whom to gather fresh trains of thought and receive the +stimulus of their successes or failures. In the natural course of +events, however, neighbors who were interested in somewhat +similar pursuits, not of the character of the rivalry of trade or +commerce, would meet more or less frequently and discuss their +progress. The mutual advantages of such intercourse would be at +once appreciated; and it would be but a short step from the +casual meeting of two neighborly scientists to the establishment +of "societies," meeting at fixed times, and composed of members +living within reasonable travelling distance. There would, +perhaps, be the weekly or monthly meetings of men in a limited +area; and as the natural outgrowth of these little local +societies, with frequent meetings, would come the formation of +larger societies, meeting less often, where members travelled a +considerable distance to attend. And, finally, with increased +facilities for communication and travel, the great international +societies of to-day would be produced--the natural outcome of the +neighborly meetings of the primitive mediaeval investigators. + +In Italy, at about the time of Galileo, several small societies +were formed. One of the most important of these was the Lyncean +Society, founded about the year 1611, Galileo himself being a +member. This society was succeeded by the Accademia del Cimento, +at Florence, in 1657, which for a time flourished, with such a +famous scientist as Torricelli as one of its members. + +In England an impetus seems to have been given by Sir Francis +Bacon's writings in criticism and censure of the systern of +teaching in colleges. It is supposed that his suggestions as to +what should be the aims of a scientific society led eventually to +the establishment of the Royal Society. He pointed out how little +had really been accomplished by the existing institutions of +learning in advancing science, and asserted that little good +could ever come from them while their methods of teaching +remained unchanged. He contended that the system which made the +lectures and exercises of such a nature that no deviation from +the established routine could be thought of was pernicious. But +he showed that if any teacher had the temerity to turn from the +traditional paths, the daring pioneer was likely to find +insurmountable obstacles placed in the way of his advancement. +The studies were "imprisoned" within the limits of a certain set +of authors, and originality in thought or teaching was to be +neither contemplated nor tolerated. + +The words of Bacon, given in strong and unsparing terms of +censure and condemnation, but nevertheless with perfect +justification, soon bore fruit. As early as the year 1645 a small +company of scientists had been in the habit of meeting at some +place in London to discuss philosophical and scientific subjects +for mental advancement. In 1648, owing to the political +disturbances of the time, some of the members of these meetings +removed to Oxford, among them Boyle, Wallis, and Wren, where the +meetings were continued, as were also the meetings of those left +in London. In 1662, however, when the political situation bad +become more settled, these two bodies of men were united under a +charter from Charles II., and Bacon's ideas were practically +expressed in that learned body, the Royal Society of London. And +it matters little that in some respects Bacon's views were not +followed in the practical workings of the society, or that the +division of labor in the early stages was somewhat different than +at present. The aim of the society has always been one for the +advancement of learning; and if Bacon himself could look over its +records, he would surely have little fault to find with the aid +it has given in carrying out his ideas for the promulgation of +useful knowledge. + +Ten years after the charter was granted to the Royal Society of +London, Lord Bacon's words took practical effect in Germany, with +the result that the Academia Naturae Curiosorum was founded, +under the leadership of Professor J. C. Sturm. The early labors +of this society were devoted to a repetition of the most notable +experiments of the time, and the work of the embryo society was +published in two volumes, in 1672 and 1685 respectively, which +were practically text-books of the physics of the period. It was +not until 1700 that Frederick I. founded the Royal Academy of +Sciences at Berlin, after the elaborate plan of Leibnitz, who was +himself the first president. + +Perhaps the nearest realization of Bacon's ideal, however, is in +the Royal Academy of Sciences at Paris, which was founded in 1666 +under the administration of Colbert, during the reign of Louis +XIV. This institution not only recognized independent members, +but had besides twenty pensionnaires who received salaries from +the government. In this way a select body of scientists were +enabled to pursue their investigations without being obliged to +"give thought to the morrow" for their sustenance. In return they +were to furnish the meetings with scientific memoirs, and once a +year give an account of the work they were engaged upon. Thus a +certain number of the brightest minds were encouraged to devote +their entire time to scientific research, "delivered alike from +the temptations of wealth or the embarrassments of poverty." That +such a plan works well is amply attested by the results emanating +from the French academy. Pensionnaires in various branches of +science, however, either paid by the state or by learned +societies, are no longer confined to France. + +Among the other early scientific societies was the Imperial +Academy of Sciences at St. Petersburg, projected by Peter the +Great, and established by his widow, Catharine I., in 1725; and +also the Royal Swedish Academy, incorporated in 1781, and +counting among its early members such men as the celebrated +Linnaeus. But after the first impulse had resulted in a few +learned societies, their manifest advantage was so evident that +additional numbers increased rapidly, until at present almost +every branch of every science is represented by more or less +important bodies; and these are, individually and collectively, +adding to knowledge and stimulating interest in the many fields +of science, thus vindicating Lord Bacon's asseverations that +knowledge could be satisfactorily promulgated in this manner. + + + +X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +We have now to witness the diversified efforts of a company of +men who, working for the most part independently, greatly added +to the data of the physical sciences--such men as Boyle, Huygens, +Von Gericke, and Hooke. It will be found that the studies of +these men covered the whole field of physical sciences as then +understood--the field of so-called natural philosophy. We shall +best treat these successors of Galileo and precursors of Newton +somewhat biographically, pointing out the correspondences and +differences between their various accomplishments as we proceed. +It will be noted in due course that the work of some of them was +anticipatory of great achievements of a later century. + + +ROBERT BOYLE (1627-1691) + +Some of Robert Boyle's views as to the possible structure of +atmospheric air will be considered a little farther on in this +chapter, but for the moment we will take up the consideration of +some of his experiments upon that as well as other gases. Boyle +was always much interested in alchemy, and carried on extensive +experiments in attempting to accomplish the transmutation of +metals; but he did not confine himself to these experiments, +devoting himself to researches in all the fields of natural +philosophy. He was associated at Oxford with a company of +scientists, including Wallis and Wren, who held meetings and made +experiments together, these gatherings being the beginning, as +mentioned a moment ago, of what finally became the Royal Society. +It was during this residence at Oxford that many of his valuable +researches upon air were made, and during this time be invented +his air-pump, now exhibited in the Royal Society rooms at +Burlington House.[1] + +His experiments to prove the atmospheric pressure are most +interesting and conclusive. "Having three small, round glass +bubbles, blown at the flame of a lamp, about the size of +hazel-nuts," he says, "each of them with a short, slender stem, +by means whereof they were so exactly poised in water that a very +small change of weight would make them either emerge or sink; at +a time when the atmosphere was of convenient weight, I put them +into a wide-mouthed glass of common water, and leaving them in a +quiet place, where they were frequently in my eye, I observed +that sometimes they would be at the top of the water, and remain +there for several days, or perhaps weeks, together, and sometimes +fall to the bottom, and after having continued there for some +time rise again. And sometimes they would rise or fall as the air +was hot or cold."[2] + +It was in the course of these experiments that the observations +made by Boyle led to the invention of his "statical barometer," +the mercurial barometer having been invented, as we have seen, by +Torricelli, in 1643. In describing this invention he says: +"Making choice of a large, thin, and light glass bubble, blown at +the flame of a lamp, I counterpoised it with a metallic weight, +in a pair of scales that were suspended in a frame, that would +turn with the thirtieth part of a grain. Both the frame and the +balance were then placed near a good barometer, whence I might +learn the present weight of the atmosphere; when, though the +scales were unable to show all the variations that appeared in +the mercurial barometer, yet they gave notice of those that +altered the height of the mercury half a quarter of an inch."[3] +A fairly sensitive barometer, after all. This statical barometer +suggested several useful applications to the fertile imagination +of its inventor, among others the measuring of mountain-peaks, as +with the mercurial barometer, the rarefication of the air at the +top giving a definite ratio to the more condensed air in the +valley. + +Another of his experiments was made to discover the atmospheric +pressure to the square inch. After considerable difficulty he +determined that the relative weight of a cubic inch of water and +mercury was about one to fourteen, and computing from other known +weights he determined that "when a column of quicksilver thirty +inches high is sustained in the barometer, as it frequently +happens, a column of air that presses upon an inch square near +the surface of the earth must weigh about fifteen avoirdupois +pounds."[4] As the pressure of air at the sea-level is now +estimated at 14.7304 pounds to the square inch, it will be seen +that Boyle's calculation was not far wrong. + +From his numerous experiments upon the air, Boyle was led to +believe that there were many "latent qualities" due to substances +contained in it that science had as yet been unable to fathom, +believing that there is "not a more heterogeneous body in the +world." He believed that contagious diseases were carried by the +air, and suggested that eruptions of the earth, such as those +made by earthquakes, might send up "venomous exhalations" that +produced diseases. He suggested also that the air might play an +important part in some processes of calcination, which, as we +shall see, was proved to be true by Lavoisier late in the +eighteenth century. Boyle's notions of the exact chemical action +in these phenomena were of course vague and indefinite, but he +had observed that some part was played by the air, and he was +right in supposing that the air "may have a great share in +varying the salts obtainable from calcined vitriol."[5] + +Although he was himself such a painstaking observer of facts, he +had the fault of his age of placing too much faith in hear-say +evidence of untrained observers. Thus, from the numerous stories +he heard concerning the growth of metals in previously exhausted +mines, he believed that the air was responsible for producing +this growth--in which he undoubtedly believed. The story of a +tin-miner that, in his own time, after a lapse of only +twenty-five years, a heap, of earth previously exhausted of its +ore became again even more richly impregnated than before by +lying exposed to the air, seems to have been believed by the +philosopher. + +As Boyle was an alchemist, and undoubtedly believed in the +alchemic theory that metals have "spirits" and various other +qualities that do not exist, it is not surprising that he was +credulous in the matter of beliefs concerning peculiar phenomena +exhibited by them. Furthermore, he undoubtedly fell into the +error common to "specialists," or persons working for long +periods of time on one subject--the error of over-enthusiasm in +his subject. He had discovered so many remarkable qualities in +the air that it is not surprising to find that he attributed to +it many more that he could not demonstrate. + +Boyle's work upon colors, although probably of less importance +than his experiments and deductions upon air, show that he was in +the van as far as the science of his day was concerned. As he +points out, the schools of his time generally taught that "color +is a penetrating quality, reaching to the innermost part of the +substance," and, as an example of this, sealing-wax was cited, +which could be broken into minute bits, each particle retaining +the same color as its fellows or the original mass. To refute +this theory, and to show instances to the contrary, Boyle, among +other things, shows that various colors--blue, red, yellow--may +be produced upon tempered steel, and yet the metal within "a +hair's-breadth of its surface" have none of these colors. +Therefore, he was led to believe that color, in opaque bodies at +least, is superficial. + +"But before we descend to a more particular consideration of our +subject," he says, " 'tis proper to observe that colors may be +regarded either as a quality residing in bodies to modify light +after a particular manner, or else as light itself so modified as +to strike upon the organs of sight, and cause the sensation we +call color; and that this latter is the more proper acceptation +of the word color will appear hereafter. And indeed it is the +light itself, which after a certain manner, either mixed with +shades or other-wise, strikes our eyes and immediately produces +that motion in the organ which gives us the color of an +object."[6] + +In examining smooth and rough surfaces to determine the cause of +their color, he made use of the microscope, and pointed out the +very obvious example of the difference in color of a rough and a +polished piece of the same block of stone. He used some striking +illustrations of the effect of light and the position of the eye +upon colors. "Thus the color of plush or velvet will appear +various if you stroke part of it one way and part another, the +posture of the particular threads in regard to the light, or the +eye, being thereby varied. And 'tis observable that in a field of +ripe corn, blown upon by the wind, there will appear waves of a +color different from that of the rest of the corn, because the +wind, by depressing some of the ears more than others, causes one +to reflect more light from the lateral and strawy parts than +another."[7] His work upon color, however, as upon light, was +entirely overshadowed by the work of his great fellow-countryman +Newton. + +Boyle's work on electricity was a continuation of Gilbert's, to +which he added several new facts. He added several substances to +Gilbert's list of "electrics," experimented on smooth and rough +surfaces in exciting of electricity, and made the important +discovery that amber retained its attractive virtue after the +friction that excited it bad ceased. "For the attrition having +caused an intestine motion in its parts," he says, "the heat +thereby excited ought not to cease as soon as ever the rubbing is +over, but to continue capable of emitting effluvia for some time +afterwards, longer or shorter according to the goodness of the +electric and the degree of the commotion made; all which, joined +together, may sometimes make the effect considerable; and by this +means, on a warm day, I, with a certain body not bigger than a +pea, but very vigorously attractive, moved a steel needle, freely +poised, about three minutes after I had left off rubbing it."[8] + + +MARIOTTE AND VON GUERICKE + +Working contemporaneously with Boyle, and a man whose name is +usually associated with his as the propounder of the law of +density of gases, was Edme Mariotte (died 1684), a native of +Burgundy. Mariotte demonstrated that but for the resistance of +the atmosphere, all bodies, whether light or heavy, dense or +thin, would fall with equal rapidity, and he proved this by the +well-known "guinea-and-feather" experiment. Having exhausted the +air from a long glass tube in which a guinea piece and a feather +had been placed, he showed that in the vacuum thus formed they +fell with equal rapidity as often as the tube was reversed. From +his various experiments as to the pressure of the atmosphere he +deduced the law that the density and elasticity of the atmosphere +are precisely proportional to the compressing force (the law of +Boyle and Mariotte). He also ascertained that air existed in a +state of mechanical mixture with liquids, "existing between their +particles in a state of condensation." He made many other +experiments, especially on the collision of bodies, but his most +important work was upon the atmosphere. + +But meanwhile another contemporary of Boyle and Mariotte was +interesting himself in the study of the atmosphere, and had made +a wonderful invention and a most striking demonstration. This was +Otto von Guericke (1602-1686), Burgomaster of Magdeburg, and +councillor to his "most serene and potent Highness" the elector +of that place. When not engrossed with the duties of public +office, he devoted his time to the study of the sciences, +particularly pneumatics and electricity, both then in their +infancy. The discoveries of Galileo, Pascal, and Torricelli +incited him to solve the problem of the creation of a vacuum--a +desideratum since before the days of Aristotle. His first +experiments were with a wooden pump and a barrel of water, but he +soon found that with such porous material as wood a vacuum could +not be created or maintained. He therefore made use of a globe of +copper, with pump and stop-cock; and with this he was able to +pump out air almost as easily as water. Thus, in 1650, the +air-pump was invented. Continuing his experiments upon vacuums +and atmospheric pressure with his newly discovered pump, he made +some startling discoveries as to the enormous pressure exerted by +the air. + +It was not his intention, however, to demonstrate his newly +acquired knowledge by words or theories alone, nor by mere +laboratory experiments; but he chose instead an open field, to +which were invited Emperor Ferdinand III., and all the princes of +the Diet at Ratisbon. When they were assembled he produced two +hollow brass hemispheres about two feet in diameter, and placing +their exactly fitting surfaces together, proceeded to pump out +the air from their hollow interior, thus causing them to stick +together firmly in a most remarkable way, apparently without +anything holding them. This of itself was strange enough; but now +the worthy burgomaster produced teams of horses, and harnessing +them to either side of the hemispheres, attempted to pull the +adhering brasses apart. Five, ten, fifteen teams--thirty horses, +in all--were attached; but pull and tug as they would they could +not separate the firmly clasped hemispheres. The enormous +pressure of the atmosphere had been most strikingly demonstrated. + +But it is one thing to demonstrate, another to convince; and many +of the good people of Magdeburg shook their heads over this +"devil's contrivance," and predicted that Heaven would punish the +Herr Burgomaster, as indeed it had once by striking his house +with lightning and injuring some of his infernal contrivances. +They predicted his future punishment, but they did not molest +him, for to his fellow-citizens, who talked and laughed, drank +and smoked with him, and knew him for the honest citizen that he +was, he did not seem bewitched at all. And so he lived and worked +and added other facts to science, and his brass hemispheres were +not destroyed by fanatical Inquisitors, but are still preserved +in the royal library at Berlin. + +In his experiments with his air-pump he discovered many things +regarding the action of gases, among others, that animals cannot +live in a vacuum. He invented the anemoscope and the air-balance, +and being thus enabled to weight the air and note the changes +that preceded storms and calms, he was able still further to +dumfound his wondering fellow-Magde-burgers by more or less +accurate predictions about the weather. + +Von Guericke did not accept Gilbert's theory that the earth was a +great magnet, but in his experiments along lines similar to those +pursued by Gilbert, he not only invented the first electrical +machine, but discovered electrical attraction and repulsion. The +electrical machine which he invented consisted of a sphere of +sulphur mounted on an iron axis to imitate the rotation of the +earth, and which, when rubbed, manifested electrical reactions. +When this globe was revolved and stroked with the dry hand it was +found that it attached to it "all sorts of little fragments, like +leaves of gold, silver, paper, etc." "Thus this globe," he says, +"when brought rather near drops of water causes them to swell and +puff up. It likewise attracts air, smoke, etc."