256 POPULAR LECTURES AND ADDRESSES. 



the sense of heat Reid's idea has not I think 

 been carried out so much as it deserves. We do 

 not, I believe, find in any of the elementary 

 treatises on Natural Philosophy, or in the 

 physiologists' writings upon the senses, a distinct 

 reckoning of six senses. We have a great deal 

 of explanation about the muscular sense, and the 

 tactile sense ; but we have not a clear and broad 

 distinction of the sense of touch into two depart- 

 ments, which seems to me to follow from Dr. 

 Thomas Reid's way of explaining the sense of 

 touch, although he does not himself distinctly 

 formulate the distinction I am now going to 

 explain. 



The sense of touch, of which the organ com- 

 monly considered is the hand, but which is 

 possessed by the whole sensitive surface of the 

 body, is very distinctly a double quality. If I 

 touch any object, I perceive a complication of 

 sensations. I perceive a certain sense of rough- 

 ness, but I also perceive a very distinct sensation, 

 which is not of roughness, or of smoothness. 

 There are two sensations here, let us try to analyse 



