332 
PHYSICS: W. W. COBLENTZ 
Proc. N. a. S. 
No doubt this is owing partly to experimental errors; but some of it may- 
be attributed to the low (selective) infra-red emission of the Sun, the earth's 
atmosphere being quite transparent to radiations greater than T/x. 
For the purposes of this investigation the agreement between the ob- 
served temperatures of a Aurigae and the Sun is considered satisfactory, 
verifying the previous measurements of stellar temperatures which range 
from 3000° K for red, class-M stars, to 12,000° K for blue, class-B stars. 
Planetary Radiation. — The thermal radiation emitted from a planet 
as a result of warming by exposure to solar radiation, including heat which 
may be radiated by virtue of a possible high internal temperature of the 
planet itself, is essentially of long wave-lengths Tju to 12 /x. Hence, by 
means of a 1 cm. cell of water, interposed in the path of the total radiation 
emanating from the planet, this long wave-length radiation can be sep- 
arated from the reflected solar radiation, and in this manner a measurement 
obtained of the energy reradiated. If there is planetary radiation, the 
water cell transmission will be less than that of the direct solar radiation. 
The observed transmission of planetary radiation through a cell of 
water 1 cm. in thickness is given in table 2. This table shows that the 
TABLE 2 
Transmission of Planetary Radiation through a Cell op Water 1 cm. in 
Thickness; Also the Per Cent of Planetary Radiation Emitted 
PER CENT TRANSMISSION 
Planetary 
Object Date No. of sets Deviation Mean Mean radiation in 
June, 1922 of measure- from value value per cent of 
MST ments mean 1922 1914 the total 
Sun 17th; 11:30 a.m. 5 1.2% 69.3 
4:15 p.m. 4 0.5 69.8 
Jupiter 
Central disk 14th; 10:15 p.m. 2 1.4 69.7 65.6 
Southern hemis- 
phere 10:20 p.m. 2 3.0 66.8 65.8 
Venus 15th; 8:00 p.m. 2 2.3 66.3 59.0 5 
Saturn 14th; 9:00 p.m. 3 1.1 60.0 55 15 
Mars 15th; and 18th . 6.0 50.3 .... 30 
Moon 14.7 80 
water cell transmission of the total radiation from Jupiter is practically 
the same as that of the direct solar radiation. From this it appears that 
the outer atmosphere of Jupiter does not radiate appreciable energy as. 
the result of warming by solar rays and that the atmosphere is sufficiently 
thick and opaque to trap all the energy reradiated as the result of warming 
of its interior by solar radiation, or by internal heating. 
The radiometric measurements on Venus, Jupiter and Saturn are in 
good agreement with similar measurements made at Mt. Hamilton, Calif. ^. 
