24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



crepancy is undoubtedly due to variation in the transmissibility of our 

 atmosphere to the peculiar rays emitted by the moon. 



" From measures in different parts of the lunar image, we find that 

 the rays absorbed by glass are present in greater proportion in the 



radiation coming from the dark areas, or so-called " seas " 



The smaller radiation of the dark regions is presumably due to the 

 presence of a larger proportion of those longer waves to which our 

 atmosphere is partially opaque. 



" Measurements in the lunar image during an eclipse of the moon 

 showed a very rapid diminution of the heat as the eclipse progressed, 

 a small amount (not over 2 percent, however) remaining in the 

 umbra, of a quality to which glass was entirely opaque. The incre- 

 ment of the lunar radiation on the passing of the eclipse was appar- 

 ently almost as rapid as its previous decrease. 



" Less rapid than the change during an eclipse, but still strongly 

 marked, is the transposition which occurs in the degree of heat 

 observable at the east and west limbs, respectively, a few hours before 

 and after the full. Thirty-six hours before the full the radiation of the 

 west limb in terms of that from the central region of the moon was 

 0.958, that of the east limb being 0.574 ; while thirteen hours after 

 the full the order was reversed, the west limb giving 0.61 1 and the 

 east 0.727. 



" We next give the observations reduced to the full and to a mean 

 distance, but uncorrected for atmospheric absorption, arranged ac- 

 cording to the season in two groups, the object of this arrangement 

 being to compare any systematic variation of the atmospheric absorp- 

 tion with the change of season. [Only the mean values given here.] 



Lunar Spectrum — Winter Observations (November to April), 

 Reduced to Full Moon and Mean Distance 



No. .. 40°oo' 39°4S' 39°30' 39°i5' 39°oo' 38°45' 38°3o' 38''i5' 38°oo' 37°45' 37°30 



Mean.. 16.9 15.6 17.4 16. i iS-3 M-i ii-4 12.4 24- 1 39-2 48-» 



No 37°iS' 37°uo' 36°45' 3^°3o' 36°i5' 36°oo' 35°45' 35 3o 35 i5 35 00 



Mean 43-o 360 38.4 32.2 25.9 25.6 21.8 18.3 17.4 ii-6 



Lumr spectrum — Summer Observations (May to October), 

 Reduced to Full Moon and Mean Distance 



Mean.. 15.7 22.5 19.9 178 150 6.5 48 4-2 lo.i 30. S 35-7 



Mean 41.0 37-i 33-9 20.4 27.4 15.5 i7-2 130 10.7 9-7 



" It will be seen from the above table and from the curves in 

 Plate 1 1 that there is on the whole a slight increase in the atmospheric 



