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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/1706-h.zip b/1706-h.zip Binary files differnew file mode 100644 index 0000000..071ef65 --- /dev/null +++ b/1706-h.zip diff --git a/1706-h/1706-h.htm b/1706-h/1706-h.htm new file mode 100644 index 0000000..4844e1b --- /dev/null +++ b/1706-h/1706-h.htm @@ -0,0 +1,9493 @@ +<?xml version="1.0" encoding="us-ascii"?> + +<!DOCTYPE html + PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" > + +<html xmlns="http://www.w3.org/1999/xhtml" lang="en"> + <head> + <title> + A History of Science, Vol. II by Henry Smith Williams + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +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: November 17, 2009 [EBook #1706] +Last Updated: January 26, 2013 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V2 *** + + + + +Produced by Charles Keller, and David Widger + + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + A HISTORY OF SCIENCE + </h1> + <h2> + BY HENRY SMITH WILLIAMS, M.D., LL.D. <br /> <br /> <br /> ASSISTED BY EDWARD + H. WILLIAMS, M.D. <br /> <br /> <br /> IN FIVE VOLUMES <br /> <br /> VOLUME II. + </h2> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <blockquote> + <p class="toc"> + <big><b>CONTENTS</b></big> + </p> + <p> + <br /> <a href="#link2H_4_0001"> <b>A HISTORY OF SCIENCE</b> </a><br /> + <br /> <a href="#link2H_4_0002"> <b>BOOK II. THE BEGINNINGS OF MODERN + SCIENCE</b> </a> + </p> + <p class="toc"> + <a href="#link2H_4_0003"> I. SCIENCE IN THE DARK AGE </a> + </p> + <p class="toc"> + <a href="#link2H_4_0004"> II. MEDIAEVAL SCIENCE AMONG THE ARABIANS </a> + </p> + <p class="toc"> + <a href="#link2H_4_0005"> III. MEDIAEVAL SCIENCE IN THE WEST </a> + </p> + <p class="toc"> + <a href="#link2H_4_0006"> IV. THE NEW COSMOLOGY—COPERNICUS TO + KEPLER AND GALILEO </a> + </p> + <p class="toc"> + <a href="#link2H_4_0007"> V. GALILEO AND THE NEW PHYSICS </a> + </p> + <p class="toc"> + <a href="#link2H_4_0008"> VI. TWO PSEUDO-SCIENCES—ALCHEMY AND + ASTROLOGY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0009"> VII. FROM PARACELSUS TO HARVEY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0010"> VIII. MEDICINE IN THE SIXTEENTH AND + SEVENTEENTH CENTURIES </a> + </p> + <p class="toc"> + <a href="#link2H_4_0011"> IX. PHILOSOPHER-SCIENTISTS AND NEW + INSTITUTIONS OF LEARNING </a> + </p> + <p class="toc"> + <a href="#link2H_4_0012"> X. THE SUCCESSORS OF GALILEO IN PHYSICAL + SCIENCE </a> + </p> + <p class="toc"> + <a href="#link2H_4_0013"> XI. NEWTON AND THE COMPOSITION OF LIGHT </a> + </p> + <p class="toc"> + <a href="#link2H_4_0014"> XII. NEWTON AND THE LAW OF GRAVITATION </a> + </p> + <p class="toc"> + <a href="#link2H_4_0015"> XIII. INSTRUMENTS OF PRECISION IN THE AGE OF + NEWTON </a> + </p> + <p class="toc"> + <a href="#link2H_4_0016"> XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND + VON GUERICKE TO FRANKLIN </a> + </p> + <p class="toc"> + <a href="#link2H_4_0017"> XV. NATURAL HISTORY TO THE TIME OF LINNAEUS + </a> + </p> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <p class="toc2"> + <a href="#link2H_APPE"> APPENDIX </a> + </p> + <p class="toc2"> + <a href="#link2HCH0001"> CHAPTER I </a> + </p> + <p class="toc2"> + <a href="#link2HCH0002"> CHAPTER III </a> + </p> + <p class="toc2"> + <a href="#link2HCH0003"> CHAPTER IV </a> + </p> + <p class="toc2"> + <a href="#link2HCH0004"> CHAPTER V </a> + </p> + <p class="toc2"> + <a href="#link2HCH0005"> CHAPTER VI </a> + </p> + <p class="toc2"> + <a href="#link2HCH0006"> CHAPTER VII </a> + </p> + <p class="toc2"> + <a href="#link2HCH0007"> CHAPTER VIII </a> + </p> + <p class="toc2"> + <a href="#link2HCH0008"> CHAPTER IX </a> + </p> + <p class="toc2"> + <a href="#link2HCH0009"> CHAPTER X </a> + </p> + <p class="toc2"> + <a href="#link2HCH0010"> CHAPTER XI </a> + </p> + <p class="toc2"> + <a href="#link2HCH0011"> CHAPTER XII </a> + </p> + <p class="toc2"> + <a href="#link2HCH0012"> CHAPTER XIV </a> + </p> + </blockquote> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a name="link2H_4_0001" id="link2H_4_0001"> + <!-- H2 anchor --> </a> + </p> + <h1> + A HISTORY OF SCIENCE + </h1> + <p> + <a name="link2H_4_0002" id="link2H_4_0002"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + BOOK II. THE BEGINNINGS OF MODERN SCIENCE + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0003" id="link2H_4_0003"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + I. SCIENCE IN THE DARK AGE + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0004" id="link2H_4_0004"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + II. MEDIAEVAL SCIENCE AMONG THE ARABIANS + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ARABIAN MEDICINE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ARABIAN HOSPITALS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0005" id="link2H_4_0005"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + III. MEDIAEVAL SCIENCE IN THE WEST + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THIRTEENTH-CENTURY MEDICINE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + FIFTEENTH-CENTURY MEDICINE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + NEW BEGINNINGS IN GENERAL SCIENCE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ROGER BACON + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LEONARDO DA VINCI + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0006" id="link2H_4_0006"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + IV. THE NEW COSMOLOGY—COPERNICUS TO KEPLER AND GALILEO + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The work of Copernicus, published thus in the year 1543 at Nuremberg, + bears the title De Orbium Coelestium Revolutionibus. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + In chapter X. of book I., "On the Order of the Spheres," occurs a more + detailed presentation of the system, as follows: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + 1. That the planetary orbits are not circular, but elliptical, the sun + occupying one focus of the ellipses. + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + GALILEO GALILEI + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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? + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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? + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0007" id="link2H_4_0007"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + V. GALILEO AND THE NEW PHYSICS + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + STEVINUS AND THE LAW OF EQUILIBRIUM + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + GALILEO AND THE EQUILIBRIUM OF FLUIDS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + WILLIAM GILBERT AND THE STUDY OF MAGNETISM + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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) + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + TORRICELLI + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0008" id="link2H_4_0008"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VI. TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ASTROLOGY + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + "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." + </p> + <p> + 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." + </p> + <p> + Continuing this list of peculiar phenomena he comes down to within a few + years of his own time. + </p> + <p> + "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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "The elements of his calculation were adverse, and a feeling of gloom cast + a shade of serious thought, if not dejection, over his countenance. + </p> + <p> + "'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. + </p> + <p> + "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. + </p> + <p> + "'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.'" + </p> + <p> + "'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?' + </p> + <p> + "'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.' + </p> + <p> + "'How short?' eagerly inquired the excited and anxious stranger. + </p> + <p> + "'Give me a momentary truce,' said the astrologer; 'I will consult the + horoscope, and may possibly find some mitigating circumstances.' + </p> + <p> + "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.' + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + But, on the other hand, these predictions were sometimes turned to account + by interested friends to warn certain persons of approaching dangers. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0009" id="link2H_4_0009"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VII. FROM PARACELSUS TO HARVEY + </h2> + <h3> + PARACELSUS + </h3> + <p> + 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). + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + THE GREAT ANATOMISTS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE COMING OF HARVEY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LEEUWENHOEK DISCOVERS BACTERIA + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0010" id="link2H_4_0010"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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! + </p> + <p> + THOMAS SYDENHAM + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0011" id="link2H_4_0011"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + SCIENTIFIC SOCIETIES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0012" id="link2H_4_0012"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + </h2> + <p> + 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. + </p> + <p> + ROBERT BOYLE (1627-1691) + </p> + <p> + 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) + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + MARIOTTE AND VON GUERICKE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ROBERT HOOKE + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + CHRISTIAN HUYGENS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "3. A body, however great, is moved by a body however small impelled with + any velocity whatsoever. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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...." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0013" id="link2H_4_0013"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + XI. NEWTON AND THE COMPOSITION OF LIGHT + </h2> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE COMPOSITION OF WHITE LIGHT + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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'. + </p> + <p> + "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. + </p> + <p> + "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'." + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + THE NATURE OF COLOR + </p> + <p> + 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: + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + <a name="link2H_4_0014" id="link2H_4_0014"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + XII. NEWTON AND THE LAW OF GRAVITATION + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + {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.)} + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> +<pre xml:space="preserve"> + "PROPOSITION V., THEOREM V. +</pre> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> +<pre xml:space="preserve"> + "SCHOLIUM +</pre> + <p> + "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. + </p> +<pre xml:space="preserve"> + "PROPOSITION VI., THEOREM VI. +</pre> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> +<pre xml:space="preserve"> + "PROPOSITION VII., THEOREM VII. +</pre> + <p> + "That there is a power of gravity tending to all bodies, proportional to + the several quantities of matter which they contain. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "HENCE IT WOULD APPEAR THAT the force of the whole must arise from the + force of the component parts." + </p> + <p> + Newton closes this remarkable Book iii. with the following words: + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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: + </p> +<pre xml:space="preserve"> + "Nature and Nature's laws lay hid in night; + God said 'Let Newton be!' and all was light." +</pre> + <p> + <a name="link2H_4_0015" id="link2H_4_0015"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0016" id="link2H_4_0016"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE EXPERIMENTS OF STEPHEN GRAY + </p> + <p> + 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. + </p> + <p> + "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." + </p> + <p> + 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. + </p> + <p> + "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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + EXPERIMENTS OF CISTERNAY DUFAY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LUDOLFF'S EXPERIMENT WITH THE ELECTRIC SPARK + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE LEYDEN JAR DISCOVERED + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + WILLIAM WATSON + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + BENJAMIN FRANKLIN + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + FRANKLIN'S THEORY OF ELECTRICITY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + FRANKLIN INVENTS THE LIGHTNING-ROD + </p> + <p> + 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? + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + In a brief but direct letter, he sent an account of his kite and his + experiment to England: + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0017" id="link2H_4_0017"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + XV. NATURAL HISTORY TO THE TIME OF LINNAEUS + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_APPE" id="link2H_APPE"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + APPENDIX + </h2> + <h3> + REFERENCE LIST + </h3> + <p> + <a name="link2HCH0001" id="link2HCH0001"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER I + </h2> + <h3> + SCIENCE IN THE DARK AGE + </h3> + <p> + (1) (p. 4). James Harvey Robinson, An Introduction to the History of + Western Europe, New York, 1898, p. 330. + </p> + <p> + (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. + </p> + <p> + <a name="link2HCH0002" id="link2HCH0002"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER III + </h2> + <h3> + MEDIAEVAL SCIENCE IN THE WEST + </h3> + <p> + (1) (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, and Man of + Science, 2 vols., New York, 1892. Vol. II., p. 73. + </p> + <p> + <a name="link2HCH0003" id="link2HCH0003"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER IV + </h2> + <h3> + THE NEW COSMOLOGY—COPERNICUS TO KEPLER AND GALILEO + </h3> + <p> + (1) (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, trans. + from Dannemann's Geschichle du Naturwissenschaften, 2 vols., Leipzig, + 1896. + </p> + <p> + (2) (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, trans. + from Dannemann, op. cit. + </p> + <p> + <a name="link2HCH0004" id="link2HCH0004"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER V + </h2> + <p> + GALILEO AND THE NEW PHYSICS (1) (p. 101). Rothmann, History of Astronomy + (in the Library of Useful Knowledge), London, 1834. + </p> + <p> + (2) (p. 102). William Whewell, History of the Inductive Sciences, 3 Vols, + London, 1847-Vol. II., p. 48. + </p> + <p> + (3) (p. 111). The Lives of Eminent Persons, by Biot, Jardine, Bethune, + etc., London, 1833. + </p> + <p> + (4) (p. 113). William Gilbert, De Magnete, translated by P. Fleury + Motteley, London, 1893. In the biographical memoir, p. xvi. + </p> + <p> + (5) (p. 114). Gilbert, op. cit., p. x1vii. + </p> + <p> + (6) (p. 114). Gilbert, op. cit., p. 24. + </p> + <p> + <a name="link2HCH0005" id="link2HCH0005"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VI + </h2> + <h3> + TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY + </h3> + <p> + (1) (p. 125). Exodus xxxii, 20. + </p> + <p> + (2) (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, 1850. + Vol. II., p. 280. + </p> + <p> + (3) (p. 140). Mackay, op. cit., Vol. 11., p. 289. + </p> + <p> + (4) (P. 145). John B. Schmalz, Astrology Vindicated, New York, 1898. + </p> + <p> + (5) (p. 146). William Lilly, The Starry Messenger, London, 1645, p. 63. + </p> + <p> + (6) (p. 149). Lilly, op. cit., p. 70. + </p> + <p> + (7) (p. 152). George Wharton, An Astrological judgement upon His Majesty's + Present March begun from Oxford, May 7, 1645, pp. 7-10. + </p> + <p> + (8) (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, 1854, p. + 29. + </p> + <p> + <a name="link2HCH0006" id="link2HCH0006"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VII + </h2> + <h3> + FROM PARACELSUS TO HARVEY + </h3> + <p> + (1) (p. 159). A. E. Waite, The Hermetic and Alchemical Writings of + Paracelsus, 2 vols., London, 1894. Vol. I., p. 21. + </p> + <p> + (2) (p. 167). E. T. Withington, Medical History from the Earliest Times, + London, 1894, p. 278. + </p> + <p> + (3) (p. 173). John Dalton, Doctrines of the Circulation, Philadelphia, + 1884, p. 179. + </p> + <p> + (4) (p. 174). William Harvey, De Motu Cordis et Sanguinis, London, 1803, + chap. X. + </p> + <p> + (5) (p. 178). The Works of William Harvey, translated by Robert Willis, + London, 1847, p. 56. + </p> + <p> + <a name="link2HCH0007" id="link2HCH0007"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VIII + </h2> + <h3> + MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + </h3> + <p> + (1) (p. 189). Hermann Baas, History of Medicine, translated by H. E. + Henderson, New York, 1894, p. 504. + </p> + <p> + (2) (p. 189). E. T. Withington, Medical History from the Earliest Times, + London, 1894, p. 320. + </p> + <p> + <a name="link2HCH0008" id="link2HCH0008"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER IX + </h2> + <h3> + PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + </h3> + <p> + (1) (p. 193). George L. Craik, Bacon and His Writings and Philosophy, 2 + vols., London, 1846. Vol. II., p. 121. + </p> + <p> + (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. + </p> + <p> + (3) (p. 195). Rene Descartes, Traite de l'Homme (Cousins's edition. in ii + vols.), Paris, 1824. Vol, VI., p. 347. + </p> + <p> + <a name="link2HCH0009" id="link2HCH0009"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER X + </h2> + <h3> + THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + </h3> + <p> + (1) (p. 205). See The Phlogiston Theory, Vol, IV. + </p> + <p> + (2) (p. 205). Robert Boyle, Philosophical Works, 3 vols., London, 1738. + Vol. III., p. 41. + </p> + <p> + (3) (p. 206). Ibid., Vol. III., p. 47. + </p> + <p> + (4) (p. 206). Ibid., Vol. II., p. 92. + </p> + <p> + (5) (p. 207). Ibid., Vol. II., p. 2. + </p> + <p> + (6) (p. 209). Ibid., Vol. I., p. 8. + </p> + <p> + (7) (p. 209). Ibid., vol. III., p. 508. + </p> + <p> + (8) (p. 210). Ibid., Vol. III., p. 361. + </p> + <p> + (9) (p. 213). Otto von Guericke, in the Philosophical Transactions of the + Royal Society of London, No. 88, for 1672, p. 5103. + </p> + <p> + (10) (p. 222). Von Guericke, Phil. Trans. for 1669, Vol I., pp. 173, 174. + </p> + <p> + <a name="link2HCH0010" id="link2HCH0010"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER XI + </h2> + <h3> + NEWTON AND THE COMPOSITION OF LIGHT + </h3> + <p> + (1) (p. 233). Phil. Trans. of Royal Soc. of London, No. 80, 1672, pp. + 3076-3079. (2) (p 234). Ibid., pp. 3084, 3085. + </p> + <p> + (3) (p. 235). Voltaire, Letters Concerning the English Nation, London, + 1811. + </p> + <p> + <a name="link2HCH0011" id="link2HCH0011"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER XII + </h2> + <h3> + NEWTON AND THE LAW OF GRAVITATION + </h3> + <p> + (1) (p. 242). Sir Isaac Newton, Principia, translated by Andrew Motte, New + York, 1848, pp. 391, 392. + </p> + <p> + (2) (p. 250). Newton op. cit., pp. 506, 507. + </p> + <p> + <a name="link2HCH0012" id="link2HCH0012"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER XIV + </h2> + <h3> + PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN + </h3> + <p> + (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. + </p> + <p> + (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. + </p> + <p> + (3) (p. 288). Benjamin Franklin, New Experiments and Observations on + Electricity, London, 1760, pp. 107, 108. + </p> + <p> + (4) (p. 291). Franklin, op. cit., pp. 62, 63. + </p> + <p> + (5) (p. 295). Franklin, op. cit., pp. 107, 108. + </p> + <p> + (For notes and bibliography to vol. II. see vol. V.) + </p> + <p> + <br /> <br /> + </p> + <hr /> + <hr /> + <p> + <br /> <br /> + </p> + <h1> + TABLE OF CONTENTS <br /><br /> FOR THE FIVE VOLUMES + </h1> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0002"> <b>BOOK + I</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0003"> + I. PREHISTORIC SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0004"> + II. EGYPTIAN SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0005"> + III. SCIENCE OF BABYLONIA AND ASSYRIA </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0006"> + IV. THE DEVELOPMENT OF THE ALPHABET </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0007"> + V. THE BEGINNINGS OF GREEK SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0008"> + VI. THE EARLY GREEK PHILOSOPHERS IN ITALY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0009"> + VII. GREEK SCIENCE IN THE EARLY ATTIC PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0010"> + VIII. POST-SOCRATIC SCIENCE AT ATHENS—PLATO, ARISTOTLE, AND + THEOPHRASTUS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0011"> + IX. GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0012"> + X. SCIENCE OF THE ROMAN PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0013"> + XI. A RETROSPECTIVE GLANCE AT CLASSICAL SCIENCE </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0002"> <b>BOOK + II. THE BEGINNINGS OF MODERN SCIENCE</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0003"> + I. SCIENCE IN THE DARK AGE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0004"> + II. MEDIAEVAL SCIENCE AMONG THE ARABIANS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0005"> + III. MEDIAEVAL SCIENCE IN THE WEST </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0006"> + IV. THE NEW COSMOLOGY—COPERNICUS TO KEPLER AND GALILEO </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0007"> + V. GALILEO AND THE NEW PHYSICS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0008"> + VI. TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0009"> + VII. FROM PARACELSUS TO HARVEY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0010"> + VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0011"> + IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0012"> + X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0013"> + XI. NEWTON AND THE COMPOSITION OF LIGHT </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0014"> + XII. NEWTON AND THE LAW OF GRAVITATION </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0015"> + XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0016"> + XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO + FRANKLIN </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0017"> + XV. NATURAL HISTORY TO THE TIME OF LINNAEUS </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0001"> <b>BOOK + III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0002"> + I. THE SUCCESSORS OF NEWTON IN ASTRONOMY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0003"> + II. THE PROGRESS OF MODERN ASTRONOMY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0004"> + III. THE NEW SCIENCE OF PALEONTOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0005"> + IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0006"> + V. THE NEW SCIENCE OF METEOROLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0007"> + VI. MODERN THEORIES OF HEAT AND LIGHT </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0008"> + VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0009"> + VIII. THE CONSERVATION OF ENERGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0010"> + IX. THE ETHER AND PONDERABLE MATTER </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0001"> <b>BOOK + IV. MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0002"> + I. THE PHLOGISTON THEORY IN CHEMISTRY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0003"> + II. THE BEGINNINGS OF MODERN CHEMISTRY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0004"> + III. CHEMISTRY SINCE THE TIME OF DALTON </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0005"> + IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0006"> + V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0007"> + VI. THEORIES OF ORGANIC EVOLUTION </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0008"> + VII. EIGHTEENTH-CENTURY MEDICINE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0009"> + VIII. NINETEENTH-CENTURY MEDICINE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0010"> + IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0011"> + X. THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0001"> + <b>BOOK V. ASPECTS OF RECENT SCIENCE</b> </a><br /> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0003"> + I. THE BRITISH MUSEUM </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0004"> + II. THE ROYAL SOCIETY OF LONDON FOR IMPROVING NATURAL KNOWLEDGE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0005"> + III. THE ROYAL INSTITUTION AND THE LOW-TEMPERATURE RESEARCHES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0006"> + IV. SOME PHYSICAL LABORATORIES AND PHYSICAL PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0007"> + V. THE MARINE BIOLOGICAL LABORATORY AT NAPLES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0008"> + VI. ERNST HAECKEL AND THE NEW ZOOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0009"> + VII. SOME MEDICAL LABORATORIES AND MEDICAL PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0010"> + VII. SOME UNSOLVED SCIENTIFIC PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0011"> + IX. RETROSPECT AND PROSPECT </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> +<pre xml:space="preserve"> + + + + + +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-h.htm or 1706-h.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, and David Widger + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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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. 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WILLIAMS, M.D. + +IN FIVE VOLUMES +VOLUME II. + + + + +CONTENTS + +BOOK II + +CHAPTER I. SCIENCE IN THE DARK AGE + +CHAPTER II. MEDIAEVAL SCIENCE AMONG THE ARABIANS + +CHAPTER III. MEDIAEVAL SCIENCE IN THE WEST + +CHAPTER IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +CHAPTER V. GALILEO AND THE NEW PHYSICS + +CHAPTER VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +CHAPTER VII. FROM PARACELSUS TO HARVEY + +CHAPTER VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +CHAPTER IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF +LEARNING + +CHAPTER X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +CHAPTER XI. NEWTON AND THE COMPOSITION OF LIGHT + +CHAPTER XII. NEWTON AND THE LAW OF GRAVITATION + +CHAPTER XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON + +CHAPTER XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON +GUERICKE TO FRANKLIN + +CHAPTER XV. NATURAL HISTORY TO THE TIME OF LINNAEUS + +APPENDIX + + + +A HISTORY OF SCIENCE + +BOOK II + +THE BEGINNINGS OF MODERN SCIENCE + +The studies of the present book cover the progress of science +from the close of the Roman period in the fifth century A.D. to +about the middle of the eighteenth century. In tracing the course +of events through so long a period, a difficulty becomes +prominent which everywhere besets the historian in less degree--a +difficulty due to the conflict between the strictly chronological +and the topical method of treatment. We must hold as closely as +possible to the actual sequence of events, since, as already +pointed out, one discovery leads on to another. But, on the other +hand, progressive steps are taken contemporaneously in the +various fields of science, and if we were to attempt to introduce +these in strict chronological order we should lose all sense of +topical continuity. + +Our method has been to adopt a compromise, following the course +of a single science in each great epoch to a convenient +stopping-point, and then turning back to bring forward the story +of another science. Thus, for example, we tell the story of +Copernicus and Galileo, bringing the record of cosmical and +mechanical progress down to about the middle of the seventeenth +century, before turning back to take up the physiological +progress of the fifteenth and sixteenth centuries. Once the +latter stream is entered, however, we follow it without +interruption to the time of Harvey and his contemporaries in the +middle of the seventeenth century, where we leave it to return to +the field of mechanics as exploited by the successors of Galileo, +who were also the predecessors and contemporaries of Newton. + +In general, it will aid the reader to recall that, so far as +possible, we hold always to the same sequences of topical +treatment of contemporary events; as a rule we treat first the +cosmical, then the physical, then the biological sciences. The +same order of treatment will be held to in succeeding volumes. + +Several of the very greatest of scientific generalizations are +developed in the period covered by the present book: for example, +the Copernican theory of the solar system, the true doctrine of +planetary motions, the laws of motion, the theory of the +circulation of the blood, and the Newtonian theory of +gravitation. The labors of the investigators of the early decades +of the eighteenth century, terminating with Franklin's discovery +of the nature of lightning and with the Linnaean classification +of plants and animals, bring us to the close of our second great +epoch; or, to put it otherwise, to the threshold of the modern +period, + + +I. SCIENCE IN THE DARK AGE + +An obvious distinction between the classical and mediaeval epochs +may be found in the fact that the former produced, whereas the +latter failed to produce, a few great thinkers in each generation +who were imbued with that scepticism which is the foundation of +the investigating spirit; who thought for themselves and supplied +more or less rational explanations of observed phenomena. Could +we eliminate the work of some score or so of classical observers +and thinkers, the classical epoch would seem as much a dark age +as does the epoch that succeeded it. + +But immediately we are met with the question: Why do no great +original investigators appear during all these later centuries? +We have already offered a part explanation in the fact that the +borders of civilization, where racial mingling naturally took +place, were peopled with semi-barbarians. But we must not forget +that in the centres of civilization all along there were many men +of powerful intellect. Indeed, it would violate the principle of +historical continuity to suppose that there was any sudden change +in the level of mentality of the Roman world at the close of the +classical period. We must assume, then, that the direction in +which the great minds turned was for some reason changed. Newton +is said to have alleged that he made his discoveries by +"intending" his mind in a certain direction continuously. It is +probable that the same explanation may be given of almost every +great scientific discovery. Anaxagoras could not have thought out +the theory of the moon's phases; Aristarchus could not have found +out the true mechanism of the solar system; Eratosthenes could +not have developed his plan for measuring the earth, had not each +of these investigators "intended" his mind persistently towards +the problems in question. + +Nor can we doubt that men lived in every generation of the dark +age who were capable of creative thought in the field of science, +bad they chosen similarly to "intend" their minds in the right +direction. The difficulty was that they did not so choose. Their +minds had a quite different bent. They were under the spell of +different ideals; all their mental efforts were directed into +different channels. What these different channels were cannot be +in doubt--they were the channels of oriental ecclesiasticism. One +all-significant fact speaks volumes here. It is the fact that, as +Professor Robinson[1] points out, from the time of Boethius (died +524 or 525 A.D.) to that of Dante (1265-1321 A.D.) there was not +a single writer of renown in western Europe who was not a +professional churchman. All the learning of the time, then, +centred in the priesthood. We know that the same condition of +things pertained in Egypt, when science became static there. But, +contrariwise, we have seen that in Greece and early Rome the +scientific workers were largely physicians or professional +teachers; there was scarcely a professional theologian among +them. + +Similarly, as we shall see in the Arabic world, where alone there +was progress in the mediaeval epoch, the learned men were, for +the most part, physicians. Now the meaning of this must be +self-evident. The physician naturally "intends" his mind towards +the practicalities. His professional studies tend to make him an +investigator of the operations of nature. He is usually a +sceptic, with a spontaneous interest in practical science. But +the theologian "intends" his mind away from practicalities and +towards mysticism. He is a professional believer in the +supernatural; he discounts the value of merely "natural" +phenomena. His whole attitude of mind is unscientific; the +fundamental tenets of his faith are based on alleged occurrences +which inductive science cannot admit--namely, miracles. And so +the minds "intended" towards the supernatural achieved only the +hazy mysticism of mediaeval thought. Instead of investigating +natural laws, they paid heed (as, for example, Thomas Aquinas +does in his Summa Theologia) to the "acts of angels," the +"speaking of angels," the "subordination of angels," the "deeds +of guardian angels," and the like. They disputed such important +questions as, How many angels can stand upon the point of a +needle? They argued pro and con as to whether Christ were coeval +with God, or whether he had been merely created "in the +beginning," perhaps ages before the creation of the world. How +could it be expected that science should flourish when the +greatest minds of the age could concern themselves with problems +such as these? + +Despite our preconceptions or prejudices, there can be but one +answer to that question. Oriental superstition cast its blight +upon the fair field of science, whatever compensation it may or +may not have brought in other fields. But we must be on our guard +lest we overestimate or incorrectly estimate this influence. +Posterity, in glancing backward, is always prone to stamp any +given age of the past with one idea, and to desire to +characterize it with a single phrase; whereas in reality all ages +are diversified, and any generalization regarding an epoch is +sure to do that epoch something less or something more than +justice. We may be sure, then, that the ideal of ecclesiasticism +is not solely responsible for the scientific stasis of the dark +age. Indeed, there was another influence of a totally different +character that is too patent to be overlooked--the influence, +namely, of the economic condition of western Europe during this +period. As I have elsewhere pointed out,[2] Italy, the centre of +western civilization, was at this time impoverished, and hence +could not provide the monetary stimulus so essential to artistic +and scientific no less than to material progress. There were no +patrons of science and literature such as the Ptolemies of that +elder Alexandrian day. There were no great libraries; no colleges +to supply opportunities and afford stimuli to the rising +generation. Worst of all, it became increasingly difficult to +secure books. + +This phase of the subject is often overlooked. Yet a moment's +consideration will show its importance. How should we fare to-day +if no new scientific books were being produced, and if the +records of former generations were destroyed? That is what +actually happened in Europe during the Middle Ages. At an earlier +day books were made and distributed much more abundantly than is +sometimes supposed. Bookmaking had, indeed, been an important +profession in Rome, the actual makers of books being slaves who +worked under the direction of a publisher. It was through the +efforts of these workers that the classical works in Greek and +Latin were multiplied and disseminated. Unfortunately the climate +of Europe does not conduce to the indefinite preservation of a +book; hence very few remnants of classical works have come down +to us in the original from a remote period. The rare exceptions +are certain papyrus fragments, found in Egypt, some of which are +Greek manuscripts dating from the third century B.C. Even from +these sources the output is meagre; and the only other repository +of classical books is a single room in the buried city of +Herculaneum, which contained several hundred manuscripts, mostly +in a charred condition, a considerable number of which, however, +have been unrolled and found more or less legible. This library +in the buried city was chiefly made up of philosophical works, +some of which were quite unknown to the modern world until +discovered there. + +But this find, interesting as it was from an archaeological +stand-point, had no very important bearing on our knowledge of +the literature of antiquity. Our chief dependence for our +knowledge of that literature must still be placed in such copies +of books as were made in the successive generations. +Comparatively few of the extant manuscripts are older than the +tenth century of our era. It requires but a momentary +consideration of the conditions under which ancient books were +produced to realize how slow and difficult the process was before +the invention of printing. The taste of the book-buying public +demanded a clearly written text, and in the Middle Ages it became +customary to produce a richly ornamented text as well. The script +employed being the prototype of the modern printed text, it will +be obvious that a scribe could produce but a few pages at best in +a day. A large work would therefore require the labor of a scribe +for many months or even for several years. We may assume, then, +that it would be a very flourishing publisher who could produce a +hundred volumes all told per annum; and probably there were not +many publishers at any given time, even in the period of Rome's +greatest glory, who had anything like this output. + +As there was a large number of authors in every generation of the +classical period, it follows that most of these authors must have +been obliged to content themselves with editions numbering very +few copies; and it goes without saying that the greater number of +books were never reproduced in what might be called a second +edition. Even books that retained their popularity for several +generations would presently fail to arouse sufficient interest to +be copied; and in due course such works would pass out of +existence altogether. Doubtless many hundreds of books were thus +lost before the close of the classical period, the names of their +authors being quite forgotten, or preserved only through a chance +reference; and of course the work of elimination went on much +more rapidly during the Middle Ages, when the interest in +classical literature sank to so low an ebb in the West. Such +collections of references and quotations as the Greek Anthology +and the famous anthologies of Stobaeus and Athanasius and +Eusebius give us glimpses of a host of writers--more than seven +hundred are quoted by Stobaeus--a very large proportion of whom +are quite unknown except through these brief excerpts from their +lost works. + +Quite naturally the scientific works suffered at least as largely +as any others in an age given over to ecclesiastical dreamings. +Yet in some regards there is matter for surprise as to the works +preserved. Thus, as we have seen, the very extensive works of +Aristotle on natural history, and the equally extensive natural +history of Pliny, which were preserved throughout this period, +and are still extant, make up relatively bulky volumes. These +works seem to have interested the monks of the Middle Ages, while +many much more important scientific books were allowed to perish. +A considerable bulk of scientific literature was also preserved +through the curious channels of Arabic and Armenian translations. +Reference has already been made to the Almagest of Ptolemy, +which, as we have seen, was translated into Arabic, and which was +at a later day brought by the Arabs into western Europe and (at +the instance of Frederick II of Sicily) translated out of their +language into mediaeval Latin. + +It remains to inquire, however, through what channels the Greek +works reached the Arabs themselves. To gain an answer to this +question we must follow the stream of history from its Roman +course eastward to the new seat of the Roman empire in Byzantium. +Here civilization centred from about the fifth century A.D., and +here the European came in contact with the civilization of the +Syrians, the Persians, the Armenians, and finally of the Arabs. +The Byzantines themselves, unlike the inhabitants of western +Europe, did not ignore the literature of old Greece; the Greek +language became the regular speech of the Byzantine people, and +their writers made a strenuous effort to perpetuate the idiom and +style of the classical period. Naturally they also made +transcriptions of the classical authors, and thus a great mass of +literature was preserved, while the corresponding works were +quite forgotten in western Europe. + +Meantime many of these works were translated into Syriac, +Armenian, and Persian, and when later on the Byzantine +civilization degenerated, many works that were no longer to be +had in the Greek originals continued to be widely circulated in +Syriac, Persian, Armenian, and, ultimately, in Arabic +translations. When the Arabs started out in their conquests, +which carried them through Egypt and along the southern coast of +the Mediterranean, until they finally invaded Europe from the +west by way of Gibraltar, they carried with them their +translations of many a Greek classical author, who was introduced +anew to the western world through this strange channel. + +We are told, for example, that Averrhoes, the famous commentator +of Aristotle, who lived in Spain in the twelfth century, did not +know a word of Greek and was obliged to gain his knowledge of the +master through a Syriac translation; or, as others alleged +(denying that he knew even Syriac), through an Arabic version +translated from the Syriac. We know, too, that the famous +chronology of Eusebius was preserved through an Armenian +translation; and reference has more than once been made to the +Arabic translation of Ptolemy's great work, to which we still +apply its Arabic title of Almagest. + +The familiar story that when the Arabs invaded Egypt they burned +the Alexandrian library is now regarded as an invention of later +times. It seems much more probable that the library bad been +largely scattered before the coming of the Moslems. Indeed, it +has even been suggested that the Christians of an earlier day +removed the records of pagan thought. Be that as it may, the +famous Alexandrian library had disappeared long before the +revival of interest in classical learning. Meanwhile, as we have +said, the Arabs, far from destroying the western literature, were +its chief preservers. Partly at least because of their regard for +the records of the creative work of earlier generations of alien +peoples, the Arabs were enabled to outstrip their contemporaries. +For it cannot be in doubt that, during that long stretch of time +when the western world was ignoring science altogether or at most +contenting itself with the casual reading of Aristotle and Pliny, +the Arabs had the unique distinction of attempting original +investigations in science. To them were due all important +progressive steps which were made in any scientific field +whatever for about a thousand years after the time of Ptolemy and +Galen. The progress made even by the Arabs during this long +period seems meagre enough, yet it has some significant features. +These will now demand our attention. + + + +II. MEDIAEVAL SCIENCE AMONG THE ARABIANS + +The successors of Mohammed showed themselves curiously receptive +of the ideas of the western people whom they conquered. They came +in contact with the Greeks in western Asia and in Egypt, and, as +has been said, became their virtual successors in carrying +forward the torch of learning. It must not be inferred, however, +that the Arabian scholars, as a class, were comparable to their +predecessors in creative genius. On the contrary, they retained +much of the conservative oriental spirit. They were under the +spell of tradition, and, in the main, what they accepted from the +Greeks they regarded as almost final in its teaching. There were, +however, a few notable exceptions among their men of science, and +to these must be ascribed several discoveries of some importance. + +The chief subjects that excited the interest and exercised the +ingenuity of the Arabian scholars were astronomy, mathematics, +and medicine. The practical phases of all these subjects were +given particular attention. Thus it is well known that our +so-called Arabian numerals date from this period. The +revolutionary effect of these characters, as applied to practical +mathematics, can hardly be overestimated; but it is generally +considered, and in fact was admitted by the Arabs themselves, +that these numerals were really borrowed from the Hindoos, with +whom the Arabs came in contact on the east. Certain of the Hindoo +alphabets, notably that of the Battaks of Sumatra, give us clews +to the originals of the numerals. It does not seem certain, +however, that the Hindoos employed these characters according to +the decimal system, which is the prime element of their +importance. Knowledge is not forthcoming as to just when or by +whom such application was made. If this was an Arabic innovation, +it was perhaps the most important one with which that nation is +to be credited. Another mathematical improvement was the +introduction into trigonometry of the sine--the half-chord of the +double arc--instead of the chord of the arc itself which the +Greek astronomers had employed. This improvement was due to the +famous Albategnius, whose work in other fields we shall examine +in a moment. + +Another evidence of practicality was shown in the Arabian method +of attempting to advance upon Eratosthenes' measurement of the +earth. Instead of trusting to the measurement of angles, the +Arabs decided to measure directly a degree of the earth's +surface--or rather two degrees. Selecting a level plain in +Mesopotamia for the experiment, one party of the surveyors +progressed northward, another party southward, from a given point +to the distance of one degree of arc, as determined by +astronomical observations. The result found was fifty-six miles +for the northern degree, and fifty-six and two-third miles for +the southern. Unfortunately, we do not know the precise length of +the mile in question, and therefore cannot be assured as to the +accuracy of the measurement. It is interesting to note, however, +that the two degrees were found of unequal lengths, suggesting +that the earth is not a perfect sphere--a suggestion the validity +of which was not to be put to the test of conclusive measurements +until about the close of the eighteenth century. The Arab +measurement was made in the time of Caliph Abdallah al-Mamun, the +son of the famous Harun-al-Rashid. Both father and son were +famous for their interest in science. Harun-al-Rashid was, it +will be recalled, the friend of Charlemagne. It is said that he +sent that ruler, as a token of friendship, a marvellous clock +which let fall a metal ball to mark the hours. This mechanism, +which is alleged to have excited great wonder in the West, +furnishes yet another instance of Arabian practicality. + +Perhaps the greatest of the Arabian astronomers was Mohammed ben +Jabir Albategnius, or El-batani, who was born at Batan, in +Mesopotamia, about the year 850 A.D., and died in 929. +Albategnius was a student of the Ptolemaic astronomy, but he was +also a practical observer. He made the important discovery of the +motion of the solar apogee. That is to say, he found that the +position of the sun among the stars, at the time of its greatest +distance from the earth, was not what it had been in the time of +Ptolemy. The Greek astronomer placed the sun in longitude 65 +degrees, but Albategnius found it in longitude 82 degrees, a +distance too great to be accounted for by inaccuracy of +measurement. The modern inference from this observation is that +the solar system is moving through space; but of course this +inference could not well be drawn while the earth was regarded as +the fixed centre of the universe. + +In the eleventh century another Arabian discoverer, Arzachel, +observing the sun to be less advanced than Albategnius had found +it, inferred incorrectly that the sun had receded in the mean +time. The modern explanation of this observation is that the +measurement of Albategnius was somewhat in error, since we know +that the sun's motion is steadily progressive. Arzachel, however, +accepting the measurement of his predecessor, drew the false +inference of an oscillatory motion of the stars, the idea of the +motion of the solar system not being permissible. This assumed +phenomenon, which really has no existence in point of fact, was +named the "trepidation of the fixed stars," and was for centuries +accepted as an actual phenomenon. Arzachel explained this +supposed phenomenon by assuming that the equinoctial points, or +the points of intersection of the equator and the ecliptic, +revolve in circles of eight degrees' radius. The first points of +Aries and Libra were supposed to describe the circumference of +these circles in about eight hundred years. All of which +illustrates how a difficult and false explanation may take the +place of a simple and correct one. The observations of later +generations have shown conclusively that the sun's shift of +position is regularly progressive, hence that there is no +"trepidation" of the stars and no revolution of the equinoctial +points. + +If the Arabs were wrong as regards this supposed motion of the +fixed stars, they made at least one correct observation as to the +inequality of motion of the moon. Two inequalities of the motion +of this body were already known. A third, called the moon's +variation, was discovered by an Arabian astronomer who lived at +Cairo and observed at Bagdad in 975, and who bore the formidable +name of Mohammed Aboul Wefaal-Bouzdjani. The inequality of motion +in question, in virtue of which the moon moves quickest when she +is at new or full, and slowest at the first and third quarter, +was rediscovered by Tycho Brahe six centuries later; a fact which +in itself evidences the neglect of the Arabian astronomer's +discovery by his immediate successors. + +In the ninth and tenth centuries the Arabian city of Cordova, in +Spain, was another important centre of scientific influence. +There was a library of several hundred thousand volumes here, and +a college where mathematics and astronomy were taught. Granada, +Toledo, and Salamanca were also important centres, to which +students flocked from western Europe. It was the proximity of +these Arabian centres that stimulated the scientific interests of +Alfonso X. of Castile, at whose instance the celebrated Alfonsine +tables were constructed. A familiar story records that Alfonso, +pondering the complications of the Ptolemaic cycles and +epicycles, was led to remark that, had he been consulted at the +time of creation, he could have suggested a much better and +simpler plan for the universe. Some centuries were to elapse +before Copernicus was to show that it was not the plan of the +universe, but man's interpretation of it, that was at fault. + +Another royal personage who came under Arabian influence was +Frederick II. of Sicily--the "Wonder of the World," as he was +called by his contemporaries. The Almagest of Ptolemy was +translated into Latin at his instance, being introduced to the +Western world through this curious channel. At this time it +became quite usual for the Italian and Spanish scholars to +understand Arabic although they were totally ignorant of Greek. + +In the field of physical science one of the most important of the +Arabian scientists was Alhazen. His work, published about the +year 1100 A.D., had great celebrity throughout the mediaeval +period. The original investigations of Alhazen had to do largely +with optics. He made particular studies of the eye itself, and +the names given by him to various parts of the eye, as the +vitreous humor, the cornea, and the retina, are still retained by +anatomists. It is known that Ptolemy had studied the refraction +of light, and that he, in common with his immediate predecessors, +was aware that atmospheric refraction affects the apparent +position of stars near the horizon. Alhazen carried forward these +studies, and was led through them to make the first recorded +scientific estimate of the phenomena of twilight and of the +height of the atmosphere. The persistence of a glow in the +atmosphere after the sun has disappeared beneath the horizon is +so familiar a phenomenon that the ancient philosophers seem not +to have thought of it as requiring an explanation. Yet a moment's +consideration makes it clear that, if light travels in straight +lines and the rays of the sun were in no wise deflected, the +complete darkness of night should instantly succeed to day when +the sun passes below the horizon. That this sudden change does +not occur, Alhazen explained as due to the reflection of light by +the earth's atmosphere. + +Alhazen appears to have conceived the atmosphere as a sharply +defined layer, and, assuming that twilight continues only so long +as rays of the sun reflected from the outer surface of this layer +can reach the spectator at any given point, he hit upon a means +of measurement that seemed to solve the hitherto inscrutable +problem as to the atmospheric depth. Like the measurements of +Aristarchus and Eratosthenes, this calculation of Alhazen is +simple enough in theory. Its defect consists largely in the +difficulty of fixing its terms with precision, combined with the +further fact that the rays of the sun, in taking the slanting +course through the earth's atmosphere, are really deflected from +a straight line in virtue of the constantly increasing density of +the air near the earth's surface. Alhazen must have been aware of +this latter fact, since it was known to the later Alexandrian +astronomers, but he takes no account of it in the present +measurement. The diagram will make the method of Alhazen clear. + +His important premises are two: first, the well-recognized fact +that, when light is reflected from any surface, the angle of +incidence is equal to the angle of reflection; and, second, the +much more doubtful observation that twilight continues until such +time as the sun, according to a simple calculation, is nineteen +degrees below the horizon. Referring to the diagram, let the +inner circle represent the earth's surface, the outer circle the +limits of the atmosphere, C being the earth's centre, and RR +radii of the earth. Then the observer at the point A will +continue to receive the reflected rays of the sun until that body +reaches the point S, which is, according to the hypothesis, +nineteen degrees below the horizon line of the observer at A. +This horizon line, being represented by AH, and the sun's ray by +SM, the angle HMS is an angle of nineteen degrees. The +complementary angle SMA is, obviously, an angle of (180-19) one +hundred and sixty-one degrees. But since M is the reflecting +surface and the angle of incidence equals the angle of +reflection, the angle AMC is an angle of one-half of one hundred +and sixty-one degrees, or eighty degrees and thirty minutes. Now +this angle AMC, being known, the right-angled triangle MAC is +easily resolved, since the side AC of that triangle, being the +radius of the earth, is a known dimension. Resolution of this +triangle gives us the length of the hypotenuse MC, and the +difference between this and the radius (AC), or CD, is obviously +the height of the atmosphere (h), which was the measurement +desired. According to the calculation of Alhazen, this h, or the +height of the atmosphere, represents from twenty to thirty miles. +The modern computation extends this to about fifty miles. But, +considering the various ambiguities that necessarily attended the +experiment, the result was a remarkably close approximation to +the truth. + +Turning from physics to chemistry, we find as perhaps the +greatest Arabian name that of Geber, who taught in the College of +Seville in the first half of the eighth century. The most +important researches of this really remarkable experimenter had +to do with the acids. The ancient world had had no knowledge of +any acid more powerful than acetic. Geber, however, vastly +increased the possibilities of chemical experiment by the +discovery of sulphuric, nitric, and nitromuriatic acids. He made +use also of the processes of sublimation and filtration, and his +works describe the water bath and the chemical oven. Among the +important chemicals which he first differentiated is oxide of +mercury, and his studies of sulphur in its various compounds have +peculiar interest. In particular is this true of his observation +that, tinder certain conditions of oxidation, the weight of a +metal was lessened. + +From the record of these studies in the fields of astronomy, +physics, and chemistry, we turn to a somewhat extended survey of +the Arabian advances in the field of medicine. + + +ARABIAN MEDICINE + +The influence of Arabian physicians rested chiefly upon their use +of drugs rather than upon anatomical knowledge. Like the +mediaeval Christians, they looked with horror on dissection of +the human body; yet there were always among them investigators +who turned constantly to nature herself for hidden truths, and +were ready to uphold the superiority of actual observation to +mere reading. Thus the physician Abd el-Letif, while in Egypt, +made careful studies of a mound of bones containing more than +twenty thousand skeletons. While examining these bones he +discovered that the lower jaw consists of a single bone, not of +two, as had been taught by Galen. He also discovered several +other important mistakes in Galenic anatomy, and was so impressed +with his discoveries that he contemplated writing a work on +anatomy which should correct the great classical authority's +mistakes. + +It was the Arabs who invented the apothecary, and their +pharmacopoeia, issued from the hospital at Gondisapor, and +elaborated from time to time, formed the basis for Western +pharmacopoeias. Just how many drugs originated with them, and how +many were borrowed from the Hindoos, Jews, Syrians, and Persians, +cannot be determined. It is certain, however, that through them +various new and useful drugs, such as senna, aconite, rhubarb, +camphor, and mercury, were handed down through the Middle Ages, +and that they are responsible for the introduction of alcohol in +the field of therapeutics. + +In mediaeval Europe, Arabian science came to be regarded with +superstitious awe, and the works of certain Arabian physicians +were exalted to a position above all the ancient writers. In +modern times, however, there has been a reaction and a tendency +to depreciation of their work. By some they are held to be mere +copyists or translators of Greek books, and in no sense original +investigators in medicine. Yet there can be little doubt that +while the Arabians did copy and translate freely, they also +originated and added considerably to medical knowledge. It is +certain that in the time when Christian monarchs in western +Europe were paying little attention to science or education, the +caliphs and vizirs were encouraging physicians and philosophers, +building schools, and erecting libraries and hospitals. They made +at least a creditable effort to uphold and advance upon the +scientific standards of an earlier age. + +The first distinguished Arabian physician was Harets ben Kaladah, +who received his education in the Nestonian school at Gondisapor, +about the beginning of the seventh century. Notwithstanding the +fact that Harets was a Christian, he was chosen by Mohammed as +his chief medical adviser, and recommended as such to his +successor, the Caliph Abu Bekr. Thus, at the very outset, the +science of medicine was divorced from religion among the +Arabians; for if the prophet himself could employ the services of +an unbeliever, surely others might follow his example. And that +this example was followed is shown in the fact that many +Christian physicians were raised to honorable positions by +succeeding generations of Arabian monarchs. This broad-minded +view of medicine taken by the Arabs undoubtedly assisted as much +as any one single factor in upbuilding the science, just as the +narrow and superstitious view taken by Western nations helped to +destroy it. + +The education of the Arabians made it natural for them to +associate medicine with the natural sciences, rather than with +religion. An Arabian savant was supposed to be equally well +educated in philosophy, jurisprudence, theology, mathematics, and +medicine, and to practise law, theology, and medicine with equal +skill upon occasion. It is easy to understand, therefore, why +these religious fanatics were willing to employ unbelieving +physicians, and their physicians themselves to turn to the +scientific works of Hippocrates and Galen for medical +instruction, rather than to religious works. Even Mohammed +himself professed some knowledge of medicine, and often relied +upon this knowledge in treating ailments rather than upon prayers +or incantations. He is said, for example, to have recommended and +applied the cautery in the case of a friend who, when suffering +from angina, had sought his aid. + +The list of eminent Arabian physicians is too long to be given +here, but some of them are of such importance in their influence +upon later medicine that they cannot be entirely ignored. One of +the first of these was Honain ben Isaac (809-873 A.D.), a +Christian Arab of Bagdad. He made translations of the works of +Hippocrates, and practised the art along the lines indicated by +his teachings and those of Galen. He is considered the greatest +translator of the ninth century and one of the greatest +philosophers of that period. + +Another great Arabian physician, whose work was just beginning as +Honain's was drawing to a close, was Rhazes (850-923 A.D.), who +during his life was no less noted as a philosopher and musician +than as a physician. He continued the work of Honain, and +advanced therapeutics by introducing more extensive use of +chemical remedies, such as mercurial ointments, sulphuric acid, +and aqua vitae. He is also credited with being the first +physician to describe small-pox and measles accurately. + +While Rhazes was still alive another Arabian, Haly Abbas (died +about 994), was writing his famous encyclopaedia of medicine, +called The Royal Book. But the names of all these great +physicians have been considerably obscured by the reputation of +Avicenna (980-1037), the Arabian "Prince of Physicians," the +greatest name in Arabic medicine, and one of the most remarkable +men in history. Leclerc says that "he was perhaps never surpassed +by any man in