■3.' t?." ^-a.'^.::^. 
 
Cornell University 
 Library 
 
 The original of tiiis book is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924012340638 
 
OLIVET COLLEGE 
 
 BULLETIN 
 
 VOL. X. Published BY Ouvet College. No. 7. 
 
 APEIL, 1911 
 THE GENESIS OF THE LAW OF GEAVITY^ 
 
 By Pkofessoe JOHN C. SHBDD 
 
 SCNCE the earliest ages man has been interested in the world outside 
 of himself. Thunderstorms, waterfalls, winds, waves, fire, the 
 starry heavens have aroused his wonder, admiration or fear. 
 
 During the earlier stages of racial development the simplest phe- 
 nomenon was explained by reference to some arbitrary power, and soon 
 gods and demigods were conceived of as presiding over the agencies 
 of nature. Later men who had wrested some of her secrets from 
 nature or had won some victory over her were exalted to the position 
 of heroes and worshipped, while their exploits, greatly magnified, be- 
 came part of the legendary history of the race. Slowly man began 
 to realize that there is a constancy about nature that may be expressed 
 in general statements. These statements were often vaguely expressed 
 as, "Nature abhors a vacuum," "Water and fire are antagonistic," 
 " There are three elements, earth, air and water " or " earth, fire and 
 water." These crude beginnings led to more careful and more sys- 
 tematic study of nature, and to more exact statements of what we 
 now call the laws of nature. 
 
 It took long ages — perhaps we have not even yet reached the goal 
 — for man to realize that the content of his study is here objective, so 
 that the method of study must be inductive and not deductive. This 
 being the case, the conclusions arrived at must be allowed to shape 
 themselves regardless of consequences to antecedent beliefs. Thus it 
 happened that the study of nature has been for ages hampered by 
 many a prejudice and by many a " Thou shalt not " from churchman 
 and philosopher. 
 
 Another and perhaps greater impediment than the inertia of the 
 human mind was the ravage wrought by war and time. Could each 
 
 ' Reprinted from Pop. Sei. Mo., Vol. LXXVIII— 22; Apr., 1911. 
 
 The Olivet College Bulletin is issued eight times a year; in Julj^, August, 
 October, November, January, February, April and May. Entered July 22d, igO^,, 
 at Olivet, Mich., as second class matter under Act of Congress of July 16tli, 1894. 
 OLIVET, MICHIGAN. 
 
2 OLIVET COLLEGE BULLETIN 
 
 age have the full benefit of all preceding ages, could man in very truth 
 be "the heir of all the ages;"' there would be no lost arts and the 
 world would not have to learn over and over again lessons once mastered. 
 
 A last impediment may be mentioned, peculiar perhaps to problems 
 like the discovery of the law under discussion. It is hard for a worker 
 in any field not to attempt to reach forward to the final solution of 
 his problem. This is true even if the data for generalization be most 
 meager. Thus it has happened time after time that ill-formed theories 
 have been advanced even by great minds. Indeed the very greatness 
 of the man whose name the theory bears proves an added obstacle. 
 Thus the dicta of Aristotle held sway for centuries and even Galileo's 
 brilliant experiments at the leaning tower of Pisa could scarce over- 
 come the false Aristotelian theory of falling bodies. Another example 
 is Newton's theory of light which survived at least a hundred years, 
 simply because it was Newton's. 
 
 We shall in the present paper seek to trace the history of the prob- 
 lem which found its final answer in Newton's Law of Universal Gravi- 
 tation. This law may be stated in the following familiar terms: 
 "Every particle of matter attracts every other particle of matter ivith 
 a force proportional to iJie mass of each and to the inverse square of 
 the distance between them." 
 
 In tracing the history of how the race came into a clear knowledge 
 of this law we find two streams with their headwaters far back in 
 history, slowly gathering volume age by age and finally uniting and 
 bearing tlie world on to the long-sought-for goal. The first of these 
 streams may be called tJie study of pure motion, or of Icinematics, the 
 second the study of the causes of motion, or of dynamics. The first is 
 best illustrated by the history of astronomy as developed down to the 
 seventeenth century, while the second is best illustrated by the history 
 of mechanics during the same period. 
 
 In astronomy we shall pay attention only to those persons whose 
 work has a bearing upon the present problem. The first name of 
 worth seems to be that of Thales of Miletus (640-546 B.C.). With 
 remarkable clearness he maintained the sphericity of the eartli, the 
 present theory of lunar eclipses, and the correct view regarding the 
 source of the light received from the earth's satellite. He also suggested 
 that tlie stars may be regarded as being of the same material as the 
 earth. Tliales was followed by his disciple, Anaximander (611—547), 
 who was the first of the ancients to view the heavens with the eye of 
 a philosopher. His name should be immortal, for it was he who 
 first suggested that the earth moves about the sun as a center, a doctrine 
 which became one of the tenets of the Ionian school. 
 
 Perhaps rapid progress might have been made in the explanation 
 by natural causes of tlie phenomena of the heavens, but soon the jealous 
 
THE GENESIS OF THE LAW OF GRAVITY 
 
 ^, , , PYTAGORA.5^. . ,. 
 
 ■^ ' j-itcdio/grn appej.lav%t ' _ j 
 <^< nurnmi? cere in J heJ'eii4-7*oi.hriJiinai\eaz7ziS AuiJ 
 
 ire of the Athenians was aroused in behalf of their gods. As a result, 
 history would have claimed the first martyr to scientific truth in the 
 person of Anaxagoras (400-428), had not the great Pericles inter- 
 posed in his behalf. Even so, the death penalty was but exchanged 
 for that of banishment. 
 
 Another disciple of Thales was the illustrious Pythagoras (572- 
 400), who not only held the views of his master, but, from observations 
 on the altitude of the stars, measured in different places, demonstrated 
 that the earth was round, or, at least, not flat. He conceived Venus 
 to be both the morning and evening star — a view lost sight of, later, 
 as shown by the double name, Lucifer and Hesperus, long applied to 
 this planet. Most remarkable, perhaps, was his doctrine of the diurnal 
 rotation of the earth and its annual motion about the sun. Less sub- 
 stantial, but longer-lived, was his fanciful notion of the harmony of 
 
OLIVET COLLEGE BULLETIN 
 
 the spheres. He coDceived each planet as held in place by being fixed 
 in a celestial crystalline sphere which, in its rotation about the sun 
 as center, carried the planet with it. Having observed that the planets 
 move at different rates, it followed that the various spheres had dif- 
 ferent rates of rotation, and Pythagoras believed that some law con- 
 trolled their motions. This he expressed by supposing that each 
 sphere emitted sounds or notes like the strings of a harp, and the har- 
 mony was expressed by the belief that the several notes united in a 
 beautiful celestial harmony of most exquisite music. More fantastic 
 than suggestive, yet here in the far-away dawn of scientific history is 
 the foreshadowing of the great thought which two millenniums later 
 was given in Xcwton's universal law of gravitation. 
 
