THE VALUE OF SCIENCE 557 



space, limiting ourselves to the sensations of a single finger, that is 

 in sum the assemblage of positions this finger can occupy. This tactile 

 space that we shall analyze in the following section and which conse- 

 quently I ask permission not to consider further for the moment, this 

 tactile space, I say, has three dimensions. Why has space properly 

 so called as many dimensions as tactile space and more than simple 

 visual space? It is because touch does not operate at a distance, 

 while vision does operate at a distance. These two assertions have 

 the same meaning and we have just seen what this is. 



Now I return to a point over which I passed rapidly in order not 

 to interrupt the discussion. How do we know that the impressions 

 made on our retina by A at the instant a and B at the instant (5 are 

 transmitted by the same retinal fiber, although these impressions are 

 qualitatively different? I have suggested a simple hypothesis, while 

 adding that other hypotheses, decidedly more complex, would seem to 

 me more probably true. Here then are these hypotheses, of which I 

 have already said a word. How do we know that the impressions pro- 

 duced by the red object A at the instant a, and by the blue object B 

 at the instant /?, if these two objects have been imaged on the same 

 point of the retina, have something in common? The simple hy- 

 pothesis above made may be rejected and we may suppose that these 

 two impressions, qualitatively different, are transmitted by two different 

 though contiguous nervous fibers. What means have I then of know- 

 ing that these fibers are contiguous? It is probable that we should 

 have none, if the eye were immovable. It is the movements of the 

 eye which have told us that there is the same relation between the 

 sensation of blue at the point A and the sensation of blue at the point 

 B of the retina as between the sensation of red at the point A and the 

 sensation of red at the point B. They have shown us, in fact, that the 

 same movements, corresponding to the same muscular sensations, carry 

 us from the first to the second, or from the third to the fourth. I do 

 not emphasize these considerations, which belong, as one sees, to the 

 question of local signs raised by Lotze. 



