SEC. 6. ON TACTILE PERCEPTIONS AND JUDGMENTS. 



895. As a means of gaining knowledge of external things 

 the sense of touch ranks next in importance to that of sight. 

 Auditory sensations enter largely and in several ways into our life ; 

 they serve as an important means of communication; together 

 with smell and taste they afford pleasure and guide our acts ; but, 

 as regards our direct knowledge of the external world, we learn by 

 means of them very little compared with what we learn by sight 

 and touch. To a certain extent we make use of touch by itself ; 

 we bring the surface of a body into contact with some region of 

 the skin such as the finger, and by the several sensations which 

 we receive either from several points of that region at the same 

 time, or from one or more points in succession, we learn certain 

 characters of the surface, whether for instance it is rough or 

 smooth. We thus also ascertain whether the body be hot or cold ; 

 and we may, within certain limits, form a judgment of the size of 

 the surface by simply estimating the size of the area of our skin 

 with which the body can be in contact at the same time. 



But though we may and do thus base conclusions on tactile 

 perceptions alone, we most frequently employ touch in association 

 with sight on the one hand and with the muscular sense on the 

 other. 



The ties indeed between touch and the muscular sense are 

 many and close. When we explore the nature of a body by touch 

 we press the skin, of the finger for instance, on the body ; and we 

 do that not merely in order to determine to what extent the 

 tactile sensation is increased by the increase of pressure, but also 

 and indeed chiefly to ascertain the amount of resistance to pressure 

 which is offered by the body. But that resistance, through which 

 chiefly we judge whether the body be soft or hard, is appreciated 

 not by the tactile but by the muscular sense. 



Or again, placing the finger on the surface of a body, and 

 moving the finger over the surface in such a way that the contact, 

 as judged by the pure tactile sensation, remains the same, we find 

 that in one case the movement has been continued in the same 

 plane, whereupon we judge the surface to be flat, that in another 