 The fate of Anaxagoras warned Pythagoras against being too overt 
 
THE GENESIS OF THE LAW OF GRAVITY 
 
 " 0/ 'B(es%e' 
 
 Ptolemaic System. 
 
 in his public teaching, so that much that he taught was under the seal 
 of secrecy. He also sought greater freedom by removing from Samoa 
 to Italy. 
 
 It might be expected that with so much to build upon the genius 
 of Aristotle (384^332) would have accomplished great things in astro- 
 nomical science. But not so 1 For some reason he rejected the theories 
 of Pythagoras and, although he is said to have come into possession 
 of great stores of Chaldean observations, on the capture of Babylon by 
 Alexander the Great, be made no use of them. Perhaps the task of 
 
 ^^^^yhrTo^''' 
 
 APPARENT Path of Maes. 
 
6 OLIVET COLLEGE BULLETIN 
 
 mastering these treasures was too great, perhaps his studies in anatomy 
 and metaphysics prevented, but be that as it may, it must be acknowl- 
 edged that his few pronouncements on physical science were for the 
 most part erroneous and proved hindrances and not helps to those 
 who followed him. 
 
 With the founding of the schools of Alexandria in the palmy days 
 of the Ptolemys astronomy became a science. It was during this 
 period that simultaneous measurements were made upon the altitude 
 of the sun at Alexandria and Syene. At the latter place the 
 sun at the summer solstice was on the zenith and at the former place 
 7° 12' therefrom. From this and the known distance between stations 
 the circumference of the earth was calculated as 250,000 stadia or 28,- 
 000 miles. This measurement was first made by Eratosthenes (276- 
 196) and places him in the first rank in the Hall of Fame. 
 
 The centuries immediately preceding and following the beginning 
 of the Christian era mark the rise both of astronomy and of geometry. 
 It was probably due to progress in the latter science that Hipparchus 
 (190-120 B.C.) and, later, Ptolemy (a.d. 120-170), were led to pro- 
 pound the system that still bears their names. This was a far more 
 ambitious system than any that had preceded it, and sought, for the 
 first time perhaps, to describe the exact path of the heavenly bodies. 
 From our vantage point of wider knowledge it is easy to see its 
 absurdities. Hasty judgment, how^ever, must not be passed either 
 upon its founders or upon the system itself. 
 
 In the first place, it was based upon observations; in other words, 
 it was a generalization from data. 
 
 Secondly, it satisfactorily explained the observations contained in 
 the premises. 
 
 Thirdly, it made possible the forecasting of eclipses. 
 
 The characteristics of the system may be given as follows : 
 
 1. The earth is a globe set immovable at the center of the celestial 
 sphere — which sphere carries the fixed stars and revolves once per day. 
 
 2. The size of the earth is insignificant in comparison with that 
 of the celestial sphere. 
 
 3. Seven planets revolve around the earth in the following order — 
 the moon. Mercury, Venus, the Sun, Mars, Jupiter, Saturn. 
 
 4. The moon and sun move in excentric circles, the rest in epicycles. 
 Of the several considerations that must have induced the Alex- 
 andrian school to adopt this system we may note : 
 
 I. The Pythagorean system called for a moving earth, the Ptolemaic 
 did not. 
 
 II. The observed motions of the planets were explained by the 
 Ptolemaic system, and, while it is true that the Pythagorean system 
 was capable of this also, it does not appear that the test by actual calcu- 
 lation had been made. 
 
THE GENESIS OF THE LAW OF GRAVITY 7 
 
 III. The system seemed adequate, was geocentric and appealed to 
 the popular imagination. 
 
 Some of the more obvious criticisms of the system may be men- 
 tioned : 
 
 I. The ancients believed the sun to be larger than the earth — it 
 would be more lilcely to be the center of the system. 
 
 II. The diurnal motion of the earth offered a simple explanation 
 of the apparent motion of the heavens — the simple should prevail when 
 opposed to the complex. 
 
 III. The Pythagorean system gave the same law of motion (the 
 circle) to all the members of the system, while in the Ptolemaic system 
 the moon and sun moved in circles and the rest in epicycles. 
 
 The cumbersome Ptolemaic system, having been adopted, became 
 with the passage of time deeply rooted in the philosophy and religion 
 of the race. Its complexity became greater and greater, for with more 
 accurate observations came the necessity of adding " cycle on epicj'cle, 
 orb on orb " to keep track of the required corrections. It is not sur- 
 prising, therefore, to find Alphonso X., in the thirteenth century, when 
 contemplating the system, exclaiming, " if the Deity had called him to 
 His councils at the creation of the world, he could have given Him 
 good advice." Indeed the system finally crumbled and fell from the 
 very weight of its superstructure. 
 
 We have spoken of the ravages of time and of war as hindering the 
 progress of knowledge. We have now to note the greatest calamity that 
 has in modern history overtaken the cause of human knowledge. In 
 the third century before Christ, was founded the Alexandrian library 
 with its treasures of art, of literature and of science collected from 
 every part of the known world. Century by century it grew, and could 
 it have survived what untold treasures would have been ours to-day ! 
 But in the seventh century a.d. the Caliph Omar in a day reduced to 
 ashes this storehouse of wisdom, and by one act set the world back a 
 thousand years. Perhaps this disaster can be overrated; perhaps, in 
 the dissemination of copies of the old masters, the Alexandrian library 
 had done its real work ; but to me it seems otherwise ; for many a 
 priceless gem of literature and of science must have perished in the 
 wanton Arab's destruction. As a single example, it is doubtless due 
 to this cause that we have none of the astronomical writings of Hip- 
 parchus. 
 
