In the first108of these letters Sir Isaac mentions that when he wrote his treatise about our system, viz. the Third Book of the Principia, “he had an eye upon such principles as might work, with considering men, for the belief of a Deity, and he expresses his happiness that it has been found useful for that purpose. In answering the first query of Dr. Bentley, the exact import of which we do not know, he states, that, if matter were evenly diffused through a finite space, and endowed with innate gravity, it would fall down into the middle of the space, and form one great spherical mass; but if it were diffused through an infinite space, some of it would collect into one mass, and some into another,so as to form an infinite number of great masses. In this manner the sun and stars might be formed if the matter were of a lucid nature. But he thinks it inexplicable by natural causes, and to be ascribed to the counsel and contrivance of a voluntary Agent, that the matter should divide itself into two sorts, part of it composing a shining body like the sun, and part an opaque body like the planets. Had a natural and blind cause, without contrivance and design, placed the earth in the centre of the moon’s orbit, and Jupiter in the centre of his system of satellites, and the sun in the centre of the planetary system, the sun would have been a body like Jupiter and the earth, that is, without light and heat, and consequently he knows no reason why there is only one body qualified to give light and heat to all the rest, but because the Author of the system thought it convenient, and because one was sufficient to warm and enlighten all the rest.
To the second query of Dr. Bentley, he replies that the motions which the planets now have could not spring from any natural cause alone, but were impressed by an intelligent Agent. “To make such a system with all its motions required a cause which understood and compared together the quantities of matter in the several bodies of the sun and planets, and the gravitating powers resulting from thence; the several distances of the primary planets from the sun, and of the secondary ones from Saturn, Jupiter, and the earth, and the velocities with which those planets could revolve about those quantities of matter in the central bodies; and to compare and adjust all these things together in so great a variety of bodies, argues that cause to be not blind and fortuitous, but very well skilled in mechanics and geometry.”
In the second109letter, he admits that the sphericalmass formed by the aggregation of particles would affect the figure of the space in which the matter was diffused, provided the matter descends directly downwards to that body, and the body has no diurnal rotation; but he states, that by earthquakes loosening the parts of this solid, the protuberance might sink a little by their weight, and the mass by degrees approach a spherical figure. He then proceeds to correct an error of Dr. Bentley’s in supposing that all infinites are equal. He admits that gravity might put the planets in motion, but he maintains that, without the Divine power, it could never give them such a circulating motion as they have about the sun, because a proper quantity of a transverse motion is necessary for this purpose; and he concludes that he is compelled to ascribe the frame of this system to an intelligent Agent.
The third letter contains opinions confirming or correcting several positions which Dr. Bentley had laid down, and he concludes it with a curious examination of the opinion of Plato, that the motion of the planets is such as if they had been all created by God in some region very remote from our system, and let fall from thence towards the sun, their falling motion being turned aside into a transverse one whenever they arrived at their several orbits. Sir Isaac shows that there is no common place such as that conjectured by Plato, provided the gravitating power of the sun remains constant; but that Plato’s affirmation is true if we suppose the gravitating power of the sun to be doubled at that moment of time when they all arrive at their several orbits. “If we suppose,” says he, “the gravity of all the planets towards the sun to be of such a quantity as it really is, and that the motions of the planets are turned upwards, every planet will ascend to twice its height from the sun. Saturn will ascend till he be twice as high from the sun as he is at present, and no higher; Jupiter will ascend ashigh again as at present, that is, a little above the orb of Saturn; Mercury will ascend to twice his present height, that is, to the orb of Venus; and so of the rest; and then, by falling down again from the places to which they ascended, they will arise again at their several orbs with the same velocities they had at first, and with which they now revolve.
“But if so soon as their motions by which they revolve are turned upwards, the gravitating power of the sun, by which their ascent is perpetually retarded, be diminished by one-half, they will now ascend perpetually, and all of them, at all equal distances from the sun, will be equally swift. Mercury, when he arrives at the orb of Venus, will be as swift as Venus; and he and Venus, when they arrive at the orb of the earth, will be as swift as the earth; and so of the rest. If they begin all of them to ascend at once, and ascend in the same line, they will constantly, in ascending, become nearer and nearer together, and their motions will constantly approach to an equality, and become at length slower than any motion assignable. Suppose, therefore, that they ascended till they were almost contiguous, and their motions inconsiderably little, and that all their motions were at the same moment of time turned back again, or, which comes almost to the same thing, that they were only deprived of their motions, and let fall at that time, they would all at once arrive at their several orbs, each with the velocity it had at first; and if their motions were then turned sideways, and at the same time the gravitating power of the sun doubled, that it might be strong enough to retain them in their orbs, they would revolve in them as before their ascent. But if the gravitating power of the sun was not doubled, they would go away from their orbs into the highest heavens in parabolical lines.”110
In the fourth letter111he states, that the hypothesis that matter is at first evenly diffused through the universe is in his opinion inconsistent with the hypothesis of innate gravity without a supernatural power to reconcile them, and therefore it infers a Deity. “For if there be innate gravity, it is impossible now for the matter of the earth and all the planets and stars to fly up from them, and become evenly spread throughout all the heavens without a supernatural power; and certainly that which can never be hereafter without a supernatural power, could never be heretofore without the same power.”
These letters, of which we have endeavoured to give a brief summary, will well repay the most attentive perusal by the philosopher as well as the divine. They are written with much perspicuity of language and great power of thought, and they contain results which incontestably prove that their author was fully master of his noblest faculties, and comprehended the profoundest parts of his own writings.112
The logical acuteness, the varied erudition, and the absolute freedom from all prejudice which shine throughout the theological writings of Newton, might have protected them from the charge of having been written in his old age, and at a time when a failure of mind was supposed to have unfitted him for his mathematical investigations. But it is fortunate for his reputation, as well as for the interests of Christianity, that we have been able to prove the incorrectness of such insinuations, and to exhibit the most irrefragable evidence thatall the theologicalwritingsof Newton were composed in the vigour of his life, and before the crisis of that bodily disorder which is supposed to have affected his reason. The able letters to Dr. Bentley were even written in the middle of that period when want of sleep and appetite had disturbed the serenity of his mind, and enable us to prove that this disturbance, whatever was its amount, never affected the higher functions of his understanding.
