June 20, 3913] 



SCIENCE 



955 



measured in the image of the eclipsed moon 

 that the radiation is reflected and not radi- 

 ated; but the curves which he has drawn"" for 

 the eclipse of September 23, 1885, as meas- 

 ured at Allegheny by Mr. J. E. Keeler and 

 myself, are incorrect, since the heat at no time 

 vanished, although it diminished continually 

 until the end of totality; and in other eclipses 

 which I have observed, the heat measured in 

 the image of the eclipsed moon has never been 

 less than 1 per cent, of its value before eclipse, 

 while the diminution of the light is some- 

 times a millionfold greater; that is to say, 

 there is simply no comparison between the re- 

 flected radiation and that emitted by the 

 heated lunar surface during totality. The 

 radiation enormously exceeds the reflection at 

 that time."* 



I am at a loss to know the source of the 

 statement by Dr. Coblentz that " at the last 

 quarter the heat of the moon is certainly not 

 less than at the full." "° This statement is 

 totally at variance with all published observa- 

 tions. 



One other misapprehension needs to be cor- 

 rected. It is found in the work on " The 

 Moon " by Professor W. H. Pickering."' Pro- 

 fessor Pickering says (p. 20) : 



The most satisfactory test hitherto made seems 

 to be that of Professor Very (Astrophysical Jour- 

 nal, 1898, VIII., p. 266), who compared the 

 amount of heat received from the moon by a 

 bolometer with that received from an equal an- 

 gular area of sunlit melting snow. The heat was 

 nest in each case allowed to pass through a piece 

 of clear glass before reaching the bolometer. The 

 glass allows nearly all the reflected heat to pass, 

 but absorbs that radiated by the body itself. The 

 total radiation in the two cases was about the 

 same, but while the reflected heat was much 

 greater from the snow than from the moon, it 

 was found that the radiated heat was much greater 

 from the moon than from the snow. This means 

 that while the snow is the better reflector, as, 



'^Physical Review, Vol. 24, Fig. 1, p. 310. 



" Compare Frank W. Very, ' ' The Temperature 

 of the Moon," Astrophysical Journal, Vol. 24, p. 

 354, December, 1906. 



* Carnegie Institution publication, p. 112. 



" Published by John Murray, London, 1904. 



indeed, we can see by inspection, the moon is the 

 hotter body. The observation is so direct and 

 simple that it seems impossible to deny the accu- 

 racy of the conclusion, but of course it gives us 

 no clue as to what the actual temperature is. 



The recognition of the value of this par- 

 ticular observation is all that could be asked, 

 but the really convincing and conclusive ex- 

 periments with radiating heated minerals, 

 which were performed under identical experi- 

 mental conditions, and which do give us a 

 " clue as to what the actual temperature is," 

 are not even mentioned in this work, and have 

 been strangely underrated elsewhere. 

 Professor Pickering goes on to say: 

 It would be interesting to repeat Professor 

 Very's observation, comparing the radiation from 

 the surface of the moon with that from the sur- 

 face of rock illuminated by the sun at tempera- 

 tures ranging from the melting point of snow to 

 the highest attained by rocks on the earth's sur- 

 face when exposed to a nearly vertical sun. 



Experiments somewhat resembling those 

 suggested, but more instructive, had already 

 been performed. 



Another instance of the same misapprehen- 

 sion follows. Abbot and Eowle say: 



Coblentz has lately shown that some of the 

 materials likely to be prevalent on the moon 's 

 surface are very poor radiators at such tempera- 

 tures as these, and this would tend to explain why 

 Very has found a temperature so much higher 

 than that of a "black body" under similar con- 

 ditions. 



They also remark: 



We do not know what its surface is composed 

 of, and therefore have no means of discovering 

 the relations which connect the lunar temperature 

 and radiation." 



The opinion that " the moon is probably a 

 very bad radiator " is also reiterated by these 

 authors in a recent article,™ where are some 

 personalities to which I need make no further 

 allusion, as they only obscure the real ques- 

 tion. 



" Annals Smithsonian Observatory, Vol. 2, p. 

 174. 



^Astrophysical Journal, Vol. 25, p. 95, March, 



