246 ANTIENT METAPHYSICS. Book IV. 



thod pofTiWe, fir ft to fludy what others have faid upon any rubjed, 

 and then to try what you can add to their difcoveiies, or corred in 

 tliem. 



Ariftotle, as I have laid, has v/ritten two books upon the fubjed, 

 one upon Dreams, another upon Divination by Dreams. In the 

 firft, his theory of Dreams is as follows : All Senfations, he fays, are 

 produced by a certain movement of the Organs of Senfe ; which 

 movement is caufed by external objedls. This movement of the 

 Organs being carried on, and propagated to that internal principle 

 of animal life within us, which we call the Senforiumy and which he 

 calls a Common Senfe, produces that perception of the Mind called 

 Senfat'ion. The Motion of the organs, fays he, continues after the 

 aftion of external objeds upon them ceafcs, in the fame manner as 

 the Motion of a Body, impelled by another Body, continues after the 

 impelling Body ceafes to touch the Body impelled, the Motion being 

 continued by the Air propagating the Motion, which it receives from 

 the Body impelling, to other Air, and that Air to other Air \ and fo 

 on, till the impelling force growing weaker and weaker by degrees, 

 the Motion at laft ceafes *. And that this general Law of Motion 

 holds with refpedl to our Organs of Senfe, he proves by fundry ex- 

 periments. A man who has been looking at the fun for fome time, 

 when he is brought into a dark place, or a place with much lefs light, 

 fees nothing : And a man who has looked ftedfaftly, for fome time, at 

 one colour, when he transfers his fight to an objedt of a different 

 colour, it appears to him to be of the fame colour. All which, fays he, 

 can be owing to nothing elfe but the Motion of the Organ of Sight, 

 produced by the firft impreflion upon it, ftill continuing "f". Now, 

 this continued Motion in the Organ of Senfe is not perceiveable by 



us. 



• Lib. de Infomniis, cap. 2. in initio, 

 t Ibid. cap. 2. p. 693. Edit.du Fal. 