 To Alphonso X., of Castile, belongs the honor of being the first 
 European monarch to foster astronomy. In the thirteenth century he 
 founded a college in Toledo, and gathered together savants from all 
 parts of his realm. From the Arabs they acquired much both in 
 mathematics and in astronomy. Original sources were also sought out 
 in the Greek. Other schools were rapidly established and centers of 
 
OLIVET COLLEGE BULLETIN 
 
 scientific culture formed. Among tlie notable workers and tliinkers of 
 the thirteenth and fourteenth centuries were Eoger Bacon (1214—1292) 
 in Cambridge and Paris, John Miiller of Konigsberg (1436-1476), and 
 Leonardo da A^inci (1452-1519), the artist philosopher of Florence. 
 In the early part of the sixteenth century the illustrious Copernicus ap- 
 pears (1473-1543). Copernicus, or Copernic, had a keen mind and a 
 firm belief in what may be called the simplicity of nature. On examin- 
 ing the Ptolemaic system he was embarrassed by its epicycles and ex- 
 centrics, producing, as they did, complexity where he believed there 
 should be simplicity. He, therefore, turned with relief to the ancient 
 ideas of Pythagoras, and of his system he says : 
 
 The several appearances of the heavenly bodies will not only follow from 
 this hypothesis, but it will so connect the order of the planets, their orbits, 
 magnitudes and distances, and even the apparent motion of the fixed stars, that 
 it would be impossible to remove one of these bodies out of its place without 
 disordering the rest and even the whole universe also. 
 
 Under the hand of Copernic this system was elaborated and shaped 
 80 as to acquire a dignity equal to that of the older system, and, but 
 
TEE GENESIS OF THE LAW OF GRAVITY 9 
 
 for the retarding hand of superstition and bigotry, the dawning day 
 might have rapidly advanced. 
 
 As it was, Copernic, fearful perhaps of the fate of Eoger Bacon, 
 taught in private a few select pupils, and only on his death bed did he 
 see his printed work (1543). Copernic's sudden death was all that 
 saved him from the hands of his enemies. As it was, his book was 
 soon proscribed and his theory placed under the ban of the church. 
 
 With the printing of Copernic's work the battle between the geo- 
 centric and helio-ceniric hypotheses may be said to have been fairly 
 joined. Copernic himself foresaw the coming conflict. He also saw 
 
 The Solae System as conceived by Coiernicus. 
 
 that the real conflict would be, not with astronomers, but with church- 
 men. In the dedication of his book he says : 
 
 If there be some babblers who, ignorant of all mathematics, take upon them 
 to judge of these things, and dare to blame and cavil at my work, because of 
 some passage of Scripture which they have wrested to their own purpose, I 
 regard them not, and will not scruple to hold their judgment in contempt. 
 
 Sir Oliver Lodge, in summing up the life-work of this pioneer of 
 science, says : 
 
 We are to remember, then, as the life-work of Copernicus, that he placed 
 the sun in its true place as the center of the solar system, instead of the earth. 
 
lo OLIVET COLLEGE BULLETIN 
 
 that he greatly sijiiplified the theory of phinetary motion by this step . . . which 
 he worked out mathematically . . . and, that by means of his simpler theory 
 and more exact planetary tables, he reduced to some sort of order the confused 
 chaos of the Ptolemaic system, whose accumulations of complexity and of out- 
 standing errors threatened to render astronomy impossible by the mere burden 
 of its detail. There are many imperfections in his system, it is true, but his 
 great merit is that he dared to look at the facts of nature with his own eyes 
 unhampered by the prejudice of centuries. A system, venerable with age and 
 supported by great names, was universally believed and had been believed for 
 centuries. To doubt this sj'stem, and to seek after another and better one, at a 
 time when all men's minds were governed by tradition and authority, and when 
 to doubt was sin — ^this required a great mind and a high character. Such a 
 mind and such a character had this monk of Franenburg. 
 
 Mr. E. J. C. Morton in a biography of Copernic says : 
 
 Kopernicus can not be said to have flooded with light the dark places of 
 nature — in the way that one stupendous mind subsequently did — but still, as 
 we look back through the long vista of the history of science, the dim. Titanic 
 figure of the old monk seems to rear itself out of the dull flats around it, pierces 
 with its head the mists that overshadow them, and catches the first gleam of 
 the rising sun, 
 
 "... like some iron peak, by the Creator 
 Fired with the red glow of the rushing morn." 
 
 It is not to be supposed tliat tliere were not weighty objections to 
 be urged against the Copernican system. Of tliese three may be noted : 
 
 1. If it be true tliat the earth moves, wliy do not the configurations 
 of the stars change with the changing seasons ? It is evident that the 
 grouping of the stars depends upon the distance of the earth from them, 
 and if the earth moves the groups of stars in front of the earth's motion 
 should appear to open out while those behind should appear to close 
 up. We now know the correct answer, that is, that the 184 millions 
 of miles making up the diameter of the earth's orbit is lost in the 
 immensity of stellar space and its effect can only be detected by the 
 most refined of modern methods. 
 
 8. If the earth moves about the sun. Mercury and Venus should 
 show phases as does the moon. 
 
 The only answer Copernicus could make was that, were the powers 
 of man's eyesight sufficiently increased, this would doubtless be found 
 to be the case. Seventy years later, Galileo furnished the required 
 proof. 
 
 Before looking so far ahead, two important workers must be noted. 
 The first of these is the Danish astronomer, Tycho Brahe (1545-1601), 
 who is well called the father of instrumental astronomy. His aid in the 
 solution of the present problem did not consist in the advocacy of the 
 Copernican system — for he rejected it — but in his patient, faithful gath- 
 ering of data. His tables of planetary motions and his star tables were 
 the most extensive and the most accurate of his time. Even when 
 
TEE GENESIS OF THE LAW OF GRAVITY 
 
 n<i 
 
 ' .i 
 
 1 1 
 
 M 
 
 ' t 
 
 
 judged by the standards of to-day they are to be viewed with respect. 
 When we remember tliat the telescope and microscope were then un- 
 known, respect rises to admiration and wonder. So careful was he that 
 not a single mistake due to carelessness has ever been detected in his 
 work. 
 
 From 1576 to 1597 Tycho Brahe worked in his well-equipped ob- 
 servatory at Uraniburg on the island of Huen. For twenty years this 
 temple of science was the greatest center of its sort in Europe. Philos- 
 ophers, statesmen and even kings visited him in his island home. Year 
 by year the great tables of observations grew until further additions 
 seemed but repetitions of oft-told tales. Indeed, the tables grew beyond 
 the ability of their maker to interpret, and some keener mind was 
 needed to unfold their hidden meaning. The possessor of such a mind 
 was even then living in Austria in the person of John Kepler. 
 
I2 
 
 OLIVET COLLEGE BULLETIN 
 
 John Kepler was born and reared in poverty, and all his life had to 
 struggle to keep actual want from the door. There could scarcely be 
 a greater contrast than that presented by these two men: Brahe, the 
 favored son of fortune, possessing all that wealth and princely favor 
 could procure, acknowledged as the foremost philosopher of his day; 
 Kepler, with nothing to commend him to notice save a passion 
 for knowledge and longing to learn the hidden meaning of equations 
 and formulas and mystic numbers. The common bond between them 
 was the love of the truth and the capacity for taking infinite pains. 
 For the progress of the race each of these men needed the other, and 
 dame fortune's immediate problem was the bringing them together. 
 