When a philosopher of distinguished eminence, and we believe not inimical to the Christian faith, has found it necessary to make a laboured apology for a man like Newton writing on theological subjects, and has been led to render that apology more complete by referring this class of his labours to a mind debilitated by age and weakened by its previous aberrations, it may be expected from an English biographer, and one who acknowledges the importance of revealed truth, and the paramount interest of such subjects above all secular studies, to suggest the true origin of Newton’s theological inquiries.
When a mind of great and acknowledged power first directs its energies to the study of the material universe, no indications of order attract his notice, and no proofs of design call forth his admiration. In the starry firmament he sees no bodies of stupendous magnitude, and no distances of immeasurable span. The two great luminaries appear vastly inferior in magnitude to many objects around him, and the greatest distances in the heavens seem even inferior to those which his own eye can embrace on the surface of the earth. The planets, when observed with care, are seen to have a motion among the fixed stars, and to vary in their magnitude and distances, but these changes appear to follow no law. Sometimes they move to the east, sometimes to the west, sometimes towards the north, and sometimes towards the south, and at other timesthey are absolutely stationary. No system, in short, appears, and no general law seems to direct their motions. By the observations and inquiries of astronomers, however, during successive ages, a regular system has been recognised in this chaos of moving bodies, and the magnitudes, distances, and revolutions of every planet which composes it has been determined with the most extraordinary accuracy. Minds fitted and prepared for this species of inquiry are capable of understanding the great variety of evidence by which the truth of the planetary system is established; but thousands of individuals who are even distinguished in other branches of knowledge are incapable of such researches, and view with a skeptical eye the great and irrefragable truths of astronomy.
That the sun is stationary in the centre of our system,—that the earth moves round the sun, and round its own axis,—that the earth is 8000 miles in diameter, and the sunone hundred and tentimes as large,—that the earth’s orbit is 190 millions of miles in breadth,—and that if this immense space were filled with light, it would appear only like a luminous point at the nearest fixed star,—are positions absolutely unintelligible and incredible to all who have not carefully studied the subject. To millions of our species, then, the great book of nature is absolutely sealed, though it is in the power of all to unfold its pages, and to peruse those glowing passages which proclaim the power and wisdom of its mighty Author.
The book of revelation exhibits to us the same peculiarities as that of nature. To the ordinary eye it presents no immediate indications of its Divine origin. Events apparently insignificant—supernatural interferences seemingly unnecessary—doctrines almost contradictory—and prophecies nearly unintelligible occupy its pages. The history of the fall of man—of the introduction of moraland physical evil—the prediction of a Messiah—the actual advent of our Saviour—his instructions—his miracles—his death—his resurrection—and the subsequent propagation of his religion by the unlettered fishermen of Galilee, are each a stumbling block to the wisdom of this world. The youthful and vigorous mind, when first summoned to peruse the Scriptures, turns from them with disappointment. It recognises in them no profound science—no secular wisdom—no Divine eloquence—no disclosures of nature’s secrets—no direct impress of an Almighty hand. But, though the system of revealed truth which this book contains is, like that of the universe, concealed from common observation, yet the labours of centuries have established its Divine origin, and developed in all its order and beauty the great plan of human restoration. In the chaos of its incidents we discover the whole history of our species, whether it is delineated in events that are past or shadowed forth in those which are to come,—from the creation of man and the origin of evil, to the extinction of his earthly dynasty and the commencement of his immortal career.
The antiquity and authenticity of the books which compose the sacred canon,—the fulfilment of its prophecies,—the miraculous works of its founder,—his death and resurrection, have been demonstrated to all who are capable of appreciating the force of historical evidence; and in the poetical and prose compositions of the inspired authors we discover a system of doctrine and a code of morality traced in characters as distinct and legible as the most unerring truths in the material world. False systems of religion have indeed been deduced from the sacred record,—as false systems of the universe have sprung from the study of the book of nature,—but the very prevalence of a false system proves the existence of one that is true; and though the two classes of facts necessarily depend on differentkinds of evidence, yet we scruple not to say that the Copernican system is not more demonstrably true than the system of theological truth contained in the Bible. If men of high powers, then, are still found, who are insensible to the evidence which sustains the system of the universe, need we wonder that there are others whose minds are shut against the effulgent evidence which intrenches the strongholds of our faith.
If such, then, is the character of the Christian faith, we need not be surprised that it was embraced and expounded by such a genius as Sir Isaac Newton. Cherishing its doctrines, and leaning on its promises, he felt it his duty, as it was his pleasure, to apply to it that intellectual strength which had successfully surmounted the difficulties of the material universe. The fame which that success procured him he could not but feel to be the breath of popular applause, which administered only to his personal feelings; but the investigation of the sacred mysteries, while it prepared his own mind for its final destiny, was calculated to promote the spiritual interests of thousands. This noble impulse he did not hesitate to obey, and by thus uniting philosophy with religion, he dissolved the league which genius had formed with skepticism, and added to the cloud of witnesses the brightest name of ancient or of modern times.
The minor Discoveries and Inventions of Newton—His Researches on Heat—On Fire and Flame—On Elective Attraction—On the Structure of Bodies—His supposed Attachment to Alchymy—His Hypothesis respecting Ether as the Cause of Light and Gravity—On the Excitation of Electricity in Glass—His Reflecting Sextant invented before 1700—His Reflecting Microscope—His Prismatic Reflector as a Substitute for the small Speculum of Reflecting Telescopes—His Method of varying the Magnifying Power of Newtonian Telescopes—His Experiments on Impressions on the Retina.
