332 L iterary and Philosophical Society. 



themselves to be compressed more and more, according to 

 the increased force applied." T Speaking of a vessel of air 

 with a weighted cover, and which he illustrates with a 

 diagram, he says, " So the minute bodies, whilst they 

 impinge on the cover E F, keep it up by their continually 

 repeated strokes, and form an elastic fluid which expands 

 itself when the weight is removed or diminished. 2 We 

 shall consider the corpuscles enclosed in the hollow of the 

 cylinder as infinite in number, and when they occupy the 

 space E c D F we shall say that they constitute the natural 

 air." 3 



' Davy and Count Rumford entered the field when this 

 theory of gaseous motion was forgotten, and inaugurated 

 a new theory of heat founded on molecular activity. That 

 heat is immaterial was no rare opinion last century, or 

 since Lord Bacon spoke of it as " motus et nihil aliud." 

 However, atomic motion ceased from the time of Rumford 

 to be a vague idea. Davy 4 spoke definitely when, without 

 calling in the aid of repulsions, he supposed that in solids 

 the particles are in a vibratory motion, the particles of the 

 hottest bodies moving with greatest velocity and through 

 the greatest space ; that in fluids and elastic fluids, besides 

 the vibratory motion which must be considered greatest in 



1 Fluidorum autem elasticorum prsecipuae affectiones in eo positse sunt : 

 i, ut sint gravia ; 2, ut se in omnes plagas explicent, nisi contineantur, et 

 3, ut se continue magis magisque comprimi patiantur crescentibus potentiis 

 compressionis : ita comparatus est aer, ad quern potissimum presentes nostrse 

 pertinent cogitationes.' 



2 '. . . Sic corpuscula dura impingunt in operculum EF idemque suis sus- 

 tinent impetibus continue repetitis fluidum componunt elasticum quod remote 

 aut diminuto pondere P sese expandit ' 



' Corpuscula cavitati cylindri inclusa considerabimus tanquam numero 

 infinita, et cum spatium ECDF occupant, tune ae'rem ilia dicemus formare 

 naturalem.' 



4 Collected Works, vol. iv. p. 67. 