 Geocbxteic System aftek Tycho Beahiii 
 
 By so doing it would be possible for Brahe to pass on to Kepler the 
 completion of his own work, and at the same time train him for an 
 even greater task. 
 
 In 1590 James I., of England, visited Denmark and spent eight 
 days with Tycho and his wonderful instruments. On leaving he pre- 
 sented the astronomer witli various gifts, and among these was a pet 
 dog of which the astronomer became very fond. Now this canine be- 
 came the innocent cause of much trouble to his master, for it seems that 
 one day the cliancellor of Denmark brutally kicked the poor beast. This 
 was too much for Tycho's temjier — never very even — and he roundly be- 
 rated the chancellor for his cruelty. Of course there is more to the 
 story than just this, but at all events Tycho made a powerful enemy. 
 
THE GENESIS OF THE LAW OF GRAVITY 
 
 13 
 
 who, after the death of the king, stripped the astronomer of all his 
 estates and drove him penniless from the kingdom. For two years he 
 was without a home, but in 1599 found refuge and a pension with 
 Emperor Eudolph II., of Bohemia. Becoming established in Prague, 
 he set up his instruments, and soon students flocked to him again. 
 Among them came the poor youth, Kepler, who soon made himself 
 invaluable to his master. In return, Tycho was kind to Kepler, and 
 together they labored until the former's death in 1601. 
 
 With the advent of Kepler (1571-1630) the real problem of gravity 
 together with its solution took definite form. Always a firm believer 
 in the unity and simplicity of the solar system, Kepler rejected the 
 teaching of Tycho Brahe and adopted Copernicus's scheme in toto. 
 Next, he set about bringing order out of the mass of observations ac- 
 
14 OLIVET COLLEGE BULLETIN 
 
 cumulated (for the most part) b}' Brahe. He took infinite pains, test- 
 ing hj actual calculation ei^ery hypothesis or rule that he could think 
 of. For example, he tried circular orbits with constant velocities for 
 the planets and the sun at the center. Finding that this did not tit 
 the facts, he placed the sun a little off center and tried again, but the 
 theory did not yet fit the observed facts. " After incredible labor, 
 through innumerable wrong guesses, and six years of almost incessant 
 calculation " the truth began to dawn upon him, until he was able to 
 enunciate three laws which have since gone by his name. The first of 
 these to yield itself to his zeal was the so-called second law which gives 
 the rule governing the velocitj' of the planet in its orbit. 
 
 Law II., The radius vector stveeps out equal areas in equal times. 
 Having determined, as he believed, the law of speed, he next inquired 
 into the exact shape of the orbit. Here " however, the geometrical and 
 mathematical difficulties of calculation threatened to become over- 
 whelming," and as the days dragged into months he had every reason 
 to become disheartened. By day he worked, by night he dreamed of 
 his problem, and it is said that the hint which led to its solution came 
 to him as he slept and awoke him. Arising at once, he lighted his lamp 
 and set to work anew at his calculations. Step by step he progressed, 
 and finally, in a paroxysm of delight, he proved what is now known as 
 
 Kepler's first law. 
 
 Law I., The planets move in ellipses with the sun at one focus. 
 
 To these two laws Kepler nine years later in 1618 added a third. 
 
 Law III., The square of the time of revolution of each planet is 
 
 proportional to the cule of its mean distance from the sun. 
 
 In these three statements Kepler brought order out of chaos and 
 
 reduced to system a heterogeneous mass of observations and records. 
 
 When we remember that these laws of Kepler's furnished Newton not 
 
 only a point of departure, but also gave him a criterion by which to test 
 
 his results, we begin to see that without Kepler, Newton might not 
 
 have been possible. Lodge says of him : 
 
 A man of keen imagination, indomitable perseverance and uncompromising 
 love of truth, Kepler overcame ill-health, poverty and misfortune, and placed 
 himself in the very highest rank of scientific men. His laws so extraordinarily 
 discovered introduced order and simplicity into what else would have been a 
 chaos of detailed observations; and they served as a secure basis for the 
 splendid erection made on them by Newton. 
 
 While Kepler was laying the enduring foundations of the Coperni- 
 can theory, Galileo (1564—1612), was carrj'ing on an open propaganda 
 in Italy. In 1609 he perfected the telescope, and with it, night by 
 night, questioned the heavens. The mountains on the moon, the 
 satellites of Jupiter, sun-spots, the strange appearance of Saturn due 
 to its rings, the changing phases of A'^enus, were discoveries rapidly 
 
TEE GENESIS OF THE LAW OF GRAVITY 
 
 IS 
 
 announced to an astonished public. Some of tlie discoveries, such as 
 those relating to Saturn and A'enus, were of such an astonishing and 
 revolutionary nature that Galileo first published them in the form of 
 anagrams. The one announcing the phases of Venus, when deciphered, 
 reads as follows : " Cynthise Figuras iEmulatur Mater Amorum." 
 Freely translated : " Venus emulates the phases of the moon." The 
 immediate result of Galileo's brilliant work was to convince all un- 
 biased minds of the truth and to array the church in solid phalanx 
 against both him and his system. Of Galileo personally we have not 
 time to speak — suffice it to say that he was made to suffer most cruelly 
 for his beliefs. 
 
 In the year he died (1642) was Ijorn — on Christmas Day — the man 
 
 who was destined to establish forever the trutlis for which so many had 
 toiled and suffered before him. 
 
 We have tried to follow one of the lines of succession leading up to 
 Newton, giving, as it were, his pedigree upon the side of astronomy. It 
 is a noble line : Pythagoras, Eratosthenes, Hipparchus, Ptolemy, Co- 
 pernicus, Brahe, Kepler, Galileo, with many lesser names unmentioned. 
 There is another line of succession to be traced, and to this I invite 
 your attention for a brief moment — for I have kept you all too long 
 from the main theme of the paper. 
 
 In the study of mechanics as in the study of astronomy we must 
 begin with the Greeks. Thus, we find Aristotle attempting to teach 
 the law of falling bodies, and also giving the reason why heavy bodies 
 
t6 
 
 OLIVET COLLEGE BULLETIN 
 
 Galileo. 
 
 sink while liglit ones arise. All his statements relating to mechanics 
 are erroneous and some are positively childish. 
 
