528 Mr Wade, Method of facilitating the measurement [May 10, 



'•2 



constantly -~- , the method of § 2 is shewn to be justifiable. The 

 constant — will in future be called S. 



In order to make this result practically serviceable, it must be 

 remembered that at the present day it is usual to find the values 

 of the constants 0, 8, R , (see § 3 equation (3)), in preference to 

 any three others, and it will be necessary to shew how to obtain 

 z, a, and S from these quantities. 



To find z, 



a = a' - 2/3z, 



R = a'z — (3z 2 , 



R - /3z" . 



z 



DuttiDe a _ (100 + 8)0 80 



putting o- (100)2 , £- 100 3> 



we easily get 



2z 100 + 8 // lOO + j jy 4R n x 100 



100 8 -V V 8 / 08 



Again a = — 



*+iw J ' 



_ a /2 10 3 



08 ' 



as a control of the accuracy of the calculations we may use 



R = z—^. 



Messrs Neville and Heycock have kindly furnished me with 

 the constants of several pyrometers and from these I have 

 calculated the values of S, a', z, which would convert them into 

 direct reading instruments. 



