Rays emitted by Glowing Platinum, 467 
responding to the extreme red begin to appear. As the bod 
becomes hotter and hotter, rays of shorter and shorter wave 
lengths show themselves, so that for each temperature a new 
set of rays first makes its appearance, while at the same time, 
the intensity of those already at hand continues to increase. 
Applying the principle we have already proved to this case, we 
see that the function I for any given wave length is equal to 0 
for all points below a certain temperature corresponding to this 
wave length; and that for all temperatures above this point, 
the function I increases with the temperature.” 
Strictly speaking, however, the temperature at which each 
individual wavelength becomes visible depends solely upon 
the sensitiveness of the observer's eye. We are furthermore 
In view of the present ignorance of the law of expansion for 
stead of try- 
scale for the platinum thermometer, which should be quite 
independent of other standards, and which could easily be 
expressed in terms of the existing scales so soon as the neces- 
coat investigations of the expansion of platinum had been 
made 
Theal ready existi ng resear che tend onl J -m.- 
peratures, and the empirical formule based upon them being 
_ only strictly applicable to the interval covered by actual experi- 
ment, a reduction obtained by use of them for an interval 
between the red heat and melting point would be at best of 
doubtful value. I give, nevertheless, such a reduction, founded 
_ Am. Jour. Scr.—Tump ge wabcoe XVII, No. 108.—Dec., 1879. 
