Hays emitted by Substances exposed to y Mays. 623 

 Table I. 



Differences 



Difference 



Difference 



Differences 



Difference 



Difference 



of 

 substances. 



in 



in 



of 

 substances. 



Se-Al 



Zr-Al 



Mo-Al 



in 



in 



secondary 

 radiation. 



atomic 

 weight. 



secondary 

 radiation. 



atomic 

 weight. 



B-Al 



+ 12 



— 155 



-52 



-16 



-15 



-4 



238 

 205 

 207 



524 



6:5-7 

 689 



C-Al 



Na-Al 



Mg-Al 



+ 13 



-26 



Ru-Al 



245 



74-7 



Si-Al 



-27 



+ 1-4 



Ag-Al 



348 



81 



P-Al 



-1 



4 



Cd-Al 



373 



85 



S — Al 



+ 11 

 99 



5 

 13 



Sn-Al 



Sb-Al 



401 

 405 



91 

 93 



Ca-Al 



Mn-Al 



151 



28 



I-Al 



441 



100 



Fe-Al 



166 



29 



W-Al 



552 



157 



Ni-Al 



176 



31-7 



Pt-Al 



743 



168 



Co-Al 



181 



31 



Hg-Al 



794 



173 



Cu-Al 



206 



36-3 



Pb-Al 



800 



180 



Zn-Al 



215 



38-5 



Bi-Al 



1018 



181 



As-Al ...... 



225 



48 









An approxi 



mate value 



of the radii 



ition from alui 



ninium, corresponding 



to (Pb-Al)= 



:800, is 330 











form of plates, little disks were turned by means of a lathe, 

 equal in dimensions to the little dish a. The substances used 

 in the form of filings or powder were : B, C (pure graphite), 

 Mg, Si, P (red), S, Mn, Se, As, Co, Zr, Mo, Ru, 8b, I, W, 

 Pt (black), Bi. 



The radiating powers of the various elements, obtained 

 from the table by making aluminium equal to 330, are 

 plotted against their atomic weights in fig. 2 ; and the 

 elements belonging to the same chemical period joined, in 

 each case, by a smooth curve. The method by means of 

 which the radiating power of aluminium was determined 

 will be described later. For our present purpose it does not 

 matter what value is assigned to aluminium, since the general 

 form of the curves will thereby not be altered. 



It will be seen afterwards that the 7 rays from radium are 

 heterogeneous, and that the constituent rays possess different 

 powers of producing secondar}^ radiation from a given sub- 

 stance. A partial separation of the rays can be effected, 

 since they are selectively absorbed, by means of metal screens. 

 Since the 7 rays in this experiment passed through a lead 

 screen only 3 mm. thick, the curves represent, at any rate 

 approximately, the general nature of the curves showing the 

 relation between the atomic weight of a substance and the 

 secondary cathode radiation with the heterogeneous y rays 

 of radium. 



2T2 