The minor Discoveries and Inventions of Newton—His Researches on Heat—On Fire and Flame—On Elective Attraction—On the Structure of Bodies—His supposed Attachment to Alchymy—His Hypothesis respecting Ether as the Cause of Light and Gravity—On the Excitation of Electricity in Glass—His Reflecting Sextant invented before 1700—His Reflecting Microscope—His Prismatic Reflector as a Substitute for the small Speculum of Reflecting Telescopes—His Method of varying the Magnifying Power of Newtonian Telescopes—His Experiments on Impressions on the Retina.
In the preceding chapters we have given an account of the principal labours of Sir Isaac Newton; but there still remain to be noticed several of his minor discoveries and inventions, which could not properly be introduced under any general head.
The most important of these, perhaps, are his chymical researches, which he seems to have pursued with more or less diligence from the time when he first witnessed the practical operations of chymistry during his residence at the apothecary’s at Grantham. His first chymical experiments were probably made on the alloys of metals, for the purpose of obtaining a good metallic composition for the specula of reflecting telescopes. In his paper on thin plates he treats of the combinations of solids and fluids; but he enters more largely on these and other subjects in the queries published at the end of his Optics.
One of his most important chymical papers is hisTabula quantitatum et graduum caloris, which was published in the Philosophical Transactions. This short paper contains a comparative scale of temperature from that of melting ice to that of a small kitchen coal-fire. The following are the principal points of the scale, the intermediatedegrees of heat having been determined with great care.
The first column of this table contains the degrees of heat in arithmetical progression, and the second in geometrical progression,—the second degree being twice as great as the first, and so on. It is obvious from this table, that the heat at which equal parts of tin and bismuth melt isfourtimes greater than that of blood-heat, the heat of melting leadeighttimes greater, and the heat of a small coal-firesixteentimes greater.
This table was constructed by the help of a thermometer, and of red-hot iron. By the former he measured all heats as far as that of melting tin; and by the latter he measured all the higher heats. For the heat which heated iron loses in a given time is as the total heat of the iron; and therefore, if the times of cooling are taken equal, the heats will be in a geometrical progression, and may therefore be easily found by a table of logarithms.
He found by a thermometer constructed with linseed oil, that if the oil, when the thermometer was placed in melting snow, occupied a space of 1000 parts, the same oil, rarefied withonedegree of heat, or that of the human body, occupied a space of 10256; in the heat of water beginning to boil, a space of 10705; in the heat of water boiling violently, 10725; in the heat of melted tin beginning to cool, and putting on the consistency of an amalgam,11516, and when the tin had become solid, 11496. Hence the oil was rarefied in the ratio of 40 to 39 by the heat of the human body; of 15 to 14 by the heat of boiling water; of 15 to 13 in the heat of melting tin beginning to solidify; and of 23 to 20 in the same tin when solid. The rarefaction of air was, with the same heat,tentimes greater than that of oil, and the rarefaction of oilfifteentimes greater than that of spirit of wine. By making the heats of oil proportional to its rarefaction, and by calling the heat of the human body 12 parts, we obtain the heat of water beginning to boil, 33; of water boiling violently, 34; of melted tin beginning to solidify, 72; and of the same become solid, 70.
Sir Isaac then heated a sufficiently thick piece of iron till it was red-hot; and having fixed it in a cold place, where the wind blew uniformly, he put upon it small pieces of different metals and other fusible bodies, and noted the times of cooling, till all the particles, having lost their fluidity, grew cold, and the heat of the iron was equal to that of the human body. Then, by assuming that the excesses of the heats of the iron and of the solidified particles of metal above the heat of the atmosphere, were in geometrical progression when the times were in arithmetical progression, all the heats were obtained. The iron was placed in a current of air, in order that the air heated by the iron might always be carried away by the wind, and that cold air might replace it with a uniform motion; for thus equal parts of the air were heated in equal times, and received a heat proportional to that of the iron. But the heats thus found had the same ratio to one another with the heats found by the thermometer; and hence he was right in assuming that the rarefactions of the oil were proportional to its heats.
Another short chymical paper by Sir Isaac Newton has been published by Dr. Horsley. It is entitledDe Natura Acidorum, but is principally occupied with a number of brief opinions on chymical subjects. This paper was written later than 1687, as it bears a reference to the Principia; and the most important facts which it contains seem to have been more distinctly reproduced in the queries at the end of the Optics.
The most important of these queries relate to fire, flame, and electric attractions, and as they were revised in the year 1716 and 1717, they may be regarded as containing the most matured opinions of their author. Fire he regards as a body heated so hot as to emit light copiously, and flame as a vapour, fume, or exhalation heated so hot as to shine. In his long query on elective attractions, he considers the small particles of bodies as acting upon one another at distances so minute as to escape observation. When salt of tartar deliquesces, he supposes that this arises from an attraction between the saline particles and the aqueous particles held in solution in the atmosphere, and to the same attraction he ascribes it that the water will not distil from the salt of tartar without great heat. For the same reason sulphuric acid attracts water powerfully, and parts with it with great difficulty. When this attractive force becomes very powerful, as in the union between sulphuric acid and water, so as to make the particles “coalesce with violence,” and rush towards one another with an accelerated motion, heat is produced by the mixture of the two fluids. In like manner, he explains the production of flame from the mixture of cold fluids,—the action of fulminating powders,—the combination of iron filings with sulphur,—and all the other chymical phenomena of precipitation, combination, solution, and crystallization, and the mechanical phenomena of cohesion and capillary attraction. He ascribes hot springs, volcanoes, fire-damps, mineral coruscations, earthquakes, hot suffocatingexhalations, hurricanes, lightning, thunder, fiery meteors, subterraneous explosions, land-slips, ebullitions of the sea, and waterspouts, to sulphureous steams abounding in the bowels of the earth, and fermenting with minerals, or escaping into the atmosphere, where they ferment with acid vapours fitted to promote fermentation.