[9] Before the +time of Guericke's demonstrations, Cabaeus had noted that chaff +leaped back from an "electric," but he did not interpret the +phenomenon as electrical repulsion. Von Guericke, however, +recognized it as such, and refers to it as what he calls +"expulsive virtue." "Even expulsive virtue is seen in this +globe," he says, "for it not only attracts, but also REPELS again +from itself little bodies of this sort, nor does it receive them +until they have touched something else." It will be observed from +this that he was very close to discovering the discharge of the +electrification of attracted bodies by contact with some other +object, after which they are reattracted by the electric. + +He performed a most interesting experiment with his sulphur globe +and a feather, and in doing so came near anticipating Benjamin +Franklin in his discovery of the effects of pointed conductors in +drawing off the discharge. Having revolved and stroked his globe +until it repelled a bit of down, he removed the globe from its +rack and advancing it towards the now repellent down, drove it +before him about the room. In this chase he observed that the +down preferred to alight against "the points of any object +whatsoever." He noticed that should the down chance to be driven +within a few inches of a lighted candle, its attitude towards the +globe suddenly changed, and instead of running away from it, it +now "flew to it for protection" --the charge on the down having +been dissipated by the hot air. He also noted that if one face of +a feather had been first attracted and then repelled by the +sulphur ball, that the surface so affected was always turned +towards the globe; so that if the positions of the two were +reversed, the sides of the feather reversed also. + +Still another important discovery, that of electrical conduction, +was made by Von Guericke. Until his discovery no one had observed +the transference of electricity from one body to another, +although Gilbert had some time before noted that a rod rendered +magnetic at one end became so at the other. Von Guericke's +experiments were made upon a linen thread with his sulphur globe, +which, he says, "having been previously excited by rubbing, can +exercise likewise its virtue through a linen thread an ell or +more long, and there attract something." But this discovery, and +his equally important one that the sulphur ball becomes luminous +when rubbed, were practically forgotten until again brought to +notice by the discoveries of Francis Hauksbee and Stephen Gray +early in the eighteenth century. From this we may gather that Von +Guericke himself did not realize the import of his discoveries, +for otherwise he would certainly have carried his investigations +still further. But as it was he turned his attention to other +fields of research. + + +ROBERT HOOKE + +A slender, crooked, shrivelled-limbed, cantankerous little man, +with dishevelled hair and haggard countenance, bad-tempered and +irritable, penurious and dishonest, at least in his claims for +priority in discoveries--this is the picture usually drawn, alike +by friends and enemies, of Robert Hooke (1635-1703), a man with +an almost unparalleled genius for scientific discoveries in +almost all branches of science. History gives few examples so +striking of a man whose really great achievements in science +would alone have made his name immortal, and yet who had the +pusillanimous spirit of a charlatan--an almost insane mania, as +it seems--for claiming the credit of discoveries made by others. +This attitude of mind can hardly be explained except as a mania: +it is certainly more charitable so to regard it. For his own +discoveries and inventions were so numerous that a few more or +less would hardly have added to his fame, as his reputation as a +philosopher was well established. Admiration for his ability and +his philosophical knowledge must always be marred by the +recollection of his arrogant claims to the discoveries of other +philosophers. + +It seems pretty definitely determined that Hooke should be +credited with the invention of the balance-spring for regulating +watches; but for a long time a heated controversy was waged +between Hooke and Huygens as to who was the real inventor. It +appears that Hooke conceived the idea of the balance-spring, +while to Huygens belongs the credit of having adapted the COILED +spring in a working model. He thus made practical Hooke's +conception, which is without value except as applied by the +coiled spring; but, nevertheless, the inventor, as well as the +perfector, should receive credit. In this controversy, unlike +many others, the blame cannot be laid at Hooke's door. + +Hooke was the first curator of the Royal Society, and when +anything was to be investigated, usually invented the mechanical +devices for doing so. Astronomical apparatus, instruments for +measuring specific weights, clocks and chronometers, methods of +measuring the velocity of falling bodies, freezing and boiling +points, strength of gunpowder, magnetic instruments--in short, +all kinds of ingenious mechanical devices in all branches of +science and mechanics. It was he who made the famous air-pump of +Robert Boyle, based on Boyle's plans. Incidentally, Hooke claimed +to be the inventor of the first air-pump himself, although this +claim is now entirely discredited. + +Within a period of two years he devised no less than thirty +different methods of flying, all of which, of course, came to +nothing, but go to show the fertile imagination of the man, and +his tireless energy. He experimented with electricity and made +some novel suggestions upon the difference between the electric +spark and the glow, although on the whole his contributions in +this field are unimportant. He also first pointed out that the +motions of the heavenly bodies must be looked upon as a +mechanical problem, and was almost within grasping distance of +the exact theory of gravitation, himself originating the idea of +making use of the pendulum in measuring gravity. Likewise, he +first proposed the wave theory of light; although it was Huygens +who established it on its present foundation. + +Hooke published, among other things, a book of plates and +descriptions of his Microscopical Observations, which gives an +idea of the advance that had already been made in microscopy in +his time. Two of these plates are given here, which, even in this +age of microscopy, are both interesting and instructive. These +plates are made from prints of Hooke's original copper plates, +and show that excellent lenses were made even at that time. They +illustrate, also, how much might have been accomplished in the +field of medicine if more attention had been given to microscopy +by physicians. Even a century later, had physicians made better +use of their microscopes, they could hardly have overlooked such +an easily found parasite as the itch mite, which is quite as +easily detected as the cheese mite, pictured in Hooke's book. + +In justice to Hooke, and in extenuation of his otherwise +inexcusable peculiarities of mind, it should be remembered that +for many years he suffered from a painful and wasting disease. +This may have affected his mental equilibrium, without +appreciably affecting his ingenuity. In his own time this +condition would hardly have been considered a disease; but +to-day, with our advanced ideas as to mental diseases, we should +be more inclined to ascribe his unfortunate attitude of mind to a +pathological condition, rather than to any manifestation of +normal mentality. From this point of view his mental deformity +seems not unlike that of Cavendish's, later, except that in the +case of Cavendish it manifested itself as an abnormal +sensitiveness instead of an abnormal irritability. + + +CHRISTIAN HUYGENS + +If for nothing else, the world is indebted to the man who +invented the pendulum clock, Christian Huygens (1629-1695), of +the Hague, inventor, mathematician, mechanician, astronomer, and +physicist. Huygens was the descendant of a noble and +distinguished family, his father, Sir Constantine Huygens, being +a well-known poet and diplomatist. Early in life young Huygens +began his career in the legal profession, completing his +education in the juridical school at Breda; but his taste for +mathematics soon led him to neglect his legal studies, and his +aptitude for scientific researches was so marked that Descartes +predicted great things of him even while he was a mere tyro in +the field of scientific investigation. + +One of his first endeavors in science was to attempt an +improvement of the telescope. Reflecting upon the process of +making lenses then in vogue, young Huygens and his brother +Constantine attempted a new method of grinding and polishing, +whereby they overcame a great deal of the spherical and chromatic +aberration. With this new telescope a much clearer field of +vision was obtained, so much so that Huygens was able to detect, +among other things, a hitherto unknown satellite of Saturn. It +was these astronomical researches that led him to apply the +pendulum to regulate the movements of clocks. The need for some +more exact method of measuring time in his observations of the +stars was keenly felt by the young astronomer, and after several +experiments along different lines, Huygens hit upon the use of a +swinging weight; and in 1656 made his invention of the pendulum +clock. The year following, his clock was presented to the +states-general. Accuracy as to time is absolutely essential in +astronomy, but until the invention of Huygens's clock there was +no precise, nor even approximately precise, means of measuring +short intervals. + +Huygens was one of the first to adapt the micrometer to the +telescope--a mechanical device on which all the nice +determination of minute distances depends. He also took up the +controversy against Hooke as to the superiority of telescopic +over plain sights to quadrants, Hooke contending in favor of the +plain. In this controversy, the subject of which attracted wide +attention, Huygens was completely victorious; and Hooke, being +unable to refute Huygens's arguments, exhibited such irritability +that he increased his already general unpopularity. All of the +arguments for and against the telescope sight are too numerous to +be given here. In contending in its favor Huygens pointed out +that the unaided eye is unable to appreciate an angular space in +the sky less than about thirty seconds. Even in the best quadrant +with a plain sight, therefore, the altitude must be uncertain by +that quantity. If in place of the plain sight a telescope is +substituted, even if it magnify only thirty times, it will enable +the observer to fix the position to one second, with +progressively increased accuracy as the magnifying power of the +telescope is increased. This was only one of the many telling +arguments advanced by Huygens. + +In the field of optics, also, Huygens has added considerably to +science, and his work, Dioptrics, is said to have been a favorite +book with Newton. During the later part of his life, however, +Huygens again devoted himself to inventing and constructing +telescopes, grinding the lenses, and devising, if not actually +making, the frame for holding them. These telescopes were of +enormous lengths, three of his object-glasses, now in possession +of the Royal Society, being of 123, 180, and 210 feet focal +length respectively. Such instruments, if constructed in the +ordinary form of the long tube, were very unmanageable, and to +obviate this Huygens adopted the plan of dispensing with the tube +altogether, mounting his lenses on long poles manipulated by +machinery. Even these were unwieldy enough, but the difficulties +of manipulation were fully compensated by the results obtained. + +It had been discovered, among other things, that in oblique +refraction light is separated into colors. Therefore, any small +portion of the convex lens of the telescope, being a prism, the +rays proceed to the focus, separated into prismatic colors, which +make the image thus formed edged with a fringe of color and +indistinct. But, fortunately for the early telescope makers, the +degree of this aberration is independent of the focal length of +the lens; so that, by increasing this focal length and using the +appropriate eye-piece, the image can be greatly magnified, while +the fringe of colors remains about the same as when a less +powerful lens is used. Hence the advantage of Huygens's long +telescope. He did not confine his efforts to simply lengthening +the focal length of his telescopes, however, but also added to +their efficiency by inventing an almost perfect achromatic +eye-piece. + +In 1663 he was elected a fellow of the Royal Society of London, +and in 1669 he gave to that body a concise statement of the laws +governing the collision of elastic bodies. Although the same +views had been given by Wallis and Wren a few weeks earlier, +there is no doubt that Huygens's views were reached +independently; and it is probable that he had arrived at his +conclusions several years before. In the Philosophical +Transactions for 1669 it is recorded that the society, being +interested in the laws of the principles of motion, a request was +made that M. Huygens, Dr. Wallis, and Sir Christopher Wren submit +their views on the subject. Wallis submitted his paper first, +November 15, 1668. A month later, December 17th, Wren imparted to +the society his laws as to the nature of the collision of bodies. +And a few days later, January 5, 1669, Huygens sent in his "Rules +Concerning the Motion of Bodies after Mutual Impulse." Although +Huygens's report was received last, he was anticipated by such a +brief space of time, and his views are so clearly stated--on the +whole rather more so than those of the other two--that we give +them in part here: + + +"1. If a hard body should strike against a body equally hard at +rest, after contact the former will rest and the latter acquire a +velocity equal to that of the moving body. + +"2. But if that other equal body be likewise in motion, and +moving in the same direction, after contact they will move with +reciprocal velocities. + +"3. A body, however great, is moved by a body however small +impelled with any velocity whatsoever. + +"5. The quantity of motion of two bodies may be either increased +or diminished by their shock; but the same quantity towards the +same part remains, after subtracting the quantity of the contrary +motion. + +"6. The sum of the products arising from multiplying the mass of +any hard body into the squares of its velocity is the same both +before and after the stroke. + +"7. A hard body at rest will receive a greater quantity of motion +from another hard body, either greater or less than itself, by +the interposition of any third body of a mean quantity, than if +it was immediately struck by the body itself; and if the +interposing body be a mean proportional between the other two, +its action upon the quiescent body will be the greatest of +all."[10] + + +This was only one of several interesting and important +communications sent to the Royal Society during his lifetime. One +of these was a report on what he calls "Pneumatical Experiments." +"Upon including in a vacuum an insect resembling a beetle, but +somewhat larger," he says, "when it seemed to be dead, the air +was readmitted, and soon after it revived; putting it again in +the vacuum, and leaving it for an hour, after which the air was +readmitted, it was observed that the insect required a longer +time to recover; including it the third time for two days, after +which the air was admitted, it was ten hours before it began to +stir; but, putting it in a fourth time, for eight days, it never +afterwards recovered.... Several birds, rats, mice, rabbits, and +cats were killed in a vacuum, but if the air was admitted before +the engine was quite exhausted some of them would recover; yet +none revived that had been in a perfect vacuum.... Upon putting +the weight of eighteen grains of powder with a gauge into a +receiver that held several pounds of water, and firing the +powder, it raised the mercury an inch and a half; from which it +appears that there is one-fifth of air in gunpowder, upon the +supposition that air is about one thousand times lighter than +water; for in this experiment the mercury rose to the eighteenth +part of the height at which the air commonly sustains it, and +consequently the weight of eighteen grains of powder yielded air +enough to fill the eighteenth part of a receiver that contained +seven pounds of water; now this eighteenth part contains +forty-nine drachms of water; wherefore the air, that takes up an +equal space, being a thousand times lighter, weighs +one-thousandth part of forty-nine drachms, which is more than +three grains and a half; it follows, therefore, that the weight +of eighteen grains of powder contains more than three and a half +of air, which is about one-fifth of eighteen grains...." + +From 1665 to 1681, accepting the tempting offer made him through +Colbert, by Louis XIV., Huygens pursued his studies at the +Bibliotheque du Roi as a resident of France. Here he published +his Horologium Oscillatorium, dedicated to the king, containing, +among other things, his solution of the problem of the "centre of +oscillation." This in itself was an important step in the history +of mechanics. Assuming as true that the centre of gravity of any +number of interdependent bodies cannot rise higher than the point +from which it falls, he reached correct conclusions as to the +general principle of the conservation of vis viva, although he +did not actually prove his conclusions. This was the first +attempt to deal with the dynamics of a system. In this work, +also, was the true determination of the relation between the +length of a pendulum and the time of its oscillation. + +In 1681 he returned to Holland, influenced, it is believed, by +the attitude that was being taken in France against his religion. +Here he continued his investigations, built his immense +telescopes, and, among other things, discovered "polarization," +which is recorded in Traite de la Lumiere, published at Leyden in +1690. Five years later he died, bequeathing his manuscripts to +the University of Leyden. It is interesting to note that he never +accepted Newton's theory of gravitation as a universal property +of matter. + + + +XI. NEWTON AND THE COMPOSITION OF LIGHT + +Galileo, that giant in physical science of the early seventeenth +century, died in 1642. On Christmas day of the same year there +was born in England another intellectual giant who was destined +to carry forward the work of Copernicus, Kepler, and Galileo to a +marvellous consummation through the discovery of the great +unifying law in accordance with which the planetary motions are +performed. We refer, of course, to the greatest of English +physical scientists, Isaac Newton, the Shakespeare of the +scientific world. Born thus before the middle of the seventeenth +century, Newton lived beyond the first quarter of the eighteenth +(1727). For the last forty years of that period his was the +dominating scientific personality of the world. With full +propriety that time has been spoken of as the "Age of Newton." + +Yet the man who was to achieve such distinction gave no early +premonition of future greatness. He was a sickly child from +birth, and a boy of little seeming promise. He was an indifferent +student, yet, on the other hand, he cared little for the common +amusements of boyhood. He early exhibited, however, a taste for +mechanical contrivances, and spent much time in devising +windmills, water-clocks, sun-dials, and kites. While other boys +were interested only in having kites that would fly, Newton--at +least so the stories of a later time would have us +understand--cared more for the investigation of the seeming +principles involved, or for testing the best methods of attaching +the strings, or the best materials to be used in construction. + +Meanwhile the future philosopher was acquiring a taste for +reading and study, delving into old volumes whenever he found an +opportunity. These habits convinced his relatives that it was +useless to attempt to make a farmer of the youth, as had been +their intention. He was therefore sent back to school, and in the +summer of 1661 he matriculated at Trinity College, Cambridge. +Even at college Newton seems to have shown no unusual mental +capacity, and in 1664, when examined for a scholarship by Dr. +Barrow, that gentleman is said to have formed a poor opinion of +the applicant. It is said that the knowledge of the estimate +placed upon his abilities by his instructor piqued Newton, and +led him to take up in earnest the mathematical studies in which +he afterwards attained such distinction. The study of Euclid and +Descartes's "Geometry" roused in him a latent interest in +mathematics, and from that time