brilliancy of intellect and indefatigable +activity." His career was a most varied one. He was at all times +a boisterous reveller, but whether flaunting gayly among the +guests of an emir or biding in some obscure apothecary cellar, +his work of philosophical writing was carried on steadily. When a +friendly emir was in power, he taught and wrote and caroused at +court; but between times, when some unfriendly ruler was supreme, +he was hiding away obscurely, still pouring out his great mass of +manuscripts. In this way his entire life was spent. + +By his extensive writings he revived and kept alive the best of +the teachings of the Greek physicians, adding to them such +observations as he had made in anatomy, physiology, and materia +medica. Among his discoveries is that of the contagiousness of +pulmonary tuberculosis. His works for several centuries continued +to be looked upon as the highest standard by physicians, and he +should undoubtedly be credited with having at least retarded the +decline of mediaeval medicine. + +But it was not the Eastern Arabs alone who were active in the +field of medicine. Cordova, the capital of the western caliphate, +became also a great centre of learning and produced several great +physicians. One of these, Albucasis (died in 1013 A.D.), is +credited with having published the first illustrated work on +surgery, this book being remarkable in still another way, in that +it was also the first book, since classical times, written from +the practical experience of the physician, and not a mere +compilation of ancient authors. A century after Albucasis came +the great physician Avenzoar (1113-1196), with whom he divides +about equally the medical honors of the western caliphate. Among +Avenzoar's discoveries was that of the cause of "itch"--a little +parasite, "so small that he is hardly visible." The discovery of +the cause of this common disease seems of minor importance now, +but it is of interest in medical history because, had Avenzoar's +discovery been remembered a hundred years ago, "itch struck in" +could hardly have been considered the cause of three-fourths of +all diseases, as it was by the famous Hahnemann. + +The illustrious pupil of Avenzoar, Averrhoes, who died in 1198 +A.D., was the last of the great Arabian physicians who, by +rational conception of medicine, attempted to stem the flood of +superstition that was overwhelming medicine. For a time he +succeeded; but at last the Moslem theologians prevailed, and he +was degraded and banished to a town inhabited only by the +despised Jews. + + +ARABIAN HOSPITALS + +To early Christians belong the credit of having established the +first charitable institutions for caring for the sick; but their +efforts were soon eclipsed by both Eastern and Western +Mohammedans. As early as the eighth century the Arabs had begun +building hospitals, but the flourishing time of hospital building +seems to have begun early in the tenth century. Lady Seidel, in +918 A.D., opened a hospital at Bagdad, endowed with an amount +corresponding to about three hundred pounds sterling a month. +Other similar hospitals were erected in the years immediately +following, and in 977 the Emir Adad-adaula established an +enormous institution with a staff of twenty-four medical +officers. The great physician Rhazes is said to have selected the +site for one of these hospitals by hanging pieces of meat in +various places about the city, selecting the site near the place +at which putrefaction was slowest in making its appearance. By +the middle of the twelfth century there were something like sixty +medical institutions in Bagdad alone, and these institutions were +free to all patients and supported by official charity. + +The Emir Nureddin, about the year 1160, founded a great hospital +at Damascus, as a thank-offering for his victories over the +Crusaders. This great institution completely overshadowed all the +earlier Moslem hospitals in size and in the completeness of its +equipment. It was furnished with facilities for teaching, and was +conducted for several centuries in a lavish manner, regardless of +expense. But little over a century after its foundation the fame +of its methods of treatment led to the establishment of a larger +and still more luxurious institution--the Mansuri hospital at +Cairo. It seems that a certain sultan, having been cured by +medicines from the Damascene hospital, determined to build one of +his own at Cairo which should eclipse even the great Damascene +institution. + +In a single year (1283-1284) this hospital was begun and +completed. No efforts were spared in hurrying on the good work, +and no one was exempt from performing labor on the building if he +chanced to pass one of the adjoining streets. It was the order of +the sultan that any person passing near could be impressed into +the work, and this order was carried out to the letter, noblemen +and beggars alike being forced to lend a hand. Very naturally, +the adjacent thoroughfares became unpopular and practically +deserted, but still the holy work progressed rapidly and was +shortly completed. + +This immense structure is said to have contained four courts, +each having a fountain in the centre; lecture-halls, wards for +isolating certain diseases, and a department that corresponded to +the modern hospital's "out-patient" department. The yearly +endowment amounted to something like the equivalent of one +hundred and twenty-five thousand dollars. A novel feature was a +hall where musicians played day and night, and another where +story-tellers were employed, so that persons troubled with +insomnia were amused and melancholiacs cheered. Those of a +religious turn of mind could listen to readings of the Koran, +conducted continuously by a staff of some fifty chaplains. Each +patient on leaving the hospital received some gold pieces, that +he need not be obliged to attempt hard labor at once. + +In considering the astonishing tales of these sumptuous Arabian +institutions, it should be borne in mind that our accounts of +them are, for the most part, from Mohammedan sources. +Nevertheless, there can be little question that they were +enormous institutions, far surpassing any similar institutions in +western Europe. The so-called hospitals in the West were, at this +time, branches of monasteries under supervision of the monks, and +did not compare favorably with the Arabian hospitals. + +But while the medical science of the Mohammedans greatly +overshadowed that of the Christians during this period, it did +not completely obliterate it. About the year 1000 A.D. came into +prominence the Christian medical school at Salerno, situated on +the Italian coast, some thirty miles southeast of Naples. Just +how long this school had been in existence, or by whom it was +founded, cannot be determined, but its period of greatest +influence was the eleventh, twelfth, and thirteenth centuries. +The members of this school gradually adopted Arabic medicine, +making use of many drugs from the Arabic pharmacopoeia, and this +formed one of the stepping-stones to the introduction of Arabian +medicine all through western Europe. + +It was not the adoption of Arabian medicines, however, that has +made the school at Salerno famous both in rhyme and prose, but +rather the fact that women there practised the healing art. +Greatest among them was Trotula, who lived in the eleventh +century, and whose learning is reputed to have equalled that of +the greatest physicians of the day. She is accredited with a work +on Diseases of Women, still extant, and many of her writings on +general medical subjects were quoted through two succeeding +centuries. If we may judge from these writings, she seemed to +have had many excellent ideas as to the proper methods of +treating diseases, but it is difficult to determine just which of +the writings credited to her are in reality hers. Indeed, the +uncertainty is even greater than this implies, for, according to +some writers, "Trotula" is merely the title of a book. Such an +authority as Malgaigne, however, believed that such a woman +existed, and that the works accredited to her are authentic. The +truth of the matter may perhaps never be fully established, but +this at least is certain--the tradition in regard to Trotula +could never have arisen had not women held a far different +position among the Arabians of this period from that accorded +them in contemporary Christendom. + + + +III. MEDIAEVAL SCIENCE IN THE WEST + +We have previously referred to the influence of the Byzantine +civilization in transmitting the learning of antiquity across the +abysm of the dark age. It must be admitted, however, that the +importance of that civilization did not extend much beyond the +task of the common carrier. There were no great creative +scientists in the later Roman empire of the East any more than in +the corresponding empire of the West. There was, however, one +field in which the Byzantine made respectable progress and +regarding which their efforts require a few words of special +comment. This was the field of medicine. + +The Byzantines of this time could boast of two great medical men, +Aetius of Amida (about 502-575 A.D.) and Paul of Aegina (about +620-690). The works of Aetius were of value largely because they +recorded the teachings of many of his eminent predecessors, but +he was not entirely lacking in originality, and was perhaps the +first physician to mention diphtheria, with an allusion to some +observations of the paralysis of the palate which sometimes +follows this disease. + +Paul of Aegina, who came from the Alexandrian school about a +century later, was one of those remarkable men whose ideas are +centuries ahead of their time. This was particularly true of Paul +in regard to surgery, and his attitude towards the supernatural +in the causation and treatment of diseases. He was essentially a +surgeon, being particularly familiar with military surgery, and +some of his descriptions of complicated and difficult operations +have been little improved upon even in modern times. In his books +he describes such operations as the removal of foreign bodies +from the nose, ear, and esophagus; and he recognizes foreign +growths such as polypi in the air-passages, and gives the method +of their removal. Such operations as tracheotomy, tonsellotomy, +bronchotomy, staphylotomy, etc., were performed by him, and he +even advocated and described puncture of the abdominal cavity, +giving careful directions as to the location in which such +punctures should be made. He advocated amputation of the breast +for the cure of cancer, and described extirpation of the uterus. +Just how successful this last operation may have been as +performed by him does not appear; but he would hardly have +recommended it if it had not been sometimes, at least, +successful. That he mentions it at all, however, is significant, +as this difficult operation is considered one of the great +triumphs of modern surgery. + +But Paul of Aegina is a striking exception to the rule among +Byzantine surgeons, and as he was their greatest, so he was also +their last important surgeon. The energies of all Byzantium were +so expended in religious controversies that medicine, like the +other sciences, was soon relegated to a place among the other +superstitions, and the influence of the Byzantine school was +presently replaced by that of the conquering Arabians. + + +THIRTEENTH-CENTURY MEDICINE + +The thirteenth century marks the beginning of a gradual change in +medicine, and a tendency to leave the time-worn rut of +superstitious dogmas that so long retarded the progress of +science. It is thought that the great epidemics which raged +during the Middle Ages acted powerfully in diverting the medical +thought of the times into new and entirely different channels. It +will be remembered that the teachings of Galen were handed +through mediaeval times as the highest and best authority on the +subject of all diseases. When, however, the great epidemics made +their appearance, the medical men appealed to the works of Galen +in vain for enlightenment, as these works, having been written +several centuries before the time of the plagues, naturally +contained no information concerning them. It was evident, +therefore, that on this subject, at least, Galen was not +infallible; and it would naturally follow that, one fallible +point having been revealed, others would be sought for. In other +words, scepticism in regard to accepted methods would be aroused, +and would lead naturally, as such scepticism usually does, to +progress. The devastating effects of these plagues, despite +prayers and incantations, would arouse doubt in the minds of many +as to the efficacy of superstitious rites and ceremonies in +curing diseases. They had seen thousands and tens of thousands of +their fellow-beings swept away by these awful scourges. They had +seen the ravages of these epidemics continue for months or even +years, notwithstanding the fact that multitudes of God-fearing +people prayed hourly that such ravages might be checked. And they +must have observed also that when even very simple rules of +cleanliness and hygiene were followed there was a diminution in +the ravages of the plague, even without the aid of incantations. +Such observations as these would have a tendency to awaken a +suspicion in the minds of many of the physicians that disease was +not a manifestation of the supernatural, but a natural +phenomenon, to be treated by natural methods. + +But, be the causes what they may, it is a fact that the +thirteenth century marks a turning-point, or the beginning of an +attitude of mind which resulted in bringing medicine to a much +more rational position. Among the thirteenth-century physicians, +two men are deserving of special mention. These are Arnald of +Villanova (1235-1312) and Peter of Abano (1250-1315). Both these +men suffered persecution for expressing their belief in natural, +as against the supernatural, causes of disease, and at one time +Arnald was obliged to flee from Barcelona for declaring that the +"bulls" of popes were human works, and that "acts of charity were +dearer to God than hecatombs." He was also accused of alchemy. +Fleeing from persecution, he finally perished by shipwreck. + +Arnald was the first great representative of the school of +Montpellier. He devoted much time to the study of chemicals, and +was active in attempting to re-establish the teachings of +Hippocrates and Galen. He was one of the first of a long line of +alchemists who, for several succeeding centuries, expended so +much time and energy in attempting to find the "elixir of life." +The Arab discovery of alcohol first deluded him into the belief +that the "elixir" had at last been found; but later he discarded +it and made extensive experiments with brandy, employing it in +the treatment of certain diseases--the first record of the +administration of this liquor as a medicine. Arnald also revived +the search for some anaesthetic that would produce insensibility +to pain in surgical operations. This idea was not original with +him, for since very early times physicians had attempted to +discover such an anaesthetic, and even so early a writer as +Herodotus tells how the Scythians, by inhalation of the vapors of +some kind of hemp, produced complete insensibility. It may have +been these writings that stimulated Arnald to search for such an +anaesthetic. In a book usually credited to him, medicines are +named and methods of administration described which will make the +patient insensible to pain, so that "he may be cut and feel +nothing, as though he were dead." For this purpose a mixture of +opium, mandragora, and henbane is to be used. This mixture was +held at the patient's nostrils much as ether and chloroform are +administered by the modern surgeon. The method was modified by +Hugo of Lucca (died in 1252 or 1268), who added certain other +narcotics, such as hemlock, to the mixture, and boiled a new +sponge in this decoction. After boiling for a certain time, this +sponge was dried, and when wanted for use was dipped in hot water +and applied to the nostrils. + +Just how frequently patients recovered from the administration of +such a combination of powerful poisons does not appear, but the +percentage of deaths must have been very high, as the practice +was generally condemned. Insensibility could have been produced +only by swallowing large quantities of the liquid, which dripped +into the nose and mouth when the sponge was applied, and a lethal +quantity might thus be swallowed. The method was revived, with +various modifications, from time to time, but as often fell into +disuse. As late as 1782 it was sometimes attempted, and in that +year the King of Poland is said to have been completely +anaesthetized and to have recovered, after a painless amputation +had been performed by the surgeons. + +Peter of Abano was one of the first great men produced by the +University of Padua. His fate would have been even more tragic +than that of the shipwrecked Arnald had he not cheated the +purifying fagots of the church by dying opportunely on the eve of +his execution for heresy. But if his spirit had cheated the +fanatics, his body could not, and his bones were burned for his +heresy. He had dared to deny the existence of a devil, and had +suggested that the case of a patient who lay in a trance for +three days might help to explain some miracles, like the raising +of Lazarus. + +His great work was Conciliator Differentiarum, an attempt to +reconcile physicians and philosophers. But his researches were +not confined to medicine, for he seems to have had an inkling of +the hitherto unknown fact that air possesses weight, and his +calculation of the length of the year at three hundred and +sixty-five days, six hours, and four minutes, is exceptionally +accurate for the age in which he lived. He was probably the first +of the Western writers to teach that the brain is the source of +the nerves, and the heart the source of the vessels. From this it +is seen that he was groping in the direction of an explanation of +the circulation of the blood, as demonstrated by Harvey three +centuries later. + +The work of Arnald and Peter of Abano in "reviving" medicine was +continued actively by Mondino (1276-1326) of Bologna, the +"restorer of anatomy," and by Guy of Chauliac: (born about 1300), +the "restorer of surgery." All through the early Middle Ages +dissections of human bodies had been forbidden, and even +dissection of the lower animals gradually fell into disrepute +because physicians detected in such practices were sometimes +accused of sorcery. Before the close of the thirteenth century, +however, a reaction had begun, physicians were protected, and +dissections were occasionally sanctioned by the ruling monarch. +Thus Emperor Frederick H. (1194-1250 A.D.)--whose services to +science we have already had occasion to mention--ordered that at +least one human body should be dissected by physicians in his +kingdom every five years. By the time of Mondino dissections were +becoming more frequent, and he himself is known to have dissected +and demonstrated several bodies. His writings on anatomy have +been called merely plagiarisms of Galen, but in all probability +be made many discoveries independently, and on the whole, his +work may be taken as more advanced than Galen's. His description +of the heart is particularly accurate, and he seems to have come +nearer to determining the course of the blood in its circulation +than any of his predecessors. In this quest he was greatly +handicapped by the prevailing belief in the idea that +blood-vessels must contain air as well as blood, and this led him +to assume that one of the cavities of the heart contained +"spirits," or air. It is probable, however, that his accurate +observations, so far as they went, were helpful stepping-stones +to Harvey in his discovery of the circulation. + +Guy of Chauliac, whose innovations in surgery reestablished that +science on a firm basis, was not only one of the most cultured, +but also the most practical surgeon of his time. He had great +reverence for the works of Galen, Albucasis, and others of his +noted predecessors; but this reverence did not blind him to their +mistakes nor prevent him from using rational methods of treatment +far in advance of theirs. His practicality is shown in some of +his simple but useful inventions for the sick-room, such as the +device of a rope, suspended from the ceiling over the bed, by +which a patient may move himself about more easily; and in some +of his improvements in surgical dressings, such as stiffening +bandages by dipping them in the white of an egg so that they are +held firmly. He treated broken limbs in the suspended cradle +still in use, and introduced the method of making "traction" on a +broken limb by means of a weight and pulley, to prevent deformity +through shortening of the member. He was one of the first +physicians to recognize the utility of spectacles, and +recommended them in cases not amenable to treatment with lotions +and eye-waters. In some of his surgical operations, such as +trephining for fracture of the skull, his technique has been +little improved upon even in modern times. In one of these +operations he successfully removed a portion of a man's brain. + + +Surgery was undoubtedly stimulated greatly at this period by the +constant wars. Lay physicians, as a class, had been looked down +upon during the Dark Ages; but with the beginning of the return +to rationalism, the services of surgeons on the battle-field, to +remove missiles from wounds, and to care for wounds and apply +dressings, came to be more fully appreciated. In return for his +labors the surgeon was thus afforded better opportunities for +observing wounds and diseases, which led naturally to a gradual +improvement in surgical methods. + + +FIFTEENTH-CENTURY MEDICINE + +The thirteenth and fourteenth centuries had seen some slight +advancement in the science of medicine; at least, certain +surgeons and physicians, if not the generality, had made +advances; but it was not until the fifteenth century that the +general revival of medical learning became assured. In this +movement, naturally, the printing-press played an all-important +part. Medical books, hitherto practically inaccessible to the +great mass of physicians, now became common, and this output of +reprints of Greek and Arabic treatises revealed the fact that +many of the supposed true copies were spurious. These discoveries +very naturally aroused all manner of doubt and criticism, which +in turn helped in the development of independent thought. + +A certain manuscript of the great Cornelius Celsus, the De +Medicine, which had been lost for many centuries, was found in +the church of St. Ambrose, at Milan, in 1443, and was at once put +into print. The effect of the publication of this book, which had +lain in hiding for so many centuries, was a revelation, showing +the medical profession how far most of their supposed true copies +of Celsus had drifted away from the original. The indisputable +authenticity of this manuscript, discovered and vouched for by +the man who shortly after became Pope Nicholas V., made its +publication the more impressive. The output in book form of other +authorities followed rapidly, and the manifest discrepancies +between such teachers as Celsus, Hippocrates, Galen, and Pliny +heightened still more the growing spirit of criticism. + +These doubts resulted in great controversies as to the proper +treatment of certain diseases, some physicians following +Hippocrates, others Galen or Celsus, still others the Arabian +masters. One of the most bitter of these contests was over the +question of "revulsion," and "derivation"--that is, whether in +cases of pleurisy treated by bleeding, the venesection should be +made at a point distant from the seat of the disease, as held by +the "revulsionists," or at a point nearer and on the same side of +the body, as practised by the "derivationists." That any great +point for discussion could be raised in the fifteenth or +sixteenth centuries on so simple a matter as it seems to-day +shows how necessary to the progress of medicine was the discovery +of the circulation of the blood made by Harvey two centuries +later. After Harvey's discovery no such discussion could have +been possible, because this discovery made it evident that as far +as the general effect upon the circulation is concerned, it made +little difference whether the bleeding was done near a diseased +part or remote from it. But in the sixteenth century this +question was the all-absorbing one among the doctors. At one time +the faculty of Paris condemned "derivation"; but the supporters +of this method carried the war still higher, and Emperor Charles +V. himself was appealed to. He reversed the decision of the Paris +faculty, and decided in favor of "derivation." His decision was +further supported by Pope Clement VII., although the discussion +dragged on until cut short by Harvey's discovery. + +But a new form of injury now claimed the attention of the +surgeons, something that could be decided by neither Greek nor +Arabian authors, as the treatment of gun-shot wounds was, for +obvious reasons, not given in their writings. About this time, +also, came the great epidemics, "the sweating sickness" and +scurvy; and upon these subjects, also, the Greeks and Arabians +were silent. John of Vigo, in his book, the Practica Copiosa, +published in 1514, and repeated in many editions, became the +standard authority on all these subjects, and thus supplanted the +works of the ancient writers. + +According to Vigo, gun-shot wounds differed from the wounds made +by ordinary weapons--that is, spear, arrow, sword, or axe--in +that the bullet, being round, bruised rather than cut its way +through the tissues; it burned the flesh; and, worst of all, it +poisoned it. Vigo laid especial stress upon treating this last +condition, recommending the use of the cautery or the oil of +elder, boiling hot. It is little wonder that gun-shot wounds were +so likely to prove fatal. Yet, after all, here was the germ of +the idea of antisepsis. + + +NEW BEGINNINGS IN GENERAL SCIENCE + +We have dwelt thus at length on the subject of medical science, +because it was chiefly in this field that progress was made in +the Western world during the mediaeval period, and because these +studies furnished the point of departure for the revival all +along the line. It will be understood, however, from what was +stated in the preceding chapter, that the Arabian influences in +particular were to some extent making themselves felt along other +lines. The opportunity afforded a portion of the Western +world--notably Spain and Sicily --to gain access to the +scientific ideas of antiquity through Arabic translations could +not fail of influence. Of like character, and perhaps even more +pronounced in degree, was the influence wrought by the Byzantine +refugees, who, when Constantinople began to be threatened by the +Turks, migrated to the West in considerable numbers, bringing +with them a knowledge of Greek literature and a large number of +precious works which for centuries had been quite forgotten or +absolutely ignored in Italy. Now Western scholars began to take +an interest in the Greek language, which had been utterly +neglected since the beginning of the Middle Ages. Interesting +stories are told of the efforts made by such men as Cosmo de' +Medici to gain possession of classical manuscripts. The revival +of learning thus brought about had its first permanent influence +in the fields of literature and art, but its effect on science +could not be long delayed. Quite independently of the Byzantine +influence, however, the striving for better intellectual things +had manifested itself in many ways before the close of the +thirteenth century. An illustration of this is found in the +almost simultaneous development of centres of teaching, which +developed into the universities of Italy, France, England, and, a +little later, of Germany. + +The regular list of studies that came to be adopted everywhere +comprised seven nominal branches, divided into two groups--the +so-called quadrivium, comprising music, arithmetic, geometry, and +astronomy; and the trivium comprising grammar, rhetoric, and +logic. The vagueness of implication of some of these branches +gave opportunity to the teacher for the promulgation of almost +any knowledge of which he might be possessed, but there can be no +doubt that, in general, science had but meagre share in the +curriculum. In so far as it was given representation, its chief +field must have been Ptolemaic astronomy. The utter lack of +scientific thought and scientific method is illustrated most +vividly in the works of the greatest men of that period--such men +as Albertus Magnus, Thomas Aquinas, Bonaventura, and the hosts of +other scholastics of lesser rank. Yet the mental awakening +implied in their efforts was sure to extend to other fields, and +in point of fact there was at least one contemporary of these +great scholastics whose mind was intended towards scientific +subjects, and who produced writings strangely at variance in tone +and in content with the others. This anachronistic thinker was +the English monk, Roger Bacon. + + +ROGER BACON + +Bacon was born in 1214 and died in 1292. By some it is held that +he was not appreciated in his own time because he was really a +modern scientist living in an age two centuries before modern +science or methods of modern scientific thinking were known. Such +an estimate, however, is a manifest exaggeration of the facts, +although there is probably a grain of truth in it withal. His +learning certainly brought him into contact with the great +thinkers of the time, and his writings caused him to be +imprisoned by his fellow-churchmen at different times, from which +circumstances we may gather that he was advanced thinker, even if +not a modern scientist. + +Although Bacon was at various times in durance, or under +surveillance, and forbidden to write, he was nevertheless a +marvellously prolific writer, as is shown by the numerous books +and unpublished manuscripts of his still extant. His +master-production was the Opus Majus. In Part IV. of this work he +attempts to show that all sciences rest ultimately on +mathematics; but Part V., which treats of perspective, is of +particular interest to modern scientists, because in this he +discusses reflection and refraction, and the properties of +mirrors and lenses. In this part, also, it is evident that he is +making use of such Arabian writers as Alkindi and Alhazen, and +this is of especial interest, since it has been used by his +detractors, who accuse him of lack of originality, to prove that +his seeming inventions and discoveries were in reality +adaptations of the Arab scientists. It is difficult to determine +just how fully such criticisms are justified. It is certain, +however, that in this part he describes the anatomy of the eye +with great accuracy, and discusses mirrors and lenses. + +The magnifying power of the segment of a glass sphere had been +noted by Alhazen, who had observed also that the magnification +was increased by increasing the size of the segment used. Bacon +took up the discussion of the comparative advantages of segments, +and in this discussion seems to show that he understood how to +trace the progress of the rays of light through a spherical +transparent body, and how to determine the place of the image. He +also described a method of constructing a telescope, but it is by +no means clear that he had ever actually constructed such an +instrument. It is also a mooted question as to whether his +instructions as to the construction of such an instrument would +have enabled any one to construct one. The vagaries of the names +of terms as he uses them allow such latitude in interpretation +that modern scientists are not agreed as to the practicability of +Bacon's suggestions. For example, he constantly refers to force +under such names as virtus, species, imago, agentis, and a score +of other names, and this naturally gives rise to the great +differences in the interpretations of his writings, with +corresponding differences in estimates of them. + +The claim that Bacon originated the use of lenses, in the form of +spectacles, cannot be proven. Smith has determined that as early +as the opening years of the fourteenth century such lenses were +in use, but this proves nothing as regards Bacon's connection +with their invention. The knowledge of lenses seems to be very +ancient, if we may judge from the convex lens of rock crystal +found by Layard in his excavations at Nimrud. There is nothing to +show, however, that the ancients ever thought of using them to +correct defects of vision. Neither, apparently, is it feasible to +determine whether the idea of such an application originated with +Bacon. + +Another mechanical discovery about which there has been a great +deal of discussion is Bacon's supposed invention of gunpowder. It +appears that in a certain passage of his work he describes the +process of making a substance that is, in effect, ordinary +gunpowder; but it is more than doubtful whether he understood the +properties of the substance he describes. It is fairly well +established, however, that in Bacon's time gunpowder was known to +the Arabs, so that it should not be surprising to find references +made to it in Bacon's work, since there is reason to believe that +he constantly consulted Arabian writings. + +The great merit of Bacon's work, however, depends on the +principles taught as regards experiment and the observation of +nature, rather than on any single invention. He had the +all-important idea of breaking with tradition. He championed +unfettered inquiry in every field of thought. He had the instinct +of a scientific worker--a rare instinct indeed in that age. Nor +need we doubt that to the best of his opportunities he was +himself an original investigator. + + +LEONARDO DA VINCI + +The relative infertility of Bacon's thought is shown by the fact +that he founded no school and left no trace of discipleship. The +entire century after his death shows no single European name that +need claim the attention of the historian of science. In the +latter part of the fifteenth century, however, there is evidence +of a renaissance of science no less than of art. The German +Muller became famous under the latinized named of Regio Montanus +(1437-1472), although his actual scientific attainments would +appear to have been important only in comparison with the utter +ignorance of his contemporaries. The most distinguished worker of +the new era was the famous Italian Leonardo da Vinci--a man who +has been called by Hamerton the most universal genius that ever +lived. Leonardo's position in the history of art is known to +every one. With that, of course, we have no present concern; but +it is worth our while to inquire at some length as to the famous +painter's accomplishments as a scientist. + +From a passage in the works of Leonardo, first brought to light +by Venturi,[1] it would seem that the great painter anticipated +Copernicus in determining the movement of the earth. He made +mathematical calculations to prove this, and appears to have +reached the definite conclusion that the earth does move--or what +amounts to the same thing, that the sun does not move. Muntz is +authority for the statement that in one of his writings he +declares, "Il sole non si mouve"--the sun does not move.[2] + +Among his inventions is a dynamometer for determining the +traction power of machines and animals, and his experiments with +steam have led some of his enthusiastic partisans to claim for +him priority to Watt in the invention of the steam-engine. In +these experiments, however, Leonardo seems to have advanced +little beyond Hero of Alexandria and his steam toy. Hero's +steam-engine did nothing but rotate itself by virtue of escaping +jets of steam forced from the bent tubes, while Leonardo's +"steam-engine" "drove a ball weighing one talent over a distance +of six stadia." In a manuscript now in the library of the +Institut de France, Da Vinci describes this engine minutely. The +action of this machine was due to the sudden conversion of small +quantities of water into steam ("smoke," as he called it) by +coming suddenly in contact with a heated surface in a proper +receptacle, the rapidly formed steam acting as a propulsive force +after the manner of an explosive. It is really a steam-gun, +rather than a steam-engine, and it is not unlikely that the study +of the action of gunpowder may have suggested it to Leonardo. + +It is believed that Leonardo is the true discoverer of the +camera-obscura, although the Neapolitan philosopher, Giambattista +Porta, who was not born until some twenty years after the death +of Leonardo, is usually credited with first describing this +device. There is little doubt, however, that Da Vinci understood +the principle of this mechanism, for he describes how such a +camera can be made by cutting a small, round hole through the +shutter of a darkened room, the reversed image of objects outside +being shown on the opposite wall. + +Like other philosophers in all ages, he had observed a great +number of facts which he was unable to explain correctly. But +such accumulations of scientific observations are always +interesting, as showing how many centuries of observation +frequently precede correct explanation. He observed many facts +about sounds, among others that blows struck upon a bell produced +sympathetic sounds in a bell of the same kind; and that striking +the string of a lute produced vibration in corresponding strings +of lutes strung to the same pitch. He knew, also, that sounds +could be heard at a distance at sea by listening at one end of a +tube, the other end of which was placed in the water; and that +the same expedient worked successfully on land, the end of the +tube being placed against the ground. + +The knowledge of this great number of unexplained facts is often +interpreted by the admirers of Da Vinci, as showing an almost +occult insight into science many centuries in advance of his +time. Such interpretations, however, are illusive. The +observation, for example, that a tube placed against the ground +enables one to hear movements on the earth at a distance, is not +in itself evidence of anything more than acute scientific +observation, as a similar method is in use among almost every +race of savages, notably the American Indians. On the other hand, +one is inclined to give credence to almost any story of the +breadth of knowledge of the man who came so near anticipating +Hutton, Lyell, and Darwin in his interpretation of the geological +records as he found them written on the rocks. + +It is in this field of geology that Leonardo is entitled to the +greatest admiration by modern scientists. He had observed the +deposit of fossil shells in various strata of rocks, even on the +tops of mountains, and he rejected once for all the theory that +they had been deposited there by the Deluge. He rightly +interpreted their presence as evidence that they had once been +deposited at the bottom of the sea. This process he assumed bad +taken hundreds and thousands of centuries, thus tacitly rejecting +the biblical tradition as to the date of the creation. + +Notwithstanding the obvious interest that attaches to the +investigations of Leonardo, it must be admitted that his work in +science remained almost as infertile as that of his great +precursor, Bacon. The really stimulative work of this generation +was done by a man of affairs, who knew little of theoretical +science except in one line, but who pursued that one practical +line until he achieved a wonderful result. This man was +Christopher Columbus. It is not necessary here to tell the trite +story of his accomplishment. Suffice it that his practical +demonstration of the rotundity of the earth is regarded by most +modern writers as marking an epoch in history. With the year of +his voyage the epoch of the Middle Ages is usually regarded as +coming to an end. It must not be supposed that any very sudden +change came over the aspect of scholarship of the time, but the +preliminaries of great things had been achieved, and when +Columbus made his famous voyage in 1492, the man was already +alive who was to bring forward the first great vitalizing thought +in the field of pure science that the Western world had +originated for more than a thousand years. This man bore the name +of Kopernik, or in its familiar Anglicized form, Copernicus. His +life work and that of his disciples will claim our attention in +the succeeding chapter. + + + +IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +We have seen that the Ptolemaic astronomy, which was the accepted +doctrine throughout the Middle Ages, taught that the earth is +round. Doubtless there was a popular opinion current which +regarded the earth as flat, but it must be understood that this +opinion had no champions among men of science during the Middle +Ages. When, in the year 1492, Columbus sailed out to the west on +his memorable voyage, his expectation of reaching India had full +scientific warrant, however much it may have been scouted by +certain ecclesiastics and by the average man of the period. +Nevertheless, we may well suppose that the successful voyage of +Columbus, and the still more demonstrative one made about thirty +years later by Magellan, gave the theory of the earth's rotundity +a certainty it could never previously have had. Alexandrian +geographers had measured the size of the earth, and had not +hesitated to assert that by sailing westward one might reach +India. But there is a wide gap between theory and practice, and +it required the voyages of Columbus and his successors to bridge +that gap. + +After the companions of Magellan completed the circumnavigation +of the globe, the general shape of our earth would, obviously, +never again be called in question. But demonstration of the +sphericity of the earth had, of course, no direct bearing upon +the question of the earth's position in the universe. Therefore +the voyage of Magellan served to fortify, rather than to dispute, +the Ptolemaic theory. According to that theory, as we have seen, +the earth was supposed to lie immovable at the centre of the +universe; the various heavenly bodies, including the sun, +revolving about it in eccentric circles. We have seen that +several of the ancient Greeks, notably Aristarchus, disputed this +conception, declaring for the central position of the sun in the +universe, and the motion of the earth and other planets about +that body. But this revolutionary theory seemed so opposed to the +ordinary observation that, having been discountenanced by +Hipparchus and Ptolemy, it did not find a single important +champion for more than a thousand years after the time of the +last great Alexandrian astronomer. + +The first man, seemingly, to hark back to the Aristarchian +conception in the new scientific era that was now dawning was the +noted cardinal, Nikolaus of Cusa, who lived in the first half of +the fifteenth century, and was distinguished as a philosophical +writer and mathematician. His De Docta Ignorantia expressly +propounds the doctrine of the earth's motion. No one, however, +paid the slightest attention to his suggestion, which, therefore, +merely serves to furnish us with another interesting illustration +of the futility of propounding even a correct hypothesis before +the time is ripe to receive it--particularly if the hypothesis is +not fully fortified by reasoning based on experiment or +observation. + +The man who was destined to put forward the theory of the earth's +motion in a way to command attention was born in 1473, at the +village of Thorn, in eastern Prussia. His name was Nicholas +Copernicus. There is no more famous name in the entire annals of +science than this, yet posterity has never been able fully to +establish the lineage of the famous expositor of the true +doctrine of the solar system. The city of Thorn lies in a +province of that border territory which was then under control of +Poland, but which subsequently became a part of Prussia. It is +claimed that the aspects of the city were essentially German, and +it is admitted that the mother of Copernicus belonged to that +race. The nationality of the father is more in doubt, but it is +urged that Copernicus used German as his mother-tongue. His great +work was, of course, written in Latin, according to the custom of +the time; but it is said that, when not employing that language, +he always wrote in German. The disputed nationality of Copernicus +strongly suggests that he came of a mixed racial lineage, and we +are reminded again of the influences of those ethnical minglings +to which we have previously more than once referred. The +acknowledged centres of civilization towards the close of the +fifteenth century were Italy and Spain. Therefore, the birthplace +of Copernicus lay almost at the confines of civilization, +reminding us of that earlier period when Greece was the centre of +culture, but when the great Greek thinkers were born in Asia +Minor and in Italy. + +As a young man, Copernicus made his way to Vienna to study +medicine, and subsequently he journeyed into Italy and remained +there many years, About the year 1500 he held the chair of +mathematics in a college at Rome. Subsequently he returned to his +native land and passed his remaining years there, dying at +Domkerr, in Frauenburg, East Prussia, in the year 1543. + +It would appear that Copernicus conceived the idea of the +heliocentric system of the universe while he was a comparatively +young man, since in the introduction to his great work, which he +addressed to Pope Paul III., he states that he has pondered his +system not merely nine years, in accordance with the maxim of +Horace, but well into the fourth period of nine years. Throughout +a considerable portion of this period the great work of +Copernicus was in manuscript, but it was not published until the +year of his death. The reasons for the delay are not very fully +established. Copernicus undoubtedly taught his system throughout +the later decades of his life. He himself tells us that he had +even questioned whether it were not better for him to confine +himself to such verbal teaching, following thus the example of +Pythagoras. Just as his life was drawing to a close, he decided +to pursue the opposite course, and the first copy of his work is +said to have been placed in his hands as he lay on his deathbed. + +The violent opposition which the new system met from +ecclesiastical sources led subsequent commentators to suppose +that Copernicus had delayed publication of his work through fear +of the church authorities. There seems, however, to be no direct +evidence for this opinion. It has been thought significant that +Copernicus addressed his work to the pope. It is, of course, +quite conceivable that the aged astronomer might wish by this +means to demonstrate that he wrote in no spirit of hostility to +the church. His address to the pope might have been considered as +a desirable shield precisely because the author recognized that +his work must needs meet with ecclesiastical criticism. Be that +as it may, Copernicus was removed by death from the danger of +attack, and it remained for his disciples of a later generation +to run the gauntlet of criticism and suffer the charges of +heresy. + +The work of Copernicus, published thus in the year 1543 at +Nuremberg, bears the title De Orbium Coelestium Revolutionibus. + +It is not necessary to go into details as to the cosmological +system which Copernicus advocated, since it is familiar to every +one. In a word, he supposed the sun to be the centre of all the +planetary motions, the earth taking its place among the other +planets, the list of which, as known at that time, comprised +Mercury, Venus, the Earth, Mars, Jupiter, and Saturn. The fixed +stars were alleged to be stationary, and it was necessary to +suppose that they are almost infinitely distant, inasmuch as they +showed to the observers of that time no parallax; that is to say, +they preserved the same apparent position when viewed from the +opposite points of the earth's orbit. + +But let us allow Copernicus to speak for himself regarding his +system, His exposition is full of interest. We quote first the +introduction just referred to, in which appeal is made directly +to the pope. + +"I can well believe, most holy father, that certain people, when +they hear of my attributing motion to the earth in these books of +mine, will at once declare that such an opinion ought to be +rejected. Now, my own theories do not please me so much as not to +consider what others may judge of them. Accordingly, when I began +to reflect upon what those persons who accept the stability of +the earth, as confirmed by the opinion of many centuries, would +say when I claimed that the earth moves, I hesitated for a long +time as to whether I should publish that which I have written to +demonstrate its motion, or whether it would not be better to +follow the example of the Pythagoreans, who used to hand down the +secrets of philosophy to their relatives and friends only in oral +form. As I well considered all this, I was almost impelled to put +the finished work wholly aside, through the scorn I had reason to +anticipate on account of the newness and apparent contrariness to +reason of my theory. + +"My friends, however, dissuaded me from such a course and +admonished me that I ought to publish my book, which had lain +concealed in my possession not only nine years, but already into +four times the ninth year. Not a few other distinguished and very +learned men asked me to do the same thing, and told me that I +ought not, on account of my anxiety, to delay any longer in +consecrating my work to the general service of mathematicians. + +"But your holiness will perhaps not so much wonder that I have +dared to bring the results of my night labors to the light of +day, after having taken so much care in elaborating them, but is +waiting instead to hear how it entered my mind to imagine that +the earth moved, contrary to the accepted opinion of +mathematicians--nay, almost contrary to ordinary human +understanding. Therefore I will not conceal from your holiness +that what moved me to consider another way of reckoning the +motions of the heavenly bodies was nothing else than the fact +that the mathematicians do not agree with one another in their +investigations. In the first place, they are so uncertain about +the motions of the sun and moon that they cannot find out the +length of a full year. In the second place, they apply neither +the same laws of cause and effect, in determining the motions of +the sun and moon and of the five planets, nor the same proofs. +Some employ only concentric circles, others use eccentric and +epicyclic ones, with which, however, they do not fully attain the +desired end. They could not even discover nor compute the main +thing--namely, the form of the universe and the symmetry of its +parts. It was with them as if some should, from different places, +take hands, feet, head, and other parts of the body, which, +although very beautiful, were not drawn in their proper +relations, and, without making them in any way correspond, should +construct a monster instead of a human being. + +"Accordingly, when I had long reflected on this uncertainty of +mathematical tradition, I took the trouble to read again the +books of all the philosophers I could get hold of, to see if some +one of them had not once believed that there were other motions +of the heavenly bodies. First I found in Cicero that Niceties had +believed in the motion of the earth. Afterwards I found in +Plutarch, likewise, that some others had held the same opinion. +This induced me also to begin to consider the movability of the +earth, and, although the theory appeared contrary to reason, I +did so because I knew that others before me had been allowed to +assume rotary movements at will, in order to explain the +phenomena of these celestial bodies. I was of the opinion that I, +too, might be permitted to see whether, by presupposing motion in +the earth, more reliable conclusions than hitherto reached could +not be discovered for the rotary motions of the spheres. And +thus, acting on the hypothesis of the motion which, in the +following book, I ascribe to the earth, and by long and continued +observations, I have finally discovered that if the motion of the +other planets be carried over to the relation of the earth and +this is made the basis for the rotation of every star, not only +will the phenomena of the planets be explained thereby, but also +the laws and the size of the stars; all their spheres and the +heavens themselves will appear so harmoniously connected that +nothing could be changed in any part of them without confusion in +the remaining parts and in the whole universe. I do not doubt +that clever and learned men will agree with me if they are +willing fully to comprehend and to consider the proofs which I +advance in the book before us. In order, however, that both the +learned and the unlearned may see that I fear no man's judgment, +I wanted to dedicate these, my night labors, to your holiness, +rather than to any one else, because you, even in this remote +corner of the earth where I live, are held to be the greatest in +dignity of station and in love for all sciences and for +mathematics, so that you, through your position and judgment, can +easily suppress the bites of slanderers, although the proverb +says that there is no remedy against the bite of calumny." + + +In chapter X. of book I., "On the Order of the Spheres," occurs a +more detailed presentation of the system, as follows: + +"That which Martianus Capella, and a few other Latins, very well +knew, appears to me extremely noteworthy. He believed that Venus +and Mercury revolve about the sun as their centre and that they +cannot go farther away from it than the circles of their orbits +permit, since they do not revolve about the earth like the other +planets. According to this theory, then, Mercury's orbit would be +included within that of Venus, which is more than twice as great, +and would find room enough within it for its revolution. + +"If, acting upon this supposition, we connect Saturn, Jupiter, +and Mars with the same centre, keeping in mind the greater extent +of their orbits, which include the earth's sphere besides those +of Mercury and Venus, we cannot fail to see the explanation of +the regular order of their motions. He is certain that Saturn, +Jupiter, and Mars are always nearest the earth when they rise in +the evening--that is, when they appear over against the sun, or +the earth stands between them and the sun--but that they are +farthest from the earth when they set in the evening--that is, +when we have the sun between them and the earth. This proves +sufficiently that their centre belongs to the sun and is the same +about which the orbits of Venus and Mercury circle. Since, +however, all have one centre, it is necessary for the space +intervening between the orbits of Venus and Mars to include the +earth with her accompanying moon and all that is beneath the +moon; for the moon, which stands unquestionably nearest the +earth, can in no way be separated from her, especially as there +is sufficient room for the moon in the aforesaid space. Hence we +do not hesitate to claim that the whole system, which includes +the moon with the earth for its centre, makes the round of that +great circle between the planets, in yearly motion about the sun, +and revolves about the centre of the universe, in which the sun +rests motionless, and that all which looks like motion in the sun +is explained by the motion of the earth. The extent of the +universe, however, is so great that, whereas the distance of the +earth from the sun is considerable in comparison with the size of +the other planetary orbits, it disappears when compared with the +sphere of the fixed stars. I hold this to be more easily +comprehensible than when the mind is confused by an almost +endless number of circles, which is necessarily the case with +those who keep the earth in the middle of the universe. Although +this may appear incomprehensible and contrary to the opinion of +many, I shall, if God wills, make it clearer than the sun, at +least to those who are not ignorant of mathematics. + +"The order of the spheres is as follows: The first and lightest +of all the spheres is that of the fixed stars, which includes +itself and all others, and hence is motionless as the place in +the universe to which the motion and position of all other stars +is referred. + +"Then follows the outermost planet, Saturn, which completes its +revolution around the sun in thirty years; next comes Jupiter +with a twelve years' revolution; then Mars, which completes its +course in two years. The fourth one in order is the yearly +revolution which includes the earth with the moon's orbit as an +epicycle. In the fifth place is Venus with a revolution of nine +months. The sixth place is taken by Mercury, which completes its +course in eighty days. In the middle of all stands the sun, and +who could wish to place the lamp of this most beautiful temple in +another or better place. Thus, in fact, the sun, seated upon the +royal throne, controls the family of the stars which circle +around him. We find in their order a harmonious connection which +cannot be found elsewhere. Here the attentive observer can see +why the waxing and waning of Jupiter seems greater than with +Saturn and smaller than with Mars, and again greater with Venus +than with Mercury. Also, why Saturn, Jupiter, and Mars are nearer +to the earth when they rise in the evening than when they +disappear in the rays of the sun. More prominently, however, is +it seen in the case of Mars, which when it appears in the heavens +at night, seems to equal Jupiter in size, but soon afterwards is +found among the stars of second magnitude. All of this results +from the same cause--namely, from the earth's motion. The fact +that nothing of this is to be seen in the case of the fixed stars +is a proof of their immeasurable distance, which makes even the +orbit of yearly motion or its counterpart invisible to us."[1] + + +The fact that the stars show no parallax had been regarded as an +important argument against the motion of the earth, and it was +still so considered by the opponents of the system of Copernicus. +It had, indeed, been necessary for Aristarchus to explain the +fact as due to the extreme distance of the stars; a perfectly +correct explanation, but one that implies distances that are +altogether inconceivable. It remained for nineteenth-century +astronomers to show, with the aid of instruments of greater +precision, that certain of the stars have a parallax. But long +before this demonstration had been brought forward, the system of +Copernicus had been accepted as a part of common knowledge. + +While Copernicus postulated a cosmical scheme that was correct as +to its main features, he did not altogether break away from +certain defects of the Ptolemaic hypothesis. Indeed, he seems to +have retained as much of this as practicable, in deference to the +prejudice of his time. Thus he records the planetary orbits as +circular, and explains their eccentricities by resorting to the +theory of epicycles, quite after the Ptolemaic method. But now, +of course, a much more simple mechanism sufficed to explain the +planetary motions, since the orbits were correctly referred to +the central sun and not to the earth. + +Needless to say, the revolutionary conception of Copernicus did +not meet with immediate acceptance. A number of prominent +astronomers, however, took it up almost at once, among these +being Rhaeticus, who wrote a commentary on the evolutions; +Erasmus Reinhold, the author of the Prutenic tables; Rothmann, +astronomer to the Landgrave of Hesse, and Maestlin, the +instructor of Kepler. The Prutenic tables, just referred to, so +called because of their Prussian origin, were considered an +improvement on the tables of Copernicus, and were highly esteemed +by the astronomers of the time. The commentary of Rhaeticus gives +us the interesting information that it was the observation of the +orbit of Mars and of the very great difference between his +apparent diameters at different times which first led Copernicus +to conceive the heliocentric idea. Of Reinhold it is recorded +that he considered the orbit of Mercury elliptical, and that he +advocated a theory of the moon, according to which her epicycle +revolved on an elliptical orbit, thus in a measure anticipating +one of the great discoveries of Kepler to which we shall refer +presently. The Landgrave of Hesse was a practical astronomer, who +produced a catalogue of fixed stars which has been compared with +that of Tycho Brahe. He was assisted by Rothmann and by Justus +Byrgius. Maestlin, the preceptor of Kepler, is reputed to have +been the first modern observer to give a correct explanation of +the light seen on portions of the moon not directly illumined by +the sun. He explained this as not due to any proper light of the +moon itself, but as light reflected from the earth. Certain of +the Greek philosophers, however, are said to have given the same +explanation, and it is alleged also that Leonardo da Vinci +anticipated Maestlin in this regard.