TEMPERATURE; OF THE MOON. 



in 



an anomalous distribution of light, which was thought to be due to 

 variations in the terrestrial atmosphere at different points along the 

 great circle at which the solar rays touched the surface. However, the 

 results as a whole show a sudden change in the radiation (reflection) 

 from the moon, with change in illumination. The penumbra began to 

 affect the center of the moon at + lh 44 m - The predicted time for the 

 moon to enter the penumbra was -|-2 h 48. In other words, in the short 



time of about 1.5 hours, in 

 passing from the penumbra 

 into the umbra, the radiation 

 from the west limb has fallen 

 from a maximum to a mini- 

 mum value. Without actually 

 computing 1 this fall in radia- 

 tion, which is so sudden as to 

 indicate a small conductivity 

 and a very superficial cooling, 

 one would think that at the 

 beginning of totality the radia- 

 tion would still be detectable. 

 The question of the gain (or 

 loss) of heat on the surface of 

 an isolated body like the moon 

 does not lend itself readily to 

 a coherent line of reasoning, 

 because of the fact that we 

 know so little about the phe- 

 nomena connected with it. A 

 thin surface, like a radiometer 

 vane, placed in a vacuum and 

 subjected to radiation, acquires 

 a maximum temperature in a 

 very short time. The same is 

 not true of the earth and its 

 atmosphere, isolated in space. It is difficult to say what one ought to 

 expect of the moon, but from ordinary experiences one would anticipate 

 an appreciable lapse of time for the surface to acquire an extreme 

 change in temperature, after subjecting it to the sun's heat. 



At great elevations on the earth, where the atmosphere is rare, we 

 know that the soil grows colder, although the direct rays become hotter 

 with rise in height, and one would infer that similar conditions obtain 

 over the whole lunar surface. 



FlG. 89. Abscissas = time in hours to mid-eclipse 

 ordinates = galvanometer deflections. 



1 See page 115. 



