' 



120 JAMKS rl.KIlK MAXWKI.I. 



These two papers appear to have attracted Max- 

 well's attention to the matter, and his first paper, 

 entitled "Illustrations of the .Dynamical Theory of 

 Gases," was read to the British Association at Aber- 

 deen and Oxford in 1850 and KSCO, and appeared in 

 the Phtto*ophicul 3f<n/<tzine, January and July, I860. 



In the introduction to this paper Maxwell points 

 out, while there was then no means of measuring the 

 quantities which occurred in Clausiiis' expression for 

 the mean free path, " the phenomena of the internal 

 friction of gases, the conduction of heat through a gas, 

 and the diffusion of one gas through another, seem to 

 indicate the possibility of determining accurately the 

 mean length of path which a particle describes between 

 two collisions. In order, therefore, to lay the founda- 

 tion of such investigations cm strict mechanical prin- 

 ciples," he continues, "I shall demonstrate the laws 

 of motion of an indefinite number of small, hard and 

 perfectly elastic spheres acting on one another only 

 during impact." 



Maxwell then proceeds to consider in the first case 

 the impact of two spheres. 



But a gas consists of an indefinite number of 

 molecules. Now it is impossible to deal with each 

 molecule individually, to trace its history and follow 

 its path. In order, therefore, to avoid this difficulty 

 Maxwell introduced the statistical method of dealing 

 with such problems, and this introduction is the first 

 great step in molecular theory with which his name 

 is connected. 



He was led to this method by his investigation 

 into the theory of Sat urn's rings, which had been com- 