In explaining the structure of solid bodies, he is of opinion, “that the smallest particles of matter may cohere by the strongest attractions, and compose bigger particles of weaker virtue; and many of these may cohere and compose bigger particles whose virtue is still weaker; and so on for divers successions, until the progression end in the biggest particles, on which the operations in chymistry and the colours of natural bodies depend, and which, by adhering, compose bodies of a sensible magnitude. If the body is compact, and bends or yields inward to pression, without any sliding of its parts, it is hard and elastic, returning to its figure with a force rising from the mutual attraction of its parts. If the parts slide upon one another, the body is malleable or soft. If they slip easily, and are of a fit size to be agitated by heat, and the heat is big enough to keep them in agitation, the body is fluid; and if it be apt to stick to things, it is humid; and the drops of every fluid affect a round figure, by the mutual attraction of their parts, as the globe of the earth and sea affects a round figure, by the mutual attraction of its parts, by gravity.”
Sir Isaac then supposes, that, as the attractive force of bodies can reach but to a small distance from them, “a repulsive virtue ought to succeed;” and he considers such a virtue as following from the reflection of the rays of light, the rays being repelled without the immediate contact of the reflecting body, and also from the emission of light, the ray, as soon as it is shaken off from a shining body by the vibrating motion of the parts of the body, getting beyond thereach of attraction, and being driven away with exceeding great velocity by the force of reflection.113
Many of the chymical views which Sir Isaac thus published in the form of queries were in his own lifetime illustrated and confirmed by Dr. Stephen Hales, in his book onVegetable Statics,—a work of great originality, which contains the germ of some of the finest discoveries in modern chymistry.
Although there is no reason to suppose that Sir Isaac Newton was a believer in the doctrines of alchymy, yet we are informed by the Reverend Mr. Law that he had been a diligent student of Jacob Behmen’s writings, and that there were found among his papers copious abstracts from them in his own handwriting.114He states also that Sir Isaac, together with one Dr. Newton, his relation, had, in the earlier part of his life, set up furnaces, and were for several months at work in quest of the philosopher’s tincture. These statements may receive some confirmation from the fact, that there exist among the Portsmouth papers many sheets, in Sir Isaac’s own writing, of Flammel’s Explication of Hieroglyphic Figures, and in another hand, many sheets of William Yworth’sProcessus Mysterii Magni Philosophicus, and also from the manner in which Sir Isaac requests Mr. Aston to inquire after one Borry in Holland, who always went clothed in green, and who was said to possess valuable secrets; but Mr. Law has weakened the force of his own testimony, whenhe asserts that Newton borrowed the doctrine of attraction from Behmen’s first three propositions of eternal nature.
On the 7th December, 1675, Sir Isaac Newton communicated to the Royal Society a paper entitledAn hypothesis explaining properties of light, in which he, for the first time, introduces his opinions respecting ether, and employs them to explain the nature of light, and the cause of gravity. “He was induced,” he says, “to do this, because he had observed the heads of some great virtuosos to run much upon hypotheses, and he therefore gave one which he was inclined to consider as the most probable, if he were obliged to adopt one.”115
This hypothesis seems to have been afterward a subject of discussion between him and Mr. Boyle, to whom he promised to communicate his opinion more fully in writing. He accordingly addressed to him a long letter, dated February 28th, 1678–9, in which he explains his views respecting ether, and employs them to account for the refraction of light,—the cohesion of two polished pieces of metal in an exhausted receiver,—the adhesion of quicksilver to glass tubes,—the cohesion of the parts of all bodies,—the cause of filtration,—the phenomena of capillary attraction,—the action of menstrua on bodies,—the transmutation of gross compact substances into aerial ones,—and the cause of gravity. From the language used in this paper, we should be led to suppose that Sir Isaac had entirely forgotten that he had formerly treated the general subject of ether, and applied it to the explanation of gravity. “I shall set down,” says he, “one conjecture morewhich came into my mind now as I was writing this letter; it is about the cause of gravity,” which he goes on to explain;116andhe concludes by saying, that “he has so little fancy to things of this nature, that,had not your encouragement moved me to it, I should never, I think, thus far have set pen to paper about them.”
These opinions, however, about the existence of ether, Newton seems to have subsequently renounced; for in the manuscript in the possession of Dr. J. C. Gregory, which we have already mentioned, and which was written previous to 1702, he states, that ether is neither obvious to our senses, nor supported by any arguments, but is a gratuitous assumption, which, if we are to trust to reason and to our senses, must be banished from the nature of things; and he goes on to establish, by various arguments, the validity of this opinion. This renunciation of his former hypothesis probably arose from his having examined more carefully some of the phenomena which he endeavoured to explain by it. Those of capillary attraction, for example, he had ascribed to the ether “standing rarer in the very sensible cavities of the capillary tubes than without them,” whereas he afterward discovered their true cause, and ascribed them to the reciprocal attraction of the tube and the fluid. But, however this may be, there can be no doubt that he resumed his early opinions before the publication of his Optics, which may be considered as containing his views upon this subject.
The queries which contain these opinions are the 18th–24th, all of which appeared for the first time in the second English edition of the Optics. If a body is either heated or loses its heat when placed in vacuo, he ascribes the conveyance of the heat in both cases “to the vibration of a much subtiler medium than air;” and he considers this medium as the same with that by which light is refracted and reflected, and by whose vibrations light communicates heat to bodies, and is put into fits of easy reflection and transmission.
This ethereal medium, according to our author, is exceedingly more rare and more elastic than air. It pervades all bodies, and is expanded through all the heavens. It is much rarer within the dense bodies of the sun, stars, planets, and comets, than in the celestial spaces between them, and also more rare within glass, water, &c. than in the free and open spaces void of air and other grosser bodies. In passing out of glass, water, &c. and other dense bodies into empty space, it grows denser and denser by degrees, and this gradual condensation extends to some distance from the bodies. Owing to its great elasticity, and, consequently, its efforts to spread in all directions, it presses against itself, and, consequently, against the solid particles of bodies, so as to make them continually approach to one another, the body being impelled from the denser parts of the medium towards the rarer with all that power which we call gravity.
