Joule. 331 



CHAPTER XII. 

 Dr. Joule. 



ALMOST concurrent with later chemical search on the 

 constituents of matter we see an inquiry in physics, where 

 also atoms have done full duty, and without which the 

 existence of gases, for example, has been found to be 

 difficult to conceive. The condition may be shortly 

 described in a summary serving as an introduction to the 

 works of the late Thomas Graham, Master of the Mint. 1 



' When we arrive at this point we pass to the next 

 important stage, namely, the motion of gaseous molecules, 

 if not of atoms, and the beginning of the attempt to define 

 it precisely. The first definite ideas are by D. Bernouilli. 2 

 They are explained in his ( Hydrodynamics,' which, although 

 published in Strasburg in 1738, were previously worked at 

 when he was Professor in St. Petersburg. 



' D. Bernouilli says : " The chief peculiarities of fluids are 

 these : first, they are heavy ; second, they expand in all 

 directions unless they are confined ; and third, they allow 



1 Chemical and Physical Researches, by Thomas Graham, with introduc- 

 tion and analytical contents or abridgment by R. Angus Smith, edition dis- 

 tributed by Dr. Young, F.R.S. 



2 Danielis Bernouilli, Joh. Fil., Med. Prof. Basil, Hydrodynamica sive 

 deviribusetmotibusfluidorum Commentarii ( Argentorati, 1738), p. 200. Sectio 

 decima. ' Fluida nunc elastica consideraturis licebit nobis talem iis amngere 

 constitutionem, quse cum omnibus adhuc cognitis conveniat affectionibus, ut 

 sic ad reliquas etiam nonduni satis exploratas detur adit us. ' 



