284 PQYSIOLOGY OF MUSCLES AND NERVES. 



end of the nerve of hearing, then the sound of an 

 orchestra would elicit in us the sensation of light and 

 colour, and the sight of a highly coloured picture 

 would elicit in us impressions of sound. The sensa- 

 tions which we receive from outward impressions are 

 therefore not dependent on the nature of these im- 

 pressions, but on the nature of our nerve-cells. We 

 feel not that which acts on our bodies, but only that 

 which goes on in our brain. 



Under these circumstances it may appear strange 

 that our sensations and the outward processes by 

 which they are evoked are so entirely in agreement ; 

 that light elicits sensations of light, sound sensations 

 of sound, and so on. But this agreement does not really 

 exist ; its apparent existence is only due to the use of 

 the same name to express two processes which have 

 nothing in common. The process of the sensation of 

 light bears no likeness to the physical process of the 

 ether vibrations which elicit it; and this is evident 

 even in the fact that the same vibrations of ether 

 meeting the skin elicit an entirely different sensation, 

 namely, that of warmth. The vibrations of a tuning-fork 

 are capable of exciting the nerves of the human skin, 

 and then they are felt ; they may excite our auditory 

 nerves, and then they are heard ; and under certain 

 circumstances they may be seen. The vibrations of 

 the tuning-fork are always the same, and they have 

 nothing in common with the sensations which they 

 elicit. Though the physical processes of the vibrations 

 of ether are called, sometimes light, and at another time 

 heat, a more accurate study of physics shows that the 

 process is the same. The usual classification of physical 

 processes into those of sound, light, warmth, and so on. 



