every line or quantity is generated, he gave the name of FLUXIONS, and to the lines or quantities themselves, that of FLUENTS.A discovery that successively baffled the acutest and strongestLIFE OF SIR ISAAC NEWTON. 15intellects : that, variously modified, has proved of incalculableservice in aiding to develope the most abstruse and the highestruths in Mathematics and Astronomy : and that was of itselfenough to render any name illustrious in the crowded Annals ofScience.At this period, the most distinguished philosophers were directing all their energies to the subject of light and the improvementof the refracting telescope. Newton, having applied himself tothe grinding of "optic glasses of other figures than spherical," experienced the impracticability of executing such lenses ; and conjectured that their defects, and consequently those of refractingtelescopes, might arise from some other cause than the imperfectconvergency of rays to a single point. He accordingly "procureda triangular glass prism to try therewith the celebrated phenomena of colours." His experiments, entered upon with zeal, andconducted with that industry, accuracy, and patient thought, forwhich he was so remarkable, resulted in the grand conclusion,that LIGHT WAS NOT HOMOGENEOUS, BUT CONSISTED OF RAYS,SOME OF WHICH WERE MORE REFRANGIBLE THAN OTHERS. Thisprofound and beautiful discovery opened up a new era in theHistory of Optics. As bearing, however, directly upon the construction of telescopes, he saw that a lens refracting exactly like a prismwould necessarily bring the different rays to different foci, atdifferent distances from the glass, confusing and rendering thevision indistinct. Taking for granted that all bodies producedspectra of ^jtial length, he dismissed all further consideration ofthe refracting instrument, and took up the principle of reflection.Rays of all colours, he found, were reflected regularly, so that theangle of reflection was equal to the angle of incidence, and hencehe concluded that ojitical instruments might be brought to anydegree of perfection imaginable, provided reflecting specula ofthe requisite figure and finish could be obtained. At this stageof his optical researches, he was forced to leave Cambridge onaccount of the plague which was then desolating England.He retired to Woolsthorpe. The old manor-house, in which hewas born, was situated in a beautiful little valley, on the west sideof the river Witham ; and here in the quiet home of his boyhood,216 LIFE OF SIR ISAAC NEWTON.he passed his days in serene contemplation, while the stalkingpestilence was hurrying its tens of thousands into undistinguishable graves.Towards the close of a pleasant day in the early autumn of1666, he was seated alone beneath a tree, in his garden, absorbedin meditation. He was a slight young man ;in the twenty-fourthyear of his age ; his countenance mild and full of thought. Fora century previous, the science of Astronomy had advanced withrapid strides. The human mind had risen from the gloom andbondage of the middle ages, in unparalleled vigour, to unfold thesystem, to investigate the phenomena, and to establish the lawsof the heavenly bodies. Copernicus, Tycho Brahe, Kepler,Galileo, and others had prepared and lighted the way for himwho was ta give to their labour its just value, and to their geniusits true lustre. At his bidding isolated facts were to take orderas parts of one harmonious whole, and sagacious conjectures growluminous in the certain splendour of demonstrated truth. Andthis ablest man had come was here. His mind, familiar withthe knowledge of past effort, and its unequalled faculties developed in transcendant strength, was now moving on to the verythreshold of Its grandest achievement. Step by step the untrodden path was measured, till, at length, the entrance seemed disclosed, and the tireless explorer to stand amid the first openingwonders of the universe.The nature of gravity that mysterious power which causesall bodies to descend towards the centre of the earth had, indeed, dawned upon him. And reason busily united link to linkof that chain which was yet to be traced joining the least to thevastest, the most remote to the nearest, in one harmonious bond.From the bottoms of the deepest caverns to the summits of thehighest mountains, this power suffers no sensible change : may notits action, then, extend to the moon ? Undoubtedly : and furtheireflection convinced him that such a power might be .sufficient forretaining that luminary in her orbit round the earth. But, thoughthis power suffers no sensible variation, in the little change ofdistance from the earth s centre, at which we may place our-. lves, yet, at the distance of the moon, :miy not its force undergoLIFE OF SIR ISAAC NEWTON. 17more or less diminution ? The conjecture appeared most probable : and, in order to estimate what the degree of diminutionmight be, he considered that if the moon be retained in her orbitby the force of gravity, the primary planets must also be carriedround the sun by the like power; and, by comparing the periodsof the several planets with their distances from the sun, he foundthat, if they were held in their courses by any power like gravity,its strength must decrease in the duplicate proportion of the increase of distance. In forming this conclusion, he supposed theplanets to move in perfect circles, concentric to the sun. Nowwas this the law of the moon s motion ? Was such a force, emanating from the earth and directed to the moon, sufficient, whendiminished as the square of the distance, to retain her in herorbit ? To ascertain this