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’ o where is the angle of rotation of the nicol analyzer, 
and for the Le Chatelier J = (1/d)* where d is the length of one side of 
the iris diaphragm. Ka, K, and R are constants and can all be determined 
without reference to any temperature observation. 
Wanner Pyrometer.—this method of calibration will be made clear by 
an example. For a particular Wanner pyrometer the value of 4 was 
0.656 2, 
Therefore 
14.500 0.4343 
.656 
= 9,600. 
It is seen from (4) that if Ki were known, various values of ¢@ might 
be substituted in the equation and the corresponding temperatures calcu- 
lated. Now by assuming some angle of rotation ¢ for some particular 
temperature T, as in the above case, Ki may be found. For example, let 
T = 1273 and ¢ = 45°. 
Then from (4) 
1 
K, = log tan? ¢ + K, — 
, 
9,600 
—( + == lay 
1,273 
For @ 10, and n= 0, t may be calculated from (7), 
9,600 
t = 273 
7.55 + 1.51 
— TF i= C. 
— 
Le Chatelicr Pyrometer.—ihe wave length for the red glass used on a 
Le Chatelier pyrometer was found to be 0.649 1. The constant K then 
becomes 
14,500 0.4343 
y= 
0.649 
==) 700: 
Holborn-Kivtbaum Pyrometer.—Such an instrument must be calibrated 
empirically and the calibration will be different for every lamp used. It 
