318 



Equa. (7) is a general equation for connecting the relation between 

 temperature t and luminous intensity J and can be applied to any pyrom- 

 eter in which J can be determined theoretically. For the Wanner pyrom- 

 eter J = tan= where o is the angle of rotation of the nicol analyzer, 

 and for the Le Chatelier J = (l/d)" where d is the length of one side of 

 the iris diaphragm. Ki, Ko and R are constants and can all be determined 

 without reference to any temperature observation. 



Wanner Pyrometer.—lhis method of calibration will be made clear by 

 an example. For a particular Wanner pyrometer the value of ?. was 

 0.056 //. 



Therefore 



14.500 X 0.4343 



K, = 



.656 

 ^ 9,600. 



It is seen from (4) that if Ki were known, various values of 9 might 

 be substituted in the equation and the corresponding temperatures calcu- 

 lated. Now by assuming some angle of rotation 6 for some particular 

 temperature T, as in the above case, Ki may be found. For example, let 



T = 127.3 and <p = 45°. 

 Then from (4) 



1 



Ki ^ log tan- (p + K2 — 



T 



9,600 



= H = 7.55. 



1,273 



For 9 = 10, and n = 0, t may be calculated from (7), 



9,600 



t = 273 



7.55 + 1.51 



--= 787° C. 



Lc Chafrlicr Pyrometer. — 'Ilie wave length for the red glass used on a 



Le Chatelier pyrometer was found to be 0.G49 u . The constant K then 



becomes 



14,500 X 0.4343 



K, = 



0.649 



= 9,700. 

 II(dh(tni KiirlbdKin I'uroineter. — Such an instrument nuist be calibrated 

 empirically and the calibration will be different for every lamp used. It 