In employing this medium to explain the nature of light, Newton does not suppose, with Descartes, Hooke, Huygens, and others, that light is nothing more than the impression of those undulations on the retina. He regards light as a peculiar substance, composed of heterogeneous particles thrown off with great velocity, and in all directions, from luminous bodies; and he supposes that these particles while passing through the ether, excite in it vibrations or pulses which accelerate or retard the particles of light, and thus throw them into their alternate fits of easy reflection and transmission.
Hence, if a ray of light falls upon a transparent body, in which the ether consists of strata of variable density, the particles of light acted upon by the vibrations which they create will be urged with an accelerated velocity in entering the body, while their velocity will be retarded in quitting it. In this manner he conceives the phenomena of refraction to be produced, and he shows how in such a case therefraction would be regulated by the law of the sines.
In order that the ethereal medium may produce the fits of easy reflection and transmission, he conceives that its vibrations must be swifter than light. He computes its elasticity to be 490,000,000,000 times greater than that of air, in proportion to its density, and about 600,000,000 times more rare than water, from which he infers that the resistance which it would oppose to the motions of the planets would not be sensible in 10,000 years. He considers that the functions of vision and hearing may be performed chiefly by the vibrations of this medium, executed in the bottom of the eye, or in the auditory nerve by the rays of light, and propagated through the solid, pellucid, and uniform capillamenta of the optic or auditory nerves into the place of sensation; and he is of opinion that animal motion may be performed by the vibrations of the same medium, excited in the brain by the power of the will, and propagated from thence by the solid, pellucid, and uniform capillamenta of the nerves into the muscles for contracting and dilating them.
In the registers of the Royal Society there exist several letters117on the excitation of electricity in glass, which were occasioned by an experiment of this kind having been mentioned in Sir Isaac’s hypothesis of light. The society had ordered the experiment to be tried at their meeting of the 16th December, 1675; but, in order to secure its success, Mr. Oldenburg wrote to Sir Isaac for a more particular account of it. Sir Isaac being thus “put upon recollecting himself a little farther about it,” remembers that he made the experiment with a glass fixed at the distance of the 1/3d of an inch from one end of a brass hoop, and only the 1/8th of an inch from the other. Small pieces of thin paper werethen laid upon the table; when the glass was laid above them and rubbed, the pieces of paper leaped from the one part of the glass to the other, and twirled about in the air. Notwithstanding this explicit account of the experiment, it entirely failed at the Royal Society, and the secretary was desired to request the loan of Sir Isaac’s apparatus, and to inquire whether or not he had secured the papers from being moved by the air, which might have somewhere stole in. In a letter, dated 21st December, Sir Isaac recommended to the society to rub the glass “with stuff whose threads may rake its surface, and, if that will not do, to rub it with the fingers’ ends to and fro, and knock them as often upon the glass.” These directions enabled the society to succeed with the experiment on the 13th January, 1676, when they used a scrubbing brush of short hog’s bristles, and the heft of a knife made with whalebone.
Among the minor inventions of Sir Isaac Newton, we must enumerate his reflecting instrument for observing the moon’s distance from the fixed stars at sea. The description of this instrument was communicated to Dr. Halley in the year 1700; but, either from having mislaid the manuscript, or from attaching no value to the invention, he never communicated it to the Royal Society, and it remained among his papers till after his death in 1742, when it was published in the Philosophical Transactions. The following is Sir Isaac’s own description of it as communicated to Dr. Halley.
“In the annexed figure PQRS denotes a plate of brass, accurately divided in the limb DQ, into ½ degrees, ½ minutes, and 1/12 minutes, by a diagonal scale; and the ½ degrees, and ½ minutes, and 1/12 minutes, counted for degrees, minutes, and 1/6 minutes. AB is a telescope three or four feet long, fixed on the edge of that brass plate. G is a speculum fixedon the brass plate perpendicularly as near as may be to the object-glass of the telescope, so as to be inclined forty-five degrees to the axis of the telescope, and intercept half the light which would otherwise come through the telescope to the eye. CD is a moveable index turning about the centre C, and, with its fiducial edge, showing the degrees, minutes, and 1/6 minutes on the limb of the brass plate PQ; the centre C must be over against the middle of the speculum G. H is another speculum, parallel to the former, when the fiducial edge of index falls on 0° 0′ 0″; so that the same star may then appear through the telescope in one and the same place, both by the direct rays and by the reflexed ones; but if the index be turned, the star shall appear in two places, whose distance is showed on the brass limb by the index.
Fig. 12.
Fig. 12.
“By this instrument the distance of the moon from any fixed star is thus observed: view the starthrough the perspicil by the direct light, and the moon by the reflexed (or on the contrary); and turn the index till the star touch the limb of the moon, and the index shall show on the brass limb of the instrument the distance of the star from the moon’s limb; and though the instrument shake by the motion of the ship at sea, yet the moon and star will move together as if they did really touch one another in the heavens; so that an observation may be made as exactly at sea as at land.
“And by the same instrument may be observed exactly the altitudes of the moon and stars, by bringing them to the horizon; and thereby the latitude and times of observation may be determined more exactly than by the ways now in use.
“In the time of the observation, if the instrument move angularly about the axis of the telescope, the star will move in a tangent of the moon’s limb, or of the horizon; but the observation may notwithstanding be made exactly, by noting when the line described by the star is a tangent to the moon’s limb, or to the horizon.
“To make the instrument useful, the telescope ought to take in a large angle; and to make the observation true, let the star touch the moon’s limb, not on the outside, but on the inside.”
This ingenious contrivance is obviously the very same invention as that which Mr. Hadley produced in 1731, and which, under the name of Hadley’s Quadrant, has been of so great service in navigation. The merit of its first invention must therefore be transferred to Sir Isaac Newton.
