of Gases and Molecular Force, 513 



viscosity, thermal conduction, diffusion, and characteristic 

 equation. 



The coefficient of viscosity for forceless spheres with the 

 Maxwell distribution of velocities is given by Tait (Trans. 

 Roy. Soc. Edin. vols, xxxiii. and xxxv.) as 



001 000 in /2v 2 \i nnA m ( v ' 2 )* 



^=' 882x 838 3^r W =' 064 ikr : 



hence when we take account of molecular force, the coefficient 

 of viscosity is 



„_ -064m(y> 



2m/(l/2fl) " 



(*,(!+ *S^Si)' 



but mv 2 is proportional to absolute temperature ; let mv 2 = cT, 

 and therefore mY 2 =2cT, then 



•064CMT 1 • (2) 



(2a) 2 ( 



m 2 /(l/2a) 

 i+ ^T 



Now for a given substance 'OQichni, 2a, and m 2 /(l/2a)/c 

 remain constant ; denote m 2 /(l/2a)/c by ; and then 



T t 

 C 



*?*— V ( 3 ) 



i + T 



is the law of variation of viscosity with temperature in the 

 case of gases at temperatures not below the critical, and at 

 pressures for which the departure from Boyle's law is not 

 great. 



There is some fine experimental material for testing the 

 above theoretical law, for Holman (Phil. Mag. 5th ser. 

 vol. xxi.), in the light of results already obtained by 0. E. 

 Meyer, Puluj, Obermayer, and E. Wiedemann, made special 

 measurements of great exactness of the variation of the 

 viscosity of air and carbonic dioxide at temperatures from 

 0° G. to 124° and from 0° to 225°. Barus for air and 

 hydrogen pushed the temperature range up to 1400° C. 

 (Amer. Journ. Sc. 3rd ser. vol. cxxxv.). 

 If i} is the value of ij at 0° C, then, from our equation (3), 



y /T y i + C/273 ,_. 



Vo"\273j 1 + C/T ; W 



Phil. Mag. S. 5. Vol. 36. No. 223. Dec. 1893. 2 M 



