XXXVI.] PERCEPTION. 125 



centre would be its own eye ; but it would be totally un- 

 conscious of any distance between its eye and the objects. 

 Not, however, that they would seem close to its eye ; the 

 question whether they were near or far would for it have 

 no meaning.^ If in the course of its development it were 

 to acquire a hand or a tentacle, by means of the motions 

 of that organ it would acquire the sense of distance, and 

 then its knowledge of the properties of space would be as 

 complete as ours ; but, as its ideas of angular magnitude 

 were more early acquired than its ideas of distance or 

 linear magnitude, it would always think more easily of 

 the former ; and it would spontaneously think of space in 

 terras of polar co-ordinates. But if, on the contrary, the 

 organ of touch were developed first and the eye after- 

 wards, it would acquire its ideas of distance or linear ■ 

 magnitude first, and of angular magnitude later; and it 

 would consequently always think of space in terms of recti- 

 linear co-ordinates. Now this last is practically our case. 

 In all perceptions and ideas of bodies as existing in 

 space, impressions of sight are combined and practically impres- 

 identified with impressions of touch. Thus, if I perceive ^he'two 

 the size of a book by the eye, I know of what size it will senses are 

 seem to the hand ; or if I first perceive its size by the hand, ^^ t^e 

 I know of what size it will seem to the eye. In common ^^^'^' 

 laneuase it would be said that it seems of the same size to 

 both. But how can it be possible to identify an angidar 

 magnitude and a linear one with each other ? The identi- as the 



lip 



fication is the result solely of habitual experience. If we had ^^^^}^^ °' 

 no means of ever touching what we saw, and no means of 

 ever seeing what we touched, we should have no notion of 

 identifying the two, nor would it be possible for us to do 

 so, even in imagination ; for there is no common measure 

 for linear and angular magnitudes ; nor is there any resem- 

 blance between the sensations of light and colour felt by 

 the eye, and the impressions of contact and resistance felt 

 by the touch. Without experience there would be no 

 more connexion in perception or thought between the 

 objects of sight and of touch, than there is between colours 



' See Nnte at rnrl of chapter. 



