176 PSYCHOLOGY. 



sizes of things by either eye or skin the movements of these 

 organs are incessant and nnrestrainable. Every such move- 

 ment draws the points and lines of the object across the 

 surface, imprints them a hundred times more sharply, 

 and drives them home to the attention. The immense part 

 thus played by movements in our perceptive activity is held 

 by manj^ psychologists* to prove that the muscles are them- 

 selves the space-perceiving organ. Not surface-sensibility, 

 but ' the muscular sense,' is for these writers the original 

 and only revealer of objective extension. But they have 

 all failed to notice with what peculiar intensity muscular 

 contractions call surface-sensibilities into play, and that the 

 mere discrimination of impressions (quite apart from any 

 question of measuring the space between them) largely 

 depends on the mobility of the surface upon which they 

 fall, t 



*Biowu, Bain. J. S. Mill, and in a modified manner Wundt. Helmholtz. 

 Sully, etc. 



fM. Ch. Diinan, in bis forcibly written essay ' 1 Espace Visuel et 

 I'Espaee Tactile' in the Revue Philosophique for 1888, endeavors to prove 

 that surfaces alone give no perception of extent, by citing the way in 

 which the blind go to work to gain an idea of an object's shape. If surfaces 

 were the percipient organ, he says, " both the seeing and the blind ought 

 to gain an e.xact idea of the size (and shape) of an object by merely laying 

 their hand fiat upon it (provided of course that it were smaller than the 

 hand), and this because of their direct appreciation of the amount of tactile 

 surface affected, and with no recourse to the muscular sense. . . . But the 

 fact is that a person born blind never proceeds in this way to measure ob- 

 jective surfaces. The only means which he has of getting at the size of a 

 body is that of running his finger along the lines by which it is bounded. 

 For instance, if you put into the hands of one born blind a book whose 

 dimensions are unknown to him, he will begin by resting it against his 

 chest so as to hold it horizontal ; then, bringing his two hands together at 

 the middle of the edge opposite to the one iigainst his body, he will draw 

 them asunder till they reach the ends of the edge in question ; and then, 

 and not till then, will he be able to say what the length of the object is " 

 (vol. XXV. p. 148). I think that anyone who will try to appreciate the size 

 and shape of an object by simply ' laying his hand flat upon it ' will find 

 that the great obstacle is that he feels the contours so imperfectly. The 

 moment, however, the hands move, the contours are emphatically and dis- 

 tinctly felt. All perception of shape and size is perception of contours, and 

 first of all these must be made sharp. Motion does this ; and the impulse 

 to move our organs in perception is jirimarily due to the craving which we 

 leel to get our surface-sensations sharp. When it comes to the naming and 



