jkt. iv.] DISSERTATION SECOND. 147 



4. Descartes, Huygens, &c. 



Descartes flourished about this period, and has the merit 

 of being the first who undertook to give an explanation of 

 the celestial motions, or who formed the great and philoso- 

 phick conception of reducing all the phenomena of the 

 universe to the same law. The time was now arrived 

 when, from the acknowledged assimilation of the planets to 

 the earth, this might be undertaken with some reasonable 

 prospect of success. No such attempt had hitherto been 

 made, unless the crystalline spheres or horaocentrick orbs 

 of the ancients are to be considered in that light. The 

 conjectures of Kepler about a kind of animation, and of or- 

 ganick structure, which pervaded the planetary regions, were 

 too vague and indefinite, and too little analogous to any thing 

 known on the earth, to be entitled to the name of a theory. 

 To Descartes, therefore, belongs the honour of being the 

 first who ventured on the solution of the most arduous pro- 

 blem which the material world offers to the consideration of 

 philosophy. For this solution he sought no other data than 

 matter and motion, and with them alone proposed to explain 

 the structure and constitution of the universe. The matter 

 which he required, too, was of the simplest kind, possessing 

 no properties but extension, impenetrability, and inertia. 

 It was matter in the abstract, without any of its peculiar or 

 distinguishing characters. To explain these characters, 

 was indeed a part of the task which he proposed to himself, 

 and thus, by the simplicity of his assumptions, he added 

 infinitely to the difficulty of the problem which he under- 

 took to resolve. 



The matter thus constituted was supposed to fill all 

 space, and its parts, both great and small, to be endued 

 with motion in an infinite variety of directions. From the 



