Rays emitted by Glowing Platinum. 449 
of the leucoscope to this purpose. Its sensitiveness is best 
shown by the final test, the comparison of two parts of the same 
petroleum flame. These portions, a cooler and a warmer, were 
so similar in color that with the unaided eye no difference 
could be detected. The mean of twenty observations with the 
leucoscope gave for the position of the ocular Nicol, 
Tasie I. 
For the upper part of the flame 64° 4’ 
For the lower part of the flame 62 16 
Difference E48 
to determine whether, during the twelve to fifteen minutes 
course of a single experiment, any important change was caused 
by the loss of energy in the battery. Experience showed that 
the loss of intensity during a single experiment was so sm 
that it could be left out of account. 
II. 
The experiments to be described in this paper were simply 
Spectro-photometrie comparisons of the light emitted by the two 
3. 
Ww: \ 
set INS 
= 
Wires. One of the wires was given successively various tem- 
peratures between 1200° and 1900° of the platinum thermom- 
eter,* and all visible wave lengths radiated by this wire were 
Compared with the corresponding rays from the other. 
* See page 451. 