In the year 1672, Sir Isaac communicated to Mr. Oldenburg his design for a microscope, which he considered to be as capable of improvement as the telescope, and perhaps more so, because it requires only one speculum. This microscope is shown in the annexed diagram, where AB is the object-metal, CD the eye-glass, F their commonfocus, and O the other focus of the metal in which the object is placed. This ingenious idea has been greatly improved in modern times by Professor Amici, who makes AB a portion of an ellipsoid, whose foci are O and F, and who places a small plain speculum between O and AB, in order to reflect the object, which is placed on one side AP, for the purpose of being illuminated.
Fig. 13.
Fig. 13.
In another letter to Mr. Oldenburg, dated July 11th in the same year, he suggests another improvement in microscopes, which is to “illuminate the object in a darkened room with the light of any convenient colour not too much compounded: for by that means the microscope will, with distinctness, bear a deeper charge and larger aperture, especially if its construction be such as I may hereafter describe.”118This happy idea I have some years ago succeeded in realizing, by illuminating microscopic objects with the light of a monochromatic lamp, which discharges a copious flame of pure yellow light of definite refrangibility.119
Fig. 14.
Fig. 14.
Fig. 15.
Fig. 15.
In order to remedy the evils arising from the weak reflecting power of speculum metal, and from its tarnishing by exposure to the air, Sir Isaac proposed to substitute for the small oval speculum a triangular prism of glass or crystal ABC. Its sideABbahe supposes to perform the office of that metal, by reflecting towards the eye-glass the light which comes from the concave speculum DF,fig. 13, whose light he supposes to enter into this prism at its side CBbc, and lest any colours should be produced by the refraction of these planes, it is requisite that the angles of the prism at Aaand Bbbe precisely equal. This may be done most conveniently, by making them half right angles, and consequently the third angle at Cca right one. The plane ABbawill reflect all the light incident upon it; but in order to exclude unnecessary light, it will be proper to cover it all over with some black substance excepting two circular spaces of the planes Acand Bc, through which the useful light may pass. The length of the prism should be such that its sides Acand Bcmay be square, and so much of the angles B andbas aresuperfluous ought to be ground off, to give passage for as much light as is possible from the object to the speculum.
Fig. 16.
Fig. 16.
One great advantage of this prism, which cannot be obtained from the oval metal, is, that without using two glasses the object may be erected, and the magnifying power of the telescope varied at pleasure, by merely varying the distances of the speculum, the prism, and the eye-glass. This will be understood fromfig. 16, where AI represents the great concave speculum, EF the eye-glass, and BCD the prism of glass, whose sides BC and CD are not flat, but spherically convex. The rays which come from G, the focus of the great speculum AI, will, by the refraction of the first side BC, be reduced to parallelism, and after reflection from the base CD, will be made by the refraction of the next side BD to converge to the focus H of the eye-glass EF. If we now bring the prism BCD nearer the image at G, the point H will recede from BD, and the image formed there will be greater than that at G, and if we remove the prism BCD from G, the point H will approach to BD, and the image at Hwill be less than that at G. The prism BCD performs the same part as a convex lens, G and H being its conjugate foci, and the relative size of the images formed at these points being proportional to their distance from the lens. This construction would be a good one for varying optically the angular distance of a pair of wires placed in the focus of the eye-glass EF; and by bisecting the lenticular prism BCD, and giving the halves a slight inclination, we should be able to separate and to close the two images or disks which would thus be produced, and thus form a double image micrometer.
Among the minor and detached labours of Sir Isaac, we must not omit his curious experiments on the action of light upon the retina. Locke seems to have wished his opinion respecting a fact stated in Boyle’s Book on Colours, and in a letter from Cambridge, dated June 30th, 1691, he communicated to his friend the following very remarkable observations made by himself.
“The observation you mention in Mr. Boyle’s book of colours I once made upon myself with the hazard of my eyes. The manner was this; I looked a very little while upon the sun in the looking-glass with my right eye, and then turned my eyes into a dark corner of my chamber, and winked, to observe the impression made, and the circles of colours which encompassed it, and how they decayed by degrees, and at last vanished. This I repeated a second and a third time. At the third time, when the phantasm of light and colours about it were almost vanished, intending my fancy upon them to see their last appearance, I found, to my amazement, that they began to return, and by little and little to become as lively and vivid as when I had newly looked upon the sun. But when I ceased to intend my fancy upon them, they vanished again. After this, I found, that as often as I went into the dark, and intended my mind upon them, as whena man looks earnestly to see any thing which is difficult to be seen, I could make the phantasm return without looking any more upon the sun; and the oftener I made it return, the more easily I could make it return again. And at length, by repeating this without looking any more upon the sun, I made such an impression on my eye, that, if I looked upon the clouds, or a book, or any bright object, I saw upon it a round bright spot of light like the sun, and, which is still stranger, though I looked upon the sun with my right eye only, and not with my left, yet my fancy began to make an impression upon my left eye, as well as upon my right. For if I shut my right eye, or looked upon a book or the clouds with my left eye, I could see the spectrum of the sun almost as plain as with my right eye, if I did but intend my fancy a little while upon it; for at first, if I shut my right eye, and looked with my left, the spectrum of the sun did not appear till I intended my fancy upon it; but by repeating, this appeared every time more easily. And now, in a few hours’ time, I had brought my eyes to such a pass, that I could look upon no bright object with either eye but I saw the sun before me, so that I durst neither write nor read; but to recover the use of my eyes, shut myself up in my chamber made dark, for three days together, and used all means to divert my imagination from the sun. For if I thought upon him, I presently saw his picture, though I was in the dark. But by keeping in the dark, and employing my mind about other things, I began in three or four days to have some use of my eyes again; and, by forbearing to look upon bright objects, recovered them pretty well, though not so well but that, for some months after, the spectrum of the sun began to return as often as I began to meditate upon the phenomena, even though I lay in bed at midnight with my curtains drawn. But now I have been very well for many years, though I amapt to think, if I durst venture my eyes, I could still make the phantasm return by the power of my fancy. This story I tell you, to let you understand, that in the observation related by Mr. Boyle, the man’s fancy probably concurred with the impression made by the sun’s light to produce that phantasm of the sun which he constantly saw in bright objects. And so your question about the cause of this phantasm involves another about the power of fancy, which I must confess is too hard a knot for me to untie. To place this effect in a constant motion is hard, because the sun ought then to appear perpetually. It seems rather to consist in a disposition of the sensorium to move the imagination strongly, and to be easily moved, both by the imagination and by the light, as often as bright objects are looked upon.”