forward his investigations were +carried on with enthusiasm. In 1667 he was elected Fellow of +Trinity College, taking the degree of M.A. the following spring. + +It will thus appear that Newton's boyhood and early manhood were +passed during that troublous time in British political annals +which saw the overthrow of Charles I., the autocracy of Cromwell, +and the eventual restoration of the Stuarts. His maturer years +witnessed the overthrow of the last Stuart and the reign of the +Dutchman, William of Orange. In his old age he saw the first of +the Hanoverians mount the throne of England. Within a decade of +his death such scientific path-finders as Cavendish, Black, and +Priestley were born--men who lived on to the close of the +eighteenth century. In a full sense, then, the age of Newton +bridges the gap from that early time of scientific awakening +under Kepler and Galileo to the time which we of the twentieth +century think of as essentially modern. + + +THE COMPOSITION OF WHITE LIGHT + +In December, 1672, Newton was elected a Fellow of the Royal +Society, and at this meeting a paper describing his invention of +the refracting telescope was read. A few days later he wrote to +the secretary, making some inquiries as to the weekly meetings of +the society, and intimating that he had an account of an +interesting discovery that he wished to lay before the society. +When this communication was made public, it proved to be an +explanation of the discovery of the composition of white light. +We have seen that the question as to the nature of color had +commanded the attention of such investigators as Huygens, but +that no very satisfactory solution of the question had been +attained. Newton proved by demonstrative experiments that white +light is composed of the blending of the rays of diverse colors, +and that the color that we ascribe to any object is merely due to +the fact that the object in question reflects rays of that color, +absorbing the rest. That white light is really made up of many +colors blended would seem incredible had not the experiments by +which this composition is demonstrated become familiar to every +one. The experiments were absolutely novel when Newton brought +them forward, and his demonstration of the composition of light +was one of the most striking expositions ever brought to the +attention of the Royal Society. It is hardly necessary to add +that, notwithstanding the conclusive character of Newton's work, +his explanations did not for a long time meet with general +acceptance. + +Newton was led to his discovery by some experiments made with an +ordinary glass prism applied to a hole in the shutter of a +darkened room, the refracted rays of the sunlight being received +upon the opposite wall and forming there the familiar spectrum. +"It was a very pleasing diversion," he wrote, "to view the vivid +and intense colors produced thereby; and after a time, applying +myself to consider them very circumspectly, I became surprised to +see them in varying form, which, according to the received laws +of refraction, I expected should have been circular. They were +terminated at the sides with straight lines, but at the ends the +decay of light was so gradual that it was difficult to determine +justly what was their figure, yet they seemed semicircular. + +"Comparing the length of this colored spectrum with its breadth, +I found it almost five times greater; a disproportion so +extravagant that it excited me to a more than ordinary curiosity +of examining from whence it might proceed. I could scarce think +that the various thicknesses of the glass, or the termination +with shadow or darkness, could have any influence on light to +produce such an effect; yet I thought it not amiss, first, to +examine those circumstances, and so tried what would happen by +transmitting light through parts of the glass of divers +thickness, or through holes in the window of divers bigness, or +by setting the prism without so that the light might pass through +it and be refracted before it was transmitted through the hole; +but I found none of those circumstances material. The fashion of +the colors was in all these cases the same. + +"Then I suspected whether by any unevenness of the glass or other +contingent irregularity these colors might be thus dilated. And +to try this I took another prism like the former, and so placed +it that the light, passing through them both, might be refracted +contrary ways, and so by the latter returned into that course +from which the former diverted it. For, by this means, I thought, +the regular effects of the first prism would be destroyed by the +second prism, but the irregular ones more augmented by the +multiplicity of refractions. The event was that the light, which +by the first prism was diffused into an oblong form, was by the +second reduced into an orbicular one with as much regularity as +when it did not all pass through them. So that, whatever was the +cause of that length, 'twas not any contingent irregularity. + +"I then proceeded to examine more critically what might be +effected by the difference of the incidence of rays coming from +divers parts of the sun; and to that end measured the several +lines and angles belonging to the image. Its distance from the +hole or prism was 22 feet; its utmost length 13 1/4 inches; its +breadth 2 5/8; the diameter of the hole 1/4 of an inch; the angle +which the rays, tending towards the middle of the image, made +with those lines, in which they would have proceeded without +refraction, was 44 degrees 56'; and the vertical angle of the +prism, 63 degrees 12'. Also the refractions on both sides of the +prism--that is, of the incident and emergent rays--were, as near +as I could make them, equal, and consequently about 54 degrees +4'; and the rays fell perpendicularly upon the wall. Now, +subducting the diameter of the hole from the length and breadth +of the image, there remains 13 inches the length, and 2 3/8 the +breadth, comprehended by those rays, which, passing through the +centre of the said hole, which that breadth subtended, was about +31', answerable to the sun's diameter; but the angle which its +length subtended was more than five such diameters, namely 2 +degrees 49'. + +"Having made these observations, I first computed from them the +refractive power of the glass, and found it measured by the ratio +of the sines 20 to 31. And then, by that ratio, I computed the +refractions of two rays flowing from opposite parts of the sun's +discus, so as to differ 31' in their obliquity of incidence, and +found that the emergent rays should have comprehended an angle of +31', as they did, before they were incident. + +"But because this computation was founded on the hypothesis of +the proportionality of the sines of incidence and refraction, +which though by my own experience I could not imagine to be so +erroneous as to make that angle but 31', which in reality was 2 +degrees 49', yet my curiosity caused me again to make my prism. +And having placed it at my window, as before, I observed that by +turning it a little about its axis to and fro, so as to vary its +obliquity to the light more than an angle of 4 degrees or 5 +degrees, the colors were not thereby sensibly translated from +their place on the wall, and consequently by that variation of +incidence the quantity of refraction was not sensibly varied. By +this experiment, therefore, as well as by the former computation, +it was evident that the difference of the incidence of rays +flowing from divers parts of the sun could not make them after +decussation diverge at a sensibly greater angle than that at +which they before converged; which being, at most, but about 31' +or 32', there still remained some other cause to be found out, +from whence it could be 2 degrees 49'." + +All this caused Newton to suspect that the rays, after their +trajection through the prism, moved in curved rather than in +straight lines, thus tending to be cast upon the wall at +different places according to the amount of this curve. His +suspicions were increased, also, by happening to recall that a +tennis-ball sometimes describes such a curve when "cut" by a +tennis-racket striking the ball obliquely. + +"For a circular as well as a progressive motion being +communicated to it by the stroke," he says, "its parts on that +side where the motions conspire must press and beat the +contiguous air more violently than on the other, and there excite +a reluctancy and reaction of the air proportionately greater. And +for the same reason, if the rays of light should possibly be +globular bodies, and by their oblique passage out of one medium +into another acquire a circulating motion, they ought to feel the +greater resistance from the ambient ether on that side where the +motions conspire, and thence be continually bowed to the other. +But notwithstanding this plausible ground of suspicion, when I +came to examine it I could observe no such curvity in them. And, +besides (which was enough for my purpose), I observed that the +difference 'twixt the length of the image and diameter of the +hole through which the light was transmitted was proportionable +to their distance. + +"The gradual removal of these suspicions at length led me to the +experimentum crucis, which was this: I took two boards, and, +placing one of them close behind the prism at the window, so that +the light must pass through a small hole, made in it for the +purpose, and fall on the other board, which I placed at about +twelve feet distance, having first made a small hole in it also, +for some of the incident light to pass through. Then I placed +another prism behind this second board, so that the light +trajected through both the boards might pass through that also, +and be again refracted before it arrived at the wall. This done, +I took the first prism in my hands and turned it to and fro +slowly about its axis, so much as to make the several parts of +the image, cast on the second board, successively pass through +the hole in it, that I might observe to what places on the wall +the second prism would refract them. And I saw by the variation +of these places that the light, tending to that end of the image +towards which the refraction of the first prism was made, did in +the second prism suffer a refraction considerably greater than +the light tending to the other end. And so the true cause of the +length of that image was detected to be no other than that LIGHT +consists of RAYS DIFFERENTLY REFRANGIBLE, which, without any +respect to a difference in their incidence, were, according to +their degrees of refrangibility, transmitted towards divers parts +of the wall."[1] + + +THE NATURE OF COLOR + +Having thus proved the composition of light, Newton took up an +exhaustive discussion as to colors, which cannot be entered into +at length here. Some of his remarks on the subject of compound +colors, however, may be stated in part. Newton's views are of +particular interest in this connection, since, as we have already +pointed out, the question as to what constituted color could not +be agreed upon by the philosophers. Some held that color was an +integral part of the substance; others maintained that it was +simply a reflection from the surface; and no scientific +explanation had been generally accepted. Newton concludes his +paper as follows: + +"I might add more instances of this nature, but I shall conclude +with the general one that the colors of all natural bodies have +no other origin than this, that they are variously qualified to +reflect one sort of light in greater plenty than another. And +this I have experimented in a dark room by illuminating those +bodies with uncompounded light of divers colors. For by that +means any body may be made to appear of any color. They have +there no appropriate color, but ever appear of the color of the +light cast upon them, but yet with this difference, that they are +most brisk and vivid in the light of their own daylight color. +Minium appeareth there of any color indifferently with which 'tis +illustrated, but yet most luminous in red; and so Bise appeareth +indifferently of any color with which 'tis illustrated, but yet +most luminous in blue. And therefore Minium reflecteth rays of +any color, but most copiously those indued with red; and +consequently, when illustrated with daylight--that is, with all +sorts of rays promiscuously blended--those qualified with red +shall abound most in the reflected light, and by their prevalence +cause it to appear of that color. And for the same reason, Bise, +reflecting blue most copiously, shall appear blue by the excess +of those rays in its reflected light; and the like of other +bodies. And that this is the entire and adequate cause of their +colors is manifest, because they have no power to change or alter +the colors of any sort of rays incident apart, but put on all +colors indifferently with which they are enlightened."[2] + +This epoch-making paper aroused a storm of opposition. Some of +Newton's opponents criticised his methods, others even doubted +the truth of his experiments. There was one slight mistake in +Newton's belief that all prisms would give a spectrum of exactly +the same length, and it was some time before he corrected this +error. Meanwhile he patiently met and answered the arguments of +his opponents until he began to feel that patience was no longer +a virtue. At one time he even went so far as to declare that, +once he was "free of this business," he would renounce scientific +research forever, at least in a public way. Fortunately for the +world, however, he did not adhere to this determination, but went +on to even greater discoveries--which, it may be added, involved +still greater controversies. + +In commenting on Newton's discovery of the composition of light, +Voltaire said: "Sir Isaac Newton has demonstrated to the eye, by +the bare assistance of a prism, that light is a composition of +colored rays, which, being united, form white color. A single ray +is by him divided into seven, which all fall upon a piece of +linen or a sheet of white paper, in their order one above the +other, and at equal distances. The first is red, the second +orange, the third yellow, the fourth green, the fifth blue, the +sixth indigo, the seventh a violet purple. Each of these rays +transmitted afterwards by a hundred other prisms will never +change the color it bears; in like manner as gold, when +completely purged from its dross, will never change afterwards in +the crucible."[3] + + + +XII. NEWTON AND THE LAW OF GRAVITATION + +We come now to the story of what is by common consent the +greatest of scientific achievements. The law of universal +gravitation is the most far-reaching principle as yet discovered. +It has application equally to the minutest particle of matter and +to the most distant suns in the universe, yet it is amazing in +its very simplicity. As usually phrased, the law is this: That +every particle of matter in the universe attracts every other +particle with a force that varies directly with the mass of the +particles and inversely as the squares of their mutual distance. +Newton did not vault at once to the full expression of this law, +though he had formulated it fully before he gave the results of +his investigations to the world. We have now to follow the steps +by which he reached this culminating achievement. + +At the very beginning we must understand that the idea of +universal gravitation was not absolutely original with Newton. +Away back in the old Greek days, as we have seen, Anaxagoras +conceived and clearly expressed the idea that the force which +holds the heavenly bodies in their orbits may be the same that +operates upon substances at the surface of the earth. With +Anaxagoras this was scarcely more than a guess. After his day the +idea seems not to have been expressed by any one until the +seventeenth century's awakening of science. Then the +consideration of Kepler's Third Law of planetary motion suggested +to many minds perhaps independently the probability that the +force hitherto mentioned merely as centripetal, through the +operation of which the planets are held in their orbits is a +force varying inversely as the square of the distance from the +sun. This idea had come to Robert Hooke, to Wren, and perhaps to +Halley, as well as to Newton; but as yet no one had conceived a +method by which the validity of the suggestion might be tested. +It was claimed later on by Hooke that he had discovered a method +demonstrating the truth of the theory of inverse squares, and +after the full announcement of Newton's discovery a heated +controversy was precipitated in which Hooke put forward his +claims with accustomed acrimony. Hooke, however, never produced +his demonstration, and it may well be doubted whether he had +found a method which did more than vaguely suggest the law which +the observations of Kepler had partially revealed. Newton's great +merit lay not so much in conceiving the law of inverse squares as +in the demonstration of the law. He was led to this demonstration +through considering the orbital motion of the moon. According to +the familiar story, which has become one of the classic myths of +science, Newton was led to take up the problem through observing +the fall of an apple. Voltaire is responsible for the story, +which serves as well as another; its truth or falsity need not in +the least concern us. Suffice it that through pondering on the +familiar fact of terrestrial gravitation, Newton was led to +question whether this force which operates so tangibly here at +the earth's surface may not extend its influence out into the +depths of space, so as to include, for example, the moon. +Obviously some force pulls the moon constantly towards the earth; +otherwise that body would fly off at a tangent and never return. +May not this so-called centripetal force be identical with +terrestrial gravitation? Such was Newton's query. Probably many +another man since Anaxagoras had asked the same question, but +assuredly Newton was the first man to find an answer. + +The thought that suggested itself to Newton's mind was this: If +we make a diagram illustrating the orbital course of the moon for +any given period, say one minute, we shall find that the course +of the moon departs from a straight line during that period by a +measurable distance--that: is to say, the moon has been virtually +pulled towards the earth by an amount that is represented by the +difference between its actual position at the end of the minute +under observation and the position it would occupy had its course +been tangential, as, according to the first law of motion, it +must have been had not some force deflected it towards the earth. +Measuring the deflection in question--which is equivalent to the +so-called versed sine of the arc traversed--we have a basis for +determining the strength of the deflecting force. Newton +constructed such a diagram, and, measuring the amount of the +moon's departure from a tangential rectilinear course in one +minute, determined this to be, by his calculation, thirteen feet. +Obviously, then, the force acting upon the moon is one that would +cause that body to fall towards the earth to the distance of +thirteen feet in the first minute of its fall. Would such be the +force of gravitation acting at the distance of the moon if the +power of gravitation varies inversely as the square of the +distance? That was the tangible form in which the problem +presented itself to Newton. The mathematical solution of the +problem was simple enough. It is based on a comparison of the +moon's distance with the length of the earth's radius. On making +this calculation, Newton found that the pull of gravitation--if +that were really the force that controls the moon--gives that +body a fall of slightly over fifteen feet in the first minute, +instead of thirteen feet. Here was surely a suggestive +approximation, yet, on the other band, the discrepancy seemed to +be too great to warrant him in the supposition that he had found +the true solution. He therefore dismissed the matter from his +mind for the time being, nor did he return to it definitely for +some years. + +{illustration caption = DIAGRAM TO ILLUSTRATE NEWTON'S LAW OF +GRAVITATION (E represents the earth and A the moon. Were the +earth's pull on the moon to cease, the moon's inertia would cause +it to take the tangential course, AB. On the other hand, were the +moon's motion to be stopped for an instant, the moon would fall +directly towards the earth, along the line AD. The moon's actual +orbit, resulting from these component forces, is AC. Let AC +represent the actual flight of the moon in one minute. Then BC, +which is obviously equal to AD, represents the distance which the +moon virtually falls towards the earth in one minute. Actual +computation, based on measurements of the moon's orbit, showed +this distance to be about fifteen feet. Another computation +showed that this is the distance that the moon would fall towards +the earth under the influence of gravity, on the supposition that +the force of gravity decreases inversely with the square of the +distance; the basis of comparison being furnished by falling +bodies at the surface of the earth. Theory and observations thus +coinciding, Newton was justified in declaring that the force that +pulls the moon towards the earth and keeps it in its orbit, is +the familiar force of gravity, and that this varies inversely as +the square of the distance.)