478 Dr. S. Brodetsky and Dr. B. Hodgson on the 



therefore rests the priority in calling attention to this point. The 

 formula ('./Ether and Matter,' p. 200) gives for the rotation per 

 molecule (/x 2 + 2) 2 r)/9/j, where n is a molecular constant proportional 

 to the field. I have also just received through the kindness of 

 Prof. Siertsema a paper on the magnetic rotation in titanium 

 •chloride, communicated to the Amsterdam Academy on Oct. 30, 

 1915, in which he deduces a polarization formula in the form — 



_ 2v*(n 2 -{-2)\ D 



X ~ 9^ ^-(^ ._„')*• 



As the value of D is not given in terms of the electronic 

 constants I am unable to say at present to what extent Prof. 

 Siertsema's formula agrees with that deduced in this paper, except 

 that it clearly supports the use of the factor n/(n 2 -\-2) 2 . 



The George Holt Physics Laboratory, 

 University of Liverpool. 



LY. The Absorption of Gases in Vacuum- Tabes, and Allied 

 Phenomena. By S. Brodetsky, M.A., B.Sc, Ph.D., 

 P.P. A. S.j Lecturer in Applied Mathematics, and B. Hodg- 

 son, M.Sc.,Ph.D., Assistant Lecturer in Physics, University 

 of Bristol*. 



1. rilHE absorption of gases in vacuum-tubes has been 

 -L the subject of research by many investigators ; 

 a satisfactory or unanimous explanation has not, however, 

 tbeen found. The following explanations have been pro- 

 posed : — 



(1) Chemical action between the gas and the glass 1 . 



(2) Chemical action between the gas and the cathode 2 . 



(3) Chemical or mechanical action between the gas 



and the anode 3 » 4 ' 5 . 



(4) Chemical action due to active nitrogen 6 . 



>(5) Mechanical occlusion of the gas in the glass 7 . 



(6) Mechanical occlusion of the gas in the cathode 8 . 



(7) Mechanical occlusion of the gas in the disintegrated 



part of the cathode 9 . 

 * Communicated by the Authors. 



1 Willows, Phil. Mag. i. p. 503 (1901). 



2 Mey, Ann. d. Phys. (4) xi. p. 127 (1903). 



3 Skinner, Phil. Mag. xii. p. 481 (1906). 



4 Hodgson, Phys. Zeit. xiii. p. 595 (1912). 



5 Chrisler, Phys. Zeit. x. p. 745 '1909). 



6 Hill, Proc. Phys. Soc. p. 35 (1912). 



7 Campbell Swinton, Proc. Roy. Soc. lxxix. A, p. 134 (1907). 



8 Riecke, Ann. d. Phys. xv. p. 1003 (1904). 



9 Soddy and Mackenzie, Proc. Roy. Soc. lxxx. A, p. 92 (1908). 