master-fact, he compared the spacethrough which heavy bodies fall, in a second of time, at a givendistance from the centre of the earth, namely, at its surface, withthe space through which the moon falls, as it were, to the earth,in the same time, while revolving in a circular orbit. He wasabsent from books ; and, therefore, adopted, in computing theearth s diameter, the common estimate of sixty miles to a degreeof latitude as then in use among geographers and navigators.The result of his calculations did not, ot course, answer his expectations ; hence, he concluded that some other cause, beyond thereach of observation analogous, perhaps, to the vortices of Descartes joined its action to that of the power of gravity upon thernooil. Though by no means satisfied, he yet abandoned awhilefurther inquiry, and remained totally silent upon the subject.These rapid marches in the career of discovery, combined withthe youth of Newton, seem to evince a penetration the mostlively, and an invention the most exuberant. But in him therewas a conjunction of influences as extraordinary as fortunate.Study, unbroken, persevering and profound carried on its informing and disciplining work upon a genius, natively the greatest,and rendered freest in its movements, and clearest in its vision,through the untrammelling and enlig} tenirig power of religion.And, in this happy concurrence, are to be sought the elements ofthose amazing abilities, which, grasping, with equal facility, the18 LIFE OF SIR ISAAC NEWTON.minute and the stupendous, brought these successively to light,and caused science to make them her own.In 1667, Newton was made a Junior Fellow ; and, in the yearfollowing, he took his degree of Master of Arts, and was appointed to a Senior Fellowship.On his return to Cambridge, in 1668, he resumed his opticallabours. Having thought of a delicate method of polishing metal,he proceeded to the construction of his newly projected reflecting telescope ; a small specimen of which he actually made withhis own hands, It was six inches long ; and magnified aboutforty times ;a power greater than a refracting instrument of sixfeet tube could exert with distinctness. Jupiter, with his foursatellites, and the horns, or moon-like phases of Venus wereplainly visible through it. THIS WAS THE FIRST REFLECTINGTELESCOPE EVER EXECUTED AND DIRECTED TO THE HEAVENS.He gave an account of it, in a letter to a friend, dated February 23d,1668-9 a letter which is also remarkable for containing the firsallusion to his discoveries "concerning the nature of light." Encouraged by the success of his first experiment, he again executedwith his own hands, not long afterward, a second and superiorinstrument of the same kind. The existence of this having cometo the knowledge of the Royal Society of London, in 1671, theyrequested it of Newton for examination. He accordingly sent itto them, It excited great admiration; it was shown to the king*a drawing and description of it was sent to Paris ; and the telescopeitself was carefully preserved in the Library of the Society.Newton lived to see his invention in public use, and of eminentservice in the cause of science.In the spring of 1669, he wrote to his friend Francis Aston,Esq., then about setting out on his travels, a letter of advice anddirections, it was dated May 18th, and is interesting as exhibiting some of the prominent features in Newton s character.Thus :" Since in your letter you give me so much liberty of spendingmy judgment about what may be to your advantage in travelling,1 shall do it more freely than perhaps otherwise would have beendecent, Fir,ct, then, I will lay down some general rules, most ofLIFE OF SIR ISAAC NEWTON. 19which, I bolieA e, you have considered already ; but if any ofthem be new to you, they may excuse the rest ;if none at all,yet is my punishment more in writing than yours in reading."When you come into any fresh company. 1. Observe theirhumours. 2. Suit your own carriage thereto, by which insinuation you will make their converse more free and open. 3. Letyour discourse be more in queries and doubtings than peremptoryassertions or disputings, it being the design of travellers to learn,not to teach. Besides, it will persuade your acquaintance thatyou have the greater esteem of them, and so make them moreready to communicate what they know to you ; whereas nothingsooner occasions disrespect and quarrels than peremptoriness.You will find little or no advantage in seeming wiser or muchmore ignorant than your company. 4. Seldom discommend anything though never so bad, or do it but moderately, lest you beunexpectedly forced to an unhandsome retraction. It is safer tocommend any thing more than it deserves, than to discommenda thing so much as it deserves; for commendations meet notso often with oppositions, or, at least, are not usually so ill resented by men that think otherwise, as discommendations ; andyou will insinuate into men s favour by nothing sooner than seeming to approve and commend what they like; but beware odoing it by comparison. 