} + +It was to appear in due time that Newton's hypothesis was +perfectly valid and that his method of attempted demonstration +was equally so. The difficulty was that the earth's proper +dimensions were not at that time known. A wrong estimate of the +earth's size vitiated all the other calculations involved, since +the measurement of the moon's distance depends upon the +observation of the parallax, which cannot lead to a correct +computation unless the length of the earth's radius is accurately +known. Newton's first calculation was made as early as 1666, and +it was not until 1682 that his attention was called to a new and +apparently accurate measurement of a degree of the earth's +meridian made by the French astronomer Picard. The new +measurement made a degree of the earth's surface 69.10 miles, +instead of sixty miles. + +Learning of this materially altered calculation as to the earth's +size, Newton was led to take up again his problem of the falling +moon. As he proceeded with his computation, it became more and +more certain that this time the result was to harmonize with the +observed facts. As the story goes, he was so completely +overwhelmed with emotion that he was forced to ask a friend to +complete the simple calculation. That story may well be true, +for, simple though the computation was, its result was perhaps +the most wonderful demonstration hitherto achieved in the entire +field of science. Now at last it was known that the force of +gravitation operates at the distance of the moon, and holds that +body in its elliptical orbit, and it required but a slight effort +of the imagination to assume that the force which operates +through such a reach of space extends its influence yet more +widely. That such is really the case was demonstrated presently +through calculations as to the moons of Jupiter and by similar +computations regarding the orbital motions of the various +planets. All results harmonizing, Newton was justified in +reaching the conclusion that gravitation is a universal property +of matter. It remained, as we shall see, for nineteenth-century +scientists to prove that the same force actually operates upon +the stars, though it should be added that this demonstration +merely fortified a belief that had already found full acceptance. + +Having thus epitomized Newton's discovery, we must now take up +the steps of his progress somewhat in detail, and state his +theories and their demonstration in his own words. Proposition +IV., theorem 4, of his Principia is as follows: + +"That the moon gravitates towards the earth and by the force of +gravity is continually drawn off from a rectilinear motion and +retained in its orbit. + +"The mean distance of the moon from the earth, in the syzygies in +semi-diameters of the earth, is, according to Ptolemy and most +astronomers, 59; according to Vendelin and Huygens, 60; to +Copernicus, 60 1/3; to Street, 60 2/3; and to Tycho, 56 1/2. But +Tycho, and all that follow his tables of refractions, making the +refractions of the sun and moon (altogether against the nature of +light) to exceed the refractions of the fixed stars, and that by +four or five minutes NEAR THE HORIZON, did thereby increase the +moon's HORIZONTAL parallax by a like number of minutes, that is, +by a twelfth or fifteenth part of the whole parallax. Correct +this error and the distance will become about 60 1/2 +semi-diameters of the earth, near to what others have assigned. +Let us assume the mean distance of 60 diameters in the syzygies; +and suppose one revolution of the moon, in respect to the fixed +stars, to be completed in 27d. 7h. 43', as astronomers have +determined; and the circumference of the earth to amount to +123,249,600 Paris feet, as the French have found by mensuration. +And now, if we imagine the moon, deprived of all motion, to be +let go, so as to descend towards the earth with the impulse of +all that force by which (by Cor. Prop. iii.) it is retained in +its orb, it will in the space of one minute of time describe in +its fall 15 1/12 Paris feet. For the versed sine of that arc +which the moon, in the space of one minute of time, would by its +mean motion describe at the distance of sixty semi-diameters of +the earth, is nearly 15 1/12 Paris feet, or more accurately 15 +feet, 1 inch, 1 line 4/9. Wherefore, since that force, in +approaching the earth, increases in the reciprocal-duplicate +proportion of the distance, and upon that account, at the surface +of the earth, is 60 x 60 times greater than at the moon, a body +in our regions, falling with that force, ought in the space of +one minute of time to describe 60 x 60 x 15 1/12 Paris feet; and +in the space of one second of time, to describe 15 1/12 of those +feet, or more accurately, 15 feet, 1 inch, 1 line 4/9. And with +this very force we actually find that bodies here upon earth do +really descend; for a pendulum oscillating seconds in the +latitude of Paris will be 3 Paris feet, and 8 lines 1/2 in +length, as Mr. Huygens has observed. And the space which a heavy +body describes by falling in one second of time is to half the +length of the pendulum in the duplicate ratio of the +circumference of a circle to its diameter (as Mr. Huygens has +also shown), and is therefore 15 Paris feet, 1 inch, 1 line 4/9. +And therefore the force by which the moon is retained in its +orbit is that very same force which we commonly call gravity; +for, were gravity another force different from that, then bodies +descending to the earth with the joint impulse of both forces +would fall with a double velocity, and in the space of one second +of time would describe 30 1/6 Paris feet; altogether against +experience."[1] + +All this is beautifully clear, and its validity has never in +recent generations been called in question; yet it should be +explained that the argument does not amount to an actually +indisputable demonstration. It is at least possible that the +coincidence between the observed and computed motion of the moon +may be a mere coincidence and nothing more. This probability, +however, is so remote that Newton is fully justified in +disregarding it, and, as has been said, all subsequent +generations have accepted the computation as demonstrative. + +Let us produce now Newton's further computations as to the other +planetary bodies, passing on to his final conclusion that gravity +is a universal force. + + "PROPOSITION V., THEOREM V. + +"That the circumjovial planets gravitate towards Jupiter; the +circumsaturnal towards Saturn; the circumsolar towards the sun; +and by the forces of their gravity are drawn off from rectilinear +motions, and retained in curvilinear orbits. + + +"For the revolutions of the circumjovial planets about Jupiter, +of the circumsaturnal about Saturn, and of Mercury and Venus and +the other circumsolar planets about the sun, are appearances of +the same sort with the revolution of the moon about the earth; +and therefore, by Rule ii., must be owing to the same sort of +causes; especially since it has been demonstrated that the forces +upon which those revolutions depend tend to the centres of +Jupiter, of Saturn, and of the sun; and that those forces, in +receding from Jupiter, from Saturn, and from the sun, decrease in +the same proportion, and according to the same law, as the force +of gravity does in receding from the earth. + +"COR. 1.--There is, therefore, a power of gravity tending to all +the planets; for doubtless Venus, Mercury, and the rest are +bodies of the same sort with Jupiter and Saturn. And since all +attraction (by Law iii.) is mutual, Jupiter will therefore +gravitate towards all his own satellites, Saturn towards his, the +earth towards the moon, and the sun towards all the primary +planets. + +"COR. 2.--The force of gravity which tends to any one planet is +reciprocally as the square of the distance of places from the +planet's centre. + +"COR. 3.--All the planets do mutually gravitate towards one +another, by Cor. 1 and 2, and hence it is that Jupiter and +Saturn, when near their conjunction, by their mutual attractions +sensibly disturb each other's motions. So the sun disturbs the +motions of the moon; and both sun and moon disturb our sea, as we +shall hereafter explain. + + "SCHOLIUM + +"The force which retains the celestial bodies in their orbits has +been hitherto called centripetal force; but it being now made +plain that it can be no other than a gravitating force, we shall +hereafter call it gravity. For the cause of the centripetal force +which retains the moon in its orbit will extend itself to all the +planets by Rules i., ii., and iii. + + "PROPOSITION VI., THEOREM VI. + +"That all bodies gravitate towards every planet; and that the +weights of the bodies towards any the same planet, at equal +distances from the centre of the planet, are proportional to the +quantities of matter which they severally contain. + + +"It has been now a long time observed by others that all sorts of +heavy bodies (allowance being made for the inability of +retardation which they suffer from a small power of resistance in +the air) descend to the earth FROM EQUAL HEIGHTS in equal times; +and that equality of times we may distinguish to a great accuracy +by help of pendulums. I tried the thing in gold, silver, lead, +glass, sand, common salt, wood, water, and wheat. I provided two +wooden boxes, round and equal: I filled the one with wood, and +suspended an equal weight of gold (as exactly as I could) in the +centre of oscillation of the other. The boxes hanging by eleven +feet, made a couple of pendulums exactly equal in weight and +figure, and equally receiving the resistance of the air. And, +placing the one by the other, I observed them to play together +forward and backward, for a long time, with equal vibrations. And +therefore the quantity of matter in gold was to the quantity of +matter in the wood as the action of the motive force (or vis +motrix) upon all the gold to the action of the same upon all the +wood--that is, as the weight of the one to the weight of the +other: and the like happened in the other bodies. By these +experiments, in bodies of the same weight, I could manifestly +have discovered a difference of matter less than the thousandth +part of the whole, had any such been. But, without all doubt, the +nature of gravity towards the planets is the same as towards the +earth. For, should we imagine our terrestrial bodies removed to +the orb of the moon, and there, together with the moon, deprived +of all motion, to be let go, so as to fall together towards the +earth, it is certain, from what we have demonstrated before, +that, in equal times, they would describe equal spaces with the +moon, and of consequence are to the moon, in quantity and matter, +as their weights to its weight. + +"Moreover, since the satellites of Jupiter perform their +revolutions in times which observe the sesquiplicate proportion +of their distances from Jupiter's centre, their accelerative +gravities towards Jupiter will be reciprocally as the square of +their distances from Jupiter's centre--that is, equal, at equal +distances. And, therefore, these satellites, if supposed to fall +TOWARDS JUPITER from equal heights, would describe equal spaces +in equal times, in like manner as heavy bodies do on our earth. +And, by the same argument, if the circumsolar planets were +supposed to be let fall at equal distances from the sun, they +would, in their descent towards the sun, describe equal spaces in +equal times. But forces which equally accelerate unequal bodies +must be as those bodies--that is to say, the weights of the +planets (TOWARDS THE SUN must be as their quantities of matter. +Further, that the weights of Jupiter and his satellites towards +the sun are proportional to the several quantities of their +matter, appears from the exceedingly regular motions of the +satellites. For if some of these bodies were more strongly +attracted to the sun in proportion to their quantity of matter +than others, the motions of the satellites would be disturbed by +that inequality of attraction. If at equal distances from the sun +any satellite, in proportion to the quantity of its matter, did +gravitate towards the sun with a force greater than Jupiter in +proportion to his, according to any given proportion, suppose d +to e; then the distance between the centres of the sun and of the +satellite's orbit would be always greater than the distance +between the centres of the sun and of Jupiter nearly in the +subduplicate of that proportion: as by some computations I have +found. And if the satellite did gravitate towards the sun with a +force, lesser in the proportion of e to d, the distance of the +centre of the satellite's orb from the sun would be less than the +distance of the centre of Jupiter from the sun in the +subduplicate of the same proportion. Therefore, if at equal +distances from the sun, the accelerative gravity of any satellite +towards the sun were greater or less than the accelerative +gravity of Jupiter towards the sun by one-one-thousandth part of +the whole gravity, the distance of the centre of the satellite's +orbit from the sun would be greater or less than the distance of +Jupiter from the sun by one one-two-thousandth part of the whole +distance--that is, by a fifth part of the distance of the utmost +satellite from the centre of Jupiter; an eccentricity of the +orbit which would be very sensible. But the orbits of the +satellites are concentric to Jupiter, and therefore the +accelerative gravities of Jupiter and of all its satellites +towards the sun, at equal distances from the sun, are as their +several quantities of matter; and the weights of the moon and of +the earth towards the sun are either none, or accurately +proportional to the masses of matter which they contain. + +"COR. 5.--The power of gravity is of a different nature from the +power of magnetism; for the magnetic attraction is not as the +matter attracted. Some bodies are attracted more by the magnet; +others less; most bodies not at all. The power of magnetism in +one and the same body may be increased and diminished; and is +sometimes far stronger, for the quantity of matter, than the +power of gravity; and in receding from the magnet decreases not +in the duplicate, but almost in the triplicate proportion of the +distance, as nearly as I could judge from some rude observations. + + + "PROPOSITION VII., THEOREM VII. + +"That there is a power of gravity tending to all bodies, +proportional to the several quantities of matter which they +contain. + + +That all the planets mutually gravitate one towards another we +have proved before; as well as that the force of gravity towards +every one of them considered apart, is reciprocally as the square +of the distance of places from the centre of the planet. And +thence it follows, that the gravity tending towards all the +planets is proportional to the matter which they contain. + +"Moreover, since all the parts of any planet A gravitates towards +any other planet B; and the gravity of every part is to the +gravity of the whole as the matter of the part is to the matter +of the whole; and to every action corresponds a reaction; +therefore the planet B will, on the other hand, gravitate towards +all the parts of planet A, and its gravity towards any one part +will be to the gravity towards the whole as the matter of the +part to the matter of the whole. Q.E.D. + + +"HENCE IT WOULD APPEAR THAT the force of the whole must arise +from the force of the component parts." + + +Newton closes this remarkable Book iii. with the following words: + +"Hitherto we have explained the phenomena of the heavens and of +our sea by the power of gravity, but have not yet assigned the +cause of this power. This is certain, that it must proceed from a +cause that penetrates to the very centre of the sun and planets, +without suffering the least diminution of its force; that +operates not according to the quantity of the surfaces of the +particles upon which it acts (as mechanical causes used to do), +but according to the quantity of solid matter which they contain, +and propagates its virtue on all sides to immense distances, +decreasing always in the duplicate proportions of the distances. +Gravitation towards the sun is made up out of the gravitations +towards the several particles of which the body of the sun is +composed; and in receding from the sun decreases accurately in +the duplicate proportion of the distances as far as the orb of +Saturn, as evidently appears from the quiescence of the aphelions +of the planets; nay, and even to the remotest aphelions of the +comets, if those aphelions are also quiescent. But hitherto I +have not been able to discover the cause of those properties of +gravity from phenomena, and I frame no hypothesis; for whatever +is not deduced from the phenomena is to be called an hypothesis; +and hypotheses, whether metaphysical or physical, whether of +occult qualities or mechanical, have no place in experimental +philosophy. . . . And to us it is enough that gravity does really +exist, and act according to the laws which we have explained, and +abundantly serves to account for all the motions of the celestial +bodies and of our sea."[2] + + +The very magnitude of the importance of the theory of universal +gravitation made its general acceptance a matter of considerable +time after the actual discovery. This opposition had of course +been foreseen by Newton, and, much as be dreaded controversy, he +was prepared to face it and combat it to the bitter end. He knew +that his theory was right; it remained for him to convince the +world of its truth. He knew that some of his contemporary +philosophers would accept it at once; others would at first +doubt, question, and dispute, but finally accept; while still +others would doubt and dispute until the end of their days. This +had been the history of other great discoveries; and this will +probably be the history of most great discoveries for all time. +But in this case the discoverer lived to see his theory accepted +by practically all the great minds of his time. + +Delambre is authority for the following estimate of Newton by +Lagrange. "The celebrated Lagrange," he says, "who frequently +asserted that Newton was the greatest genius that ever existed, +used to add--'and the most fortunate, for we cannot find MORE +THAN ONCE a system of the world to establish.' " With pardonable +exaggeration the admiring followers of the great generalizer +pronounced this epitaph: + + "Nature and Nature's laws lay hid in night; + God said `Let Newton be!' and all was light." + + + +XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON + +During the Newtonian epoch there were numerous important +inventions of scientific instruments, as well as many +improvements made upon the older ones. Some of these discoveries +have been referred to briefly in other places, but their +importance in promoting scientific investigation warrants a +fuller treatment of some of the more significant. + +Many of the errors that had arisen in various scientific +calculations before the seventeenth century may be ascribed to +the crudeness and inaccuracy in the construction of most +scientific instruments. Scientists had not as yet learned that an +approach to absolute accuracy was necessary in every +investigation in the field of science, and that such accuracy +must be extended to the construction of the instruments used in +these investigations and observations. In astronomy it is obvious +that instruments of delicate exactness are most essential; yet +Tycho Brahe, who lived in the sixteenth century, is credited with +being the first astronomer whose instruments show extreme care in +construction. + +It seems practically settled that the first telescope was +invented in Holland in 1608; but three men, Hans Lippershey, +James Metius, and Zacharias Jansen, have been given the credit of +the invention at different times. It would seem from certain +papers, now in the library of the University of Leyden, and +included in Huygens's papers, that Lippershey was probably the +first to invent a telescope and to describe his invention. The +story is told that Lippershey, who was a spectacle-maker, +stumbled by accident upon the discovery that when two lenses are +held at a certain distance apart, objects at a distance appear +nearer and larger. Having made this discovery, be fitted two +lenses with a tube so as to maintain them at the proper distance, +and thus constructed the first telescope. + +It was Galileo, however, as referred to in a preceding chapter, +who first constructed a telescope based on his knowledge of the +laws of refraction. In 1609, having heard that an instrument had +been invented, consisting of two lenses fixed in a tube, whereby +objects were made to appear larger and nearer, he set about +constructing such an instrument that should follow out the known +effects of refraction. His first telescope, made of two lenses +fixed in a lead pipe, was soon followed by others of improved +types, Galileo devoting much time and labor to perfecting lenses +and correcting errors. In fact, his work in developing the +instrument was so important that the telescope came gradually to +be known as the "Galilean telescope." + +In the construction of his telescope Galileo made use of a convex +and a concave lens; but shortly after this Kepler invented an +instrument in which both the lenses used were convex. This +telescope gave a much larger field of view than the Galilean +telescope, but did not give as clear an image, and in consequence +did not come into general use until the middle of the seventeenth +century. The first powerful telescope of this type was made by +Huygens and his brother. It was of twelve feet focal length, and +enabled Huygens to discover a new satellite of Saturn, and to +determine also the true explanation of Saturn's ring. + +It was Huygens, together with Malvasia and Auzout, who first +applied the micrometer to the telescope, although the inventor of +the first micrometer was William Gascoigne, of Yorkshire, about +1636. The micrometer as used in telescopes enables the observer +to measure accurately small angular distances. Before the +invention of the telescope such measurements were limited to the +angle that could be distinguished by the naked eye, and were, of +course, only approximately accurate. Even very careful observers, +such as Tycho Brahe, were able to obtain only fairly accurate +results. But by applying Gascoigne's invention to the telescope +almost absolute accuracy became at once possible. The principle +of Gascoigne's micrometer was that of two pointers lying +parallel, and in this position pointing to zero. These were +arranged so that the turning of a single screw separated or +approximated them at will, and the angle thus formed could be +determined with absolute accuracy. + +Huygens's micrometer was a slip of metal of variable breadth +inserted at the focus of the telescope. By observing at what +point this exactly covered an object under examination, and +knowing the focal length of the telescope and the width of the +metal, he could then deduce the apparent angular breadth of the +object. Huygens discovered also that an object placed in the +common focus of the two lenses of a Kepler telescope appears +distinct and clearly defined. The micrometers of Malvasia, and +later of Auzout and Picard, are the development of this +discovery. Malvasia's micrometer, which he described in 1662, +consisted of fine silver wires placed at right-angles at the +focus of his telescope. + +As telescopes increased in power, however, it was found that even +the finest wire, or silk filaments, were much too thick for +astronomical observations, as they obliterated the image, and so, +finally, the spider-web came into use and is still used in +micrometers and other similar instruments. Before that time, +however, the fine crossed wires had revolutionized astronomical +observations. "We may judge how great was the improvement which +these contrivances introduced into the art of observing," says +Whewell, "by finding that Hevelius refused to adopt them because +they would make all the old observations of no value. He had +spent a laborious and active life in the exercise of the old +methods, and could not bear to think that all the treasures which +he had accumulated had lost their worth by the discovery of a new +mine of richer ones."