178 Mr. W. Makower on the Number and Absoiytion 



It will be seen that the absorption-curves for aluminium and 

 glass do not differ appreciably from each other. The points 

 marked (0) indicate the value of the charge in arbitrary 

 units received by the brass cylinder surrounding the tube 

 containing the emanation in the experiments described above. 

 It will be seen that these points, too, lie fairly closely on the 

 curve obtained for aluminium by measuring the ionization 

 caused by the rays after passing through different thicknesses. 

 This shows that when the ft rays are absorbed by glass, the 

 charge carried by the particles which are absorbed remains 

 in the glass, indicating that the rays are actually stopped by 

 the glass and not merely scattered. 



Corrected Value of the number of ft particles emitted by- 

 Radium C. 



The value for the number of ft particles emitted by radium C 

 given above is incorrect, for two reasons. In the first place, 

 some of the radiation from radium C is absorbed even in 

 passing through the very thin glass tube used to contain the 

 emanation ; and in the second place, a small amount of 

 radiation passing through the walls of the glass tube is due 

 to the ft rays from radium B. It remains to apply a cor- 

 rection for these two errors. Now the absorption-curves for 

 the ft rays from radium B and C have been calculated 

 separately by Schmidt *. On the assumption that radium B 

 and C, when in radioactive equilibrium, emit the same number 

 of ft particles, it is possible to deduce the number of particles 

 emitted by either separately, i. e. the number which would 

 impinge on the outer brass cylinder (fig. 1) when no glass is 

 interposed between the emanation and the cylinder. Table I. 

 shows the experimental numbers obtained, and fig. 3 shows 

 the method by which the above-mentioned correction was 

 applied. The curve obtained from the experiments described 

 above is shown by the continuous line. The dotted curve has 

 been obtained by subtracting from the ordinates at each point 

 the charge due to the ft rays from radium B, and then extra- 

 polating back to thickness zero from the values given by 

 Schmidt in his paper. The value so obtained for the number 

 of ft particles emitted by radium C per gram of radium per 

 second is 5'0 x 10 1Q . 



In a recent determination of the number of a particles emitted 

 by radium C Rutherford and Geiger give the number 3*4 x 10 10 . 

 Considering the uncertainty in applying the corrections just 

 given, the values for the numbers of a and ft particles emitted 



* Schmidt, he. cit. 



