622 Profs. Rutherford and Barnes on the 



about one or two per cent, of the total ionization due to the 

 a rays. If the relative number of ions produced by complete 

 absorption of the different types of radiation may be taken 

 as a comparative measure of the energy of the radiations, it 

 is seen that the heating effect of the 7 rays from radium 

 should not be more than a few per cent, of that resulting from 

 the a rays. 



Paschen*, however, in a recent paper concluded that 

 radium, when surrounded by a sufficient thickness of metal 

 to absorb all the 7 rays, gave out heat at the rate of 226 

 gram-calories per gram per hour, or, in other words, the 

 heating effect of the 7 rays was greater than that of the a 

 rays. 



Such a conclusion followed naturally from the hypothesis 

 of the nature of the 7 rays which Paschen had advocated in 

 a series of papers. He considered that the 7 rays consisted 

 of negatively charged particles (electrons) projected with a 

 velocity exceedingly close to the velocity of light. Since, 

 according to the theory, the apparent mass of the electron 

 increases with the speed as the velocity of light is approached, 

 these electrons, if projected with very nearly the velocity of 

 light, would have a considerable mass. 



In order to account for the absence of any appreciable 

 deflexion of the 7 rays in a magnetic field, it was necessary 

 to suppose that the apparent mass of the electron was at least 

 forty times as great as that of the hydrogen atom. 



Even if the number of such high-speed electrons were only 

 a small fraction of the total number of electrons expelled 

 from radium, yet, on account of their great energy of motion, 

 thev should produce considerable heating effect in bodies in 

 which they were absorbed. If this theory of the nature of 

 the 7 rays were correct, a large heating effect of the rays due 

 to these electrons might be reasonably expected. 



Before describing the experiments we have made in this 

 subject, a brief account will be given of the experimental 

 arrangement employed by Paschen. Recourse w T as had to a 

 form of Bunsen ice calorimeter, which had already been 

 used for the determination of the heating effect of radium 

 by Curie and Laborde. Paschen used 50 milligrams of 

 pure radium bromide, which was enclosed in a glass tube 

 17 mm. long with walls *3 mm. thick. This was inserted 

 in a small ice. calorimeter which was placed inside the 

 vessel of a large ice calorimeter. The amount of mercury 

 drawn in to compensate for the melted ice w r as obtained by 

 weighing. Several observations were made which agreed 

 * Paschen, Phys. Zeit. v. p. 563 (1904). 



