Properties of the a Rays from Radium. 169 



one gram o£ radium in radioactive equilibrium, is equal to 

 the total number n o£ a particles expelled per second from 

 one gram of radium at its minimum activity. I have recently 

 determined this number by measuring the charge carried by 

 the a rays emitted from a thin film of radium bromide at its 

 minimum activity. Assuming that each a particle carries 

 the usual ionic charge of 1*13 x 10 -20 electromagnetic units, 

 it was deduced that 6'2 x 10 10 particles are expelled per 

 second from radium itself. 



Thus n = 6'2 xlO 10 . 



Now ^»mV 2 = heating effect of a. particles expelled per 

 second from radium C. 

 =3-6 X 10 5 ergs. 



Substituting again the value of the ionic charge e and the 



mV 2 

 value of n, — = T03 x 10 16 . 



In this result the value of e has not been assumed, since 



n = - , where i was the measured current due to the charge 

 e> to 



carried by the a rays. We have previously seen that 



^=4-0x10*. 



e 



From these two equations, it is seen that 

 V= 2*6 x 10 9 cms. per second 

 and e/m = Q'o x 10 8 electromagnetic units. 



These values are in surprisingly good agreement with those 

 previously deduced by Des Coudres, and myself, from the 

 amount of deviation of the rays in passing through a magnetic 

 and electric field. Des Coudres found that V=l/6 X 10 9 and 

 *?/m==6-3xl0 3 , while I found that V = 2-5xl0 9 , and 

 e/m=6xlO d . 



While the application of the heating effect of radium to 

 determine the values of the constants of the a rays is of 

 interest, I do not think that at present much weight can be 

 given to the results, on account of the uncertainty attaching 

 to the value of n, which is very difficult to measure with 

 accuracy. 



When the experiments at present in progress on the electric 

 deflexion of the a ra} r s from radium C are completed, it is 

 hoped that the vaiue of e/m will be obtained with sufficient 

 accuracy to settle definitely the important question, whether 

 the a particle is a projected helium atom. 