These observations possess in many respects a high degree of interest. The fact of the transmission of the impression from the retina of the one eye to that of the other is particularly important; and it deserves to be remarked, as a singular coincidence, that I had occasion to observe and to describe the same phenomena above twenty years ago,120and long before the observations of Sir Isaac were communicated to the scientific world.
His Acquaintance with Dr. Pemberton, who edits the Third Edition of the Principia—His first Attack of ill Health—His Recovery—He is taken ill in consequence of attending the Royal Society—His Death on the 20th March, 1727—His Body lies in state—His Funeral—He is buried in Westminster Abbey—His Monument described—His Epitaph—A Medal struck in honour of him—Roubiliac’s full-length Statue of him erected in Cambridge—Division of his Property—His Successors.
His Acquaintance with Dr. Pemberton, who edits the Third Edition of the Principia—His first Attack of ill Health—His Recovery—He is taken ill in consequence of attending the Royal Society—His Death on the 20th March, 1727—His Body lies in state—His Funeral—He is buried in Westminster Abbey—His Monument described—His Epitaph—A Medal struck in honour of him—Roubiliac’s full-length Statue of him erected in Cambridge—Division of his Property—His Successors.
About the year 1722, Sir Isaac was desirous of publishing a third edition of his Principia, and the premature death of Mr. Cotes having deprived him of his valuable aid, he had the good fortune to become acquainted with Dr. Henry Pemberton, a young and accomplished physician, who had cultivated mathematical learning with considerable success. M. Poleni, an eminent professor in the University of Padua, having endeavoured, on the authority of a new experiment, to overturn the common opinion respecting the force of bodies in motion, and to establish that of Leibnitz in its place, Dr. Pemberton transmitted to Dr. Mead a demonstration of its inaccuracy. Dr. Mead communicated this paper to Sir Isaac, who not only highly approved of it, but added a demonstration of his own, drawn from another consideration of the subject; and this was printed without his name, as a postscript to Pemberton’s paper, when it appeared in the Transactions.121
In a short time after the commencement of their acquaintance, Sir Isaac engaged Dr. Pemberton to superintend the new edition of the Principia. In discharging this duty, Dr. Pemberton had occasion to make many remarks on this work, which Sir Isaacalways received with the utmost goodness, and the new edition appeared with numerous alterations in 1726. On the occasions upon which he had personal intercourse with Sir Isaac, and which were necessarily numerous, he endeavoured to learn his opinions on various mathematical subjects, and to obtain some historical information respecting his inventions and discoveries. Sir Isaac entered freely into all these topics and during the conversations which took place, and while they were reading together Dr. Pemberton’s popular account of Sir Isaac’s discoveries, he obtained the most perfect evidence that, though his memory was much decayed, yet he was fully able to understand his own writings.
During the last twenty years of his life, which he spent in London, the charge of his domestic concerns devolved upon his beautiful and accomplished niece, Mrs. Catharine Barton, the wife of Colonel Barton, for whom, as we have already seen, the Earl of Halifax had conceived the warmest affection. This lady, who had been educated at her uncle’s expense, married Mr. Conduit, and continued to reside with her husband in Sir Isaac’s house till the time of his death.
In the year 1722, when he had reached the eightieth year of his age, he was seized with an incontinence of urine, which was ascribed to stone in the bladder, and was considered incurable. By means of a strict regimen, however, and other precautions, he was enabled to alleviate his complaint, and to procure long intervals of ease. At this time he gave up the use of his carriage, and always went out in a chair. He declined all invitations to dinner, and at his own house he had only small parties. In his diet he was extremely temperate. Though he took a little butcher meat, yet the principal articles of his food were broth, vegetables, and fruit, of which he always ate very heartily. In spite of allhis precautions, however, he experienced a return of his old complaint, and in August, 1724, he passed a stone the size of a pea, which came away in two pieces, the one at the distance of two days from the other. After some months of tolerable good health, he was seized in January, 1725, with a violent cough and inflammation of the lungs; and in consequence of this attack, he was prevailed upon, with some difficulty, to take up his residence at Kensington, where his health experienced a decided improvement. In February, 1725, he was attacked in both his feet with a fit of the gout, of which he had received a slight warning a few years before, and the effect of this new complaint was to produce a great and beneficial change in his general health. On Sunday the 7th March, when his head was clearer and his memory stronger than Mr. Conduit had known it to be for some time, he entered into a long conversation on various subjects in astronomy. He explained to Mr. Conduit how comets might be formed out of the light of vapours discharged from the sun and the fixed stars as the centres of systems. He conceived that these luminaries were replenished by the same comets being again returned to them; and upon this principle he explained the extraordinary lights which were seen among the fixed stars by Hipparchus, Tycho Brahe, and Kepler’s disciples, and which he supposed to arise from the additional fuel which they received.122
Notwithstanding the improvement which his health had experienced, his indisposition was still sufficiently severe to unfit him for the discharge of his duties at the mint; and as his old deputy was confined with the dropsy, he was desirous in 1725 of resigning his office to Mr. Conduit. Difficulties probably were experienced in making this arrangement, but his nephew discharged for him all theduties of his office; and during the last year of his life he hardly ever went to the mint.
