Vol. 8, 1922 
PHYSICS: W. W. COBLENTZ 
331 
ments recently made on the Sun; also to give some measurements of the 
radiation from the major planets. 
2. Apparatus and Procedure. — The apparatus used in this work con- 
sisted of the 40-inch reflector of the Lowell Observatory, to which was 
attached a special radiometer mentioned in a previous issue of these Pro- 
ceedings/ and fully described elsewhere. ^ The thermocouples were new 
and were made of fine bismuth wire, with receivers 0.2 mm. in diameter. 
The crucial part of this investigation consisted in obtaining an exact 
measurement of the water cell transmission of the direct sunlight. For 
this purpose, the great reflecting mirror and the end of the telescope tube 
were covered. Parallel light, entering a small opening in the cover of the 
telescope tube, fell upon a small, plane, silvered mirror, placed in the axis 
of the tube, and from thence reflected upon the diagonal mirror to a ther- 
mopile which was especially constructed for these measurements. 
3. Experimental Data— The solar radiation data are given in table 1, 
in which column 1 gives the spectral range, and columns 2 and 4 give the 
Spectral radiation components (a.m. and p.m.) of the Sun (also of a 
Aurigae, column 6) corrected for all losses except atmospheric absorption. 
The corresponding temperatures are given in columns 3, 5 and 7. 
TABLE 1 
Spectral Radiation Component of the vSun and oe a Aurigae in Per Cent of 
THE Total 
SUN a AURIGA^ 
A. 
M. 
p. 
M. 
Spectral 
Spectral 
Temper- 
Spectral 
Temper- 
spectral 
Temper- 
ran^e. 
radiation 
ature 
radiation 
ature 
radiation 
ature 
|i = 0.001 mm. 
component 
°K 
component 
°K 
component 
°K 
O.BOac to 0.43m 
25.0% 
5670 
25.6% 
5750 
18.4% 
5000? 
0.43iuto 0.60m 
22.1 
6500 
19.0 
5760 
18.2 
5800 
0.60m to 1-40m 
31.8 
5860 . 
35.0 
5050? 
30.6 
6000 
1 .40m to 4.10m 
20.6 
6060 
20.1 
6140 
26.4 
5200? 
4.10m to 10.00m 
0.5 
0.8 
6.4 
Average 
6000° K 
5900° K 
5900° K 
These data are interesting in showing a close agreement between the 
spectral radiation components of the Sun and a Aurigae in the visible 
spectrum (0.43 m to 0.6 /u) which is in agreement with the visual and photo- 
graphic observations. However, in the ultra-violet the radiation com- 
ponent of a Aurigae is less, and in the infra-red it is greater (owing 
partly to the low-temperature radiation from the companion star), than that 
of the Sun. The lower value in the ultra-violet might be owing, in part, 
to the larger air mass traversed and hence to the greater amount of scatter- 
ing of the incoming radiations. But this does not explain, and is in- 
consistent with, the higher values observed in the infra-red, in many of 
the stars previously measured, in spite of the greater air mass traversed. 
