Residual Ionization in Gases. 417 



ionization in air should increase very rapidly with a rise 

 in temperature. Patterson *, however, has shown experi- 

 mentally that the conductivity o£ air remains practically 

 the same from 0° C. to 180° C. Again, on the basis of 

 tangential collisions, Wolfke f has shown that if the con- 

 ductivity of air be taken to be 4 ions per c.c. per second at 

 room-temperatures, it should be represented by 2 ions per c.c. 

 per second at 130° (J. and by about 6 ions per c.c. per second 

 at —20° C. As this result is also in contradiction to the 

 measurements of Patterson, it would appear that the residual 

 ionization in air cannot be explained on any theory of col- 

 lisions as yet brought forward. There remains, therefore, 

 the possibility of the ionization being brought about by a 

 spontaneous breaking-up of the atoms or through the agency 

 of a radiation from the walls of the containing-vessel. 



With a view to examining the validity of these two 

 hypotheses, some measurements were made on the residual 

 ionization in a number of gases including air, and the 

 following paper contains an account of these experiments. 

 The investigation was begun by one of us in the summer 

 of 1913 (see < Nature,' Dec. 11, 1913), but had to be dis- 

 continued through an accident to the electrometer. The 

 apparatus having been repaired, the investigation was 

 resumed last autumn, and from the results which are given 

 below it will be seen that while evidence has been obtained 

 which points to the existence of a spontaneous ionization in 

 acetylene, there is no direct evidence of such an ionization 

 in air, carbon dioxide, hydrogen, ethylene, or nitrous oxide. 

 With the last-mentioned gases, however, the results point to 

 the residual ionization being due to a feeble radiation from 

 the walls of the zinc electrometer, consisting of alpha and 

 beta and possibly gamma rays. 



II. Apparatus. 



The WolfE electrometer used in this investigation is shown 

 in the Plate accompanying the paper by McLennan and 

 Murray on " The Residual Ionization in Air enclosed in a 

 vessel of Ice," published in this number of the Phil. Mag. 

 A diagrammatic sketch of its electrical system is given in 

 fig. 1. The instrument consisted of a cylindrical vessel of 

 zinc, provided with plane sides and having a capacity of 

 about two litres. The electrical system consisted of two 

 conducting silvered f used-quartz fibres, attached at their 



* Patterson, Phil. Mag. vol. vi. p. 231 (1S03). 

 t Wolfke, Le liadium, Aug. 191o, p. 265. 



Phil. Mag. S. 6. Vol. 30. No. 177. Sept. 1915. 2 E 



