THE SIX GA TE WA YS OF KNO WLEDGE. 297 



ceive a difference. What is the difference ? It 

 is the sense of roughness as distinguished from 

 smoothness. Physiologists and anatomists have 

 used the word " tactile " sense, to designate it. 

 I confess that this does not convey much to my 

 mind. " Tactile " is merely " of or belonging to 

 touch," and in saying we perceive roughness and 

 smoothness by a tactile sense, we are where we 

 were. We are not enlightened by being told that 

 there is a tactile sense as a department of our 

 sense of touch. But I say the thing thought of 

 is a sense of force. We cannot away with it ; 

 it is a sense of force, of directions of forces, and 

 of places of application of forces. If the places 

 of application of the forces are the palms of the 

 two hands, we perceive accordingly, and know that 

 we perceive, in the muscles of the arms, effects of 

 large pressures on the palms of the hands. But 

 if the places of application are a hundred little 

 areas on one ringer, we still perceive the effect 

 as force. We distinguish between a uniformly 

 distributed force like the force of a piece of 

 smooth glass, and forces distributed over ten or 

 a hundred little areas. And this is the sense of 



