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diff --git a/1706.txt b/1706.txt new file mode 100644 index 0000000..a7245fb --- /dev/null +++ b/1706.txt @@ -0,0 +1,8422 @@ +The Project Gutenberg EBook of A History of Science, Volume 2(of 5), by +Henry Smith Williams + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: A History of Science, Volume 2(of 5) + +Author: Henry Smith Williams + +Release Date: April, 1999 [Etext #1706] +Posting Date: November 17, 2009 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V2 *** + + + + +Produced by Charles Keller + + + + + +A HISTORY OF SCIENCE + +BY HENRY SMITH WILLIAMS, M.D., LL.D. + +ASSISTED BY EDWARD H. 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, tonsillotomy, +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, he 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, discovered 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 system 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 he 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, he 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 +Leeuwenhoek, 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, he +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 judgement 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 the Project Gutenberg EBook of A History of Science, Volume 2(of 5), by +Henry Smith Williams + +*** END OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V2 *** + +***** This file should be named 1706.txt or 1706.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/7/0/1706/ + +Produced by Charles Keller + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. 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