[2] + +While, various astronomers of some eminence thus gave support to +the Copernican system, almost from the beginning, it +unfortunately chanced that by far the most famous of the +immediate successors of Copernicus declined to accept the theory +of the earth's motion. This was Tycho Brahe, one of the greatest +observing astronomers of any age. Tycho Brahe was a Dane, born at +Knudstrup in the year 1546. He died in 1601 at Prague, in +Bohemia. During a considerable portion of his life he found a +patron in Frederick, King of Denmark, who assisted him to build a +splendid observatory on the Island of Huene. On the death of his +patron Tycho moved to Germany, where, as good luck would have it, +he came in contact with the youthful Kepler, and thus, no doubt, +was instrumental in stimulating the ambitions of one who in later +years was to be known as a far greater theorist than himself. As +has been said, Tycho rejected the Copernican theory of the +earth's motion. It should be added, however, that he accepted +that part of the Copernican theory which makes the sun the centre +of all the planetary motions, the earth being excepted. He thus +developed a system of his own, which was in some sort a +compromise between the Ptolemaic and the Copernican systems. As +Tycho conceived it, the sun revolves about the earth, carrying +with it the planets-Mercury, Venus, Mars, Jupiter, and Saturn, +which planets have the sun and not the earth as the centre of +their orbits. This cosmical scheme, it should be added, may be +made to explain the observed motions of the heavenly bodies, but +it involves a much more complex mechanism than is postulated by +the Copernican theory. + +Various explanations have been offered of the conservatism which +held the great Danish astronomer back from full acceptance of the +relatively simple and, as we now know, correct Copernican +doctrine. From our latter-day point of view, it seems so much +more natural to accept than to reject the Copernican system, that +we find it difficult to put ourselves in the place of a +sixteenth-century observer. Yet if we recall that the traditional +view, having warrant of acceptance by nearly all thinkers of +every age, recorded the earth as a fixed, immovable body, we +shall see that our surprise should be excited rather by the +thinker who can break away from this view than by the one who +still tends to cling to it. + +Moreover, it is useless to attempt to disguise the fact that +something more than a mere vague tradition was supposed to +support the idea of the earth's overshadowing importance in the +cosmical scheme. The sixteenth-century mind was overmastered by +the tenets of ecclesiasticism, and it was a dangerous heresy to +doubt that the Hebrew writings, upon which ecclesiasticism based +its claim, contained the last word regarding matters of science. +But the writers of the Hebrew text had been under the influence +of that Babylonian conception of the universe which accepted the +earth as unqualifiedly central--which, indeed, had never so much +as conceived a contradictory hypothesis; and so the Western +world, which had come to accept these writings as actually +supernatural in origin, lay under the spell of Oriental ideas of +a pre-scientific era. In our own day, no one speaking with +authority thinks of these Hebrew writings as having any +scientific weight whatever. Their interest in this regard is +purely antiquarian; hence from our changed point of view it seems +scarcely credible that Tycho Brahe can have been in earnest when +he quotes the Hebrew traditions as proof that the sun revolves +about the earth. Yet we shall see that for almost three centuries +after the time of Tycho, these same dreamings continued to be +cited in opposition to those scientific advances which new +observations made necessary; and this notwithstanding the fact +that the Oriental phrasing is, for the most part, poetically +ambiguous and susceptible of shifting interpretations, as the +criticism of successive generations has amply testified. + +As we have said, Tycho Brahe, great observer as he was, could not +shake himself free from the Oriental incubus. He began his +objections, then, to the Copernican system by quoting the adverse +testimony of a Hebrew prophet who lived more than a thousand +years B.C. All of this shows sufficiently that Tycho Brahe was +not a great theorist. He was essentially an observer, but in this +regard he won a secure place in the very first rank. Indeed, he +was easily the greatest observing astronomer since Hipparchus, +between whom and himself there were many points of resemblance. +Hipparchus, it will be recalled, rejected the Aristarchian +conception of the universe just as Tycho rejected the conception +of Copernicus. + +But if Tycho propounded no great generalizations, the list of +specific advances due to him is a long one, and some of these +were to prove important aids in the hands of later workers to the +secure demonstration of the Copernican idea. One of his most +important series of studies had to do with comets. Regarding +these bodies there had been the greatest uncertainty in the minds +of astronomers. The greatest variety of opinions regarding them +prevailed; they were thought on the one hand to be divine +messengers, and on the other to be merely igneous phenomena of +the earth's atmosphere. Tycho Brahe declared that a comet which +he observed in the year 1577 had no parallax, proving its extreme +distance. The observed course of the comet intersected the +planetary orbits, which fact gave a quietus to the long-mooted +question as to whether the Ptolemaic spheres were transparent +solids or merely imaginary; since the comet was seen to intersect +these alleged spheres, it was obvious that they could not be the +solid substance that they were commonly imagined to be, and this +fact in itself went far towards discrediting the Ptolemaic +system. It should be recalled, however, that this supposition of +tangible spheres for the various planetary and stellar orbits was +a mediaeval interpretation of Ptolemy's theory rather than an +interpretation of Ptolemy himself, there being nothing to show +that the Alexandrian astronomer regarded his cycles and epicycles +as other than theoretical. + +An interesting practical discovery made by Tycho was his method +of determining the latitude of a place by means of two +observations made at an interval of twelve hours. Hitherto it had +been necessary to observe the sun's angle on the equinoctial +days, a period of six months being therefore required. Tycho +measured the angle of elevation of some star situated near the +pole, when on the meridian, and then, twelve hours later, +measured the angle of elevation of the same star when it again +came to the meridian at the opposite point of its apparent circle +about the polestar. Half the sum of these angles gives the +latitude of the place of observation. + +As illustrating the accuracy of Tycho's observations, it may be +noted that he rediscovered a third inequality of the moon's +motion at its variation, he, in common with other European +astronomers, being then quite unaware that this inequality had +been observed by an Arabian astronomer. Tycho proved also that +the angle of inclination of the moon's orbit to the ecliptic is +subject to slight variation. + +The very brilliant new star which shone forth suddenly in the +constellation of Cassiopeia in the year 1572, was made the object +of special studies by Tycho, who proved that the star had no +sensible parallax and consequently was far beyond the planetary +regions. The appearance of a new star was a phenomenon not +unknown to the ancients, since Pliny records that Hipparchus was +led by such an appearance to make his catalogue of the fixed +stars. But the phenomenon is sufficiently uncommon to attract +unusual attention. A similar phenomenon occurred in the year +1604, when the new star--in this case appearing in the +constellation of Serpentarius--was explained by Kepler as +probably proceeding from a vast combustion. This explanation--in +which Kepler is said to have followed. Tycho--is fully in accord +with the most recent theories on the subject, as we shall see in +due course. It is surprising to hear Tycho credited with so +startling a theory, but, on the other hand, such an explanation +is precisely what should be expected from the other astronomer +named. For Johann Kepler, or, as he was originally named, Johann +von Kappel, was one of the most speculative astronomers of any +age. He was forever theorizing, but such was the peculiar quality +of his mind that his theories never satisfied him for long unless +he could put them to the test of observation. Thanks to this +happy combination of qualities, Kepler became the discoverer of +three famous laws of planetary motion which lie at the very +foundation of modern astronomy, and which were to be largely +instrumental in guiding Newton to his still greater +generalization. These laws of planetary motion were vastly +important as corroborating the Copernican theory of the universe, +though their position in this regard was not immediately +recognized by contemporary thinkers. Let us examine with some +detail into their discovery, meantime catching a glimpse of the +life history of the remarkable man whose name they bear. + + +JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION + +Johann Kepler was born the 27th of December, 1571, in the little +town of Weil, in Wurtemburg. He was a weak, sickly child, further +enfeebled by a severe attack of small-pox. It would seem +paradoxical to assert that the parents of such a genius were +mismated, but their home was not a happy one, the mother being of +a nervous temperament, which perhaps in some measure accounted +for the genius of the child. The father led the life of a +soldier, and finally perished in the campaign against the Turks. +Young Kepler's studies were directed with an eye to the ministry. +After a preliminary training he attended the university at +Tubingen, where he came under the influence of the celebrated +Maestlin and became his life-long friend. + +Curiously enough, it is recorded that at first Kepler had no +taste for astronomy or for mathematics. But the doors of the +ministry being presently barred to him, he turned with enthusiasm +to the study of astronomy, being from the first an ardent +advocate of the Copernican system. His teacher, Maestlin, +accepted the same doctrine, though he was obliged, for +theological reasons, to teach the Ptolemaic system, as also to +oppose the Gregorian reform of the calendar. + +The Gregorian calendar, it should be explained, is so called +because it was instituted by Pope Gregory XIII., who put it into +effect in the year 1582, up to which time the so-called Julian +calendar, as introduced by Julius Caesar, had been everywhere +accepted in Christendom. This Julian calendar, as we have seen, +was a great improvement on preceding ones, but still lacked +something of perfection inasmuch as its theoretical day differed +appreciably from the actual day. In the course of fifteen hundred +years, since the time of Caesar, this defect amounted to a +discrepancy of about eleven days. Pope Gregory proposed to +correct this by omitting ten days from the calendar, which was +done in September, 1582. To prevent similar inaccuracies in the +future, the Gregorian calendar provided that once in four +centuries the additional day to make a leap-year should be +omitted, the date selected for such omission being the last year +of every fourth century. Thus the years 1500, 1900, and 2300, +A.D., would not be leap-years. By this arrangement an approximate +rectification of the calendar was effected, though even this does +not make it absolutely exact. + +Such a rectification as this was obviously desirable, but there +was really no necessity for the omission of the ten days from the +calendar. The equinoctial day had shifted so that in the year +1582 it fell on the 10th of March and September. There was no +reason why it should not have remained there. It would greatly +have simplified the task of future historians had Gregory +contented himself with providing for the future stability of the +calendar without making the needless shift in question. We are so +accustomed to think of the 21st of March and 21st of September as +the natural periods of the equinox, that we are likely to forget +that these are purely arbitrary dates for which the 10th might +have been substituted without any inconvenience or inconsistency. + +But the opposition to the new calendar, to which reference has +been made, was not based on any such considerations as these. It +was due, largely at any rate, to the fact that Germany at this +time was under sway of the Lutheran revolt against the papacy. So +effective was the opposition that the Gregorian calendar did not +come into vogue in Germany until the year 1699. It may be added +that England, under stress of the same manner of prejudice, held +out against the new reckoning until the year 1751, while Russia +does not accept it even now. + +As the Protestant leaders thus opposed the papal attitude in a +matter of so practical a character as the calendar, it might +perhaps have been expected that the Lutherans would have had a +leaning towards the Copernican theory of the universe, since this +theory was opposed by the papacy. Such, however, was not the +case. Luther himself pointed out with great strenuousness, as a +final and demonstrative argument, the fact that Joshua commanded +the sun and not the earth to stand still; and his followers were +quite as intolerant towards the new teaching as were their +ultramontane opponents. Kepler himself was, at various times, to +feel the restraint of ecclesiastical opposition, though he was +never subjected to direct persecution, as was his friend and +contemporary, Galileo. At the very outset of Kepler's career +there was, indeed, question as to the publication of a work he +had written, because that work took for granted the truth of the +Copernican doctrine. This work appeared, however, in the year +1596. It bore the title Mysterium Cosmographium, and it attempted +to explain the positions of the various planetary bodies. +Copernicus had devoted much time to observation of the planets +with reference to measuring their distance, and his efforts had +been attended with considerable success. He did not, indeed, know +the actual distance of the sun, and, therefore, was quite unable +to fix the distance of any planet; but, on the other hand, he +determined the relative distance of all the planets then known, +as measured in terms of the sun's distance, with remarkable +accuracy. + +With these measurements as a guide, Kepler was led to a very +fanciful theory, according to which the orbits of the five +principal planets sustain a peculiar relation to the five regular +solids of geometry. His theory was this: "Around the orbit of the +earth describe a dodecahedron--the circle comprising it will be +that of Mars; around Mars describe a tetrahedron--the circle +comprising it will be that of Jupiter; around Jupiter describe a +cube--the circle comprising it will be that of Saturn; now within +the earth's orbit inscribe an icosahedron--the inscribed circle +will be that of Venus; in the orbit of Venus inscribe an +octahedron --the circle inscribed will be that of Mercury."[3] + +Though this arrangement was a fanciful one, which no one would +now recall had not the theorizer obtained subsequent fame on more +substantial grounds, yet it evidenced a philosophical spirit on +the part of the astronomer which, misdirected as it was in this +instance, promised well for the future. Tycho Brahe, to whom a +copy of the work was sent, had the acumen to recognize it as a +work of genius. He summoned the young astronomer to be his +assistant at Prague, and no doubt the association thus begun was +instrumental in determining the character of Kepler's future +work. It was precisely the training in minute observation that +could avail most for a mind which, like Kepler's, tended +instinctively to the formulation of theories. When Tycho Brahe +died, in 1601, Kepler became his successor. In due time he +secured access to all the unpublished observations of his great +predecessor, and these were of inestimable value to him in the +progress of his own studies. + +Kepler was not only an ardent worker and an enthusiastic +theorizer, but he was an indefatigable writer, and it pleased him +to take the public fully into his confidence, not merely as to +his successes, but as to his failures. Thus his works elaborate +false theories as well as correct ones, and detail the +observations through which the incorrect guesses were refuted by +their originator. Some of these accounts are highly interesting, +but they must not detain us here. For our present purpose it must +suffice to point out the three important theories, which, as +culled from among a score or so of incorrect ones, Kepler was +able to demonstrate to his own satisfaction and to that of +subsequent observers. Stated in a few words, these theories, +which have come to bear the name of Kepler's Laws, are the +following: + +1. That the planetary orbits are not circular, but elliptical, +the sun occupying one focus of the ellipses. + +2. That the speed of planetary motion varies in different parts +of the orbit in such a way that an imaginary line drawn from the +sun to the planet--that is to say, the radius vector of the +planet's orbit--always sweeps the same area in a given time. + + +These two laws Kepler published as early as 1609. Many years more +of patient investigation were required before he found out the +secret of the relation between planetary distances and times of +revolution which his third law expresses. In 1618, however, he +was able to formulate this relation also, as follows: + +3. The squares of the distance of the various planets from the +sun are proportional to the cubes of their periods of revolution +about the sun. + + +All these laws, it will be observed, take for granted the fact +that the sun is the centre of the planetary orbits. It must be +understood, too, that the earth is constantly regarded, in +accordance with the Copernican system, as being itself a member +of the planetary system, subject to precisely the same laws as +the other planets. Long familiarity has made these wonderful laws +of Kepler seem such a matter of course that it is difficult now +to appreciate them at their full value. Yet, as has been already +pointed out, it was the knowledge of these marvellously simple +relations between the planetary orbits that laid the foundation +for the Newtonian law of universal gravitation. Contemporary +judgment could not, of course, anticipate this culmination of a +later generation. What it could understand was that the first law +of Kepler attacked one of the most time-honored of metaphysical +conceptions--namely, the Aristotelian idea that the circle is the +perfect figure, and hence that the planetary orbits must be +circular. Not even Copernicus had doubted the validity of this +assumption. That Kepler dared dispute so firmly fixed a belief, +and one that seemingly had so sound a philosophical basis, +evidenced the iconoclastic nature of his genius. That he did not +rest content until he had demonstrated the validity of his +revolutionary assumption shows how truly this great theorizer +made his hypotheses subservient to the most rigid inductions. + + +GALILEO GALILEI + +While Kepler was solving these riddles of planetary motion, there +was an even more famous man in Italy whose championship of the +Copernican doctrine was destined to give the greatest possible +publicity to the new ideas. This was Galileo Galilei, one of the +most extraordinary scientific observers of any age. Galileo was +born at Pisa, on the 18th of February (old style), 1564. The day +of his birth is doubly memorable, since on the same day the +greatest Italian of the preceding epoch, Michael Angelo, breathed +his last. Persons fond of symbolism have found in the coincidence +a forecast of the transit from the artistic to the scientific +epoch of the later Renaissance. Galileo came of an impoverished +noble family. He was educated for the profession of medicine, but +did not progress far before his natural proclivities directed him +towards the physical sciences. Meeting with opposition in Pisa, +he early accepted a call to the chair of natural philosophy in +the University of Padua, and later in life he made his home at +Florence. The mechanical and physical discoveries of Galileo will +claim our attention in another chapter. Our present concern is +with his contribution to the Copernican theory. + +Galileo himself records in a letter to Kepler that he became a +convert to this theory at an early day. He was not enabled, +however, to make any marked contribution to the subject, beyond +the influence of his general teachings, until about the year +1610. The brilliant contributions which he made were due largely +to a single discovery--namely, that of the telescope. Hitherto +the astronomical observations had been made with the unaided eye. +Glass lenses had been known since the thirteenth century, but, +until now, no one had thought of their possible use as aids to +distant vision. The question of priority of discovery has never +been settled. It is admitted, however, that the chief honors +belong to the opticians of the Netherlands. + +As early as the year 1590 the Dutch optician Zacharias Jensen +placed a concave and a convex lens respectively at the ends of a +tube about eighteen inches long, and used this instrument for the +purpose of magnifying small objects--producing, in short, a crude +microscope. Some years later, Johannes Lippershey, of whom not +much is known except that he died in 1619, experimented with a +somewhat similar combination of lenses, and made the startling +observation that the weather-vane on a distant church-steeple +seemed to be brought much nearer when viewed through the lens. +The combination of lenses he employed is that still used in the +construction of opera-glasses; the Germans still call such a +combination a Dutch telescope. + +Doubtless a large number of experimenters took the matter up and +the fame of the new instrument spread rapidly abroad. Galileo, +down in Italy, heard rumors of this remarkable contrivance, +through the use of which it was said "distant objects might be +seen as clearly as those near at hand." He at once set to work to +construct for himself a similar instrument, and his efforts were +so far successful that at first he "saw objects three times as +near and nine times enlarged." Continuing his efforts, he +presently so improved his glass that objects were enlarged almost +a thousand times and made to appear thirty times nearer than when +seen with the naked eye. Naturally enough, Galileo turned this +fascinating instrument towards the skies, and he was almost +immediately rewarded by several startling discoveries. At the +very outset, his magnifying-glass brought to view a vast number +of stars that are invisible to the naked eye, and enabled the +observer to reach the conclusion that the hazy light of the Milky +Way is merely due to the aggregation of a vast number of tiny +stars. + +Turning his telescope towards the moon, Galileo found that body +rough and earth-like in contour, its surface covered with +mountains, whose height could be approximately measured through +study of their shadows. This was disquieting, because the current +Aristotelian doctrine supposed the moon, in common with the +planets, to be a perfectly spherical, smooth body. The +metaphysical idea of a perfect universe was sure to be disturbed +by this seemingly rough workmanship of the moon. Thus far, +however, there was nothing in the observations of Galileo to bear +directly upon the Copernican theory; but when an inspection was +made of the planets the case was quite different. With the aid of +his telescope, Galileo saw that Venus, for example, passes +through phases precisely similar to those of the moon, due, of +course, to the same cause. Here, then, was demonstrative evidence +that the planets are dark bodies reflecting the light of the sun, +and an explanation was given of the fact, hitherto urged in +opposition to the Copernican theory, that the inferior planets do +not seem many times brighter when nearer the earth than when in +the most distant parts of their orbits; the explanation being, of +course, that when the planets are between the earth and the sun +only a small portion of their illumined surfaces is visible from +the earth. + +On inspecting the planet Jupiter, a still more striking +revelation was made, as four tiny stars were observed to occupy +an equatorial position near that planet, and were seen, when +watched night after night, to be circling about the planet, +precisely as the moon circles about the earth. Here, obviously, +was a miniature solar system--a tangible object-lesson in the +Copernican theory. In honor of the ruling Florentine house of the +period, Galileo named these moons of Jupiter, Medicean stars. + +Turning attention to the sun itself, Galileo observed on the +surface of that luminary a spot or blemish which gradually +changed its shape, suggesting that changes were taking place in +the substance of the sun--changes obviously incompatible with the +perfect condition demanded by the metaphysical theorists. But +however disquieting for the conservative, the sun's spots served +a most useful purpose in enabling Galileo to demonstrate that the +sun itself revolves on its axis, since a given spot was seen to +pass across the disk and after disappearing to reappear in due +course. The period of rotation was found to be about twenty-four +days. + +It must be added that various observers disputed priority of +discovery of the sun's spots with Galileo. Unquestionably a +sun-spot had been seen by earlier observers, and by them mistaken +for the transit of an inferior planet. Kepler himself had made +this mistake. Before the day of the telescope, he had viewed the +image of the sun as thrown on a screen in a camera-obscura, and +had observed a spot on the disk which be interpreted as +representing the planet Mercury, but which, as is now known, must +have been a sun-spot, since the planetary disk is too small to +have been revealed by this method. Such observations as these, +however interesting, cannot be claimed as discoveries of the +sun-spots. It is probable, however, that several discoverers +(notably Johann Fabricius) made the telescopic observation of the +spots, and recognized them as having to do with the sun's +surface, almost simultaneously with Galileo. One of these +claimants was a Jesuit named Scheiner, and the jealousy of this +man is said to have had a share in bringing about that +persecution to which we must now refer. + +There is no more famous incident in the history of science than +the heresy trial through which Galileo was led to the nominal +renunciation of his cherished doctrines. There is scarcely +another incident that has been commented upon so variously. Each +succeeding generation has put its own interpretation on it. The +facts, however, have been but little questioned. It appears that +in the year 1616 the church became at last aroused to the +implications of the heliocentric doctrine of the universe. +Apparently it seemed clear to the church authorities that the +authors of the Bible believed the world to be immovably fixed at +the centre of the universe. Such, indeed, would seem to be the +natural inference from various familiar phrases of the Hebrew +text, and what we now know of the status of Oriental science in +antiquity gives full warrant to this interpretation. There is no +reason to suppose that the conception of the subordinate place of +the world in the solar system had ever so much as occurred, even +as a vague speculation, to the authors of Genesis. In common with +their contemporaries, they believed the earth to be the +all-important body in the universe, and the sun a luminary placed +in the sky for the sole purpose of giving light to the earth. +There is nothing strange, nothing anomalous, in this view; it +merely reflects the current notions of Oriental peoples in +antiquity. What is strange and anomalous is the fact that the +Oriental dreamings thus expressed could have been supposed to +represent the acme of scientific knowledge. Yet such a hold had +these writings taken upon the Western world that not even a +Galileo dared contradict them openly; and when the church fathers +gravely declared the heliocentric theory necessarily false, +because contradictory to Scripture, there were probably few +people in Christendom whose mental attitude would permit them +justly to appreciate the humor of such a pronouncement. And, +indeed, if here and there a man might have risen to such an +appreciation, there were abundant reasons for the repression of +the impulse, for there was nothing humorous about the response +with which the authorities of the time were wont to meet the +expression of iconoclastic opinions. The burning at the stake of +Giordano Bruno, in the year 1600, was, for example, an +object-lesson well calculated to restrain the enthusiasm of other +similarly minded teachers. + +Doubtless it was such considerations that explained the relative +silence of the champions of the Copernican theory, accounting for +the otherwise inexplicable fact that about eighty years elapsed +after the death of Copernicus himself before a single text-book +expounded his theory. The text-book which then appeared, under +date of 1622, was written by the famous Kepler, who perhaps was +shielded in a measure from the papal consequences of such +hardihood by the fact of residence in a Protestant country. Not +that the Protestants of the time favored the heliocentric +doctrine--we have already quoted Luther in an adverse sense--but +of course it was characteristic of the Reformation temper to +oppose any papal pronouncement, hence the ultramontane +declaration of 1616 may indirectly have aided the doctrine which +it attacked, by making that doctrine less obnoxious to Lutheran +eyes. Be that as it may, the work of Kepler brought its author +into no direct conflict with the authorities. But the result was +quite different when, in 1632, Galileo at last broke silence and +gave the world, under cover of the form of dialogue, an elaborate +exposition of the Copernican theory. Galileo, it must be +explained, had previously been warned to keep silent on the +subject, hence his publication doubly offended the authorities. +To be sure, he could reply that his dialogue introduced a +champion of the Ptolemaic system to dispute with the upholder of +the opposite view, and that, both views being presented with full +array of argument, the reader was left to reach a verdict for +himself, the author having nowhere pointedly expressed an +opinion. But such an argument, of course, was specious, for no +one who read the dialogue could be in doubt as to the opinion of +the author. Moreover, it was hinted that Simplicio, the character +who upheld the Ptolemaic doctrine and who was everywhere worsted +in the argument, was intended to represent the pope himself--a +suggestion which probably did no good to Galileo's cause. + +The character of Galileo's artistic presentation may best be +judged from an example, illustrating the vigorous assault of +Salviati, the champion of the new theory, and the feeble retorts +of his conservative antagonist: + +"Salviati. Let us then begin our discussion with the +consideration that, whatever motion may be attributed to the +earth, yet we, as dwellers upon it, and hence as participators in +its motion, cannot possibly perceive anything of it, presupposing +that we are to consider only earthly things. On the other hand, +it is just as necessary that this same motion belong apparently +to all other bodies and visible objects, which, being separated +from the earth, do not take part in its motion. The correct +method to discover whether one can ascribe motion to the earth, +and what kind of motion, is, therefore, to investigate and +observe whether in bodies outside the earth a perceptible motion +may be discovered which belongs to all alike. Because a movement +which is perceptible only in the moon, for instance, and has +nothing to do with Venus or Jupiter or other stars, cannot +possibly be peculiar to the earth, nor can its seat be anywhere +else than in the moon. Now there is one such universal movement +which controls all others--namely, that which the sun, moon, the +other planets, the fixed stars--in short, the whole universe, +with the single exception of the earth--appears to execute from +east to west in the space of twenty-four hours. This now, as it +appears at the first glance anyway, might just as well be a +motion of the earth alone as of all the rest of the universe with +the exception of the earth, for the same phenomena would result +from either hypothesis. Beginning with the most general, I will +enumerate the reasons which seem to speak in favor of the earth's +motion. When we merely consider the immensity of the starry +sphere in comparison with the smallness of the terrestrial ball, +which is contained many million times in the former, and then +think of the rapidity of the motion which completes a whole +rotation in one day and night, I cannot persuade myself how any +one can hold it to be more reasonable and credible that it is the +heavenly sphere which rotates, while the earth stands still. + +"Simplicio. I do not well understand how that powerful motion may +be said to as good as not exist for the sun, the moon, the other +planets, and the innumerable host of fixed stars. Do you call +that nothing when the sun goes from one meridian to another, +rises up over this horizon and sinks behind that one, brings now +day, and now night; when the moon goes through similar changes, +and the other planets and fixed stars in the same way? + +"Salviati. All the changes you mention are such only in respect +to the earth. To convince yourself of it, only imagine the earth +out of existence. There would then be no rising and setting of +the sun or of the moon, no horizon, no meridian, no day, no +night--in short, the said motion causes no change of any sort in +the relation of the sun to the moon or to any of the other +heavenly bodies, be they planets or fixed stars. All changes are +rather in respect to the earth; they may all be reduced to the +simple fact that the sun is first visible in China, then in +Persia, afterwards in Egypt, Greece, France, Spain, America, +etc., and that the same thing happens with the moon and the other +heavenly bodies. Exactly the same thing happens and in exactly +the same way if, instead of disturbing so large a part of the +universe, you let the earth revolve about itself. The difficulty +is, however, doubled, inasmuch as a second very important problem +presents itself. If, namely, that powerful motion is ascribed to +the heavens, it is absolutely necessary to regard it as opposed +to the individual motion of all the planets, every one of which +indubitably has its own very leisurely and moderate movement from +west to east. If, on the other hand, you let the earth move about +itself, this opposition of motion disappears. + +"The improbability is tripled by the complete overthrow of that +order which rules all the heavenly bodies in which the revolving +motion is definitely established. The greater the sphere is in +such a case, so much longer is the time required for its +revolution; the smaller the sphere the shorter the time. Saturn, +whose orbit surpasses those of all the planets in size, traverses +it in thirty years. Jupiter[4] completes its smaller course in +twelve years, Mars in two; the moon performs its much smaller +revolution within a month. Just as clearly in the Medicean stars, +we see that the one nearest Jupiter completes its revolution in a +very short time--about forty-two hours; the next in about three +and one-half days, the third in seven, and the most distant one +in sixteen days. This rule, which is followed throughout, will +still remain if we ascribe the twenty-four-hourly motion to a +rotation of the earth. If, however, the earth is left motionless, +we must go first from the very short rule of the moon to ever +greater ones--to the two-yearly rule of Mars, from that to the +twelve-yearly one of Jupiter, from here to the thirty-yearly one +of Saturn, and then suddenly to an incomparably greater sphere, +to which also we must ascribe a complete rotation in twenty-four +hours. If, however, we assume a motion of the earth, the rapidity +of the periods is very well preserved; from the slowest sphere of +Saturn we come to the wholly motionless fixed stars. We also +escape thereby a fourth difficulty, which arises as soon as we +assume that there is motion in the sphere of the stars. I mean +the great unevenness in the movement of these very stars, some of +which would have to revolve with extraordinary rapidity in +immense circles, while others moved very slowly in small circles, +since some of them are at a greater, others at a less, distance +from the pole. That is likewise an inconvenience, for, on the one +hand, we see all those stars, the motion of which is indubitable, +revolve in great circles, while, on the other hand, there seems +to be little object in placing bodies, which are to move in +circles, at an enormous distance from the centre and then let +them move in very small circles. And not only are the size of the +different circles and therewith the rapidity of the movement very +different in the different fixed stars, but the same stars also +change their orbits and their rapidity of motion. Therein +consists the fifth inconvenience. Those stars, namely, which were +at the equator two thousand years ago, and hence described great +circles in their revolutions, must to-day move more slowly and in +smaller circles, because they are many degrees removed from it. +It will even happen, after not so very long a time, that one of +those which have hitherto been continually in motion will finally +coincide with the pole and stand still, but after a period of +repose will again begin to move. The other stars in the mean +while, which unquestionably move, all have, as was said, a great +circle for an orbit and keep this unchangeably. + +"The improbability is further increased--this may be considered +the sixth inconvenience--by the fact that it is impossible to +conceive what degree of solidity those immense spheres must have, +in the depths of which so many stars are fixed so enduringly that +they are kept revolving evenly in spite of such difference of +motion without changing their respective positions. Or if, +according to the much more probable theory, the heavens are +fluid, and every star describes an orbit of its own, according to +what law then, or for what reason, are their orbits so arranged +that, when looked at from the earth, they appear to be contained +in one single sphere? To attain this it seems to me much easier +and more convenient to make them motionless instead of moving, +just as the paving-stones on the market-place, for instance, +remain in order more easily than the swarms of children running +about on them. + +"Finally, the seventh difficulty: If we attribute the daily +rotation to the higher region of the heavens, we should have to +endow it with force and power sufficient to carry with it the +innumerable host of the fixed stars --every one a body of very +great compass and much larger than the earth--and all the +planets, although the latter, like the earth, move naturally in +an opposite direction. In the midst of all this the little earth, +single and alone, would obstinately and wilfully withstand such +force--a supposition which, it appears to me, has much against +it. I could also not explain why the earth, a freely poised body, +balancing itself about its centre, and surrounded on all sides by +a fluid medium, should not be affected by the universal rotation. +Such difficulties, however, do not confront us if we attribute +motion to the earth--such a small, insignificant body in +comparison with the whole universe, and which for that very +reason cannot exercise any power over the latter. + +"Simplicio. You support your arguments throughout, it seems to +me, on the greater ease and simplicity with which the said +effects are produced. You mean that as a cause the motion of the +earth alone is just as satisfactory as the motion of all the rest +of the universe with the exception of the earth; you hold the +actual event to be much easier in the former case than in the +latter. For the ruler of the universe, however, whose might is +infinite, it is no less easy to move the universe than the earth +or a straw balm. But if his power is infinite, why should not a +greater, rather than a very small, part of it be revealed to me? + +"Salviati. If I had said that the universe does not move on +account of the impotence of its ruler, I should have been wrong +and your rebuke would have been in order. I admit that it is just +as easy for an infinite power to move a hundred thousand as to +move one. What I said, however, does not refer to him who causes +the motion, but to that which is moved. In answer to your remark +that it is more fitting for an infinite power to reveal a large +part of itself rather than a little, I answer that, in relation +to the infinite, one part is not greater than another, if both +are finite. Hence it is unallowable to say that a hundred +thousand is a larger part of an infinite number than two, +although the former is fifty thousand times greater than the +latter. If, therefore, we consider the moving bodies, we must +unquestionably regard the motion of the earth as a much simpler +process than that of the universe; if, furthermore, we direct our +attention to so many other simplifications which may be reached +only by this theory, the daily movement of the earth must appear +much more probable than the motion of the universe without the +earth, for, according to Aristotle's just axiom, 'Frustra fit per +plura, quod potest fieri per p auciora' (It is vain to expend +many means where a few are sufficient)."[2] + + +The work was widely circulated, and it was received with an +interest which bespeaks a wide-spread undercurrent of belief in +the Copernican doctrine. Naturally enough, it attracted immediate +attention from the church authorities. Galileo was summoned to +appear at Rome to defend his conduct. The philosopher, who was +now in his seventieth year, pleaded age and infirmity. He had no +desire for personal experience of the tribunal of the +Inquisition; but the mandate was repeated, and Galileo went to +Rome. There, as every one knows, he disavowed any intention to +oppose the teachings of Scripture, and formally renounced the +heretical doctrine of the earth's motion. According to a tale +which so long passed current that every historian must still +repeat it though no one now believes it authentic, Galileo +qualified his renunciation by muttering to himself, "E pur si +muove" (It does move, none the less), as he rose to his feet and +retired from the presence of his persecutors. The tale is one of +those fictions which the dramatic sense of humanity is wont to +impose upon history, but, like most such fictions, it expresses +the spirit if not the letter of truth; for just as no one +believes that Galileo's lips uttered the phrase, so no one doubts +that the rebellious words were in his mind. + +After his formal renunciation, Galileo was allowed to depart, but +with the injunction that he abstain in future from heretical +teaching. The remaining ten years of his life were devoted +chiefly to mechanics, where his experiments fortunately opposed +the Aristotelian rather than the Hebrew teachings. Galileo's +death occurred in 1642, a hundred years after the death of +Copernicus. Kepler had died thirteen years before, and there +remained no astronomer in the field who is conspicuous in the +history of science as a champion of the Copernican doctrine. But +in truth it might be said that the theory no longer needed a +champion. The researches of Kepler and Galileo had produced a +mass of evidence for the Copernican theory which amounted to +demonstration. A generation or two might be required for this +evidence to make itself everywhere known among men of science, +and of course the ecclesiastical authorities must be expected to +stand by their guns for a somewhat longer period. In point of +fact, the ecclesiastical ban was not technically removed by the +striking of the Copernican books from the list of the Index +Expurgatorius until the year 1822, almost two hundred years after +the date of Galileo's dialogue. But this, of course, is in no +sense a guide to the state of general opinion regarding the +theory. We shall gain a true gauge as to this if we assume that +the greater number of important thinkers had accepted the +heliocentric doctrine before the middle of the seventeenth +century, and that before the close of that century the old +Ptolemaic idea had been quite abandoned. A wonderful revolution +in man's estimate of the universe had thus been effected within +about two centuries after the birth of Copernicus. + + + +V. GALILEO AND THE NEW PHYSICS + +After Galileo had felt the strong hand of the Inquisition, in +1632, he was careful to confine his researches, or at least his +publications, to topics that seemed free from theological +implications. In doing so he reverted to the field of his +earliest studies --namely, the field of mechanics; and the +Dialoghi delle Nuove Scienze, which he finished in 1636, and +which was printed two years later, attained a celebrity no less +than that of the heretical dialogue that had preceded it. The +later work was free from all apparent heresies, yet perhaps it +did more towards the establishment of the Copernican doctrine, +through the teaching of correct mechanical principles, than the +other work had accomplished by a more direct method. + +Galileo's astronomical discoveries were, as we have seen, in a +sense accidental; at least, they received their inception through +the inventive genius of another. His mechanical discoveries, on +the other hand, were the natural output of his own creative +genius. At the very beginning of his career, while yet a very +young man, though a professor of mathematics at Pisa, he had +begun that onslaught upon the old Aristotelian ideas which he was +to continue throughout his life. At the famous leaning tower in +Pisa, the young iconoclast performed, in the year 1590, one of +the most theatrical demonstrations in the history of science. +Assembling a multitude of champions of the old ideas, he proposed +to demonstrate the falsity of the Aristotelian doctrine that the +velocity of falling bodies is proportionate to their weight. +There is perhaps no fact more strongly illustrative of the temper +of the Middle Ages than the fact that this doctrine, as taught by +the Aristotelian philosopher, should so long have gone +unchallenged. Now, however, it was put to the test; Galileo +released a half-pound weight and a hundred-pound cannon-ball from +near the top of the tower, and, needless to say, they reached the +ground together. Of course, the spectators were but little +pleased with what they saw. They could not doubt the evidence of +their own senses as to the particular experiment in question; +they could suggest, however, that the experiment involved a +violation of the laws of nature through the practice of magic. To +controvert so firmly established an idea savored of heresy. The +young man guilty of such iconoclasm was naturally looked at +askance by the scholarship of his time. Instead of being +applauded, he was hissed, and he found it expedient presently to +retire from Pisa. + +Fortunately, however, the new spirit of progress had made itself +felt more effectively in some other portions of Italy, and so +Galileo found a refuge and a following in Padua, and afterwards +in Florence; and while, as we have seen, he was obliged to curb +his enthusiasm regarding the subject that was perhaps nearest his +heart--the promulgation of the Copernican theory--yet he was +permitted in the main to carry on his experimental observations +unrestrained. These experiments gave him a place of unquestioned +authority among his contemporaries, and they have transmitted his +name to posterity as that of one of the greatest of experimenters +and the virtual founder of modern mechanical science. The +experiments in question range over a wide field; but for the most +part they have to do with moving bodies and with questions of +force, or, as we should now say, of energy. The experiment at the +leaning tower showed that the velocity of falling bodies is +independent of the weight of the bodies, provided the weight is +sufficient to overcome the resistance of the atmosphere. Later +experiments with falling bodies led to the discovery of laws +regarding the accelerated velocity of fall. Such velocities were +found to bear a simple relation to the period of time from the +beginning of the fall. Other experiments, in which balls were +allowed to roll down inclined planes, corroborated the +observation that the pull of gravitation gave a velocity +proportionate to the length of fall, whether such fall were +direct or in a slanting direction. + +These studies were associated with observations on projectiles, +regarding which Galileo was the first to entertain correct +notions. According to the current idea, a projectile fired, for +example, from a cannon, moved in a straight horizontal line until +the propulsive force was exhausted, and then fell to the ground +in a perpendicular line. Galileo taught that the projectile +begins to fall at once on leaving the mouth of the cannon and +traverses a parabolic course. According to his idea, which is now +familiar to every one, a cannon-ball dropped from the level of +the cannon's muzzle will strike the ground simultaneously with a +ball fired horizontally from the cannon. As to the paraboloid +course pursued by the projectile, the resistance of the air is a +factor which Galileo could not accurately compute, and which +interferes with the practical realization of his theory. But this +is a minor consideration. The great importance of his idea +consists in the recognition that such a force as that of +gravitation acts in precisely the same way upon all unsupported +bodies, whether or not such bodies be at the same time acted upon +by a force of translation. + +Out of these studies of moving bodies was gradually developed a +correct notion of several important general laws of +mechanics--laws a knowledge of which was absolutely essential to +the progress of physical science. The belief in the rotation of +the earth made necessary a clear conception that all bodies at +the surface of the earth partake of that motion quite +independently of their various observed motions in relation to +one another. This idea was hard to grasp, as an oft-repeated +argument shows. It was asserted again and again that, if the +earth rotates, a stone dropped from the top of a tower could not +fall at the foot of the tower, since the earth's motion would +sweep the tower far away from its original position while the +stone is in transit. + +This was one of the stock arguments against the earth's motion, +yet it was one that could be refuted with the greatest ease by +reasoning from strictly analogous experiments. It might readily +be observed, for example, that a stone dropped from a moving cart +does not strike the ground directly below the point from which it +is dropped, but partakes of the forward motion of the cart. If +any one doubt this he has but to jump from a moving cart to be +given a practical demonstration of the fact that his entire body +was in some way influenced by the motion of translation. +Similarly, the simple experiment of tossing a ball from the deck +of a moving ship will convince any one that the ball partakes of +the motion of the ship, so that it can be manipulated precisely +as if the manipulator were standing on the earth. In short, +every-day experience gives us illustrations of what might be +called compound motion, which makes it seem altogether plausible +that, if the earth is in motion, objects at its surface will +partake of that motion in a way that does not interfere with any +other movements to which they may be subjected. As the Copernican +doctrine made its way, this idea of compound motion naturally +received more and more attention, and such experiments as those +of Galileo prepared the way for a new interpretation of the +mechanical principles involved. + +The great difficulty was that the subject of moving bodies had +all along been contemplated from a wrong point of view. Since +force must be applied to an object to put it in motion, it was +perhaps not unnaturally assumed that similar force must continue +to be applied to keep the object in motion. When, for example, a +stone is thrown from the hand, the direct force applied +necessarily ceases as soon as the projectile leaves the hand. The +stone, nevertheless, flies on for a certain distance and then +falls to the ground. How is this flight of the stone to be +explained? The ancient philosophers puzzled more than a little +over this problem, and the Aristotelians reached the conclusion +that the motion of the hand had imparted a propulsive motion to +the air, and that this propulsive motion was transmitted to the +stone, pushing it on. Just how the air took on this propulsive +property was not explained, and the vagueness of thought that +characterized the time did not demand an explanation. Possibly +the dying away of ripples in water may have furnished, by +analogy, an explanation of the gradual dying out of the impulse +which propels the stone. + +All of this was, of course, an unfortunate maladjustment of the +point of view. As every one nowadays knows, the air retards the +progress of the stone, enabling the pull of gravitation to drag +it to the earth earlier than it otherwise could. Were the +resistance of the air and the pull of gravitation removed, the +stone as projected from the hand would fly on in a straight line, +at an unchanged velocity, forever. But this fact, which is +expressed in what we now term the first law of motion, was +extremely difficult to grasp. The first important step towards it +was perhaps implied in Galileo's study of falling bodies. These +studies, as we have seen, demonstrated that a half-pound weight +and a hundred-pound weight fall with the same velocity. It is, +however, matter of common experience that certain bodies, as, for +example, feathers, do not fall at the same rate of speed with +these heavier bodies. This anomaly demands an explanation, and +the explanation is found in the resistance offered the relatively +light object by the air. Once the idea that the air may thus act +as an impeding force was grasped, the investigator of mechanical +principles had entered on a new and promising course. + +Galileo could not demonstrate the retarding influence of air in +the way which became familiar a generation or two later; he could +not put a feather and a coin in a vacuum tube and prove that the +two would there fall with equal velocity, because, in his day, +the air-pump had not yet been invented. The experiment was made +only a generation after the time of Galileo, as we shall see; +but, meantime, the great Italian had fully grasped the idea that +atmospheric resistance plays a most important part in regard to +the motion of falling and projected bodies. Thanks largely to his +own experiments, but partly also to the efforts of others, he had +come, before the end of his life, pretty definitely to realize +that the motion of a projectile, for example, must be thought of +as inherent in the projectile itself, and that the retardation or +ultimate cessation of that motion is due to the action of +antagonistic forces. In other words, he had come to grasp the +meaning of the first law of motion. It remained, however, for the +great Frenchman Descartes to give precise expression to this law +two years after Galileo's death. As Descartes expressed it in his +Principia Philosophiae, published in 1644, any body once in +motion tends to go on in a straight line, at a uniform rate of +speed, forever. Contrariwise, a stationary body will remain +forever at rest unless acted on by some disturbing force. + +This all-important law, which lies at the very foundation of all +true conceptions of mechanics, was thus worked out during the +first half of the seventeenth century, as the outcome of +numberless experiments for which Galileo's experiments with +failing bodies furnished the foundation. So numerous and so +gradual were the steps by which the reversal of view regarding +moving bodies was effected that it is impossible to trace them in +detail. We must be content to reflect that at the beginning of +the Galilean epoch utterly false notions regarding the subject +were entertained by the very greatest philosophers--by Galileo +himself, for example, and by Kepler--whereas at the close of that +epoch the correct and highly illuminative view had been attained. + +We must now consider some other experiments of Galileo which led +to scarcely less-important results. The experiments in question +had to do with the movements of bodies passing down an inclined +plane, and with the allied subject of the motion of a pendulum. +The elaborate experiments of Galileo regarding the former subject +were made by measuring the velocity of a ball rolling down a +plane inclined at various angles. He found that the velocity +acquired by a ball was proportional to the height from which the +ball descended regardless of the steepness of the incline. +Experiments were made also with a ball rolling down a curved +gutter, the curve representing the are of a circle. These +experiments led to the study of the curvilinear motions of a +weight suspended by a cord; in other words, of the pendulum. + +Regarding the motion of the pendulum, some very curious facts +were soon ascertained. Galileo found, for example, that a +pendulum of a given length performs its oscillations with the +same frequency though the arc described by the pendulum be varied +greatly.[1] He found, also, that the rate of oscillation for +pendulums of different lengths varies according to a simple law. +In order that one pendulum shall oscillate one-half as fast as +another, the length of the pendulums must be as four to one. +Similarly, by lengthening the pendulums nine times, the +oscillation is reduced to one-third, In other words, the rate of +oscillation of pendulums varies inversely as the square of their +length. Here, then, is a simple relation between the motions of +swinging bodies which suggests the relation which Kepler bad +discovered between the relative motions of the planets. Every +such discovery coming in this age of the rejuvenation of +experimental science had a peculiar force in teaching men the +all-important lesson that simple laws lie back of most of the +diverse phenomena of nature, if only these laws can be +discovered. + +Galileo further observed that his pendulum might be constructed +of any weight sufficiently heavy readily to overcome the +atmospheric resistance, and that, with this qualification, +neither the weight nor the material had any influence upon the +time of oscillation, this being solely determined by the length +of the cord. Naturally, the practical utility of these +discoveries was not overlooked by Galileo. Since a pendulum of a +given length oscillates with unvarying rapidity, here is an +obvious means of measuring time. Galileo, however, appears not to +have met with any great measure of success in putting this idea +into practice. It remained for the mechanical ingenuity of +Huyghens to construct a satisfactory pendulum clock. + +As a theoretical result of the studies of rolling and oscillating +bodies, there was developed what is usually spoken of as the +third law of motion--namely, the law that a given force operates +upon a moving body with an effect proportionate to its effect +upon the same body when at rest. Or, as Whewell states the law: +"The dynamical effect of force is as the statical effect; that +is, the velocity which any force generates in a given time, when +it puts the body in motion, is proportional to the pressure which +this same force produces in a body at rest."