62 



perception is in every instance in the brain 

 alone. * 



The researches of science seem to have 

 confirmed the conjectures of Hartley rela- 

 tive to the functions of the nervous system, 

 and shewn that there is a subtile substance, 

 which he called aether, occasioning vibra^ 

 tions in the nervous fibrils, and thus excit- 

 ing sensation, and communicating volition. 

 These vibrations may recur as miniature 

 vibrations in the brain, and reproduce sen- 

 sations, and also imagination and thought. 

 They may recur in the same order in which 

 they have formerly taken place, or pro- 

 miscuously, so as to produce perceptions 

 which could never have been excited by 

 objects in nature. If a person who has 

 been " long in populous cities pent," goes 



* See Introductory Lectures. 