[1] + +Until the time of Newton, all the telescopes in use were either +of the Galilean or Keplerian type, that is, refractors. But about +the year 1670 Newton constructed his first reflecting telescope, +which was greatly superior to, although much smaller than, the +telescopes then in use. He was led to this invention by his +experiments with light and colors. In 1671 he presented to the +Royal Society a second and somewhat larger telescope, which he +had made; and this type of instrument was little improved upon +until the introduction of the achromatic telescope, invented by +Chester Moor Hall in 1733. + +As is generally known, the element of accurate measurements of +time plays an important part in the measurements of the movements +of the heavenly bodies. In fact, one was scarcely possible +without the other, and as it happened it was the same man, +Huygens, who perfected Kepler's telescope and invented the +pendulum clock. The general idea had been suggested by Galileo; +or, better perhaps, the equal time occupied by the successive +oscillations of the pendulum had been noted by him. He had not +been able, however, to put this discovery to practical account. +But in 1656 Huygens invented the necessary machinery for +maintaining the motion of the pendulum and perfected several +accurate clocks. These clocks were of invaluable assistance to +the astronomers, affording as they did a means of keeping time +"more accurate than the sun itself." When Picard had corrected +the variation caused by heat and cold acting upon the pendulum +rod by combining metals of different degrees of expansibility, a +high degree of accuracy was possible. + +But while the pendulum clock was an unequalled stationary +time-piece, it was useless in such unstable situations as, for +example, on shipboard. But here again Huygens played a prominent +part by first applying the coiled balance-spring for regulating +watches and marine clocks. The idea of applying a spring to the +balance-wheel was not original with Huygens, however, as it had +been first conceived by Robert Hooke; but Huygens's application +made practical Hooke's idea. In England the importance of +securing accurate watches or marine clocks was so fully +appreciated that a reward of L20,000 sterling was offered by +Parliament as a stimulus to the inventor of such a time-piece. +The immediate incentive for this offer was the obvious fact that +with such an instrument the determination of the longitude of +places would be much simplified. Encouraged by these offers, a +certain carpenter named Harrison turned his attention to the +subject of watch-making, and, after many years of labor, in 1758 +produced a spring time-keeper which, during a sea-voyage +occupying one hundred and sixty-one days, varied only one minute +and five seconds. This gained for Harrison a reward Of L5000 +sterling at once, and a little later L10,000 more, from +Parliament. + +While inventors were busy with the problem of accurate +chronometers, however, another instrument for taking longitude at +sea had been invented. This was the reflecting quadrant, or +sextant, as the improved instrument is now called, invented by +John Hadley in 1731, and independently by Thomas Godfrey, a poor +glazier of Philadelphia, in 1730. Godfrey's invention, which was +constructed on the same principle as that of the Hadley +instrument, was not generally recognized until two years after +Hadley's discovery, although the instrument was finished and +actually in use on a sea-voyage some months before Hadley +reported his invention. The principle of the sextant, however, +seems to have been known to Newton, who constructed an instrument +not very unlike that of Hadley; but this invention was lost sight +of until several years after the philosopher's death and some +time after Hadley's invention. + +The introduction of the sextant greatly simplified taking +reckonings at sea as well as facilitating taking the correct +longitude of distant places. Before that time the mariner was +obliged to depend upon his compass, a cross-staff, or an +astrolabe, a table of the sun's declination and a correction for +the altitude of the polestar, and very inadequate and incorrect +charts. Such were the instruments used by Columbus and Vasco da +Gama and their immediate successors. + +During the Newtonian period the microscopes generally in use were +those constructed of simple lenses, for although compound +microscopes were known, the difficulties of correcting aberration +had not been surmounted, and a much clearer field was given by +the simple instrument. The results obtained by the use of such +instruments, however, were very satisfactory in many ways. By +referring to certain plates in this volume, which reproduce +illustrations from Robert Hooke's work on the microscope, it will +be seen that quite a high degree of effectiveness had been +attained. And it should be recalled that Antony von Leeuwenboek, +whose death took place shortly before Newton's, had discovered +such micro-organisms as bacteria, had seen the blood corpuscles +in circulation, and examined and described other microscopic +structures of the body. + + + +XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO +FRANKLIN + +We have seen how Gilbert, by his experiments with magnets, gave +an impetus to the study of magnetism and electricity. Gilbert +himself demonstrated some facts and advanced some theories, but +the system of general laws was to come later. To this end the +discovery of electrical repulsion, as well as attraction, by Von +Guericke, with his sulphur ball, was a step forward; but +something like a century passed after Gilbert's beginning before +anything of much importance was done in the field of electricity. + +In 1705, however, Francis Hauksbee began a series of experiments +that resulted in some startling demonstrations. For many years it +had been observed that a peculiar light was seen sometimes in the +mercurial barometer, but Hauksbee and the other scientific +investigators supposed the radiance to be due to the mercury in a +vacuum, brought about, perhaps, by some agitation. That this +light might have any connection with electricity did not, at +first, occur to Hauksbee any more than it had to his +predecessors. The problem that interested him was whether the +vacuum in the tube of the barometer was essential to the light; +and in experimenting to determine this, he invented his +"mercurial fountain." Having exhausted the air in a receiver +containing some mercury, he found that by allowing air to rush +through the mercury the metal became a jet thrown in all +directions against the sides of the vessel, making a great, +flaming shower, "like flashes of lightning," as he said. But it +seemed to him that there was a difference between this light and +the glow noted in the barometer. This was a bright light, whereas +the barometer light was only a glow. Pondering over this, +Hauksbee tried various experiments, revolving pieces of amber, +flint, steel, and other substances in his exhausted air-pump +receiver, with negative, or unsatisfactory, results. Finally, it +occurred to him to revolve an exhausted glass tube itself. +Mounting such a globe of glass on an axis so that it could be +revolved rapidly by a belt running on a large wheel, he found +that by holding his fingers against the whirling globe a purplish +glow appeared, giving sufficient light so that coarse print could +be read, and the walls of a dark room sensibly lightened several +feet away. As air was admitted to the globe the light gradually +diminished, and it seemed to him that this diminished glow was +very similar in appearance to the pale light seen in the +mercurial barometer. Could it be that it was the glass, and not +the mercury, that caused it? Going to a barometer he proceeded to +rub the glass above the column of mercury over the vacuum, +without disturbing the mercury, when, to his astonishment, the +same faint light, to all appearances identical with the glow seen +in the whirling globe, was produced. + +Turning these demonstrations over in his mind, he recalled the +well-known fact that rubbed glass attracted bits of paper, +leaf-brass, and other light substances, and that this phenomenon +was supposed to be electrical. This led him finally to determine +the hitherto unsuspected fact, that the glow in the barometer was +electrical as was also the glow seen in his whirling globe. +Continuing his investigations, he soon discovered that solid +glass rods when rubbed produced the same effects as the tube. By +mere chance, happening to hold a rubbed tube to his cheek, he +felt the effect of electricity upon the skin like "a number of +fine, limber hairs," and this suggested to him that, since the +mysterious manifestation was so plain, it could be made to show +its effects upon various substances. Suspending some woollen +threads over the whirling glass cylinder, he found that as soon +as he touched the glass with his hands the threads, which were +waved about by the wind of the revolution, suddenly straightened +themselves in a peculiar manner, and stood in a radical position, +pointing to the axis of the cylinder. + +Encouraged by these successes, he continued his experiments with +breathless expectancy, and soon made another important discovery, +that of "induction," although the real significance of this +discovery was not appreciated by him or, for that matter, by any +one else for several generations following. This discovery was +made by placing two revolving cylinders within an inch of each +other, one with the air exhausted and the other unexhausted. +Placing his hand on the unexhausted tube caused the light to +appear not only upon it, but on the other tube as well. A little +later he discovered that it is not necessary to whirl the +exhausted tube to produce this effect, but simply to place it in +close proximity to the other whirling cylinder. + +These demonstrations of Hauksbee attracted wide attention and +gave an impetus to investigators in the field of electricity; but +still no great advance was made for something like a quarter of a +century. Possibly the energies of the scientists were exhausted +for the moment in exploring the new fields thrown open to +investigation by the colossal work of Newton. + + +THE EXPERIMENTS OF STEPHEN GRAY + +In 1729 Stephen Gray (died in 1736), an eccentric and irascible +old pensioner of the Charter House in London, undertook some +investigations along lines similar to those of Hauksbee. While +experimenting with a glass tube for producing electricity, as +Hauksbee had done, he noticed that the corks with which he had +stopped the ends of the tube to exclude the dust, seemed to +attract bits of paper and leaf-brass as well as the glass itself. +He surmised at once that this mysterious electricity, or +"virtue," as it was called, might be transmitted through other +substances as it seemed to be through glass. + +"Having by me an ivory ball of about one and three-tenths of an +inch in diameter," he writes, "with a hole through it, this I +fixed upon a fir-stick about four inches long, thrusting the +other end into the cork, and upon rubbing the tube found that the +ball attracted and repelled the feather with more vigor than the +cork had done, repeating its attractions and repulsions for many +times together. I then fixed the ball on longer sticks, first +upon one of eight inches, and afterwards upon one of twenty-four +inches long, and found the effect the same. Then I made use of +iron, and then brass wire, to fix the ball on, inserting the +other end of the wire in the cork, as before, and found that the +attraction was the same as when the fir-sticks were made use of, +and that when the feather was held over against any part of the +wire it was attracted by it; but though it was then nearer the +tube, yet its attraction was not so strong as that of the ball. +When the wire of two or three feet long was used, its vibrations, +caused by the rubbing of the tube, made it somewhat troublesome +to be managed. This put me to thinking whether, if the ball was +hung by a pack-thread and suspended by a loop on the tube, the +electricity would not be carried down the line to the ball; I +found it to succeed accordingly; for upon suspending the ball on +the tube by a pack-thread about three feet long, when the tube +had been excited by rubbing, the ivory ball attracted and +repelled the leaf-brass over which it was held as freely as it +had done when it was suspended on sticks or wire, as did also a +ball of cork, and another of lead that weighed one pound and a +quarter." + +Gray next attempted to determine what other bodies would attract +the bits of paper, and for this purpose he tried coins, pieces of +metal, and even a tea-kettle, "both empty and filled with hot or +cold water"; but he found that the attractive power appeared to +be the same regardless of the substance used. + +"I next proceeded," he continues, "to try at what greater +distances the electric virtues might be carried, and having by me +a hollow walking-cane, which I suppose was part of a fishing-rod, +two feet seven inches long, I cut the great end of it to fit into +the bore of the tube, into which it went about five inches; then +when the cane was put into the end of the tube, and this excited, +the cane drew the leaf-brass to the height of more than two +inches, as did also the ivory ball, when by a cork and stick it +had been fixed to the end of the cane.... With several pieces of +Spanish cane and fir-sticks I afterwards made a rod, which, +together with the tube, was somewhat more than eighteen feet +long, which was the greatest length I could conveniently use in +my chamber, and found the attraction very nearly, if not +altogether, as strong as when the ball was placed on the shorter +rods." + +This experiment exhausted the capacity of his small room, but on +going to the country a little later he was able to continue his +experiments. "To a pole of eighteen feet there was tied a line of +thirty-four feet in length, so that the pole and line together +were fifty-two feet. With the pole and tube I stood in the +balcony, the assistant below in the court, where he held the +board with the leaf-brass on it. Then the tube being excited, as +usual, the electric virtue passed from the tube up the pole and +down the line to the ivory ball, which attracted the leaf-brass, +and as the ball passed over it in its vibrations the leaf-brass +would follow it till it was carried off the board." + +Gray next attempted to send the electricity over a line suspended +horizontally. To do this he suspended the pack-thread by pieces +of string looped over nails driven into beams for that purpose. +But when thus suspended he found that the ivory ball no longer +excited the leaf-brass, and he guessed correctly that the +explanation of this lay in the fact that "when the electric +virtue came to the loop that was suspended on the beam it went up +the same to the beam," none of it reaching the ball. As we shall +see from what follows, however, Gray had not as yet determined +that certain substances will conduct electricity while others +will not. But by a lucky accident he made the discovery that +silk, for example, was a poor conductor, and could be turned to +account in insulating the conducting-cord. + +A certain Mr. Wheler had become much interested in the old +pensioner and his work, and, as a guest at the Wheler house, Gray +had been repeating some of his former experiments with the +fishing-rod, line, and ivory ball. He had finally exhausted the +heights from which these experiments could be made by climbing to +the clock-tower and exciting bits of leaf-brass on the ground +below. + +"As we had no greater heights here," he says, "Mr. Wheler was +desirous to try whether we could not carry the electric virtue +horizontally. I then told him of the attempt I had made with that +design, but without success, telling him the method and materials +made use of, as mentioned above. He then proposed a silk line to +support the line by which the electric virtue was to pass. I told +him it might do better upon account of its smallness; so that +there would be less virtue carried from the line of +communication. + +"The first experiment was made in the matted gallery, July 2, +1729, about ten in the morning. About four feet from the end of +the gallery there was a cross line that was fixed by its ends to +each side of the gallery by two nails; the middle part of the +line was silk, the rest at each end pack-thread; then the line to +which the ivory ball was hung and by which the electric virtue +was to be conveyed to it from the tube, being eighty and one-half +feet in length, was laid on the cross silk line, so that the ball +hung about nine feet below it. Then the other end of the line was +by a loop suspended on the glass cane, and the leaf-brass held +under the ball on a piece of white paper; when, the tube being +rubbed, the ball attracted the leaf-brass, and kept it suspended +on it for some time." + +This experiment succeeded so well that the string was lengthened +until it was some two hundred and ninety-three feet long; and +still the attractive force continued, apparently as strong as +ever. On lengthening the string still more, however, the extra +weight proved too much for the strength of the silk +suspending-thread. "Upon this," says Gray, "having brought with +me both brass and iron wire, instead of the silk we put up small +iron wire; but this was too weak to bear the weight of the line. +We then took brass wire of a somewhat larger size than that of +iron. This supported our line of communication; but though the +tube was well rubbed, yet there was not the least motion or +attraction given by the ball, neither with the great tube, which +we made use of when we found the small solid cane to be +ineffectual; by which we were now convinced that the success we +had before depended upon the lines that supported the line of +communication being silk, and not upon their being small, as +before trial I had imagined it might be; the same effect +happening here as it did when the line that is to convey the +electric virtue is supported by pack-thread." + +Soon after this Gray and his host suspended a pack-thread six +hundred and sixty-six feet long on poles across a field, these +poles being slightly inclined so that the thread could be +suspended from the top by small silk cords, thus securing the +necessary insulation. This pack-thread line, suspended upon poles +along which Gray was able to transmit the electricity, is very +suggestive of the modern telegraph, but the idea of signalling or +making use of it for communicating in any way seems not to have +occurred to any one at that time. Even the successors of Gray who +constructed lines some thousands of feet long made no attempt to +use them for anything but experimental purposes--simply to test +the distances that the current could be sent. Nevertheless, Gray +should probably be credited with the discovery of two of the most +important properties of electricity--that it can be conducted and +insulated, although, as we have seen, Gilbert and Von Guericke +had an inkling of both these properties. + + +EXPERIMENTS OF CISTERNAY DUFAY + +So far England had produced the two foremost workers in +electricity. It was now France's turn to take a hand, and, +through the efforts of Charles Francois de Cisternay Dufay, to +advance the science of electricity very materially. Dufay was a +highly educated savant, who had been soldier and diplomat +betimes, but whose versatility and ability as a scientist is +shown by the fact that he was the only man who had ever +contributed to the annals of the academy investigations in every +one of the six subjects admitted by that institution as worthy of +recognition. Dufay upheld his reputation in this new field of +science, making many discoveries and correcting many mistakes of +former observers. In this work also he proved himself a great +diplomat by remaining on terms of intimate friendship with Dr. +Gray--a thing that few people were able to do. + +Almost his first step was to overthrow the belief that certain +bodies are "electrics" and others "non-electrics"--that is, that +some substances when rubbed show certain peculiarities in +attracting pieces of paper and foil which others do not. Dufay +proved that all bodies possess this quality in a certain degree. + +"I have found that all bodies (metallic, soft, or fluid ones +excepted)," he says, "may be made electric by first heating them +more or less and then rubbing them on any sort of cloth. So that +all kinds of stones, as well precious as common, all kinds of +wood, and, in general, everything that I have made trial of, +became electric by beating and rubbing, except such bodies as +grow soft by beat, as the gums, which dissolve in water, glue, +and such like substances. 