31 MAXWELL'S LAW 65 



here abandon, and all the more so as it has obtained a 

 thorough treatment in a treatise by my brother. 1 



32. Coefficient of Expansion 



From the relation found in 16 between the temperature 

 of a gas and the mean value of the kinetic energy of its 

 molecules, follows another law which has in like manner 

 been confirmed by experiment. 



Since two gases have the same temperature 3 when the 

 mean values of the kinetic energy of their molecules are 

 equal, i.e. when 



*,<?, = %m,G*, 



the values also of their molecular energies are equal when 

 they are both at the temperature 0, or, in the notation already 

 used in 14, 



im^ 2 == im 2 2 2 . 



But, if a v 2 are the thermal expansibilities of the two gases, 



From these four formulae we obtain the equation 



Or the law that thf> thermal fixpansihilitip.* c\f nil qn.RP.R rt.ra 



the same. 



This law, which has been already mentioned in 15, in 

 the determination of the absolute zero of temperature, was 

 empirically established by Gay-Lussac 2 and Dal ton, 3 and 

 still earlier, as the former tells us, by Charles. If it now 

 appears as a logical deduction from the theory, we must 

 see in this coincidence a weighty and convincing argument 

 for the truth of the theoretical views from which we have 

 started in explaining gaseous pressure. 



1 Lothar Meyer, Die, modernen Theorien der Chemie, 5. Aufl., Breslau 

 1884 ; 6. Aufl. I. 1895. 



2 Ann. Chiin. Phys. xliii. 1802, p. 137 ; Gilb. Ann. xii. p. 257. 



3 Mem. of the Manchester Lit. and Phil. Soc. v. 1802, p. 595 ; Gilb. Ann. 

 xii. p. 310. 



F 



