In the opening chapter, and elsewhere, it was made clear that our present interest lies in the lives of these heroes, but it will be necessary to touch upon two very prominent parts of Newton's work, so that we may form a clear conception of his greatness.

His extension of the laws of Gravity to the whole wide Universe is the most prominent of all his works, but his researches in the subject of Light  are of immense importance to Science. To the general reader the most noteworthy discovery which Newton made in Optics, and which is understandable without any scientific training, is the composition of Light. It was he who advanced the theory that Light is a combination of different rays producing different colour sensations, and that white light is a mixture of all these.

It is true that Newton's idea that Light was a projection of infinitesimally small corpuscles had to be abandoned long afterwards, but I believe his contemporaries were more responsible for the existence of this theory than Newton was. He did not wish to make any "guess" as to the physical nature of Light. This is made quite clear in his Hypothesis  which he communicated to the Royal Society. He explains that the reason why he has advanced this theory is because he has observed "the heads of some great virtuosos to run much upon hypothesis," and because some people seemed incapable of understanding his theory of Light when put in an abstract form, whereas they readily understood it when he used this hypothesis , he therefore made use of it. Then he adds: ". . . I shall not assume this or any other hypothesis, not thinking it necessary, . . . yet while I am describing this, to avoid circumlocution and to represent it more conveniently, I shall speak of it as if I assumed it and proposed it to be believed." He further states that he is not willing to answer objections against this idea.

The italics in the foregoing quotations are mine; I am desirous of emphasising the ideas with which Newton set out, for we shall see in a later chapter how the Scientists of a later century cried out when Thomas Young dared to declare Light itself to be merely waves in the ether of space. Young's undulatory theory was accepted later, but at that time a scathing criticism was poured upon him, because he said these flying corpuscles did not exist. I think it is not generally understood that Newton laid no stress upon these corpuscles; their invention was merely to please the "virtuosos" who insisted upon something graphic.

In urging this defence of Newton, I do not suggest that Newton ever thought for a moment that Light itself consisted of ether waves. I am not overlooking the fact that he would have a very real difficulty in accepting such a suggestion, for the waves which he pictured were longitudinal like those of Sound, whereas Light consists of transverse waves, such as those on the surface of water. What I maintain is that Newton personally did not care for the corpuscular idea. Speaking of it in another place, he says, "To avoid dispute, let every man here take his fancy."

It should be noted in passing, that Newton invented a reflecting telescope, a class of instrument which will be referred to later in connection with Herschel.

Early in the preceding chapter we saw that Newton had tried, but had failed, to prove his idea that it was Gravity which held the heavenly bodies in their fixed orbits. He had calculated the effect of Gravity at the distance of the Moon, and he found that the resulting figures did not agree with observed facts, so he laid the matter aside without even mentioning it to any one.. This was when he was about twenty-three years of age. When he was forty years of age he heard of a new measurement of the Earth, which would materially affect his former calculation. The result of his new calculation was that he had very evident proof that it was our old friend Gravity that was the pulling force in the whole wide Universe. It is difficult to realise that Newton should put the papers away in his desk and tell no one of his great discovery, and yet that is just what did happen. It may be that he wished to avoid any controversy, and either publish the papers later or even to leave them to be published after he had gone; but these are merely guesses at his reasons. The way in which his discovery became known is of interest.

About two years after Newton's solution of the problem, it so happened that Sir Christopher Wren, well known to us as the architect of St. Paul's Cathedral, in London, was discussing with two friends the possibility of the motion of the planets being due to a force obeying the inverse square law. The idea had occurred to these men quite independently; they knew nothing of the papers lying in Newton's desk, or of his early idea in the garden at his home. Sir Christopher's two friends are of interest to us. One was the astronomer Edmund Halley, whose name is familiar to us in connection with "Halley's Cornet," which he had discovered shortly before the time of this meeting with which we are dealing. The visit of this comet to the neighbourhood of our planet so recently as 1911 attracted a good deal of attention. The other friend was Robert Hooke, a very learned man, who anticipated Newton in some points.

What interests us at present is that Sir Christopher Wren and Halley both acknowledged they could not find any way of proving the idea of Universal Gravitation, but Hooke said that he had done so. Halley tells us that Sir Christopher thereupon said that he would give them two months to show him a proof, "and besides the honour, he of us that did it should have from him the present of a book of forty shillings." As nothing came of this challenge, Halley went to Cambridge to consult his friend Newton upon the subject. Without telling of the discussion in London, Halley merely asked what would be the curve described by the planets on the supposition that they were controlled by a force obeying the inverse square law. When Newton replied off-hand that it would be an Ellipse, Halley was greatly surprised, and asked him how he knew it, whereupon Newton told for the first time that he had worked the matter out, and that he had proved also beyond a doubt that it was Gravity that linked the Solar System together. Newton looked for the papers which he had placed in his desk two years earlier, but he could not find them. However, he promised to send them to Halley, and he did so.

During this visit of Halley to Cambridge, Newton had shown him the manuscript of a tract which he had entitled De Motu, and which dealt with the subject of celestial motion. Halley asked that this might be sent to him also, so that he might have it recorded in the Transactions of the Royal Society. It is interesting to note that the secretary who acknowledges the receipt of this was the young man (Aston) to whom Newton had written the letter of advice on travelling some fifteen years earlier; which letter is referred to at page 117. This tract De Motu  was the forerunner of the truly great book which Newton wrote later, and which is known throughout the scientific world as Newton's Principia.

Newton sat in the House of Commons for one year, during the reign of William and Mary. He was Member for Cambridge University, and he conscientiously looked after the interests of that great seat of learning with which his life is so intimately connected. He would be about forty years of age at that time.

