VORTEX. The theory of Descartes on the formation and mechanical laws of the universe was first published in 1637, in his Principle Philosophies.' One part of this theory, namely, the hypothesis of vortices, is almost the only one which generally passes by the name of Des Cartes. But it should be remembered that this is only a part, and a small part, of the system which rendered the Newtonian view of astronomy for a long time unacceptable to the continental philosophers. The metaphysics, the mechanics, and the astronomy, of the once cele brated Cartesian system, combined as they were by one writer, and that writer a most skilful and elegant proposer of his own views, are to be looked at together as that which Newton's philosophy had to meet. Perhaps we should not be wrong in saying that the impossibility of a vacuum, maintained by Des Cartes as self-evident, was a greater ob stacle in the way of the theory of gravitation, with which it seemed incompatible, than the theory of vortices, which Des Cartes proposed as an hypothesis, and which did not necessarily contradict Newton's deductions. Wo shall here present a brief sketch of the system, so far as is necessary, from the third book of the Principia Philosophias:' this sketch is, as far as it goes, only a table of contents of the work The human imagination must not either limit the power of God or unduly exalt its own : And it must not suppose that all things were made for man's use only. In enumerating phenomena Descartes pre fers rather to deduce them from causes than to make them serve in finding causes. He then describes the relative distances of the planets, and asserts the immensity of the distances of the fixed stars. After the usual statements relative to the light of the suu, planets, and fixed stars, he rejects the Ptolemaic hypothesis, and observes that those of Copernicus and Tycho Brah6 differ very little as hypotheses, and ex plain phenomena in the same manner. He says also that Tycho, though lie denies the motion of the earth, yet in reality gives it more motion than the former (with Descartes. relative motion was a most absolute idea); whence, differing from both, he will, with more truth – — — than Tycho, and more care than Copernicus, take away the motion of the earth. To this end he proposes an hypothesis, which will be very fit to explain phenomena ; but only as an hypothesis, not as an abso lute truth. Tho fixed stars are exceedingly distant ; the sun consists of a fluid and mobile matter, which would carry the circumjacent parts of the heavens with it, but which does not change its place In the heavens : the solar matter does not need aliment. Each one of the fixed stars has en immense space about it, in which there is no other fixed star. The heavens are filled with fluid matter, as astronomers commonly suppose, because they do not see how the phenomena of the planets, can be otherwise explained. Each of the heavens carries with it all bodies therein contained. Tho earth and every planet is at rest in its heaven, though it may be carried with that heaven : the earth therefore, or any one planet, may be said not to move, but all the others must be said to move. The whole heaven of the sun is moved round it in the manner of a whirlpool, "in moduin cujusdam vorticie," the more distant parts moving more slowly than the nearer ; and the planets are carried round with this heaven. And as in the larger
whirlpool are sometimes seen smaller ones, which are carried round in the larger ; so each planet is the centre of a smaller vortex, in which its satellites are carried round their primary. The sun and planets are carried round their axes by the motion of their vortices (the inclina tions of the planetary orbits to the ecliptic have an obvious explana tion : the inequalities in longitude are mentioned without explanation). It can hardly be that an hypothesis which thus explains phenomena can be false : to say this would seem to be an imputation upon the Deity, namely, the supposition that He made us so imperfect, that a right use of reason might lead us to deceive ourselves (Descartes is not the only one who has used this sort of argument). Nevertheless, he is willing that it should be put forward only as an hypothesis. And though both religion and reason teach that God made the world com plete, that not only the seeds of plants were formed, but plants them selves, &c., yet the nature of things will be better explained if it can be shown how, as from seed, the solar system was produced (Descartes here fears the imputation which was afterwards cast upon the author of the nebular hypothesis [SOLAR ST8TEIld). All matter originally Con sisted of particles, forming numbers of fluid heavens, revolving about their several axes. These particles were originally equal in size and motion ; they also became spherical, when the corners had been woru down by rubbing against each other. And since no portion of space can be vacuous [Vacuum], the interstices of these spheres must be filled by matter, of form perpetually changing, derived from the parts worn off the angles : this last kind of matter moves more quickly than the other. Besides this there is a third sort of particles of matter, more solid, or else of form more adapted to motion : of this planets and comets are composed. There are three classes of celestial heavens : the first, that of our sun and its system ; the second, the various heavens of the fixed stare immediately adjoining ; the third, including all which are beyond, and which never can be seen in this life. The primary particles, as those are called which are obtained by attrition from the secondary particles, at last become more than enough to fill the intervening spaces (how this could be Descartes does not say), and the residue, as fast as it arises, was forced to the centres of the vortices, where it formed certain very fluid spherical bodies : these are the sue and fixed stars. The secondary particles receded from the centres to make room. The efflux of these primary particles from the fluid bodies just described is light. The centrifugal force of particles In motion round a centre is then dwelt on, and tho circular form of the sun and fixed stars is attributed to it. The motion of the vortices must be such that their contiguous parte may have a common motion. The primary particles flow from the poles of each vortex towards the centre, and from the centre towards the other parts. But the same must not be said of the secondary or spherical particles (the reasons given are fanciful in the extreme, consisting entirely in different motive powers given to the two species of particles).