94 



HABIT AND INTELLIGENCE. 



[chap. 



White. 



Sounds do 

 not so 

 combine, 



but may 

 be discri- 

 minated. 



Reason of 

 this in the 

 constitu- 

 tion of the 

 nerves of 

 hearing. 



The 



nerves of 

 smell, 

 sight, and 

 hearing 

 transmit 

 no other 

 sensation. 



colours are combined, the resultant is white, which is 

 totally unlike any of them, and could not possibly have 

 been predicted from them.^ The sense of hearing is the 

 only one among the senses which has any power of cog- 

 nising, as distinct, sensations of the same order which come 

 mixed together. We have a power of distinguishing simul- 

 taneous sounds, and even of directing the consciousness, by 

 a voluntary act of attention, to one sound among many ; 

 thus, any one can, by a little effort of attention, hear 

 what a particular person is saying amidst a buzz of con- 

 versation ; and some persons acquire the power of listening 

 to a single instrument in a whole orchestra. This is no 

 doubt an acquired power — that is to say, it is not likely 

 that infants are born with it ; but it is a power which is 

 not the less characteristic of the sense of hearing ; no 

 amount of practice would give to the eye the slightest 

 vestige of any power analogous to this ; — no practice could 

 confer the power of seeing any of the separate prismatic 

 colours in white light. There is reason, however, to 

 believe that the sense of hearing is no exception to the 

 law that sensations of the same sense, when transmitted by 

 the same nerve, combine into a single sensation. There is 

 reason to believe that distinct sounds are not transmitted 

 to the auditory ganglia by the same nerve, but that on the 

 contrary sounds of different pitch excite each a different 

 nerve. I shall have to return to this subject. 



I think there are no cases of sensations of different 

 senses being transmitted hj the same nerves, except those 

 already mentioned, of the nerv^es of the sldn being at once 

 nerves of touch and of heat, and those of the mouth bein" 

 at once nerves of touch, of heat, aud of taste. The nerves 

 of smell, of sight, and of hearing appear to transmit no 

 sensations except those which are peculiar to them. 



As stated above, I believe it is a law that when the 

 same nerve transmits two or more sensations of the same 

 sense, they combine into a single sensation ; but when the 

 sensations transmitted by the same nerve belong to distinct 

 senses, they are cognised as distinct. I think we may with 



1 On tlie laws of the combination of colours, see Note at end of chapter. 



