ITS EFFECT ON TEMPEKATURE AND ITS PRESSURE ON SMALL BODIES. 527 
The Radiation from the Sun’s Surface. 
If s is the radius of the sun’s surface, R the radiation per square centimetre, then the 
total rate of emission is 47r^~R. This passing through the sphere of radius r, at 
the distance of the earth and with surface gives 
4775^11 = 47rr^S, 
where S is the solar constant. 
Hence 
11= % S = 
9-23 X 10^ 
4-3 X 1U= 
S = 46,000S. 
Corresponding to the three values of S just given we have three values of R, viz., 
R„ = 1-29 X IQi'; R/= 0-945 X 10^1 ; R, = 0-805 X 10”. 
The Effective Temperature of the Sun. 
If we equate the sun’s radiation to a6\ where cr is the radiation constant, we get 6, 
the effective temperature ” of the sun, that is the temperature of a full radiator 
which is emitting energy at the same rate. 
Thus 
whence 
Similarly 
5-32 X 10-5^/ = 1-29 X 10”, 
= 7000° A approximately. 
^^ = 0500° A; C— 6200° A. 
Wilson'-^ made a direct comparison of the radiation from the sun with that from 
a full radiator at known temperature. Assuming a zenith transmission of 71 per cent., 
he obtained 5773° A as the effective solar temperature. If we put 
we get 
46,000S = 5-32 X 10"" X 5773^ 
S = 0-128 X 10b 
Tins is no doubt too low a value. Either then Wilson’s zenith transmission was less 
than 71 per cent, or Kurlbaum’s constant is too small. 
The low value is probably to be accounted for chiefly by the first supposition. 
Wilson points out that if x is the true value of the transmission, his value of the 
temperature is to be multiplied by (71/x)b If we take 9,- = 6200° as the true value 
then X will be given by 
= miW X 71 = 53. 
Tins low value is not necessarily inconsistent with the much higher value 71 per cent. 
* ‘Roy. Soc. Proc.,’ vol. 69, 1901-2, p. 312. 
