Temperature of the Moon. 37 



atmosphere for radiations from bodies of low temperature, and 

 as to the spectral region where it chiefly occurred. 



This list includes, besides the described heat observations 

 on the moon at every obtainable lunation, the following 

 others : — 



(1) On the heat during a lunar eclipse. 



(2) On the quality of the heat in the lunar spectrum at 

 different stages of the moon's age. 



(3) On the direct heat observable from different regions of 



the moon's face in an enlarged lunar image, and com- 

 parisons of the heat radiated by the dark and by the 

 bright regions of the moon. 



(4) A supplementary investigation showing that different 

 percentages of the radiations from these dark and bright 

 regions were transmitted by glass. 



(5) Observations giving the means of comparing the atmo- 

 spheric absorption of lunar radiations in summer with 

 that in winter for equal altitudes. 



(6) Very numerous observations of the spectrum of the mid- 

 night sky. 



(These last are specially important here, where they 

 are rendered necessary by the fact that this sky is the 

 standard with which the lunar radiations are to be 

 compared. These last observations give, for example, 

 certain evidence of a great " hot band " in the nega- 

 tive sky spectrum, corresponding in position to the 

 great cold band in the lunar spectrum, which is thus 

 shown to be produced jointly by the absorption of the 

 moon's rays and by the absorption of the radiation of 

 the bolometer due to the intervening air-column be- 

 tween it and the moon.) 



(7) Observations supplementary to the last, by comparative 



measurements of the sky radiation from the zenith to the 

 horizon. 



(8) On further supplementary measurements made by com- 

 paring the energy in the spectrum of a lampblack 

 screen at 100° C. with that of the sky, showing the 

 existence of several regions of atmospheric absorption, 

 giving " hot bands " in the negative sky spectrum. 



(We only allude here, in passing, to the important 

 inference to be drawn with regard to the nocturnal 

 radiations from the soil of our own planet, to which 

 these observations show that our atmosphere is partially 

 diathermanous. ) 



