CH. II.] MATERIAL IDEAS. 81 



expectations, forebodings, instincts, and emotions bring into 

 the mind. 



150. When the nerves which feel these imperfect sensations 

 are distributed to mechanical machines, they excite the same 

 movements, as if the sensation had been real. But these im- 

 perfect sensations must not be confounded with others aiising 

 from circumstances external to the nerves, although not external 

 to the organs of the senses ; as for example, when sparks are 

 seen in inflammation of the eye, or singing and humming in 

 inflammation or diseases of the cavity of the ear. These are 

 true external sensations, connected with an erroneous judgment. 

 The nerves of the eye and ear are really impressed by some- 

 thing external to them, but it is within the organ of hearing 

 or of vision itself, and the mind judges falsely, that the sen- 

 sations arise from objects which have customarily excited them ; 

 as, for example, that sparks of fire are seen, that bells are 

 heard ringing, water rushing, &c. [Vide § 378.) 



151. Since cerebral impressions excite movements at the 

 terminations of the nerves, where their course is obstructed 

 or reflected (147), it is highly probable, that very vivid sensa- 

 tional impressions are also deflected in their course from the 

 brain downwards to the periphery, either at the bifurcations of 

 the nerves, or in the ganglia, especially whei*e nerves are given 

 ofi* to other parts, or to surround the arteries, and excite such 

 gentle movements, as may have an influence on the contiguous 

 mechanical machines. 



