Bumstead — Heating Effects produced ~by Rontgen Rays. 11 



The variation of the temperature with the time during cooling 

 will have different values of the JL's and7's, but (again except- 

 ing the initial part) the curves of heating and cooling will have 

 very nearly the same form. This is seen in the "figure, and 

 it also appears mathematically that with the values of the con- 

 ductivity and emissivity involved, there is a nearly uniform 

 temperature throughout the metal within less than" a minute 

 after the rays are turned on. We may therefore, for such 











































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Minutes. 



accuracy as is needed in this discussion take the curve of cool- 

 ing to be represented by 



V=V 8 e-K 



the time being counted from the moment the rays are cut off. 

 In this equation 



1 dV 



y = — 



V dt' 



and one may get rough values of 7 for lead and for zinc by 

 drawing tangents to the curves of cooling. In the following 

 tables are several values found for different points of the 

 curves in fig. 3 ; the zero for the zinc curve was taken as the 

 mean of the position at 2 m and 10 m and, for lead, the mean 

 of 10 m and 18 m . 



