Bolt 
Radiation Pyrometers.—Hqua. (1) may be written in the form 
P ae 
leg K, hee, (4) 
Al 
where 
loge 
k= Cr 
C, for a black body temperature equals 14,500 when 7 is given in terms 
of x, 
Equa. (4) may be applied to any pyrometer, using monochromatic 
light, in which the luminous intensity can be varied in a continuous and 
determinate manner as in the Wanner and Le Chatelier. Wither of the 
instruments will, therefore, indicate temperature indefinitely high, but the 
limit of accuracy is reached at about 2,000° C., so that at higher tempera- 
tures the incident radiation is usually cut down by means of one or more 
absorption glasses. The amount by which it is cut down is determined as 
follows: 
Let J’ equal’ the luminous intensity of the incident radiation and Ji 
the value as indicated by the instrument when one glass is used, then 
eee ote 
where R is the absorption factor. For two absorption glasses 
ian (el ER Ee rene 
and for n glasses 
If = (5) 
also 
1S Ike (6) 
The general expression, then, for the relation between energy and abso- 
lute temperature, is from (4) 
log J’ = Ki — K,—. 
T 
From (5) 
1 
log J + nlog R= K, — K, —, 
‘TT 
whence 
t 
= + — 278, (7) 
K, — log J—nlogR 
where t is temperature in degrees C. 