[2] According to the +second law of motion, each one of the different forces, operating +at the same time upon a moving body, produces the same effect as +if it operated upon the body while at rest. + + +STEVINUS AND THE LAW OF EQUILIBRIUM + +It appears, then, that the mechanical studies of Galileo, taken +as a whole, were nothing less than revolutionary. They +constituted the first great advance upon the dynamic studies of +Archimedes, and then led to the secure foundation for one of the +most important of modern sciences. We shall see that an important +company of students entered the field immediately after the time +of Galileo, and carried forward the work he had so well begun. +But before passing on to the consideration of their labors, we +must consider work in allied fields of two men who were +contemporaries of Galileo and whose original labors were in some +respects scarcely less important than his own. These men are the +Dutchman Stevinus, who must always be remembered as a co-laborer +with Galileo in the foundation of the science of dynamics, and +the Englishman Gilbert, to whom is due the unqualified praise of +first subjecting the phenomenon of magnetism to a strictly +scientific investigation. + +Stevinus was born in the year 1548, and died in 1620. He was a +man of a practical genius, and he attracted the attention of his +non-scientific contemporaries, among other ways, by the +construction of a curious land-craft, which, mounted on wheels, +was to be propelled by sails like a boat. Not only did he write a +book on this curious horseless carriage, but he put his idea into +practical application, producing a vehicle which actually +traversed the distance between Scheveningen and Petton, with no +fewer than twenty-seven passengers, one of them being Prince +Maurice of Orange. This demonstration was made about the year +1600. It does not appear, however, that any important use was +made of the strange vehicle; but the man who invented it put his +mechanical ingenuity to other use with better effect. It was he +who solved the problem of oblique forces, and who discovered the +important hydrostatic principle that the pressure of fluids is +proportionate to their depth, without regard to the shape of the +including vessel. + +The study of oblique forces was made by Stevinus with the aid of +inclined planes. His most demonstrative experiment was a very +simple one, in which a chain of balls of equal weight was hung +from a triangle; the triangle being so constructed as to rest on +a horizontal base, the oblique sides bearing the relation to each +other of two to one. Stevinus found that his chain of balls just +balanced when four balls were on the longer side and two on the +shorter and steeper side. The balancing of force thus brought +about constituted a stable equilibrium, Stevinus being the first +to discriminate between such a condition and the unbalanced +condition called unstable equilibrium. By this simple experiment +was laid the foundation of the science of statics. Stevinus had a +full grasp of the principle which his experiment involved, and he +applied it to the solution of oblique forces in all directions. +Earlier investigations of Stevinus were published in 1608. His +collected works were published at Leyden in 1634. + +This study of the equilibrium of pressure of bodies at rest led +Stevinus, not unnaturally, to consider the allied subject of the +pressure of liquids. He is to be credited with the explanation of +the so-called hydrostatic paradox. The familiar modern experiment +which illustrates this paradox is made by inserting a long +perpendicular tube of small caliber into the top of a tight +barrel. On filling the barrel and tube with water, it is possible +to produce a pressure which will burst the barrel, though it be a +strong one, and though the actual weight of water in the tube is +comparatively insignificant. This illustrates the fact that the +pressure at the bottom of a column of liquid is proportionate to +the height of the column, and not to its bulk, this being the +hydrostatic paradox in question. The explanation is that an +enclosed fluid under pressure exerts an equal force upon all +parts of the circumscribing wall; the aggregate pressure may, +therefore, be increased indefinitely by increasing the surface. +It is this principle, of course, which is utilized in the +familiar hydrostatic press. Theoretical explanations of the +pressure of liquids were supplied a generation or two later by +numerous investigators, including Newton, but the practical +refoundation of the science of hydrostatics in modern times dates +from the experiments of Stevinus. + + +GALILEO AND THE EQUILIBRIUM OF FLUIDS + +Experiments of an allied character, having to do with the +equilibrium of fluids, exercised the ingenuity of Galileo. Some +of his most interesting experiments have to do with the subject +of floating bodies. It will be recalled that Archimedes, away +back in the Alexandrian epoch, had solved the most important +problems of hydrostatic equilibrium. Now, however, his +experiments were overlooked or forgotten, and Galileo was obliged +to make experiments anew, and to combat fallacious views that +ought long since to have been abandoned. Perhaps the most +illuminative view of the spirit of the times can be gained by +quoting at length a paper of Galileo's, in which he details his +own experiments with floating bodies and controverts the views of +his opponents. The paper has further value as illustrating +Galileo's methods both as experimenter and as speculative +reasoner. + +The current view, which Galileo here undertakes to refute, +asserts that water offers resistance to penetration, and that +this resistance is instrumental in determining whether a body +placed in water will float or sink. Galileo contends that water +is non-resistant, and that bodies float or sink in virtue of +their respective weights. This, of course, is merely a +restatement of the law of Archimedes. But it remains to explain +the fact that bodies of a certain shape will float, while bodies +of the same material and weight, but of a different shape, will +sink. We shall see what explanation Galileo finds of this anomaly +as we proceed. + +In the first place, Galileo makes a cone of wood or of wax, and +shows that when it floats with either its point or its base in +the water, it displaces exactly the same amount of fluid, +although the apex is by its shape better adapted to overcome the +resistance of the water, if that were the cause of buoyancy. +Again, the experiment may be varied by tempering the wax with +filings of lead till it sinks in the water, when it will be found +that in any figure the same quantity of cork must be added to it +to raise the surface. + +"But," says Galileo, "this silences not my antagonists; they say +that all the discourse hitherto made by me imports little to +them, and that it serves their turn; that they have demonstrated +in one instance, and in such manner and figure as pleases them +best --namely, in a board and in a ball of ebony--that one when +put into the water sinks to the bottom, and that the other stays +to swim on the top; and the matter being the same, and the two +bodies differing in nothing but in figure, they affirm that with +all perspicuity they have demonstrated and sensibly manifested +what they undertook. Nevertheless, I believe, and think I can +prove, that this very experiment proves nothing against my +theory. And first, it is false that the ball sinks and the board +not; for the board will sink, too, if you do to both the figures +as the words of our question require; that is, if you put them +both in the water; for to be in the water implies to be placed in +the water, and by Aristotle's own definition of place, to be +placed imports to be environed by the surface of the ambient +body; but when my antagonists show the floating board of ebony, +they put it not into the water, but upon the water; where, being +detained by a certain impediment (of which more anon), it is +surrounded, partly with water, partly with air, which is contrary +to our agreement, for that was that bodies should be in the +water, and not part in the water, part in the air. + +"I will not omit another reason, founded also upon experience, +and, if I deceive not myself, conclusive against the notion that +figure, and the resistance of the water to penetration, have +anything to do with the buoyancy of bodies. Choose a piece of +wood or other matter, as, for instance, walnut-wood, of which a +ball rises from the bottom of the water to the surface more +slowly than a ball of ebony of the same size sinks, so that, +clearly, the ball of ebony divides the water more readily in +sinking than the ball of wood does in rising. Then take a board +of walnut-tree equal to and like the floating one of my +antagonists; and if it be true that this latter floats by reason +of the figure being unable to penetrate the water, the other of +walnut-tree, without a question, if thrust to the bottom, ought +to stay there, as having the same impeding figure, and being less +apt to overcome the said resistance of the water. But if we find +by experience that not only the thin board, but every other +figure of the same walnut-tree, will return to float, as +unquestionably we shall, then I must desire my opponents to +forbear to attribute the floating of the ebony to the figure of +the board, since the resistance of the water is the same in +rising as in sinking, and the force of ascension of the +walnut-tree is less than the ebony's force for going to the +bottom. + +"Now let us return to the thin plate of gold or silver, or the +thin board of ebony, and let us lay it lightly upon the water, so +that it may stay there without sinking, and carefully observe the +effect. It will appear clearly that the plates are a considerable +matter lower than the surface of the water, which rises up and +makes a kind of rampart round them on every side. But if it has +already penetrated and overcome the continuity of the water, and +is of its own nature heavier than the water, why does it not +continue to sink, but stop and suspend itself in that little +dimple that its weight has made in the water? My answer is, +because in sinking till its surface is below the water, which +rises up in a bank round it, it draws after and carries along +with it the air above it, so that that which, in this case, +descends in the water is not only the board of ebony or the plate +of iron, but a compound of ebony and air, from which composition +results a solid no longer specifically heavier than the water, as +was the ebony or gold alone. But, gentlemen, we want the same +matter; you are to alter nothing but the shape, and, therefore, +have the goodness to remove this air, which may be done simply by +washing the surface of the board, for the water having once got +between the board and the air will run together, and the ebony +will go to the bottom; and if it does not, you have won the day. + +"But methinks I hear some of my antagonists cunningly opposing +this, and telling me that they will not on any account allow +their boards to be wetted, because the weight of the water so +added, by making it heavier than it was before, draws it to the +bottom, and that the addition of new weight is contrary to our +agreement, which was that the matter should be the same. + +"To this I answer, first, that nobody can suppose bodies to be +put into the water without their being wet, nor do I wish to do +more to the board than you may do to the ball. Moreover, it is +not true that the board sinks on account of the weight of the +water added in the washing; for I will put ten or twenty drops on +the floating board, and so long as they stand separate it shall +not sink; but if the board be taken out and all that water wiped +off, and the whole surface bathed with one single drop, and put +it again upon the water, there is no question but it will sink, +the other water running to cover it, being no longer hindered by +the air. In the next place, it is altogether false that water can +in any way increase the weight of bodies immersed in it, for +water has no weight in water, since it does not sink. Now just as +he who should say that brass by its own nature sinks, but that +when formed into the shape of a kettle it acquires from that +figure the virtue of lying in water without sinking, would say +what is false, because that is not purely brass which then is put +into the water, but a compound of brass and air; so is it neither +more nor less false that a thin plate of brass or ebony swims by +virtue of its dilated and broad figure. Also, I cannot omit to +tell my opponents that this conceit of refusing to bathe the +surface of the board might beget an opinion in a third person of +a poverty of argument on their side, especially as the +conversation began about flakes of ice, in which it would be +simple to require that the surfaces should be kept dry; not to +mention that such pieces of ice, whether wet or dry, always +float, and so my antagonists say, because of their shape. + +"Some may wonder that I affirm this power to be in the air of +keeping plate of brass or silver above water, as if in a certain +sense I would attribute to the air a kind of magnetic virtue for +sustaining heavy bodies with which it is in contact. To satisfy +all these doubts I have contrived the following experiment to +demonstrate how truly the air does support these bodies; for I +have found, when one of these bodies which floats when placed +lightly on the water is thoroughly bathed and sunk to the bottom, +that by carrying down to it a little air without otherwise +touching it in the least, I am able to raise and carry it back to +the top, where it floats as before. To this effect, I take a ball +of wax, and with a little lead make it just heavy enough to sink +very slowly to the bottom, taking care that its surface be quite +smooth and even. This, if put gently into the water, submerges +almost entirely, there remaining visible only a little of the +very top, which, so long as it is joined to the air, keeps the +ball afloat; but if we take away the contact of the air by +wetting this top, the ball sinks to the bottom and remains there. +Now to make it return to the surface by virtue of the air which +before sustained it, thrust into the water a glass with the mouth +downward, which will carry with it the air it contains, and move +this down towards the ball until you see, by the transparency of +the glass, that the air has reached the top of it; then gently +draw the glass upward, and you will see the ball rise, and +afterwards stay on the top of the water, if you carefully part +the glass and water without too much disturbing it."[3] + +It will be seen that Galileo, while holding in the main to a +correct thesis, yet mingles with it some false ideas. At the very +outset, of course, it is not true that water has no resistance to +penetration; it is true, however, in the sense in which Galileo +uses the term--that is to say, the resistance of the water to +penetration is not the determining factor ordinarily in deciding +whether a body sinks or floats. Yet in the case of the flat body +it is not altogether inappropriate to say that the water resists +penetration and thus supports the body. The modern physicist +explains the phenomenon as due to surface-tension of the fluid. +Of course, Galileo's disquisition on the mixing of air with the +floating body is utterly fanciful. His experiments were +beautifully exact; his theorizing from them was, in this +instance, altogether fallacious. Thus, as already intimated, his +paper is admirably adapted to convey a double lesson to the +student of science. + + +WILLIAM GILBERT AND THE STUDY OF MAGNETISM + +It will be observed that the studies of Galileo and Stevinus were +chiefly concerned with the force of gravitation. Meanwhile, there +was an English philosopher of corresponding genius, whose +attention was directed towards investigation of the equally +mysterious force of terrestrial magnetism. With the doubtful +exception of Bacon, Gilbert was the most distinguished man of +science in England during the reign of Queen Elizabeth. He was +for many years court physician, and Queen Elizabeth ultimately +settled upon him a pension that enabled him to continue his +researches in pure science. + +His investigations in chemistry, although supposed to be of great +importance, are mostly lost; but his great work, De Magnete, on +which he labored for upwards of eighteen years, is a work of +sufficient importance, as Hallam says, "to raise a lasting +reputation for its author." From its first appearance it created +a profound impression upon the learned men of the continent, +although in England Gilbert's theories seem to have been somewhat +less favorably received. Galileo freely expressed his admiration +for the work and its author; Bacon, who admired the author, did +not express the same admiration for his theories; but Dr. +Priestley, later, declared him to be "the father of modern +electricity." + +Strangely enough, Gilbert's book had never been translated into +English, or apparently into any other language, until recent +years, although at the time of its publication certain learned +men, unable to read the book in the original, had asked that it +should be. By this neglect, or oversight, a great number of +general readers as well as many scientists, through succeeding +centuries, have been deprived of the benefit of writings that +contained a good share of the fundamental facts about magnetism +as known to-day. + +Gilbert was the first to discover that the earth is a great +magnet, and he not only gave the name of "pole" to the +extremities of the magnetic needle, but also spoke of these +"poles" as north and south pole, although he used these names in +the opposite sense from that in which we now use them, his south +pole being the extremity which pointed towards the north, and +vice versa. He was also first to make use of the terms "electric +force," "electric emanations," and "electric attractions." + +It is hardly necessary to say that some of the views taken by +Gilbert, many of his theories, and the accuracy of some of his +experiments have in recent times been found to be erroneous. As a +pioneer in an unexplored field of science, however, his work is +remarkably accurate. "On the whole," says Dr. John Robinson, +"this performance contains more real information than any writing +of the age in which he lived, and is scarcely exceeded by any +that has appeared since."[4] + +In the preface to his work Gilbert says: "Since in the discovery +of secret things, and in the investigation of hidden causes, +stronger reasons are obtained from sure experiments and +demonstrated arguments than from probable conjectures and the +opinions of philosophical speculators of the common sort, +therefore, to the end of that noble substance of that great +loadstone, our common mother (the earth), still quite unknown, +and also that the forces extraordinary and exalted of this globe +may the better be understood, we have decided, first, to begin +with the common stony and ferruginous matter, and magnetic +bodies, and the part of the earth that we may handle and may +perceive with senses, and then to proceed with plain magnetic +experiments, and to penetrate to the inner parts of the +earth."[5] + +Before taking up the demonstration that the earth is simply a +giant loadstone, Gilbert demonstrated in an ingenious way that +every loadstone, of whatever size, has definite and fixed poles. +He did this by placing the stone in a metal lathe and converting +it into a sphere, and upon this sphere demonstrated how the poles +can be found. To this round loadstone he gave the name of +terrella--that is, little earth. + +"To find, then, poles answering to the earth," he says, "take in +your hand the round stone, and lay on it a needle or a piece of +iron wire: the ends of the wire move round their middle point, +and suddenly come to a standstill. Now, with ochre or with chalk, +mark where the wire lies still and sticks. Then move the middle +or centre of the wire to another spot, and so to a third and +fourth, always marking the stone along the length of the wire +where it stands still; the lines so marked will exhibit meridian +circles, or circles like meridians, on the stone or terrella; and +manifestly they will all come together at the poles of the stone. +The circle being continued in this way, the poles appear, both +the north and the south, and betwixt these, midway, we may draw a +large circle for an equator, as is done by the astronomer in the +heavens and on his spheres, and by the geographer on the +terrestrial globe."[6] + +Gilbert had tried the familiar experiment of placing the +loadstone on a float in water, and observed that the poles always +revolved until they pointed north and south, which he explained +as due to the earth's magnetic attraction. In this same +connection he noticed that a piece of wrought iron mounted on a +cork float was attracted by other metals to a slight degree, and +he observed also that an ordinary iron bar, if suspended +horizontally by a thread, assumes invariably a north and south +direction. These, with many other experiments of a similar +nature, convinced him that the earth "is a magnet and a +loadstone," which he says is a "new and till now unheard-of view +of the earth." + +Fully to appreciate Gilbert's revolutionary views concerning the +earth as a magnet, it should be remembered that numberless +theories to explain the action of the electric needle had been +advanced. Columbus and Paracelsus, for example, believed that the +magnet was attracted by some point in the heavens, such as a +magnetic star. Gilbert himself tells of some of the beliefs that +had been held by his predecessors, many of whom he declares +"wilfully falsify." One of his first steps was to refute by +experiment such assertions as that of Cardan, that "a wound by a +magnetized needle was painless"; and also the assertion of +Fracastoni that loadstone attracts silver; or that of Scalinger, +that the diamond will attract iron; and the statement of +Matthiolus that "iron rubbed with garlic is no longer attracted +to the loadstone." + +Gilbert made extensive experiments to explain the dipping of the +needle, which had been first noticed by William Norman. His +deduction as to this phenomenon led him to believe that this was +also explained by the magnetic attraction of the earth, and to +predict where the vertical dip would be found. These deductions +seem the more wonderful because at the time he made them the dip +had just been discovered, and had not been studied except at +London. His theory of the dip was, therefore, a scientific +prediction, based on a preconceived hypothesis. Gilbert found the +dip to be 72 degrees at London; eight years later Hudson found +the dip at 75 degrees 22' north latitude to be 89 degrees 30'; +but it was not until over two hundred years later, in 1831, that +the vertical dip was first observed by Sir James Ross at about 70 +degrees 5' north latitude, and 96 degrees 43' west longitude. +This was not the exact point assumed by Gilbert, and his +scientific predictions, therefore, were not quite correct; but +such comparatively slight and excusable errors mar but little the +excellence of his work as a whole. + +A brief epitome of some of his other important discoveries +suffices to show that the exalted position in science accorded +him by contemporaries, as well as succeeding generations of +scientists, was well merited. He was first to distinguish between +magnetism and electricity, giving the latter its name. He +discovered also the "electrical charge," and pointed the way to +the discovery of insulation by showing that the charge could be +retained some time in the excited body by covering it with some +non-conducting substance, such as silk; although, of course, +electrical conduction can hardly be said to have been more than +vaguely surmised, if understood at all by him. The first +electrical instrument ever made, and known as such, was invented +by him, as was also the first magnetometer, and the first +electrical indicating device. Although three centuries have +elapsed since his death, the method of magnetizing iron first +introduced by him is in common use to-day. + +He made exhaustive experiments with a needle balanced on a pivot +to see how many substances he could find which, like amber, on +being rubbed affected the needle. In this way he discovered that +light substances were attracted by alum, mica, arsenic, +sealing-wax, lac sulphur, slags, beryl, amethyst, rock-crystal, +sapphire, jet, carbuncle, diamond, opal, Bristol stone, glass, +glass of antimony, gum-mastic, hard resin, rock-salt, and, of +course, amber. He discovered also that atmospheric conditions +affected the production of electricity, dryness being unfavorable +and moisture favorable. + +Galileo's estimate of this first electrician is the verdict of +succeeding generations. "I extremely admire and envy this +author," he said. "I think him worthy of the greatest praise for +the many new and true observations which he has made, to the +disgrace of so many vain and fabling authors." + + +STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE + +We have seen that Gilbert was by no means lacking in versatility, +yet the investigations upon which his fame is founded were all +pursued along one line, so that the father of magnetism may be +considered one of the earliest of specialists in physical +science. Most workers of the time, on the other band, extended +their investigations in many directions. The sum total of +scientific knowledge of that day had not bulked so large as to +exclude the possibility that one man might master it all. So we +find a Galileo, for example, making revolutionary discoveries in +astronomy, and performing fundamental experiments in various +fields of physics. Galileo's great contemporary, Kepler, was +almost equally versatile, though his astronomical studies were of +such pre-eminent importance that his other investigations sink +into relative insignificance. Yet he performed some notable +experiments in at least one department of physics. These +experiments had to do with the refraction of light, a subject +which Kepler was led to investigate, in part at least, through +his interest in the telescope. + +We have seen that Ptolemy in the Alexandrian time, and Alhazen, +the Arab, made studies of refraction. Kepler repeated their +experiments, and, striving as always to generalize his +observations, he attempted to find the law that governed the +observed change of direction which a ray of light assumes in +passing from one medium to another. Kepler measured the angle of +refraction by means of a simple yet ingenious trough-like +apparatus which enabled him to compare readily the direct and +refracted rays. He discovered that when a ray of light passes +through a glass plate, if it strikes the farther surface of the +glass at an angle greater than 45 degrees it will be totally +refracted instead of passing through into the air. He could not +well fail to know that different mediums refract light +differently, and that for the same medium the amount of light +valies with the change in the angle of incidence. He was not +able, however, to generalize his observations as he desired, and +to the last the law that governs refraction escaped him. It +remained for Willebrord Snell, a Dutchman, about the year 1621, +to discover the law in question, and for Descartes, a little +later, to formulate it. Descartes, indeed, has sometimes been +supposed to be the discoverer of the law. There is reason to +believe that he based his generalizations on the experiment of +Snell, though he did not openly acknowledge his indebtedness. The +law, as Descartes expressed it, states that the sine of the angle +of incidence bears a fixed ratio to the sine of the angle of +refraction for any given medium. Here, then, was another +illustration of the fact that almost infinitely varied phenomena +may be brought within the scope of a simple law. Once the law had +been expressed, it could be tested and verified with the greatest +ease; and, as usual, the discovery being made, it seems +surprising that earlier investigators--in particular so sagacious +a guesser as Kepler--should have missed it. + +Galileo himself must have been to some extent a student of light, +since, as we have seen, he made such notable contributions to +practical optics through perfecting the telescope; but he seems +not to have added anything to the theory of light. The subject of +heat, however, attracted his attention in a somewhat different +way, and he was led to the invention of the first contrivance for +measuring temperatures. His thermometer was based on the +afterwards familiar principle of the expansion of a liquid under +the influence of heat; but as a practical means of measuring +temperature it was a very crude affair, because the tube that +contained the measuring liquid was exposed to the air, hence +barometric changes of pressure vitiated the experiment. It +remained for Galileo's Italian successors of the Accademia del +Cimento of Florence to improve upon the apparatus, after the +experiments of Torricelli--to which we shall refer in a +moment--had thrown new light on the question of atmospheric +pressure. Still later the celebrated Huygens hit upon the idea of +using the melting and the boiling point of water as fixed points +in a scale of measurements, which first gave definiteness to +thermometric tests. + + +TORRICELLI + +In the closing years of his life Galileo took into his family, as +his adopted disciple in science, a young man, Evangelista +Torricelli (1608-1647), who proved himself, during his short +lifetime, to be a worthy follower of his great master. Not only +worthy on account of his great scientific discoveries, but +grateful as well, for when he had made the great discovery that +the "suction" made by a vacuum was really nothing but air +pressure, and not suction at all, he regretted that so important +a step in science might not have been made by his great teacher, +Galileo, instead of by himself. "This generosity of Torricelli," +says Playfair, "was, perhaps, rarer than his genius: there are +more who might have discovered the suspension of mercury in the +barometer than who would have been willing to part with the honor +of the discovery to a master or a friend." + +Torricelli's discovery was made in 1643, less than two years +after the death of his master. Galileo had observed that water +will not rise in an exhausted tube, such as a pump, to a height +greater than thirty-three feet, but he was never able to offer a +satisfactory explanation of the principle. Torricelli was able to +demonstrate that the height at which the water stood depended +upon nothing but its weight as compared with the weight of air. +If this be true, it is evident that any fluid will be supported +at a definite height, according to its relative weight as +compared with air. Thus mercury, which is about thirteen times +more dense than water, should only rise to one-thirteenth the +height of a column of water--that is, about thirty inches. +Reasoning in this way, Torricelli proceeded to prove that his +theory was correct. Filling a long tube, closed at one end, with +mercury, he inverted the tube with its open orifice in a vessel +of mercury. The column of mercury fell at once, but at a height +of about thirty inches it stopped and remained stationary, the +pressure of the air on the mercury in the vessel maintaining it +at that height. This discovery was a shattering blow to the old +theory that had dominated that field of physics for so many +centuries. It was completely revolutionary to prove that, instead +of a mysterious something within the tube being responsible for +the suspension of liquids at certain heights, it was simply the +ordinary atmospheric pressure mysterious enough, it is +true--pushing upon them from without. The pressure exerted by the +atmosphere was but little understood at that time, but +Torricelli's discovery aided materially in solving the mystery. +The whole class of similar phenomena of air pressure, which had +been held in the trammel of long-established but false doctrines, +was now reduced to one simple law, and the door to a solution of +a host of unsolved problems thrown open. + +It had long been suspected and believed that the density of the +atmosphere varies at certain times. That the air is sometimes +"heavy" and at other times "light" is apparent to the senses +without scientific apparatus for demonstration. It is evident, +then, that Torricelli's column of mercury should rise and fall +just in proportion to the lightness or heaviness of the air. A +short series of observations proved that it did so, and with +those observations went naturally the observations as to changes +in the weather. It was only necessary, therefore, to scratch a +scale on the glass tube, indicating relative atmospheric +pressures, and the Torricellian barometer was complete. + +Such a revolutionary theory and such an important discovery were, +of course, not to be accepted without controversy, but the feeble +arguments of the opponents showed how untenable the old theory +had become. In 1648 Pascal suggested that if the theory of the +pressure of air upon the mercury was correct, it could be +demonstrated by ascending a mountain with the mercury tube. As +the air was known to get progressively lighter from base to +summit, the height of the column should be progressively lessened +as the ascent was made, and increase again on the descent into +the denser air. The experiment was made on the mountain called +the Puy-de-Dome, in Auvergne, and the column of mercury fell and +rose progressively through a space of about three inches as the +ascent and descent were made. + +This experiment practically sealed the verdict on the new theory, +but it also suggested something more. If the mercury descended to +a certain mark on the scale on a mountain-top whose height was +known, why was not this a means of measuring the heights of all +other elevations? And so the beginning was made which, with +certain modifications and corrections in details, is now the +basis of barometrical measurements of heights. + +In hydraulics, also, Torricelli seems to have taken one of the +first steps. He did this by showing that the water which issues +from a hole in the side or bottom of a vessel does so at the same +velocity as that which a body would acquire by falling from the +level of the surface of the water to that of the orifice. This +discovery was of the greatest importance to a correct +understanding of the science of the motions of fluids. He also +discovered the valuable mechanical principle that if any number +of bodies be connected so that by their motion there is neither +ascent nor descent of their centre of gravity, these bodies are +in equilibrium. + +Besides making these discoveries, he greatly improved the +microscope and the telescope, and invented a simple microscope +made of a globule of glass. In 1644 he published a tract on the +properties of the cycloid in which he suggested a solution of the +problem of its quadrature. As soon as this pamphlet appeared its +author was accused by Gilles Roberval (1602-1675) of having +appropriated a solution already offered by him. This led to a +long debate, during which Torricelli was seized with a fever, +from the effects of which he died, in Florence, October 25, 1647. +There is reason to believe, however, that while Roberval's +discovery was made before Torricelli's, the latter reached his +conclusions independently. + + + +VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +In recent chapters we have seen science come forward with +tremendous strides. A new era is obviously at hand. But we shall +misconceive the spirit of the times if we fail to understand that +in the midst of all this progress there was still room for +mediaeval superstition and for the pursuit of fallacious ideals. +Two forms of pseudo-science were peculiarly prevalent --alchemy +and astrology. Neither of these can with full propriety be called +a science, yet both were pursued by many of the greatest +scientific workers of the period. Moreover, the studies of the +alchemist may with some propriety be said to have laid the +foundation for the latter-day science of chemistry; while +astrology was closely allied to astronomy, though its relations +to that science are not as intimate as has sometimes been +supposed. + +Just when the study of alchemy began is undetermined. It was +certainly of very ancient origin, perhaps Egyptian, but its most +flourishing time was from about the eighth century A.D. to the +eighteenth century. The stories of the Old Testament formed a +basis for some of the strange beliefs regarding the properties of +the magic "elixir," or "philosopher's stone." Alchemists believed +that most of the antediluvians, perhaps all of them, possessed a +knowledge of this stone. How, otherwise, could they have +prolonged their lives to nine and a half centuries? And Moses was +surely a first-rate alchemist, as is proved by the story of the +Golden Calf.[1] After Aaron had made the calf of gold, Moses +performed the much more difficult task of grinding it to powder +and "strewing it upon the waters," thus showing that he had +transmuted it into some lighter substance. + +But antediluvians and Biblical characters were not the only +persons who were thought to have discovered the coveted. +"elixir." Hundreds of aged mediaeval chemists were credited with +having made the discovery, and were thought to be living on +through the centuries by its means. Alaies de Lisle, for example, +who died in 1298, at the age of 110, was alleged to have been at +the point of death at the age of fifty, but just at this time he +made the fortunate discovery of the magic stone, and so continued +to live in health and affluence for sixty years more. And De +Lisle was but one case among hundreds. + +An aged and wealthy alchemist could claim with seeming +plausibility that he was prolonging his life by his magic; +whereas a younger man might assert that, knowing the great +secret, he was keeping himself young through the centuries. In +either case such a statement, or rumor, about a learned and +wealthy alchemist was likely to be believed, particularly among +strangers; and as such a man would, of course, be the object of +much attention, the claim was frequently made by persons seeking +notoriety. One of the most celebrated of these impostors was a +certain Count de Saint-Germain, who was connected with the court +of Louis XV. His statements carried the more weight because, +having apparently no means of maintenance, he continued to live +in affluence year after year--for two thousand years, as he +himself admitted--by means of the magic stone. If at any time his +statements were doubted, he was in the habit of referring to his +valet for confirmation, this valet being also under the influence +of the elixir of life. + +"Upon one occasion his master was telling a party of ladies and +gentlemen, at dinner, some conversation he had had in Palestine, +with King Richard I., of England, whom he described as a very +particular friend of his. Signs of astonishment and incredulity +were visible on the faces of the company, upon which +Saint-Germain very coolly turned to his servant, who stood behind +his chair, and asked him if he had not spoken the truth. 'I +really cannot say,' replied the man, without moving a muscle; +'you forget, sir, I have been only five hundred years in your +service.' 'Ah, true,' said his master, 'I remember now; it was a +little before your time!' "[2] + +In the time of Saint-Germain, only a little over a century ago, +belief in alchemy had almost disappeared, and his extraordinary +tales were probably regarded in the light of amusing stories. +Still there was undoubtedly a lingering suspicion in the minds of +many that this man possessed some peculiar secret. A few +centuries earlier his tales would hardly have been questioned, +for at that time the belief in the existence of this magic +something was so strong that the search for it became almost a +form of mania; and once a man was seized with it, lie gambled +away health, position, and life itself in pursuing the coveted +stake. An example of this is seen in Albertus Magnus, one of the +most learned men of his time, who it is said resigned his +position as bishop of Ratisbon in order that he might pursue his +researches in alchemy. + +If self-sacrifice was not sufficient to secure the prize, crime +would naturally follow, for there could be no limit to the price +of the stakes in this game. The notorious Marechal de Reys, +failing to find the coveted stone by ordinary methods of +laboratory research, was persuaded by an impostor that if he +would propitiate the friendship of the devil the secret would be +revealed. To this end De Reys began secretly capturing young +children as they passed his castle and murdering them. When he +was at last brought to justice it was proved that he had murdered +something like a hundred children within a period of three years. +So, at least, runs one version of the story of this perverted +being. + +Naturally monarchs, constantly in need of funds, were interested +in these alchemists. Even sober England did not escape, and +Raymond Lully, one of the most famous of the thirteenth and +fourteenth century alchemists, is said to have been secretly +invited by King Edward I. (or II.) to leave Milan and settle in +England. According to some accounts, apartments were assigned to +his use in the Tower of London, where he is alleged to have made +some six million pounds sterling for the monarch, out of iron, +mercury, lead, and pewter. + +Pope John XXII., a friend and pupil of the alchemist Arnold de +Villeneuve, is reported to have learned the secrets of alchemy +from his master. Later he issued two bulls against "pretenders" +in the art, which, far from showing his disbelief, were cited by +alchemists as proving that he recognized pretenders as distinct +from true masters of magic. + +To moderns the attitude of mind of the alchemist is difficult to +comprehend. It is, perhaps, possible to conceive of animals or +plants possessing souls, but the early alchemist attributed the +same thing--or something kin to it--to metals also. Furthermore, +just as plants germinated from seeds, so metals were supposed to +germinate also, and hence a constant growth of metals in the +ground. To prove this the alchemist cited cases where previously +exhausted gold-mines were found, after a lapse of time, to +contain fresh quantities of gold. The "seed" of the remaining +particles of gold had multiplied and increased. But this +germinating process could only take place under favorable +conditions, just as the seed of a plant must have its proper +surroundings before germinating; and it was believed that the +action of the philosopher's stone was to hasten this process, as +man may hasten the growth of plants by artificial means. Gold was +looked upon as the most perfect metal, and all other metals +imperfect, because not yet "purified." By some alchemists they +were regarded as lepers, who, when cured of their leprosy, would +become gold. And since nature intended that all things should be +perfect, it was the aim of the alchemist to assist her in this +purifying process, and incidentally to gain wealth and prolong +his life. + +By other alchemists the process of transition from baser metals +into gold was conceived to be like a process of ripening fruit. +The ripened product was gold, while the green fruit, in various +stages of maturity, was represented by the base metals. Silver, +for example, was more nearly ripe than lead; but the difference +was only one of "digestion," and it was thought that by further +"digestion" lead might first become silver and eventually gold. +In other words, Nature had not completed her work, and was +wofully slow at it at best; but man, with his superior faculties, +was to hasten the process in his laboratories--if he could but +hit upon the right method of doing so. + +It should not be inferred that the alchemist set about his task +of assisting nature in a haphazard way, and without training in +the various alchemic laboratory methods. On the contrary, he +usually served a long apprenticeship in the rudiments of his +calling. He was obliged to learn, in a general way, many of the +same things that must be understood in either chemical or +alchemical laboratories. The general knowledge that certain +liquids vaporize at lower temperatures than others, and that the +melting-points of metals differ greatly, for example, was just as +necessary to alchemy as to chemistry. The knowledge of the gross +structure, or nature, of materials was much the same to the +alchemist as to the chemist, and, for that matter, many of the +experiments in calcining, distilling, etc., were practically +identical. + +To the alchemist there were three principles--salt, sulphur, and +mercury--and the sources of these principles were the four +elements--earth, water, fire, and air. These four elements were +accountable for every substance in nature. Some of the +experiments to prove this were so illusive, and yet apparently so +simple, that one is not surprised that it took centuries to +disprove them. That water was composed of earth and air seemed +easily proven by the simple process of boiling it in a +tea-kettle, for the residue left was obviously an earthy +substance, whereas the steam driven off was supposed to be air. +The fact that pure water leaves no residue was not demonstrated +until after alchemy had practically ceased to exist. It was +possible also to demonstrate that water could be turned into fire +by thrusting a red-hot poker under a bellglass containing a dish +of water. Not only did the quantity of water diminish, but, if a +lighted candle was thrust under the glass, the contents ignited +and burned, proving, apparently, that water had been converted +into fire. These, and scores of other similar experiments, seemed +so easily explained, and to accord so well with the "four +elements" theory, that they were seldom questioned until a later +age of inductive science. + +But there was one experiment to which the alchemist pinned his +faith in showing that metals could be "killed" and "revived," +when proper means were employed. It had been known for many +centuries that if any metal, other than gold or silver, were +calcined in an open crucible, it turned, after a time, into a +peculiar kind of ash. This ash was thought by the alchemist to +represent the death of the metal. But if to this same ash a few +grains of wheat were added and heat again applied to the +crucible, the metal was seen to "rise from its ashes" and resume +its original form--a well-known phenomenon of reducing metals +from oxides by the use of carbon, in the form of wheat, or, for +that matter, any other carbonaceous substance. Wheat was, +therefore, made the symbol of the resurrection of the life +eternal. Oats, corn, or a piece of charcoal would have "revived" +the metals from the ashes equally well, but the mediaeval +alchemist seems not to have known this. However, in this +experiment the metal seemed actually to be destroyed and +revivified, and, as science had not as yet explained this +striking phenomenon, it is little wonder that it deceived the +alchemist. + +Since the alchemists pursued their search of the magic stone in +such a methodical way, it would seem that they must have some +idea of the appearance of the substance they sought. Probably +they did, each according to his own mental bias; but, if so, they +seldom committed themselves to writing, confining their +discourses largely to speculations as to the properties of this +illusive substance. Furthermore, the desire for secrecy would +prevent them from expressing so important a piece of information. +But on the subject of the properties, if not on the appearance of +the "essence," they were voluminous writers. It was supposed to +be the only perfect substance in existence, and to be confined in +various substances, in quantities proportionate to the state of +perfection of the substance. Thus, gold being most nearly perfect +would contain more, silver less, lead still less, and so on. The +"essence" contained in the more nearly perfect metals was thought +to be more potent, a very small quantity of it being capable of +creating large quantities of gold and of prolonging life +indefinitely. + +It would appear from many of the writings of the alchemists that +their conception of nature and the supernatural was so confused +and entangled in an inexplicable philosophy that they themselves +did not really understand the meaning of what they were +attempting to convey. But it should not be forgotten that alchemy +was kept as much as possible from the ignorant general public, +and the alchemists themselves had knowledge of secret words and +expressions which conveyed a definite meaning to one of their +number, but which would appear a meaningless jumble to an +outsider. Some of these writers declared openly that their +writings were intended to convey an entirely erroneous +impression, and were sent out only for that purpose. + +However, while it may have been true that the vagaries of their +writings were made purposely, the case is probably more correctly +explained by saying that the very nature of the art made definite +statements impossible. They were dealing with something that did +not exist--could not exist. Their attempted descriptions became, +therefore, the language of romance rather than the language of +science. + +But if the alchemists themselves were usually silent as to the +appearance of the actual substance of the philosopher's stone, +there were numberless other writers who were less reticent. By +some it was supposed to be a stone, by others a liquid or elixir, +but more commonly it was described as a black powder. It also +possessed different degrees of efficiency according to its +degrees of purity, certain forms only possessing the power of +turning base metals into gold, while others gave eternal youth +and life or different degrees of health. Thus an alchemist, who +had made a partial discovery of this substance, could prolong +life a certain number of years only, or, possessing only a small +and inadequate amount of the magic powder, he was obliged to give +up the ghost when the effect of this small quantity had passed +away. + +This belief in the supernatural power of the philosopher's stone +to prolong life and heal diseases was probably a later phase of +alchemy, possibly developed by attempts to connect the power of +the mysterious essence with Biblical teachings. The early Roman +alchemists, who claimed to be able to transmute metals, seem not +to have made other claims for their magic stone. + +By the fifteenth century the belief in the philosopher's stone +had become so fixed that governments began to be alarmed lest +some lucky possessor of the secret should flood the country with +gold, thus rendering the existing coin of little value. Some +little consolation was found in the thought that in case all the +baser metals were converted into gold iron would then become the +"precious metal," and would remain so until some new +philosopher's stone was found to convert gold back into iron--a +much more difficult feat, it was thought. However, to be on the +safe side, the English Parliament, in 1404, saw fit to pass an +act declaring the making of gold and silver to be a felony. +Nevertheless, in 1455, King Henry VI. granted permission to +several "knights, citizens of London, chemists, and monks" to +find the philosopher's stone, or elixir, that the crown might +thus be enabled to pay off its debts. The monks and ecclesiastics +were supposed to be most likely to discover the secret process, +since "they were such good artists in transubstantiating bread +and wine." + +In Germany the emperors Maximilian I., Rudolf II., and Frederick +II. gave considerable attention to the search, and the example +they set was followed by thousands of their subjects. It is said +that some noblemen developed the unpleasant custom of inviting to +their courts men who were reputed to have found the stone, and +then imprisoning the poor alchemists until they had made a +certain quantity of gold, stimulating their activity with +tortures of the most atrocious kinds. Thus this danger of being +imprisoned and held for ransom until some fabulous amount of gold +should be made became the constant menace of the alchemist. It +was useless for an alchemist to plead poverty once it was noised +about that he had learned the secret. For how could such a man be +poor when, with a piece of metal and a few grains of magic +powder, he was able to provide himself with gold? It was, +therefore, a reckless alchemist indeed who dared boast that he +had made the coveted discovery. + +The fate of a certain indiscreet alchemist, supposed by many to +have been Seton, a Scotchman, was not an uncommon one. Word +having been brought to the elector of Saxony that this alchemist +was in Dresden and boasting of his powers, the elector caused him +to be arrested and imprisoned. Forty guards were stationed to see +that he did not escape and that no one visited him save the +elector himself. For some time the elector tried by argument and +persuasion to penetrate his secret or to induce him to make a +certain quantity of gold; but as Seton steadily refused, the rack +was tried, and for several months he suffered torture, until +finally, reduced to a mere skeleton, be was rescued by a rival +candidate of the elector, a Pole named Michael Sendivogins, who +drugged the guards. However, before Seton could be "persuaded" by +his new captor, he died of his injuries. + +But Sendivogins was also ambitious in alchemy, and, since Seton +was beyond his reach, he took the next best step and married his +widow. From her, as the story goes, he received an ounce of black +powder--the veritable philosopher's stone. With this he +manufactured great quantities of gold, even inviting Emperor +Rudolf II. to see him work the miracle. That monarch was so +impressed that he caused a tablet to be inserted in the wall of +the room in which he had seen the gold made. + +Sendivogins had learned discretion from the misfortune of Seton, +so that he took the precaution of concealing most of the precious +powder in a secret chamber of his carriage when he travelled, +having only a small quantity carried by his steward in a gold +box. In particularly dangerous places, he is said to have +exchanged clothes with his coachman, making the servant take his +place in the carriage while he mounted the box. + + +About the middle of the seventeenth century alchemy took such +firm root in the religious field that it became the basis of the +sect known as the Rosicrucians. The name was derived from the +teaching of a German philosopher, Rosenkreutz, who, having been +healed of a dangerous illness by an Arabian supposed to possess +the philosopher's stone, returned home and gathered about him a +chosen band of friends, to whom he imparted the secret. This sect +came rapidly into prominence, and for a short time at least +created a sensation in Europe, and at the time were credited with +having "refined and spiritualized" alchemy. But by the end of the +seventeenth century their number had dwindled to a mere handful, +and henceforth they exerted little influence. + +Another and earlier religious sect was the Aureacrucians, founded +by Jacob Bohme, a shoemaker, born in Prussia in 1575. According +to his teachings the philosopher's stone could be discovered by a +diligent search of the Old and the New Testaments, and more +particularly the Apocalypse, which contained all the secrets of +alchemy. This sect found quite a number of followers during the +life of Bohme, but gradually died out after his death; not, +however, until many of its members had been tortured for heresy, +and one at least, Kuhlmann, of Moscow, burned as a sorcerer. + +The names of the different substances that at various times were +thought to contain the large quantities of the "essence" during +the many centuries of searching for it, form a list of +practically all substances that were known, discovered, or +invented during the period. Some believed that acids contained +the substance; others sought it in minerals or in animal or +vegetable products; while still others looked to find it among +the distilled "spirits"--the alcoholic liquors and distilled +products. On the introduction of alcohol by the Arabs that +substance became of all-absorbing interest, and for a long time +allured the alchemist into believing that through it they were +soon to be rewarded. They rectified and refined it until +"sometimes it was so strong that it broke the vessels containing +it," but still it failed in its magic power. Later, brandy was +substituted for it, and this in turn discarded for more recent +discoveries. + +There were always, of course, two classes of alchemists: serious +investigators whose honesty could not be questioned, and clever +impostors whose legerdemain was probably largely responsible for +the extended belief in the existence of the philosopher's stone. +Sometimes an alchemist practised both, using the profits of his +sleight-of-hand to procure the means of carrying on his serious +alchemical researches. The impostures of some of these jugglers +deceived even the most intelligent and learned men of the time, +and so kept the flame of hope constantly burning. The age of cold +investigation had not arrived, and it is easy to understand how +an unscrupulous mediaeval Hermann or Kellar might completely +deceive even the most intelligent and thoughtful scholars. In +scoffing at the credulity of such an age, it should not be +forgotten that the "Keely motor" was a late nineteenth-century +illusion. + +But long before the belief in the philosopher's stone had died +out, the methods of the legerdemain alchemist had been +investigated and reported upon officially by bodies of men +appointed to make such investigations, although it took several +generations completely to overthrow a superstition that had been +handed down through several thousand years. In April of 1772 +Monsieur Geoffroy made a report to the Royal Academy of Sciences, +at Paris, on the alchemic cheats principally of the sixteenth and +seventeenth centuries. In this report he explains many of the +seemingly marvellous feats of the unscrupulous alchemists. A very +common form of deception was the use of a double-bottomed +crucible. A copper or brass crucible was covered on the inside +with a layer of wax, cleverly painted so as to resemble the +ordinary metal. Between this layer of wax and the bottom of the +crucible, however, was a layer of gold dust or silver. When the +alchemist wished to demonstrate his power, he had but to place +some mercury or whatever substance he chose in the crucible, heat +it, throw in a grain or two of some mysterious powder, pronounce +a few equally mysterious phrases to impress his audience, and, +behold, a lump of precious metal would be found in the bottom of +his pot. This was the favorite method of mediocre performers, but +was, of course, easily detected. + +An equally successful but more difficult way was to insert +surreptitiously a lump of metal into the mixture, using an +ordinary crucible. This required great dexterity, but was +facilitated by the use of many mysterious ceremonies on the part +of the operator while performing, just as the modern vaudeville +performer diverts the attention of the audience to his right hand +while his left is engaged in the trick. Such ceremonies were not +questioned, for it was the common belief that the whole process +"lay in the spirit as much as in the substance," many, as we have +seen, regarding the whole process as a divine manifestation. + +Sometimes a hollow rod was used for stirring the mixture in the +crucible, this rod containing gold dust, and having the end +plugged either with wax or soft metal that was easily melted. +Again, pieces of lead were used which had been plugged with lumps +of gold carefully covered over; and a very simple and impressive +demonstration was making use of a nugget of gold that had been +coated over with quicksilver and tarnished so as to resemble lead +or some base metal. When this was thrown into acid the coating +was removed by chemical action, leaving the shining metal in the +bottom of the vessel. In order to perform some of these tricks, +it is obvious that the alchemist must have been well supplied +with gold, as some of them, when performing before a royal +audience, gave the products to their visitors. But it was always +a paying investment, for once his reputation was established the +gold-maker found an endless variety of ways of turning his +alleged knowledge to account, frequently amassing great wealth. + +Some of the cleverest of the charlatans often invited royal or +other distinguished guests to bring with them iron nails to be +turned into gold ones. They were transmuted in the alchemist's +crucible before the eyes of the visitors, the juggler adroitly +extracting the iron nail and inserting a gold one without +detection. It mattered little if the converted gold nail differed +in size and shape from the original, for this change in shape +could be laid to the process of transmutation; and even the very +critical were hardly likely to find fault with the exchange thus +made. Furthermore, it was believed that gold possessed the +property of changing its bulk under certain conditions, some of +the more conservative alchemists maintaining that gold was only +increased in bulk, not necessarily created, by certain forms of +the magic stone. Thus a very proficient operator was thought to +be able to increase a grain of gold into a pound of pure metal, +while one less expert could only double, or possibly treble, its +original weight. + +The actual number of useful discoveries resulting from the +efforts of the alchemists is considerable, some of them of +incalculable value. Roger Bacon, who lived in the thirteenth +century, while devoting much of his time to alchemy, made such +valuable discoveries as the theory, at least, of the telescope, +and probably gunpowder. Of this latter we cannot be sure that the +discovery was his own and that he had not learned of it through +the source of old manuscripts. But it is not impossible nor +improbable that he may have hit upon the mixture that makes the +explosives while searching for the philosopher's stone in his +laboratory. "Von Helmont, in the same pursuit, discoverd the +properties of gas," says Mackay; "Geber made discoveries in +chemistry, which were equally important; and Paracelsus, amid his +perpetual visions of the transmutation of metals, found that +mercury was a remedy for one of the most odious and excruciating +of all the diseases that afflict humanity."' As we shall see a +little farther on, alchemy finally evolved into modern chemistry, +but not until it had passed through several important +transitional stages. + + +ASTROLOGY + +In a general way modern astronomy may be considered as the +outgrowth of astrology, just as modern chemistry is the result of +alchemy. It is quite possible, however, that astronomy is the +older of the two; but astrology must have developed very shortly +after. The primitive astronomer, having acquired enough knowledge +from his observations of the heavenly bodies to make correct +predictions, such as the time of the coming of the new moon, +would be led, naturally, to believe that certain predictions +other than purely astronomical ones could be made by studying the +heavens. Even if the astronomer himself did not believe this, +some of his superstitious admirers would; for to the unscientific +mind predictions of earthly events would surely seem no more +miraculous than correct predictions as to the future movements of +the sun, moon, and stars. When astronomy had reached a stage of +development so that such things as eclipses could be predicted +with anything like accuracy, the occult knowledge of the +astronomer would be unquestioned. Turning this apparently occult +knowledge to account in a mercenary way would then be the +inevitable result, although it cannot be doubted that many of the +astrologers, in all ages, were sincere in their beliefs. + +Later, as the business of astrology became a profitable one, +sincere astronomers would find it expedient to practise astrology +as a means of gaining a livelihood. Such a philosopher as Kepler +freely admitted that he practised astrology "to keep from +starving," although he confessed no faith in such predictions. +"Ye otherwise philosophers," he said, "ye censure this daughter +of astronomy beyond her deserts; know ye not that she must +support her mother by her charms." + +Once astrology had become an established practice, any +considerable knowledge of astronomy was unnecessary, for as it +was at best but a system of good guessing as to future events, +clever impostors could thrive equally well without troubling to +study astronomy. The celebrated astrologers, however, were +usually astronomers as well, and undoubtedly based many of their +predictions on the position and movements of the heavenly bodies. +Thus, the casting of a horoscope that is, the methods by which +the astrologers ascertained the relative position of the heavenly +bodies at the time of a birth--was a simple but fairly exact +procedure. Its basis was the zodiac, or the path traced by the +sun in his yearly course through certain constellations. At the +moment of the birth of a child, the first care of the astrologer +was to note the particular part of the zodiac that appeared on +the horizon. The zodiac was then divided into "houses"--that is, +into twelve spaces--on a chart. In these houses were inserted the +places of the planets, sun, and moon, with reference to the +zodiac. When this chart was completed it made a fairly correct +diagram of the heavens and the position of the heavenly bodies as +they would appear to a person standing at the place of birth at a +certain time. + +Up to this point the process was a simple one of astronomy. But +the next step--the really important one--that of interpreting +this chart, was the one which called forth the skill and +imagination of the astrologer. In this interpretation, not in his +mere observations, lay the secret of his success. Nor did his +task cease with simply foretelling future events that were to +happen in the life of the newly born infant. He must not only +point out the dangers, but show the means whereby they could be +averted, and his prophylactic measures, like his predictions, +were alleged to be based on his reading of the stars. + +But casting a horoscope at the time of births was, of course, +only a small part of the astrologer's duty. His offices were +sought by persons of all ages for predictions as to their +futures, the movements of an enemy, where to find stolen goods, +and a host of everyday occurrences. In such cases it is more than +probable that the astrologers did very little consulting of the +stars in making their predictions. They became expert +physiognomists and excellent judges of human nature, and were +thus able to foretell futures with the same shrewdness and by the +same methods as the modern "mediums," palmists, and +fortune-tellers. To strengthen belief in their powers, it became +a common thing for some supposedly lost document of the +astrologer to be mysteriously discovered after an important +event, this document purporting to foretell this very event. It +was also a common practice with astrologers to retain, or have +access to, their original charts, cleverly altering them from +time to time to fit conditions. + +The dangers attendant upon astrology were of such a nature that +the lot of the astrologer was likely to prove anything but an +enviable one. As in the case of the alchemist, the greater the +reputation of an astrologer the greater dangers he was likely to +fall into. If he became so famous that he was employed by kings +or noblemen, his too true or too false prophecies were likely to +bring him into disrepute--even to endanger his life. + +Throughout the dark age the astrologers flourished, but the +sixteenth and seventeenth centuries were the golden age of these +impostors. A skilful astrologer was as much an essential to the +government as the highest official, and it would have been a bold +monarch, indeed, who would undertake any expedition of importance +unless sanctioned by the governing stars as interpreted by these +officials. + +It should not be understood, however, that belief in astrology +died with the advent of the Copernican doctrine. It did become +separated from astronomy very shortly after, to be sure, and +undoubtedly among the scientists it lost much of its prestige. +But it cannot be considered as entirely passed away, even to-day, +and even if we leave out of consideration street-corner +"astrologers" and fortune-tellers, whose signs may be seen in +every large city, there still remains quite a large class of +relatively intelligent people who believe in what they call "the +science of astrology." Needless to say, such people are not found +among the scientific thinkers; but it is significant that +scarcely a year passes that some book or pamphlet is not +published by some ardent believer in astrology, attempting to +prove by the illogical dogmas characteristic of unscientific +thinkers that astrology is a science. The arguments contained in +these pamphlets are very much the same as those of the +astrologers three hundred years ago, except that they lack the +quaint form of wording which is one of the features that lends +interest to the older documents. These pamphlets need not be +taken seriously, but they are interesting as exemplifying how +difficult it is, even in an age of science, to entirely stamp out +firmly established superstitions. Here are some of the arguments +advanced in defence of astrology, taken from a little brochure +entitled "Astrology Vindicated," published in 1898: It will be +found that a person born when the Sun is in twenty degrees +Scorpio has the left ear as his exceptional feature and the nose +(Sagittarius) bent towards the left ear. A person born when the +Sun is in any of the latter degrees of Taurus, say the +twenty-fifth degree, will have a small, sharp, weak chin, curved +up towards Gemini, the two vertical lines on the upper lip."