XXXVI.J 



PERCEPTION. 121 



over the skin ; this will be cognised as a change, not in the Coguitiou 

 character of the sensation, but in its locality ; and this also "he motion 

 will give rise to a cognition of space. I do not say that of a sensa- 

 such experiences as these will give a fully developed cog- j^^ ^-^^^^ 

 nition of space. They can only give the cognition of space ways, only 

 of two dimensions ; of surface only, not of solidity. But extension 

 I believe they can, and do, give the first rudimentary can be 



. . „ cognised. 



cognition 01 space. 



I do not suppose that the cognition of space could be Cognitions 

 produced by a uniform sensation spread over a sensitive "[j^^^^gf ^ 

 surface, such as the sensation of heat over the whole skin time 

 of the body when in a warm bath : just as the cognition "n^parallel 

 of time could not be produced by the unchanging con- '*^*y'*- 

 tinuance of the same sensation. The cognition of time 

 is produced by the commencement, the cessation, or the 

 change of sensations ; and the cognition of space, as I 

 believe, is produced in an exactly parallel way, by the 

 existence of sensations at the same time in different parts 

 of a sensitive surface. 



By these merely passive sensations, we acquire the 

 cognition of space-relation between our own sensations 

 only ; and that, I think, in space of only two dunensions. 

 The cognition of a third dimension in space is, I think, 

 due not to any merely passive sensation, but to our motor 

 activity, and the sensation of it ; and to the same " mus- Pereep- 

 cular sense " is due the perception of objects in external o\°"(.°g 

 space^external, that is, to the body. Our perceptions of e.xtemal to 

 external objects, in so far as they are derived from touch is^acqnired 

 and not from sight, consist of combined impressions of^y*** 



„ , . ^ ' . . 1.. •, motor 



Torm and resistance (this analysis is admitted by all sense. 

 writers on the subject) ; and I believe that these percep- 

 tions are inferences from our sensations of motion and of 

 resistance to motion. This will be intelligible to any one 

 who will watch, or imagine, a blind man examining a new 

 object with his hands. He moves them round it in order 

 to ascertain its form, and feels its resisting power in order 

 to ascertain its hardness or softness. 



There are thus three possible ways in which impressions Summary. 

 on the senses may produce a cognition of space ; and I 



