154 HISTORY OF SC'IENCE. 



the same. This proposition is nearly equivalent to one of those great 

 generalizations which modern science has produced. Be it observed, 

 however, that Descartes, so far from reaching it by inductions from ex- 

 periments and measurements, derives it by a short process of deduc- 

 tions from the immutability of the divine attributes, as he conceives 

 them. Such modes of reasoning are, of course, productive of many 

 fallacious conclusions in other cases, and Descartes' writings abound 

 in such fallacies. 



It was from his ideas of motion, and of matter endued with certain 

 attributes, as extension, impenetrability, inertia, etc., that Descartes 

 evolved his famous theory of the planetary movements. He con- 

 ceived that all space was filled with matter, the parts of which had 

 originally been endued with motion in an infinite variety of directions ; 

 and as it was impossible that motion in a straight line could result from 

 combination of such various motions, there must have been continued 

 deflections from the rectilinear directions. Hence arose circular mo- 

 tion and its attendant centrifugal force. At length matter came to 

 gather itself for the most part into whirling eddies, or vortexes, in which 

 also the more solid concretions were swept round. And, according 

 to Descartes, the solar system is formed by a vast whirlpool or vortex, 

 sweeping round the sun and carrying with it the planets, which move 

 with different velocities according to the position they occupy in the 

 vortex. Those planets which have satellites are themselves the centres 

 of smaller vortexes, which float in the great vortex. This theory ap- 

 peared simple, and it was certainly a great improvement on the crys- 

 talline spheres of Ptolemy, or the intelligence which Kepler supposed 

 to be seated in each planet in order to guide it in its course. It 

 seemed also to present itself to the understanding with that clearness 

 of conception which the author and his followers esteemed the best 

 criterion of truth. It was discussed, defended, and finally taught in 

 nearly every place of learning in Europe, supplanting in the English 

 universities the doctrines of Aristotle himself. A book embodying 

 Descartes' physical theories was, in fact, for long afterwards the esta- 

 blished text-book at the University of Cambridge. Although the vortex 

 theory appeared to account for the planetary motions by a single prin- 

 ciple, and that one quite intelligible to the popular mind, for every- 

 body could witness the formation of eddies and whirlpools in water, 

 and observe how in 'these floating bodies are carried round, its sim- 

 plicity was apparent only. For several facts were known which the 

 theory in its simple form failed to explain. For instance, Kepler had 

 shown that the planetary orbits were elliptical, hence the vortex of the 

 solar system must also be elliptical. Descartes tries to explain this by 

 the pressure of adjoining vortexes. But the planetary elliptical orbits 

 have not their longest axes in the same direction, and the position of 

 the sun is in a. focus of each ellipse, and not in the centre of each ellipse, 

 Besides, the planets do not revolve in the plane of the sun's equator. 



