the ordinary concerns of life. It is said that frequently, on rising in the morning, he would sit down on his bedside, arrested by some new conception, and would remain for hours together engaged in tracing it out, without dressing himself. It is also related, that he sometimes forgot his meals, unless reminded by those about him. To those concentrated powers of thought, totally abstracted from all external objects, he owed his intellectual conquests. At a later period, when asked by what means he had arrived at his great discoveries, he is said to have replied, "By always thinking unto them." And on another occasion, " I keep the subject," he observed, "constantly before me, and wait till the first dawnings open slowly by little and little into a full and clear light." And again, in a letter to Dr. Bentley, he says, "If I have done the public any service this way, it is due to nothing but industry and patient thought."

We have already observed, that the immediate occasion which directed Newton's enquiries more parti.. cularly to the subject of elliptic motion, was the suggestion of Hooke relative to falling bodies. We have noticed the approaches already made to investigating the subject. We have observed some of the most eminent philosophers acknowledging their inability to discover the law in question; and even Hooke, though hazarding an assertion, yet unable to give a proof.

In January, 1684, Dr. Halley, on the hypothesis of circular orbits, by means of Huyghens's theorems respecting centrifugal force, had determined the tendency in the different planets to recede from the sun; and from the analogies of Kepler he had recognised these tendencies to be reciprocally as the squares of the distances; so that the force of the sun to retain them in their orbits, which must be exactly equal to this, must follow the same law. Halley, however, clearly saw that this, though true in circular, was not proved for elliptic, orbits. In a discussion on the subject with sir C.

Wren and Dr. Hooke, the former candidly owned the failure of his attempts to investigate the general problem, and offered to make a present to any philosopher who should solve it within two months. Hooke affirmed that he had some time since discovered the whole, and was in possession of a complete demonstration of it; but when pressed to disclose it, he stated his intention to keep it secret for some time, that others trying and failing might know how to value it, when he should make it public." It appears, also, that Hooke had frequently, before this, stated his ideas, and had even given some kind of arguments in support of them, to sir C. Wren; but that able mathematician found them totally inconclusive.

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Halley, knowing the powers of Newton's genius, and possibly having some intimation that his attention had been turned to this subject, went to Cambridge in Au gust, 1684, for the express purpose of consulting him on the question. Newton showed him the solution of the whole; and, upon his earnest request, promised him a copy of it. He was, however, very slow in fulfilling this promise; and though he allowed Halley to mention to the Royal Society that he had such an investigation complete in its essential points, yet he wished to reserve it for some time, as not considering it yet in a fit state to meet the public eye. Halley privately, and the society officially, urged him at least to enter his discovery on their register, in order to secure his just claim to priority. To this he consented; and promised all expedition in preparing his manuscript. It was not however, till April, 1686, that it was actually presented to the Royal Society. It comprised very nearly the contents of what now constitutes the first book of the "Principia," that is, the chief of the abstract dynamical part, but not including its actual application to the planetary system. The reading of Newton's communication was followed by some just encomiums upon it, and especially one from sir J. Hoskins, who was in the chair on that occasion, a particular friend of Hooke.

At this the latter took violent offence, and bitterly accused the vice-president of not having done him justice, by recording his own prior discovery of the same truths. After the meeting, Hooke publicly declared to the members, not only that he had made the same discovery, but that Newton had derived the solution of it, at least in part, from him. We have already seen enough to show what ground there was for such a pretence; and the general opinion of the members of the Royal Society appears to have been unfavourable to Hooke's claim. Halley communicated an account of what had taken place to Newton, who wrote a temperate and complete reply. But before his letter was sent, receiving a different, and, in fact, exaggerated account from another friend, he hastily added a very severe postscript. No sooner, however, was he assured in reply by Halley that his remarks were stronger than the occasion really demanded, than, with his usual candour, he apologised, and suggested the addition of a scholium (which now stands in the Principia), acknowledging that in circular orbits Wren, Hooke, and Halley, had already found the law of force inversely as the squares of the distances. This happily had the effect of putting an end to the dispute.

The council of the Royal Society ordered a letter of thanks to be addressed to Newton; and undertook the printing of the whole, as a separate treatise, at their own expense. Newton, on learning this determination from Halley, was still desirous to improve further upon his work before it was printed: and though he had now completed the third book on the system of the world, yet he determined to suppress it. Philosophy, he says, "is such an impertinently litigious lady, that a man had as good be engaged in lawsuits as have to do with her. I found it so formerly; and now I can sooner come near her again, but she gives me warning."

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In replying to this letter, Halley expresses regret that Newton's tranquillity should have been thus dis

turbed by envious rivals, but implores and conjures him, in the name of the society, and for the good of science, not to persist in withholding the third book; "especially," he adds, " as this will be the most interesting, and by far the most popular part of the whole, and will render it acceptable to those who will call themselves philosophers without mathematics, which are much the greater number." Newton, thus urged, could not do otherwise than comply. The second book was communicated in March, 1687; the third in the next month; and the whole published in May the same year, under the title of "Philosophiæ Naturalis Principia Mathematica." The first two books bear the more specific title "De Motu Corporum ;" and the third, that of "De Mundi Systemate."

Reception o, the System of Gravitation.

The reception which these brilliant discoveries met with was that which they so justly merited among those who were really capable of appreciating them; but when we allow for the real difficulty of the subject on the one hand, and the force of prejudice on the other, we shall not be surprised to find the number of Newton's followers at first but few, and the progress of his philosophy slow.

We have before observed how extensively the Cartesian system at this time prevailed, and how firmly it aad entrenched itself in the strong-holds of learning.

nd again, independently of this prepossession, the doctrine of Newton presented a vast extent of ideas of a nature wholly new to the apprehension. The minds of men were almost totally unprepared for such notions as those of central forces, even in abstract conceptions, and much less when connected with the idea of a physical attraction. The great masses of the planets suspended in empty space, and retained in their orbits by an invisible influence residing in the sun, were conceptions far too remote from any thing to which philo

sophy had hitherto been accustomed, to admit of their being received without hesitation and difficulty; and so entire was the absence of all association with any thing as yet understood, that it was not to be wondered at if even the force of demonstration should fail in securing the adoption of conclusions so unexpected. If we add to this the circumstance, that the establishment of the proofs was unattainable by any previously existing methods of mathematical investigation, and that they had to be carried on by a new sort of geometry invented for the purpose, and which even, when, with all Newton's skill and admirable taste for the old synthesis, it had been accommodated to that style and language, in a way which any other geometer would have shrunk from attempting, was in itself open to considerable appearance of objection, and involved in some obscurity;-putting these considerations together, we repeat, the slow and limited progress of the Newtonian philosophy will not be matter of wonder.

To the continental philosophers, in particular, this last circumstance operated as an obstacle, perhaps, in a stronger degree than with those of England. Nor was the former consideration without its force.

Leibnitz, from his own peculiar metaphysical views, felt great objections to the Newtonian ideas of gravitation, which he considered as a revival of the occult qualities of the peripatetics. Yet, admitting all the ultimate conclusions, he sought to establish them on principles of his own.

Huyghens was unable to admit the mutual attraction of all particles of matter, though he saw that the law subsisted between the planetary masses. John Bernoulli opposed the whole system. Cassini and Maraldi were quite unable to appreciate Newton's demonstrations, and continued to calculate the orbits of comets on the most unfounded hypotheses. Fontenelle continued a decided Cartesian to the end of his life. Mairan was, perhaps, one of the first instances of a convert, after having for a considerable time continued to adhere to the vortices.