[4] +The time was when science went out of its way to prove that such +statements were untrue; but that time is past, and such writers +are usually classed among those energetic but misguided persons +who are unable to distinguish between logic and sophistry. + + +In England, from the time of Elizabeth to the reign of William +and Mary, judicial astrology was at its height. After the great +London fire, in 1666, a committee of the House of Commons +publicly summoned the famous astrologer, Lilly, to come before +Parliament and report to them on his alleged prediction of the +calamity that had befallen the city. Lilly, for some reason best +known to himself, denied having made such a prediction, being, as +he explained, "more interested in determining affairs of much +more importance to the future welfare of the country." Some of +the explanations of his interpretations will suffice to show +their absurdities, which, however, were by no means regarded as +absurdities at that time, for Lilly was one of the greatest +astrologers of his day. He said that in 1588 a prophecy had been +printed in Greek characters which foretold exactly the troubles +of England between the years 1641. and 1660. "And after him shall +come a dreadful dead man," ran the prophecy, "and with him a +royal G of the best blood in the world, and he shall have the +crown and shall set England on the right way and put out all +heresies. His interpretation of this was that, "Monkery being +extinguished above eighty or ninety years, and the Lord General's +name being Monk, is the dead man. The royal G or C (it is gamma +in the Greek, intending C in the Latin, being the third letter in +the alphabet) is Charles II., who, for his extraction, may be +said to be of the best blood of the world."[5] + +This may be taken as a fair sample of Lilly's interpretations of +astrological prophesies, but many of his own writings, while +somewhat more definite and direct, are still left sufficiently +vague to allow his skilful interpretations to set right an +apparent mistake. One of his famous documents was "The Starry +Messenger," a little pamphlet purporting to explain the +phenomenon of a "strange apparition of three suns" that were seen +in London on November 19, 1644---the anniversary of the birth of +Charles I., then the reigning monarch. This phenomenon caused a +great stir among the English astrologers, coming, as it did, at a +time of great political disturbance. Prophecies were numerous, +and Lilly's brochure is only one of many that appeared at that +time, most of which, however, have been lost. Lilly, in his +preface, says: "If there be any of so prevaricate a judgment as +to think that the apparition of these three Suns doth intimate no +Novelle thing to happen in our own Climate, where they were +manifestly visible, I shall lament their indisposition, and +conceive their brains to be shallow, and voyde of understanding +humanity, or notice of common History." + +Having thus forgiven his few doubting readers, who were by no +means in the majority in his day, he takes up in review the +records of the various appearances of three suns as they have +occurred during the Christian era, showing how such phenomena +have governed certain human events in a very definite manner. +Some of these are worth recording. + +"Anno 66. A comet was seen, and also three Suns: In which yeer, +Florus President of the Jews was by them slain. Paul writes to +Timothy. The Christians are warned by a divine Oracle, and depart +out of Jerusalem. Boadice a British Queen, killeth seventy +thousand Romans. The Nazareni, a scurvie Sect, begun, that +boasted much of Revelations and Visions. About a year after Nero +was proclaimed enemy to the State of Rome." + +Again, "Anno 1157, in September, there were seen three Suns +together, in as clear weather as could be: And a few days after, +in the same month, three Moons, and, in the Moon that stood in +the middle, a white Crosse. Sueno, King of Denmark, at a great +Feast, killeth Canutus: Sueno is himself slain, in pursuit of +Waldemar. The Order of Eremites, according to the rule of Saint +Augustine, begun this year; and in the next, the Pope submits to +the Emperour: (was not this miraculous?) Lombardy was also +adjudged to the Emperour." + +Continuing this list of peculiar phenomena he comes down to +within a few years of his own time. + +"Anno 1622, three Suns appeared at Heidelberg. The woful +Calamities that have ever since fallen upon the Palatinate, we +are all sensible of, and of the loss of it, for any thing I see, +for ever, from the right Heir. Osman the great Turk is strangled +that year; and Spinola besiegeth Bergen up Zoom, etc." + +Fortified by the enumeration of these past events, he then +proceeds to make his deductions. "Only this I must tell thee," he +writes, "that the interpretation I write is, I conceive, grounded +upon probable foundations; and who lives to see a few years over +his head, will easily perceive I have unfolded as much as was fit +to discover, and that my judgment was not a mile and a half from +truth." + +There is a great significance in this "as much as was fit to +discover"--a mysterious something that Lilly thinks it expedient +not to divulge. But, nevertheless, one would imagine that he was +about to make some definite prediction about Charles I., since +these three suns appeared upon his birthday and surely must +portend something concerning him. But after rambling on through +many pages of dissertations upon planets and prophecies, he +finally makes his own indefinite prediction. + +"O all you Emperors, Kings, Princes, Rulers and Magistrates of +Europe, this unaccustomed Apparition is like the Handwriting in +Daniel to some of you; it premonisheth you, above all other +people, to make your peace with God in time. You shall every one +of you smart, and every one of you taste (none excepted) the +heavie hand of God, who will strengthen your subjects with +invincible courage to suppress your misgovernments and +Oppressions in Church or Common-wealth; . . . Those words are +general: a word for my own country of England. . . . Look to +yourselves; here's some monstrous death towards you. But to whom? +wilt thou say. Herein we consider the Signe, Lord thereof, and +the House; The Sun signifies in that Royal Signe, great ones; the +House signifies captivity, poison, Treachery: From which is +derived thus much, That some very great man, what King, Prince, +Duke, or the like, I really affirm I perfectly know not, shall, I +say, come to some such untimely end."[6] + +Here is shown a typical example of astrological prophecy, which +seems to tell something or nothing, according to the point of +view of the reader. According to a believer in astrology, after +the execution of Charles I., five years later, this could be made +to seem a direct and exact prophecy. For example, he says: "You +Kings, Princes, etc., ... it premonisheth you ... to make your +peace with God.... Look to yourselves; here's some monstrous +death towards you. ... That some very great man, what King, +Prince, . shall, I say, come to such untimely end." + +But by the doubter the complete prophecy could be shown to be +absolutely indefinite, and applicable as much to the king of +France or Spain as to Charles I., or to any king in the future, +since no definite time is stated. Furthermore, Lilly distinctly +states, "What King, Prince, Duke, or the like, I really affirm I +perfectly know not"--which last, at least, was a most truthful +statement. The same ingenuity that made "Gen. Monk" the "dreadful +dead man," could easily make such a prediction apply to the +execution of Charles I. Such a definite statement that, on such +and such a day a certain number of years in the future, the +monarch of England would be beheaded--such an exact statement can +scarcely be found in any of the works on astrology. It should be +borne in mind, also, that Lilly was of the Cromwell party and +opposed to the king. + +After the death of Charles I., Lilly admitted that the monarch +had given him a thousand pounds to cast his horoscope. "I advised +him," says Lilly, "to proceed eastwards; he went west, and all +the world knows the result." It is an unfortunate thing for the +cause of astrology that Lilly failed to mention this until after +the downfall of the monarch. In fact, the sudden death, or +decline in power, of any monarch, even to-day, brings out the +perennial post-mortem predictions of astrologers. + +We see how Lilly, an opponent of the king, made his so-called +prophecy of the disaster of the king and his army. At the same +time another celebrated astrologer and rival of Lilly, George +Wharton, also made some predictions about the outcome of the +eventful march from Oxford. Wharton, unlike Lilly, was a follower +of the king's party, but that, of course, should have had no +influence in his "scientific" reading of the stars. Wharton's +predictions are much less verbose than Lilly's, much more +explicit, and, incidentally, much more incorrect in this +particular instance. "The Moon Lady of the 12," he wrote, "and +moving betwixt the 8 degree, 34 min., and 21 degree, 26 min. of +Aquarius, gives us to understand that His Majesty shall receive +much contentment by certain Messages brought him from foreign +parts; and that he shall receive some sudden and unexpected +supply of . . . by the means of some that assimilate the +condition of his Enemies: And withal this comfort; that His +Majesty shall be exceeding successful in Besieging Towns, +Castles, or Forts, and in persuing the enemy. + +"Mars his Sextile to the Sun, Lord of the Ascendant (which +happeneth the 18 day of May) will encourage our Soldiers to +advance with much alacrity and cheerfulness of spirit; to show +themselves gallant in the most dangerous attempt.... And now to +sum up all: It is most apparent to every impartial and ingenuous +judgment; That although His Majesty cannot expect to be secured +from every trivial disaster that may befall his army, either by +the too much Presumption, Ignorance, or Negligence of some +particular Persons (which is frequently incident and unavoidable +in the best of Armies), yet the several positions of the Heavens +duly considered and compared among themselves, as well in the +prefixed Scheme as at the Quarterly Ingresses, do generally +render His Majesty and his whole Army unexpectedly victorious and +successful in all his designs; Believe it (London), thy Miseries +approach, they are like to be many, great, and grievous, and not +to be diverted, unless thou seasonably crave Pardon of God for +being Nurse to this present Rebellion, and speedily submit to thy +Prince's Mercy; Which shall be the daily Prayer of Geo. +Wharton."[7] + +In the light of after events, it is probable that Wharton's stock +as an astrologer was not greatly enhanced by this document, at +least among members of the Royal family. Lilly's book, on the +other hand, became a favorite with the Parliamentary army. + +After the downfall and death of Napoleon there were unearthed +many alleged authentic astrological documents foretelling his +ruin. And on the death of George IV., in 1830, there appeared a +document (unknown, as usual, until that time) purporting to +foretell the death of the monarch to the day, and this without +the astrologer knowing that his horoscope was being cast for a +monarch. A full account of this prophecy is told, with full +belief, by Roback, a nineteenth-century astrologer. He says: + +"In the year 1828, a stranger of noble mien, advanced in life, +but possessing the most bland manners, arrived at the abode of a +celebrated astrologer in London," asking that the learned man +foretell his future. "The astrologer complied with the request of +the mysterious visitor, drew forth his tables, consulted his +ephemeris, and cast the horoscope or celestial map for the hour +and the moment of the inquiry, according to the established rules +of his art. + +"The elements of his calculation were adverse, and a feeling of +gloom cast a shade of serious thought, if not dejection, over his +countenance. + +" 'You are of high rank,' said the astrologer, as he calculated +and looked on the stranger, 'and of illustrious title.' The +stranger made a graceful inclination of the head in token of +acknowledgment of the complimentary remarks, and the astrologer +proceeded with his mission. + +"The celestial signs were ominous of calamity to the stranger, +who, probably observing a sudden change in the countenance of the +astrologer, eagerly inquired what evil or good fortune had been +assigned him by the celestial orbs. + +'To the first part of your inquiry,' said the astrologer, 'I can +readily reply. You have been a favorite of fortune; her smiles on +you have been abundant, her frowns but few; you have had, perhaps +now possess, wealth and power; the impossibility of their +accomplishment is the only limit to the fulfilment of your +desires.' " + +" 'You have spoken truly of the past,' said the stranger. 'I have +full faith in your revelations of the future: what say you of my +pilgrimage in this life--is it short or long?' + +" 'I regret,' replied the astrologer, in answer to this inquiry, +'to be the herald of ill, though TRUE, fortune; your sojourn on +earth will be short.' + +" 'How short?' eagerly inquired the excited and anxious stranger. + +" 'Give me a momentary truce,' said the astrologer; 'I will +consult the horoscope, and may possibly find some mitigating +circumstances.' + +"Having cast his eyes over the celestial map, and paused for some +moments, he surveyed the countenance of the stranger with great +sympathy, and said, 'I am sorry that I can find no planetary +influences that oppose your destiny--your death will take place +in two years.' + +"The event justified the astrologic prediction: George IV. died +on May 18, 1830, exactly two years from the day on which he had +visited the astrologer."[8] + +This makes a very pretty story, but it hardly seems like occult +insight that an astrologer should have been able to predict an +early death of a man nearly seventy years old, or to have guessed +that his well-groomed visitor "had, perhaps now possesses, wealth +and power." Here again, however, the point of view of each +individual plays the governing part in determining the importance +of such a document. To the scientist it proves nothing; to the +believer in astrology, everything. The significant thing is that +it appeared shortly AFTER the death of the monarch. + + +On the Continent astrologers were even more in favor than in +England. Charlemagne, and some of his immediate successors, to be +sure, attempted to exterminate them, but such rulers as Louis XI. +and Catherine de' Medici patronized and encouraged them, and it +was many years after the time of Copernicus before their +influence was entirely stamped out even in official life. There +can be no question that what gave the color of truth to many of +the predictions was the fact that so many of the prophecies of +sudden deaths and great conflagrations were known to have come +true--in many instances were made to come true by the astrologer +himself. And so it happened that when the prediction of a great +conflagration at a certain time culminated in such a +conflagration, many times a second but less-important burning +took place, in which the ambitious astrologer, or his followers, +took a central part about a stake, being convicted of +incendiarism, which they had committed in order that their +prophecies might be fulfilled. + +But, on the other hand, these predictions were sometimes turned +to account by interested friends to warn certain persons of +approaching dangers. + +For example, a certain astrologer foretold the death of Prince +Alexander de' Medici. He not only foretold the death, but +described so minutely the circumstances that would attend it, and +gave such a correct description of the assassin who should murder +the prince, that he was at once suspected of having a hand in the +assassination. It developed later, however, that such was +probably not the case; but that some friend of Prince Alexander, +knowing of the plot to take his life, had induced the astrologer +to foretell the event in order that the prince might have timely +warning and so elude the conspirators. + +The cause of the decline of astrology was the growing prevalence +of the new spirit of experimental science. Doubtless the most +direct blow was dealt by the Copernican theory. So soon as this +was established, the recognition of the earth's subordinate place +in the universe must have made it difficult for astronomers to be +longer deceived by such coincidences as had sufficed to convince +the observers of a more credulous generation. Tycho Brahe was, +perhaps, the last astronomer of prominence who was a +conscientious practiser of the art of the astrologer. + + + +VII. FROM PARACELSUS TO HARVEY + +PARACELSUS + +In the year 1526 there appeared a new lecturer on the platform at +the University at Basel--a small, beardless, effeminate-looking +person--who had already inflamed all Christendom with his +peculiar philosophy, his revolutionary methods of treating +diseases, and his unparalleled success in curing them. A man who +was to be remembered in after-time by some as the father of +modern chemistry and the founder of modern medicine; by others as +madman, charlatan, impostor; and by still others as a combination +of all these. This soft-cheeked, effeminate, woman-hating man, +whose very sex has been questioned, was Theophrastus von +Hohenheim, better known as Paracelsus (1493-1541). + +To appreciate his work, something must be known of the life of +the man. He was born near Maria-Einsiedeln, in Switzerland, the +son of a poor physician of the place. He began the study of +medicine under the instruction of his father, and later on came +under the instruction of several learned churchmen. At the age of +sixteen he entered the University of Basel, but, soon becoming +disgusted with the philosophical teachings of the time, he +quitted the scholarly world of dogmas and theories and went to +live among the miners in the Tyrol, in order that he might study +nature and men at first hand. Ordinary methods of study were +thrown aside, and he devoted his time to personal +observation--the only true means of gaining useful knowledge, as +he preached and practised ever after. Here he became familiar +with the art of mining, learned the physical properties of +minerals, ores, and metals, and acquired some knowledge of +mineral waters. More important still, he came in contact with +such diseases, wounds, and injuries as miners are subject to, and +he tried his hand at the practical treatment of these conditions, +untrammelled by the traditions of a profession in which his +training had been so scant. + +Having acquired some empirical skill in treating diseases, +Paracelsus set out wandering from place to place all over Europe, +gathering practical information as he went, and learning more and +more of the medicinal virtues of plants and minerals. His +wanderings covered a period of about ten years, at the end of +which time he returned to Basel, where he was soon invited to +give a course of lectures in the university. + +These lectures were revolutionary in two respects--they were +given in German instead of time-honored Latin, and they were +based upon personal experience rather than upon the works of such +writers as Galen and Avicenna. Indeed, the iconoclastic teacher +spoke with open disparagement of these revered masters, and +openly upbraided his fellow-practitioners for following their +tenets. Naturally such teaching raised a storm of opposition +among the older physicians, but for a time the unparalleled +success of Paracelsus in curing diseases more than offset his +unpopularity. Gradually, however, his bitter tongue and his +coarse personality rendered him so unpopular, even among his +patients, that, finally, his liberty and life being jeopardized, +he was obliged to flee from Basel, and became a wanderer. He +lived for brief periods in Colmar, Nuremberg, Appenzell, Zurich, +Pfeffers, Augsburg, and several other cities, until finally at +Salzburg his eventful life came to a close in 1541. His enemies +said that he had died in a tavern from the effects of a +protracted debauch; his supporters maintained that he had been +murdered at the instigation of rival physicians and apothecaries. + +But the effects of his teachings had taken firm root, and +continued to spread after his death. He had shown the fallibility +of many of the teachings of the hitherto standard methods of +treating diseases, and had demonstrated the advantages of +independent reasoning based on observation. In his Magicum he +gives his reasons for breaking with tradition. "I did," he says, +"embrace at the beginning these doctrines, as my adversaries +(followers of Galen) have done, but since I saw that from their +procedures nothing resulted but death, murder, stranglings, +anchylosed limbs, paralysis, and so forth, that they held most +diseases incurable. . . . therefore have I quitted this wretched +art, and sought for truth in any other direction. I asked myself +if there were no such thing as a teacher in medicine, where could +I learn this art best? Nowhere better than the open book of +nature, written with God's own finger." We shall see, however, +that this "book of nature" taught Paracelsus some very strange +lessons. Modesty was not one of these. "Now at this time," he +declares, "I, Theophrastus Paracelsus, Bombast, Monarch of the +Arcana, was endowed by God with special gifts for this end, that +every searcher after this supreme philosopher's work may be +forced to imitate and to follow me, be he Italian, Pole, Gaul, +German, or whatsoever or whosoever he be. Come hither after me, +all ye philosophers, astronomers, and spagirists. . . . I will +show and open to you ... this corporeal regeneration."[1] + +Paracelsus based his medical teachings on four "pillars" +--philosophy, astronomy, alchemy, and virtue of the physician--a +strange-enough equipment surely, and yet, properly interpreted, +not quite so anomalous as it seems at first blush. Philosophy was +the "gate of medicine," whereby the physician entered rightly +upon the true course of learning; astronomy, the study of the +stars, was all-important because "they (the stars) caused disease +by their exhalations, as, for instance, the sun by excessive +heat"; alchemy, as he interpreted it, meant the improvement of +natural substances for man's benefit; while virtue in the +physician was necessary since "only the virtuous are permitted to +penetrate into the innermost nature of man and the universe." + +All his writings aim to promote progress in medicine, and to hold +before the physician a grand ideal of his profession. In this his +views are wide and far-reaching, based on the relationship which +man bears to nature as a whole; but in his sweeping condemnations +he not only rejected Galenic therapeutics and Galenic anatomy, +but condemned dissections of any kind. He laid the cause of all +diseases at the door of the three mystic elements--salt, sulphur, +and mercury. In health he supposed these to be mingled in the +body so as to be indistinguishable; a slight separation of them +produced disease; and death he supposed to be the result of their +complete separation. The spiritual agencies of diseases, he said, +had nothing to do with either angels or devils, but were the +spirits of human beings. + +He believed that all food contained poisons, and that the +function of digestion was to separate the poisonous from the +nutritious. In the stomach was an archaeus, or alchemist, whose +duty was to make this separation. In digestive disorders the +archaeus failed to do this, and the poisons thus gaining access +to the system were "coagulated" and deposited in the joints and +various other parts of the body. Thus the deposits in the kidneys +and tartar on the teeth were formed; and the stony deposits of +gout were particularly familiar examples of this. All this is +visionary enough, yet it shows at least a groping after rational +explanations of vital phenomena. + +Like most others of his time, Paracelsus believed firmly in the +doctrine of "signatures"--a belief that every organ and part of +the body had a corresponding form in nature, whose function was +to heal diseases of the organ it resembled. The vagaries of this +peculiar doctrine are too numerous and complicated for lengthy +discussion, and varied greatly from generation to generation. In +general, however, the theory may be summed up in the words of +Paracelsus: "As a woman is known by her shape, so are the +medicines." Hence the physicians were constantly searching for +some object of corresponding shape to an organ of the body. The +most natural application of this doctrine would be the use of the +organs of the lower animals for the treatment of the +corresponding diseased organs in man. Thus diseases of the heart +were to be treated with the hearts of animals, liver disorders +with livers, and so on. But this apparently simple form of +treatment had endless modifications and restrictions, for not all +animals were useful. For example, it was useless to give the +stomach of an ox in gastric diseases when the indication in such +cases was really for the stomach of a rat. Nor were the organs of +animals the only "signatures" in nature. Plants also played a +very important role, and the herb-doctors devoted endless labor +to searching for such plants. Thus the blood-root, with its red +juice, was supposed to be useful in blood diseases, in stopping +hemorrhage, or in subduing the redness of an inflammation. + +Paracelsus's system of signatures, however, was so complicated by +his theories of astronomy and alchemy that it is practically +beyond comprehension. It is possible that he himself may have +understood it, but it is improbable that any one else did--as +shown by the endless discussions that have taken place about it. +But with all the vagaries of his theories he was still rational +in his applications, and he attacked to good purpose the +complicated "shot-gun" prescriptions of his contemporaries, +advocating more simple methods of treatment. + +The ever-fascinating subject of electricity, or, more +specifically, "magnetism," found great favor with him, and with +properly adjusted magnets he claimed to be able to cure many +diseases. In epilepsy and lockjaw, for example, one had but to +fasten magnets to the four extremities of the body, and then, +"when the proper medicines were given," the cure would be +effected. The easy loop-hole for excusing failure on the ground +of improper medicines is obvious, but Paracelsus declares that +this one prescription is of more value than "all the humoralists +have ever written or taught." + +Since Paracelsus condemned the study of anatomy as useless, he +quite naturally regarded surgery in the same light. In this he +would have done far better to have studied some of his +predecessors, such as Galen, Paul of Aegina, and Avicenna. But +instead of "cutting men to pieces," he taught that surgeons would +gain more by devoting their time to searching for the universal +panacea which would cure all diseases, surgical as well as +medical. In this we detect a taint of the popular belief in the +philosopher's stone and the magic elixir of life, his belief in +which have been stoutly denied by some of his followers. He did +admit, however, that one operation alone was perhaps +permissible--lithotomy, or the "cutting for stone." + +His influence upon medicine rests undoubtedly upon his +revolutionary attitude, rather than on any great or new +discoveries made by him. It is claimed by many that he brought +prominently into use opium and mercury, and if this were +indisputably proven his services to medicine could hardly be +overestimated. Unfortunately, however, there are good grounds for +doubting that he was particularly influential in reintroducing +these medicines. His chief influence may perhaps be summed up in +a single phrase--he overthrew old traditions. + +To Paracelsus's endeavors, however, if not to the actual products +of his work, is due the credit of setting in motion the chain of +thought that developed finally into scientific chemistry. Nor can +the ultimate aim of the modern chemist seek a higher object than +that of this sixteenth-century alchemist, who taught that "true +alchemy has but one aim and object, to extract the quintessence +of things, and to prepare arcana, tinctures, and elixirs which +may restore to man the health and soundness he has lost." + + +THE GREAT ANATOMISTS + +About the beginning of the sixteenth century, while Paracelsus +was scoffing at the study of anatomy as useless, and using his +influence against it, there had already come upon the scene the +first of the great anatomists whose work was to make the century +conspicuous in that branch of medicine. + +The young anatomist Charles etienne (1503-1564) made one of the +first noteworthy discoveries, pointing out for the first time +that the spinal cord contains a canal, continuous throughout its +length. He also made other minor discoveries of some importance, +but his researches were completely overshadowed and obscured by +the work of a young Fleming who came upon the scene a few years +later, and who shone with such brilliancy in the medical world +that he obscured completely the work of his contemporary until +many years later. This young physician, who was destined to lead +such an eventful career and meet such an untimely end as a martyr +to science, was Andrew Vesalius (1514-1564), who is called the +"greatest of anatomists." At the time he came into the field +medicine was struggling against the dominating Galenic teachings +and the theories of Paracelsus, but perhaps most of all against +the superstitions of the time. In France human dissections were +attended with such dangers that the young Vesalius transferred +his field of labors to Italy, where such investigations were +covertly permitted, if not openly countenanced. + +From the very start the young Fleming looked askance at the +accepted teachings of the day, and began a series of independent +investigations based upon his own observations. The results of +these investigations he gave in a treatise on the subject which +is regarded as the first comprehensive and systematic work on +human anatomy. This remarkable work was published in the author's +twenty-eighth or twenty-ninth year. Soon after this Vesalius was +invited as imperial physician to the court of Emperor Charles V. +He continued to act in the same capacity at the court of Philip +II., after the abdication of his patron. But in spite of this +royal favor there was at work a factor more powerful than the +influence of the monarch himself--an instrument that did so much +to retard scientific progress, and by which so many lives were +brought to a premature close. + +Vesalius had received permission from the kinsmen of a certain +grandee to perform an autopsy. While making his observations the +heart of the outraged body was seen to palpitate--so at least it +was reported. This was brought immediately to the attention of +the Inquisition, and it was only by the intervention of the king +himself that the anatomist escaped the usual fate of those +accused by that tribunal. As it was, he was obliged to perform a +pilgrimage to the Holy Land. While returning from this he was +shipwrecked, and perished from hunger and exposure on the island +of Zante. + +At the very time when the anatomical writings of Vesalius were +startling the medical world, there was living and working +contemporaneously another great anatomist, Eustachius (died +1574), whose records of his anatomical investigations were ready +for publication only nine years after the publication of the work +of Vesalius. Owing to the unfortunate circumstances of the +anatomist, however, they were never published during his +lifetime--not, in fact, until 1714. When at last they were given +to the world as Anatomical Engravings, they showed conclusively +that Eustachius was equal, if not superior to Vesalius in his +knowledge of anatomy. It has been said of this remarkable +collection of engravings that if they had been published when +they were made in the sixteenth century, anatomy would have been +advanced by at least two centuries. But be this as it may, they +certainly show that their author was a most careful dissector and +observer. + +Eustachius described accurately for the first time certain +structures of the middle ear, and rediscovered the tube leading +from the ear to the throat that bears his name. He also made +careful studies of the teeth and the phenomena of first and +second dentition. He was not baffled by the minuteness of +structures and where he was unable to study them with the naked +eye he used glasses for the purpose, and resorted to macerations +and injections for the study of certain complicated structures. +But while the fruit of his pen and pencil were lost for more than +a century after his death, the effects of his teachings were not; +and his two pupils, Fallopius and Columbus, are almost as well +known to-day as their illustrious teacher. Columbus (1490-1559) +did much in correcting the mistakes made in the anatomy of the +bones as described by Vesalius. He also added much to the science +by giving correct accounts of the shape and cavities of the +heart, and made many other discoveries of minor importance. +Fallopius (1523-1562) added considerably to the general knowledge +of anatomy, made several discoveries in the anatomy of the ear, +and also several organs in the abdominal cavity. + +At this time a most vitally important controversy was in progress +as to whether or not the veins of the bodies were supplied with +valves, many anatomists being unable to find them. etienne had +first described these structures, and Vesalius had confirmed his +observations. It would seem as if there could be no difficulty in +settling the question as to the fact of such valves being present +in the vessels, for the demonstration is so simple that it is now +made daily by medical students in all physiological laboratories +and dissecting-rooms. But many of the great anatomists of the +sixteenth century were unable to make this demonstration, even +when it had been brought to their attention by such an authority +as Vesalius. Fallopius, writing to Vesalius on the subject in +1562, declared that he was unable to find such valves. Others, +however, such as Eustachius and Fabricius (1537-1619), were more +successful, and found and described these structures. But the +purpose served by these valves was entirely misinterpreted. That +they act in preventing the backward flow of the blood in the +veins on its way to the heart, just as the valves of the heart +itself prevent regurgitation, has been known since the time of +Harvey; but the best interpretation that could be given at that +time, even by such a man as Fabricius, was that they acted in +retarding the flow of the blood as it comes from the heart, and +thus prevent its too rapid distribution throughout the body. The +fact that the blood might have been going towards the heart, +instead of coming from it, seems never to have been considered +seriously until demonstrated so conclusively by Harvey. + +Of this important and remarkable controversy over the valves in +veins, Withington has this to say: "This is truly a marvellous +story. A great Galenic anatomist is first to give a full and +correct description of the valves and their function, but fails +to see that any modification of the old view as to the motion of +the blood is required. Two able dissectors carefully test their +action by experiment, and come to a result. the exact reverse of +the truth. Urged by them, the two foremost anatomists of the age +make a special search for valves and fail to find them. Finally, +passing over lesser peculiarities, an aged and honorable +professor, who has lived through all this, calmly asserts that no +anatomist, ancient or modern, has ever mentioned valves in veins +till he discovered them in 1574!"[2] + +Among the anatomists who probably discovered these valves was +Michael Servetus (1511-1553); but if this is somewhat in doubt, +it is certain that he discovered and described the pulmonary +circulation, and had a very clear idea of the process of +respiration as carried on in the lungs. The description was +contained in a famous document sent to Calvin in 1545--a document +which the reformer carefully kept for seven years in order that +he might make use of some of the heretical statements it +contained to accomplish his desire of bringing its writer to the +stake. The awful fate of Servetus, the interesting character of +the man, and the fact that he came so near to anticipating the +discoveries of Harvey make him one of the most interesting +figures in medical history. + +In this document which was sent to Calvin, Servetus rejected the +doctrine of natural, vital, and animal spirits, as contained in +the veins, arteries, and nerves respectively, and made the +all-important statement that the fluids contained in veins and +arteries are the same. He showed also that the blood is "purged +from fume" and purified by respiration in the lungs, and declared +that there is a new vessel in the lungs, "formed out of vein and +artery." Even at the present day there is little to add to or +change in this description of Servetus's. + +By keeping this document, pregnant with advanced scientific +views, from the world, and in the end only using it as a means of +destroying its author, the great reformer showed the same +jealousy in retarding scientific progress as had his arch-enemies +of the Inquisition, at whose dictates Vesalius became a martyr to +science, and in whose dungeons etienne perished. + + +THE COMING OF HARVEY + +The time was ripe for the culminating discovery of the +circulation of the blood; but as yet no one had determined the +all-important fact that there are two currents of blood in the +body, one going to the heart, one coming from it. The valves in +the veins would seem to show conclusively that the venous current +did not come from the heart, and surgeons must have observed +thousands of times the every-day phenomenon of congested veins at +the distal extremity of a limb around which a ligature or +constriction of any kind had been placed, and the simultaneous +depletion of the vessels at the proximal points above the +ligature. But it should be remembered that inductive science was +in its infancy. This was the sixteenth, not the nineteenth +century, and few men had learned to put implicit confidence in +their observations and convictions when opposed to existing +doctrines. The time was at hand, however, when such a man was to +make his appearance, and, as in the case of so many revolutionary +doctrines in science, this man was an Englishman. It remained for +William Harvey (1578-1657) to solve the great mystery which had +puzzled the medical world since the beginning of history; not +only to solve it, but to prove his case so conclusively and so +simply that for all time his little booklet must he handed down +as one of the great masterpieces of lucid and almost faultless +demonstration. + +Harvey, the son of a prosperous Kentish yeoman, was born at +Folkestone. His education was begun at the grammar-school of +Canterbury, and later he became a pensioner of Caius College, +Cambridge. Soon after taking his degree of B.A., at the age of +nineteen, he decided upon the profession of medicine, and went to +Padua as a pupil of Fabricius and Casserius. Returning to England +at the age of twenty-four, he soon after (1609) obtained the +reversion of the post of physician to St. Bartholomew's Hospital, +his application being supported by James I. himself. Even at this +time he was a popular physician, counting among his patients such +men as Francis Bacon. In 1618 he was appointed physician +extraordinary to the king, and, a little later, physician in +ordinary. He was in attendance upon Charles I. at the battle of +Edgehill, in 1642, where, with the young Prince of Wales and the +Duke of York, after seeking shelter under a hedge, he drew a book +out of his pocket and, forgetful of the battle, became absorbed +in study, until finally the cannon-balls from the enemy's +artillery made him seek a more sheltered position. + +On the fall of Charles I. he retired from practice, and lived in +retirement with his brother. He was then well along in years, but +still pursued his scientific researches with the same vigor as +before, directing his attention chiefly to the study of +embryology. On June 3, 1657, he was attacked by paralysis and +died, in his eightieth year. He had lived to see his theory of +the circulation accepted, several years before, by all the +eminent anatomists of the civilized world. + +A keenness in the observation of facts, characteristic of the +mind of the man, had led Harvey to doubt the truth of existing +doctrines as to the phenomena of the circulation. Galen had +taught that "the arteries are filled, like bellows, because they +are expanded," but Harvey thought that the action of spurting +blood from a severed vessel disproved this. For the spurting was +remittant, "now with greater, now with less impetus," and its +greater force always corresponded to the expansion (diastole), +not the contraction (systole) of the vessel. Furthermore, it was +evident that contraction of the heart and the arteries was not +simultaneous, as was commonly taught, because in that case there +would be no marked propulsion of the blood in any direction; and +there was no gainsaying the fact that the blood was forcibly +propelled in a definite direction, and that direction away from +the heart. + +Harvey's investigations led him to doubt also the accepted theory +that there was a porosity in the septum of tissue that divides +the two ventricles of the heart. It seemed unreasonable to +suppose that a thick fluid like the blood could find its way +through pores so small that they could not be demonstrated by any +means devised by man. In evidence that there could be no such +openings he pointed out that, since the two ventricles contract +at the same time, this process would impede rather than +facilitate such an intra-ventricular passage of blood. But what +seemed the most conclusive proof of all was the fact that in the +foetus there existed a demonstrable opening between the two +ventricles, and yet this is closed in the fully developed heart. +Why should Nature, if she intended that blood should pass between +the two cavities, choose to close this opening and substitute +microscopic openings in place of it? It would surely seem more +reasonable to have the small perforations in the thin, easily +permeable membrane of the foetus, and the opening in the adult +heart, rather than the reverse. From all this Harvey drew his +correct conclusions, declaring earnestly, "By Hercules, there ARE +no such porosities, and they cannot be demonstrated." + +Having convinced himself that no intra-ventricular opening +existed, he proceeded to study the action of the heart itself, +untrammelled by too much faith in established theories, and, as +yet, with no theory of his own. He soon discovered that the +commonly accepted theory of the heart striking against the +chest-wall during the period of relaxation was entirely wrong, +and that its action was exactly the reverse of this, the heart +striking the chest-wall during contraction. Having thus disproved +the accepted theory concerning the heart's action, he took up the +subject of the action of arteries, and soon was able to +demonstrate by vivisection that the contraction of the arteries +was not simultaneous with contractions of the heart. His +experiments demonstrated that these vessels were simply elastic +tubes whose pulsations were "nothing else than the impulse of the +blood within them." The reason that the arterial pulsation was +not simultaneous with the heart-beat he found to be because of +the time required to carry the impulse along the tube, + +By a series of further careful examinations and experiments, +which are too extended to be given here, he was soon able further +to demonstrate the action and course of the blood during the +contractions of the heart. His explanations were practically the +same as those given to-day--first the contraction of the auricle, +sending blood into the ventricle; then ventricular contraction, +making the pulse, and sending the blood into the arteries. He had +thus demonstrated what had not been generally accepted before, +that the heart was an organ for the propulsion of blood. To make +such a statement to-day seems not unlike the sober announcement +that the earth is round or that the sun does not revolve about +it. Before Harvey's time, however, it was considered as an organ +that was "in some mysterious way the source of vitality and +warmth, as an animated crucible for the concoction of blood and +the generation of vital spirits."[3] + +In watching the rapid and ceaseless contractions of the heart, +Harvey was impressed with the fact that, even if a very small +amount of blood was sent out at each pulsation, an enormous +quantity must pass through the organ in a day, or even in an +hour. Estimating the size of the cavities of the heart, and +noting that at least a drachm must be sent out with each +pulsation, it was evident that the two thousand beats given by a +very slow human heart in an hour must send out some forty pounds +of blood--more than twice the amount in the entire body. The +question was, what became of it all? For it should be remembered +that the return of the blood by the veins was unknown, and +nothing like a "circulation" more than vaguely conceived even by +Harvey himself. Once it could be shown that the veins were +constantly returning blood to the heart, the discovery that the +blood in some way passes from the arteries to the veins was only +a short step. Harvey, by resorting to vivisections of lower +animals and reptiles, soon demonstrated beyond question the fact +that the veins do carry the return blood. "But this, in +particular, can be shown clearer than daylight," says Harvey. +"The vena cava enters the heart at an inferior portion, while the +artery passes out above. Now if the vena cava be taken up with +forceps or the thumb and finger, and the course of the blood +intercepted for some distance below the heart, you will at once +see it almost emptied between the fingers and the heart, the +blood being exhausted by the heart's pulsation, the heart at the +same time becoming much paler even in its dilatation, smaller in +size, owing to the deficiency of blood, and at length languid in +pulsation, as if about to die. On the other hand, when you +release the vein the heart immediately regains its color and +dimensions. After that, if you leave the vein free and tie and +compress the arteries at some distance from the heart, you will +see, on the contrary, their included portion grow excessively +turgid, the heart becoming so beyond measure, assuming a dark-red +color, even to lividity, and at length so overloaded with blood +as to seem in danger of suffocation; but when the obstruction is +removed it returns to its normal condition, in size, color, and +movement."[4] + +This conclusive demonstration that the veins return the blood to +the heart must have been most impressive to Harvey, who had been +taught to believe that the blood current in the veins pursued an +opposite course, and must have tended to shake his faith in all +existing doctrines of the day. + +His next step was the natural one of demonstrating that the blood +passes from the arteries to the veins. He demonstrated +conclusively that this did occur, but for once his rejection of +the ancient writers and one modern one was a mistake. For Galen +had taught, and had attempted to demonstrate, that there are sets +of minute vessels connecting the arteries and the veins; and +Servetus had shown that there must be such vessels, at least in +the lungs. + +However, the little flaw in the otherwise complete demonstration +of Harvey detracts nothing from the main issue at stake. It was +for others who followed to show just how these small vessels +acted in effecting the transfer of the blood from artery to vein, +and the grand general statement that such a transfer does take +place was, after all, the all-important one, and the exact method +of how it takes place a detail. Harvey's experiments to +demonstrate that the blood passes from the arteries to the veins +are so simply and concisely stated that they may best be given in +his own words. + +"I have here to cite certain experiments," he wrote, "from which +it seems obvious that the blood enters a limb by the arteries, +and returns from it by the veins; that the arteries are the +vessels carrying the blood from the heart, and the veins the +returning channels of the blood to the heart; that in the limbs +and extreme parts of the body the blood passes either by +anastomosis from the arteries into the veins, or immediately by +the pores of the flesh, or in both ways, as has already been said +in speaking of the passage of the blood through the lungs; whence +it appears manifest that in the circuit the blood moves from +thence hither, and hence thither; from the centre to the +extremities, to wit, and from the extreme parts back again to the +centre. Finally, upon grounds of circulation, with the same +elements as before, it will be obvious that the quantity can +neither be accounted for by the ingesta, nor yet be held +necessary to nutrition. + +"Now let any one make an experiment on the arm of a man, either +using such a fillet as is employed in blood-letting or grasping +the limb tightly with his hand, the best subject for it being one +who is lean, and who has large veins, and the best time after +exercise, when the body is warm, the pulse is full, and the blood +carried in large quantities to the extremities, for all then is +more conspicuous; under such circumstances let a ligature be +thrown about the extremity and drawn as tightly as can be borne: +it will first be perceived that beyond the ligature neither in +the wrist nor anywhere else do the arteries pulsate, that at the +same time immediately above the ligature the artery begins to +rise higher at each diastole, to throb more violently, and to +swell in its vicinity with a kind of tide, as if it strove to +break through and overcome the obstacle to its current; the +artery here, in short, appears as if it were permanently full. +The hand under such circumstances retains its natural color and +appearances; in the course of time it begins to fall somewhat in +temperature, indeed, but nothing is DRAWN into it. + +"After the bandage has been kept on some short time in this way, +let it be slackened a little, brought to the state or term of +middling tightness which is used in bleeding, and it will be seen +that the whole hand and arm will instantly become deeply suffused +and distended, injected, gorged with blood, DRAWN, as it is said, +by this middling ligature, without pain, or heat, or any horror +of a vacuum, or any other cause yet indicated. + +"As we have noted, in connection with the tight ligature, that +the artery above the bandage was distended and pulsated, not +below it, so, in the case of the moderately tight bandage, on the +contrary, do we find that the veins below, never above, the +fillet swell and become dilated, while the arteries shrink; and +such is the degree of distention of the veins here that it is +only very strong pressure that will force the blood beyond the +fillet and cause any of the veins in the upper part of the arm to +rise. + +"From these facts it is easy for any careful observer to learn +that the blood enters an extremity by the arteries; for when they +are effectively compressed nothing is DRAWN to the member; the +hand preserves its color; nothing flows into it, neither is it +distended; but when the pressure is diminished, as it is with the +bleeding fillet, it is manifest that the blood is instantly +thrown in with force, for then the hand begins to swell; which is +as much as to say that when the arteries pulsate the blood is +flowing through them, as it is when the moderately tight ligature +is applied; but when they do not pulsate, or when a tight +ligature is used, they cease from transmitting anything; they are +only distended above the part where the ligature is applied. The +veins again being compressed, nothing can flow through them; the +certain indication of which is that below the ligature they are +much more tumid than above it, and than they usually appear when +there is no bandage upon the arm. + +"It therefore plainly appears that the ligature prevents the +return of the blood through the veins to the parts above it, and +maintains those beneath it in a state of permanent distention. +But the arteries, in spite of the pressure, and under the force +and impulse of the heart, send on the blood from the internal +parts of the body to the parts beyond the bandage."[5] + + +This use of ligatures is very significant, because, as shown, a +very tight ligature stops circulation in both arteries and veins, +while a loose one, while checking the circulation in the veins, +which lie nearer the surface and are not so directly influenced +by the force of the heart, does not stop the passage of blood in +the arteries, which are usually deeply imbedded in the tissues, +and not so easily influenced by pressure from without. + +The last step of Harvey's demonstration was to prove that the +blood does flow along the veins to the heart, aided by the valves +that had been the cause of so much discussion and dispute between +the great sixteenth-century anatomists. Harvey not only +demonstrated the presence of these valves, but showed +conclusively, by simple experiments, what their function was, +thus completing his demonstration of the phenomena of the +circulation. + +The final ocular demonstration of the passage of the blood from +the arteries to the veins was not to be made until four years +after Harvey's death. This process, which can be observed easily +in the web of a frog's foot by the aid of a low-power lens, was +first demonstrated by Marcello Malpighi (1628-1694) in 1661. By +the aid of a lens he first saw the small "capillary" vessels +connecting the veins and arteries in a piece of dried lung. +Taking his cue from this, he examined the lung of a turtle, and +was able to see in it the passage of the corpuscles through these +minute vessels, making their way along these previously unknown +channels from the arteries into the veins on their journey back +to the heart. Thus the work of Harvey, all but complete, was made +absolutely entire by the great Italian. And all this in a single +generation. + + +LEEUWENHOEK DISCOVERS BACTERIA + +The seventeenth century was not to close, however, without +another discovery in science, which, when applied to the +causation of disease almost two centuries later, revolutionized +therapeutics more completely than any one discovery. This was the +discovery of microbes, by Antonius von Leeuwenhoek (1632-1723), +in 1683. Von Leeuwenhoek discovered that "in the white matter +between his teeth" there were millions of microscopic +"animals"--more, in fact, than "there were human beings in the +united Netherlands," and all "moving in the most delightful +manner." There can be no question that he saw them, for we can +recognize in his descriptions of these various forms of little +"animals" the four principal forms of microbes--the long and +short rods of bacilli and bacteria, the spheres of micrococci, +and the corkscrew spirillum. + +The presence of these microbes in his mouth greatly annoyed +Antonius, and he tried various methods of getting rid of them, +such as using vinegar and hot coffee. In doing this he little +suspected that he was anticipating modern antiseptic surgery by a +century and three-quarters, and to be attempting what antiseptic +surgery is now able to accomplish. For the fundamental principle +of antisepsis is the use of medicines for ridding wounds of +similar microscopic organisms. Von Leenwenhoek was only +temporarily successful in his attempts, however, and took +occasion to communicate his discovery to the Royal Society of +England, hoping that they would be "interested in this novelty." +Probably they were, but not sufficiently so for any member to +pursue any protracted investigations or reach any satisfactory +conclusions, and the whole matter was practically forgotten until +the middle of the nineteenth century. + + + +VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +Of the half-dozen surgeons who were prominent in the sixteenth +century, Ambroise Pare (1517-1590), called the father of French +surgery, is perhaps the most widely known. He rose from the +position of a common barber to that of surgeon to three French +monarchs, Henry II., Francis II., and Charles IX. Some of his +mottoes are still first principles of the medical man. Among +others are: "He who becomes a surgeon for the sake of money, and +not for the sake of knowledge, will accomplish nothing"; and "A +tried remedy is better than a newly invented." On his statue is +his modest estimate of his work in caring for the wounded, "Je le +pansay, Dieu le guarit"--I dressed him, God cured him. + +It was in this dressing of wounds on the battlefield that he +accidentally discovered how useless and harmful was the terribly +painful treatment of applying boiling oil to gunshot wounds as +advocated by John of Vigo. It happened that after a certain +battle, where there was an unusually large number of casualties, +Pare found, to his horror, that no more boiling oil was available +for the surgeons, and that he should be obliged to dress the +wounded by other simpler methods. To his amazement the results +proved entirely satisfactory, and from that day he discarded the +hot-oil treatment. + +As Pare did not understand Latin he wrote his treatises in +French, thus inaugurating a custom in France that was begun by +Paracelsus in Germany half a century before. He reintroduced the +use of the ligature in controlling hemorrhage, introduced the +"figure of eight" suture in the operation for hare-lip, improved +many of the medico-legal doctrines, and advanced the practice of +surgery generally. He is credited with having successfully +performed the operation for strangulated hernia, but he probably +borrowed it from Peter Franco (1505-1570), who published an +account of this operation in 1556. As this operation is +considered by some the most important operation in surgery, its +discoverer is entitled to more than passing notice, although he +was despised and ignored by the surgeons of his time. + +Franco was an illiterate travelling lithotomist--a class of +itinerant physicians who were very generally frowned down by the +regular practitioners of medicine. But Franco possessed such +skill as an operator, and appears to have been so earnest in the +pursuit of what he considered a legitimate calling, that he +finally overcame the popular prejudice and became one of the +salaried surgeons of the republic of Bern. He was the first +surgeon to perform the suprapubic lithotomy operation--the +removal of stone through the abdomen instead of through the +perineum. His works, while written in an illiterate style, give +the clearest descriptions of any of the early modern writers. + +As the fame of Franco rests upon his operation for prolonging +human life, so the fame of his Italian contemporary, Gaspar +Tagliacozzi (1545-1599), rests upon his operation for increasing +human comfort and happiness by restoring amputated noses. At the +time in which he lived amputation of the nose was very common, +partly from disease, but also because a certain pope had fixed +the amputation of that member as the penalty for larceny. +Tagliacozzi probably borrowed his operation from the East; but he +was the first Western surgeon to perform it and describe it. So +great was the fame of his operations that patients flocked to him +from all over Europe, and each "went away with as many noses as +he liked." Naturally, the man who directed his efforts to +restoring structures that bad been removed by order of the Church +was regarded in the light of a heretic by many theologians; and +though he succeeded in cheating the stake or dungeon, and died a +natural death, his body was finally cast out of the church in +which it had been buried. + +In the sixteenth century Germany produced a surgeon, Fabricius +Hildanes (1560-1639), whose work compares favorably with that of +Pare, and whose name would undoubtedly have been much better +known had not the circumstances of the time in which he lived +tended to obscure his merits. The blind followers of Paracelsus +could see nothing outside the pale of their master's teachings, +and the disastrous Thirty Years' War tended to obscure and retard +all scientific advances in Germany. Unlike many of his +fellow-surgeons, Hildanes was well versed in Latin and Greek; +and, contrary to the teachings of Paracelsus, he laid particular +stress upon the necessity of the surgeon having a thorough +knowledge of anatomy. He had a helpmate in his wife, who was also +something of a surgeon, and she is credited with having first +made use of the magnet in removing particles of metal from the +eye. Hildanes tells of a certain man who had been injured by a +small piece of steel in the cornea, which resisted all his +efforts to remove it. After observing Hildanes' fruitless efforts +for a time, it suddenly occurred to his wife to attempt to make +the extraction with a piece of loadstone. While the physician +held open the two lids, his wife attempted to withdraw the steel +with the magnet held close to the cornea, and after several +efforts she was successful--which Hildanes enumerates as one of +the advantages of being a married man. + +Hildanes was particularly happy in his inventions of surgical +instruments, many of which were designed for locating and +removing the various missiles recently introduced in warfare. + + +The seventeenth century, which was such a flourishing one for +anatomy and physiology, was not as productive of great surgeons +or advances in surgery as the sixteenth had been or the +eighteenth was to be. There was a gradual improvement all along +the line, however, and much of the work begun by such surgeons as +Pare and Hildanes was perfected or improved. Perhaps the most +progressive surgeon of the century was an Englishman, Richard +Wiseman (1625-1686), who, like Harvey, enjoyed royal favor, being +in the service of all the Stuart kings. He was the first surgeon +to advocate primary amputation, in gunshot wounds, of the limbs, +and also to introduce the treatment of aneurisms by compression; +but he is generally rated as a conservative operator, who favored +medication rather than radical operations, where possible. + +In Italy, Marcus Aurelius Severinus (1580-1656) and Peter +Marchettis (1589-1675) were the leading surgeons of their nation. +Like many of his predecessors in Europe, Severinus ran amuck with +the Holy Inquisition and fled from Naples. But the waning of the +powerful arm of the Church is shown by the fact that he was +brought back by the unanimous voice of the grateful citizens, and +lived in safety despite the frowns of the theologians. + + +The sixteenth century cannot be said to have added much of +importance in the field of practical medicine, and, as in the +preceding and succeeding centuries, was at best only struggling +along in the wake of anatomy, physiology, and surgery. In the +seventeenth century, however, at least one discovery in +therapeutics was made that has been an inestimable boon to +humanity ever since. This was the introduction of cinchona bark +(from which quinine is obtained) in 1640. But this century was +productive of many medical SYSTEMS, and could boast of many great +names among the medical profession, and, on the whole, made +considerably more progress than the preceding century. + +Of the founders of medical systems, one of the most widely known +is Jan Baptista van Helmont (1578-1644), an eccentric genius who +constructed a system of medicine of his own and for a time +exerted considerable influence. But in the end his system was +destined to pass out of existence, not very long after the death +of its author. Van Helmont was not only a physician, but was +master of all the other branches of learning of the time, taking +up the study of medicine and chemistry as an after-thought, but +devoting himself to them with the greatest enthusiasm once he had +begun his investigations. His attitude towards existing doctrines +was as revolutionary as that of Paracelsus, and he rejected the +teachings of Galen and all the ancient writers, although +retaining some of the views of Paracelsus. He modified the +archaeus of Paracelsus, and added many complications to it. He +believed the whole body to be controlled by an archaeus influus, +the soul by the archaei insiti, and these in turn controlled by +the central archeus. His system is too elaborate and complicated +for full explanation, but its chief service to medicine was in +introducing new chemical methods in the preparation of drugs. In +this way he was indirectly connected with the establishment of +the Iatrochemical school. It was he who first used the word +"gas"--a word coined by him, along with many others that soon +fell into disuse. + +The principles of the Iatrochemical school were the use of +chemical medicines, and a theory of pathology different from the +prevailing "humoral" pathology. The founder of this school was +Sylvius (Franz de le Boe, 1614-1672), professor of medicine at +Leyden. He attempted to establish a permanent system of medicine +based on the newly discovered theory of the circulation and the +new chemistry, but his name is remembered by medical men because +of the fissure in the brain (fissure of Sylvius) that bears it. +He laid great stress on the cause of fevers and other diseases as +originating in the disturbances of the process of fermentation in +the stomach. The doctrines of Sylvius spread widely over the +continent, but were not generally accepted in England until +modified by Thomas Willis (1622-1675), whose name, like that of +Sylvius, is perpetuated by a structure in the brain named after +him, the circle of Willis. Willis's descriptions of certain +nervous diseases, and an account of diabetes, are the first +recorded, and added materially to scientific medicine. These +schools of medicine lasted until the end of the seventeenth +century, when they were finally overthrown by Sydenham. + +The Iatrophysical school (also called iatromathematical, +iatromechanical, or physiatric) was founded on theories of +physiology, probably by Borelli, of Naples (1608-1679), although +Sanctorius; Sanctorius, a professor at Padua, was a precursor, if +not directly interested in establishing it. Sanctorius discovered +the fact that an "insensible perspiration" is being given off by +the body continually, and was amazed to find that loss of weight +in this way far exceeded the loss of weight by all other +excretions of the body combined. He made this discovery by means +of a peculiar weighing-machine to which a chair was attached, and +in which he spent most of his time. Very naturally he +overestimated the importance of this discovery, but it was, +nevertheless, of great value in pointing out the hygienic +importance of the care of the skin. He also introduced a +thermometer which he advocated as valuable in cases of fever, but +the instrument was probably not his own invention, but borrowed +from his friend Galileo. + +Harvey's discovery of the circulation of the blood laid the +foundation of the Iatrophysical school by showing that this vital +process was comparable to a hydraulic system. In his On the +Motive of Animals, Borelli first attempted to account for the +phenomena of life and diseases on these principles. The +iatromechanics held that the great cause of disease is due to +different states of elasticity of the solids of the body +interfering with the movements of the fluids, which are +themselves subject to changes in density, one or both of these +conditions continuing to cause stagnation or congestion. The +school thus founded by Borelli was the outcome of the unbounded +enthusiasm, with its accompanying exaggeration of certain +phenomena with the corresponding belittling of others that +naturally follows such a revolutionary discovery as that of +Harvey. Having such a founder as the brilliant Italian Borelli, +it was given a sufficient impetus by his writings to carry it +some distance before it finally collapsed. Some of the +exaggerated mathematical calculations of Borelli himself are +worth noting. Each heart-beat, as he calculated it, overcomes a +resistance equal to one hundred and eighty thousand pounds;--the +modern physiologist estimates its force at from five to nine +ounces! + + +THOMAS SYDENHAM + +But while the Continent was struggling with these illusive +"systems," and dabbling in mystic theories that were to scarcely +outlive the men who conceived + +them, there appeared in England--the "land of common-sense," as a +German scientist has called it--"a cool, clear, and unprejudiced +spirit," who in the golden age of systems declined "to be like +the man who builds the chambers of the upper story of his house +before he had laid securely the foundation walls."