92 
LUMMER. 
Let us put T e = 20° + 273° = 293° absolute. For a solid angle 
of 32' and for an interval of time of GO seconds we have, there- 
fore, 
- s e = 1 .3 x 10 " 1: '' x GO x sin* 16' x [ T* - 293 4 ] , 
gr. cals. 
which energy is equal to the solar constant 2.5 £ . ac- 
1 cm. nun. 
cording to Abbot. Thus we get, 
T = G250° Abs. 
If the sun’s radiation is not black, it can emit the same energy 
only at a higher temperature. Let us assume the absorptive 
power, a , of the sun to he not unity, hut less than that of a 
black body — for example, 0.4, 0.1, or 0.01; then, since T va- 
ries as V a we get 
a. 
temp. 
1.0 
7000 ° 
0.4 
9000 ° 
0.1 
13000 ° 
0.01 
24000 ° 
You will observe that the temperature determined by the 
total energy does not depend very much on the hypothesis 
that the radiating body is black. 
Thus we can assume with reasonable certainty that the 
sun’s temperature is about 7000°, and we need make no 
distinction between the various temperature scales. You 
will recall that in earlier times the temperature of our sun 
was estimated to be 1500° by the application of incorrect 
radiation laws, or to be ten million degrees by the applica- 
tion of mechanical laws. Such a temperature (7000°) sur- 
passes the critical temperature of all our terrestrial substances. 
Above their critical temperatures, substances cannot ex- 
ist at the same time in two phases, as liquids and as vapors. 
The highest possible pressure may compress a gas above its 
critical temperature to about the density of a liquid; but 
there never occurs a rapid transition between the gaseous 
and liquid phase — that is, there is never a liquid surface; 