5. If you be affronted, it is better, in cforeign country, to pass it by in silence, and with a jest, thoughwith some dishonour, than to endeavour revenge ; for, in the firstcase, your credit s ne er the worse when you return into England,or come into other company that have not heard of the quarrel.But, in the second case, you may bear the marks of the quarrelwhile you live, if you outlive it at all. But, if you find yoursellunavoidably engaged, tis best, I think, if you can command yourpassion and language, to keep them pretty evenly at some certainmoderate pitch, not much heightening them to exasperate youradversary, or provoke his friends, nor letting them grow overmuchdejected to make him insult. In a word, if you can keep reasonabove passion, that and watchfulness will be your best defendants.To which purpose you may consider, that, though such excusesis this He provok t me so much I could not forbear may pass20 LIFE OF SIR ISAAC NEWTON.among friends, yet amongst strangers they are insignificant, inaonly argue a traveller s weakness." To these I may add some general heads for inquiries or observations, such as at present I can think on. As, 1. To observethe policies, wealth, and state affairs of nations, so far as a solifary traveller may conveniently do. 2. Their impositions uponall sorts of people, trades, or commodities, that are remarkable.3. Their laws and customs, how far they differ from ours. 4.Their trades and arts wherein they excel or come short of us inEngland. 5. Such fortifications as you shall meet with, theirfashion, strength, and advantages for defence, and other such military affairs as are considerable. 6. The power and respect belonging to their degrees of nobility or magistracy. 7. It will notbe time misspent to make a catalogue of the names and excellencies of those men that are most wise, learned, or esteemed in anynation. 8. Observe the mechanism and manner of guiding ships.9. Observe the products of Nature in several places, especially inmines, with the circumstances of mining and of extracting metalsor minerals out of their ore, and of refining them ; and if youmeet with any transmutations out of their own species intoanother (as out of iron into copper, out of any metal into quicksilver, out of one salt into another, or into an insipid body, &c.),those, above all, will be worth your noting, being the most luciferous,and many times lucriferous experiments, too, in philosophy.10. The prices of diet and other things. 11. And the staplecommodities of places." These generals (such as at present I could think of), if theywill serve for nothing else, yet they may assist you in drawing upa model to regulate your travels by. As for particulars, these thatfollow are all that 1 can now think of, viz.; whether at Schemnitium,in Hungary (where there are mines of gold, copper, iron,vitriol, antimony, &c.). they change iron into copper by dissolvingt in a vitriolate water, which they find in cavities of rocks in themines, and then melting the slimy solution in a stroi ig fire, whichin the cooling proves copper. The like is said to be done in otherplaces, which I cannot now remember ; perhaps, too, it may belone in Italy. For about twenty or thirty years agone there wasLIFE OF SIR ISAAC NEWTON, 21a certain vitriol came from thence (called Roman vitriol), but ofa nobler virtue than that which is now called by that name ;which vitriol is not now to be gotten, because, perhaps, they makea greater gain by some such trick as turning iron into copperwith it than by selling it. 2. Whether, in Hungary, Sclavonia,Bohemia, near the town Eila, or at the mountains of Bohemianear Silesia, there be rivers whose waters are impregnated withgold ; perhaps, the gold being dissolved by some corrosive waterlike aqua regis, and the solution carried along with the stream,that runs through the mines. And whether the practice of layingmercury in the rivers, till it be tinged with gold, and then straining the mercury through leather, that the gold may stay behind,be a secret yet, or openly practised. 3. There is newly contrived, in Holland, a mill to grind glasses plane withal, and Ithink polishing them too ; perhaps it will be worth the while to seeit. 4. There is in Holland one Borry, who some years sincewas imprisoned by the Pope, to have extorted from him secrets(as I am told) of great worth, both as to medicine and profit, buthe escaped into Holland, where they have granted him a guard.I think he usually goes clothed in green. Pray inquire what youcan of him, and whether his ingenuity be any profit to the Dutch.You may inform yourself whether the Dutch have any tricks tokeep their ships from being all worm-eaten in their voyages tothe Indies. Whether pendulum clocks do any service in findingout the longitude, &c." I am very weary, and shall not stay to part with a longcompliment, only I wish you a good journey, and God be withyou."It was not till the month of June, 1669, that our author madeknown his Method of Fluxions. He then communicated thework which he had composed upon the subject, and entitled,ANALYSIS PER EQUATIONES NUMERO TERMINORUM INFINITAS,to his friend Dr. Barrow. The latter, in a letter dated 20th of thesame month, mentioned it to Mr. Collins, and transmitted it tohim, on the 31st of July thereafter. Mr. Collins greatly approv>ed of the work ; took a copy of it; and sent the original backto Dr. Barrow. During the same and the two following years, Mr< LIFE OF SIR ISAAC NEWTON.Collins, by his extensive correspondence, spread the knowledgeof this discovery among the mathematicians in England, Scotland,France, Holland and Italy.Dr. Barrow, having resolved to devote himself to Theology,resigned the Lucasian Professorship of Mathematics, in 1669, infavour of Newton, who accordingly received the appointment tothe vacant chair.During the years 1669, 1670, and 1671, our author, as suchProfessor, delivered a course of Optical Lectures. Though thesecontained his principal discoveries relative to the different refrangibilityof light, yet the discoveries themselves did not become publicly known, it seems, till he communicated them to theRoyal Society, a few weeks after being elected a member