278 Method of Determining the Radiation Constant. 

 (iii) To find p : 

 From the exponential law we have 



and therefore 



§ = A^,, 



dfl 



~-~ oc Ape~P^ = A 1 pe-P^ say. 



Similarly for time t 2 (where t 2 = 2t 1 ) 



'0 2 =A 1 pe-^ = A i pe~ 2 ^ , 

 that is _• . • 



eje 2 =ep\ 



or 



pt 1 =\og6 1 /e 2 . 



But by plotting the deflexions against the times we get 

 the deflexion curve n » /i „ A 



and from this curve we may measure 1 and 6 2 for a pair of 

 times such that t 2 = 2t 1} and consequently we find 



1, 0, 



h 2 



With the galvanometer used in these experiments the 

 following values were obtained for these quantities : 



p = O0069; ^=0-654; and &=0*127, 



which, when substituted, give 



p 2 -kp + n 2 _427 



428 



which may be taken as 1, that is to say, the observed value 

 of -j- \ could be taken as a measu 

 rise of temperature of the silver disk. 



of -j7 /A- could be taken as a measure of the initial rate of 