 The first real student of mechanics was Archimedes (287-312 B.C.) 
 To him we owe the foundations of the science. For example, to him 
 we owe the theory of the lever, from which he developed the idea of the 
 center of gravity. He was especially interested in the subject of hydro- 
 statics, and established principles that are of universal application 
 to-day. His practical applications are best illustiated in the engines 
 of war which he devised to aid in the defense of Syracuse. So effective 
 were these that the Eomans took the city not by assault but by starva- 
 tion. For fifteen hundred years thereafter practically no advance was 
 made. In 1452 the Turks took Constantinople, and fugitive Greeks 
 
THE GENESIS OF THE LAW OF GRAVITY 
 
 17 
 
 IIUYGENS. 
 
 carried Greek manuscripts westward to Europe. These stiaj' documents 
 gave a fresh impetus to science as they did to letters. The first one 
 really to grasp the subject of mechanics and develop it was Galileo 
 (1564-1642). To him we owe the true tlieor}^ of falling liodies, the law 
 of the pendulum, the theoiy of ])rojectilcs and two of the three great 
 laws of motion, which were j)ut into thoii- final form by Newton himself. 
 Two stories about Galileo will serve to show what manner of man 
 he was and also to illustrate his methods. In 1583, while worshipping 
 in the cathedral in Pisa, he chanced to notice the swaying of the great 
 chandelier, the lamps of which had been freshly lighted. From watch- 
 ing its stately vibration he fell to timing it, using as a standard his 
 pulse-beat. Thus there dawned upon him one of the laws of the pen- 
 dulum — that the time of vibration is independent of the arc of motion. 
 How manv thousands of times had that same chandelier been observed 
 
3 8 OLIVET COLLEGE BULLETIN 
 
 swinging to and fro, and j'et it had awaited tlie coining of Galileo to 
 read its inner meaning ! 
 
 On the question of falling bodies Galileo ran counter to Aristotle. 
 That philosopher had taught that bodies in falling acquire velocity in 
 proportion to their weight. Galileo found by a simple but careful 
 study that all bodies acquire the same velocity in falling. With the 
 imprudence of youth he forthwith proclaimed the errors of Aristotle 
 from the house-tops, much to the scandal of his classical friends. In 
 answer to their protests he proposed an experiment, and this experi- 
 ment was made. The faculty of the University of Pisa together with 
 the interested or curious of the city gathered at the leaning tower — • 
 " Pisa's leaning miracle," as Whittier calls it. From the top and at the 
 overhanging side Galileo let fall a one-pound and a one-hundred-pound 
 shot. The two shot started, fell — and struck the ground together. As 
 Lodge exclaims, " The simultaneous clang of those two weights sounded 
 the death-knell of the old system of philosophy and heralded the birth 
 of the new." And yet, it is recorded that while some saw, and were con- 
 vinced, others — nor is their race extinct to-day — saw, but, consulting 
 their copies of Aristotle, disbelieved. 
 
 Following in Galileo's foot-steps — perhaps more cautiously lest he 
 be made to suffer for it — Huygens (1629-1699) further developed and 
 extended the science of mechanics. In particular may be noted his 
 development of the theory of circular motion ; the invention, or at least 
 perfection, of the pendulum clock, and the determination of the accel- 
 eration of gravity from pendulum observations, a method which is 
 to-day the most accurate one in use. Huygens shares with Galileo all 
 the honors due a scholar and original worker of the first rank. They 
 resemble each other in character, in method and in the great value of 
 their labors. 
 
 As bearing upon the law of gravitation the theory of circular motion 
 was of the very greatest value. Without it, Newton must either have 
 failed in his task or have discovered these principles for himself. As 
 a matter of fact he did the latter. Huygens was also the first to grasp 
 the significance of the following occurrence. In 1671 Jean Eichter, in 
 the course of astronomical work, carried a pendulum clock from Paris 
 to Cayenne in South America. The clock kept correct time in Paris, 
 but at the latter station it daily fell two and a half minutes behind 
 mean solar time. The pendulum was shortened to correct it, but on 
 returning to Paris it was found to gain time at the same rate that it 
 had before lost it. Huygens at once correctly explained this as due to 
 the rotation of the earth on its axis; thus furnishing the first experi- 
 mental evidence of the earth's rotation. 
 
 The span of Galileo's life was from 1564 to 1642. He died dis- 
 credited by his church, deprived of his liberty and afflicted with blind- 
 
THE GENESIS OF THE LAW OF GRAVITY 19 
 
 ness. His enemies thought that they had vanquished him and his 
 ideas. They even attempted to blot out his memory from among men by 
 refusing to allow his grave to be marked. How little they knew ! 
 Already through Huj'gens the new knowledge had made great advances ; 
 and in the very year of Galileo's death was born the man whose mighty 
 intellect was to flood with light the dark places of nature and to carry 
 Galileo's work to a proud completion. 
 
 The year 1660 was in England an important year for science. This 
 is the year of the founding of the Royal Society, and in the same year 
 Isaac Newton, a young man of eighteen, entered the University of 
 Cambridge from the town of Woolsthorpe in Lincolnshire. In 1663 
 the society received a royal charter, and some time after King Charles 
 is said to have sent it a weighty problem with which to test its powers, 
 " Why is it," said the king, " that the same fish weighs less when alive 
 and swimming in a pan of water, than when dead and floating on its 
 surface ? " There must have been rapid improvement in the caliber 
 of its meetings, for in 1665 its members are listening to Eobert Boyle's 
 brilliant papers on the air-pump and the barometer. 
 
 In the meantime, Isaac Newton, destined for twenty-five years to be 
 president of the society, was pursuing his studies at Cambridge and in 
 1665 was given the A.B. degree. This and the following )'ear were 
 the years of the great plague. For a time the Royal Society took refuge 
 in Oxford, while the University at Cambridge was, in the fall of 1666 
 " sent down," the students and faculty scattering to escape contagion. 
 
 Newton returned home, his mind teeming with new ideas and hard 
 problems. He had already mastered the most advanced scientific works 
 of his time — Kepler's " Optics," Descartes's " Analytical Geometry " 
 and Wallis's "Arithmetica Infinitorum." In reading, Newton was in 
 the habit of noting what seemed to him capable of improvement. At 
 this time (1666) he had already projected experiments in optics which 
 were to be the first of his achievements to make him known to the world. 
 In. mathematics he had originated the binomial theorem and had laid 
 the foundations of the infinitesimal calculus. Armed with this new 
 weapon of analysis, Newton pushed his mathematical researches in 
 many directions, solving with ease problems that had so far baffled 
 attack. Whatever he touched turned to gold under his hand. So 
 rapidly did his mind work that he seems not to have needed to work 
 out each step in detail ; his printed papers sometimes read like a list of 
 answers to difficult propositions. For example, he presents a classifica- 
 tion of cubic curves, giving seventy classes in all. Yet in all this list 
 there is no suggestion of the process by which the results were obtained. 
 Among the books that Newton read was Galileo's " Dialogues on 
 Motion," and here as elsewhere he found abundant material for work. 
 In this field of mechanics his mind worked with its usual clearness and 
 
20 OLIVET COLLEGE BULLETIN 
 
 rapidity. He restated the laws of motion in such clear and simple 
 terms that for two and a half centuries no word or line has been 
 changed. Bringing to bear his new calculus he readily solved the 
 problem of falling bodies, and in 1666 discovered the laws of circular 
 motion, seven years before they were published by Huygens in 1673. 
 
