A NEW CRATER IN THE MOON. 99 



affects the moon's surface. In the lunar year of seasons, 

 lasting 346 of our days, there are only uf lunar days, each 

 lasting 29! of ours. Thus day lasts more than a fortnight, 

 and is followed by a night of equal length. Nor is this all. 

 There is neither air nor moisture to produce such effects as 

 a.e produced by our air and the moisture it contains in 

 mitigating the heat of day and the cold of night. Under 

 the sun's rays the moon's surface becomes hotter and hotter 

 as the long lunar day proceeds, until at last its heat exceeds 

 that of boiling water. But so soon as the sun has set the 

 heat thus received is rapidly radiated away into space (no 

 screen of moisture-laden air checking its escape), and long 

 before lunar midnight a cold exists compared with which the 

 bitterest weather ever experienced by Arctic voyagers would 

 be oppressively hot. These are not merely theoretical con- 

 clusions, though even as such they could be thoroughly 

 relied upon. The moon's heat has been measured by the 

 present Lord Rosse (using his father's splendid six-feet 

 mirror). He separated the heat which the moon simply re- 

 flects to us from that which her heated surface itself gives 

 out (or, technically, he separated the reflected from the 

 radiated heat), by using a glass screen which allowed the 

 former heat to pass while it intercepted the latter. He thus 

 found that about six-sevenths of the heat we receive from the 

 moon is due 10 the heating of her own substance. From 

 the entire serie: of observations it appeared that the change 

 of temperature during the entire lunar day that is, from 

 near midnight to near midday on the moon amounts to 

 fully 500 Fahrenheit. If we assume that the cold at lunar mid- 

 night corresponds with about 250 below zero (the greatest 

 cold experienced in Arctic travelling has never exceeded 

 140 below zero), it would follow that the midday heat is 

 considerably greater than that of boiling water on the earth 

 at the sea-level. But the range of change is not a matter of 

 speculation. It certainly amounts to about 500, and in 

 whatever way we distribute it, we must admit, first, that no 

 such life as we are familiar with could possibly exist on the 



H 2 



