Now the first or subtilest element, ac cording to the laws of motion, must oc cupy the centre of each system, or vortex, by reason of the smallness of its parts ; and this is the matter which constitutes the sun and the fixed stars above, and the fire below. The second element, made up of spheres, forms the atmosphere, and all thereafter between the earth and the fixed stars : in such sort, that the largest spheres are always next the cir cumference of the vortex, and the small est next its centre. The third element, formed of the irregular particles, is the matter that composes the earth, and all terrestrial bodies, together with comets, spots in the sun, &c.
He accounts for the gravity of terres trial bodies from the centrifugal force of the ether revolving round the earth: and upon the same general principles he pre tends to explain the phenomena of the magnet, and to account for all the other operations in nature.
Of this great man many eulogia have been published, by persons very capable of appreciating his worth and his talents. We shall mention the opinion entertained of him by two or thee of our own coun trymen.
Dr. Barrow, in his " Opuscula," ob serves, that Des Cartes was doubtless a very ingenious man, and a real philoso pher, and one who seems to have brought those assistances to that part of philoso phy relating to matter and motion, which perhaps no one had done before; namely, a great skill in mathematics ; a mind ha bituated, both by nature and custom, to profound meditation; a judgment exempt from all prejudices and popular errors, and furnished with a good number of cer tain and select experiments ; a great deal of leisure ; an entire disengagement, by his own choice, from the reading of use less books,and the avocations of life: with an incomparable acuteness of wit, and an excellent talent of thinking clearly and distinctly, and of expressing his thoughts with the utmost perspicuity.
Dr. Halley, in a paper concerning op tics, affirms that Des Cartes was the first, who, in modern times, discovered the laws of refraction, and brought dioptrics to a science. And Dr. Keil says, that Des Cartes was so far from applying geo metry and observations to natural philo sophy, that his whole system is but one continued blunder, on account of his ne gligence in that point ; which he could easily prove, by showing that his theory of the vortices, upon which his system is founded, is absolutely false, for that New ton has shewn that the periodical times of all bodies that swim in vortices must be directly as the squares of their dis tances from the centre of them ; but it is evident, from observations, that the planets, in moving round the sun, ob serve a law quite different from this ; for the squares of their periodical times are always as the cubes of their distances : and therefore, since they do not observe that law, which of necessity they must, if they swim in a vortex, it is a demon stration, that there are no vortices is which the planets are carried round the sun.