42 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



CONCLUSION. 



While we Lave fouud abuudaut evidence of heat from the uioou, every method we have tried, 

 or that has heeu tried by others for determiuiug the character of this heat appears to us incouclu- 

 sive; and, without questioning that the moon radiates lieat earthward from its soil, we have not 

 yet found any experimental means of discriminating with such certainty between this and reflected 

 heat that it is not open to misinterpretation. "Whether we do so or not in the future will probably 

 depend on our ability to measure by some process which will inform us directly of the wave-lengths 

 of the heat observed. 



Note added February, 1885. — Since the above paragraph was written, we have succeeded in 

 obtaining measures with rock-salt prisms and lenses in a lunar heat spectrum. These difiticult 

 measures must be repeated at many lunations before complete results can be obtained; but, con- 

 sidering their importance to the present subject, we think it best to state now in general terms, 

 and with the reserve due to the necessity of future experiment, that they indicate two maxima in 

 the heat curve, one corresponding within the limits of errors of observation to the solar curve 

 maximum, the second indefinitely lower down in the spectrum, corresponding to a greater amount 

 of heat at a lower temperature. Exactly what temperature this latter corresponds to, we have 

 no present means of knowing. We have succeeded, however, in forming a measurable heat spec- 

 trum from the surface of a Leslie cube containing boiling water, and the maximum ordinate in the 

 Innar heat curve appears to be below the maximum ordinate in the hot water curve. The inference 

 from this is, of course, that the temperature of the lunar soil is, at any rate, below that of boiling 

 water and in an indefinite degree. 



We cannot close this note without calling attention to the remarkable fact that we here seem 

 to have radiations from the moon of lower wave-length than from the sun, which implies an appar- 

 ent contradiction to the almost universally accei)ted belief that the sun's emanations, like those 

 from any heated solid body, include all low wave-lengths representing temperatures inferior to 

 those certainly emitted. 



