74 



he is of the difference bet ween divineand human power. 

 It is true, God can intermingle those things one with 

 another, and then sever them at his pleasure, because 

 lie is, at the same time, all-knowing and all-powerful; 

 but there is no man now exists nor ever will perhaps, 

 who shall ever be able to accomplish things so very diffi- 

 cult." What an eulogium are these words in the mouth 

 of such a philosopher as Plato, and how glorious is 

 he who hath successfully accomplished what appeared 

 impracticable to that prince of philosophers ! And 

 what elevation of genius, what piercing penetration 

 into the most intimate secrets of nature, displays it* 

 self in what we have just now recited from Plato, 

 concerning the nature and theory of colours, at a time 

 when philosophy was but yet in its infancy ! 



3. Although the system of Descartes, respecting the 

 propagation of light in an instant, is scarcely admit- 

 ted at present by the most part of philosophers, nor 

 has been ever since Messrs. Cassini and Romer disco. 

 vered that its motion was progressive; yet, as that 

 system was for a long while in vogue, and the whole 

 honour of the invention of it ascribed to Descartes, 

 it will not be amiss, in a few words, to make appear, 

 that he drew the idea of it from Aristotle and his 

 commentators. The opinion of the modern philoso- 

 phers is, that light is nothing else but the action of a 

 subtle matter upon the organs of sight. This subtle 

 matter is supposed to fill all that space which lies be. 

 tween the sun and us ;._and^hat particle of it, which is 

 oext to the sun, receiving thnce an impulse, must in- 

 stantaneously commuaicite it to all the rest which 

 3ic between the sun and the organ of sight. To ren- 

 der this the more cvit!ent,Descartes introduces the com. 

 parison of a stick; which, by reason of the conti- 

 nuity of its parts, cannot in any degree be moved 

 lengthways at one end, without instantaneously be. 

 ing put iuto the same degree of motion at the other 

 end. 



