xiii.] THE METAPHYSICS OF SENSATION. 345 



field of vision towards another point, or feel the like 

 motion, the idea of the gradual diminution of the number 

 of sensible units between the two points appears to me 

 to be common to both kinds of motion. 



Hence, I conceive, that though it be true that there 

 is no likeness between the primary feelings given by 

 sight and those given by touch, yet there is a com- 

 plete likeness between the secondary feelings aroused 

 by each sense. 



Indeed, if it were not so, how could Logic, which 

 deals with those forms of thought which are applicable 

 to every kind of subject-matter, be possible ? How could 

 numerical proportion be as true of visibilia t as of tan- 

 gibilia, unless there were some ideas common to the 

 two ? And to come directly to the heart of the matter, 

 is there any more difference between the relations 

 between tangible sensations which we call place and 

 direction, and those between visible sensations which go 

 by the same name, than there is between those relations 

 of tangible and visible sensations which we call suc- 

 cession 1 And if there be none, why is Geometry not 

 just as much a matter of visibilia as of tangibilia? 



Moreover, as a matter of fact, it is certain that the 

 muscular sense is so closely connected with both the 

 visual and the tactile senses, that, by the ordinary laws 

 of association, the ideas which it suggests must needs be 

 common to both. 



From what has been said it will follow that the ninth 

 proposition falls to the ground ; and that vision, combined 

 with the muscular sensations produced by the movement 

 of the eyes, gives us as complete a notion of corporeal 

 separation and of distance in the third dimension of space, 

 as touch, combined with the muscular sensations pro- 

 duced by the movements of the hand, does. The tenth 

 proposition seems to contain a perfectly true statement, 



