334 Literary and Philosophical Society. 



which the atoms have to move being less, their motions or 

 periods must be shorter, and the number of them in a 

 given time consequently greater; on both of which accounts 

 the elasticity is greater the greater the compression. 

 Besides, when other things are the same, the elastic force 

 augments with an augmentation of temperature and 

 diminishes with a diminution ; for an increase of tempera- 

 ture, according to our theory, must necessarily be attended 

 with an increase of velocity, and therefore with an increase 

 in the number of collisions.' 



'Dr. Joule continued the subject, and introduced it into 

 the region of experiment and observation, or, in other 

 words, to the science of modern times.^ Joule might have 

 added that the view he adopted is not only in accordance 

 with the known laws of the elasticity of gases, but conforms 

 to the ratio of the specific heats of gases. The mathe- 

 matical development continued to make progress in the 

 hands of Clausius, Clerk Maxwell, Holtzmann, and others, 

 taking us to new fields, &c.' 



In 'Some remarks on Heat, and the Constitution of 

 Elastic Fluids,' by J. P. Joule, F.R.S. &c. Mem. Lit. and 

 Phil. Soc, vol. ix. 2nd series, p. iii, read Oct. 3, 1848, we 

 find:— 



' I have myself endeavoured to prove that a rotary 

 motion such as that described by Sir H. Davy, will account 

 for the law of Boyle and Mariotte, and other phenomena 

 presented by elastic fluids ; nevertheless, since the hypo- 

 thesis of Herapath, in which it is assumed that the particles 

 of a gas are constantly flying about in every direction with 

 great velocity, the pressure of the gas being owing to the 

 impact of the particles against any surface presented to 



' See Math, Physics, vol. i. p. 264. 



