[ 231 ] 



XXYII. On the Ionization in Air at different Temperatures and 

 Pressures. Bij J. Patterson, B.A., Professor of Physics^ 

 JIui)' Central College, Allahabad j India; 1851 Exhibition 

 Science Scholar, Emmanuel College, Cambridge *. 



ELSTER and Geitelf and C. T. R. Wilson t have 

 shown that ions are being continuously produced in air 

 and other gases confined in a closed vessel without being- 

 exposed to any known ionizing agent. 



Hitherto it has not been known whether this ionization, 

 which has been called spontaneous ionization, was due to 

 some property in the air itself, to the vessel being slightly 

 radioactive, or to very penetrating rays that easily pass 

 through the walls of the vessel. 



Wilson §, in his experiments^ used very small volumes of 

 gas, and he found that, except for high pressures, the ioniza- 

 tion in air and CO2 was proportional to the pressure, while 

 for hydrogen it varied as the pressure throughout the range 

 of the experiments. These results led him to suspect that 

 the ionization was due to the walls of the vessel being slightly 

 radioactive, the radiation having only moderate penetrating- 

 power ; consequently, if this is the cause one should get the 

 ionization independent of the pressure over a considerable 

 range by using a large volume of gas. 



Rutherford || has shown that certain rays of radium can 

 penetrate great thicknesses of metal, and suggests that the 

 cause of the ionization in closed vessels may be due, in part 

 at least, to some very penetrating rays. 



If the ionization were due to some property of the air itself 

 one would expect that it w^ould be some function of the tem- 

 perature and pressure, consequently, by measuring the ioniza- 

 tion at different temperatures and pressures and using a large 

 volume of gas one should discover the cause of the ionization. 

 It was with this object that the present investigation was 

 undertaken. 



The results of the experiments showed that the ionization 

 was due to a slight radioactivity in the walls of the vessel. 

 This conclusion was communicated to the Cambridge Philo- 

 sophical Society in a preliminary note " On the Ionization 

 in Air at different Temperatures and Pressures " H . 



* Communicated by Prof. .J. J. Thomson, F.R.S, 



t Physikalische Zeitschrift, ii. Jahrgang, No. 8, pp. 116-119, Nov. 24, 

 1901. 



t Roy. Soc. Proc. vol. Ixviii. p. 151 (1901). 



§ Eov. Soc, Proc. vol. Ixix. p. 278. 



H 'Nature,' vol. Ixvi. p. .318 (1902). 



•] Proc. Caml). Phil. Soc. vol. xii. p. 44. 



