Thus far Newton proceeded in ascertaining the existence, and in tracing the effects, of the principle of gravitation, and had done so with a success of which there had been no instance in the history of human knowledge. At the same time that it was the most successful, it was the most difficult research that had yet been undertaken. The reasonings upward from the facts to the general principle, and again down from that principle to its effects, both required the application of a mathematical analysis which was but newly invented ; and Newton had not only the difficulties of the investigation to encounter, but the instrument to invent, without which the investigation could not have been conducted. Every one who considers all this, will readily join in the sentiment with which Bailly closes a eulogy as just as it is eloquent. Si, comtne Platon a pense, it existoit dans la nature une echelle d'etres et de substances intel ligentes jusqu'a 'Etre Supreme,respece humaine, defendant ses droits, auroit une finite de grands hommes a presenter; mail Newton, suivi de ses verites pures, mon treroit le plus haut degri de force de l'esprit humain, et sujiroit soul pour lui as signer sa vrai place.' Though the creative power of genius was never more clearly evinced than in the discoveries of this great philosopher, yet the influence of circumstances, always exten sive and irresistible in human affairs, can readily be traced. The condition of know ledge at the time when Newton appeared was favourable to great exertions ; it was a moment when things might be said to be prepared for a revolution in the matiemati cal and physical sciences. The genius of Copernicus had unfolded the true system of the world; and Galileo had shown its excellence, and established it by argu ments, the force of which were generally acknowledged. Kepler had done still more, having, by an admirable effort of generalisation, reduced the facts concerning the planetary motions to three general laws. Cassini's observations had also extended the third of these laws to the satellites of Jupiter, showing that the squares of their periodic times were as the cubes of their distances from the centre of the body round which they revolved. The imaginary 'apparatus of cycles and epicycles,—the immobility of the earth,—the supposed essential distinction between celestial and ter restrial substances, those insuperable obstacles to real knowledge, which the prejudice of the ancients had established as physical truths, were entirely removed; and Bacon had taught the true laws of philosophising, and pointed out the genuine method of extracting knowledge from experiment and observation. The leading principles of mechanics were established; and it was no unimportant circumstance, that the Vor tices of Descartes had exhausted one of the sources of error, most seducing on account of its simplicity.
All this bad been done when the genius of Newton arose upon the earth. Never till now had there been set before any of the human race so brilliant a career to run, or so noble a prize to be obtained. In the progress of knowledge, a moment had arrived more favourable to the developement of talent than any other, either later or earlier, and in which it might produce the greatest possible effect. But, let it not be supposed, while I thus admit the influence of external circumstances on the exertions of intellectual power, that I am lessening the merit of this last, or taking any thingirom the admiration that is due to it. I am, in truth, only distinguish ing between what it is possible, and what it is impossible, for the human mind to effect. With all the aid that circumstances could give, it required the highest degree of intel lectual power to accomplish what Newton performed. We have here a memorable, perhaps a singular instance, of the highest degree of intellectual power, united to the most favourable condition of things for its exertion. Though Newton's situation was
more favourable than that of the men of science who had gone before him, it was not more so than that of those men who pursued the same objects at the same time with himself, placed in a situation equally favourable.
When one considers the splendour of Newton's discoveries, the beauty, the sim plicity, and grandeur of the system they unfolded, and the demonstrative evidence by which that system was supported, one could hardly doubt, that, to be received, it re quired only to be made known, and that the establishment of the Newtonian philoso phy all over Europe would very quickly have followed the publication of it In drawing this conclusion, however, we should make much too small an allowance for the influence of received opinion, and the resistance that mere habit is able, for a time, to oppose to the strongest evidence. The Cartesian system of vortices had many followers in all the countries of Europe, and particularly in France. In the univer sities of England, though the Aristotelian physics had made an obstinate resistance, they had been supplanted by the Cartesian, which became firmly established about the time when their foundation began to be sapped by the general progress of science, and particularly by the discoveries of Newton. For more than thirty years after the publication of those discoveries, the system of vortices kept its ground, and a translation from the French into Latin of the Physics of Rohault, a work en tirely Cartesian, continued at Cambridge to be the text for philosophical instruction. About the year 1718, a new and more elegant translation of the same book was pub lished by Dr Samuel Clarke, with the addition of notes, in which that profound and ingenious writer explained the views of Newton on the principal objects of discussion, • so that the notes contained virtually a refutation of the text ; they did so, however, only virtually, all appearance of argument and controversy being carefully avoided. Whether this escaped the notice of the learned Docters or not is uncertain, but the new translation, from its better Latinity, and the name of the editor, was readily ad mitted to all the academical honours which the old one had enjoyed. Thus, the stra tagem of Dr Clarke completely succeeded ; the tutor might prelect from the text, but the pupil would sometimes look into the notes, and error is never so sure of being exposed as when the truth is placed close to it, side by side, without any thing to alarm prejudice, or awaken from its lethargy the dread of innovation. Thus, there fore, the Newtonian philosophy first entered the university of Cambridge under the protection of the Cartesian' If such were the obstacles to its progress that the new philosophy experienced in a oountry that was proud of having given birth to its author, we must expect it to ad vance very slowly indeed among foreign nations. In France, we find the first astro nomers and mathematicians, such men as Cassini and Maraldi, quite unacquainted with it, and employed in calculating the paths of the comets they were observing on hypotheses the most unfounded and imaginary; long after Halley, following the principles of Newton, had computed tables from which the motions of all the comets that ever had appeared, or ever could appear, might be easily deduced. Fontenelle, with great talents and enlarged views, and, as one may say, officially informed of the progress of science all over Europe, continued a Cartesian to the end of his days. Mairan in his youth was a zealous defender of the vortices, though he became after wards one of the most strenuous supporters of the doctrine of gravitation.