1088 
friction of the sphere in vapour 20° K. with u = 0:0012*) and 
7 — 0:000011*) a decrement d= 000015 was calculated. We 
conclude from this that the decrement caused by the friction of the 
liquid alone was d, = 0:00334. The liquid was under a mean 
pressure of 766 mms. mercury; the temperature was thus 20°-36K. *) 
and the density 0:0708*). From this it follows that = 0-000117. 
This determination was made before the investigation of the 
suitability of the method was completed (see Comm. N°. 151d). 
From that investigation it appears probable, that the value found 
for 7 was a few percent too high, but the data are wanting by 
which the necessary correction might be estimated. We therefore 
give as the approximate value of the viscosity of liquid hydrogen 
n= O:OU0TT. *) 
Physics. — “Critical point, critical phenomena and a few conden- 
___sation-constants of air’. By J. P. Kurnen and A. L. Crark. 
(Communication N°. 1506 from the Physical Laboratory of 
Leiden). 
(Communicated at the meeting of February 24, 1917). 
The critical temperature and pressure of air have been determined 
by OrszewskKr®), Wrosiewski’), and Wirkowski*). Their results do not 
agree amongst each other as well as might be desired: 
OLSZEWSKI W ROBLEWSKI WITKOWSKI 
fe ess about — 140:%5 ales 
Pk 39 atm. von den 39 
The main object of our investigation was to obtain reliable values 
for the critical constants, including the critical density, which involves 
a detailed study of the condensation-phenomena in the critical region. 
Wrosiewsk! noticed that air behaves differently near its critical point 
\ 
1) The vapour still behaves approximately as an ideal gas. 
2) According to H. KAMERLINGH ONNES, C. DorsMAN and SopHUS WEBER. 
Comm. N°. 134a. 
on t dp m.M 
3) Normal boiling point: 20°,33 Kp = 200 gegree (see Comm. N°. 137d). 
4) See Comm. NO. 137a. 
5) This value agrees satisfactorily with that calculated in Comm. N°. 1485 on 
the basis of the law of corresponding states. 
6) K. Orszewski. C. r. 99, p. 184, 1884. 
1) S. v. WROBLEWSKI. Wied. 26, p. 134, 1885. 
8) A. W. Wrirkowskr. Phil. Mag. (5) 41, p. 288, 1896. 
