12 JSumstead — Heating Effects produced by Rbntgen Bays. 





Zinc 







Lead 





V 



dt 



7 



V 



dV 

 dt 



7 



3'0 



1-8 



0-6 



6-0 



6-2 



1-0 



2-0 



16 



0-8 



3-0 



4-0 



1-3 



1-5 



1-05 



0-7 



1-5 



2-5 



1-7 



0-8 



0'50 



0-6 



0-8 



1-3 



16 



Average - 68 Average 1*4 



In order to determine the steady value from the value at 

 the end of three minutes we have 



v - v 



i-e-n 

 which gives, for lead V^ =13 - 95, and for zinc V^ =7*4. 



Approximately the same rates of cooling and heating were 

 obtained in all the experiments made upon this point. A sec- 

 ond example is given in figure 4, in which weaker rays were used 

 for ten minutes instead of three. Curve I is for zinc, curve II 

 for lead ; the two experiments were made at different times 

 and with rays of different intensity, so that the magni- 

 tudes of the deflection have nothing to do with each other. 

 To show that the inertia and damping of the suspended sys- 

 tem have no sensible effect upon the determination of the rates 

 of heating and cooling, curve III is added for comparison. 

 This was obtained by suddenly moving the controlling mag- 

 net at the time t = o ; it represents the response of the sus- 

 pension to a sudden impulse. The following values for y for 

 zinc and lead were obtained from the cooling portions of these 

 curves : 



Zinc Lead 



dt 



7 



V 



dV 

 dt 



7 



2-0 1-2 

 1-0 0-58 

 0-5 0-38 



0-6 



0-58 



0-76 



1-0 



0-5 

 0-3 



1-5 



0-8 

 0-48 



1-5 

 L6 

 1-6 



Average 



0-65 





Average 



1-6 



Later in the course of the experiments, the aluminium win- 

 dow was replaced by a one of glass and the strips heated by 

 means of a beam of light ; the- result of such an experiment 

 is shown in fig. 5 below. The following values of 7 are 

 obtained in the same manner from these curves : 





Zinc 







Lead 





V 



dV 

 di 



7 



V 



dY 



7 



4-0 



2-15 



0-54 



4-0 



5-2 



1-3 



2-0 



1-22 



0-61 



2-0 



2-6 



1-3 



1-0 



0-57 



0-57 



1-0 



1-1 



1'] 



Average 57 Average 1*23 