 To such a wide reader and deep thinker as Newton, the problem 
 of " gravity " would appeal with keen interest. It would have been 
 but natural that he should have gathered together all that was avail- 
 able of the literature of the subject. Thus he was familiar with 
 Kepler's views expressed in the following citation : 
 
 The true theory of gravity is founded on the following axioms. Gravity is 
 a mutual affection between cognate bodies toward union or conjunction, similar 
 to the magnetic virtue. ... It the moon and the earth were not retained in 
 their orbits by their animal force or some other equivalent, the earth would 
 mount to the moon by a fifty-fourth part of their distance from each other, and 
 the moon would fall toward the earth through the other fifty-three parts, that 
 is, assuming that the substance of the earth is of the same density. . . . The 
 sphere of the attractive virtue which is in the moon extends to the earth and 
 entices up the waters, but as the moon flies rapidly across the zenith and the 
 waters can not follow so quickly, a flow of the ocean is occasioned toward the 
 westward. If the attractive virtue of the moon extends to the earth, it follows, 
 with greater reason, that the attractive virtue of the earth extends to the moon 
 and much farther, and, in short, nothing which consists of earthy substance, 
 however constituted, although thrown up to any height, can ever escape the 
 powerful operation of this attractive virtue. 
 
 Borelli (1608-1679) also expresses views no less explicit, and, in his 
 work, " On the Satellites of Jupiter," distinctly attributes the revolu- 
 tions of the heavenly bodies to the force of gravity. So also Bullialdus 
 wrote " that all force respecting the sun as its center, and depending 
 upon matter, must be in a reciprocally duplicate ratio of the distance 
 from the center." This last sentence is quoted from one of Newton's 
 letters, and shows how carefully he had read on the subject. 
 
 Of Newton's immediate contemporaries, Eobert Hooke and Edmund 
 Halley were actively working in this field. Hooke (1635-1702) espe- 
 cially is ambitious to secure the honor of the solution of the problem the 
 answer to which he reads almost exactly right, but the proof of which — 
 poor man — he can not give. Failing in the demonstration himself, he 
 talks on the subject, about the subject, and all over the subject, in the 
 meetings of the Boyal Societ)^, in his papers and in his letters. So full 
 of it is he that he imagines that whatever any one else does is stolen from 
 him. Finally Sir Cristopher Wren offers him a prize if in two months 
 he will produce the boasted of solution. None is forthcoming and 
 history must write Hooke down as a most ardent worker and ingenious 
 man, but as totally unequal to the great task imposed upon Newton. 
 
 Halley is more modest; he applies the laws of circular motion pub- 
 lished by Huygens in 1673, sees clearly thnt t)ie law of inverse squares 
 
THE GENESIS OF THE LAW OF GRAVITY 
 
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 H^'4 
 
 1 
 
 ^H 
 
 H 
 
 77 [mBm' 
 
 /ml 
 
 
 ^B 
 
 ^^.^hH 
 
 iM 
 
 ■■■j 
 
 B^ 
 
 
 
 ^1 
 
 B 
 
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 Newton. 
 
 must hold good, does liold good for the circular orbit; sees also from 
 Kepler's third law that if it can be a|.i]ilied to the elliptical orbit as well 
 then all the planets immediately fall into that celestial harmony pre- 
 dicted by Pythagoi'as two millenniums before. The law holds for the 
 circle, does it not hold for the ellipse also? We can imagine with what 
 nervous eagerness Halley argues the question with Wren and Hooke 
 and then — Heaven-inspired thought — posts him down to Cambridge tc 
 consult Newton. This was in August, 1684. 
 
 We must now rapidly review Newton's own work during the twentj 
 years following his graduation from Cambridge in 1665. From thf 
 
2 2 OLIVET COLLEGE BULLETIN 
 
 very beginning he was interested in this particular problem of gravity, 
 but it was only one of many. Moreover, his was not a mind to stop 
 short of the full and complete solution. This force of gravity— if it 
 be this force that governs the universe— must be expressed by an exact 
 law; he sees more clearly than any one else what is involved. So he 
 ponders over tlie problem, and one day — would that we knew the date 
 ^he is seated in his garden studying, beside him his books and papers. 
 In the sky is the pale moon and as Newton gazes upon her he ponders 
 
 Solar System aftee Newton. 
 
 on the world-old problem, this riddle of the ages. What force holds 
 that moon forever circling about the earth? An apple falls to the 
 ground beside him and its thud awakens a train of thought in his mind. 
 Can it be the same force in the two cases — is the moon but a larger 
 apple forever falling toward the earth, urged by the force of gravity, 
 and forever receding from the earth, urged by her own uniform motion ? 
 Fascinated by the thought, Newton sets to calculating. He has studied 
 out the laws of uniform motion and of accelerated motion — now he 
 combines the two and gets the law of circular motion. He draws a 
 
THE GENESIS OF THE LAW OF GRAVITY 23 
 
 circle to represent the moon's orbit and calculates by what amount the 
 moon ought to fall toward the earth in a minute, assuming that its 
 distance from the earth is that given in the books. In his own words 
 he finds the figures " to answer pretty nearly." But this does not 
 satisfy him ; to a mind like Newton's " pretty nearly " is as bad as " not 
 at all," so he lays aside his papers until more exact data are at hand. 
 He has, however, made the first stage of the journey toward the goal. 
 This was in the plague year, 1666. As soon as the university is again 
 convened, ISTewton returns to Cambridge and for a number of years 
 is engrossed in the study of optics. In 1672 he is momentarily re- 
 minded of the problem while editing a revised edition of Varenius's 
 " Geography." In this he gives the accepted value for the earth's 
 degree sixty-one and one half miles. This was probably the value 
 Newton used in his calculations of 1666 and which fitted "pretty well," 
 as he said. In 1679-80 Newton has an unwilling and one-sided corre- 
 spondence with Hooke relating to the theory of projectiles, and in 
 which the subject of gravity is involved. 
 