But though every kind of motion was calculated to aggravate his complaint, and though he had derived from absolute rest and from the air at Kensington the highest benefit, yet great difficulty was experienced in preventing him from occasionally going to town. Feeling himself able for the journey, he went to London on Tuesday the 28th of February, 1727, to preside at a meeting of the Royal Society. On the following day Mr. Conduit considered him better than he had been for many years, and Sir Isaac was himself so sensible of this improvement in his health, that he assured his nephew that on the Sunday preceding, he had slept from eleven o’clock at night till eight o’clock next morning without waking. He had undergone, however, great fatigue in attending the meeting of the Royal Society, and in paying and receiving visits, and the consequence of this was a violent return of his former complaint. He returned to Kensington on Saturday the 4th March, and was attended by Dr. Mead and Dr. Cheselden, who pronounced his disease to be stone, and held out no hopes of his recovery. From the time of his last journey to London he had experienced violent fits of pain with very short intermissions; and though the drops of sweat ran down his face during these severe paroxysms, yet he never uttered a cry or a complaint, or displayed the least marks of peevishness or impatience; but during the short intervals of relief which occurred, he smiled and conversed with his usual gayety and cheerfulness. On Wednesday the 15th of March he seemed a little better; and slight, though groundless hopes were entertained of his recovery. On the morning of Saturday the 18th he read the newspapers, and carried on a pretty long conversation with Dr. Mead, when all his senses and faculties were strong and vigorous; but at six o’clockof the same evening he became insensible, and he continued in that state during the whole of Sunday, and till Monday the 20th, when he expired between one and two o’clock in the morning, in the eighty-fifth year of his age.
His body was removed from Kensington to London, and on Tuesday the 28th March it lay in state in the Jerusalem Chamber, and was thence conveyed to Westminster Abbey, where it was buried near the entrance into the choir on the left-hand. The pall was supported by the Lord High Chancellor, the Dukes of Roxburghe and Montrose, and the Earls of Pembroke, Sussex, and Macclesfield, who were Fellows of the Royal Society. The Hon. Sir Michael Newton, Knight of the Bath, was chief mourner, and was followed by some other relations, and several distinguished characters who were intimately acquainted with the deceased. The funeral service was performed by the Bishop of Rochester, attended by the prebend and choir.
Sensible of the high honour which they derived from their connexion with so distinguished a philosopher, the relations of Sir Isaac Newton who inherited his personal estate,123agreed to devote 500l.to the erection of a monument to his memory, and the dean and chapter of Westminster appropriated for it a place in the most conspicuous part of the Abbey, which had often been refused to the greatest of our nobility. This monument was erected in 1731. On the front of a sarcophagus resting on a pedestal are sculptured in basso-relievo youths bearing in their hands the emblems of Sir Isaac’s principal discoveries. One carries a prism, another a reflecting telescope, a third is weighing the sun andplanets with a steelyard, a fourth is employed about a furnace, and two others are loaded with money newly coined. On the sarcophagus is placed the figure of Sir Isaac in a cumbent posture, with his elbow resting on several of his works. Two youths stand before him with a scroll, on which is drawn a remarkable diagram relative to the solar system, and above that is a converging series. Behind the sarcophagus is a pyramid, from the middle of which rises a globe in mezzo-relievo, upon which several of the constellations are drawn, in order to show the path of the comet of 1681, whose period Sir Isaac had determined, and also the position of the solstitial colure mentioned by Hipparchus, and by means of which Sir Isaac had, in his Chronology, fixed the time of the Argonautic expedition. A figure of Astronomy as Queen of the Sciences sits weeping on the Globe with a sceptre in her hand, and a star surmounts the summit of the pyramid. The following epitaph is inscribed on the monument.
Hic situs estIsaacus Newton, Eques Auratus,Qui Animi Vi prope divina,Planetarum Motus, Figuras,Cometarum Semitas, Oceanique Æstus,Sua Mathesi facem preferente,Primus demonstravit.Radiorum Lucis dissimilitudines,Colorumque inde nascentium Proprietates,Quas nemo antea vel suspicatus erat, pervestigavit,Naturæ, Antiquitates, S. Scripturæ,Sedulus, sagax, fidus Interpres,Dei Opt. Max. Majestatem Philosophia asseruit,Evangelii simplicitatem moribus expressit.Sibi gratulentur Mortales, tale tantumque extitisse,Humani Generis Decus.Natus xxv. Decemb. MDCXLII. Obiit. xx. Mar.MDCCXXVII.
Of which the following is a literal translation:
Here liesIsaac Newton, Knight,Who, by a Vigour of Mind almost supernatural,First demonstratedThe Motions and Figures of the Planets,The Paths of the Comets, and the Tides of the Ocean.He diligently investigatedThe different Refrangibilities of the Rays of Light,And the Properties of the Colours to which they give rise.An assiduous, sagacious, and faithful InterpreterOf Nature, Antiquity, and the Holy Scriptures,He asserted in his Philosophy the Majesty of God,And exhibited in his conduct the Simplicity of the Gospel.Let Mortals rejoiceThat there has existed such and so greatAn Ornament of Human Nature.Born 25th Dec. 1642, Died 20th March, 1727.
In the beginning of 1731, a medal was struck at the Tower in honour of Sir Isaac Newton. It had on one side the head of the philosopher, with the motto,Felix cognoscere causas, and on the reverse a figure representing the mathematics.
On the 4th February, 1755, a magnificent full-length statue of Sir Isaac Newton in white marble was erected in the antechapel of Trinity College. He is represented standing on a pedestal in a loose gown, holding a prism, and looking upwards with an expression of the deepest thought. On the pedestal is the inscription,
Qui genus humanum ingenio superavit.Who surpassed all men in genius.
This statue, executed by Roubiliac, was erected at the expense of Dr. Robert Smith, the author of theCompleat System of Optics, and professor of astronomy and experimental philosophy at Cambridge.—It has been thus described by a modern poet: