THE TEMPERATURE OF MARS n 



sq. cm. per sec. It is true that the value is not quite constant 

 (appearing to indicate that the sun is a variable star), but this 

 cannot have any great effect on the planetary temperatures. 

 If we substitute this value in Prof. Poynting's expression, then, 

 giving e its maximum possible value of unity, we shall not get 

 6 higher than 6° C, and since e must be considerably less than 

 i, the theoretical temperature must be still less. There is a 

 certain discrepancy here which still awaits explanation. 



This, however, will not influence the temperature of Mars, 

 for S will not appear in the ratio of the temperatures of the 

 two planets. If the absorbing powers of the two planets are 

 sufficiently different — and the difference between the albedoes 

 of Mars and Venus seems to indicate the possibility — the 

 temperature of Mars need not vary much from that on the 

 earth. 



The difference in the absorbing powers seems to be due, 

 as Prof. Lowell remarks, to a lack of clouds in the Martian 

 atmosphere. We know that clouds reflect 72 per cent, of the 

 incident light, and their permanent absence will cause the 

 greater absorption. The nights, however, owing to the rarity 

 of the atmosphere, may be very cold. 



