112 Dr. Russell and Mr. Chadwick on the y Rays of 



one mm. deflexion is 



^ / 3*23x0080 Annnn ^A i , ,- ".. 



R = =-h-^tak -aoss =O*0000d4 ) electromagnetic unit. 

 \12,100 x 0*393 / 



Hence this experiment indicates that in solid mercury there 

 is no Hall coefficient larger than 0*000011 electromagnetic 

 unit, which is about one-fourth that of tin. 



After this investigation was begun, Alterthum * published 

 some theoretical work indicating the absence of a Hall 

 effect in liquids ; but the experiments described here show 

 that the observations which have been made on liquid mercury 

 cannot be adduced to support that theory. 



I am indebted to Professor Barnett for proposing this 

 investigation and for many valuable suggestions. For similar 

 suggestions I am also indebted to Professor A. W. Smith. 



The Physical Laboratory, 



Ohio State University, 



June 1, 1913. 



XI. The 7 Rays of Polonium, Radium, and Radioactinium. 

 By A. S. Russell, M.A.,D.Sc., Carnegie Research Felloio 

 of the University of Glasgow, and J. Chad WICK. M.Sc, 

 Beyer Felloio of the University of Manchester], 



I^HE work, an account of which is given in this paper, is 

 a continuation of that already described in two previous 

 communications J. In the first of these it was shown that 

 when the a-rays of radium C impinge upon plates of dif- 

 ferent materials, a small but definite amount of 7-radiation is 

 produced. The amount of this radiation was, however, too 

 small to permit of analysis. Later we showed that strong 

 preparations of ionium and of radiothorium, when freed from 

 all bodies emitting /3- and 7-rays, emitted a small quantity 

 of 7-radiation. For various reasons the radiation emitted by 

 radiothorium was not analysed. Analysis of the radiation 

 of ionium, however, showed that it consisted of three types 

 of rays varying widely in penetrating power and in intensity. 

 A small quantity of /3-radiation, too large to be ascribed to 

 thorium products, but too small to be analysed, was found 

 also to accompany the 7-radiation from ionium. 



* Ann. tier Phys. no. 15, 1912, p. 933. 

 t Communicated by Prof. E. Rutherford, F.R.S. 

 t J. Chadwick, Phil. Mag. vol. xxv. p. 193 (1913) ; J. Chadwick & 

 A. S. Russell, Proc. Roy. Soc. A. vol. lxxxvii. p. 489. 



