222 POPULAR LECTURES AND ADDRESSES. 



among the three properties of diffusion, thermal con- 

 duction, and viscosity, have annexed to the domain 

 of science a vast and ever-growing province. 



Rich as it is in practical results, the kinetic 

 theory of gases, as hitherto developed, stops 

 absolutely short at the atom or molecule, and 

 gives not even a suggestion towards explaining 

 the properties in virtue of which the atoms or 

 molecules mutually influence one another. For 

 some guidance towards a deeper and more com- 

 prehensive theory of matter, we may look back 

 with advantage to the end of last century and to 

 the beginning of this century, and find Rumford's 

 conclusion regarding the heat generated in boring 

 a brass gun : " It appears to me to be extremely 

 difficult, if not quite impossible, to form any dis- 

 tinct idea of anything capable of being excited 

 and communicated in the manner the heat was 

 excited and communicated in these experiments, 

 except it be MOTION;" 1 and Davy's still more 

 suggestive statement : " The phenomena of re- 



1 Count Rumford's Works, Vol. I. p. 90 : published by the 

 American Academy of Arts and Sciences, Boston, 187 . 



