CHAP, ix.] OF THE SENSE OF SIGHT. 429 



Now no one dreams of seeing in the deflagration of the powder and 

 the propulsion of the ball which succeed the shock from the dis- 

 charge of a musket, the direct transformation of the movement 

 operated by that discharge. It would be just as little logical to 

 wish to find in the conscious phenomenon of sensation the 

 mechanical agitation which has brought into play the sensitive 

 apparatus. In the firearm and in the nervous system, the exterior 

 shock has simply determined a perturbation of equilibrium ; it has 

 let loose forces which neutralised each other ; it has acted as a 

 force of disengagement. 