thereof, in the spring of 1671-2. He now rose rapidly in reputation,and was soon regarded as foremost among the philosophers of theage. His paper on light excited the deepest interest in the RoyalSociety, who manifested an anxious solicitude to secure the authorfrom the "arrogations of others," and proposed to publish hisdiscourse in the monthly numbers in which the Transactions weregiven to the world. Newton, gratefully sensible of these expressions of esteem, willingly accepted of the proposal for publication.He gave them also, at this time, the results of some further experiments in the decomposition and re-composition of light : thatthe same degree of refrangibility always belonged to the samecolour, and the same colour to the same degree of refrangibility :that the seven different colours of the spectrum were original, orsimple, and that whiteness^ or white light was a compound of allthese seven colours.The publication of his new doctrines on light soon called forthviolent opposition as to their soundness. Hooke and Huygensmen eminent for ability and learning were the most conspicuousof the assailants. And though Newton effectually silenced all hisadversaries, yet he felt the triumph of little gain in comparison.vith the loss his tranquillity had sustained. He subsequently renarkedin allusion to this controversy and to one with whomhe was destined to have a longer and a bitterer conflict " I wasso persecuted with discussions arising from the publication of m vLIFE OF SIR ISAAC NEWTON. 23theory ot light, that I blamed my own imprudence for partingwith so substantial a blessing as rny quiet to run after a shadow.7In a communication to Mr. Oldenburg, Secretary of the RoyalSociety, in 1672, our author stated many valuable suggestions relative to the construction of REFLECTING MICROSCOPES which heconsidered even more capable of improvement than telescopes.He also contemplated, about the same time, an edition of Kirickhuysens Algebra, with notes and additions; partially arranging,as an introduction to the work, a treatise, entitled, A Method ofFluxions ; but he finally abandoned the design. This treatise,however, he resolved, or rather consented, at a late period of hislife, to put forth separately ; and the plan would probably havebeen carried into execution had riot his death intervened. It wastranslated into English, and published in 1736 by John Colson,Professor of Mathematics in Cambridge.Newton, it is thought, made his discoveries concerning theINFLECTION and DIFFRACTION of light before 1674. The phenomena of the inflection of light had been first discovered morethan ten years before by Grimaldi. And Newton began by repeating one of the experiments of the learned Jesuit admittinga beam of the sun s light through a small pin hole into a darkchamber : the light diverged from the aperture in the form of a,cone, and the shadows of all bodies placed in this light werelarger than might have been expected, and surrounded with threecoloured fringes, the nearest being widest, and the most remotethe narrowest. Newton, advancing upon this experiment, tookexact measures of the diameter of the shadow of a human hair,and of the breadth of the fringes, at different distances behind it,and discovered that these diameters and breadths were not proportional to the distances at which they were measured. Hehence supposed that the rays which passed by the edge of thehair were deflected or turned aside from it, as if by a repulsiveforce, the nearest rays suffering the greatest, the more remote aless degree of deflection. In explanation of the coloured fringes,he queried : whether the rays which differ in refrangibility do notdiffer also in flexibility, and whether they are n<t, by these different inflections, separated from one another, so as after separa< LIFE OF SIR ISAAC NEWTON.tion to make the colours in the three fringes above described ?Also, whether the rays, in passing by the edges and sides olbodies, are not bent several times backwards and forwards withan eel-like motion the three fringes arising from three suchbendings ? His inquiries on this subject were here interruptedand fiever renewed.His Theory of the COLOURS of NATURAL BODIES was communicated to the Royal Society, in February, 1675. This is justlyregarded as one of the profoundest of his speculations. The fundamental principles of the Theory in brief, are : That bodiespossessing the greatest refractive powers reflect the greatestquantity of light ; and that, at the confines of equally refractingmedia, there is no reflection. That the minutest particles of almost all natural bodies are in some degree transparent. Thatbetween the particles of bodies there are pores, or spaces, eitherempty or filled with media of a less density than the particlesthemselves. That these particles, and pores or spaces, have somedefinite size. Hence he deduced the Transparency, Opacity, andcolours of natural bodies. Transparency arises from the particlesand their pores being too small to cause reflection at their common surfaces the light all passing through ; Opacity from theopposite cause of the particles and their pores being sufficientlylarge to reflect the light which is "stopped or stifled7by themultitude of reflections ; and colours from the particles, according to their several sizes, reflecting rays of one colour and transmitting those of another or in other words, the colour thatmeets the eye is the colour reflected, while all the other rays aretransmitted or absorbed.Analogous in origin to the colours of natural bodies, he considered the COLOURS OF THIN PLATES. This subject was interest