Bumstead — Heating Effects produced by Rontgen Rays. 23 



down-scale and varied from 0*1 to - 3 cm ; it was determined 

 each time by allowing the coil to run with the lead screen 

 in front of the window of the radiometer. The plus and 

 minus signs indicate the direction of the deflection ; thus a 

 change of sign in either column represents a shift of the 

 wheel, so that the positions of the strips are interchanged. 

 Columns IV and Y contain the deflections corrected for lack 

 of balance of the radiometer. In experiments 1, 2, 3 and 9, 

 the radiometer was sensibly balanced when tested by the two 

 lead strips ; in 4, 5 and 6, there was a lack of balance of 15 

 per cent in the positive direction ; in 7 and 8 the lack of balance 

 was 10 per cent in the same direction. Accordingly, in the 

 first case the positive deflections (zinc) are reduced 15 per cent, 

 in the second case the positive deflections (lead) are reduced 

 10 per cent. The changes in the conditions are explained by 

 the fact that between the groups of experiments mentioned 

 the radiometer, for one reason or another, had to be taken 

 down and readjusted. 



Columns VI and VII contain the deflections reduced to 

 the steady state, by dividing by (1 — e~ yt ). The values of 

 y used were, for lead 1*5, for zinc 0*67. Column Till contains 

 the ratios of YI to YII ; it is the ratio of the heat generated 

 2?er second in the lead strip to that generated in the zinc strip. 



The first three experiments were made with the vanes 

 between the window and the strips ; the last six with the strips 

 between the window and the vanes. 



Exp. I II III IV V VI VII VIII 



5 —3-45 +1-30 —3-85 +2-06 1*87 



5 —6'84 +2-26 — 7'65 +3-58 2"13 



5 +5-20 —1-90 +5-82 —3-01 T93 



5 —5-51 +2-43 +2-16 —6*18 +3*41 1-81 



5 —6-67 +2-64 +2-25 — 7'46 4-3'55 2*10 



5 —7-07 +2-96 +2-51 — 7'90 +3'96 2'00 



7 1-5 +7-09 —2-30 +6-39 +7'12 —3-63 1-96 



8 1-5 +9-76 —3-21 +8'80 +9"85 — 5"07 1'94 



9 3-0 —13-75 +6-4 —13-95 +7'40 1-88 



The average of the ratios in Column VIII is 1-96 ; reducing 

 to equal absorptions, we get, as the result of these measure- 

 ments, that when Hontgen rays are equally absorbed in lead 

 and in zinc, the quantity of heat generated in the lead is 1 # 93 

 times the quantity generated in the zinc. 



The necessity of the writer's returning to America has 

 temporarily interrupted this investigation. Further experi- 

 ments are, however, now under way in which other metals 

 will be compared, and the experimental conditions varied as 



1 1 



2 1 



3 1 



4 1 



5 1 



6 1 



