1084 
5. The above application of the theory of similarity also shows, 
that in making experiments with various liquids, as described in 
section 4 of Comm. N°. 151d, by changing K and 7, in all 
possible ways a double set of curves would be obtained forming a 
net-work which would be identically the same for all liquids’). By 
the equations (2) the elements belonging to the curves in one net 
could be calculated from those belonging to the corresponding curves 
in the other; conversely having obtained the nets for two liquids 
the values of u and » might be composed and in this manner these 
quantities (more especially 7) might be determined for one of the 
liquids. 
Possibly this method may find its practical application some time. 
Physics. — “The viscosity of liquefied gases. IX. Preliminary 
determination of the viscosity of liquid hydrogen.” By J. E. 
VerscHarreLT and Cu. Nriearse. (Communication N°. 151g from 
the Physical Laboratory at Leiden). (Communicated by 
Prof. H. KAMERLINGH ONNFs). 
(Communicated in the meeting of February 24, 1917). 
1. The measurements were made with the same apparatus as was 
used for the determination of the viscosity of liquid air (see Comm. 
N°. 1495, IV), into which, however, some improvements were intro- 
duced. In the first place, some nickel plated paper screens were placed 
under the cap to intercept the radiation of the cap; in the second 
place a small tinned hand-pump was introduced *) into the liquid, 
the rod of which passed through a small metal tube in the cap and 
could be worked up and down by means of an india-rubber tube 
which made an air-tight connection with the metal tube, by which 
means the liquid could be stirred previously to each experiment, and 
any slight differences of temperature or density could be equalized. 
The thermometer and the syphon tubes were taken away, as being 
unnecessary in these experiments; the temperature was deduced 
from the atmospheric pressure (the liquid, which in this case possessed 
1) As an instance. with the same restriction aS in the experiments of section 3, 
curve lf would also be found for water with K = 807 and 7 = 15.21. 
*) Of the pattern generally used in the cryostats of the laboratory (see for 
instance Comm. N°. 123). 
