532 PROFESSOR J. 11. POYXTIXG OX RADIATIOX IX THE SOLAR SYSTEM; 
We then have a receiving surface virtually ttv", and a radiating surface inr. Then 
we get the radiation emitted per square centimetre • 
0-9S7rr2 
47rr3 
9S . 
40 ’ 
and if 6 is the temperature required for this, 
5-32 X = 
9S . 
40 ’ 
whence 
Uniform 0,, - 330° A approximately 
e, = 307° A 
,, 0, = 293° A 
values not more than 5° above those obtained for the average on the supposition of 
no convection. . . 
Comparing these results with the temperature of the real earth, it is seen at once 
that they are of the same order. ^ , o -r^ 
The average temperature of the earth’s surface is usually estimated at about 60 
say 289° A. ^ The temperature of the atmosphere is on the whole decidedly lower 
thaiWhat of the surface below it. We should therefore conclude that the earth’s 
effective temperature is somewhat below 289 A. 
Ao-ain, the earth and the atmosphere, taken as one surface, do not constitute a 
full absorber, but are to some extent selective. Hence we should expect the earth to 
be, if anything, of a higher temperature than a full absorber and radiator under the 
same conditions. 
For lioth these reasons, then, the ideal planet might be expected to have a tempera¬ 
ture lielow rather than above 289° A. The lowest estimate obtained above is 
therefore probably nearest to the truth, and it would appear that even that is 
somewhat too high. This tends to show that, if we accept Kuelbaum’s value of 
the radiation constant, we cannot put the solar constant so high as 3 or 4, but must 
accept a value much nearer to that which I have called Eosetti’s value, wz., 2-5. 
In what follov^s I shall therefore take Rosetti’s value and the resulting value of 
the-solar temperature, viz., 6200° A. 
The calculation made above may be turned the other way round, and may be 
used for a 
Dcterminraion of the EJfeetire Tempcmtvre of the Sim from the Arerage 
J^empevatyre of the Earth. 
Assumino- that the real earth may be replaced by the ideal planet already con- 
^ . . 0’9S 
sidered. the radiation per square centimetre from the equatorial liand is 
Biit the 
