402 Prof. J. J. Thomson and Mr. Rutherford on the Passage 



particles must in the time T have moved through about ^ of 

 a centimetre. The time T will depend upon the intensity of 

 the radiation ; it could be determined by measuring the rate 

 of leak at different points on the tube through which, the 

 conducting gas was blown in the experiment mentioned at 

 the beginning of this paper. We hope to make such experi- 

 ments and obtain exact values for T ; in the meantime, from 

 the rough experiments already made, we think we may con- 

 clude that with the intensity of radiation we generally 

 employed, T was of the order of Jp of a second. This would 

 make the velocities of the charged particles in the air about 

 •3o cm./sec. for a gradient of one volt per cm. This velocity 

 is very large compared with the velocity of ions through an 

 electrolyte ; it is, however, small compared with the velocity 

 with which an atom carrying an atomic charge would move 

 through a gas at atmospheric pressure; if we calculate by 

 the kinetic theory of gases this velocity, we find that for air 

 it is of the order 50 cm./sec; this result seems to imply that 

 the charged particles in the gas exposed -to the Rontgen rays 

 are the centres of an aggregation of a considerable number of 

 molecules. 



The relation between the current and electromotive force 

 given by equation (4) corresponds to that obtained by experi- 

 ment for a number of gases ; it does not, however, exhibit a 

 peculiarity which we hase sometimes observed, especially 

 when the radiation was strong, i. <?., the existence of a part of 

 the curve where the current increases faster than would be 

 the case if Ohm's law were true ; this is shown by the portion 

 EF of the curve in fig. 2, which represents the relation be- 



Fiff. 2. 



tween the current and electromotive force through sul- 

 phuretted hydrogen. When the intensity of the Rontgen 

 ravs is altered, the alteration in the current is not the same 



