62 LECTURE IL 



ductive of illusory sensations, ^nd excite 

 fallacious ideas, 



If this theory of nervous actions could 

 be proved, the extent of our knowledge 

 would only lead to this conclusion, that 

 motions of a subtile substance, propagated 

 to and fro in the nervous fibrils, take place 

 in consequence of excitement by impulses 

 and volition ; but from such motions, it 

 seems impossible to account for sensation or 

 volition. We can conceive no variety in these 

 motions, but what relates to degree, duration, 

 and succession, and it seems impossible to 

 believe that sensation can be the result of 

 such motions, or that ideas can arise from 

 any succession or train of them. Certain 

 persons will, therefore, I doubt not, con- 

 tinue to think that sensation, remem- 

 brance, comparison, judgment, and voli- 

 tion are properties of some distinct sub- 

 stance. 



The essences or primitive parts of what 

 we call matter, are too subtile to be per- 