'Tis also to be remarked that the +hardest stones or marbles require more chafing or heating than +others, and that the same rule obtains with regard to the woods; +so that box, lignum vitae, and such others must be chafed almost +to the degree of browning, whereas fir, lime-tree, and cork +require but a moderate heat. + +"Having read in one of Mr. Gray's letters that water may be made +electrical by holding the excited glass tube near it (a dish of +water being fixed to a stand and that set on a plate of glass, or +on the brim of a drinking-glass, previously chafed, or otherwise +warmed), I have found, upon trial, that the same thing happened +to all bodies without exception, whether solid or fluid, and that +for that purpose 'twas sufficient to set them on a glass stand +slightly warmed, or only dried, and then by bringing the tube +near them they immediately became electrical. I made this +experiment with ice, with a lighted wood-coal, and with +everything that came into my mind; and I constantly remarked that +such bodies of themselves as were least electrical had the +greatest degree of electricity communicated to them at the +approval of the glass tube." + +His next important discovery was that colors had nothing to do +with the conduction of electricity. "Mr. Gray says, towards the +end of one of his letters," he writes, "that bodies attract more +or less according to their colors. This led me to make several +very singular experiments. I took nine silk ribbons of equal +size, one white, one black, and the other seven of the seven +primitive colors, and having hung them all in order in the same +line, and then bringing the tube near them, the black one was +first attracted, the white one next, and others in order +successively to the red one, which was attracted least, and the +last of them all. I afterwards cut out nine square pieces of +gauze of the same colors with the ribbons, and having put them +one after another on a hoop of wood, with leaf-gold under them, +the leaf-gold was attracted through all the colored pieces of +gauze, but not through the white or black. This inclined me first +to think that colors contribute much to electricity, but three +experiments convinced me to the contrary. The first, that by +warming the pieces of gauze neither the black nor white pieces +obstructed the action of the electrical tube more than those of +the other colors. In like manner, the ribbons being warmed, the +black and white are not more strongly attracted than the rest. +The second is, the gauzes and ribbons being wetted, the ribbons +are all attracted equally, and all the pieces of gauze equally +intercept the action of electric bodies. The third is, that the +colors of a prism being thrown on a white gauze, there appear no +differences of attraction. Whence it proceeds that this +difference proceeds, not from the color, as a color, but from the +substances that are employed in the dyeing. For when I colored +ribbons by rubbing them with charcoal, carmine, and such other +substances, the differences no longer proved the same." + +In connection with his experiments with his thread suspended on +glass poles, Dufay noted that a certain amount of the current is +lost, being given off to the surrounding air. He recommended, +therefore, that the cords experimented with be wrapped with some +non-conductor--that it should be "insulated" ("isolee"), as he +said, first making use of this term. + + +DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY + +It has been shown in an earlier chapter how Von Guericke +discovered that light substances like feathers, after being +attracted to the sulphur-ball electric-machine, were repelled by +it until they touched some object. Von Guericke noted this, but +failed to explain it satisfactorily. Dufay, repeating Von +Guericke's experiments, found that if, while the excited tube or +sulphur ball is driving the repelled feather before it, the ball +be touched or rubbed anew, the feather comes to it again, and is +repelled alternately, as, the hand touches the ball, or is +withdrawn. From this he concluded that electrified bodies first +attract bodies not electrified, "charge" them with electricity, +and then repel them, the body so charged not being attracted +again until it has discharged its electricity by touching +something. + +"On making the experiment related by Otto von Guericke," he says, +"which consists in making a ball of sulphur rendered electrical +to repel a down feather, I perceived that the same effects were +produced not only by the tube, but by all electric bodies +whatsoever, and I discovered that which accounts for a great part +of the irregularities and, if I may use the term, of the caprices +that seem to accompany most of the experiments on electricity. +This principle is that electric bodies attract all that are not +so, and repel them as soon as they are become electric by the +vicinity or contact of the electric body. Thus gold-leaf is first +attracted by the tube, and acquires an electricity by approaching +it, and of consequence is immediately repelled by it. Nor is it +reattracted while it retains its electric quality. But if while +it is thus sustained in the air it chance to light on some other +body, it straightway loses its electricity, and in consequence is +reattracted by the tube, which, after having given it a new +electricity, repels it a second time, which continues as long as +the tube keeps its electricity. Upon applying this principle to +the various experiments of electricity, one will be surprised at +the number of obscure and puzzling facts that it clears up. For +Mr. Hauksbee's famous experiment of the glass globe, in which +silk threads are put, is a necessary consequence of it. When +these threads are arranged in the form of rays by the electricity +of the sides of the globe, if the finger be put near the outside +of the globe the silk threads within fly from it, as is well +known, which happens only because the finger or any other body +applied near the glass globe is thereby rendered electrical, and +consequently repels the silk threads which are endowed with the +same quality. With a little reflection we may in the same manner +account for most of the other phenomena, and which seem +inexplicable without attending to this principle. + +"Chance has thrown in my way another principle, more universal +and remarkable than the preceding one, and which throws a new +light on the subject of electricity. This principle is that there +are two distinct electricities, very different from each other, +one of which I call vitreous electricity and the other resinous +electricity. The first is that of glass, rock-crystal, precious +stones, hair of animals, wool, and many other bodies. The second +is that of amber, copal, gumsack, silk thread, paper, and a +number of other substances. The characteristic of these two +electricities is that a body of the vitreous electricity, for +example, repels all such as are of the same electricity, and on +the contrary attracts all those of the resinous electricity; so +that the tube, made electrical, will repel glass, crystal, hair +of animals, etc., when rendered electric, and will attract silk +thread, paper, etc., though rendered electrical likewise. Amber, +on the contrary, will attract electric glass and other substances +of the same class, and will repel gum-sack, copal, silk thread, +etc. Two silk ribbons rendered electrical will repel each other; +two woollen threads will do the like; but a woollen thread and a +silken thread will mutually attract each other. This principle +very naturally explains why the ends of threads of silk or wool +recede from each other, in the form of pencil or broom, when they +have acquired an electric quality. From this principle one may +with the same ease deduce the explanation of a great number of +other phenomena; and it is probable that this truth will lead us +to the further discovery of many other things. + +"In order to know immediately to which of the two classes of +electrics belongs any body whatsoever, one need only render +electric a silk thread, which is known to be of the resinuous +electricity, and see whether that body, rendered electrical, +attracts or repels it. If it attracts it, it is certainly of the +kind of electricity which I call VITREOUS; if, on the contrary, +it repels it, it is of the same kind of electricity with the +silk--that is, of the RESINOUS. I have likewise observed that +communicated electricity retains the same properties; for if a +ball of ivory or wood be set on a glass stand, and this ball be +rendered electric by the tube, it will repel such substances as +the tube repels; but if it be rendered electric by applying a +cylinder of gum-sack near it, it will produce quite contrary +effects--namely, precisely the same as gum-sack would produce. In +order to succeed in these experiments, it is requisite that the +two bodies which are put near each other, to find out the nature +of their electricity, be rendered as electrical as possible, for +if one of them was not at all or but weakly electrical, it would +be attracted by the other, though it be of that sort that should +naturally be repelled by it. But the experiment will always +succeed perfectly well if both bodies are sufficiently +electrical."[1] + +As we now know, Dufay was wrong in supposing that there were two +different kinds of electricity, vitreous and resinous. A little +later the matter was explained by calling one "positive" +electricity and the other "negative," and it was believed that +certain substances produced only the one kind peculiar to that +particular substance. We shall see presently, however, that some +twenty years later an English scientist dispelled this illusion +by producing both positive (or vitreous) and negative (or +resinous) electricity on the same tube of glass at the same time. + +After the death of Dufay his work was continued by his +fellow-countryman Dr. Joseph Desaguliers, who was the first +experimenter to electrify running water, and who was probably the +first to suggest that clouds might be electrified bodies. But +about, this time--that is, just before the middle of the +eighteenth century--the field of greatest experimental activity +was transferred to Germany, although both England and France were +still active. The two German philosophers who accomplished most +at this time were Christian August Hansen and George Matthias +Bose, both professors in Leipsic. Both seem to have conceived the +idea, simultaneously and independently, of generating electricity +by revolving globes run by belt and wheel in much the same manner +as the apparatus of Hauksbee. + +With such machines it was possible to generate a much greater +amount of electricity than Dufay had been able to do with the +rubbed tube, and so equipped, the two German professors were able +to generate electric sparks and jets of fire in a most startling +manner. Bose in particular had a love for the spectacular, which +he turned to account with his new electrical machine upon many +occasions. On one of these occasions he prepared an elaborate +dinner, to which a large number of distinguished guests were +invited. Before the arrival of the company, however, Bose +insulated the great banquet-table on cakes of pitch, and then +connected it with a huge electrical machine concealed in another +room. All being ready, and the guests in their places about to be +seated, Bose gave a secret signal for starting this machine, +when, to the astonishment of the party, flames of fire shot from +flowers, dishes, and viands, giving a most startling but +beautiful display. + +To add still further to the astonishment of his guests, Bose then +presented a beautiful young lady, to whom each of the young men +of the party was introduced. In some mysterious manner she was +insulated and connected with the concealed electrical machine, so +that as each gallant touched her fingertips he received an +electric shock that "made him reel." Not content with this, the +host invited the young men to kiss the beautiful maid. But those +who were bold enough to attempt it received an electric shock +that nearly "knocked their teeth out," as the professor tells it. + + +LUDOLFF'S EXPERIMENT WITH THE ELECTRIC SPARK + +But Bose was only one of several German scientists who were +making elaborate experiments. While Bose was constructing and +experimenting with his huge machine, another German, Christian +Friedrich Ludolff, demonstrated that electric sparks are actual +fire--a fact long suspected but hitherto unproved. Ludolff's +discovery, as it chanced, was made in the lecture-hall of the +reorganized Academy of Sciences at Berlin, before an audience of +scientists and great personages, at the opening lecture in 1744. + +In the course of this lecture on electricity, during which some +of the well-known manifestations of electricity were being shown, +it occurred to Ludolff to attempt to ignite some inflammable +fluid by projecting an electric spark upon its surface with a +glass rod. This idea was suggested to him while performing the +familiar experiment of producing a spark on the surface of a bowl +of water by touching it with a charged glass rod. He announced to +his audience the experiment he was about to attempt, and having +warmed a spoonful of sulphuric ether, he touched its surface with +the glass rod, causing it to burst into flame. This experiment +left no room for doubt that the electric spark was actual fire. + +As soon as this experiment of Ludolff's was made known to Bose, +he immediately claimed that he had previously made similar +demonstrations on various inflammable substances, both liquid and +solid; and it seems highly probable that he had done so, as he +was constantly experimenting with the sparks, and must almost +certainly have set certain substances ablaze by accident, if not +by intent. At all events, he carried on a series of experiments +along this line to good purpose, finally succeeding in exploding +gun-powder, and so making the first forerunner of the electric +fuses now so universally used in blasting, firing cannon, and +other similar purposes. It was Bose also who, observing some of +the peculiar manifestations in electrified tubes, and noticing +their resemblance to "northern lights," was one of the first, if +not the first, to suggest that the aurora borealis is of electric +origin. + +These spectacular demonstrations had the effect of calling public +attention to the fact that electricity is a most wonderful and +mysterious thing, to say the least, and kept both scientists and +laymen agog with expectancy. Bose himself was aflame with +excitement, and so determined in his efforts to produce still +stronger electric currents, that he sacrificed the tube of his +twenty-foot telescope for the construction of a mammoth +electrical machine. With this great machine a discharge of +electricity was generated powerful enough to wound the skin when +it happened to strike it. + +Until this time electricity had been little more than a plaything +of the scientists--or, at least, no practical use had been made +of it. As it was a practising physician, Gilbert, who first laid +the foundation for experimenting with the new substance, so again +it was a medical man who first attempted to put it to practical +use, and that in the field of his profession. Gottlieb Kruger, a +professor of medicine at Halle in 1743, suggested that +electricity might be of use in some branches of medicine; and the +year following Christian Gottlieb Kratzenstein made a first +experiment to determine the effects of electricity upon the body. +He found that "the action of the heart was accelerated, the +circulation increased, and that muscles were made to contract by +the discharge": and he began at once administering electricity in +the treatment of certain diseases. He found that it acted +beneficially in rheumatic affections, and that it was +particularly useful in certain nervous diseases, such as palsies. +This was over a century ago, and to-day about the most important +use made of the particular kind of electricity with which he +experimented (the static, or frictional) is for the treatment of +diseases affecting the nervous system. + +By the middle of the century a perfect mania for making +electrical machines had spread over Europe, and the whirling, +hand-rubbed globes were gradually replaced by great cylinders +rubbed by woollen cloths or pads, and generating an "enormous +power of electricity." These cylinders were run by belts and +foot-treadles, and gave a more powerful, constant, and +satisfactory current than known heretofore. While making +experiments with one of these machines, Johann Heinrichs Winkler +attempted to measure the speed at which electricity travels. To +do this he extended a cord suspended on silk threads, with the +end attached to the machine and the end which was to attract the +bits of gold-leaf near enough together so that the operator could +watch and measure the interval of time that elapsed between the +starting of the current along the cord and its attracting the +gold-leaf. The length of the cord used in this experiment was +only a little over a hundred feet, and this was, of course, +entirely inadequate, the current travelling that space apparently +instantaneously. + +The improved method of generating electricity that had come into +general use made several of the scientists again turn their +attention more particularly to attempt putting it to some +practical account. They were stimulated to these efforts by the +constant reproaches that were beginning to be heard on all sides +that electricity was merely a "philosopher's plaything." One of +the first to succeed in inventing something that approached a +practical mechanical contrivance was Andrew Gordon, a Scotch +Benedictine monk. He invented an electric bell which would ring +automatically, and a little "motor," if it may be so called. And +while neither of these inventions were of any practical +importance in themselves, they were attempts in the right +direction, and were the first ancestors of modern electric bells +and motors, although the principle upon which they worked was +entirely different from modern electrical machines. The motor was +simply a wheel with several protruding metal points around its +rim. These points were arranged to receive an electrical +discharge from a frictional machine, the discharge causing the +wheel to rotate. There was very little force given to this +rotation, however, not enough, in fact, to make it possible to +more than barely turn the wheel itself. Two more great +discoveries, galvanism and electro-magnetic induction, were +necessary before the practical