the Method of its Transmission 115 



pushed to the necessary limit. The results, however, indicate 

 that if the rays are deflectable, the deviation is minute com- 

 pared with the ft rays. This is to be expected if the mass of 

 the expelled particle is large compared with the electron. 

 If, for example, the projected body had a mass 10 times that 

 of the hydrogen atom, it would require a magnetic field about 

 10,000 times as strong to produce the same deviation as 

 for the electron moving with the same velocity. There is 

 evidence that large carriers moving with a high velocity are 

 produced in vacuum-tubes. W. Wien * has shown that the 

 ""Canal Strahlen" of Goldstein are positively charged par- 

 ticles moving with high velocity. These rays are deviated 

 by a magnetic and electric field. When the vacuum-tube is 



e 

 filled with hydrogen the ratio of the charge to the mass, — r 



of these carriers is about 10*, showing that the carriers have 

 the same mass as the hydrogen atom. In an atmosphere of 

 oxygen the size of these carriers is considerably greater than 

 the hydrogen atom. 



It is possible that the electric charge on the expelled particle 

 may be different for different radioactive bodies under different 

 conditions. For the emanations of thorium and radium the 

 expelled particles are for the most part negative. It has 

 been shown that some of the radium carriers of excited activity 

 have a negative charge, showing that the expelled body is 

 positive. In addition, Dorn has shown that in a radium 

 solution the excited radioactivity is produced on the anode, 

 and not on the cathode. This shows that the carriers of 

 excited activity in solution have a negative charge, so that 

 the expelled body is positive in sign. 



§ 11. Evidences of Chemical Change. 



In previous papers by Mr. Soddy and myself, the view has 

 been put forward that radioactivity is an accompaniment of con- 

 tinuous chemical change. Taking, for example, thorium, which 

 has been worked out more thoroughly than the other radioactive 

 bodies, it has been shown that a chemical substance Th.X is 

 produced at a constant rate by the thorium compound. This 

 Th.X undergoes further chemical change, one of the products 

 of which is the emanation. This emanation itself is not 

 stable, but expels from itself a negatively charged body. 

 The positively charged portion of the emanation is carried to 

 the electrodes, and this again undergoes further chemical 

 change, giving rise to the phenomenon of excited radioactivity. 



* Drude's Annal. No. 6, p. l>44 (1902). 

 12 



