270 PHENOMENA DEPENDENT ON MOLECULAR PATHS 101 



of viscosity r), which, according to 78, is given by the 

 formula 



97 = 0-30967 ran/7r*V2, 



into the absolute temperature or the magnitude 1 + a$, 

 where $ is the centigrade temperature and a is the co- 

 efficient of expansion. 



Now, the value of the coefficient of viscosity, according 

 to the observations described in 85, increases with the 

 temperature in such wise that it may be taken, at least 

 approximately, to be proportional to the function 



where the exponent n has values which for different gases 

 lie between 0'75 and 1 ; its value being greater for the easily 

 condensible gases than for those which were formerly con- 

 sidered permanent. We should have then to expect that 

 the coefficient of diffusion varies as 



where n has the value appropriate to the gas. 



The observations from which Loschmidt 1 has con- 

 cluded the law put forward by him were made with three 

 pairs of gases diffusing into each other, viz. carbonic acid 

 and air, carbonic acid and hydrogen, hydrogen and oxygen. 

 The value of n for carbonic acid, which occurs in the first 

 two pairs, has been found, from experiments on viscosity, to 

 be nearly equal to 1, so that Loschmidt's observations 

 on the diffusion of this gas are in excellent agreement with 

 the investigations of the viscosity of the same gas. For 

 hydrogen and oxygen the value of n given by the experi- 

 ments on viscosity is certainly less ; but the agreement in 

 Loschmidt's experiments on diffusion is not so great that 

 we are forced to assume the exponent n to be always exactly 

 equal to 1. 



In fact von Obermayer 2 found later, by experiments 



1 Wien. Sitzungsber. 1870, Ixi. Abth. 2, p. 367 ; Ixii. Abth. 2, p. 468. 



2 Ibid. 1880, Ixxxi. Abth. 2, p. 1102. 



