ii2 TEMPERATURE; OF THE MOON. 



Harrison 1 inferred that the surplus heat of the moon will reach its 

 maximum several days after the day of complete illumination. In com- 

 menting on this statement Langley (loc. cit.) reminds the reader that 

 the region of the moon, which has received at first quarter the solar 

 rays for rather more than four days, after being subjected to the most 

 intense cold during the moon's long night, has been but very little 

 warmed in comparison with the surface illuminated at last quarter, 

 which has been heated during a mean duration of eleven days, so that at 

 the last quarter the heat of the moon is certainly not less than at the full. 



During the eclipse of October 4, 1884, Boeddicker 2 showed that the 

 moon parts with its acquired heat very rapidly, and "it is hard to admit 

 that this heat from the lunar surface, which the moon has been absorb- 

 ing during many days of continuous sunshine, is parted with at once, 

 the whole earthward surface of the planet cooling almost instanta- 

 neously." 3 



From alternate exposures on bright and dark spots Langley found 

 that the radiation from the bright region around Tycho exceeded that 

 from the dark surface of the Mare Imbrium by 31 per cent, and as a 

 whole found that the bright parts of the moon radiate about 14 per cent 

 more than the dark parts. This is evidently due to a larger reflection 

 of sunlight. "If the same holds good for the invisible solar rays, it is 

 certain that less of the sun's heat is absorbed by the bright parts, and 

 hence there is a possibility that the temperature and proper radiation 

 of the light regions are less than those of dark areas, though this would 

 not necessarily follow, since many other factors must be included." 3 



II. 



The writer has examined the infra-red reflecting power of a series of 

 minerals, including quartz, feldspars, amphiboles, and micas, which are 

 the chief constituents of the rocks of the earth's crust, and has found a 

 uniformly decreasing reflecting power of 3 to 5 per cent at 4 ^ to 0.3 per 

 cent at 7/x, followed by bands of selective reflection from 8.5 to IO/A. 

 In this latter region the mean reflecting power is from 40 to 50 per cent 

 for silicates, while pure quartz has a reflecting power of 90 per cent. 

 The reflection curves are given in fig. 90 in a condensed form. In the 

 lower part of the figure several of Langley's lunar radiation (reflection) 

 curves are given, in which the ordinates are in arbitrary units. Of 

 course, the absolute reflecting power of the moon is unknown. Zollner 

 has shown that, owing to the irregularities of its surface, the full moon 



1 Harrison : British Assoc. Report, 1866, II, p. 20. 



2 Boeddicker : Nature, 30, p. 589, 1884. 



3 Langley: Mem. Nat. Acad. Sci., 3, p. 17, 1884. 



