The chevalier Louville communicated a memoir to the Royal Academy of Sciences in 1720, which was the first in their collection in which the Newtonian principles are recognised, though not to their full extent. S'Gravesande introduced the Newtonian system in the Dutch universities at a somewhat earlier period. Maupertuis became a convert during a visit to England in 1728; and in 1730 published a philosophical treatise, entitled Figure des Astres," in which he defended the property of attraction from metaphysical objections.

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Objections, in fact, of this class, seem to have been among the most formidable which the notion of attraction had to encounter. It was alleged to be a metaphysical absurdity, as amounting to the assertion "that a body acts where it is not." But the disputants did not perceive that this proposition is only absurd when understood according to a particular interpretation of the terms; and that it is no more than is literally the truth, in respect to almost every species of physical action, since we have reason to believe that no bodies are ever actually in contact.

The philosophy of the age was still involved in that sort of metaphysical realism, which could not adopt a name simply to stand as the symbol for a general class of facts, without supposing some latent reference to causation in the mystified sense then attached to that term. If told that gravitation was nothing but the general fact of a tendency of bodies to approach each other in proportion to the mass directly and the square of the distance inversely, a philosopher of that period could not recognise this as worthy the name of philosophy, unless such an announcement was understood as also conveying some reference to a latent something, he knew not what, by virtue of which the effect was produced. Notwithstanding all Newton's care and caution, in warning the readers of the Principia that he meant nothing more than he expressed, and that, when he used such terms as attraction and gravitation, he was to be understood as referring simply to the actual laws which he had established- to the bare facts as collected

in their most general forms, - yet it was evident that his readers were in general little prepared for any such simple and intelligible philosophy as this; indeed, men were hardly yet able to believe that any thing intelligible could be true philosophy. It seems highly probable that it was much more in the view of throwing out something which might accommodate itself to the taste of his readers, than of satisfying himself, that Newton proposed certain conjectures about an ether which might be supposed to fill all space, and to be somehow the medium of communication of that sort of action which constitutes gravitation. It is surely precisely in this point of view, without pretending to decide any thing as to the preference for the several hypotheses, and clearly with an equal disregard, on his own part, for them all, that he says so explicitly *, "The term gravity I here use in general to signify the tendency, of whatever nature it may be, of bodies to approach each other; whether that tendency arise from the action of the bodies mutually seeking each other, or by emitted exhalations mutually agitating each other; whether it originate from the action of an ether, or any kind of aerial medium, corporeal or incorporeal, impelling bodies floating in it continually towards each other." This, as well as several other passages in his writings, clearly show that Newton, if he adopted any such ideas, treated them as mere conjectures, the images with which his fancy sometimes amused itself; but he always carefully and resolutely kept them apart and distinct from all real philosophical conclusions.

Another question not a little agitated at that time was whether gravity be an inherent property of matter. This, like most other of those verbal disputes often designated as metaphysical, was not perceived to turn wholly upon the definition of the terms. None of the properties of matter are known except by observation; none are inherent but those which, by observation, are found to be constant and universal. If observation show this to be true of gravity, then it is inherent: but the

Schol. Prop. 69. lib. i.

phrase was, perhaps, understood differently; and it was, in some of the arguments, meant that gravitation could not be conveyed between two bodies at a distance without some interposed medium of communication. Newton's conjectures, as we have just seen, appear to refer to this view of the subject. The question then was, whether gravitation depend solely upon something in matter, or also partly on the interposed medium; a question which can never be determined until we have proved the existence and ascertained the properties of such a medium. Cotes, in the preface to the second edition of the Principia, stated gravity to be a property of matter as truly such as extension, impenetrability, or any other property, and has been censured for saying So, If he meant it in the former sense, he was undoubtedly correct; and that he did so understand it, appears to us unquestionable from the whole tenour of his observations.*

