S. P. Langley — Temperature of the Moon. 427 



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 of comparisons 

 of the heat radiated by the dark and by the bright regions 

 of the moon ; 



(4) A supplementary investigation showing that different percent- 



ages of the radiations from these dark and bright regions 

 were transmitted by glass ; 



(5) Observations giving the means of comparing the atmospheric 



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 negative sky spectrum, corre- 

 sponding 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 to the intervening air-cob 

 umn between it and the moon.) 



(7) Observations supplementary to the last, by comparative meas- 



urements of the sky radiation from the zenith to the horizon ;. 



(8) On further supplementary measurements made by comparing 



the energy in the spectrum of a lamp-black screen at 100° C. 

 with that of the sky, showing the existence of several regions 

 of atmospheric absorption, giving " hot bands " in the nega- 

 tive sky-spectrum. 



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

 ence to be drawn with regard to the nocturnal radiations 

 from the soil of our own planet, to which these observa- 

 tions show that our atmosphere is partially diathermanous.) 



(9) Of other measurements giving the means of estimating the 



total lunar radiation in terms of solar, 



but for these and many more subsidiary ones, the reader must 

 again be referred to the original memoir. 



The only one of these subsidiary researches which needs fur- 

 ther mention here is the measurement of the heat from differ- 



