298 POPULAR LECTURES AND ADDRESSES. 



smoothness and roughness. The sense of rough- 

 ness is therefore a sense of forces, and of places 

 of application of forces, just as the sense of 

 forces in your two hands stretched out, is the 

 sense of forces in places at a distance of six 

 feet apart. Whether the places be at a distance 

 of six feet or at a distance of one-hundredth 

 of an inch, it is the sense of force, and of 

 places of application of forces, and of directions 

 of forces, that we deal with in the sense of 

 touch as differing from the sense of heat. Now 

 anatomists and physiologists have a good right 

 to distinguish between the kind of excitement 

 of tissue in the finger and in the minute nerves 

 of the skin and sub-skin of the finger, by which 

 you perceive roughness and smoothness, in the 

 one case ; and of the muscles by which you per- 

 ceive places of application very distant, in the 

 other. But whether the forces be so near that 

 anatomists cannot distinguish muscles cannot 

 point out muscles resisting forces and balancing 

 them because, remember, when you take a piece 

 of glass in your fingers every bit of pressure at 

 every ten-thousandth of an inch pressed by the 