[1] This man +was Thomas Sydenham (1624-1689), who, while the great Harvey was +serving the king as surgeon, was fighting as a captain in the +parliamentary army. Sydenham took for his guide the teachings of +Hippocrates, modified to suit the advances that had been made in +scientific knowledge since the days of the great Greek, and +established, as a standard, observation and experience. He cared +little for theory unless confirmed by practice, but took the +Hippocratic view that nature cured diseases, assisted by the +physician. He gave due credit, however, to the importance of the +part played by the assistant. As he saw it, medicine could be +advanced in three ways: (1) "By accurate descriptions or natural +histories of diseases; (2) by establishing a fixed principle or +method of treatment, founded upon experience; (3) by searching +for specific remedies, which he believes must exist in +considerable numbers, though he admits that the only one yet +discovered is Peruvian bark."[2] As it happened, another equally +specific remedy, mercury, when used in certain diseases, was +already known to him, but he evidently did not recognize it as +such. + +The influence on future medicine of Sydenham's teachings was most +pronounced, due mostly to his teaching of careful observation. To +most physicians, however, he is now remembered chiefly for his +introduction of the use of laudanum, still considered one of the +most valuable remedies of modern pharmacopoeias. The German gives +the honor of introducing this preparation to Paracelsus, but the +English-speaking world will always believe that the credit should +be given to Sydenham. + + + +IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + +We saw that in the old Greek days there was no sharp line of +demarcation between the field of the philosopher and that of the +scientist. In the Hellenistic epoch, however, knowledge became +more specialized, and our recent chapters have shown us +scientific investigators whose efforts were far enough removed +from the intangibilities of the philosopher. It must not be +overlooked, however, that even in the present epoch there were +men whose intellectual efforts were primarily directed towards +the subtleties of philosophy, yet who had also a penchant for +strictly scientific imaginings, if not indeed for practical +scientific experiments. At least three of these men were of +sufficient importance in the history of the development of +science to demand more than passing notice. These three are the +Englishman Francis Bacon (1561-1626), the Frenchman Rene +Descartes (1596-1650); and the German Gottfried Leibnitz +(1646-1716). Bacon, as the earliest path-breaker, showed the way, +theoretically at least, in which the sciences should be studied; +Descartes, pursuing the methods pointed out by Bacon, carried the +same line of abstract reason into practice as well; while +Leibnitz, coming some years later, and having the advantage of +the wisdom of his two great predecessors, was naturally +influenced by both in his views of abstract scientific +principles. + +Bacon's career as a statesman and his faults and misfortunes as a +man do not concern us here. Our interest in him begins with his +entrance into Trinity College, Cambridge, where he took up the +study of all the sciences taught there at that time. During the +three years he became more and more convinced that science was +not being studied in a profitable manner, until at last, at the +end of his college course, he made ready to renounce the old +Aristotelian methods of study and advance his theory of inductive +study. For although he was a great admirer of Aristotle's work, +he became convinced that his methods of approaching study were +entirely wrong. + +"The opinion of Aristotle," he says, in his De Argumentum +Scientiarum, "seemeth to me a negligent opinion, that of those +things which exist by nature nothing can be changed by custom; +using for example, that if a stone be thrown ten thousand times +up it will not learn to ascend; and that by often seeing or +hearing we do not learn to see or hear better. For though this +principle be true in things wherein nature is peremptory (the +reason whereof we cannot now stand to discuss), yet it is +otherwise in things wherein nature admitteth a latitude. For he +might see that a straight glove will come more easily on with +use; and that a wand will by use bend otherwise than it grew; and +that by use of the voice we speak louder and stronger; and that +by use of enduring heat or cold we endure it the better, and the +like; which latter sort have a nearer resemblance unto that +subject of manners he handleth than those instances which he +allegeth."[1] + +These were his opinions, formed while a young man in college, +repeated at intervals through his maturer years, and reiterated +and emphasized in his old age. Masses of facts were to be +obtained by observing nature at first hand, and from such +accumulations of facts deductions were to be made. In short, +reasoning was to be from the specific to the general, and not +vice versa. + +It was by his teachings alone that Bacon thus contributed to the +foundation of modern science; and, while he was constantly +thinking and writing on scientific subjects, he contributed +little in the way of actual discoveries. "I only sound the +clarion," he said, "but I enter not the battle." + +The case of Descartes, however, is different. He both sounded the +clarion and entered into the fight. He himself freely +acknowledges his debt to Bacon for his teachings of inductive +methods of study, but modern criticism places his work on the +same plane as that of the great Englishman. "If you lay hold of +any characteristic product of modern ways of thinking," says +Huxley, "either in the region of philosophy or in that of +science, you find the spirit of that thought, if not its form, +has been present in the mind of the great Frenchman."[2] + +Descartes, the son of a noble family of France, was educated by +Jesuit teachers. Like Bacon, he very early conceived the idea +that the methods of teaching and studying science were wrong, but +be pondered the matter well into middle life before putting into +writing his ideas of philosophy and science. Then, in his +Discourse Touching the Method of Using One's Reason Rightly and +of Seeking Scientific Truth, he pointed out the way of seeking +after truth. His central idea in this was to emphasize the +importance of DOUBT, and avoidance of accepting as truth anything +that does not admit of absolute and unqualified proof. In +reaching these conclusions he had before him the striking +examples of scientific deductions by Galileo, and more recently +the discovery of the circulation of the blood by Harvey. This +last came as a revelation to scientists, reducing this seemingly +occult process, as it did, to the field of mechanical phenomena. +The same mechanical laws that governed the heavenly bodies, as +shown by Galileo, governed the action of the human heart, and, +for aught any one knew, every part of the body, and even the mind +itself. + +Having once conceived this idea, Descartes began a series of +dissections and experiments upon the lower animals, to find, if +possible, further proof of this general law. To him the human +body was simply a machine, a complicated mechanism, whose +functions were controlled just as any other piece of machinery. +He compared the human body to complicated machinery run by +water-falls and complicated pipes. "The nerves of the machine +which I am describing," he says, "may very well be compared to +the pipes of these waterworks; its muscles and its tendons to the +other various engines and springs which seem to move them; its +animal spirits to the water which impels them, of which the heart +is the fountain; while the cavities of the brain are the central +office. Moreover, respiration and other such actions as are +natural and usual in the body, and which depend on the course of +the spirits, are like the movements of a clock, or a mill, which +may be kept up by the ordinary flow of water."[3] + +In such passages as these Descartes anticipates the ideas of +physiology of the present time. He believed that the functions +are performed by the various organs of the bodies of animals and +men as a mechanism, to which in man was added the soul. This soul +he located in the pineal gland, a degenerate and presumably +functionless little organ in the brain. For years Descartes's +idea of the function of this gland was held by many +physiologists, and it was only the introduction of modern +high-power microscopy that reduced this also to a mere mechanism, +and showed that it is apparently the remains of a Cyclopean eye +once common to man's remote ancestors. + +Descartes was the originator of a theory of the movements of the +universe by a mechanical process--the Cartesian theory of +vortices--which for several decades after its promulgation +reigned supreme in science. It is the ingenuity of this theory, +not the truth of its assertions, that still excites admiration, +for it has long since been supplanted. It was certainly the best +hitherto advanced--the best "that the observations of the age +admitted," according to D'Alembert. + +According to this theory the infinite universe is full of matter, +there being no such thing as a vacuum. Matter, as Descartes +believed, is uniform in character throughout the entire universe, +and since motion cannot take place in any part of a space +completely filled, without simultaneous movement in all other +parts, there are constant more or less circular movements, +vortices, or whirlpools of particles, varying, of course, in size +and velocity. As a result of this circular movement the particles +of matter tend to become globular from contact with one another. +Two species of matter are thus formed, one larger and globular, +which continue their circular motion with a constant tendency to +fly from the centre of the axis of rotation, the other composed +of the clippings resulting from the grinding process. These +smaller "filings" from the main bodies, becoming smaller and +smaller, gradually lose their velocity and accumulate in the +centre of the vortex. This collection of the smaller matter in +the centre of the vortex constitutes the sun or star, while the +spherical particles propelled in straight lines from the centre +towards the circumference of the vortex produce the phenomenon of +light radiating from the central star. Thus this matter becomes +the atmosphere revolving around the accumulation at the centre. +But the small particles being constantly worn away from the +revolving spherical particles in the vortex, become entangled in +their passage, and when they reach the edge of the inner strata +of solar dust they settle upon it and form what we call +sun-spots. These are constantly dissolved and reformed, until +sometimes they form a crust round the central nucleus. + +As the expansive force of the star diminishes in the course of +time, it is encroached upon by neighboring vortices. If the part +of the encroaching star be of a less velocity than the star which +it has swept up, it will presently lose its hold, and the smaller +star pass out of range, becoming a comet. But if the velocity of +the vortex into which the incrusted star settles be equivalent to +that of the surrounded vortex, it will hold it as a captive, +still revolving and "wrapt in its own firmament." Thus the +several planets of our solar system have been captured and held +by the sun-vortex, as have the moon and other satellites. + +But although these new theories at first created great enthusiasm +among all classes of philosophers and scientists, they soon came +under the ban of the Church. While no actual harm came to +Descartes himself, his writings were condemned by the Catholic +and Protestant churches alike. The spirit of philosophical +inquiry he had engendered, however, lived on, and is largely +responsible for modern philosophy. + +In many ways the life and works of Leibnitz remind us of Bacon +rather than Descartes. His life was spent in filling high +political positions, and his philosophical and scientific +writings were by-paths of his fertile mind. He was a theoretical +rather than a practical scientist, his contributions to science +being in the nature of philosophical reasonings rather than +practical demonstrations. Had he been able to withdraw from +public life and devote himself to science alone, as Descartes +did, he would undoubtedly have proved himself equally great as a +practical worker. But during the time of his greatest activity in +philosophical fields, between the years 1690 and 1716, he was all +the time performing extraordinary active duties in entirely +foreign fields. His work may be regarded, perhaps, as doing for +Germany in particular what Bacon's did for England and the rest +of the world in general. + +Only a comparatively small part of his philosophical writings +concern us here. According to his theory of the ultimate elements +of the universe, the entire universe is composed of individual +centres, or monads. To these monads he ascribed numberless +qualities by which every phase of nature may be accounted. They +were supposed by him to be percipient, self-acting beings, not +under arbitrary control of the deity, and yet God himself was the +original monad from which all the rest are generated. With this +conception as a basis, Leibnitz deduced his doctrine of +pre-established harmony, whereby the numerous independent +substances composing the world are made to form one universe. He +believed that by virtue of an inward energy monads develop +themselves spontaneously, each being independent of every other. +In short, each monad is a kind of deity in itself--a microcosm +representing all the great features of the macrocosm. + +It would be impossible clearly to estimate the precise value of +the stimulative influence of these philosophers upon the +scientific thought of their time. There was one way, however, in +which their influence was made very tangible--namely, in the +incentive they gave to the foundation of scientific societies. + + +SCIENTIFIC SOCIETIES + +At the present time, when the elements of time and distance are +practically eliminated in the propagation of news, and when cheap +printing has minimized the difficulties of publishing scientific +discoveries, it is difficult to understand the isolated position +of the scientific investigation of the ages that preceded steam +and electricity. Shut off from the world and completely out of +touch with fellow-laborers perhaps only a few miles away, the +investigators were naturally seriously handicapped; and +inventions and discoveries were not made with the same rapidity +that they would undoubtedly have been had the same men been +receiving daily, weekly, or monthly communications from +fellow-laborers all over the world, as they do to-day. Neither +did they have the advantage of public or semi-public +laboratories, where they were brought into contact with other +men, from whom to gather fresh trains of thought and receive the +stimulus of their successes or failures. In the natural course of +events, however, neighbors who were interested in somewhat +similar pursuits, not of the character of the rivalry of trade or +commerce, would meet more or less frequently and discuss their +progress. The mutual advantages of such intercourse would be at +once appreciated; and it would be but a short step from the +casual meeting of two neighborly scientists to the establishment +of "societies," meeting at fixed times, and composed of members +living within reasonable travelling distance. There would, +perhaps, be the weekly or monthly meetings of men in a limited +area; and as the natural outgrowth of these little local +societies, with frequent meetings, would come the formation of +larger societies, meeting less often, where members travelled a +considerable distance to attend. And, finally, with increased +facilities for communication and travel, the great international +societies of to-day would be produced--the natural outcome of the +neighborly meetings of the primitive mediaeval investigators. + +In Italy, at about the time of Galileo, several small societies +were formed. One of the most important of these was the Lyncean +Society, founded about the year 1611, Galileo himself being a +member. This society was succeeded by the Accademia del Cimento, +at Florence, in 1657, which for a time flourished, with such a +famous scientist as Torricelli as one of its members. + +In England an impetus seems to have been given by Sir Francis +Bacon's writings in criticism and censure of the systern of +teaching in colleges. It is supposed that his suggestions as to +what should be the aims of a scientific society led eventually to +the establishment of the Royal Society. He pointed out how little +had really been accomplished by the existing institutions of +learning in advancing science, and asserted that little good +could ever come from them while their methods of teaching +remained unchanged. He contended that the system which made the +lectures and exercises of such a nature that no deviation from +the established routine could be thought of was pernicious. But +he showed that if any teacher had the temerity to turn from the +traditional paths, the daring pioneer was likely to find +insurmountable obstacles placed in the way of his advancement. +The studies were "imprisoned" within the limits of a certain set +of authors, and originality in thought or teaching was to be +neither contemplated nor tolerated. + +The words of Bacon, given in strong and unsparing terms of +censure and condemnation, but nevertheless with perfect +justification, soon bore fruit. As early as the year 1645 a small +company of scientists had been in the habit of meeting at some +place in London to discuss philosophical and scientific subjects +for mental advancement. In 1648, owing to the political +disturbances of the time, some of the members of these meetings +removed to Oxford, among them Boyle, Wallis, and Wren, where the +meetings were continued, as were also the meetings of those left +in London. In 1662, however, when the political situation bad +become more settled, these two bodies of men were united under a +charter from Charles II., and Bacon's ideas were practically +expressed in that learned body, the Royal Society of London. And +it matters little that in some respects Bacon's views were not +followed in the practical workings of the society, or that the +division of labor in the early stages was somewhat different than +at present. The aim of the society has always been one for the +advancement of learning; and if Bacon himself could look over its +records, he would surely have little fault to find with the aid +it has given in carrying out his ideas for the promulgation of +useful knowledge. + +Ten years after the charter was granted to the Royal Society of +London, Lord Bacon's words took practical effect in Germany, with +the result that the Academia Naturae Curiosorum was founded, +under the leadership of Professor J. C. Sturm. The early labors +of this society were devoted to a repetition of the most notable +experiments of the time, and the work of the embryo society was +published in two volumes, in 1672 and 1685 respectively, which +were practically text-books of the physics of the period. It was +not until 1700 that Frederick I. founded the Royal Academy of +Sciences at Berlin, after the elaborate plan of Leibnitz, who was +himself the first president. + +Perhaps the nearest realization of Bacon's ideal, however, is in +the Royal Academy of Sciences at Paris, which was founded in 1666 +under the administration of Colbert, during the reign of Louis +XIV. This institution not only recognized independent members, +but had besides twenty pensionnaires who received salaries from +the government. In this way a select body of scientists were +enabled to pursue their investigations without being obliged to +"give thought to the morrow" for their sustenance. In return they +were to furnish the meetings with scientific memoirs, and once a +year give an account of the work they were engaged upon. Thus a +certain number of the brightest minds were encouraged to devote +their entire time to scientific research, "delivered alike from +the temptations of wealth or the embarrassments of poverty." That +such a plan works well is amply attested by the results emanating +from the French academy. Pensionnaires in various branches of +science, however, either paid by the state or by learned +societies, are no longer confined to France. + +Among the other early scientific societies was the Imperial +Academy of Sciences at St. Petersburg, projected by Peter the +Great, and established by his widow, Catharine I., in 1725; and +also the Royal Swedish Academy, incorporated in 1781, and +counting among its early members such men as the celebrated +Linnaeus. But after the first impulse had resulted in a few +learned societies, their manifest advantage was so evident that +additional numbers increased rapidly, until at present almost +every branch of every science is represented by more or less +important bodies; and these are, individually and collectively, +adding to knowledge and stimulating interest in the many fields +of science, thus vindicating Lord Bacon's asseverations that +knowledge could be satisfactorily promulgated in this manner. + + + +X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +We have now to witness the diversified efforts of a company of +men who, working for the most part independently, greatly added +to the data of the physical sciences--such men as Boyle, Huygens, +Von Gericke, and Hooke. It will be found that the studies of +these men covered the whole field of physical sciences as then +understood--the field of so-called natural philosophy. We shall +best treat these successors of Galileo and precursors of Newton +somewhat biographically, pointing out the correspondences and +differences between their various accomplishments as we proceed. +It will be noted in due course that the work of some of them was +anticipatory of great achievements of a later century. + + +ROBERT BOYLE (1627-1691) + +Some of Robert Boyle's views as to the possible structure of +atmospheric air will be considered a little farther on in this +chapter, but for the moment we will take up the consideration of +some of his experiments upon that as well as other gases. Boyle +was always much interested in alchemy, and carried on extensive +experiments in attempting to accomplish the transmutation of +metals; but he did not confine himself to these experiments, +devoting himself to researches in all the fields of natural +philosophy. He was associated at Oxford with a company of +scientists, including Wallis and Wren, who held meetings and made +experiments together, these gatherings being the beginning, as +mentioned a moment ago, of what finally became the Royal Society. +It was during this residence at Oxford that many of his valuable +researches upon air were made, and during this time be invented +his air-pump, now exhibited in the Royal Society rooms at +Burlington House.[1] + +His experiments to prove the atmospheric pressure are most +interesting and conclusive. "Having three small, round glass +bubbles, blown at the flame of a lamp, about the size of +hazel-nuts," he says, "each of them with a short, slender stem, +by means whereof they were so exactly poised in water that a very +small change of weight would make them either emerge or sink; at +a time when the atmosphere was of convenient weight, I put them +into a wide-mouthed glass of common water, and leaving them in a +quiet place, where they were frequently in my eye, I observed +that sometimes they would be at the top of the water, and remain +there for several days, or perhaps weeks, together, and sometimes +fall to the bottom, and after having continued there for some +time rise again. And sometimes they would rise or fall as the air +was hot or cold."[2] + +It was in the course of these experiments that the observations +made by Boyle led to the invention of his "statical barometer," +the mercurial barometer having been invented, as we have seen, by +Torricelli, in 1643. In describing this invention he says: +"Making choice of a large, thin, and light glass bubble, blown at +the flame of a lamp, I counterpoised it with a metallic weight, +in a pair of scales that were suspended in a frame, that would +turn with the thirtieth part of a grain. Both the frame and the +balance were then placed near a good barometer, whence I might +learn the present weight of the atmosphere; when, though the +scales were unable to show all the variations that appeared in +the mercurial barometer, yet they gave notice of those that +altered the height of the mercury half a quarter of an inch."[3] +A fairly sensitive barometer, after all. This statical barometer +suggested several useful applications to the fertile imagination +of its inventor, among others the measuring of mountain-peaks, as +with the mercurial barometer, the rarefication of the air at the +top giving a definite ratio to the more condensed air in the +valley. + +Another of his experiments was made to discover the atmospheric +pressure to the square inch. After considerable difficulty he +determined that the relative weight of a cubic inch of water and +mercury was about one to fourteen, and computing from other known +weights he determined that "when a column of quicksilver thirty +inches high is sustained in the barometer, as it frequently +happens, a column of air that presses upon an inch square near +the surface of the earth must weigh about fifteen avoirdupois +pounds."[4] As the pressure of air at the sea-level is now +estimated at 14.7304 pounds to the square inch, it will be seen +that Boyle's calculation was not far wrong. + +From his numerous experiments upon the air, Boyle was led to +believe that there were many "latent qualities" due to substances +contained in it that science had as yet been unable to fathom, +believing that there is "not a more heterogeneous body in the +world." He believed that contagious diseases were carried by the +air, and suggested that eruptions of the earth, such as those +made by earthquakes, might send up "venomous exhalations" that +produced diseases. He suggested also that the air might play an +important part in some processes of calcination, which, as we +shall see, was proved to be true by Lavoisier late in the +eighteenth century. Boyle's notions of the exact chemical action +in these phenomena were of course vague and indefinite, but he +had observed that some part was played by the air, and he was +right in supposing that the air "may have a great share in +varying the salts obtainable from calcined vitriol."[5] + +Although he was himself such a painstaking observer of facts, he +had the fault of his age of placing too much faith in hear-say +evidence of untrained observers. Thus, from the numerous stories +he heard concerning the growth of metals in previously exhausted +mines, he believed that the air was responsible for producing +this growth--in which he undoubtedly believed. The story of a +tin-miner that, in his own time, after a lapse of only +twenty-five years, a heap, of earth previously exhausted of its +ore became again even more richly impregnated than before by +lying exposed to the air, seems to have been believed by the +philosopher. + +As Boyle was an alchemist, and undoubtedly believed in the +alchemic theory that metals have "spirits" and various other +qualities that do not exist, it is not surprising that he was +credulous in the matter of beliefs concerning peculiar phenomena +exhibited by them. Furthermore, he undoubtedly fell into the +error common to "specialists," or persons working for long +periods of time on one subject--the error of over-enthusiasm in +his subject. He had discovered so many remarkable qualities in +the air that it is not surprising to find that he attributed to +it many more that he could not demonstrate. + +Boyle's work upon colors, although probably of less importance +than his experiments and deductions upon air, show that he was in +the van as far as the science of his day was concerned. As he +points out, the schools of his time generally taught that "color +is a penetrating quality, reaching to the innermost part of the +substance," and, as an example of this, sealing-wax was cited, +which could be broken into minute bits, each particle retaining +the same color as its fellows or the original mass. To refute +this theory, and to show instances to the contrary, Boyle, among +other things, shows that various colors--blue, red, yellow--may +be produced upon tempered steel, and yet the metal within "a +hair's-breadth of its surface" have none of these colors. +Therefore, he was led to believe that color, in opaque bodies at +least, is superficial. + +"But before we descend to a more particular consideration of our +subject," he says, " 'tis proper to observe that colors may be +regarded either as a quality residing in bodies to modify light +after a particular manner, or else as light itself so modified as +to strike upon the organs of sight, and cause the sensation we +call color; and that this latter is the more proper acceptation +of the word color will appear hereafter. And indeed it is the +light itself, which after a certain manner, either mixed with +shades or other-wise, strikes our eyes and immediately produces +that motion in the organ which gives us the color of an +object."[6] + +In examining smooth and rough surfaces to determine the cause of +their color, he made use of the microscope, and pointed out the +very obvious example of the difference in color of a rough and a +polished piece of the same block of stone. He used some striking +illustrations of the effect of light and the position of the eye +upon colors. "Thus the color of plush or velvet will appear +various if you stroke part of it one way and part another, the +posture of the particular threads in regard to the light, or the +eye, being thereby varied. And 'tis observable that in a field of +ripe corn, blown upon by the wind, there will appear waves of a +color different from that of the rest of the corn, because the +wind, by depressing some of the ears more than others, causes one +to reflect more light from the lateral and strawy parts than +another."[7] His work upon color, however, as upon light, was +entirely overshadowed by the work of his great fellow-countryman +Newton. + +Boyle's work on electricity was a continuation of Gilbert's, to +which he added several new facts. He added several substances to +Gilbert's list of "electrics," experimented on smooth and rough +surfaces in exciting of electricity, and made the important +discovery that amber retained its attractive virtue after the +friction that excited it bad ceased. "For the attrition having +caused an intestine motion in its parts," he says, "the heat +thereby excited ought not to cease as soon as ever the rubbing is +over, but to continue capable of emitting effluvia for some time +afterwards, longer or shorter according to the goodness of the +electric and the degree of the commotion made; all which, joined +together, may sometimes make the effect considerable; and by this +means, on a warm day, I, with a certain body not bigger than a +pea, but very vigorously attractive, moved a steel needle, freely +poised, about three minutes after I had left off rubbing it."[8] + + +MARIOTTE AND VON GUERICKE + +Working contemporaneously with Boyle, and a man whose name is +usually associated with his as the propounder of the law of +density of gases, was Edme Mariotte (died 1684), a native of +Burgundy. Mariotte demonstrated that but for the resistance of +the atmosphere, all bodies, whether light or heavy, dense or +thin, would fall with equal rapidity, and he proved this by the +well-known "guinea-and-feather" experiment. Having exhausted the +air from a long glass tube in which a guinea piece and a feather +had been placed, he showed that in the vacuum thus formed they +fell with equal rapidity as often as the tube was reversed. From +his various experiments as to the pressure of the atmosphere he +deduced the law that the density and elasticity of the atmosphere +are precisely proportional to the compressing force (the law of +Boyle and Mariotte). He also ascertained that air existed in a +state of mechanical mixture with liquids, "existing between their +particles in a state of condensation." He made many other +experiments, especially on the collision of bodies, but his most +important work was upon the atmosphere. + +But meanwhile another contemporary of Boyle and Mariotte was +interesting himself in the study of the atmosphere, and had made +a wonderful invention and a most striking demonstration. This was +Otto von Guericke (1602-1686), Burgomaster of Magdeburg, and +councillor to his "most serene and potent Highness" the elector +of that place. When not engrossed with the duties of public +office, he devoted his time to the study of the sciences, +particularly pneumatics and electricity, both then in their +infancy. The discoveries of Galileo, Pascal, and Torricelli +incited him to solve the problem of the creation of a vacuum--a +desideratum since before the days of Aristotle. His first +experiments were with a wooden pump and a barrel of water, but he +soon found that with such porous material as wood a vacuum could +not be created or maintained. He therefore made use of a globe of +copper, with pump and stop-cock; and with this he was able to +pump out air almost as easily as water. Thus, in 1650, the +air-pump was invented. Continuing his experiments upon vacuums +and atmospheric pressure with his newly discovered pump, he made +some startling discoveries as to the enormous pressure exerted by +the air. + +It was not his intention, however, to demonstrate his newly +acquired knowledge by words or theories alone, nor by mere +laboratory experiments; but he chose instead an open field, to +which were invited Emperor Ferdinand III., and all the princes of +the Diet at Ratisbon. When they were assembled he produced two +hollow brass hemispheres about two feet in diameter, and placing +their exactly fitting surfaces together, proceeded to pump out +the air from their hollow interior, thus causing them to stick +together firmly in a most remarkable way, apparently without +anything holding them. This of itself was strange enough; but now +the worthy burgomaster produced teams of horses, and harnessing +them to either side of the hemispheres, attempted to pull the +adhering brasses apart. Five, ten, fifteen teams--thirty horses, +in all--were attached; but pull and tug as they would they could +not separate the firmly clasped hemispheres. The enormous +pressure of the atmosphere had been most strikingly demonstrated. + +But it is one thing to demonstrate, another to convince; and many +of the good people of Magdeburg shook their heads over this +"devil's contrivance," and predicted that Heaven would punish the +Herr Burgomaster, as indeed it had once by striking his house +with lightning and injuring some of his infernal contrivances. +They predicted his future punishment, but they did not molest +him, for to his fellow-citizens, who talked and laughed, drank +and smoked with him, and knew him for the honest citizen that he +was, he did not seem bewitched at all. And so he lived and worked +and added other facts to science, and his brass hemispheres were +not destroyed by fanatical Inquisitors, but are still preserved +in the royal library at Berlin. + +In his experiments with his air-pump he discovered many things +regarding the action of gases, among others, that animals cannot +live in a vacuum. He invented the anemoscope and the air-balance, +and being thus enabled to weight the air and note the changes +that preceded storms and calms, he was able still further to +dumfound his wondering fellow-Magde-burgers by more or less +accurate predictions about the weather. + +Von Guericke did not accept Gilbert's theory that the earth was a +great magnet, but in his experiments along lines similar to those +pursued by Gilbert, he not only invented the first electrical +machine, but discovered electrical attraction and repulsion. The +electrical machine which he invented consisted of a sphere of +sulphur mounted on an iron axis to imitate the rotation of the +earth, and which, when rubbed, manifested electrical reactions. +When this globe was revolved and stroked with the dry hand it was +found that it attached to it "all sorts of little fragments, like +leaves of gold, silver, paper, etc." "Thus this globe," he says, +"when brought rather near drops of water causes them to swell and +puff up. It likewise attracts air, smoke, etc."[9] Before the +time of Guericke's demonstrations, Cabaeus had noted that chaff +leaped back from an "electric," but he did not interpret the +phenomenon as electrical repulsion. Von Guericke, however, +recognized it as such, and refers to it as what he calls +"expulsive virtue." "Even expulsive virtue is seen in this +globe," he says, "for it not only attracts, but also REPELS again +from itself little bodies of this sort, nor does it receive them +until they have touched something else." It will be observed from +this that he was very close to discovering the discharge of the +electrification of attracted bodies by contact with some other +object, after which they are reattracted by the electric. + +He performed a most interesting experiment with his sulphur globe +and a feather, and in doing so came near anticipating Benjamin +Franklin in his discovery of the effects of pointed conductors in +drawing off the discharge. Having revolved and stroked his globe +until it repelled a bit of down, he removed the globe from its +rack and advancing it towards the now repellent down, drove it +before him about the room. In this chase he observed that the +down preferred to alight against "the points of any object +whatsoever." He noticed that should the down chance to be driven +within a few inches of a lighted candle, its attitude towards the +globe suddenly changed, and instead of running away from it, it +now "flew to it for protection" --the charge on the down having +been dissipated by the hot air. He also noted that if one face of +a feather had been first attracted and then repelled by the +sulphur ball, that the surface so affected was always turned +towards the globe; so that if the positions of the two were +reversed, the sides of the feather reversed also. + +Still another important discovery, that of electrical conduction, +was made by Von Guericke. Until his discovery no one had observed +the transference of electricity from one body to another, +although Gilbert had some time before noted that a rod rendered +magnetic at one end became so at the other. Von Guericke's +experiments were made upon a linen thread with his sulphur globe, +which, he says, "having been previously excited by rubbing, can +exercise likewise its virtue through a linen thread an ell or +more long, and there attract something." But this discovery, and +his equally important one that the sulphur ball becomes luminous +when rubbed, were practically forgotten until again brought to +notice by the discoveries of Francis Hauksbee and Stephen Gray +early in the eighteenth century. From this we may gather that Von +Guericke himself did not realize the import of his discoveries, +for otherwise he would certainly have carried his investigations +still further. But as it was he turned his attention to other +fields of research. + + +ROBERT HOOKE + +A slender, crooked, shrivelled-limbed, cantankerous little man, +with dishevelled hair and haggard countenance, bad-tempered and +irritable, penurious and dishonest, at least in his claims for +priority in discoveries--this is the picture usually drawn, alike +by friends and enemies, of Robert Hooke (1635-1703), a man with +an almost unparalleled genius for scientific discoveries in +almost all branches of science. History gives few examples so +striking of a man whose really great achievements in science +would alone have made his name immortal, and yet who had the +pusillanimous spirit of a charlatan--an almost insane mania, as +it seems--for claiming the credit of discoveries made by others. +This attitude of mind can hardly be explained except as a mania: +it is certainly more charitable so to regard it. For his own +discoveries and inventions were so numerous that a few more or +less would hardly have added to his fame, as his reputation as a +philosopher was well established. Admiration for his ability and +his philosophical knowledge must always be marred by the +recollection of his arrogant claims to the discoveries of other +philosophers. + +It seems pretty definitely determined that Hooke should be +credited with the invention of the balance-spring for regulating +watches; but for a long time a heated controversy was waged +between Hooke and Huygens as to who was the real inventor. It +appears that Hooke conceived the idea of the balance-spring, +while to Huygens belongs the credit of having adapted the COILED +spring in a working model. He thus made practical Hooke's +conception, which is without value except as applied by the +coiled spring; but, nevertheless, the inventor, as well as the +perfector, should receive credit. In this controversy, unlike +many others, the blame cannot be laid at Hooke's door. + +Hooke was the first curator of the Royal Society, and when +anything was to be investigated, usually invented the mechanical +devices for doing so. Astronomical apparatus, instruments for +measuring specific weights, clocks and chronometers, methods of +measuring the velocity of falling bodies, freezing and boiling +points, strength of gunpowder, magnetic instruments--in short, +all kinds of ingenious mechanical devices in all branches of +science and mechanics. It was he who made the famous air-pump of +Robert Boyle, based on Boyle's plans. Incidentally, Hooke claimed +to be the inventor of the first air-pump himself, although this +claim is now entirely discredited. + +Within a period of two years he devised no less than thirty +different methods of flying, all of which, of course, came to +nothing, but go to show the fertile imagination of the man, and +his tireless energy. He experimented with electricity and made +some novel suggestions upon the difference between the electric +spark and the glow, although on the whole his contributions in +this field are unimportant. He also first pointed out that the +motions of the heavenly bodies must be looked upon as a +mechanical problem, and was almost within grasping distance of +the exact theory of gravitation, himself originating the idea of +making use of the pendulum in measuring gravity. Likewise, he +first proposed the wave theory of light; although it was Huygens +who established it on its present foundation. + +Hooke published, among other things, a book of plates and +descriptions of his Microscopical Observations, which gives an +idea of the advance that had already been made in microscopy in +his time. Two of these plates are given here, which, even in this +age of microscopy, are both interesting and instructive. These +plates are made from prints of Hooke's original copper plates, +and show that excellent lenses were made even at that time. They +illustrate, also, how much might have been accomplished in the +field of medicine if more attention had been given to microscopy +by physicians. Even a century later, had physicians made better +use of their microscopes, they could hardly have overlooked such +an easily found parasite as the itch mite, which is quite as +easily detected as the cheese mite, pictured in Hooke's book. + +In justice to Hooke, and in extenuation of his otherwise +inexcusable peculiarities of mind, it should be remembered that +for many years he suffered from a painful and wasting disease. +This may have affected his mental equilibrium, without +appreciably affecting his ingenuity. In his own time this +condition would hardly have been considered a disease; but +to-day, with our advanced ideas as to mental diseases, we should +be more inclined to ascribe his unfortunate attitude of mind to a +pathological condition, rather than to any manifestation of +normal mentality. From this point of view his mental deformity +seems not unlike that of Cavendish's, later, except that in the +case of Cavendish it manifested itself as an abnormal +sensitiveness instead of an abnormal irritability. + + +CHRISTIAN HUYGENS + +If for nothing else, the world is indebted to the man who +invented the pendulum clock, Christian Huygens (1629-1695), of +the Hague, inventor, mathematician, mechanician, astronomer, and +physicist. Huygens was the descendant of a noble and +distinguished family, his father, Sir Constantine Huygens, being +a well-known poet and diplomatist. Early in life young Huygens +began his career in the legal profession, completing his +education in the juridical school at Breda; but his taste for +mathematics soon led him to neglect his legal studies, and his +aptitude for scientific researches was so marked that Descartes +predicted great things of him even while he was a mere tyro in +the field of scientific investigation. + +One of his first endeavors in science was to attempt an +improvement of the telescope. Reflecting upon the process of +making lenses then in vogue, young Huygens and his brother +Constantine attempted a new method of grinding and polishing, +whereby they overcame a great deal of the spherical and chromatic +aberration. With this new telescope a much clearer field of +vision was obtained, so much so that Huygens was able to detect, +among other things, a hitherto unknown satellite of Saturn. It +was these astronomical researches that led him to apply the +pendulum to regulate the movements of clocks. The need for some +more exact method of measuring time in his observations of the +stars was keenly felt by the young astronomer, and after several +experiments along different lines, Huygens hit upon the use of a +swinging weight; and in 1656 made his invention of the pendulum +clock. The year following, his clock was presented to the +states-general. Accuracy as to time is absolutely essential in +astronomy, but until the invention of Huygens's clock there was +no precise, nor even approximately precise, means of measuring +short intervals. + +Huygens was one of the first to adapt the micrometer to the +telescope--a mechanical device on which all the nice +determination of minute distances depends. He also took up the +controversy against Hooke as to the superiority of telescopic +over plain sights to quadrants, Hooke contending in favor of the +plain. In this controversy, the subject of which attracted wide +attention, Huygens was completely victorious; and Hooke, being +unable to refute Huygens's arguments, exhibited such irritability +that he increased his already general unpopularity. All of the +arguments for and against the telescope sight are too numerous to +be given here. In contending in its favor Huygens pointed out +that the unaided eye is unable to appreciate an angular space in +the sky less than about thirty seconds. Even in the best quadrant +with a plain sight, therefore, the altitude must be uncertain by +that quantity. If in place of the plain sight a telescope is +substituted, even if it magnify only thirty times, it will enable +the observer to fix the position to one second, with +progressively increased accuracy as the magnifying power of the +telescope is increased. This was only one of the many telling +arguments advanced by Huygens. + +In the field of optics, also, Huygens has added considerably to +science, and his work, Dioptrics, is said to have been a favorite +book with Newton. During the later part of his life, however, +Huygens again devoted himself to inventing and constructing +telescopes, grinding the lenses, and devising, if not actually +making, the frame for holding them. These telescopes were of +enormous lengths, three of his object-glasses, now in possession +of the Royal Society, being of 123, 180, and 210 feet focal +length respectively. Such instruments, if constructed in the +ordinary form of the long tube, were very unmanageable, and to +obviate this Huygens adopted the plan of dispensing with the tube +altogether, mounting his lenses on long poles manipulated by +machinery. Even these were unwieldy enough, but the difficulties +of manipulation were fully compensated by the results obtained. + +It had been discovered, among other things, that in oblique +refraction light is separated into colors. Therefore, any small +portion of the convex lens of the telescope, being a prism, the +rays proceed to the focus, separated into prismatic colors, which +make the image thus formed edged with a fringe of color and +indistinct. But, fortunately for the early telescope makers, the +degree of this aberration is independent of the focal length of +the lens; so that, by increasing this focal length and using the +appropriate eye-piece, the image can be greatly magnified, while +the fringe of colors remains about the same as when a less +powerful lens is used. Hence the advantage of Huygens's long +telescope. He did not confine his efforts to simply lengthening +the focal length of his telescopes, however, but also added to +their efficiency by inventing an almost perfect achromatic +eye-piece. + +In 1663 he was elected a fellow of the Royal Society of London, +and in 1669 he gave to that body a concise statement of the laws +governing the collision of elastic bodies. Although the same +views had been given by Wallis and Wren a few weeks earlier, +there is no doubt that Huygens's views were reached +independently; and it is probable that he had arrived at his +conclusions several years before. In the Philosophical +Transactions for 1669 it is recorded that the society, being +interested in the laws of the principles of motion, a request was +made that M. Huygens, Dr. Wallis, and Sir Christopher Wren submit +their views on the subject. Wallis submitted his paper first, +November 15, 1668. A month later, December 17th, Wren imparted to +the society his laws as to the nature of the collision of bodies. +And a few days later, January 5, 1669, Huygens sent in his "Rules +Concerning the Motion of Bodies after Mutual Impulse." Although +Huygens's report was received last, he was anticipated by such a +brief space of time, and his views are so clearly stated--on the +whole rather more so than those of the other two--that we give +them in part here: + + +"1. If a hard body should strike against a body equally hard at +rest, after contact the former will rest and the latter acquire a +velocity equal to that of the moving body. + +"2. But if that other equal body be likewise in motion, and +moving in the same direction, after contact they will move with +reciprocal velocities. + +"3. A body, however great, is moved by a body however small +impelled with any velocity whatsoever. + +"5. The quantity of motion of two bodies may be either increased +or diminished by their shock; but the same quantity towards the +same part remains, after subtracting the quantity of the contrary +motion. + +"6. The sum of the products arising from multiplying the mass of +any hard body into the squares of its velocity is the same both +before and after the stroke. + +"7. A hard body at rest will receive a greater quantity of motion +from another hard body, either greater or less than itself, by +the interposition of any third body of a mean quantity, than if +it was immediately struck by the body itself; and if the +interposing body be a mean proportional between the other two, +its action upon the quiescent body will be the greatest of +all."