THE METAPHYSICS OF SENSATION 275 



side the eye, and in a region exactly opposite to 

 that in which the pressure is made. 



But while it seems to me that there is no reason 

 to doubt that the extradition of sensation is more 

 complete in the case of the eye than in that of 

 the skin, and that corporeal distinctness, and 

 hence space, are directly suggested oy vision, it is 

 another, and a much more difficult question, 

 whether the notion of geometrical solidity is 

 attainable by pure vision; that is to say, by a 

 single eye, all the parts of which are immoveable. 

 However this may be for an absolutely fixed eye, 

 I conceive there can be no doubt in the case of an 

 eye that is moveable and capable of adjustment. 

 For, with the moveable eye, the muscular sense 

 comes into play in exactly the same way as with 

 the moveable hand; and the notion of change of 

 place, plus the sense of effort, gives rise to a 

 conception of visual space, which runs exactly 

 parallel with that of tangible space. When two 

 moveable eyes are present, the notion of space of 

 three dimensions is obtained in the same way as 

 it is by the two hands, but with much greater 

 precision.* And if, to take a case similar to one 

 already assumed, we suppose a man deprived of 

 every sense except vision, and of all motion except 

 that of his eyes, it surely cannot be doubted that 

 he would have a perfect conception of space; and 

 indeed a much more perfect conception than he 



* See Note C. 

 161 



