THE PERCEPTION OF SPACE. 183 



Prisms show this in an even more striking way. If tlie 

 eyes be armed with spectacles containing slightly prismatic 

 glasses with their bases turned, for example, towards the 

 right, every object looked at will be apparently translocated 

 to the left ; and the hand put forth to grasp any sncli object 

 will make the mistake of passiug beyond it on the left side. 

 But less than an hour of practice in wearing such spectacles 

 rectifies the judgment so that no more mistakes are made. 

 In fact the new-formed associations are already so strong, 

 that when the prisms are first laid aside again the opposite 

 error is committed, the habits of a lifetime violated, and 

 the hand now passed to the right of every object which it 

 seeks to touch. 



The primitive chaos thus subsists to a great degree 

 through life so far as our immediate sensibility goes. We 

 feel our various objects and their bignesses, together or in 

 succession ; but so soon as it is a question of the order and 

 relations of many of them at once our intuitive apprehension 

 remains to the very end most vague and incomplete. 

 Whilst we are attending to one, or at most to two or three 

 objects, all the others lapse, and the most we feel of them is 

 that they still linger on the outskirts and can be caught 

 again by turning in a certain way. Nevertheless throughout 

 all this confusion tve conceive of a world spread out in a perfectly 

 fixed and orderly fashion, and we believe in its existence. The 

 question is : Hoio do this conception and this belief arise ? How 

 is the chaos smoothed and straightened out ? 



Mainly by two operations : Some of the experiences are 

 apprehended to exist out- and alongside of each other, and 

 others are apprehended to interpenetrate each other, and 

 to occupy the same room. In this way what was incoherent 

 and irrelative ends by being coherent and definitely related ; 

 nor is it hard to trace the principles, by which the mind is 

 guided in this arrangement of its perceptions, in detail. 



In the first place, following the great intellectual law of 

 economy, we simplify, unify, and identify as much as we 

 possibly can. Whatever sensible data can be attended to together 

 we locate together. Their several extents seem one extent. The 

 place at which each appears is held to be the same with the place 



