on the International Standard. 



323 



Original paper. 



' Radio- 

 active 

 Sub- 

 stances.' 



Quantity. 



Rutherford & 



Boltwood 

 j Standard. 



International 



Radium 



Standard. 



Geiger, Proc. Roy. 

 Soc. A. lxxxii. p. 486 

 (1909). 



p. 502. 



Total current due 

 to the a. rays from 

 one curie of ema- 

 nation. 



(1) by itself 



(2) with its a. ray 

 products. 



275 XlO 6 



e.s. units. 

 9-46 XlO 6 



e.s. units. 



2-89 XlO 6 



e.s. units. 

 9-94 XlO 6 „ 



H. Moseley, Proc. 

 Roy. Soc. A. lxxxvii. 

 p. 230 (1912). 



p. 204. 



Total charge carried 

 by the (3 particles 

 emitted per second 

 by radium B or 

 radium C in equi- 

 librium with one 

 gram of radium. 



17*4 e.s. units. 



18*3 e.s. units. 





p. 459. 



Calculated half 

 value period of 

 transformation of 

 radium. 



1780 years. 



1690 years. 



It may be of interest at this stage to discuss briefly in 

 some cases the agreement between the observed and calculated 

 values, and to consider the fundamental data involved in the 

 calculations. 



In the first place, it can be easily shown that 

 the calculated values of (1) the production of helium by 

 radium, (2) the volume of the emanation, (3) the heating- 

 effect, (4) the life of radium, all involve the quantity ?iE, 

 where n is the number of « particles expelled per second per 

 gram of radium itself, and E the charge carried by the 

 cc particle. In other words, the agreement of calculation with 

 experiment in these cases does not involve the accuracy of 

 the actual value of n or of E (which is twice the unit charge), 

 but the product of these numbers, which is a measure of 

 the charge carried by the a particles expelled per second per 



gram of radium 



The value wE was directly determined by Rutherford and 

 Geiger, and is given by -tiE = l'llx 10" 9 e.m. units on the 

 International Standard. This value has been used in making 

 the calculations of the four quantities mentioned above. 



The value of this quantity deduced from the rate of pro- 

 duction of helium by radium (viz. 164 c.mm. per gram per 

 year) is 1*12 x 10" 9 — a close agreement with the direct 

 experimental value. 



Y2 



