BoEDDiCKEE — On Luuar Radiant Heat. 511 



of that of bodies heated below the point of luminosity) is much more readily- 

 absorbed in transversing transparent media than direct solar heat, and is 

 extinguished in the upper regions of our atmosphere, never reaching the surface 

 of the Earth at all. Some probability is given to this by the tendency to disappear- 

 ance of clouds under the Full Moon, [the italics are Sir John's] a meteorological fact 

 (for as such we think it fully entitled to rank), for which it is necessary to seek a 

 cause, and for which no other rational explanation seems to offer." 



8. Another explanation of our anomaly might be based on the following 

 paragraph from E. Neison, The Moon (1876), p. 35: — 



" Hitherto no reference has been made to a question of very considerable 

 influence in the consideration of the questions connected with the lunar surface, 

 and that is with regard to purely local atmospheric conditions ; for from a number 

 of different observations it has been considered that from local action some 

 vapours may rise from the surface and play an important part in the questions 

 connected with selenography. Reasoning from the known condition of the 

 material constituting the terrestrial surface, it seems not unlikely that when 

 exposed to the greater temperature to which it has been found that the surface of 

 the Moon is in part exposed, some such local atmospheric conditions may well 

 arise ; and that a purely local covering to the surface may well occur in the 

 interior of a deep formation, from the presence of some constituent of the surface, 

 first expelled by the heat and then reabsorbed on cooling. Of the terrestrial 

 surface strata, for example, exposed to the condition imder which the Moon exists, 

 few, if any, would be found where this might not be expected to occur in some 

 degree, and such would be most naturally supposed to occur in the interior of the 

 deeper lunar formations where the last influence of any aqueous vapour might be 

 expected to be manifested." 



From this remark we should conclude that during the progress of an eclipse a 

 steady absorption of vapour would take place, by which some heat would be 

 developed. After the eclipse the atmosphere would emanate again, and during 

 this process a certain amount of heat would be consumed or bound until the whole 

 of the atmosphere is set free. By this amount of heat the total measured after 

 the eclipse should fall short of the Full Moon value. Under these circumstances 

 the heat-curve of 1888 after the last contact with the penumbra would be the more 

 probable one. For it should run parallel to the axis of the abscissae until the 

 lunar vapourous atmosphere is fully developed, and should then rather suddenly 

 rise up to the Full Moon value. 



It may, of course, be possible that both the hypotheses discussed hold good 

 and are together adequate in bringing about the observed anomaly. 



The above theories I only mention tentatively and with considerable diflidence. 

 Yet any attempt at explaining a so far unexplainable phenomenon may, I think, 

 be of some use for future investigations. 