 We may be sure that during these years Newton had many times 
 analyzed the grand problem of solar gravity and had carefully noted 
 just what was involved therein. We may even venture to note what 
 must have been his thoughts. If, he would say to himself, it be gravity 
 that rules the motion of the moon, then I must prove the following: 
 
 1. Gravity must act on all kinds of matter alike, for the earth is a 
 composite body, and presumably the moon also. 
 
 2. We know with a fair degree of accuracy that the moon is sixty- 
 one earth-radii from us, but to make any calculation, this distance must 
 be known in feet. Hence it is important that measurements of the 
 size of the earth be made with the greatest care. 
 
 3. The same law should extend to the planets also, but the planetary 
 orbits are ellipses, hence I must prove that the ellipse is a possible or 
 necessary orbit under such a law of force. 
 
 4. I must determine some point from which measurements of dis- 
 tance between earth and moon are to be made, e. g., shall it be from 
 the centers of these bodies? Also, does the same law of force hold 
 good over the whole distance, or is it modified as the surface of the 
 earth or moon is approached ? 
 
 Whether or no Newton set the matter in orderly array, it is clear 
 from his papers and letters that each of these points was considered. 
 Thus he proves the first point by an exhaustive series of experiments 
 on pendulums in which he varies the material of which the pendulum 
 is made, proving clearly, " by experiments made with the greatest 
 accuracy, the quantity of matter in bodies to be proportional to their 
 weights." The converse must also be true — the weight or pull of 
 gravity on bodies is proportional to their mass or quantity of mat- 
 
2 4 OLIVET COLLEGE BULLETIN 
 
 ter.i The second point Newton did not himself attack, but in 1682, 
 when attending a meeting of the Eoyal Society in London, he heard of 
 Picard's recent measurements of the eartli's degree. On returning to 
 Cambridge he inserted the new value in his old calculations of 1665, 
 measuring the distance from earth center to moon center. Finding 
 as he advanced that the result was manifestly going to produce the 
 long-wished-for answer, he found it impossible — so the story goes — to 
 proceed. With the aid of a friend the calculation was completed, and 
 Newton had reached another milestone on the way towards his cherished 
 goal. The figures tally exactly — has he not solved the problem and 
 may he not proclaim the answer to a waiting world ? None but Newton 
 knew the distance yet to be traveled before complete success should 
 be his. Nothing short of this could satisfy his truth-loving mind, and 
 the world must wait. The third point may be stated thus: " Given a 
 central force varying as the inverse square of the distance, show that 
 the orbit is an ellipse with the force-center at one focus." This Newton 
 did before the year 1684, for in August of this year, when Halley, dis- 
 gusted with Hooke's bombast, came to Cambridge, he asked Newton 
 without delay the following question : " What path will a body describe 
 if it be attracted by a center with a force varying as the inverse square 
 of the distance ? " To this Newton at once replied, " An ellipse with 
 the center of force at one focus." " How on earth do you know ? " 
 exclaimed Halley in amazement and delight. " Why, I have calculated 
 it," and Newton rummaged for the paper. Failing to find it, he promised 
 to forward it to Halley by post. This promise Newton fulfilled in 
 November. It is not known how much ground was covered in this 
 paper, but, of course, the desired demonstration of the third point 
 above noted was given. Newton must now have realized that he must 
 solve the fourth point and thus complete the work so nearly finished. 
 Something of this may have been expressed in his letters to Halley, 
 for in December, 1684, Halley again visited him and urged him to 
 continue his investigations. Thus far he had shown that Kepler's laws 
 called for the inverse square law of gravity — that Picard's value of 
 the earth's radius fitted exactly into the theory. It but remained to 
 prove that he is correct in taking the distance from center to center 
 of the earth and moon. For weeks and months he works over this 
 proof and finally, some time in 1685, it yields to his unremitting toil. 
 The approximate date of the achievement we know from a letter of 
 Newton's to Halley dated June 26, 1686, in which he says, " I never 
 extended the duplicate proportion lower than to the superfices of the 
 earth, and before a certain demonstration I found the last year, have 
 suspected it not to reach accurately enough down so low." The answer 
 mathematically proved in Prop. LXXIV. of Book I. of the " Principia," 
 
 '"Principia," Book II., Prop. XXIV., Theorem XIX. 
 
TEE GENESIS OF THE LAW OF GRAVITY 25 
 
 is that a sphere attracts all outside bodies as if its mass were concen- 
 trated at its center. 
 
 Thus he reached his goal at last, and after twenty years of work, 
 ranging over many subjects, the key of the universe lies in Newton's 
 hand. Surely, now, he will publish it and proclaim its discovery to 
 the world. Not so; he must first have the joy of undisturbed posses- 
 sion. Also there is much more to be done. The law he has proved 
 is an " open sesame " to wider knowledge. Or, to cliange the figure, 
 it is as if a mountain climber, who has toiled upward and upward, now 
 stands at last on the topmost heiglit. As he is climbing he thinks that 
 if he can but gain the summit it will be enough — he will be content 
 and rest. The toiling climber does not realize what awaits him at the 
 top, until the whole panorama of plain and mountain, of crag and 
 canyon, bursts upon his astonished sight. With this before him he 
 forgets his toil, forgets to rest and devours the view. So with Newton, 
 having at last mastered the central law upon which the universe swings, 
 he saw the members of the solar system sweeping in orderly grandure 
 through space, he saw this law governing every motion of every satellite 
 and comet, accounting for the nutations and perturbations, which be- 
 fore seemed to make order impossible. He saw it causing the tides 
 with the rising and setting of the sun and moon. All this and more 
 he saw, and we can not wonder that instead of rushing into print, he 
 shut himself up and worked and thouglit and wrote, and calculated 
 and worked and thought and wrote. 
 
 For two years he labored, sleeping little, eating little, always lost 
 in thought. Often, it is said, on rising, lie would sit for hours half 
 dressed upon his bedside. Often for days, lie would seem oblivious 
 to all external events. The following story well illustrates his abstrac- 
 tion. One day a friend, Dr. Stukely, called and found Newton's 
 solitary dinner ready on the table. After waiting a long while. Dr. 
 Stukely thought to play a joke on Newton, which he proceeded to do 
 by eating his dinner for him. Ilaving done so, he rearranged the table, 
 covering the dishes so that it would not appear that anything had 
 happened. At length Newton appeared, and, after greeting his friend, 
 sat down to dinner, but, on lifting the cover, said in surprise, " Dear 
 me ! I thought I had not dined, but I see I have." 
 