[10] + + +This was only one of several interesting and important +communications sent to the Royal Society during his lifetime. One +of these was a report on what he calls "Pneumatical Experiments." +"Upon including in a vacuum an insect resembling a beetle, but +somewhat larger," he says, "when it seemed to be dead, the air +was readmitted, and soon after it revived; putting it again in +the vacuum, and leaving it for an hour, after which the air was +readmitted, it was observed that the insect required a longer +time to recover; including it the third time for two days, after +which the air was admitted, it was ten hours before it began to +stir; but, putting it in a fourth time, for eight days, it never +afterwards recovered.... Several birds, rats, mice, rabbits, and +cats were killed in a vacuum, but if the air was admitted before +the engine was quite exhausted some of them would recover; yet +none revived that had been in a perfect vacuum.... Upon putting +the weight of eighteen grains of powder with a gauge into a +receiver that held several pounds of water, and firing the +powder, it raised the mercury an inch and a half; from which it +appears that there is one-fifth of air in gunpowder, upon the +supposition that air is about one thousand times lighter than +water; for in this experiment the mercury rose to the eighteenth +part of the height at which the air commonly sustains it, and +consequently the weight of eighteen grains of powder yielded air +enough to fill the eighteenth part of a receiver that contained +seven pounds of water; now this eighteenth part contains +forty-nine drachms of water; wherefore the air, that takes up an +equal space, being a thousand times lighter, weighs +one-thousandth part of forty-nine drachms, which is more than +three grains and a half; it follows, therefore, that the weight +of eighteen grains of powder contains more than three and a half +of air, which is about one-fifth of eighteen grains...." + +From 1665 to 1681, accepting the tempting offer made him through +Colbert, by Louis XIV., Huygens pursued his studies at the +Bibliotheque du Roi as a resident of France. Here he published +his Horologium Oscillatorium, dedicated to the king, containing, +among other things, his solution of the problem of the "centre of +oscillation." This in itself was an important step in the history +of mechanics. Assuming as true that the centre of gravity of any +number of interdependent bodies cannot rise higher than the point +from which it falls, he reached correct conclusions as to the +general principle of the conservation of vis viva, although he +did not actually prove his conclusions. This was the first +attempt to deal with the dynamics of a system. In this work, +also, was the true determination of the relation between the +length of a pendulum and the time of its oscillation. + +In 1681 he returned to Holland, influenced, it is believed, by +the attitude that was being taken in France against his religion. +Here he continued his investigations, built his immense +telescopes, and, among other things, discovered "polarization," +which is recorded in Traite de la Lumiere, published at Leyden in +1690. Five years later he died, bequeathing his manuscripts to +the University of Leyden. It is interesting to note that he never +accepted Newton's theory of gravitation as a universal property +of matter. + + + +XI. NEWTON AND THE COMPOSITION OF LIGHT + +Galileo, that giant in physical science of the early seventeenth +century, died in 1642. On Christmas day of the same year there +was born in England another intellectual giant who was destined +to carry forward the work of Copernicus, Kepler, and Galileo to a +marvellous consummation through the discovery of the great +unifying law in accordance with which the planetary motions are +performed. We refer, of course, to the greatest of English +physical scientists, Isaac Newton, the Shakespeare of the +scientific world. Born thus before the middle of the seventeenth +century, Newton lived beyond the first quarter of the eighteenth +(1727). For the last forty years of that period his was the +dominating scientific personality of the world. With full +propriety that time has been spoken of as the "Age of Newton." + +Yet the man who was to achieve such distinction gave no early +premonition of future greatness. He was a sickly child from +birth, and a boy of little seeming promise. He was an indifferent +student, yet, on the other hand, he cared little for the common +amusements of boyhood. He early exhibited, however, a taste for +mechanical contrivances, and spent much time in devising +windmills, water-clocks, sun-dials, and kites. While other boys +were interested only in having kites that would fly, Newton--at +least so the stories of a later time would have us +understand--cared more for the investigation of the seeming +principles involved, or for testing the best methods of attaching +the strings, or the best materials to be used in construction. + +Meanwhile the future philosopher was acquiring a taste for +reading and study, delving into old volumes whenever he found an +opportunity. These habits convinced his relatives that it was +useless to attempt to make a farmer of the youth, as had been +their intention. He was therefore sent back to school, and in the +summer of 1661 he matriculated at Trinity College, Cambridge. +Even at college Newton seems to have shown no unusual mental +capacity, and in 1664, when examined for a scholarship by Dr. +Barrow, that gentleman is said to have formed a poor opinion of +the applicant. It is said that the knowledge of the estimate +placed upon his abilities by his instructor piqued Newton, and +led him to take up in earnest the mathematical studies in which +he afterwards attained such distinction. The study of Euclid and +Descartes's "Geometry" roused in him a latent interest in +mathematics, and from that time forward his investigations were +carried on with enthusiasm. In 1667 he was elected Fellow of +Trinity College, taking the degree of M.A. the following spring. + +It will thus appear that Newton's boyhood and early manhood were +passed during that troublous time in British political annals +which saw the overthrow of Charles I., the autocracy of Cromwell, +and the eventual restoration of the Stuarts. His maturer years +witnessed the overthrow of the last Stuart and the reign of the +Dutchman, William of Orange. In his old age he saw the first of +the Hanoverians mount the throne of England. Within a decade of +his death such scientific path-finders as Cavendish, Black, and +Priestley were born--men who lived on to the close of the +eighteenth century. In a full sense, then, the age of Newton +bridges the gap from that early time of scientific awakening +under Kepler and Galileo to the time which we of the twentieth +century think of as essentially modern. + + +THE COMPOSITION OF WHITE LIGHT + +In December, 1672, Newton was elected a Fellow of the Royal +Society, and at this meeting a paper describing his invention of +the refracting telescope was read. A few days later he wrote to +the secretary, making some inquiries as to the weekly meetings of +the society, and intimating that he had an account of an +interesting discovery that he wished to lay before the society. +When this communication was made public, it proved to be an +explanation of the discovery of the composition of white light. +We have seen that the question as to the nature of color had +commanded the attention of such investigators as Huygens, but +that no very satisfactory solution of the question had been +attained. Newton proved by demonstrative experiments that white +light is composed of the blending of the rays of diverse colors, +and that the color that we ascribe to any object is merely due to +the fact that the object in question reflects rays of that color, +absorbing the rest. That white light is really made up of many +colors blended would seem incredible had not the experiments by +which this composition is demonstrated become familiar to every +one. The experiments were absolutely novel when Newton brought +them forward, and his demonstration of the composition of light +was one of the most striking expositions ever brought to the +attention of the Royal Society. It is hardly necessary to add +that, notwithstanding the conclusive character of Newton's work, +his explanations did not for a long time meet with general +acceptance. + +Newton was led to his discovery by some experiments made with an +ordinary glass prism applied to a hole in the shutter of a +darkened room, the refracted rays of the sunlight being received +upon the opposite wall and forming there the familiar spectrum. +"It was a very pleasing diversion," he wrote, "to view the vivid +and intense colors produced thereby; and after a time, applying +myself to consider them very circumspectly, I became surprised to +see them in varying form, which, according to the received laws +of refraction, I expected should have been circular. They were +terminated at the sides with straight lines, but at the ends the +decay of light was so gradual that it was difficult to determine +justly what was their figure, yet they seemed semicircular. + +"Comparing the length of this colored spectrum with its breadth, +I found it almost five times greater; a disproportion so +extravagant that it excited me to a more than ordinary curiosity +of examining from whence it might proceed. I could scarce think +that the various thicknesses of the glass, or the termination +with shadow or darkness, could have any influence on light to +produce such an effect; yet I thought it not amiss, first, to +examine those circumstances, and so tried what would happen by +transmitting light through parts of the glass of divers +thickness, or through holes in the window of divers bigness, or +by setting the prism without so that the light might pass through +it and be refracted before it was transmitted through the hole; +but I found none of those circumstances material. The fashion of +the colors was in all these cases the same. + +"Then I suspected whether by any unevenness of the glass or other +contingent irregularity these colors might be thus dilated. And +to try this I took another prism like the former, and so placed +it that the light, passing through them both, might be refracted +contrary ways, and so by the latter returned into that course +from which the former diverted it. For, by this means, I thought, +the regular effects of the first prism would be destroyed by the +second prism, but the irregular ones more augmented by the +multiplicity of refractions. The event was that the light, which +by the first prism was diffused into an oblong form, was by the +second reduced into an orbicular one with as much regularity as +when it did not all pass through them. So that, whatever was the +cause of that length, 'twas not any contingent irregularity. + +"I then proceeded to examine more critically what might be +effected by the difference of the incidence of rays coming from +divers parts of the sun; and to that end measured the several +lines and angles belonging to the image. Its distance from the +hole or prism was 22 feet; its utmost length 13 1/4 inches; its +breadth 2 5/8; the diameter of the hole 1/4 of an inch; the angle +which the rays, tending towards the middle of the image, made +with those lines, in which they would have proceeded without +refraction, was 44 degrees 56'; and the vertical angle of the +prism, 63 degrees 12'. Also the refractions on both sides of the +prism--that is, of the incident and emergent rays--were, as near +as I could make them, equal, and consequently about 54 degrees +4'; and the rays fell perpendicularly upon the wall. Now, +subducting the diameter of the hole from the length and breadth +of the image, there remains 13 inches the length, and 2 3/8 the +breadth, comprehended by those rays, which, passing through the +centre of the said hole, which that breadth subtended, was about +31', answerable to the sun's diameter; but the angle which its +length subtended was more than five such diameters, namely 2 +degrees 49'. + +"Having made these observations, I first computed from them the +refractive power of the glass, and found it measured by the ratio +of the sines 20 to 31. And then, by that ratio, I computed the +refractions of two rays flowing from opposite parts of the sun's +discus, so as to differ 31' in their obliquity of incidence, and +found that the emergent rays should have comprehended an angle of +31', as they did, before they were incident. + +"But because this computation was founded on the hypothesis of +the proportionality of the sines of incidence and refraction, +which though by my own experience I could not imagine to be so +erroneous as to make that angle but 31', which in reality was 2 +degrees 49', yet my curiosity caused me again to make my prism. +And having placed it at my window, as before, I observed that by +turning it a little about its axis to and fro, so as to vary its +obliquity to the light more than an angle of 4 degrees or 5 +degrees, the colors were not thereby sensibly translated from +their place on the wall, and consequently by that variation of +incidence the quantity of refraction was not sensibly varied. By +this experiment, therefore, as well as by the former computation, +it was evident that the difference of the incidence of rays +flowing from divers parts of the sun could not make them after +decussation diverge at a sensibly greater angle than that at +which they before converged; which being, at most, but about 31' +or 32', there still remained some other cause to be found out, +from whence it could be 2 degrees 49'." + +All this caused Newton to suspect that the rays, after their +trajection through the prism, moved in curved rather than in +straight lines, thus tending to be cast upon the wall at +different places according to the amount of this curve. His +suspicions were increased, also, by happening to recall that a +tennis-ball sometimes describes such a curve when "cut" by a +tennis-racket striking the ball obliquely. + +"For a circular as well as a progressive motion being +communicated to it by the stroke," he says, "its parts on that +side where the motions conspire must press and beat the +contiguous air more violently than on the other, and there excite +a reluctancy and reaction of the air proportionately greater. And +for the same reason, if the rays of light should possibly be +globular bodies, and by their oblique passage out of one medium +into another acquire a circulating motion, they ought to feel the +greater resistance from the ambient ether on that side where the +motions conspire, and thence be continually bowed to the other. +But notwithstanding this plausible ground of suspicion, when I +came to examine it I could observe no such curvity in them. And, +besides (which was enough for my purpose), I observed that the +difference 'twixt the length of the image and diameter of the +hole through which the light was transmitted was proportionable +to their distance. + +"The gradual removal of these suspicions at length led me to the +experimentum crucis, which was this: I took two boards, and, +placing one of them close behind the prism at the window, so that +the light must pass through a small hole, made in it for the +purpose, and fall on the other board, which I placed at about +twelve feet distance, having first made a small hole in it also, +for some of the incident light to pass through. Then I placed +another prism behind this second board, so that the light +trajected through both the boards might pass through that also, +and be again refracted before it arrived at the wall. This done, +I took the first prism in my hands and turned it to and fro +slowly about its axis, so much as to make the several parts of +the image, cast on the second board, successively pass through +the hole in it, that I might observe to what places on the wall +the second prism would refract them. And I saw by the variation +of these places that the light, tending to that end of the image +towards which the refraction of the first prism was made, did in +the second prism suffer a refraction considerably greater than +the light tending to the other end. And so the true cause of the +length of that image was detected to be no other than that LIGHT +consists of RAYS DIFFERENTLY REFRANGIBLE, which, without any +respect to a difference in their incidence, were, according to +their degrees of refrangibility, transmitted towards divers parts +of the wall."[1] + + +THE NATURE OF COLOR + +Having thus proved the composition of light, Newton took up an +exhaustive discussion as to colors, which cannot be entered into +at length here. Some of his remarks on the subject of compound +colors, however, may be stated in part. Newton's views are of +particular interest in this connection, since, as we have already +pointed out, the question as to what constituted color could not +be agreed upon by the philosophers. Some held that color was an +integral part of the substance; others maintained that it was +simply a reflection from the surface; and no scientific +explanation had been generally accepted. Newton concludes his +paper as follows: + +"I might add more instances of this nature, but I shall conclude +with the general one that the colors of all natural bodies have +no other origin than this, that they are variously qualified to +reflect one sort of light in greater plenty than another. And +this I have experimented in a dark room by illuminating those +bodies with uncompounded light of divers colors. For by that +means any body may be made to appear of any color. They have +there no appropriate color, but ever appear of the color of the +light cast upon them, but yet with this difference, that they are +most brisk and vivid in the light of their own daylight color. +Minium appeareth there of any color indifferently with which 'tis +illustrated, but yet most luminous in red; and so Bise appeareth +indifferently of any color with which 'tis illustrated, but yet +most luminous in blue. And therefore Minium reflecteth rays of +any color, but most copiously those indued with red; and +consequently, when illustrated with daylight--that is, with all +sorts of rays promiscuously blended--those qualified with red +shall abound most in the reflected light, and by their prevalence +cause it to appear of that color. And for the same reason, Bise, +reflecting blue most copiously, shall appear blue by the excess +of those rays in its reflected light; and the like of other +bodies. And that this is the entire and adequate cause of their +colors is manifest, because they have no power to change or alter +the colors of any sort of rays incident apart, but put on all +colors indifferently with which they are enlightened."[2] + +This epoch-making paper aroused a storm of opposition. Some of +Newton's opponents criticised his methods, others even doubted +the truth of his experiments. There was one slight mistake in +Newton's belief that all prisms would give a spectrum of exactly +the same length, and it was some time before he corrected this +error. Meanwhile he patiently met and answered the arguments of +his opponents until he began to feel that patience was no longer +a virtue. At one time he even went so far as to declare that, +once he was "free of this business," he would renounce scientific +research forever, at least in a public way. Fortunately for the +world, however, he did not adhere to this determination, but went +on to even greater discoveries--which, it may be added, involved +still greater controversies. + +In commenting on Newton's discovery of the composition of light, +Voltaire said: "Sir Isaac Newton has demonstrated to the eye, by +the bare assistance of a prism, that light is a composition of +colored rays, which, being united, form white color. A single ray +is by him divided into seven, which all fall upon a piece of +linen or a sheet of white paper, in their order one above the +other, and at equal distances. The first is red, the second +orange, the third yellow, the fourth green, the fifth blue, the +sixth indigo, the seventh a violet purple. Each of these rays +transmitted afterwards by a hundred other prisms will never +change the color it bears; in like manner as gold, when +completely purged from its dross, will never change afterwards in +the crucible."[3] + + + +XII. NEWTON AND THE LAW OF GRAVITATION + +We come now to the story of what is by common consent the +greatest of scientific achievements. The law of universal +gravitation is the most far-reaching principle as yet discovered. +It has application equally to the minutest particle of matter and +to the most distant suns in the universe, yet it is amazing in +its very simplicity. As usually phrased, the law is this: That +every particle of matter in the universe attracts every other +particle with a force that varies directly with the mass of the +particles and inversely as the squares of their mutual distance. +Newton did not vault at once to the full expression of this law, +though he had formulated it fully before he gave the results of +his investigations to the world. We have now to follow the steps +by which he reached this culminating achievement. + +At the very beginning we must understand that the idea of +universal gravitation was not absolutely original with Newton. +Away back in the old Greek days, as we have seen, Anaxagoras +conceived and clearly expressed the idea that the force which +holds the heavenly bodies in their orbits may be the same that +operates upon substances at the surface of the earth. With +Anaxagoras this was scarcely more than a guess. After his day the +idea seems not to have been expressed by any one until the +seventeenth century's awakening of science. Then the +consideration of Kepler's Third Law of planetary motion suggested +to many minds perhaps independently the probability that the +force hitherto mentioned merely as centripetal, through the +operation of which the planets are held in their orbits is a +force varying inversely as the square of the distance from the +sun. This idea had come to Robert Hooke, to Wren, and perhaps to +Halley, as well as to Newton; but as yet no one had conceived a +method by which the validity of the suggestion might be tested. +It was claimed later on by Hooke that he had discovered a method +demonstrating the truth of the theory of inverse squares, and +after the full announcement of Newton's discovery a heated +controversy was precipitated in which Hooke put forward his +claims with accustomed acrimony. Hooke, however, never produced +his demonstration, and it may well be doubted whether he had +found a method which did more than vaguely suggest the law which +the observations of Kepler had partially revealed. Newton's great +merit lay not so much in conceiving the law of inverse squares as +in the demonstration of the law. He was led to this demonstration +through considering the orbital motion of the moon. According to +the familiar story, which has become one of the classic myths of +science, Newton was led to take up the problem through observing +the fall of an apple. Voltaire is responsible for the story, +which serves as well as another; its truth or falsity need not in +the least concern us. Suffice it that through pondering on the +familiar fact of terrestrial gravitation, Newton was led to +question whether this force which operates so tangibly here at +the earth's surface may not extend its influence out into the +depths of space, so as to include, for example, the moon. +Obviously some force pulls the moon constantly towards the earth; +otherwise that body would fly off at a tangent and never return. +May not this so-called centripetal force be identical with +terrestrial gravitation? Such was Newton's query. Probably many +another man since Anaxagoras had asked the same question, but +assuredly Newton was the first man to find an answer. + +The thought that suggested itself to Newton's mind was this: If +we make a diagram illustrating the orbital course of the moon for +any given period, say one minute, we shall find that the course +of the moon departs from a straight line during that period by a +measurable distance--that: is to say, the moon has been virtually +pulled towards the earth by an amount that is represented by the +difference between its actual position at the end of the minute +under observation and the position it would occupy had its course +been tangential, as, according to the first law of motion, it +must have been had not some force deflected it towards the earth. +Measuring the deflection in question--which is equivalent to the +so-called versed sine of the arc traversed--we have a basis for +determining the strength of the deflecting force. Newton +constructed such a diagram, and, measuring the amount of the +moon's departure from a tangential rectilinear course in one +minute, determined this to be, by his calculation, thirteen feet. +Obviously, then, the force acting upon the moon is one that would +cause that body to fall towards the earth to the distance of +thirteen feet in the first minute of its fall. Would such be the +force of gravitation acting at the distance of the moon if the +power of gravitation varies inversely as the square of the +distance? That was the tangible form in which the problem +presented itself to Newton. The mathematical solution of the +problem was simple enough. It is based on a comparison of the +moon's distance with the length of the earth's radius. On making +this calculation, Newton found that the pull of gravitation--if +that were really the force that controls the moon--gives that +body a fall of slightly over fifteen feet in the first minute, +instead of thirteen feet. Here was surely a suggestive +approximation, yet, on the other band, the discrepancy seemed to +be too great to warrant him in the supposition that he had found +the true solution. He therefore dismissed the matter from his +mind for the time being, nor did he return to it definitely for +some years. + +{illustration caption = DIAGRAM TO ILLUSTRATE NEWTON'S LAW OF +GRAVITATION (E represents the earth and A the moon. Were the +earth's pull on the moon to cease, the moon's inertia would cause +it to take the tangential course, AB. On the other hand, were the +moon's motion to be stopped for an instant, the moon would fall +directly towards the earth, along the line AD. The moon's actual +orbit, resulting from these component forces, is AC. Let AC +represent the actual flight of the moon in one minute. Then BC, +which is obviously equal to AD, represents the distance which the +moon virtually falls towards the earth in one minute. Actual +computation, based on measurements of the moon's orbit, showed +this distance to be about fifteen feet. Another computation +showed that this is the distance that the moon would fall towards +the earth under the influence of gravity, on the supposition that +the force of gravity decreases inversely with the square of the +distance; the basis of comparison being furnished by falling +bodies at the surface of the earth. Theory and observations thus +coinciding, Newton was justified in declaring that the force that +pulls the moon towards the earth and keeps it in its orbit, is +the familiar force of gravity, and that this varies inversely as +the square of the distance.)} + +It was to appear in due time that Newton's hypothesis was +perfectly valid and that his method of attempted demonstration +was equally so. The difficulty was that the earth's proper +dimensions were not at that time known. A wrong estimate of the +earth's size vitiated all the other calculations involved, since +the measurement of the moon's distance depends upon the +observation of the parallax, which cannot lead to a correct +computation unless the length of the earth's radius is accurately +known. Newton's first calculation was made as early as 1666, and +it was not until 1682 that his attention was called to a new and +apparently accurate measurement of a degree of the earth's +meridian made by the French astronomer Picard. The new +measurement made a degree of the earth's surface 69.10 miles, +instead of sixty miles. + +Learning of this materially altered calculation as to the earth's +size, Newton was led to take up again his problem of the falling +moon. As he proceeded with his computation, it became more and +more certain that this time the result was to harmonize with the +observed facts. As the story goes, he was so completely +overwhelmed with emotion that he was forced to ask a friend to +complete the simple calculation. That story may well be true, +for, simple though the computation was, its result was perhaps +the most wonderful demonstration hitherto achieved in the entire +field of science. Now at last it was known that the force of +gravitation operates at the distance of the moon, and holds that +body in its elliptical orbit, and it required but a slight effort +of the imagination to assume that the force which operates +through such a reach of space extends its influence yet more +widely. That such is really the case was demonstrated presently +through calculations as to the moons of Jupiter and by similar +computations regarding the orbital motions of the various +planets. All results harmonizing, Newton was justified in +reaching the conclusion that gravitation is a universal property +of matter. It remained, as we shall see, for nineteenth-century +scientists to prove that the same force actually operates upon +the stars, though it should be added that this demonstration +merely fortified a belief that had already found full acceptance. + +Having thus epitomized Newton's discovery, we must now take up +the steps of his progress somewhat in detail, and state his +theories and their demonstration in his own words. Proposition +IV., theorem 4, of his Principia is as follows: + +"That the moon gravitates towards the earth and by the force of +gravity is continually drawn off from a rectilinear motion and +retained in its orbit. + +"The mean distance of the moon from the earth, in the syzygies in +semi-diameters of the earth, is, according to Ptolemy and most +astronomers, 59; according to Vendelin and Huygens, 60; to +Copernicus, 60 1/3; to Street, 60 2/3; and to Tycho, 56 1/2. But +Tycho, and all that follow his tables of refractions, making the +refractions of the sun and moon (altogether against the nature of +light) to exceed the refractions of the fixed stars, and that by +four or five minutes NEAR THE HORIZON, did thereby increase the +moon's HORIZONTAL parallax by a like number of minutes, that is, +by a twelfth or fifteenth part of the whole parallax. Correct +this error and the distance will become about 60 1/2 +semi-diameters of the earth, near to what others have assigned. +Let us assume the mean distance of 60 diameters in the syzygies; +and suppose one revolution of the moon, in respect to the fixed +stars, to be completed in 27d. 7h. 43', as astronomers have +determined; and the circumference of the earth to amount to +123,249,600 Paris feet, as the French have found by mensuration. +And now, if we imagine the moon, deprived of all motion, to be +let go, so as to descend towards the earth with the impulse of +all that force by which (by Cor. Prop. iii.) it is retained in +its orb, it will in the space of one minute of time describe in +its fall 15 1/12 Paris feet. For the versed sine of that arc +which the moon, in the space of one minute of time, would by its +mean motion describe at the distance of sixty semi-diameters of +the earth, is nearly 15 1/12 Paris feet, or more accurately 15 +feet, 1 inch, 1 line 4/9. Wherefore, since that force, in +approaching the earth, increases in the reciprocal-duplicate +proportion of the distance, and upon that account, at the surface +of the earth, is 60 x 60 times greater than at the moon, a body +in our regions, falling with that force, ought in the space of +one minute of time to describe 60 x 60 x 15 1/12 Paris feet; and +in the space of one second of time, to describe 15 1/12 of those +feet, or more accurately, 15 feet, 1 inch, 1 line 4/9. And with +this very force we actually find that bodies here upon earth do +really descend; for a pendulum oscillating seconds in the +latitude of Paris will be 3 Paris feet, and 8 lines 1/2 in +length, as Mr. Huygens has observed. And the space which a heavy +body describes by falling in one second of time is to half the +length of the pendulum in the duplicate ratio of the +circumference of a circle to its diameter (as Mr. Huygens has +also shown), and is therefore 15 Paris feet, 1 inch, 1 line 4/9. +And therefore the force by which the moon is retained in its +orbit is that very same force which we commonly call gravity; +for, were gravity another force different from that, then bodies +descending to the earth with the joint impulse of both forces +would fall with a double velocity, and in the space of one second +of time would describe 30 1/6 Paris feet; altogether against +experience."[1] + +All this is beautifully clear, and its validity has never in +recent generations been called in question; yet it should be +explained that the argument does not amount to an actually +indisputable demonstration. It is at least possible that the +coincidence between the observed and computed motion of the moon +may be a mere coincidence and nothing more. This probability, +however, is so remote that Newton is fully justified in +disregarding it, and, as has been said, all subsequent +generations have accepted the computation as demonstrative. + +Let us produce now Newton's further computations as to the other +planetary bodies, passing on to his final conclusion that gravity +is a universal force. + + "PROPOSITION V., THEOREM V. + +"That the circumjovial planets gravitate towards Jupiter; the +circumsaturnal towards Saturn; the circumsolar towards the sun; +and by the forces of their gravity are drawn off from rectilinear +motions, and retained in curvilinear orbits. + + +"For the revolutions of the circumjovial planets about Jupiter, +of the circumsaturnal about Saturn, and of Mercury and Venus and +the other circumsolar planets about the sun, are appearances of +the same sort with the revolution of the moon about the earth; +and therefore, by Rule ii., must be owing to the same sort of +causes; especially since it has been demonstrated that the forces +upon which those revolutions depend tend to the centres of +Jupiter, of Saturn, and of the sun; and that those forces, in +receding from Jupiter, from Saturn, and from the sun, decrease in +the same proportion, and according to the same law, as the force +of gravity does in receding from the earth. + +"COR. 1.--There is, therefore, a power of gravity tending to all +the planets; for doubtless Venus, Mercury, and the rest are +bodies of the same sort with Jupiter and Saturn. And since all +attraction (by Law iii.) is mutual, Jupiter will therefore +gravitate towards all his own satellites, Saturn towards his, the +earth towards the moon, and the sun towards all the primary +planets. + +"COR. 2.--The force of gravity which tends to any one planet is +reciprocally as the square of the distance of places from the +planet's centre. + +"COR. 3.--All the planets do mutually gravitate towards one +another, by Cor. 1 and 2, and hence it is that Jupiter and +Saturn, when near their conjunction, by their mutual attractions +sensibly disturb each other's motions. So the sun disturbs the +motions of the moon; and both sun and moon disturb our sea, as we +shall hereafter explain. + + "SCHOLIUM + +"The force which retains the celestial bodies in their orbits has +been hitherto called centripetal force; but it being now made +plain that it can be no other than a gravitating force, we shall +hereafter call it gravity. For the cause of the centripetal force +which retains the moon in its orbit will extend itself to all the +planets by Rules i., ii., and iii. + + "PROPOSITION VI., THEOREM VI. + +"That all bodies gravitate towards every planet; and that the +weights of the bodies towards any the same planet, at equal +distances from the centre of the planet, are proportional to the +quantities of matter which they severally contain. + + +"It has been now a long time observed by others that all sorts of +heavy bodies (allowance being made for the inability of +retardation which they suffer from a small power of resistance in +the air) descend to the earth FROM EQUAL HEIGHTS in equal times; +and that equality of times we may distinguish to a great accuracy +by help of pendulums. I tried the thing in gold, silver, lead, +glass, sand, common salt, wood, water, and wheat. I provided two +wooden boxes, round and equal: I filled the one with wood, and +suspended an equal weight of gold (as exactly as I could) in the +centre of oscillation of the other. The boxes hanging by eleven +feet, made a couple of pendulums exactly equal in weight and +figure, and equally receiving the resistance of the air. And, +placing the one by the other, I observed them to play together +forward and backward, for a long time, with equal vibrations. And +therefore the quantity of matter in gold was to the quantity of +matter in the wood as the action of the motive force (or vis +motrix) upon all the gold to the action of the same upon all the +wood--that is, as the weight of the one to the weight of the +other: and the like happened in the other bodies. By these +experiments, in bodies of the same weight, I could manifestly +have discovered a difference of matter less than the thousandth +part of the whole, had any such been. But, without all doubt, the +nature of gravity towards the planets is the same as towards the +earth. For, should we imagine our terrestrial bodies removed to +the orb of the moon, and there, together with the moon, deprived +of all motion, to be let go, so as to fall together towards the +earth, it is certain, from what we have demonstrated before, +that, in equal times, they would describe equal spaces with the +moon, and of consequence are to the moon, in quantity and matter, +as their weights to its weight. + +"Moreover, since the satellites of Jupiter perform their +revolutions in times which observe the sesquiplicate proportion +of their distances from Jupiter's centre, their accelerative +gravities towards Jupiter will be reciprocally as the square of +their distances from Jupiter's centre--that is, equal, at equal +distances. And, therefore, these satellites, if supposed to fall +TOWARDS JUPITER from equal heights, would describe equal spaces +in equal times, in like manner as heavy bodies do on our earth. +And, by the same argument, if the circumsolar planets were +supposed to be let fall at equal distances from the sun, they +would, in their descent towards the sun, describe equal spaces in +equal times. But forces which equally accelerate unequal bodies +must be as those bodies--that is to say, the weights of the +planets (TOWARDS THE SUN must be as their quantities of matter. +Further, that the weights of Jupiter and his satellites towards +the sun are proportional to the several quantities of their +matter, appears from the exceedingly regular motions of the +satellites. For if some of these bodies were more strongly +attracted to the sun in proportion to their quantity of matter +than others, the motions of the satellites would be disturbed by +that inequality of attraction. If at equal distances from the sun +any satellite, in proportion to the quantity of its matter, did +gravitate towards the sun with a force greater than Jupiter in +proportion to his, according to any given proportion, suppose d +to e; then the distance between the centres of the sun and of the +satellite's orbit would be always greater than the distance +between the centres of the sun and of Jupiter nearly in the +subduplicate of that proportion: as by some computations I have +found. And if the satellite did gravitate towards the sun with a +force, lesser in the proportion of e to d, the distance of the +centre of the satellite's orb from the sun would be less than the +distance of the centre of Jupiter from the sun in the +subduplicate of the same proportion. Therefore, if at equal +distances from the sun, the accelerative gravity of any satellite +towards the sun were greater or less than the accelerative +gravity of Jupiter towards the sun by one-one-thousandth part of +the whole gravity, the distance of the centre of the satellite's +orbit from the sun would be greater or less than the distance of +Jupiter from the sun by one one-two-thousandth part of the whole +distance--that is, by a fifth part of the distance of the utmost +satellite from the centre of Jupiter; an eccentricity of the +orbit which would be very sensible. But the orbits of the +satellites are concentric to Jupiter, and therefore the +accelerative gravities of Jupiter and of all its satellites +towards the sun, at equal distances from the sun, are as their +several quantities of matter; and the weights of the moon and of +the earth towards the sun are either none, or accurately +proportional to the masses of matter which they contain. + +"COR. 5.--The power of gravity is of a different nature from the +power of magnetism; for the magnetic attraction is not as the +matter attracted. Some bodies are attracted more by the magnet; +others less; most bodies not at all. The power of magnetism in +one and the same body may be increased and diminished; and is +sometimes far stronger, for the quantity of matter, than the +power of gravity; and in receding from the magnet decreases not +in the duplicate, but almost in the triplicate proportion of the +distance, as nearly as I could judge from some rude observations. + + + "PROPOSITION VII., THEOREM VII. + +"That there is a power of gravity tending to all bodies, +proportional to the several quantities of matter which they +contain. + + +That all the planets mutually gravitate one towards another we +have proved before; as well as that the force of gravity towards +every one of them considered apart, is reciprocally as the square +of the distance of places from the centre of the planet. And +thence it follows, that the gravity tending towards all the +planets is proportional to the matter which they contain. + +"Moreover, since all the parts of any planet A gravitates towards +any other planet B; and the gravity of every part is to the +gravity of the whole as the matter of the part is to the matter +of the whole; and to every action corresponds a reaction; +therefore the planet B will, on the other hand, gravitate towards +all the parts of planet A, and its gravity towards any one part +will be to the gravity towards the whole as the matter of the +part to the matter of the whole. Q.E.D. + + +"HENCE IT WOULD APPEAR THAT the force of the whole must arise +from the force of the component parts." + + +Newton closes this remarkable Book iii. with the following words: + +"Hitherto we have explained the phenomena of the heavens and of +our sea by the power of gravity, but have not yet assigned the +cause of this power. This is certain, that it must proceed from a +cause that penetrates to the very centre of the sun and planets, +without suffering the least diminution of its force; that +operates not according to the quantity of the surfaces of the +particles upon which it acts (as mechanical causes used to do), +but according to the quantity of solid matter which they contain, +and propagates its virtue on all sides to immense distances, +decreasing always in the duplicate proportions of the distances. +Gravitation towards the sun is made up out of the gravitations +towards the several particles of which the body of the sun is +composed; and in receding from the sun decreases accurately in +the duplicate proportion of the distances as far as the orb of +Saturn, as evidently appears from the quiescence of the aphelions +of the planets; nay, and even to the remotest aphelions of the +comets, if those aphelions are also quiescent. But hitherto I +have not been able to discover the cause of those properties of +gravity from phenomena, and I frame no hypothesis; for whatever +is not deduced from the phenomena is to be called an hypothesis; +and hypotheses, whether metaphysical or physical, whether of +occult qualities or mechanical, have no place in experimental +philosophy. . . . And to us it is enough that gravity does really +exist, and act according to the laws which we have explained, and +abundantly serves to account for all the motions of the celestial +bodies and of our sea."[2] + + +The very magnitude of the importance of the theory of universal +gravitation made its general acceptance a matter of considerable +time after the actual discovery. This opposition had of course +been foreseen by Newton, and, much as be dreaded controversy, he +was prepared to face it and combat it to the bitter end. He knew +that his theory was right; it remained for him to convince the +world of its truth. He knew that some of his contemporary +philosophers would accept it at once; others would at first +doubt, question, and dispute, but finally accept; while still +others would doubt and dispute until the end of their days. This +had been the history of other great discoveries; and this will +probably be the history of most great discoveries for all time. +But in this case the discoverer lived to see his theory accepted +by practically all the great minds of his time. + +Delambre is authority for the following estimate of Newton by +Lagrange. "The celebrated Lagrange," he says, "who frequently +asserted that Newton was the greatest genius that ever existed, +used to add--'and the most fortunate, for we cannot find MORE +THAN ONCE a system of the world to establish.' " With pardonable +exaggeration the admiring followers of the great generalizer +pronounced this epitaph: + + "Nature and Nature's laws lay hid in night; + God said `Let Newton be!' and all was light." + + + +XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON + +During the Newtonian epoch there were numerous important +inventions of scientific instruments, as well as many +improvements made upon the older ones. Some of these discoveries +have been referred to briefly in other places, but their +importance in promoting scientific investigation warrants a +fuller treatment of some of the more significant. + +Many of the errors that had arisen in various scientific +calculations before the seventeenth century may be ascribed to +the crudeness and inaccuracy in the construction of most +scientific instruments. Scientists had not as yet learned that an +approach to absolute accuracy was necessary in every +investigation in the field of science, and that such accuracy +must be extended to the construction of the instruments used in +these investigations and observations. In astronomy it is obvious +that instruments of delicate exactness are most essential; yet +Tycho Brahe, who lived in the sixteenth century, is credited with +being the first astronomer whose instruments show extreme care in +construction. + +It seems practically settled that the first telescope was +invented in Holland in 1608; but three men, Hans Lippershey, +James Metius, and Zacharias Jansen, have been given the credit of +the invention at different times. It would seem from certain +papers, now in the library of the University of Leyden, and +included in Huygens's papers, that Lippershey was probably the +first to invent a telescope and to describe his invention. The +story is told that Lippershey, who was a spectacle-maker, +stumbled by accident upon the discovery that when two lenses are +held at a certain distance apart, objects at a distance appear +nearer and larger. Having made this discovery, be fitted two +lenses with a tube so as to maintain them at the proper distance, +and thus constructed the first telescope. + +It was Galileo, however, as referred to in a preceding chapter, +who first constructed a telescope based on his knowledge of the +laws of refraction. In 1609, having heard that an instrument had +been invented, consisting of two lenses fixed in a tube, whereby +objects were made to appear larger and nearer, he set about +constructing such an instrument that should follow out the known +effects of refraction. His first telescope, made of two lenses +fixed in a lead pipe, was soon followed by others of improved +types, Galileo devoting much time and labor to perfecting lenses +and correcting errors. In fact, his work in developing the +instrument was so important that the telescope came gradually to +be known as the "Galilean telescope." + +In the construction of his telescope Galileo made use of a convex +and a concave lens; but shortly after this Kepler invented an +instrument in which both the lenses used were convex. This +telescope gave a much larger field of view than the Galilean +telescope, but did not give as clear an image, and in consequence +did not come into general use until the middle of the seventeenth +century. The first powerful telescope of this type was made by +Huygens and his brother. It was of twelve feet focal length, and +enabled Huygens to discover a new satellite of Saturn, and to +determine also the true explanation of Saturn's ring. + +It was Huygens, together with Malvasia and Auzout, who first +applied the micrometer to the telescope, although the inventor of +the first micrometer was William Gascoigne, of Yorkshire, about +1636. The micrometer as used in telescopes enables the observer +to measure accurately small angular distances. Before the +invention of the telescope such measurements were limited to the +angle that could be distinguished by the naked eye, and were, of +course, only approximately accurate. Even very careful observers, +such as Tycho Brahe, were able to obtain only fairly accurate +results. But by applying Gascoigne's invention to the telescope +almost absolute accuracy became at once possible. The principle +of Gascoigne's micrometer was that of two pointers lying +parallel, and in this position pointing to zero. These were +arranged so that the turning of a single screw separated or +approximated them at will, and the angle thus formed could be +determined with absolute accuracy. + +Huygens's micrometer was a slip of metal of variable breadth +inserted at the focus of the telescope. By observing at what +point this exactly covered an object under examination, and +knowing the focal length of the telescope and the width of the +metal, he could then deduce the apparent angular breadth of the +object. Huygens discovered also that an object placed in the +common focus of the two lenses of a Kepler telescope appears +distinct and clearly defined. The micrometers of Malvasia, and +later of Auzout and Picard, are the development of this +discovery. Malvasia's micrometer, which he described in 1662, +consisted of fine silver wires placed at right-angles at the +focus of his telescope. + +As telescopes increased in power, however, it was found that even +the finest wire, or silk filaments, were much too thick for +astronomical observations, as they obliterated the image, and so, +finally, the spider-web came into use and is still used in +micrometers and other similar instruments. Before that time, +however, the fine crossed wires had revolutionized astronomical +observations. "We may judge how great was the improvement which +these contrivances introduced into the art of observing," says +Whewell, "by finding that Hevelius refused to adopt them because +they would make all the old observations of no value. He had +spent a laborious and active life in the exercise of the old +methods, and could not bear to think that all the treasures which +he had accumulated had lost their worth by the discovery of a new +mine of richer ones."[1] + +Until the time of Newton, all the telescopes in use were either +of the Galilean or Keplerian type, that is, refractors. But about +the year 1670 Newton constructed his first reflecting telescope, +which was greatly superior to, although much smaller than, the +telescopes then in use. He was led to this invention by his +experiments with light and colors. In 1671 he presented to the +Royal Society a second and somewhat larger telescope, which he +had made; and this type of instrument was little improved upon +until the introduction of the achromatic telescope, invented by +Chester Moor Hall in 1733. + +As is generally known, the element of accurate measurements of +time plays an important part in the measurements of the movements +of the heavenly bodies. In fact, one was scarcely possible +without the other, and as it happened it was the same man, +Huygens, who perfected Kepler's telescope and invented the +pendulum clock. The general idea had been suggested by Galileo; +or, better perhaps, the equal time occupied by the successive +oscillations of the pendulum had been noted by him. He had not +been able, however, to put this discovery to practical account. +But in 1656 Huygens invented the necessary machinery for +maintaining the motion of the pendulum and perfected several +accurate clocks. These clocks were of invaluable assistance to +the astronomers, affording as they did a means of keeping time +"more accurate than the sun itself." When Picard had corrected +the variation caused by heat and cold acting upon the pendulum +rod by combining metals of different degrees of expansibility, a +high degree of accuracy was possible. + +But while the pendulum clock was an unequalled stationary +time-piece, it was useless in such unstable situations as, for +example, on shipboard. But here again Huygens played a prominent +part by first applying the coiled balance-spring for regulating +watches and marine clocks. The idea of applying a spring to the +balance-wheel was not original with Huygens, however, as it had +been first conceived by Robert Hooke; but Huygens's application +made practical Hooke's idea. In England the importance of +securing accurate watches or marine clocks was so fully +appreciated that a reward of L20,000 sterling was offered by +Parliament as a stimulus to the inventor of such a time-piece. +The immediate incentive for this offer was the obvious fact that +with such an instrument the determination of the longitude of +places would be much simplified. Encouraged by these offers, a +certain carpenter named Harrison turned his attention to the +subject of watch-making, and, after many years of labor, in 1758 +produced a spring time-keeper which, during a sea-voyage +occupying one hundred and sixty-one days, varied only one minute +and five seconds. This gained for Harrison a reward Of L5000 +sterling at once, and a little later L10,000 more, from +Parliament. + +While inventors were busy with the problem of accurate +chronometers, however, another instrument for taking longitude at +sea had been invented. This was the reflecting quadrant, or +sextant, as the improved instrument is now called, invented by +John Hadley in 1731, and independently by Thomas Godfrey, a poor +glazier of Philadelphia, in 1730. Godfrey's invention, which was +constructed on the same principle as that of the Hadley +instrument, was not generally recognized until two years after +Hadley's discovery, although the instrument was finished and +actually in use on a sea-voyage some months before Hadley +reported his invention. The principle of the sextant, however, +seems to have been known to Newton, who constructed an instrument +not very unlike that of Hadley; but this invention was lost sight +of until several years after the philosopher's death and some +time after Hadley's invention. + +The introduction of the sextant greatly simplified taking +reckonings at sea as well as facilitating taking the correct +longitude of distant places. Before that time the mariner was +obliged to depend upon his compass, a cross-staff, or an +astrolabe, a table of the sun's declination and a correction for +the altitude of the polestar, and very inadequate and incorrect +charts. Such were the instruments used by Columbus and Vasco da +Gama and their immediate successors. + +During the Newtonian period the microscopes generally in use were +those constructed of simple lenses, for although compound +microscopes were known, the difficulties of correcting aberration +had not been surmounted, and a much clearer field was given by +the simple instrument. The results obtained by the use of such +instruments, however, were very satisfactory in many ways. By +referring to certain plates in this volume, which reproduce +illustrations from Robert Hooke's work on the microscope, it will +be seen that quite a high degree of effectiveness had been +attained. And it should be recalled that Antony von Leeuwenboek, +whose death took place shortly before Newton's, had discovered +such micro-organisms as bacteria, had seen the blood corpuscles +in circulation, and examined and described other microscopic +structures of the body. + + + +XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO +FRANKLIN + +We have seen how Gilbert, by his experiments with magnets, gave +an impetus to the study of magnetism and electricity. Gilbert +himself demonstrated some facts and advanced some theories, but +the system of general laws was to come later. To this end the +discovery of electrical repulsion, as well as attraction, by Von +Guericke, with his sulphur ball, was a step forward; but +something like a century passed after Gilbert's beginning before +anything of much importance was done in the field of electricity. + +In 1705, however, Francis Hauksbee began a series of experiments +that resulted in some startling demonstrations. For many years it +had been observed that a peculiar light was seen sometimes in the +mercurial barometer, but Hauksbee and the other scientific +investigators supposed the radiance to be due to the mercury in a +vacuum, brought about, perhaps, by some agitation. That this +light might have any connection with electricity did not, at +first, occur to Hauksbee any more than it had to his +predecessors. The problem that interested him was whether the +vacuum in the tube of the barometer was essential to the light; +and in experimenting to determine this, he invented his +"mercurial fountain." Having exhausted the air in a receiver +containing some mercury, he found that by allowing air to rush +through the mercury the metal became a jet thrown in all +directions against the sides of the vessel, making a great, +flaming shower, "like flashes of lightning," as he said. But it +seemed to him that there was a difference between this light and +the glow noted in the barometer. This was a bright light, whereas +the barometer light was only a glow. Pondering over this, +Hauksbee tried various experiments, revolving pieces of amber, +flint, steel, and other substances in his exhausted air-pump +receiver, with negative, or unsatisfactory, results. Finally, it +occurred to him to revolve an exhausted glass tube itself. +Mounting such a globe of glass on an axis so that it could be +revolved rapidly by a belt running on a large wheel, he found +that by holding his fingers against the whirling globe a purplish +glow appeared, giving sufficient light so that coarse print could +be read, and the walls of a dark room sensibly lightened several +feet away. As air was admitted to the globe the light gradually +diminished, and it seemed to him that this diminished glow was +very similar in appearance to the pale light seen in the +mercurial barometer. Could it be that it was the glass, and not +the mercury, that caused it? Going to a barometer he proceeded to +rub the glass above the column of mercury over the vacuum, +without disturbing the mercury, when, to his astonishment, the +same faint light, to all appearances identical with the glow seen +in the whirling globe, was produced. + +Turning these demonstrations over in his mind, he recalled the +well-known fact that rubbed glass attracted bits of paper, +leaf-brass, and other light substances, and that this phenomenon +was supposed to be electrical. This led him finally to determine +the hitherto unsuspected fact, that the glow in the barometer was +electrical as was also the glow seen in his whirling globe. +Continuing his investigations, he soon discovered that solid +glass rods when rubbed produced the same effects as the tube. By +mere chance, happening to hold a rubbed tube to his cheek, he +felt the effect of electricity upon the skin like "a number of +fine, limber hairs," and this suggested to him that, since the +mysterious manifestation was so plain, it could be made to show +its effects upon various substances. Suspending some woollen +threads over the whirling glass cylinder, he found that as soon +as he touched the glass with his hands the threads, which were +waved about by the wind of the revolution, suddenly straightened +themselves in a peculiar manner, and stood in a radical position, +pointing to the axis of the cylinder. + +Encouraged by these successes, he continued his experiments with +breathless expectancy, and soon made another important discovery, +that of "induction," although the real significance of this +discovery was not appreciated by him or, for that matter, by any +one else for several generations following. This discovery was +made by placing two revolving cylinders within an inch of each +other, one with the air exhausted and the other unexhausted. +Placing his hand on the unexhausted tube caused the light to +appear not only upon it, but on the other tube as well. A little +later he discovered that it is not necessary to whirl the +exhausted tube to produce this effect, but simply to place it in +close proximity to the other whirling cylinder. + +These demonstrations of Hauksbee attracted wide attention and +gave an impetus to investigators in the field of electricity; but +still no great advance was made for something like a quarter of a +century. Possibly the energies of the scientists were exhausted +for the moment in exploring the new fields thrown open to +investigation by the colossal work of Newton. + + +THE EXPERIMENTS OF STEPHEN GRAY + +In 1729 Stephen Gray (died in 1736), an eccentric and irascible +old pensioner of the Charter House in London, undertook some +investigations along lines similar to those of Hauksbee. While +experimenting with a glass tube for producing electricity, as +Hauksbee had done, he noticed that the corks with which he had +stopped the ends of the tube to exclude the dust, seemed to +attract bits of paper and leaf-brass as well as the glass itself. +He surmised at once that this mysterious electricity, or +"virtue," as it was called, might be transmitted through other +substances as it seemed to be through glass. + +"Having by me an ivory ball of about one and three-tenths of an +inch in diameter," he writes, "with a hole through it, this I +fixed upon a fir-stick about four inches long, thrusting the +other end into the cork, and upon rubbing the tube found that the +ball attracted and repelled the feather with more vigor than the +cork had done, repeating its attractions and repulsions for many +times together. I then fixed the ball on longer sticks, first +upon one of eight inches, and afterwards upon one of twenty-four +inches long, and found the effect the same. Then I made use of +iron, and then brass wire, to fix the ball on, inserting the +other end of the wire in the cork, as before, and found that the +attraction was the same as when the fir-sticks were made use of, +and that when the feather was held over against any part of the +wire it was attracted by it; but though it was then nearer the +tube, yet its attraction was not so strong as that of the ball. +When the wire of two or three feet long was used, its vibrations, +caused by the rubbing of the tube, made it somewhat troublesome +to be managed. This put me to thinking whether, if the ball was +hung by a pack-thread and suspended by a loop on the tube, the +electricity would not be carried down the line to the ball; I +found it to succeed accordingly; for upon suspending the ball on +the tube by a pack-thread about three feet long, when the tube +had been excited by rubbing, the ivory ball attracted and +repelled the leaf-brass over which it was held as freely as it +had done when it was suspended on sticks or wire, as did also a +ball of cork, and another of lead that weighed one pound and a +quarter." + +Gray next attempted to determine what other bodies would attract +the bits of paper, and for this purpose he tried coins, pieces of +metal, and even a tea-kettle, "both empty and filled with hot or +cold water"; but he found that the attractive power appeared to +be the same regardless of the substance used. + +"I next proceeded," he continues, "to try at what greater +distances the electric virtues might be carried, and having by me +a hollow walking-cane, which I suppose was part of a fishing-rod, +two feet seven inches long, I cut the great end of it to fit into +the bore of the tube, into which it went about five inches; then +when the cane was put into the end of the tube, and this excited, +the cane drew the leaf-brass to the height of more than two +inches, as did also the ivory ball, when by a cork and stick it +had been fixed to the end of the cane.... With several pieces of +Spanish cane and fir-sticks I afterwards made a rod, which, +together with the tube, was somewhat more than eighteen feet +long, which was the greatest length I could conveniently use in +my chamber, and found the attraction very nearly, if not +altogether, as strong as when the ball was placed on the shorter +rods." + +This experiment exhausted the capacity of his small room, but on +going to the country a little later he was able to continue his +experiments. "To a pole of eighteen feet there was tied a line of +thirty-four feet in length, so that the pole and line together +were fifty-two feet. With the pole and tube I stood in the +balcony, the assistant below in the court, where he held the +board with the leaf-brass on it. Then the tube being excited, as +usual, the electric virtue passed from the tube up the pole and +down the line to the ivory ball, which attracted the leaf-brass, +and as the ball passed over it in its vibrations the leaf-brass +would follow it till it was carried off the board." + +Gray next attempted to send the electricity over a line suspended +horizontally. To do this he suspended the pack-thread by pieces +of string looped over nails driven into beams for that purpose. +But when thus suspended he found that the ivory ball no longer +excited the leaf-brass, and he guessed correctly that the +explanation of this lay in the fact that "when the electric +virtue came to the loop that was suspended on the beam it went up +the same to the beam," none of it reaching the ball. As we shall +see from what follows, however, Gray had not as yet determined +that certain substances will conduct electricity while others +will not. But by a lucky accident he made the discovery that +silk, for example, was a poor conductor, and could be turned to +account in insulating the conducting-cord. + +A certain Mr. Wheler had become much interested in the old +pensioner and his work, and, as a guest at the Wheler house, Gray +had been repeating some of his former experiments with the +fishing-rod, line, and ivory ball. He had finally exhausted the +heights from which these experiments could be made by climbing to +the clock-tower and exciting bits of leaf-brass on the ground +below. + +"As we had no greater heights here," he says, "Mr. Wheler was +desirous to try whether we could not carry the electric virtue +horizontally. I then told him of the attempt I had made with that +design, but without success, telling him the method and materials +made use of, as mentioned above. He then proposed a silk line to +support the line by which the electric virtue was to pass. I told +him it might do better upon account of its smallness; so that +there would be less virtue carried from the line of +communication. + +"The first experiment was made in the matted gallery, July 2, +1729, about ten in the morning. About four feet from the end of +the gallery there was a cross line that was fixed by its ends to +each side of the gallery by two nails; the middle part of the +line was silk, the rest at each end pack-thread; then the line to +which the ivory ball was hung and by which the electric virtue +was to be conveyed to it from the tube, being eighty and one-half +feet in length, was laid on the cross silk line, so that the ball +hung about nine feet below it. Then the other end of the line was +by a loop suspended on the glass cane, and the leaf-brass held +under the ball on a piece of white paper; when, the tube being +rubbed, the ball attracted the leaf-brass, and kept it suspended +on it for some time." + +This experiment succeeded so well that the string was lengthened +until it was some two hundred and ninety-three feet long; and +still the attractive force continued, apparently as strong as +ever. On lengthening the string still more, however, the extra +weight proved too much for the strength of the silk +suspending-thread. "Upon this," says Gray, "having brought with +me both brass and iron wire, instead of the silk we put up small +iron wire; but this was too weak to bear the weight of the line. +We then took brass wire of a somewhat larger size than that of +iron. This supported our line of communication; but though the +tube was well rubbed, yet there was not the least motion or +attraction given by the ball, neither with the great tube, which +we made use of when we found the small solid cane to be +ineffectual; by which we were now convinced that the success we +had before depended upon the lines that supported the line of +communication being silk, and not upon their being small, as +before trial I had imagined it might be; the same effect +happening here as it did when the line that is to convey the +electric virtue is supported by pack-thread." + +Soon after this Gray and his host suspended a pack-thread six +hundred and sixty-six feet long on poles across a field, these +poles being slightly inclined so that the thread could be +suspended from the top by small silk cords, thus securing the +necessary insulation. This pack-thread line, suspended upon poles +along which Gray was able to transmit the electricity, is very +suggestive of the modern telegraph, but the idea of signalling or +making use of it for communicating in any way seems not to have +occurred to any one at that time. Even the successors of Gray who +constructed lines some thousands of feet long made no attempt to +use them for anything but experimental purposes--simply to test +the distances that the current could be sent. Nevertheless, Gray +should probably be credited with the discovery of two of the most +important properties of electricity--that it can be conducted and +insulated, although, as we have seen, Gilbert and Von Guericke +had an inkling of both these properties. + + +EXPERIMENTS OF CISTERNAY DUFAY + +So far England had produced the two foremost workers in +electricity. It was now France's turn to take a hand, and, +through the efforts of Charles Francois de Cisternay Dufay, to +advance the science of electricity very materially. Dufay was a +highly educated savant, who had been soldier and diplomat +betimes, but whose versatility and ability as a scientist is +shown by the fact that he was the only man who had ever +contributed to the annals of the academy investigations in every +one of the six subjects admitted by that institution as worthy of +recognition. Dufay upheld his reputation in this new field of +science, making many discoveries and correcting many mistakes of +former observers. In this work also he proved himself a great +diplomat by remaining on terms of intimate friendship with Dr. +Gray--a thing that few people were able to do. + +Almost his first step was to overthrow the belief that certain +bodies are "electrics" and others "non-electrics"--that is, that +some substances when rubbed show certain peculiarities in +attracting pieces of paper and foil which others do not. Dufay +proved that all bodies possess this quality in a certain degree. + +"I have found that all bodies (metallic, soft, or fluid ones +excepted)," he says, "may be made electric by first heating them +more or less and then rubbing them on any sort of cloth. So that +all kinds of stones, as well precious as common, all kinds of +wood, and, in general, everything that I have made trial of, +became electric by beating and rubbing, except such bodies as +grow soft by beat, as the gums, which dissolve in water, glue, +and such like substances. 