462 Scientific Intelligence. 



of the comparison of viscosities at about 100° C. and at the tem- 

 perature of the room was to show that the temperature effect was 

 the same as for hydrogen. 



In the former paper the results were reduced so as to show to 

 what power (n) of the absolute temperature the viscosity was 

 proportional. 



n c 



Air.- 0-154: 111-3 



Oxygen 0-782 128-2 



Hvdrosren 



Helium - °' 681 12 ' 2 



Argon 0-815 150'2 



Since practically only two points on the temperature curve 

 were examined, the numbers obtained were of course of no avail 

 to determine whether or no any power of the temperature was 

 adequate to represent the complete curve. The question of the 

 dependence of viscosity upon temperature has been studied by 

 Sutherland, on the basis of a theoretical argument which, if not 

 absolutely rigorous, is still entitled to considerable weight. He 

 deduces from a special form of the kinetic theory as the function 

 of temperature to which the viscosity is proportional 



. i+e/'e 



c being some constant proper to the particular gas. The simple 

 law 6i, appropriate to " hard spheres," here appears as the limit- 

 ing form when is very great. In this case, the collisions are 

 sensibly uninfluenced by the molecular forces which may act at 

 distances exceeding that of impact. When, on the other hand, 

 the temperature and the molecular velocities are lower, the mutual 

 attraction of molecules which pass near one another increases the 

 number of collisions, much as if the diameter of the spheres was 

 increased. Sutherland finds a very good agreement between his 

 formula (1) and the observations of Holman and others upon 

 various gases. 



If the law be assumed, my observations suffice to determine 

 the values of c. They are shown in the table, and they agree 

 well with the numbers for air and oxygen calculated by Suther- 

 land from observatious of Obermaver. — Proc. Roy. Soc, lxxvii, 

 137. 



12. Absorption of gases by glass powder. — Early investigators 

 claimed that the absorption of gases ceased in a few days; that 

 it increased with increasing pressure ; diminished with increasing 

 temperature ; and that the presence of moisture had little influ- 

 ence. Bunsen on the other hand found that the absorption con- 

 tinued even for years ; increased with increasing temperature, 

 and was largely independent of variations of pressure. The 

 cause of the absorption he claimed to be in the capillary coating 

 of moisture. P. Mulfarth (Bonn dissertation) gives an exhaus- 