Two years later he became very seriously ill, which is not surprising considering the vast amount of brain-work he did, without taking a proper amount of sleep or food. When thinking of his constant toil, one is apt to forget how very delicate he was in infancy. It is remarkable that his health held out so long, but John Wickens, his chamber-fellow for twenty years, tells us that Newton sometimes suspected himself "to be inclining to a consumption," and that he mixed for himself certain medicines at such times.

It is generally believed that Newton's mind became deranged at this time, and while no one could be greatly surprised if his brain did suffer from the severe strain put upon it, there seems good reason to doubt that there was ever more than a nervous breakdown.

The cause of the malady was generally ascribed to the loss of valuable manuscripts in the fire which occurred in his laboratory. This well-known story runs thus: "Newton had a favourite little dog called Diamond. One winter's morning, while attending early service, he inadvertently left his dog shut up in his room; on returning from chapel, he found that the animal, by upsetting a taper on his desk, had set fire to the papers on which he had written down his experiments; and thus he saw before him the labour of so many years reduced to ashes. It is said that on first perceiving this great loss, he contented himself by exclaiming, 'Oh, Diamond! Diamond! thou little knowest the mischief thou hast done.' But the grief caused by this circumstance injured his health and, if we may venture to say so, for some time impaired his understanding." In another version of the same story, instead of quietly rebuking the poor dumb animal, we are told that his excitement was so great that every one thought he would have run mad when he saw what had happened, But there seems to be very substantial evidence to lay on the other side.

In a letter written by Newton's assistant, to whom I have referred already, he gives us the following information, which is direct evidence and not mere hearsay. "He kept neither dog nor cat in his chamber, which made well for the old woman his bed-maker, she faring much the better for it, for in a morning she has sometimes found both dinner and supper scarcely tasted of, which the old woman has very pleasantly and mumpingly gone away with."

The foregoing statement seems to me to take the whole value of the previous evidence away. Even although the story of the accident contains the name of the dog, and the words of Newton's rebuke, it must go in the face of this first-hand evidence. And if we have to discard such an apparently exact story, why not the inexact statement of the mental malady? There are some letters of Newton which are supposed to be proof that his mind was affected at this period. I have read them very carefully, and I am quite convinced that many a person, suffering merely from a nervous breakdown, has written much stranger letters. Newton's own statement, written at that time to a friend, is another piece of evidence in support of the theory of a nervous breakdowns. He wrote. "I am extremely troubled. . . . I have neither ate nor slept well this twelvemonth." No mention of sudden grief at the loss of papers.

To this day students at Cambridge are told how there were two holes cut in the door of Newton's chamber: one hole, much larger than the other, for the use of his cat, the smaller one for the convenience of the kitten. The joke is, of course, that the kitten required a smaller hole to pass through the door than did its mother. But I fear this amusing story must go also in the face of the direct evidence quoted. Indeed, it would be difficult to realise Newton taking care of a dog or a cat, he was so unmindful of himself. What he required was some one to take care of him. We have good reason to believe that the reason why Newton never married was a financial one. When he was an inmate of the apothecary's house at Grantham, there were several girls residing in the household, and the boy Isaac was very good in amusing them and in making playthings for them. One of these girls remained a friend of Newton throughout life, and at the age of eighty years she admitted to another friend of Newton that the great Philosopher would have married her but for his small income and the smallness of her portion. This lady, whose maiden name was Storey, was twice married, but Newton, as we have seen, remained a bachelor to the end.

Newton was in his eighty-fifth year at the time of his death, which occurred on the 20th of March, 1727. He presided at a meeting of the Royal Society in London on the second day of March, but was taken ill the following day, so that his last illness was of less than three weeks' duration. He suffered great pain, which he bore without a murmur. He was buried in Westminster Abbey, where one can see the monument erected in his memory. During his last illness some friends were testifying to the great esteem in which he was held in the world, but Newton replied: "I know not what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me."

The eminent poet Pope, who was about forty years of age at the time of Newton's death, wrote the following epitaph, which was placed on an iron tablet put upon the wall of the room in which Newton was born.

There has been so very much of interest in Newton's life, directly bearing upon Science, that I have not touched upon the time when he became Master of the Mint, at the age of fifty-five, which was after the serious illness to which special reference has been made already. It is of importance to note that, contrary to statements made upon the Continent, Newton's mental powers remained unimpaired to the end. At the age of seventy-five he was returning one evening from the Mint, when he received a copy of a mathematical problem sent to this country by Leibnitz "for the purpose of feeling the pulse of English Analysts." It was 5 p.m. when Newton received this problem, which was presumably a very severe test to the most expert mathematicians, but the aged Philosopher, after a busy day in making arrangements concerning the coinage of the country, was able to solve this problem set by the famous German mathematician.

In closing it may be of interest to note that Newton lived in no less than six reigns. He was born a few years before Charles I was beheaded; he lived through the inglorious reign of Charles II, and the intervening Commonwealth of Oliver Cromwell; also the reign of William and Mary, at whose coronation he was present: the twelve years of Queen Anne, at whose hands he received his knighthood, upon the occasion of her visit to Cambridge; and the slightly longer reign of George I, at whose Court Newton was a well-known figure; but George II had only entered upon the first year of his prosperous reign in the year of Newton's death.

Queen Caroline, wife of George II, seems to have been of a scientific turn of mind. While she was Princess of Wales she used to propose such difficulties to Newton "as none but himself could answer to her satisfaction"; and she was often heard to declare in public, that she thought herself happy in living at the same time and conversing with so great a man.