630 Mr. B. D. Kleeman on the Secondary Cathode 



Let us now find values of the quantities for the ft rajs 

 corresponding- to K 2 and M x for the 7 rays. Let these 

 quantities be denoted by K 2 and M 2 respectively ; they re- 

 present respectively the number of electrons ejected per c.c. 

 per second, and the number of electrons ejected per atom 

 per second, in a substance exposed to the (3 rays. 



The value of K 2 is given by K 2 = /jlk, and the value of M 2 , 



since £- M2 =K„, by M 2 =^' K . 



The values of M 2 and K 2 for the substances in Table II., 

 calculated by means of these two equations, are given in the 

 sixth and seventh columns of the table. The values of K 2 

 and Mo for aluminium have been put, as before, equal 

 to 10. 



It will be seen that the values of K 2 and M 2 are approxi- 

 mately the same as those of K x and M x . The values of M 2 

 and M. 1 measure the relative probabilities of the atoms of the 

 various substances being ionized when subjected to /3 or 7 

 rays. It is interesting that the relative chances in both 

 cases should be approximately the same when the nature of 

 the rays seems to be so entirely different. It will be seen 

 in the next section that the relative chances of ionization in 

 the case of the y rays depend to some extent on the nature 

 of the ionizing rays. 



The quantities M x and M 2 must be related to the ionization 

 in a gas. If the above substances were in the form of, say, 

 monatomic gases at the same pressure, we should expect, 

 since these quantities represent the relative number of pri- 

 mary electrons ejected per second, that the ionization per c.c. 

 in these gases would be the same with both (3 and 7 rays. 

 Now, the writer* has investigated the relative ionizations 

 per c.c. with /3 and 7 rays of a large number of complex 

 gases, and found the ionization very approximately the same 

 for both kind of rays. The results obtained are given in 

 Table III. The values of the ionization per c.c. with the 

 a particle for these gases have been placed in the table for 

 comparison, being taken from a table compiled by the writer 

 in the paper referred to. The larger number of the values 

 for the ol particle are due to Prof. Bragg, whose experimental 

 results f were incorporated in the table mentioned. 



It was also found that the ionization in a gas is approxi- 

 mately an additive property of the atoms of the molecule. 

 The atomic ionizations for the 7, j3, and a rays are given in 



* Proc. Hoy. Soc. A. rol. lxxix. p. 220 (1907). 

 f Phil. Mag. March 1907, p. 8f~ 



>oo. 