motor became possible. + +The sober Gordon had a taste for the spectacular almost equal to +that of Bose. It was he who ignited a bowl of alcohol by turning +a stream of electrified water upon it, thus presenting the +seeming paradox of fire produced by a stream of water. Gordon +also demonstrated the power of the electrical discharge by +killing small birds and animals at a distance of two hundred +ells, the electricity being conveyed that distance through small +wires. + + +THE LEYDEN JAR DISCOVERED + +As yet no one had discovered that electricity could be stored, or +generated in any way other than by some friction device. But very +soon two experimenters, Dean von Kleist, of Camin, Pomerania, and +Pieter van Musschenbroek, the famous teacher of Leyden, +apparently independently, made the discovery of what has been +known ever since as the Leyden jar. And although Musschenbroek is +sometimes credited with being the discoverer, there can be no +doubt that Von Kleist's discovery antedated his by a few months +at least. + +Von Kleist found that by a device made of a narrow-necked bottle +containing alcohol or mercury, into which an iron nail was +inserted, be was able to retain the charge of electricity, after +electrifying this apparatus with the frictional machine. He made +also a similar device, more closely resembling the modern Leyden +jar, from a thermometer tube partly filled with water and a wire +tipped with a ball of lead. With these devices he found that he +could retain the charge of electricity for several hours, and +could produce the usual electrical manifestations, even to +igniting spirits, quite as well as with the frictional machine. +These experiments were first made in October, 1745, and after a +month of further experimenting, Von Kleist sent the following +account of them to several of the leading scientists, among +others, Dr. Lieberkuhn, in Berlin, and Dr. Kruger, of Halle. + +"When a nail, or a piece of thick brass wire, is put into a small +apothecary's phial and electrified, remarkable effects follow; +but the phial must be very dry, or warm. I commonly rub it over +beforehand with a finger on which I put some pounded chalk. If a +little mercury or a few drops of spirit of wine be put into it, +the experiment succeeds better. As soon as this phial and nail +are removed from the electrifying-glass, or the prime conductor, +to which it has been exposed, is taken away, it throws out a +pencil of flame so long that, with this burning machine in my +hand, I have taken above sixty steps in walking about my room. +When it is electrified strongly, I can take it into another room +and there fire spirits of wine with it. If while it is +electrifying I put my finger, or a piece of gold which I hold in +my hand, to the nail, I receive a shock which stuns my arms and +shoulders. + +"A tin tube, or a man, placed upon electrics, is electrified much +stronger by this means than in the common way. When I present +this phial and nail to a tin tube, which I have, fifteen feet +long, nothing but experience can make a person believe how +strongly it is electrified. I am persuaded," he adds, "that in +this manner Mr. Bose would not have taken a second electrical +kiss. Two thin glasses have been broken by the shock of it. It +appears to me very extraordinary, that when this phial and nail +are in contact with either conducting or non-conducting matter, +the strong shock does not follow. I have cemented it to wood, +metal, glass, sealing-wax, etc., when I have electrified without +any great effect. The human body, therefore, must contribute +something to it. This opinion is confirmed by my observing that +unless I hold the phial in my hand I cannot fire spirits of wine +with it."[2] + +But it seems that none of the men who saw this account were able +to repeat the experiment and produce the effects claimed by Von +Kleist, and probably for this reason the discovery of the obscure +Pomeranian was for a time lost sight of. + +Musschenbroek's discovery was made within a short time after Von +Kleist's--in fact, only a matter of about two months later. But +the difference in the reputations of the two discoverers insured +a very different reception for their discoveries. Musschenbroek +was one of the foremost teachers of Europe, and so widely known +that the great universities vied with each other, and kings were +bidding, for his services. Naturally, any discovery made by such +a famous person would soon be heralded from one end of Europe to +the other. And so when this professor of Leyden made his +discovery, the apparatus came to be called the "Leyden jar," for +want of a better name. There can be little doubt that +Musschenbroek made his discovery entirely independently of any +knowledge of Von Kleist's, or, for that matter, without ever +having heard of the Pomeranian, and his actions in the matter are +entirely honorable. + +His discovery was the result of an accident. While experimenting +to determine the strength of electricity he suspended a +gun-barrel, which he charged with electricity from a revolving +glass globe. From the end of the gun-barrel opposite the globe +was a brass wire, which extended into a glass jar partly filled +with water. Musschenbroek held in one hand this jar, while with +the other he attempted to draw sparks from the barrel. Suddenly +he received a shock in the hand holding the jar, that "shook him +like a stroke of lightning," and for a moment made him believe +that "he was done for." Continuing his experiments, nevertheless, +he found that if the jar were placed on a piece of metal on the +table, a shock would be received by touching this piece of metal +with one hand and touching the wire with the other--that is, a +path was made for the electrical discharge through the body. This +was practically the same experiment as made by Von Kleist with +his bottle and nail, but carried one step farther, as it showed +that the "jar" need not necessarily be held in the hand, as +believed by Von Kleist. Further experiments, continued by many +philosophers at the time, revealed what Von Kleist had already +pointed out, that the electrified jar remained charged for some +time. + +Soon after this Daniel Gralath, wishing to obtain stronger +discharges than could be had from a single Leyden jar, conceived +the idea of combining several jars, thus for the first time +grouping the generators in a "battery" which produced a discharge +strong enough to kill birds and small animals. He also attempted +to measure the strength of the discharges, but soon gave it up in +despair, and the solution of this problem was left for late +nineteenth-century scientists. + +The advent of the Leyden jar, which made it possible to produce +strong electrical discharges from a small and comparatively +simple device, was followed by more spectacular demonstrations of +various kinds all over Europe. These exhibitions aroused the +interest of the kings and noblemen, so that electricity no longer +remained a "plaything of the philosophers" alone, but of kings as +well. A favorite demonstration was that of sending the electrical +discharge through long lines of soldiers linked together by +pieces of wire, the discharge causing them to "spring into the +air simultaneously" in a most astonishing manner. A certain monk +in Paris prepared a most elaborate series of demonstrations for +the amusement of the king, among other things linking together an +entire regiment of nine hundred men, causing them to perform +simultaneous springs and contortions in a manner most amusing to +the royal guests. But not all the experiments being made were of +a purely spectacular character, although most of them +accomplished little except in a negative way. The famous Abbe +Nollet, for example, combined useful experiments with spectacular +demonstrations, thus keeping up popular interest while aiding the +cause of scientific electricity. + + +WILLIAM WATSON + +Naturally, the new discoveries made necessary a new nomenclature, +new words and electrical terms being constantly employed by the +various writers of that day. Among these writers was the English +scientist William Watson, who was not only a most prolific writer +but a tireless investigator. Many of the words coined by him are +now obsolete, but one at least, "circuit," still remains in use. + +In 1746, a French scientist, Louis Guillaume le Monnier, bad made +a circuit including metal and water by laying a chain half-way +around the edge of a pond, a man at either end holding it. One of +these men dipped his free hand in the water, the other presenting +a Leyden jar to a rod suspended on a cork float on the water, +both men receiving a shock simultaneously. Watson, a year later, +attempted the same experiment on a larger scale. He laid a wire +about twelve hundred feet long across Westminster Bridge over the +Thames, bringing the ends to the water's edge on the opposite +banks, a man at one end holding the wire and touching the water. +A second man on the opposite side held the wire and a Leyden jar; +and a third touched the jar with one hand, while with the other +he grasped a wire that extended into the river. In this way they +not only received the shock, but fired alcohol as readily across +the stream as could be done in the laboratory. In this experiment +Watson discovered the superiority of wire over chain as a +conductor, rightly ascribing this superiority to the continuity +of the metal. + +Watson continued making similar experiments over longer +watercourses, some of them as long as eight thousand feet, and +while engaged in making one of these he made the discovery so +essential to later inventions, that the earth could be used as +part of the circuit in the same manner as bodies of water. +Lengthening his wires he continued his experiments until a +circuit of four miles was made, and still the electricity seemed +to traverse the course instantaneously, and with apparently +undiminished force, if the insulation was perfect. + + +BENJAMIN FRANKLIN + +Watson's writings now carried the field of active discovery +across the Atlantic, and for the first time an American scientist +appeared--a scientist who not only rivalled, but excelled, his +European contemporaries. Benjamin Franklin, of Philadelphia, +coming into possession of some of Watson's books, became so +interested in the experiments described in them that he began at +once experimenting with electricity. In Watson's book were given +directions for making various experiments, and these assisted +Franklin in repeating the old experiments, and eventually adding +new ones. Associated with Franklin, and equally interested and +enthusiastic, if not equally successful in making discoveries, +were three other men, Thomas Hopkinson, Philip Sing, and Ebenezer +Kinnersley. These men worked together constantly, although it +appears to have been Franklin who made independently the +important discoveries, and formulated the famous Franklinian +theory. + +Working steadily, and keeping constantly in touch with the +progress of the European investigators, Franklin soon made some +experiments which he thought demonstrated some hitherto unknown +phases of electrical manifestation. This was the effect of +pointed bodies "in DRAWING OFF and THROWING OFF the electrical +fire." In his description of this phenomenon, Franklin writes: + +"Place an iron shot of three or four inches diameter on the mouth +of a clean, dry, glass bottle. By a fine silken thread from the +ceiling right over the mouth of the bottle, suspend a small cork +ball, about the bigness of a marble; the thread of such a length +that the cork ball may rest against the side of the shot. +Electrify the shot, and the ball will be repelled to the distance +of four or five inches, more or less, according to the quantity +of electricity. When in this state, if you present to the shot +the point of a long, slender shaft-bodkin, at six or eight inches +distance, the repellency is instantly destroyed, and the cork +flies to the shot. A blunt body must be brought within an inch, +and draw a spark, to produce the same effect. + +"To prove that the electrical fire is DRAWN OFF by the point, if +you take the blade of the bodkin out of the wooden handle and fix +it in a stick of sealing-wax, and then present it at the distance +aforesaid, or if you bring it very near, no such effect follows; +but sliding one finger along the wax till you touch the blade, +and the ball flies to the shot immediately. If you present the +point in the dark you will see, sometimes at a foot distance, and +more, a light gather upon it like that of a fire-fly or +glow-worm; the less sharp the point, the nearer you must bring it +to observe the light; and at whatever distance you see the light, +you may draw off the electrical fire and destroy the repellency. +If a cork ball so suspended be repelled by the tube, and a point +be presented quick to it, though at a considerable distance, 'tis +surprising to see how suddenly it flies back to the tube. Points +of wood will do as well as those of iron, provided the wood is +not dry; for perfectly dry wood will no more conduct electricity +than sealing-wax. + +"To show that points will THROW OFF as well as DRAW OFF the +electrical fire, lay a long, sharp needle upon the shot, and you +cannot electrify the shot so as to make it repel the cork ball. +Or fix a needle to the end of a suspended gun-barrel or iron rod, +so as to point beyond it like a little bayonet, and while it +remains there, the gun-barrel or rod cannot, by applying the tube +to the other end, be electrified so as to give a spark, the fire +continually running out silently at the point. In the dark you +may see it make the same appearance as it does in the case before +mentioned."[3] + +Von Guericke, Hauksbee, and Gray had noticed that pointed bodies +attracted electricity in a peculiar manner, but this +demonstration of the "drawing off" of "electrical fire" was +original with Franklin. Original also was the theory that he now +suggested, which had at least the merit of being thinkable even +by non-philosophical minds. It assumes that electricity is like a +fluid, that will flow along conductors and accumulate in proper +receptacles, very much as ordinary fluids do. This conception is +probably entirely incorrect, but nevertheless it is likely to +remain a popular one, at least outside of scientific circles, or +until something equally tangible is substituted. + + +FRANKLIN'S THEORY OF ELECTRICITY + +According to Franklin's theory, electricity exists in all bodies +as a "common stock," and tends to seek and remain in a state of +equilibrium, just as fluids naturally tend to seek a level. But +it may, nevertheless, be raised or lowered, and this equilibrium +be thus disturbed. If a body has more electricity than its normal +amount it is said to be POSITIVELY electrified; but if it has +less, it is NEGATIVELY electrified. An over-electrified or "plus" +body tends to give its surplus stock to a body containing the +normal amount; while the "minus" or under-electrified body will +draw electricity from one containing the normal amount. + +Working along lines suggested by this theory, Franklin attempted +to show that electricity is not created by friction, but simply +collected from its diversified state, the rubbed glass globe +attracting a certain quantity of "electrical fire," but ever +ready to give it up to any body that has less. He explained the +charged Leyden jar by showing that the inner coating of tin-foil +received more than the ordinary quantity of electricity, and in +consequence is POSITIVELY electrified, while the outer coating, +having the ordinary quantity of electricity diminished, is +electrified NEGATIVELY. + +These studies of the Leyden jar, and the studies of pieces of +glass coated with sheet metal, led Franklin to invent his +battery, constructed of eleven large glass plates coated with +sheets of lead. With this machine, after overcoming some defects, +he was able to produce electrical manifestations of great +force--a force that "knew no bounds," as he declared ("except in +the matter of expense and of labor"), and which could be made to +exceed "the greatest know effects of common lightning." + +This reference to lightning would seem to show Franklin's belief, +even at that time, that lightning is electricity. Many eminent +observers, such as Hauksbee, Wall, Gray, and Nollet, had noticed +the resemblance between electric sparks and lightning, but none +of these had more than surmised that the two might be identical. +In 1746, the surgeon, John Freke, also asserted his belief in +this identity. Winkler, shortly after this time, expressed the +same belief, and, assuming that they were the same, declared that +"there is no proof that they are of different natures"; and still +he did not prove that they were the same nature. + + +FRANKLIN INVENTS THE LIGHTNING-ROD + +Even before Franklin proved conclusively the nature of lightning, +his experiments in drawing off the electric charge with points +led to some practical suggestions which resulted in the invention +of the lightning-rod. In the letter of July, 1750, which he wrote +on the subject, he gave careful instructions as to the way in +which these rods might be constructed. In part Franklin wrote: +"May not the knowledge of this power of points be of use to +mankind in preserving houses, churches, ships, etc., from the +stroke of lightning by directing us to fix on the highest parts +of the edifices upright rods of iron made sharp as a needle, and +gilt to prevent rusting, and from the foot of these rods a wire +down the outside of the building into the grounds, or down round +one of the shrouds of a ship and down her side till it reaches +the water? Would not these pointed rods probably draw the +electrical fire silently out of a cloud before it came nigh +enough to strike, and thereby secure us from that most sudden and +terrible mischief? + +"To determine this question, whether the clouds that contain the +lightning are electrified or not, I propose an experiment to be +tried where it may be done conveniently. On the top of some high +tower or steeple, place a kind of sentry-box, big enough to +contain a man and an electrical stand. From the middle of the +stand let an iron rod rise and pass, bending out of the door, and +then upright twenty or thirty feet, pointed very sharp at the +end. If the electrical stand be kept clean and dry, a man +standing on it when such clouds are passing low might be +electrified and afford sparks, the rod drawing fire to him from a +cloud. If any danger to the man be apprehended (though I think +there would be none), let him stand on the floor of his box and +now and then bring near to the rod the loop of a wire that has +one end fastened to the leads, he holding it by a wax handle; so +the sparks, if the rod is electrified, will strike from the rod +to the wire and not effect him."