Physics. — ''The viscosity of lique/ied gases. X. The viscosity of 

 /i(piid hydrocjen.'" By Prof. J. E. Verschafff.lt. Communication 

 N". 1536 from the Physical Laboratory at Leiden. (Commu- 

 nicated by Prof. H. Kamerlingh Onnës.) 



(Communicated in the meeting of November 24, 1917). 



A preliminary value having been obtained from the experiments 

 described in Comm. N°. 151(/, a new series of measurements was under- 

 taken in order to find a more accurate value of the quantity in 

 question. The construction of the apparatus to be used for this pur- 

 pose was based on the considerations referring to similarity in (he 

 oscillatory motion of a sphere in a viscous fluid (comp. Comm. N°. 148^ 

 and N°. 151/). Taking in view the matei'ials available for this construc- 

 tion it appeared to be possible to construct the apparatus in such a 

 manner, that the motion in liquid hydrogen would be approximately 

 similar to the motion in carbon disulphide') which was studied on a 

 former occasion (Conmi. N°. 151(/ §3), using a sphere of the same 

 radius (2 cm.). In this case- by equation (2) of Comm. N", 151/(comp. 

 also § 4 and the table), assuming for liquid hydrogen the preliminary 

 value of i]^=z -00011, the oscillating system had to be given a 

 moment of inertia of about 30 c.g.s. units and a time of oscillation 

 of about 40 sees. ; this would correspond to a logarithmic decrement 



of • 07 and a value of V' = -^^= • Oil ") (therefore T-l\= ■ 44). 



-* 



In these new experiments a iioUow exhausted glass sphere was 

 used (weight 8.9 grms), blown by Mr. Kesselring, glass-blower of 

 the laboratory, as nearly accurately round as was possible^). The 

 sphere ended in a tube which had served in the blowing and was 



J) Originally similarity was tried with the motion in liquid air or ether (comp. 

 Comm. N". Iblf § 4), but of all the substances included in this study of a possible 

 similarity carbon disulphide was the most advantageous, because it made it possible 

 to reach a comparatively high logarithmic decrement, without its being necessary 

 to use too high a time of oscillation (comp. Comm. N^. 151/", § 4); the higher de- 

 crement is then obtained by a smaller moment of inertia. 



^) The value of this quantity given in Comm. N". 151/" in the table is too small. 



^) The diameters measured in different directions did not differ from the mean 

 by more than Viooo- 



