86 
LUMMER. 
explains phenomena which up to the present time have been 
mysterious “question-marks” in the sky. I mean the comets, 
with their tails extending away from the sun, and growing, 
near the sun, at the rate of thousands of kilometers a second. 
One of the most fruitful applications of the black radiation 
laws is the determination of temperatures of light sources 
like our stars and our sun. Let us suppose for the moment 
that all our light sources emit black radiation. We then get 
their temperatures at once by the equation 
T= 
2940 
'■max 
degrees absolute 
when we know the wave lengths Knax, where the maxima of 
their energy curves are situated. According to the famous ex- 
periments of Langley, we have Knax = 0.5 g, and thus for the 
temperature of the sun 
T. 
sun 
2940 
0.5 
= 5880 degrees absolute 
The Hungarian astrophysicist, Baron von Harkany, has, 
by the same method, calculated from earlier observations the 
temperatures of several fixed stars and found some of these 
temperatures to be higher than that of our sun. 
This determination of the sun’s temperature is correct 
only if the sun’s radiation is really black radiation. Who 
knows anything about the nature of the sun’s radiation? 
If it does not emit black radiation, perhaps it may emit only 
platinum radiation, which is one of the least black of all. 
Pringsheim and 1 have determined as accurately as possi- 
ble the radiation laws of bright platinum in order (o throw 
some light on these problems, the solution of which are also 
of importance in artificial illumination. Our experiments 
have led to ihe following law T s: 
f E x dX = const. T 5 
E max T~’‘ = cowt. 
\ n .J= 2630 . 
