1392 
as the actual time measurer. The end of the experiment was regis- 
tered in the same way. At the same time tap a was closed. Then 
the pressure in the volumenometer was read, and herewith the 
necessary data were obtained. 
The distribution of temperature in the cryostat during the evapo- 
ration of the bath, may be a source of error, as it affects the distri- 
bution of the density in the tubes leading to the capillary tube. 
These tubes and the time of flow were therefore so chosen that 
the errors which might arise from this were negligible. 
The experiments were usually made at a mean pressure of about 
‘/, atmosphere. 
Ruckrs') has preved that Rrynoups’ criterion applies also to gases. 
When we determine the critical velocity for our experiments at 
hydrogen temperatures, we find 3253 em./sec. while the greatest 
which occurred in the experiments was 419 cm./sec. 
§ 5. Results. In the first measurements made with hydrogen in the 
manner described above, the viscosity became higher and the higher, 
which can be expiained by the hydrogen still containing some traces 
of air which froze in the capillary tube. On this account we intro- 
duced the tube with charcoal described above. The later determinations 
gave constant results. 
The whole observational material is collected in Table I. The first 
column contains the temp. in Kelvin degrees, the second and third 
the difference of pressure and the mean pressure. These results, as 
already said, are calculated from a great number of observations, 
the deviations from the mean were about 2°/,,. The fourth column 
contains the time of flow in seconds, the fifth the increase of pressure 
in the volumenometer. 
This increase of pressure combined with the volume, gives the 
amount of .gas which flows through, and this must be reduced to 
mean pressure and temperature of the tube through which it flows. 
For this purpose the equation of state was used, which had been 
deduced from the measurements of KAMERLINGH ONNEs and DE Haas 
(Comm. N°. 127) and KAMERTINGH ONNES and BRAAK (Comm. N°. 97a). 
The two first observations were used to calibrate the apparatus, 
in which we assumed with Markowskr’) 4, = 841.107, while for 
C in SvrnerLAND'’s formula 83 was taken. 
By this means the values were determined which are given under 
1) W. Ruckes Ann. d. Phys. 25, 1908 pag.-983. 
2) H. Marxowsk1 loc. cit. and K. ScrMirr loc. cit. 
