862 Mr. Otto Stuhlmann on Difference in Photoelectric 



The correction curve for tin and the original or uncorrected 

 curve for platinum, upon which experiments were carried on 

 to determine this absorption of the ultra-violet light by the 

 quarz, happen to give identical values. The broken line is 

 here used to call attention to the fact that the original un- 

 corrected curve for platinum and the correction curve for tin 

 are identical. 



Conclusions. 



If the metals are arranged in the order of their atomic 

 weights and also according to their position in the periodic 

 system as given in the table below, one notices that there is 

 a periodic increase in the ratio of the emergent to the inci- 

 dent photo-electric effect as one ascends through the periods 

 of the table. 





Metal. 



Emergent 

 Photo Effect. 



At. Wt. 



Effect. 

 A i. Wt. 



II. Period 



Mg 

 Fe 



1-06 



244 



435 





III. Period 



1-02 + 



55 9 



183 



170 

 170 





IV. Period 



Cu 



Zn 



108 

 111 



63-6 

 65-3 





VI. Period 



Ag 



Sn 



1-07 

 115 



107-9 

 118-5 



99 



97 





VIII. Period 



Pt 



1-17 



194-8 



60 





IX. Period 



Pb 



112 



2069 



54 





This becomes more apparent when the values for the ratio 

 of emergent to incident photo-electric effect are plotted 

 against their atomic weights as in fig. 6. 



Iron, although of a higher atomic weight than magnesium, 

 has a smaller forward effect. The increase in atomic weight 

 from zinc to silver is large, yet the forward effect of silver 

 has very much decreased. The increase in the effect from 

 copper to zinc is about the same as that from silver to tin, 

 while the value for lead, three periods removed, drops to a 

 value nearly equal to that of zinc in the fourth period. 



This seemingly points to a periodic variation of the forward 

 effect with the change in the atomic weight, and likewise to a 

 more rapid variation at the end than at the beginning of a 

 period. In the last column of the above table the ratio of 

 the effect to the atomic weight has been tabulated. It will 



