Vol.. 8, 1922 ASTRONOMY: W. W. COBLENTZ 51 
determined, thus obtaining for the first time an insight into the radiation 
intensities in the complete spectrum of a star. 
3. Results. — By means of this device it was found that, in the class B 
and class A stars, the maximum radiation intensity lies in the ultra-violet 
(0.3 At to 0.4 ju) while in the cooler, classes K and M, stars, the maximum 
emission lies at 0.7 m to 0.9 ^ in the infra-red. From this it appears that the 
black body temperature (i.e., the temperature which a black body would 
have to attain in order to emit a similar relative spectral energy distri- 
bution) varies from 3000° C for red, class M, stars to 10,000° for blue, 
class B, stars. 
This estimate of the effective temperature of a star was obtained by two 
methods. The first method consisted in making all corrections to the 
observations, excepting those for atmospheric absorption, and comparing 
them with the calculated values, using a solar type star {a Aurigae, class 
Go) as a standard. This seems permissible, in view of the fact that the ob- 
served temperature (6000 ° K) of a Aurigae was found to be in close agree- 
ment with that assigned to the sun. The stellar temperatures estimated in 
this manner are given in column 4 of table 1 . 
The second method consisted in applying all corrections to the ob- 
servations, including the one for atmospheric absorption, and comparing 
the results with the calculated values. Applying factors for atmospheric 
absorption introduces great irregularities in the observed spectral radia- 
tion components. This, no doubt, is owing partly to selective emission 
of the star, and partly to the use of improper transmission factors, which, 
because of lack of time, could not be determined directly. 
The temperature of a star, as estimated from the spectral energy com- 
ponents outside of the atmosphere, extends over a wide range, the average 
value of which is in good agreement with that obtained by the first method 
(see column 3 of table 1). 
In table 1 are assembled the effective stellar temperatures as deter- 
mined by various methods. The agreement is especially close for stars 
of classes G, K and M. 
Most of the stars measured are no doubt giants, of which RusselP says : 
"The mean densities of the giant stars diminish rapidly with increasing 
redness, from one-tenth that of the sun for class A to less than one-twenty- 
thousandth that of the sun for class M." In speculating on the nature 
of stellar radiation and stellar temperatures it is interesting to find that the 
observed radiometric data (see table 2) seem conclusive in showing that 
the early type (class M) stars are losing heat 3 to 4 times as fast as the 
more dense, but hotter late- type (class B, A) stars. The least dense, 
class M, stars must therefore be losing heat by radiation, in which con- 
duction cannot contribute very materially in maintaining the surface at 
a given temperature. 