Though the progress of Newton's philosophy was thus slow on the Continent, it was not unnatural that it should be somewhat more rapid in his own country, and especially in the university to which he belonged. It appears that, before the publication of the Principia, Newton gave, as parts of the course from his professorial chair, lectures on the dynamical views which he was now developing. Whiston, his friend and successor, mentions the fact; and that he heard them through at the time, without at all understanding them. This may be readily conceived, without any disparagement either to the lecturer or auditor: the subject was wholly new, and little susceptible of illustration in a formal public lecture delivered in Latin, and would have appeared very abstruse and uninteresting before its connection with the great truths of the planetary world could have been even guessed at. The Cartesian was certainly at that time the established system in the university; and though Newton continued to explain his doctrines, which, doubtless, after the publication of the Principia, must have assumed a new degree of interest, yet it was some

* Pref. xxii. edit. Jes.

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time before they were generally understood or admitted. However, in 1694, Dr. Samuel Clarke, then an undergraduate, kept the act for his bachelor's degree on a question from the Principia. This proves that the new doctrines were then recognised by the university. And, in 1697, the same distinguished individual published a new edition of the popular and standard treatise," Rohault's Physics," to which he appended acute and elaborate notes, tending to the direct refutation of the Cartesian doctrines of the text, and thus insinuating the new philosophy under the protection of the old. After this period the Newtonian system became generally read and adopted in the university. A knowledge of Newton's discoveries, as well as a just appreciation of them, appears very early to have extended itself to Scotland. In a journal kept by his contemporary at Cambridge, Mr. Pryme, we find it mentioned, in 1692, that Newton had before that time received numerous congratulatory letters on his Principia, especially from Scotland." In the Scottish universities, the system of gravitation found able and zealous supporters. It was taught by James Gregory at St. Andrew's, and David Gregory at Edinburgh, prior to 1691. In that year the latter was removed to the astronomical chair at Oxford, and was able so far to introduce the study of Newton in that university, that it is expressly mentioned by Whiston, "he had already caused several of his scholars to keep acts, as we call them, upon several branches of the Newtonian philosophy; while we at Cambridge, poor wretches! were ignominiously studying the fictitious hypotheses of the Cartesians." Dr. Keill soon after gave public experimental lectures in Oxford, in which, Desaguliers informs us, "he laid down very simple propositions, which he proved by experiments; and from these he deduced others more compound, which he still confirmed by experiments, till he had instructed his auditors in the laws of motion, the principles of hydrostatics and optics, and some of the chief propositions of sir I. Newton concerning light and colours. He began these courses in Oxford, about the year 1704 or 1705,

and in that way introduced the love of the Newtonian philosophy." The subject was new, and the university was not at that time wholly absorbed in the single subject of classical studies. In these lectures Desaguliers succeeded him in 1710, and subsequently gave lectures in London in 1713; where, he tells us, he found "the Newtonian philosophy generally received among persons of all ranks and professions, and even among the ladies, by the help of experiments."

Among the most distinguished converts to the Newtonian doctrines we may reckon Locke; and the manner in which his conviction was formed is characteristic of the clearness of his methodical understanding. His knowledge of mathematics was but quite elementary; he accordingly applied to Huyghens for his testimony whether the mathematical deductions in the Principia, considered abstractedly as such, were correct: assured of their accuracy by so eminent an authority, he took their truth for granted, and examined the physical reasoning to which they are applied; this appearing to him satisfactory, he became rationally convinced of the truth of the whole system. Desaguliers mentions this fact as told him by Newton.* It would seem that afterwards he had conversed much with Newton himself on the subject; and, among his papers, was found a letter from Newton, containing a short series of propositions, by which he seems to have endeavoured to give him the direct train of deduction leading to the theorem of elliptic motion, in a form somewhat different from that adopted in the Principia.†

Newton's subsequent Pursuits.

From what we have already seen of Newton's pursuits, it is manifest how fully his time must have been occupied from the year 1665 to 1687. But the unparalleled greatness of his achievements in physicomathematical science is yet more surprising, when we * Exper. Phil. preface.

+ Lord King's Life of Locke, p. 209.