ITS EFFECT ON TEMPERATURE AND ITS PRESSURE ON SMALL BODIES. 533 
radiation per square centimetre from the sun’s surface is 46,0OOS. If then 0^ is tlie 
earth’s equatorial temperature, and dg is the solar temperature, 
0-9S 
whence 
77 
: 46,000S = 
e. = ej'io. 
The average temperature of tlie earth is OTS of the equatorial temperature. If 
tins average is 0^^, then 
0, = d./21 -5. 
If we take the temperature of the real earth as 289° A, and as being equal to that 
of the ideal, 
ds = 21‘5 X 289° = 6200° A approximately. 
h£)per Limit to tne lenipercthirc oj ci Lully Rctdifiliviy Surface exposed noriiicdly 
to Solar Radiation at the Distance of the Earth from the Sun. 
The highest temperature which a full radiator can attain is that for which its 
radiation is equal to the energy I’eceivetl. This will only hold wlien no appreciable 
quantity of heat is conducted inwards from the surface. 
To obtain the upper limit in the case under consideration, we have to equate the 
radiation to the solar constant, which we shall now take as S,- = O'175 X lOh Then, 
5-32 X lO-‘^0^‘ = 0-175 X 10', 
and 
0 = 426° A. 
If the surface reflects some of the radiation and alisorhs a fraction x of that falling 
on it, then the effective temperature is 
X 426° A. 
The Limitiny Temperature of the Surface of the 1 
We may upi'ly this result to find an upper limit to the temperature of the moon’s 
surface. Tins iq)per limit can only he attained when it is sending out radiation as 
rapidly as it receives it, and is therefore conducting no appreciable quantity inwards. 
We shall take Langley’>s estimate iloc. cit.) of ^ted radiation _ 1 
emitted radiation 6-7' 
represented nearly enough Iiy x = |-. 
The upper limit of temperature of the surface exposed to a zenith sun is, therefore, 
0 = 426 X (If - 126 X 0-967 = 412° A. 
