290 POPULAR LECTURES AND ADDRESSES. 



limits is, perhaps, one of the most promising 

 provinces of science for the future investigator. 



In conclusion, I wish to bring before you the 

 idea that all the senses are related to force. The 

 sense of sound we have seen is merely a sense of 

 very rapid changes of air-pressure (which is force) 

 on the drum of the ear. I have passed merely 

 by name over the senses of taste and smell. I 

 may say they are chemical senses. Taste common 

 salt and taste sugar you tell in a moment the 

 difference, and the perception of that difference is 

 a perception of chemical quality. There is in this 

 perception a subtle molecular influence, due to the 

 touch of the object on the tongue or the palate, 

 and producing a sensation very different from 

 the ordinarily reckoned sense of touch, which, 

 as we have just seen, tells us only of rough- 

 ness, and of temperature. The most subtle of 

 our senses perhaps is sight ; next come smell 

 and taste. Professor Stokes recently told me that 

 he would rather look upon taste and smell and 

 sight as being continuous because they are all 

 molecular they all deal with properties of matter, 



