1387 
is chiefly of importance for the knowledge of the mechanism of the 
impact. of two molecules, or, more simply in monatomic gases, of 
two atoms. In the nature of the case it is desirable to extend this 
investigation with one substance over the largest possible range of 
reduced temperature. This gives a particular significance to very low 
temperatures and substances such as bydrogen, neon, and helium. 
The pupils of Dorn *) at Halle have made systematic researches 
into the viscosity of different gases. By these both absolute values 
and temperature coefficients have been determined, and they have 
gone as low as the temperature of liquid air. 
In our researches we particularly wished to investigate hydrogen 
temperatures, while the viscosity apparatus was so arranged that it 
could be used without alteration for helium at helium temperatures. 
3 But it. was natural for us to extend our in- 
vestigation to the viscosity of our gases at 
ch ie ina * less low temperatures. It then appeared that 
besides being of value for the confirmation 
of the above mentioned researches as far as 
the temperature of solid carbonic acid, it 
was also of value for the knowledge of 
viscosity. in the field of the temperature of 
Q liquid air. 
In the field of hydrogen temperatures we 
found the viscosity of hydrogen while flowing 
through a capillary tube dependent upon 
the mean pressure. From MAXxWELL’s') resear- 
ches we know that the viscosity of gases at 
normal density is independent of the pressure, 
and Warsure and von BaBo have shown in 
the investigation of carbon dioxide, that in 
dense vapours, it increases with the density. 
There is, therefore, every reason to further 
investigate the dependence of the viscosity 
upon the pressure in hydrogen vapour. 
§ 2. Method. The measurements were 
PP made according to the transpiration method. 
ver This presents experimentally perhaps the 
Fig. 1. greatest difficulties, but it seems to allow 
1) There is a survey of these researches by K. Scumirr. Ann. d. Phys. (30). 
p. 393, 1909. 
2) For the older litterature see H. KAMERLINGH ONNES and W. H. Kersom. 
Leiden Comm. Suppl. N°. 23, page 86. 