[4] + +Not satisfied with all the evidence that he had collected +pointing to the identity of lightning and electricity, he adds +one more striking and very suggestive piece of evidence. +Lightning was known sometimes to strike persons blind without +killing them. In experimenting on pigeons and pullets with his +electrical machine, Franklin found that a fowl, when not killed +outright, was sometimes rendered blind. The report of these +experiments were incorporated in this famous letter of the +Philadelphia philosopher. + +The attitude of the Royal Society towards this clearly stated +letter, with its useful suggestions, must always remain as a blot +on the record of this usually very receptive and liberal-minded +body. Far from publishing it or receiving it at all, they derided +the whole matter as too visionary for discussion by the society. +How was it possible that any great scientific discovery could be +made by a self-educated colonial newspaper editor, who knew +nothing of European science except by hearsay, when all the great +scientific minds of Europe had failed to make the discovery? How +indeed! And yet it would seem that if any of the influential +members of the learned society had taken the trouble to read over +Franklin's clearly stated letter, they could hardly have failed +to see that his suggestions were worthy of consideration. But at +all events, whether they did or did not matters little. The fact +remains that they refused to consider the paper seriously at the +time; and later on, when its true value became known, were +obliged to acknowledge their error by a tardy report on the +already well-known document. + +But if English scientists were cold in their reception of +Franklin's theory and suggestions, the French scientists were +not. Buffon, perceiving at once the importance of some of +Franklin's experiments, took steps to have the famous letter +translated into French, and soon not only the savants, but +members of the court and the king himself were intensely +interested. Two scientists, De Lor and D'Alibard, undertook to +test the truth of Franklin's suggestions as to pointed rods +"drawing off lightning." In a garden near Paris, the latter +erected a pointed iron rod fifty feet high and an inch in +diameter. As no thunder-clouds appeared for several days, a guard +was stationed, armed with an insulated brass wire, who was +directed to test the iron rods with it in case a storm came on +during D'Alibard's absence. The storm did come on, and the guard, +not waiting for his employer's arrival, seized the wire and +touched the rod. Instantly there was a report. Sparks flew and +the guard received such a shock that he thought his time had +come. Believing from his outcry that he was mortally hurt, his +friends rushed for a spiritual adviser, who came running through +rain and hail to administer the last rites; but when he found the +guard still alive and uninjured, he turned his visit to account +by testing the rod himself several times, and later writing a +report of his experiments to M. d'Alibard. This scientist at once +reported the affair to the French Academy, remarking that +"Franklin's idea was no longer a conjecture, but a reality." + + +FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY + +Europe, hitherto somewhat sceptical of Franklin's views, was by +this time convinced of the identity of lightning and electricity. +It was now Franklin's turn to be sceptical. To him the fact that +a rod, one hundred feet high, became electrified during a storm +did not necessarily prove that the storm-clouds were electrified. +A rod of that length was not really projected into the cloud, for +even a very low thunder-cloud was more than a hundred feet above +the ground. Irrefutable proof could only be had, as he saw it, by +"extracting" the lightning with something actually sent up into +the storm-cloud; and to accomplish this Franklin made his silk +kite, with which he finally demonstrated to his own and the +world's satisfaction that his theory was correct. + +Taking his kite out into an open common on the approach of a +thunder-storm, he flew it well up into the threatening clouds, +and then, touching, the suspended key with his knuckle, received +the electric spark; and a little later he charged a Leyden jar +from the electricity drawn from the clouds with his kite. + +In a brief but direct letter, he sent an account of his kite and +his experiment to England: + +"Make a small cross of two light strips of cedar," he wrote, "the +arms so long as to reach to the four corners of a large, thin, +silk handkerchief when extended; tie the corners of the +handkerchief to the extremities of the cross so you have the body +of a kite; which being properly accommodated with a tail, loop, +and string, will rise in the air like those made of paper; but +this being of silk is fitter to bear the wind and wet of a +thunder-gust without tearing. To the top of the upright stick of +the cross is to be fixed a very sharp-pointed wire, rising a foot +or more above the wood. To the end of the twine, next the hand, +is to be tied a silk ribbon; where the silk and twine join a key +may be fastened. This kite is to be raised when a thunder-gust +appears to be coming on, and the person who holds the string must +stand within a door or window or under some cover, so that the +silk ribbon may not be wet; and care must be taken that the twine +does not touch the frame of the door or window. As soon as any of +the thunder-clouds come over the kite, the pointed wire will draw +the electric fire from them, and the kite, with all the twine, +will be electrified and the loose filaments will stand out +everywhere and be attracted by the approaching finger, and when +the rain has wet the kite and twine so that it can conduct the +electric fire freely, you will find it stream out plentifully +from the key on the approach of your knuckle, and with this key +the phial may be charged; and from electric fire thus obtained +spirits may be kindled and all other electric experiments +performed which are usually done by the help of a rubbed glass +globe or tube, and thereby the sameness of the electric matter +with that of lightning completely demonstrated."[5] + +In experimenting with lightning and Franklin's pointed rods in +Europe, several scientists received severe shocks, in one case +with a fatal result. Professor Richman, of St. Petersburg, while +experimenting during a thunder-storm, with an iron rod which he +had erected on his house, received a shock that killed him +instantly. + +About 1733, as we have seen, Dufay had demonstrated that there +were two apparently different kinds of electricity; one called +VITREOUS because produced by rubbing glass, and the other +RESINOUS because produced by rubbed resinous bodies. Dufay +supposed that these two apparently different electricities could +only be produced by their respective substances; but twenty years +later, John Canton (1715-1772), an Englishman, demonstrated that +under certain conditions both might be produced by rubbing the +same substance. Canton's experiment, made upon a glass tube with +a roughened surface, proved that if the surface of the tube were +rubbed with oiled silk, vitreous or positive electricity was +produced, but if rubbed with flannel, resinous electricity was +produced. He discovered still further that both kinds could be +excited on the same tube simultaneously with a single rubber. To +demonstrate this he used a tube, one-half of which had a +roughened the other a glazed surface. With a single stroke of the +rubber he was able to excite both kinds of electricity on this +tube. He found also that certain substances, such as glass and +amber, were electrified positively when taken out of mercury, and +this led to his important discovery that an amalgam of mercury +and tin, when used on the surface of the rubber, was very +effective in exciting glass. + + + +XV. NATURAL HISTORY TO THE TIME OF LINNAeUS + +Modern systematic botany and zoology are usually held to have +their beginnings with Linnaeus. But there were certain precursors +of the famous Swedish naturalist, some of them antedating him by +more than a century, whose work must not be altogether +ignored--such men as Konrad Gesner (1516-1565), Andreas +Caesalpinus (1579-1603), Francisco Redi (1618-1676), Giovanni +Alfonso Borelli (1608-1679), John Ray (1628-1705), Robert Hooke +(1635-1703), John Swammerdam (1637-1680), Marcello Malpighi +(1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort +(1656-1708), Rudolf Jacob Camerarius (1665-1721), and Stephen +Hales (1677-1761). The last named of these was, to be sure, a +contemporary of Linnaeus himself, but Gesner and Caesalpinus +belong, it will be observed, to so remote an epoch as that of +Copernicus. + +Reference has been made in an earlier chapter to the microscopic +investigations of Marcello Malpighi, who, as there related, was +the first observer who actually saw blood corpuscles pass through +the capillaries. Another feat of this earliest of great +microscopists was to dissect muscular tissue, and thus become the +father of microscopic anatomy. But Malpighi did not confine his +observations to animal tissues. He dissected plants as well, and +he is almost as fully entitled to be called the father of +vegetable anatomy, though here his honors are shared by the +Englishman Grew. In 1681, while Malpighi's work, Anatomia +plantarum, was on its way to the Royal Society for publication, +Grew's Anatomy of Vegetables was in the hands of the publishers, +making its appearance a few months earlier than the work of the +great Italian. Grew's book was epoch-marking in pointing out the +sex-differences in plants. + +Robert Hooke developed the microscope, and took the first steps +towards studying vegetable anatomy, publishing in 1667, among +other results, the discovery of the cellular structure of cork. +Hooke applied the name "cell" for the first time in this +connection. These discoveries of Hooke, Malpighi, and Grew, and +the discovery of the circulation of the blood by William Harvey +shortly before, had called attention to the similarity of animal +and vegetable structures. Hales made a series of investigations +upon animals to determine the force of the blood pressure; and +similarly he made numerous statical experiments to determine the +pressure of the flow of sap in vegetables. His Vegetable Statics, +published in 1727, was the first important work on the subject of +vegetable physiology, and for this reason Hales has been called +the father of this branch of science. + +In botany, as well as in zoology, the classifications of Linnaeus +of course supplanted all preceding classifications, for the +obvious reason that they were much more satisfactory; but his +work was a culmination of many similar and more or less +satisfactory attempts of his predecessors. About the year 1670 +Dr. Robert Morison (1620-1683), of Aberdeen, published a +classification of plants, his system taking into account the +woody or herbaceous structure, as well as the flowers and fruit. +This classification was supplanted twelve years later by the +classification of Ray, who arranged all known vegetables into +thirty-three classes, the basis of this classification being the +fruit. A few years later Rivinus, a professor of botany in the +University of Leipzig, made still another classification, +determining the distinguishing character chiefly from the flower, +and Camerarius and Tournefort also made elaborate +classifications. On the Continent Tournefort's classification was +the most popular until the time of Linnaeus, his systematic +arrangement including about eight thousand species of plants, +arranged chiefly according to the form of the corolla. + +Most of these early workers gave attention to both vegetable and +animal kingdoms. They were called naturalists, and the field of +their investigations was spoken of as "natural history." The +specialization of knowledge had not reached that later stage in +which botanist, zoologist, and physiologist felt their labors to +be sharply divided. Such a division was becoming more and more +necessary as the field of knowledge extended; but it did not +become imperative until long after the time of Linnaeus. That +naturalist himself, as we shall see, was equally distinguished as +botanist and as zoologist. His great task of organizing knowledge +was applied to the entire range of living things. + +Carolus Linnaeus was born in the town of Rashult, in Sweden, on +May 13, 1707. As a child he showed great aptitude in learning +botanical names, and remembering facts about various plants as +told him by his father. His eagerness for knowledge did not +extend to the ordinary primary studies, however, and, aside from +the single exception of the study of physiology, he proved +himself an indifferent pupil. His backwardness was a sore trial +to his father, who was desirous that his son should enter the +ministry; but as the young Linnaeus showed no liking for that +calling, and as he had acquitted himself well in his study of +physiology, his father at last decided to allow him to take up +the study of medicine. Here at last was a field more to the +liking of the boy, who soon vied with the best of his +fellow-students for first honors. Meanwhile he kept steadily at +work in his study of natural history, acquiring considerable +knowledge of ornithology, entomology, and botany, and adding +continually to his collection of botanical specimens. In 1729 his +botanical knowledge was brought to the attention of Olaf Rudbeck, +professor of botany in the University of Upsala, by a short paper +on the sexes of plants which Linnaeus had prepared. Rudbeck was +so impressed by some of the ideas expressed in this paper that he +appointed the author as his assistant the following year. + +This was the beginning of Linnaes's career as a botanist. The +academic gardens were thus thrown open to him, and he found time +at his disposal for pursuing his studies between lecture hours +and in the evenings. It was at this time that he began the +preparation of his work the Systema naturae, the first of his +great works, containing a comprehensive sketch of the whole field +of natural history. When this work was published, the clearness +of the views expressed and the systematic arrangement of the +various classifications excited great astonishment and +admiration, and placed Linaeus at once in the foremost rank of +naturalists. This work was followed shortly by other +publications, mostly on botanical subjects, in which, among other +things, he worked out in detail his famous "system." + +This system is founded on the sexes of plants, and is usually +referred to as an "artificial method" of classification because +it takes into account only a few marked characters of plants, +without uniting them by more general natural affinities. At the +present time it is considered only as a stepping-stone to the +"natural" system; but at the time of its promulgation it was +epoch-marking in its directness and simplicity, and therefore +superiority, over any existing systems. + +One of the great reforms effected by Linnaeus was in the matter +of scientific terminology. Technical terms are absolutely +necessary to scientific progress, and particularly so in botany, +where obscurity, ambiguity, or prolixity in descriptions are +fatally misleading. Linnaeus's work contains something like a +thousand terms, whose meanings and uses are carefully explained. +Such an array seems at first glance arbitrary and unnecessary, +but the fact that it has remained in use for something like two +centuries is indisputable evidence of its practicality. The +descriptive language of botany, as employed by Linnaeus, still +stands as a model for all other subjects. + +Closely allied to botanical terminology is the subject of +botanical nomenclature. The old method of using a number of Latin +words to describe each different plant is obviously too +cumbersome, and several attempts had been made prior to the time +of Linnaeus to substitute simpler methods. Linnaeus himself made +several unsatisfactory attempts before he finally hit upon his +system of "trivial names," which was developed in his Species +plantarum, and which, with some, minor alterations, remains in +use to this day. The essence of the system is the introduction of +binomial nomenclature--that is to say, the use of two names and +no more to designate any single species of animal or plant. The +principle is quite the same as that according to which in modern +society a man has two names, let us say, John Doe, the one +designating his family, the other being individual. Similarly +each species of animal or plant, according to the Linnaeean +system, received a specific or "trivial" name; while various +species, associated according to their seeming natural affinities +into groups called genera, were given the same generic name. Thus +the generic name given all members of the cat tribe being Felis, +the name Felis leo designates the lion; Felis pardus, the +leopard; Felis domestica, the house cat, and so on. This seems +perfectly simple and natural now, but to understand how great a +reform the binomial nomenclature introduced we have but to +consult the work of Linnaeus's predecessors. A single +illustration will suffice. There is, for example, a kind of +grass, in referring to which the naturalist anterior to Linnaeus, +if he would be absolutely unambiguous, was obliged to use the +following descriptive formula: Gramen Xerampelino, Miliacea, +praetenuis ramosaque sparsa panicula, sive Xerampelino congener, +arvense, aestivum; gramen minutissimo semine. Linnaeus gave to +this plant the name Poa bulbosa--a name that sufficed, according +to the new system, to distinguish this from every other species +of vegetable. It does not require any special knowledge to +appreciate the advantage of such a simplification. + +While visiting Paris in 1738 Linnaeus met and botanized with the +two botanists whose "natural method" of classification was later +to supplant his own "artificial system." These were Bernard and +Antoine Laurent de Jussieu. The efforts of these two scientists +were directed towards obtaining a system which should aim at +clearness, simplicity, and precision, and at the same time be +governed by the natural affinities of plants. The natural system, +as finally propounded by them, is based on the number of +cotyledons, the structure of the seed, and the insertion of the +stamens. Succeeding writers on botany have made various +modifications of this system, but nevertheless it stands as the +foundation-stone of modern botanical classification. + + + +APPENDIX + +REFERENCE LIST + +CHAPTER I + +SCIENCE IN THE DARK AGE + +[1] (p. 4). James Harvey Robinson, An Introduction to the History +of Western Europe, New York, 1898, p. 330. + +[2] (p. 6). Henry Smith Williams, A Prefatory Characterization of +The History of Italy, in vol. IX. of The Historians' History of +the World, 25 vols., London and New York, 1904. + + +CHAPTER III + +MEDIAeVAL SCIENCE IN THE WEST + +[1] (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, +and Man of Science, 2 vols., New York, 1892. Vol. II., p. 73. + + +CHAPTER IV + +THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +[1] (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, +trans. from Dannemann's Geschichle du Naturwissenschaften, 2 +vols., Leipzig, 1896. + +[2] (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, +trans. from Dannemann, op. cit. + +CHAPTER V + +GALILEO AND THE NEW PHYSICS [1] (p. 101). Rothmann, History of +Astronomy (in the Library of Useful Knowledge), London, 1834. + +[2] (p. 102). William Whewell, History of the Inductive Sciences, +3 Vols, London, 1847-Vol. II., p. 48. + +[3] (p. 111). The Lives of Eminent Persons, by Biot, Jardine, +Bethune, etc., London, 1833. + +[4] (p. 113). William Gilbert, De Magnete, translated by P. +Fleury Motteley, London, 1893. In the biographical memoir, p. +xvi. + +[5] (p. 114). Gilbert, op. cit., p. x1vii. + +[6] (p. 114). Gilbert, op. cit., p. 24. + + +CHAPTER VI + +TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +[1] (p. 125). Exodus xxxii, 20. + +[2] (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, +1850. Vol. II., p. 280. + +[3] (p. 140). Mackay, op. cit., Vol. 11., p. 289. + +[4] (P. 145). John B. Schmalz, Astrology Vindicated, New York, +1898. + +[5] (p. 146). William Lilly, The Starry Messenger, London, 1645, +p. 63. + +[6] (p. 149). Lilly, op. cit., p. 70. + +[7] (p. 152). George Wharton, An Astrological jugement upon His +Majesty's Present March begun from Oxford, May 7, 1645, pp. 7-10. + +[8] (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, +1854, p. 29. + + +CHAPTER VII + +FROM PARACELSUS TO HARVEY + +[1] (p. 159). A. E. Waite, The Hermetic and Alchemical Writings +of Paracelsus, 2 vols., London, 1894. Vol. I., p. 21. + +[2] (p. 167). E. T. Withington, Medical History from the Earliest +Times, London, 1894, p. 278. + +[3] (p. 173). John Dalton, Doctrines of the Circulation, +Philadelphia, 1884, p. 179. + +[4] (p. 174). William Harvey, De Motu Cordis et Sanguinis, +London, 1803, chap. X. + +[5] (p. 178). The Works of William Harvey, translated by Robert +Willis, London, 1847, p. 56. + + +CHAPTER VIII + +MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +[1] (p. 189). Hermann Baas, History of Medicine, translated by H. +E. Henderson, New York, 1894, p. 504. + +[2] (p. 189). E. T. Withington, Medical History from the Earliest +Times, London, 1894, p. 320. + + +CHAPTER IX + +PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + +[1] (p. 193). George L. Craik, Bacon and His Writings and +Philosophy, 2 vols., London, 1846. Vol. II., p. 121. + +[2] (p. 193). From Huxley's address On Descartes's Discourse +Touching the Method of Using One's Reason Rightly and of Seeking +Scientific Truth. + +[3] (p. 195). Rene Descartes, Traite de l'Homme (Cousins's +edition. in ii vols.), Paris, 1824. Vol, VI., p. 347. + + +CHAPTER X + +THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +[1] (p. 205). See The Phlogiston Theory, Vol, IV. + +[2] (p. 205). Robert Boyle, Philosophical Works, 3 vols., London, +1738. Vol. III., p. 41. + +[3] (p. 206). Ibid., Vol. III., p. 47. + +[4] (p. 206). Ibid., Vol. II., p. 92. + +[5] (p. 207). Ibid., Vol. II., p. 2. + +[6] (p. 209). Ibid., Vol. I., p. 8. + +[7] (p. 209). Ibid., vol. III., p. 508. + +[8] (p. 210). Ibid., Vol. III.) p. 361. + +[9] (p. 213). Otto von Guericke, in the Philosophical +Transactions of the Royal Society of London, No. 88, for 1672, p. +5103. + +[10] (p. 222). Von Guericke, Phil. Trans. for 1669, Vol I., pp. +173, 174. + +CHAPTER XI + +NEWTON AND THE COMPOSITION OF LIGHT + +[1] (p. 233). Phil. Trans. of Royal Soc. of London, No. 80, 1672, +pp. 3076-3079. [2] (p 234). Ibid., pp. 3084, 3085. + +[3] (p. 235). Voltaire, Letters Concerning the English Nation, +London, 1811. + +CHAPTER XII + +NEWTON AND THE LAW OF GRAVITATION + +[1] (p. 242). Sir Isaac Newton, Principia, translated by Andrew +Motte, New York, 1848, pp. 391, 392. + +[2] (p. 250). Newton op. cit., pp. 506, 507. + +CHAPTER XIV + +PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN + +[1] (p. 274). A letter from M. Dufay, F.R.S. and of the Royal +Academy of Sciences at Paris, etc., in the Phil. Trans. of the +Royal Soc., vol. XXXVIII., pp. 258-265. + +[2] (p. 282). Dean von Kleist, in the Danzick Memoirs, Vol. I., +p. 407. From Joseph Priestley's History of Electricity, London, +1775, pp. 83, 84. + +[3] (p. 288). Benjamin Franklin, New Experiments and Observations +on Electricity, London, 1760, pp. 107, 108. + +[4] (p. 291). Franklin, op. cit., pp. 62, 63. + +[5] (p. 295). Franklin, op. cit., pp. 107, 108. + +[For notes and bibliography to vol. II. see vol. V.] + + + + + +End of Project Gutenberg Etext of A History of Science, V 2, by Williams + |