11C JAMES CLEHK MAXWELL 



the surface of (he solid with a finite velocity between 

 places where the temperature is different; and in an 

 appendix he proves that, on certain assumptions re- 

 garding the nature of the contact of the solid and 

 the gas, there will be, even when the pressure is con- 

 stant, a flow of gas along the surface from the colder 

 to the hotter parts. 



Among his less important papers bearing on 

 molecular theory must be mentioned a lecture on 

 " Molecules " to the British Association at its Bradford 

 meeting; "Scientific Papers of Clerk Maxwell," vol. ii., 

 p. 361 ; and another on " The Molecular Constitution 

 of Bodies," Scientific Papers, vol. ii., p. 418. 



In this latter, and also in a review in Nature of 

 Van dor Waal's book on "The Continuity of the 

 Gaseous and Liquid States,"* he explains and dis- 

 cusses Cluusius' virial equation, by moans of which 

 the variations of the permanent gases from Boyle's 

 law are explained. The lecture gives a clear account, 

 in Maxwell's own inimitable style, of the advances 

 made in the kinetic theory up to the date at which it 

 was delivered, and puts clearly the dillicultios it has 

 to meet. Maxwell thought that those arising from 

 the known values of the ratio of the specific heats 

 were the most serious. 



In the articles, "Atomic Constitution of Bodies' 1 

 and " Diffusion," in the ninth edition of the Encyclo- 

 paedia Britannica, we have Maxwell's later views on 

 the fundamental assumptions of the molecular theory. 



The text-book on "Heat" contains some further 

 developments of the theory. In particular he shows 



Y, Vol. X. 