 So it went on for two full years, until Newton felt that his work 
 was done. He divided it into three books. The first is entitled The 
 Mathematical Pi'inciples of Natural Philosophy, and comprises about 
 two hundred and fifty pages. It reminds one of a geometry, with its 
 propositions, theorems, scholiums and problems. The first book is 
 divided into fourteen sections and contains ninety-seven propositions, 
 fifty theorems and forty-seven problems. Book IT. discusses The 
 Motions of Bodies. Here are found fifty-three propositions, forty-one 
 
2 6 OLIVET COLLEGE BULLETIN 
 
 theorems and twelve problems. Book III. has fewer diagrams, less 
 mathematics and more discussion. The principles of natural philosophy 
 are applied to the explanation of the solar system, and such topics as 
 comets and tides are carefully treated. There are forty-two proposi- 
 tions, twenty-two problems and twenty theorems. The whole work 
 covers 507 printed pages, and has a total of 192 propositions, 113 prob- 
 lems and 79 theorems, besides lemmas and scholiums in abundance. 
 
 Oliver Lodge in an outline of the " Principia " selects seventeen 
 points for special emphasis. Of these a few may be reviewed. 
 
 1. Newton shows from Kepler's laws the following: (a) From the 
 first law, that the law of gravity is inversely as the square of the 
 distance. (&) From the second law, that this force is directed toward 
 the sun as center, (c) From the third law, that all the planets are acted 
 on by the same law of gravity ; i. e., that the law of gravity extends to 
 the uttermost confines of the solar system. 
 
 2. From the length of the year and the distance of any planet 
 from the sun Newton calculates the planet's mass, using the earth's 
 mass as a unit. 
 
 3. He recognized the comets as members of the solar family and 
 showed how to calculate their orbits.^ 
 
 4. He showed that the earth, as a result of its rotation, must be 
 flattened at the poles, and calculated the amount (28 miles). 
 
 5. He laid the foundation for a complete theory of the tides. 
 
 We have but noted the high lights, as it were, of Newton's work. 
 No wonder that he became lost to external events as his mind grappled 
 with problem after problem, and one by one lay bare the secrets of the 
 universe. As an example of the style in which the " Principia " is 
 written, we may quote from the beginning of the third book where he 
 lays down rules for reasoning in philosophy: 
 
 Rule I. We are to admit no more causes of natural things than such aa 
 
 are both true and sufficient to explain their appearances. To this purpose the 
 
 philosophers say that nature is pleased with simplicity and affects not the 
 pomp of superfluous causes. 
 
 The "Principia" was finished in the spring of 1686. It was pub- 
 lished by order of the Eoyal Society, being issued from the press in 
 July, 1687. Newton, from being a little-known member of the faculty 
 of Cambridge, was at once recognized as the foremost scientist of the 
 world. Honors were showered upon him. He was sent to parliament. 
 He was elected president of the Eoyal Society. The queen made him 
 a knight of the realm. He was given a lucrative position under gov- 
 ernment and moved to London. His work for science was finished, 
 and for forty years he reaped the reward of his labors. 
 
 2 The first cometary orbit to be calculated was done by Halley upon the 
 comet bearing his name, which last year made its third return since Newton's day. 
 
THE GENESIS OF THE LAW OF GRAVITY 27 
 
 What Newton accomplished in optics and in mathematics would 
 entitle him to high rank in the world of science. Of his work in 
 mathematics the German scholar, Leibnitz, said, " Taking mathematics 
 from the beginning of the world to the time when Newton lived, what 
 he had done was much the better half." 
 
 The work included in the " Principia " was most of it done between 
 1680 and 1686. By far the greater part was done during the last two 
 years of this short period, or between the forty-second and forty-fourth 
 years of his age. This work, in its scope, in its far-reaching impor- 
 tance, and in the order of mind required for its accomplishment, raises 
 Newton not merely to the first rank of the world's great minds, but 
 compels the world to admit no second in his class. His genius shone 
 resplendent even in his own day. We have already quoted Leibnitz. 
 A French admirer wrote to an English correspondent, " Does Mr. 
 Newton eat, drink, sleep like other men? I picture him to myself 
 as a celestial genius, entirely removed from the restrictions of ordinary 
 matter." Says Lagrange (1736-1813), a great French mathematician, 
 " Newton was the greatest genius that ever existed, and the most 
 fortunate, for we can not find more than once a system of the world 
 to establish." Tlie English writer, Whewell (1794-1866), writes, 
 " The (Law of Gravitation) is indisputably and incomparably the 
 greatest scientific discovery ever made, whether we look at the advance 
 which it involved, the extent of truth disclosed, or the fundamental 
 and satisfactory nature of this truth." Pope in a striking epigram 
 expresses the same thought: 
 
 Nature and Nature's laws lay liid in night; 
 God said, Let Newton be, and all was light. 
 
 La Place, who did much work along the lines laid down by Newton, 
 says of tlie " Principia " : " P''he universality and generality of the dis- 
 coveries it contains, the number of profound and original views respect- 
 ing the system of tlie universe it presents, and all presented with so 
 much elegance, will insure to it a lasting preeminence over all other 
 productions of tlie human mind." 
 
 Sir Oliver Lodge says of Newton : " In science tlie impression he 
 makes upon me is only expressed by the words ' inspired,' ' super- 
 human.' " 
 
 Of his own work Newton says: "I know not what the world will 
 think of my laboj's, hut to myself it seems that T have been but as a child 
 playing on the seashore ; now finding some pebble rather more polished, 
 and now some shell ratlier more agreeably variegated than another, 
 while the immense ocean of truth extended itself unexplored before 
 me." AVhen asked how he made his discoveries, he replied : " By always 
 thinking unto them. I keep the subject constantly before me, and 
 
2 8 OLIVET COLLEGE BULLETIN 
 
 wait till the first dawnings open slowly by little and little into a full 
 and clear light." Commenting upon this somewhat modest remark 
 Lodge says : " That is the way — quiet, steady, continuous thinking, 
 uninterrupted and unharassed brooding. Much may be done under 
 these conditions ; much ought to be sacrificed to obtain these conditions. 
 All the best thinking work of the world has been thus done." 
 
 In closing, let us pause and consider the state of knowledge before 
 and after Newton. Before him are the foreshadowings of Copernicus, 
 the dim gropings of Kepler, the elementary truths of Galileo, the 
 flashes of Borelli and Huygens, the fantastic speculations of Descartes; 
 after him is a magnificent and comprehensive system of well-ordered 
 knowledge. As we contemplate this we can understand the significance 
 of the inscription on Newton's tomb. " Let mortals congratulate them- 
 selves that so great an ornament of the human race has existed." 
 
Cornell University Library 
 QC 178.S54 
 
 The genesis of the law of gravity. 
 
 3 1924 012 340 638