'Tis also to be remarked that the +hardest stones or marbles require more chafing or heating than +others, and that the same rule obtains with regard to the woods; +so that box, lignum vitae, and such others must be chafed almost +to the degree of browning, whereas fir, lime-tree, and cork +require but a moderate heat. + +"Having read in one of Mr. Gray's letters that water may be made +electrical by holding the excited glass tube near it (a dish of +water being fixed to a stand and that set on a plate of glass, or +on the brim of a drinking-glass, previously chafed, or otherwise +warmed), I have found, upon trial, that the same thing happened +to all bodies without exception, whether solid or fluid, and that +for that purpose 'twas sufficient to set them on a glass stand +slightly warmed, or only dried, and then by bringing the tube +near them they immediately became electrical. I made this +experiment with ice, with a lighted wood-coal, and with +everything that came into my mind; and I constantly remarked that +such bodies of themselves as were least electrical had the +greatest degree of electricity communicated to them at the +approval of the glass tube." + +His next important discovery was that colors had nothing to do +with the conduction of electricity. "Mr. Gray says, towards the +end of one of his letters," he writes, "that bodies attract more +or less according to their colors. This led me to make several +very singular experiments. I took nine silk ribbons of equal +size, one white, one black, and the other seven of the seven +primitive colors, and having hung them all in order in the same +line, and then bringing the tube near them, the black one was +first attracted, the white one next, and others in order +successively to the red one, which was attracted least, and the +last of them all. I afterwards cut out nine square pieces of +gauze of the same colors with the ribbons, and having put them +one after another on a hoop of wood, with leaf-gold under them, +the leaf-gold was attracted through all the colored pieces of +gauze, but not through the white or black. This inclined me first +to think that colors contribute much to electricity, but three +experiments convinced me to the contrary. The first, that by +warming the pieces of gauze neither the black nor white pieces +obstructed the action of the electrical tube more than those of +the other colors. In like manner, the ribbons being warmed, the +black and white are not more strongly attracted than the rest. +The second is, the gauzes and ribbons being wetted, the ribbons +are all attracted equally, and all the pieces of gauze equally +intercept the action of electric bodies. The third is, that the +colors of a prism being thrown on a white gauze, there appear no +differences of attraction. Whence it proceeds that this +difference proceeds, not from the color, as a color, but from the +substances that are employed in the dyeing. For when I colored +ribbons by rubbing them with charcoal, carmine, and such other +substances, the differences no longer proved the same." + +In connection with his experiments with his thread suspended on +glass poles, Dufay noted that a certain amount of the current is +lost, being given off to the surrounding air. He recommended, +therefore, that the cords experimented with be wrapped with some +non-conductor--that it should be "insulated" ("isolee"), as he +said, first making use of this term. + + +DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY + +It has been shown in an earlier chapter how Von Guericke +discovered that light substances like feathers, after being +attracted to the sulphur-ball electric-machine, were repelled by +it until they touched some object. Von Guericke noted this, but +failed to explain it satisfactorily. Dufay, repeating Von +Guericke's experiments, found that if, while the excited tube or +sulphur ball is driving the repelled feather before it, the ball +be touched or rubbed anew, the feather comes to it again, and is +repelled alternately, as, the hand touches the ball, or is +withdrawn. From this he concluded that electrified bodies first +attract bodies not electrified, "charge" them with electricity, +and then repel them, the body so charged not being attracted +again until it has discharged its electricity by touching +something. + +"On making the experiment related by Otto von Guericke," he says, +"which consists in making a ball of sulphur rendered electrical +to repel a down feather, I perceived that the same effects were +produced not only by the tube, but by all electric bodies +whatsoever, and I discovered that which accounts for a great part +of the irregularities and, if I may use the term, of the caprices +that seem to accompany most of the experiments on electricity. +This principle is that electric bodies attract all that are not +so, and repel them as soon as they are become electric by the +vicinity or contact of the electric body. Thus gold-leaf is first +attracted by the tube, and acquires an electricity by approaching +it, and of consequence is immediately repelled by it. Nor is it +reattracted while it retains its electric quality. But if while +it is thus sustained in the air it chance to light on some other +body, it straightway loses its electricity, and in consequence is +reattracted by the tube, which, after having given it a new +electricity, repels it a second time, which continues as long as +the tube keeps its electricity. Upon applying this principle to +the various experiments of electricity, one will be surprised at +the number of obscure and puzzling facts that it clears up. For +Mr. Hauksbee's famous experiment of the glass globe, in which +silk threads are put, is a necessary consequence of it. When +these threads are arranged in the form of rays by the electricity +of the sides of the globe, if the finger be put near the outside +of the globe the silk threads within fly from it, as is well +known, which happens only because the finger or any other body +applied near the glass globe is thereby rendered electrical, and +consequently repels the silk threads which are endowed with the +same quality. With a little reflection we may in the same manner +account for most of the other phenomena, and which seem +inexplicable without attending to this principle. + +"Chance has thrown in my way another principle, more universal +and remarkable than the preceding one, and which throws a new +light on the subject of electricity. This principle is that there +are two distinct electricities, very different from each other, +one of which I call vitreous electricity and the other resinous +electricity. The first is that of glass, rock-crystal, precious +stones, hair of animals, wool, and many other bodies. The second +is that of amber, copal, gumsack, silk thread, paper, and a +number of other substances. The characteristic of these two +electricities is that a body of the vitreous electricity, for +example, repels all such as are of the same electricity, and on +the contrary attracts all those of the resinous electricity; so +that the tube, made electrical, will repel glass, crystal, hair +of animals, etc., when rendered electric, and will attract silk +thread, paper, etc., though rendered electrical likewise. Amber, +on the contrary, will attract electric glass and other substances +of the same class, and will repel gum-sack, copal, silk thread, +etc. Two silk ribbons rendered electrical will repel each other; +two woollen threads will do the like; but a woollen thread and a +silken thread will mutually attract each other. This principle +very naturally explains why the ends of threads of silk or wool +recede from each other, in the form of pencil or broom, when they +have acquired an electric quality. From this principle one may +with the same ease deduce the explanation of a great number of +other phenomena; and it is probable that this truth will lead us +to the further discovery of many other things. + +"In order to know immediately to which of the two classes of +electrics belongs any body whatsoever, one need only render +electric a silk thread, which is known to be of the resinuous +electricity, and see whether that body, rendered electrical, +attracts or repels it. If it attracts it, it is certainly of the +kind of electricity which I call VITREOUS; if, on the contrary, +it repels it, it is of the same kind of electricity with the +silk--that is, of the RESINOUS. I have likewise observed that +communicated electricity retains the same properties; for if a +ball of ivory or wood be set on a glass stand, and this ball be +rendered electric by the tube, it will repel such substances as +the tube repels; but if it be rendered electric by applying a +cylinder of gum-sack near it, it will produce quite contrary +effects--namely, precisely the same as gum-sack would produce. In +order to succeed in these experiments, it is requisite that the +two bodies which are put near each other, to find out the nature +of their electricity, be rendered as electrical as possible, for +if one of them was not at all or but weakly electrical, it would +be attracted by the other, though it be of that sort that should +naturally be repelled by it. But the experiment will always +succeed perfectly well if both bodies are sufficiently +electrical."[1] + +As we now know, Dufay was wrong in supposing that there were two +different kinds of electricity, vitreous and resinous. A little +later the matter was explained by calling one "positive" +electricity and the other "negative," and it was believed that +certain substances produced only the one kind peculiar to that +particular substance. We shall see presently, however, that some +twenty years later an English scientist dispelled this illusion +by producing both positive (or vitreous) and negative (or +resinous) electricity on the same tube of glass at the same time. + +After the death of Dufay his work was continued by his +fellow-countryman Dr. Joseph Desaguliers, who was the first +experimenter to electrify running water, and who was probably the +first to suggest that clouds might be electrified bodies. But +about, this time--that is, just before the middle of the +eighteenth century--the field of greatest experimental activity +was transferred to Germany, although both England and France were +still active. The two German philosophers who accomplished most +at this time were Christian August Hansen and George Matthias +Bose, both professors in Leipsic. Both seem to have conceived the +idea, simultaneously and independently, of generating electricity +by revolving globes run by belt and wheel in much the same manner +as the apparatus of Hauksbee. + +With such machines it was possible to generate a much greater +amount of electricity than Dufay had been able to do with the +rubbed tube, and so equipped, the two German professors were able +to generate electric sparks and jets of fire in a most startling +manner. Bose in particular had a love for the spectacular, which +he turned to account with his new electrical machine upon many +occasions. On one of these occasions he prepared an elaborate +dinner, to which a large number of distinguished guests were +invited. Before the arrival of the company, however, Bose +insulated the great banquet-table on cakes of pitch, and then +connected it with a huge electrical machine concealed in another +room. All being ready, and the guests in their places about to be +seated, Bose gave a secret signal for starting this machine, +when, to the astonishment of the party, flames of fire shot from +flowers, dishes, and viands, giving a most startling but +beautiful display. + +To add still further to the astonishment of his guests, Bose then +presented a beautiful young lady, to whom each of the young men +of the party was introduced. In some mysterious manner she was +insulated and connected with the concealed electrical machine, so +that as each gallant touched her fingertips he received an +electric shock that "made him reel." Not content with this, the +host invited the young men to kiss the beautiful maid. But those +who were bold enough to attempt it received an electric shock +that nearly "knocked their teeth out," as the professor tells it. + + +LUDOLFF'S EXPERIMENT WITH THE ELECTRIC SPARK + +But Bose was only one of several German scientists who were +making elaborate experiments. While Bose was constructing and +experimenting with his huge machine, another German, Christian +Friedrich Ludolff, demonstrated that electric sparks are actual +fire--a fact long suspected but hitherto unproved. Ludolff's +discovery, as it chanced, was made in the lecture-hall of the +reorganized Academy of Sciences at Berlin, before an audience of +scientists and great personages, at the opening lecture in 1744. + +In the course of this lecture on electricity, during which some +of the well-known manifestations of electricity were being shown, +it occurred to Ludolff to attempt to ignite some inflammable +fluid by projecting an electric spark upon its surface with a +glass rod. This idea was suggested to him while performing the +familiar experiment of producing a spark on the surface of a bowl +of water by touching it with a charged glass rod. He announced to +his audience the experiment he was about to attempt, and having +warmed a spoonful of sulphuric ether, he touched its surface with +the glass rod, causing it to burst into flame. This experiment +left no room for doubt that the electric spark was actual fire. + +As soon as this experiment of Ludolff's was made known to Bose, +he immediately claimed that he had previously made similar +demonstrations on various inflammable substances, both liquid and +solid; and it seems highly probable that he had done so, as he +was constantly experimenting with the sparks, and must almost +certainly have set certain substances ablaze by accident, if not +by intent. At all events, he carried on a series of experiments +along this line to good purpose, finally succeeding in exploding +gun-powder, and so making the first forerunner of the electric +fuses now so universally used in blasting, firing cannon, and +other similar purposes. It was Bose also who, observing some of +the peculiar manifestations in electrified tubes, and noticing +their resemblance to "northern lights," was one of the first, if +not the first, to suggest that the aurora borealis is of electric +origin. + +These spectacular demonstrations had the effect of calling public +attention to the fact that electricity is a most wonderful and +mysterious thing, to say the least, and kept both scientists and +laymen agog with expectancy. Bose himself was aflame with +excitement, and so determined in his efforts to produce still +stronger electric currents, that he sacrificed the tube of his +twenty-foot telescope for the construction of a mammoth +electrical machine. With this great machine a discharge of +electricity was generated powerful enough to wound the skin when +it happened to strike it. + +Until this time electricity had been little more than a plaything +of the scientists--or, at least, no practical use had been made +of it. As it was a practising physician, Gilbert, who first laid +the foundation for experimenting with the new substance, so again +it was a medical man who first attempted to put it to practical +use, and that in the field of his profession. Gottlieb Kruger, a +professor of medicine at Halle in 1743, suggested that +electricity might be of use in some branches of medicine; and the +year following Christian Gottlieb Kratzenstein made a first +experiment to determine the effects of electricity upon the body. +He found that "the action of the heart was accelerated, the +circulation increased, and that muscles were made to contract by +the discharge": and he began at once administering electricity in +the treatment of certain diseases. He found that it acted +beneficially in rheumatic affections, and that it was +particularly useful in certain nervous diseases, such as palsies. +This was over a century ago, and to-day about the most important +use made of the particular kind of electricity with which he +experimented (the static, or frictional) is for the treatment of +diseases affecting the nervous system. + +By the middle of the century a perfect mania for making +electrical machines had spread over Europe, and the whirling, +hand-rubbed globes were gradually replaced by great cylinders +rubbed by woollen cloths or pads, and generating an "enormous +power of electricity." These cylinders were run by belts and +foot-treadles, and gave a more powerful, constant, and +satisfactory current than known heretofore. While making +experiments with one of these machines, Johann Heinrichs Winkler +attempted to measure the speed at which electricity travels. To +do this he extended a cord suspended on silk threads, with the +end attached to the machine and the end which was to attract the +bits of gold-leaf near enough together so that the operator could +watch and measure the interval of time that elapsed between the +starting of the current along the cord and its attracting the +gold-leaf. The length of the cord used in this experiment was +only a little over a hundred feet, and this was, of course, +entirely inadequate, the current travelling that space apparently +instantaneously. + +The improved method of generating electricity that had come into +general use made several of the scientists again turn their +attention more particularly to attempt putting it to some +practical account. They were stimulated to these efforts by the +constant reproaches that were beginning to be heard on all sides +that electricity was merely a "philosopher's plaything." One of +the first to succeed in inventing something that approached a +practical mechanical contrivance was Andrew Gordon, a Scotch +Benedictine monk. He invented an electric bell which would ring +automatically, and a little "motor," if it may be so called. And +while neither of these inventions were of any practical +importance in themselves, they were attempts in the right +direction, and were the first ancestors of modern electric bells +and motors, although the principle upon which they worked was +entirely different from modern electrical machines. The motor was +simply a wheel with several protruding metal points around its +rim. These points were arranged to receive an electrical +discharge from a frictional machine, the discharge causing the +wheel to rotate. There was very little force given to this +rotation, however, not enough, in fact, to make it possible to +more than barely turn the wheel itself. Two more great +discoveries, galvanism and electro-magnetic induction, were +necessary before the practical motor became possible. + +The sober Gordon had a taste for the spectacular almost equal to +that of Bose. It was he who ignited a bowl of alcohol by turning +a stream of electrified water upon it, thus presenting the +seeming paradox of fire produced by a stream of water. Gordon +also demonstrated the power of the electrical discharge by +killing small birds and animals at a distance of two hundred +ells, the electricity being conveyed that distance through small +wires. + + +THE LEYDEN JAR DISCOVERED + +As yet no one had discovered that electricity could be stored, or +generated in any way other than by some friction device. But very +soon two experimenters, Dean von Kleist, of Camin, Pomerania, and +Pieter van Musschenbroek, the famous teacher of Leyden, +apparently independently, made the discovery of what has been +known ever since as the Leyden jar. And although Musschenbroek is +sometimes credited with being the discoverer, there can be no +doubt that Von Kleist's discovery antedated his by a few months +at least. + +Von Kleist found that by a device made of a narrow-necked bottle +containing alcohol or mercury, into which an iron nail was +inserted, be was able to retain the charge of electricity, after +electrifying this apparatus with the frictional machine. He made +also a similar device, more closely resembling the modern Leyden +jar, from a thermometer tube partly filled with water and a wire +tipped with a ball of lead. With these devices he found that he +could retain the charge of electricity for several hours, and +could produce the usual electrical manifestations, even to +igniting spirits, quite as well as with the frictional machine. +These experiments were first made in October, 1745, and after a +month of further experimenting, Von Kleist sent the following +account of them to several of the leading scientists, among +others, Dr. Lieberkuhn, in Berlin, and Dr. Kruger, of Halle. + +"When a nail, or a piece of thick brass wire, is put into a small +apothecary's phial and electrified, remarkable effects follow; +but the phial must be very dry, or warm. I commonly rub it over +beforehand with a finger on which I put some pounded chalk. If a +little mercury or a few drops of spirit of wine be put into it, +the experiment succeeds better. As soon as this phial and nail +are removed from the electrifying-glass, or the prime conductor, +to which it has been exposed, is taken away, it throws out a +pencil of flame so long that, with this burning machine in my +hand, I have taken above sixty steps in walking about my room. +When it is electrified strongly, I can take it into another room +and there fire spirits of wine with it. If while it is +electrifying I put my finger, or a piece of gold which I hold in +my hand, to the nail, I receive a shock which stuns my arms and +shoulders. + +"A tin tube, or a man, placed upon electrics, is electrified much +stronger by this means than in the common way. When I present +this phial and nail to a tin tube, which I have, fifteen feet +long, nothing but experience can make a person believe how +strongly it is electrified. I am persuaded," he adds, "that in +this manner Mr. Bose would not have taken a second electrical +kiss. Two thin glasses have been broken by the shock of it. It +appears to me very extraordinary, that when this phial and nail +are in contact with either conducting or non-conducting matter, +the strong shock does not follow. I have cemented it to wood, +metal, glass, sealing-wax, etc., when I have electrified without +any great effect. The human body, therefore, must contribute +something to it. This opinion is confirmed by my observing that +unless I hold the phial in my hand I cannot fire spirits of wine +with it."[2] + +But it seems that none of the men who saw this account were able +to repeat the experiment and produce the effects claimed by Von +Kleist, and probably for this reason the discovery of the obscure +Pomeranian was for a time lost sight of. + +Musschenbroek's discovery was made within a short time after Von +Kleist's--in fact, only a matter of about two months later. But +the difference in the reputations of the two discoverers insured +a very different reception for their discoveries. Musschenbroek +was one of the foremost teachers of Europe, and so widely known +that the great universities vied with each other, and kings were +bidding, for his services. Naturally, any discovery made by such +a famous person would soon be heralded from one end of Europe to +the other. And so when this professor of Leyden made his +discovery, the apparatus came to be called the "Leyden jar," for +want of a better name. There can be little doubt that +Musschenbroek made his discovery entirely independently of any +knowledge of Von Kleist's, or, for that matter, without ever +having heard of the Pomeranian, and his actions in the matter are +entirely honorable. + +His discovery was the result of an accident. While experimenting +to determine the strength of electricity he suspended a +gun-barrel, which he charged with electricity from a revolving +glass globe. From the end of the gun-barrel opposite the globe +was a brass wire, which extended into a glass jar partly filled +with water. Musschenbroek held in one hand this jar, while with +the other he attempted to draw sparks from the barrel. Suddenly +he received a shock in the hand holding the jar, that "shook him +like a stroke of lightning," and for a moment made him believe +that "he was done for." Continuing his experiments, nevertheless, +he found that if the jar were placed on a piece of metal on the +table, a shock would be received by touching this piece of metal +with one hand and touching the wire with the other--that is, a +path was made for the electrical discharge through the body. This +was practically the same experiment as made by Von Kleist with +his bottle and nail, but carried one step farther, as it showed +that the "jar" need not necessarily be held in the hand, as +believed by Von Kleist. Further experiments, continued by many +philosophers at the time, revealed what Von Kleist had already +pointed out, that the electrified jar remained charged for some +time. + +Soon after this Daniel Gralath, wishing to obtain stronger +discharges than could be had from a single Leyden jar, conceived +the idea of combining several jars, thus for the first time +grouping the generators in a "battery" which produced a discharge +strong enough to kill birds and small animals. He also attempted +to measure the strength of the discharges, but soon gave it up in +despair, and the solution of this problem was left for late +nineteenth-century scientists. + +The advent of the Leyden jar, which made it possible to produce +strong electrical discharges from a small and comparatively +simple device, was followed by more spectacular demonstrations of +various kinds all over Europe. These exhibitions aroused the +interest of the kings and noblemen, so that electricity no longer +remained a "plaything of the philosophers" alone, but of kings as +well. A favorite demonstration was that of sending the electrical +discharge through long lines of soldiers linked together by +pieces of wire, the discharge causing them to "spring into the +air simultaneously" in a most astonishing manner. A certain monk +in Paris prepared a most elaborate series of demonstrations for +the amusement of the king, among other things linking together an +entire regiment of nine hundred men, causing them to perform +simultaneous springs and contortions in a manner most amusing to +the royal guests. But not all the experiments being made were of +a purely spectacular character, although most of them +accomplished little except in a negative way. The famous Abbe +Nollet, for example, combined useful experiments with spectacular +demonstrations, thus keeping up popular interest while aiding the +cause of scientific electricity. + + +WILLIAM WATSON + +Naturally, the new discoveries made necessary a new nomenclature, +new words and electrical terms being constantly employed by the +various writers of that day. Among these writers was the English +scientist William Watson, who was not only a most prolific writer +but a tireless investigator. Many of the words coined by him are +now obsolete, but one at least, "circuit," still remains in use. + +In 1746, a French scientist, Louis Guillaume le Monnier, bad made +a circuit including metal and water by laying a chain half-way +around the edge of a pond, a man at either end holding it. One of +these men dipped his free hand in the water, the other presenting +a Leyden jar to a rod suspended on a cork float on the water, +both men receiving a shock simultaneously. Watson, a year later, +attempted the same experiment on a larger scale. He laid a wire +about twelve hundred feet long across Westminster Bridge over the +Thames, bringing the ends to the water's edge on the opposite +banks, a man at one end holding the wire and touching the water. +A second man on the opposite side held the wire and a Leyden jar; +and a third touched the jar with one hand, while with the other +he grasped a wire that extended into the river. In this way they +not only received the shock, but fired alcohol as readily across +the stream as could be done in the laboratory. In this experiment +Watson discovered the superiority of wire over chain as a +conductor, rightly ascribing this superiority to the continuity +of the metal. + +Watson continued making similar experiments over longer +watercourses, some of them as long as eight thousand feet, and +while engaged in making one of these he made the discovery so +essential to later inventions, that the earth could be used as +part of the circuit in the same manner as bodies of water. +Lengthening his wires he continued his experiments until a +circuit of four miles was made, and still the electricity seemed +to traverse the course instantaneously, and with apparently +undiminished force, if the insulation was perfect. + + +BENJAMIN FRANKLIN + +Watson's writings now carried the field of active discovery +across the Atlantic, and for the first time an American scientist +appeared--a scientist who not only rivalled, but excelled, his +European contemporaries. Benjamin Franklin, of Philadelphia, +coming into possession of some of Watson's books, became so +interested in the experiments described in them that he began at +once experimenting with electricity. In Watson's book were given +directions for making various experiments, and these assisted +Franklin in repeating the old experiments, and eventually adding +new ones. Associated with Franklin, and equally interested and +enthusiastic, if not equally successful in making discoveries, +were three other men, Thomas Hopkinson, Philip Sing, and Ebenezer +Kinnersley. These men worked together constantly, although it +appears to have been Franklin who made independently the +important discoveries, and formulated the famous Franklinian +theory. + +Working steadily, and keeping constantly in touch with the +progress of the European investigators, Franklin soon made some +experiments which he thought demonstrated some hitherto unknown +phases of electrical manifestation. This was the effect of +pointed bodies "in DRAWING OFF and THROWING OFF the electrical +fire." In his description of this phenomenon, Franklin writes: + +"Place an iron shot of three or four inches diameter on the mouth +of a clean, dry, glass bottle. By a fine silken thread from the +ceiling right over the mouth of the bottle, suspend a small cork +ball, about the bigness of a marble; the thread of such a length +that the cork ball may rest against the side of the shot. +Electrify the shot, and the ball will be repelled to the distance +of four or five inches, more or less, according to the quantity +of electricity. When in this state, if you present to the shot +the point of a long, slender shaft-bodkin, at six or eight inches +distance, the repellency is instantly destroyed, and the cork +flies to the shot. A blunt body must be brought within an inch, +and draw a spark, to produce the same effect. + +"To prove that the electrical fire is DRAWN OFF by the point, if +you take the blade of the bodkin out of the wooden handle and fix +it in a stick of sealing-wax, and then present it at the distance +aforesaid, or if you bring it very near, no such effect follows; +but sliding one finger along the wax till you touch the blade, +and the ball flies to the shot immediately. If you present the +point in the dark you will see, sometimes at a foot distance, and +more, a light gather upon it like that of a fire-fly or +glow-worm; the less sharp the point, the nearer you must bring it +to observe the light; and at whatever distance you see the light, +you may draw off the electrical fire and destroy the repellency. +If a cork ball so suspended be repelled by the tube, and a point +be presented quick to it, though at a considerable distance, 'tis +surprising to see how suddenly it flies back to the tube. Points +of wood will do as well as those of iron, provided the wood is +not dry; for perfectly dry wood will no more conduct electricity +than sealing-wax. + +"To show that points will THROW OFF as well as DRAW OFF the +electrical fire, lay a long, sharp needle upon the shot, and you +cannot electrify the shot so as to make it repel the cork ball. +Or fix a needle to the end of a suspended gun-barrel or iron rod, +so as to point beyond it like a little bayonet, and while it +remains there, the gun-barrel or rod cannot, by applying the tube +to the other end, be electrified so as to give a spark, the fire +continually running out silently at the point. In the dark you +may see it make the same appearance as it does in the case before +mentioned."[3] + +Von Guericke, Hauksbee, and Gray had noticed that pointed bodies +attracted electricity in a peculiar manner, but this +demonstration of the "drawing off" of "electrical fire" was +original with Franklin. Original also was the theory that he now +suggested, which had at least the merit of being thinkable even +by non-philosophical minds. It assumes that electricity is like a +fluid, that will flow along conductors and accumulate in proper +receptacles, very much as ordinary fluids do. This conception is +probably entirely incorrect, but nevertheless it is likely to +remain a popular one, at least outside of scientific circles, or +until something equally tangible is substituted. + + +FRANKLIN'S THEORY OF ELECTRICITY + +According to Franklin's theory, electricity exists in all bodies +as a "common stock," and tends to seek and remain in a state of +equilibrium, just as fluids naturally tend to seek a level. But +it may, nevertheless, be raised or lowered, and this equilibrium +be thus disturbed. If a body has more electricity than its normal +amount it is said to be POSITIVELY electrified; but if it has +less, it is NEGATIVELY electrified. An over-electrified or "plus" +body tends to give its surplus stock to a body containing the +normal amount; while the "minus" or under-electrified body will +draw electricity from one containing the normal amount. + +Working along lines suggested by this theory, Franklin attempted +to show that electricity is not created by friction, but simply +collected from its diversified state, the rubbed glass globe +attracting a certain quantity of "electrical fire," but ever +ready to give it up to any body that has less. He explained the +charged Leyden jar by showing that the inner coating of tin-foil +received more than the ordinary quantity of electricity, and in +consequence is POSITIVELY electrified, while the outer coating, +having the ordinary quantity of electricity diminished, is +electrified NEGATIVELY. + +These studies of the Leyden jar, and the studies of pieces of +glass coated with sheet metal, led Franklin to invent his +battery, constructed of eleven large glass plates coated with +sheets of lead. With this machine, after overcoming some defects, +he was able to produce electrical manifestations of great +force--a force that "knew no bounds," as he declared ("except in +the matter of expense and of labor"), and which could be made to +exceed "the greatest know effects of common lightning." + +This reference to lightning would seem to show Franklin's belief, +even at that time, that lightning is electricity. Many eminent +observers, such as Hauksbee, Wall, Gray, and Nollet, had noticed +the resemblance between electric sparks and lightning, but none +of these had more than surmised that the two might be identical. +In 1746, the surgeon, John Freke, also asserted his belief in +this identity. Winkler, shortly after this time, expressed the +same belief, and, assuming that they were the same, declared that +"there is no proof that they are of different natures"; and still +he did not prove that they were the same nature. + + +FRANKLIN INVENTS THE LIGHTNING-ROD + +Even before Franklin proved conclusively the nature of lightning, +his experiments in drawing off the electric charge with points +led to some practical suggestions which resulted in the invention +of the lightning-rod. In the letter of July, 1750, which he wrote +on the subject, he gave careful instructions as to the way in +which these rods might be constructed. In part Franklin wrote: +"May not the knowledge of this power of points be of use to +mankind in preserving houses, churches, ships, etc., from the +stroke of lightning by directing us to fix on the highest parts +of the edifices upright rods of iron made sharp as a needle, and +gilt to prevent rusting, and from the foot of these rods a wire +down the outside of the building into the grounds, or down round +one of the shrouds of a ship and down her side till it reaches +the water? Would not these pointed rods probably draw the +electrical fire silently out of a cloud before it came nigh +enough to strike, and thereby secure us from that most sudden and +terrible mischief? + +"To determine this question, whether the clouds that contain the +lightning are electrified or not, I propose an experiment to be +tried where it may be done conveniently. On the top of some high +tower or steeple, place a kind of sentry-box, big enough to +contain a man and an electrical stand. From the middle of the +stand let an iron rod rise and pass, bending out of the door, and +then upright twenty or thirty feet, pointed very sharp at the +end. If the electrical stand be kept clean and dry, a man +standing on it when such clouds are passing low might be +electrified and afford sparks, the rod drawing fire to him from a +cloud. If any danger to the man be apprehended (though I think +there would be none), let him stand on the floor of his box and +now and then bring near to the rod the loop of a wire that has +one end fastened to the leads, he holding it by a wax handle; so +the sparks, if the rod is electrified, will strike from the rod +to the wire and not effect him."[4] + +Not satisfied with all the evidence that he had collected +pointing to the identity of lightning and electricity, he adds +one more striking and very suggestive piece of evidence. +Lightning was known sometimes to strike persons blind without +killing them. In experimenting on pigeons and pullets with his +electrical machine, Franklin found that a fowl, when not killed +outright, was sometimes rendered blind. The report of these +experiments were incorporated in this famous letter of the +Philadelphia philosopher. + +The attitude of the Royal Society towards this clearly stated +letter, with its useful suggestions, must always remain as a blot +on the record of this usually very receptive and liberal-minded +body. Far from publishing it or receiving it at all, they derided +the whole matter as too visionary for discussion by the society. +How was it possible that any great scientific discovery could be +made by a self-educated colonial newspaper editor, who knew +nothing of European science except by hearsay, when all the great +scientific minds of Europe had failed to make the discovery? How +indeed! And yet it would seem that if any of the influential +members of the learned society had taken the trouble to read over +Franklin's clearly stated letter, they could hardly have failed +to see that his suggestions were worthy of consideration. But at +all events, whether they did or did not matters little. The fact +remains that they refused to consider the paper seriously at the +time; and later on, when its true value became known, were +obliged to acknowledge their error by a tardy report on the +already well-known document. + +But if English scientists were cold in their reception of +Franklin's theory and suggestions, the French scientists were +not. Buffon, perceiving at once the importance of some of +Franklin's experiments, took steps to have the famous letter +translated into French, and soon not only the savants, but +members of the court and the king himself were intensely +interested. Two scientists, De Lor and D'Alibard, undertook to +test the truth of Franklin's suggestions as to pointed rods +"drawing off lightning." In a garden near Paris, the latter +erected a pointed iron rod fifty feet high and an inch in +diameter. As no thunder-clouds appeared for several days, a guard +was stationed, armed with an insulated brass wire, who was +directed to test the iron rods with it in case a storm came on +during D'Alibard's absence. The storm did come on, and the guard, +not waiting for his employer's arrival, seized the wire and +touched the rod. Instantly there was a report. Sparks flew and +the guard received such a shock that he thought his time had +come. Believing from his outcry that he was mortally hurt, his +friends rushed for a spiritual adviser, who came running through +rain and hail to administer the last rites; but when he found the +guard still alive and uninjured, he turned his visit to account +by testing the rod himself several times, and later writing a +report of his experiments to M. d'Alibard. This scientist at once +reported the affair to the French Academy, remarking that +"Franklin's idea was no longer a conjecture, but a reality." + + +FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY + +Europe, hitherto somewhat sceptical of Franklin's views, was by +this time convinced of the identity of lightning and electricity. +It was now Franklin's turn to be sceptical. To him the fact that +a rod, one hundred feet high, became electrified during a storm +did not necessarily prove that the storm-clouds were electrified. +A rod of that length was not really projected into the cloud, for +even a very low thunder-cloud was more than a hundred feet above +the ground. Irrefutable proof could only be had, as he saw it, by +"extracting" the lightning with something actually sent up into +the storm-cloud; and to accomplish this Franklin made his silk +kite, with which he finally demonstrated to his own and the +world's satisfaction that his theory was correct. + +Taking his kite out into an open common on the approach of a +thunder-storm, he flew it well up into the threatening clouds, +and then, touching, the suspended key with his knuckle, received +the electric spark; and a little later he charged a Leyden jar +from the electricity drawn from the clouds with his kite. + +In a brief but direct letter, he sent an account of his kite and +his experiment to England: + +"Make a small cross of two light strips of cedar," he wrote, "the +arms so long as to reach to the four corners of a large, thin, +silk handkerchief when extended; tie the corners of the +handkerchief to the extremities of the cross so you have the body +of a kite; which being properly accommodated with a tail, loop, +and string, will rise in the air like those made of paper; but +this being of silk is fitter to bear the wind and wet of a +thunder-gust without tearing. To the top of the upright stick of +the cross is to be fixed a very sharp-pointed wire, rising a foot +or more above the wood. To the end of the twine, next the hand, +is to be tied a silk ribbon; where the silk and twine join a key +may be fastened. This kite is to be raised when a thunder-gust +appears to be coming on, and the person who holds the string must +stand within a door or window or under some cover, so that the +silk ribbon may not be wet; and care must be taken that the twine +does not touch the frame of the door or window. As soon as any of +the thunder-clouds come over the kite, the pointed wire will draw +the electric fire from them, and the kite, with all the twine, +will be electrified and the loose filaments will stand out +everywhere and be attracted by the approaching finger, and when +the rain has wet the kite and twine so that it can conduct the +electric fire freely, you will find it stream out plentifully +from the key on the approach of your knuckle, and with this key +the phial may be charged; and from electric fire thus obtained +spirits may be kindled and all other electric experiments +performed which are usually done by the help of a rubbed glass +globe or tube, and thereby the sameness of the electric matter +with that of lightning completely demonstrated."[5] + +In experimenting with lightning and Franklin's pointed rods in +Europe, several scientists received severe shocks, in one case +with a fatal result. Professor Richman, of St. Petersburg, while +experimenting during a thunder-storm, with an iron rod which he +had erected on his house, received a shock that killed him +instantly. + +About 1733, as we have seen, Dufay had demonstrated that there +were two apparently different kinds of electricity; one called +VITREOUS because produced by rubbing glass, and the other +RESINOUS because produced by rubbed resinous bodies. Dufay +supposed that these two apparently different electricities could +only be produced by their respective substances; but twenty years +later, John Canton (1715-1772), an Englishman, demonstrated that +under certain conditions both might be produced by rubbing the +same substance. Canton's experiment, made upon a glass tube with +a roughened surface, proved that if the surface of the tube were +rubbed with oiled silk, vitreous or positive electricity was +produced, but if rubbed with flannel, resinous electricity was +produced. He discovered still further that both kinds could be +excited on the same tube simultaneously with a single rubber. To +demonstrate this he used a tube, one-half of which had a +roughened the other a glazed surface. With a single stroke of the +rubber he was able to excite both kinds of electricity on this +tube. He found also that certain substances, such as glass and +amber, were electrified positively when taken out of mercury, and +this led to his important discovery that an amalgam of mercury +and tin, when used on the surface of the rubber, was very +effective in exciting glass. + + + +XV. NATURAL HISTORY TO THE TIME OF LINNAeUS + +Modern systematic botany and zoology are usually held to have +their beginnings with Linnaeus. But there were certain precursors +of the famous Swedish naturalist, some of them antedating him by +more than a century, whose work must not be altogether +ignored--such men as Konrad Gesner (1516-1565), Andreas +Caesalpinus (1579-1603), Francisco Redi (1618-1676), Giovanni +Alfonso Borelli (1608-1679), John Ray (1628-1705), Robert Hooke +(1635-1703), John Swammerdam (1637-1680), Marcello Malpighi +(1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort +(1656-1708), Rudolf Jacob Camerarius (1665-1721), and Stephen +Hales (1677-1761). The last named of these was, to be sure, a +contemporary of Linnaeus himself, but Gesner and Caesalpinus +belong, it will be observed, to so remote an epoch as that of +Copernicus. + +Reference has been made in an earlier chapter to the microscopic +investigations of Marcello Malpighi, who, as there related, was +the first observer who actually saw blood corpuscles pass through +the capillaries. Another feat of this earliest of great +microscopists was to dissect muscular tissue, and thus become the +father of microscopic anatomy. But Malpighi did not confine his +observations to animal tissues. He dissected plants as well, and +he is almost as fully entitled to be called the father of +vegetable anatomy, though here his honors are shared by the +Englishman Grew. In 1681, while Malpighi's work, Anatomia +plantarum, was on its way to the Royal Society for publication, +Grew's Anatomy of Vegetables was in the hands of the publishers, +making its appearance a few months earlier than the work of the +great Italian. Grew's book was epoch-marking in pointing out the +sex-differences in plants. + +Robert Hooke developed the microscope, and took the first steps +towards studying vegetable anatomy, publishing in 1667, among +other results, the discovery of the cellular structure of cork. +Hooke applied the name "cell" for the first time in this +connection. These discoveries of Hooke, Malpighi, and Grew, and +the discovery of the circulation of the blood by William Harvey +shortly before, had called attention to the similarity of animal +and vegetable structures. Hales made a series of investigations +upon animals to determine the force of the blood pressure; and +similarly he made numerous statical experiments to determine the +pressure of the flow of sap in vegetables. His Vegetable Statics, +published in 1727, was the first important work on the subject of +vegetable physiology, and for this reason Hales has been called +the father of this branch of science. + +In botany, as well as in zoology, the classifications of Linnaeus +of course supplanted all preceding classifications, for the +obvious reason that they were much more satisfactory; but his +work was a culmination of many similar and more or less +satisfactory attempts of his predecessors. About the year 1670 +Dr. Robert Morison (1620-1683), of Aberdeen, published a +classification of plants, his system taking into account the +woody or herbaceous structure, as well as the flowers and fruit. +This classification was supplanted twelve years later by the +classification of Ray, who arranged all known vegetables into +thirty-three classes, the basis of this classification being the +fruit. A few years later Rivinus, a professor of botany in the +University of Leipzig, made still another classification, +determining the distinguishing character chiefly from the flower, +and Camerarius and Tournefort also made elaborate +classifications. On the Continent Tournefort's classification was +the most popular until the time of Linnaeus, his systematic +arrangement including about eight thousand species of plants, +arranged chiefly according to the form of the corolla. + +Most of these early workers gave attention to both vegetable and +animal kingdoms. They were called naturalists, and the field of +their investigations was spoken of as "natural history." The +specialization of knowledge had not reached that later stage in +which botanist, zoologist, and physiologist felt their labors to +be sharply divided. Such a division was becoming more and more +necessary as the field of knowledge extended; but it did not +become imperative until long after the time of Linnaeus. That +naturalist himself, as we shall see, was equally distinguished as +botanist and as zoologist. His great task of organizing knowledge +was applied to the entire range of living things. + +Carolus Linnaeus was born in the town of Rashult, in Sweden, on +May 13, 1707. As a child he showed great aptitude in learning +botanical names, and remembering facts about various plants as +told him by his father. His eagerness for knowledge did not +extend to the ordinary primary studies, however, and, aside from +the single exception of the study of physiology, he proved +himself an indifferent pupil. His backwardness was a sore trial +to his father, who was desirous that his son should enter the +ministry; but as the young Linnaeus showed no liking for that +calling, and as he had acquitted himself well in his study of +physiology, his father at last decided to allow him to take up +the study of medicine. Here at last was a field more to the +liking of the boy, who soon vied with the best of his +fellow-students for first honors. Meanwhile he kept steadily at +work in his study of natural history, acquiring considerable +knowledge of ornithology, entomology, and botany, and adding +continually to his collection of botanical specimens. In 1729 his +botanical knowledge was brought to the attention of Olaf Rudbeck, +professor of botany in the University of Upsala, by a short paper +on the sexes of plants which Linnaeus had prepared. Rudbeck was +so impressed by some of the ideas expressed in this paper that he +appointed the author as his assistant the following year. + +This was the beginning of Linnaes's career as a botanist. The +academic gardens were thus thrown open to him, and he found time +at his disposal for pursuing his studies between lecture hours +and in the evenings. It was at this time that he began the +preparation of his work the Systema naturae, the first of his +great works, containing a comprehensive sketch of the whole field +of natural history. When this work was published, the clearness +of the views expressed and the systematic arrangement of the +various classifications excited great astonishment and +admiration, and placed Linaeus at once in the foremost rank of +naturalists. This work was followed shortly by other +publications, mostly on botanical subjects, in which, among other +things, he worked out in detail his famous "system." + +This system is founded on the sexes of plants, and is usually +referred to as an "artificial method" of classification because +it takes into account only a few marked characters of plants, +without uniting them by more general natural affinities. At the +present time it is considered only as a stepping-stone to the +"natural" system; but at the time of its promulgation it was +epoch-marking in its directness and simplicity, and therefore +superiority, over any existing systems. + +One of the great reforms effected by Linnaeus was in the matter +of scientific terminology. Technical terms are absolutely +necessary to scientific progress, and particularly so in botany, +where obscurity, ambiguity, or prolixity in descriptions are +fatally misleading. Linnaeus's work contains something like a +thousand terms, whose meanings and uses are carefully explained. +Such an array seems at first glance arbitrary and unnecessary, +but the fact that it has remained in use for something like two +centuries is indisputable evidence of its practicality. The +descriptive language of botany, as employed by Linnaeus, still +stands as a model for all other subjects. + +Closely allied to botanical terminology is the subject of +botanical nomenclature. The old method of using a number of Latin +words to describe each different plant is obviously too +cumbersome, and several attempts had been made prior to the time +of Linnaeus to substitute simpler methods. Linnaeus himself made +several unsatisfactory attempts before he finally hit upon his +system of "trivial names," which was developed in his Species +plantarum, and which, with some, minor alterations, remains in +use to this day. The essence of the system is the introduction of +binomial nomenclature--that is to say, the use of two names and +no more to designate any single species of animal or plant. The +principle is quite the same as that according to which in modern +society a man has two names, let us say, John Doe, the one +designating his family, the other being individual. Similarly +each species of animal or plant, according to the Linnaeean +system, received a specific or "trivial" name; while various +species, associated according to their seeming natural affinities +into groups called genera, were given the same generic name. Thus +the generic name given all members of the cat tribe being Felis, +the name Felis leo designates the lion; Felis pardus, the +leopard; Felis domestica, the house cat, and so on. This seems +perfectly simple and natural now, but to understand how great a +reform the binomial nomenclature introduced we have but to +consult the work of Linnaeus's predecessors. A single +illustration will suffice. There is, for example, a kind of +grass, in referring to which the naturalist anterior to Linnaeus, +if he would be absolutely unambiguous, was obliged to use the +following descriptive formula: Gramen Xerampelino, Miliacea, +praetenuis ramosaque sparsa panicula, sive Xerampelino congener, +arvense, aestivum; gramen minutissimo semine. Linnaeus gave to +this plant the name Poa bulbosa--a name that sufficed, according +to the new system, to distinguish this from every other species +of vegetable. It does not require any special knowledge to +appreciate the advantage of such a simplification. + +While visiting Paris in 1738 Linnaeus met and botanized with the +two botanists whose "natural method" of classification was later +to supplant his own "artificial system." These were Bernard and +Antoine Laurent de Jussieu. The efforts of these two scientists +were directed towards obtaining a system which should aim at +clearness, simplicity, and precision, and at the same time be +governed by the natural affinities of plants. The natural system, +as finally propounded by them, is based on the number of +cotyledons, the structure of the seed, and the insertion of the +stamens. Succeeding writers on botany have made various +modifications of this system, but nevertheless it stands as the +foundation-stone of modern botanical classification. + + + +APPENDIX + +REFERENCE LIST + +CHAPTER I + +SCIENCE IN THE DARK AGE + +[1] (p. 4). James Harvey Robinson, An Introduction to the History +of Western Europe, New York, 1898, p. 330. + +[2] (p. 6). Henry Smith Williams, A Prefatory Characterization of +The History of Italy, in vol. IX. of The Historians' History of +the World, 25 vols., London and New York, 1904. + + +CHAPTER III + +MEDIAeVAL SCIENCE IN THE WEST + +[1] (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, +and Man of Science, 2 vols., New York, 1892. Vol. II., p. 73. + + +CHAPTER IV + +THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO + +[1] (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, +trans. from Dannemann's Geschichle du Naturwissenschaften, 2 +vols., Leipzig, 1896. + +[2] (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, +trans. from Dannemann, op. cit. + +CHAPTER V + +GALILEO AND THE NEW PHYSICS [1] (p. 101). Rothmann, History of +Astronomy (in the Library of Useful Knowledge), London, 1834. + +[2] (p. 102). William Whewell, History of the Inductive Sciences, +3 Vols, London, 1847-Vol. II., p. 48. + +[3] (p. 111). The Lives of Eminent Persons, by Biot, Jardine, +Bethune, etc., London, 1833. + +[4] (p. 113). William Gilbert, De Magnete, translated by P. +Fleury Motteley, London, 1893. In the biographical memoir, p. +xvi. + +[5] (p. 114). Gilbert, op. cit., p. x1vii. + +[6] (p. 114). Gilbert, op. cit., p. 24. + + +CHAPTER VI + +TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY + +[1] (p. 125). Exodus xxxii, 20. + +[2] (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, +1850. Vol. II., p. 280. + +[3] (p. 140). Mackay, op. cit., Vol. 11., p. 289. + +[4] (P. 145). John B. Schmalz, Astrology Vindicated, New York, +1898. + +[5] (p. 146). William Lilly, The Starry Messenger, London, 1645, +p. 63. + +[6] (p. 149). Lilly, op. cit., p. 70. + +[7] (p. 152). George Wharton, An Astrological jugement upon His +Majesty's Present March begun from Oxford, May 7, 1645, pp. 7-10. + +[8] (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, +1854, p. 29. + + +CHAPTER VII + +FROM PARACELSUS TO HARVEY + +[1] (p. 159). A. E. Waite, The Hermetic and Alchemical Writings +of Paracelsus, 2 vols., London, 1894. Vol. I., p. 21. + +[2] (p. 167). E. T. Withington, Medical History from the Earliest +Times, London, 1894, p. 278. + +[3] (p. 173). John Dalton, Doctrines of the Circulation, +Philadelphia, 1884, p. 179. + +[4] (p. 174). William Harvey, De Motu Cordis et Sanguinis, +London, 1803, chap. X. + +[5] (p. 178). The Works of William Harvey, translated by Robert +Willis, London, 1847, p. 56. + + +CHAPTER VIII + +MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES + +[1] (p. 189). Hermann Baas, History of Medicine, translated by H. +E. Henderson, New York, 1894, p. 504. + +[2] (p. 189). E. T. Withington, Medical History from the Earliest +Times, London, 1894, p. 320. + + +CHAPTER IX + +PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING + +[1] (p. 193). George L. Craik, Bacon and His Writings and +Philosophy, 2 vols., London, 1846. Vol. II., p. 121. + +[2] (p. 193). From Huxley's address On Descartes's Discourse +Touching the Method of Using One's Reason Rightly and of Seeking +Scientific Truth. + +[3] (p. 195). Rene Descartes, Traite de l'Homme (Cousins's +edition. in ii vols.), Paris, 1824. Vol, VI., p. 347. + + +CHAPTER X + +THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE + +[1] (p. 205). See The Phlogiston Theory, Vol, IV. + +[2] (p. 205). Robert Boyle, Philosophical Works, 3 vols., London, +1738. Vol. III., p. 41. + +[3] (p. 206). Ibid., Vol. III., p. 47. + +[4] (p. 206). Ibid., Vol. II., p. 92. + +[5] (p. 207). Ibid., Vol. II., p. 2. + +[6] (p. 209). Ibid., Vol. I., p. 8. + +[7] (p. 209). Ibid., vol. III., p. 508. + +[8] (p. 210). Ibid., Vol. III.) p. 361. + +[9] (p. 213). Otto von Guericke, in the Philosophical +Transactions of the Royal Society of London, No. 88, for 1672, p. +5103. + +[10] (p. 222). Von Guericke, Phil. Trans. for 1669, Vol I., pp. +173, 174. + +CHAPTER XI + +NEWTON AND THE COMPOSITION OF LIGHT + +[1] (p. 233). Phil. Trans. of Royal Soc. of London, No. 80, 1672, +pp. 3076-3079. [2] (p 234). Ibid., pp. 3084, 3085. + +[3] (p. 235). Voltaire, Letters Concerning the English Nation, +London, 1811. + +CHAPTER XII + +NEWTON AND THE LAW OF GRAVITATION + +[1] (p. 242). Sir Isaac Newton, Principia, translated by Andrew +Motte, New York, 1848, pp. 391, 392. + +[2] (p. 250). Newton op. cit., pp. 506, 507. + +CHAPTER XIV + +PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN + +[1] (p. 274). A letter from M. Dufay, F.R.S. and of the Royal +Academy of Sciences at Paris, etc., in the Phil. Trans. of the +Royal Soc., vol. XXXVIII., pp. 258-265. + +[2] (p. 282). Dean von Kleist, in the Danzick Memoirs, Vol. I., +p. 407. From Joseph Priestley's History of Electricity, London, +1775, pp. 83, 84. + +[3] (p. 288). Benjamin Franklin, New Experiments and Observations +on Electricity, London, 1760, pp. 107, 108. + +[4] (p. 291). Franklin, op. cit., pp. 62, 63. + +[5] (p. 295). Franklin, op. cit., pp. 107, 108. + +[For notes and bibliography to vol. II. see vol. V.] + + + + + +End of Project Gutenberg Etext of A History of Science, V 2, by Williams + diff --git a/old/2hsci10.zip b/old/2hsci10.zip Binary files differnew file mode 100644 index 0000000..3c9ee3a --- /dev/null +++ b/old/2hsci10.zip |