THE SIX GA TE WA YS OF KNO W LEDGE. 291 



not in the gross, but in their molecular actions 

 he would rather group those three together, than 

 he would couple any one of them with any of the 

 other senses. It is not necessary, however, for us 

 to reduce all the six senses to one, but I would 

 just point out that they are all related to force. 

 Chemical action is a force, tearing molecules apart, 

 throwing or pushing them together : and our 

 chemical sense or senses may, therefore, so far 

 at least, be regarded as concerned with force. 

 That the senses of smell and taste are related to 

 one another, seems obvious ; and if physiologists 

 would pardon me, I would suggest that they 

 might, without impropriety, be regarded as ex- 

 tremes of one sense. This at all events can be 

 said of them, they can be compared which can- 

 not be said of any other two senses. You cannot 

 say that the shape of a cube, or the roughness 

 of a piece of loaf sugar or sandstone, is comparable 

 with the temperature of hot water, or is like 

 the sound of a trumpet ; or that the sound of a 

 trumpet is like scarlet, or like a rocket, or like a 

 blue-light signal. There is no comparability 



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