of ol-P articles per Second emitted by Th 



wrium C. 



1045 



practically to zero by passage through 1*5 cm. of lead. The 

 absorption curve of the radium standard, therefore, should 

 drop rapidly at first, and should finally attain a rate of fall 

 identical with radium C. Consequently, if the ratio of the 

 activities of a radium standard and radium C for different 

 thicknesses of lead 13 plotted, it should show an initial fall, 



Fiff. 3. 



75 



725 



■70 



3-3 4-3 6-3 8-3 10 3 123 14-3 



Ratio of number of oc-Particles ThC : RaC for equal y- Activities. 



but a final constant value when all the radium B radiation 

 has been absorbed. Curve III. fig. 2 is the absorption curve 

 of the radium standard and curve V. is the curve of the 

 ratio, radium standard/radium C, plotted from II. and III. 

 The truth of the statements above is evident from this curve. 

 The curve becomes flat at a value *91. Consequently the 

 ionization which was produced at 3*3 mm. of lead by the 

 radium B in the standard, and which has been eliminated by 

 1*4 cm. of lead, must have represented 9 per cent, of the 

 total ionization produced in the electroscope by the radiation 

 from the standard. 



The following table gives the 7-ray measurements from 

 which the curves were plotted : — 















































• 























Mms. 



leac/. 





















Mm. of Lead. 



Radium Standard. 



Radium C. 



Thorium C. 



33 



1-000 



1-000 



1000 



5-52 



•836 



•884 



•890 



7'62 



•727 



•777 



•791 



9-87 



•631 



•679 



•705 



11-95 



•552 



•597 



•640 



1415 



•484 



•535 



•565 



The determination by Hess and Lawson* of the number 

 of particles emitted by the amount of radium C which is in 



* Publication 105 of the Radium Institute at Vienna. 



