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III. The Temperature of the Moon. From Studies at the 

 Allegheny Observatory by S. P. L ANGLE Y, with the assist- 

 ance o/F. W. Very*. 



THIS memoir may be regarded as the completion of the 

 investigation commenced in 1883, and continued during 

 the next four years, and of which previous portions have been 

 published in the Memoirs of the National Academy of Sci- 

 ences, in a paper read Oct. 17, 1884 (vol. iii.), and in that 

 read Nov. 9, 1886 (vol. iv.), the latter having been published 

 in abstract in the American Journal of Science! . 



The original memoir, of which the following is a very 

 succinct abstract, can, from its special character, hardly claim 

 the attention of the general reader ; but the latter may, 

 perhaps, be here reminded that the main questions at issue 

 are the temperature of an airless planet at the earth's distance 

 from the sun, the action of the atmosphere in modifying the 

 temperature of such a planet, and, in general, the study of 

 those conditions of radiation and absorption which have 

 actually rendered life possible on our own. He may be re- 

 minded also that it has been generally assumed hitherto that 

 the temperature of the sunlit surface of an airless planet at 

 such a distance, e. g. of the moon, would be excessively high. 

 Thus Sir John Herschel, in his latest i Outlines of Astronomy,' 

 says : — " The surface of the full moon exposed to us must 

 necessarily be very much heated, possibly to a degree much 

 exceeding that of boiling water." The only experimental 

 evidence obtainable appeared to lend support to this view, 

 for though Lord Rosse did not undertake to directly deter- 

 mine the lunar temperature (as he is often supposed to have 

 done), any inference which can be drawn from his experi- 

 ments appears to support the above views of Herschel, which 

 he also cites } . 



It has also been almost universally supposed that our at- 

 mosphere was nearly impervious to the lunar radiant heat, so 

 that, if any existed, it could still not be perceived by us at 



* Memoir read to the National Academy of Sciences, November 1887. 

 Communicated by the Author. 



t For December 1888. See also ' London, Edinburgh, and Dublin 

 Philosophical Magazine,' December 1888 ; also Ann, de Chemie et de 

 Physique, July 1889. 



\ See Proc. Royal Society, xvii. 1869, p. 443 ; xix. 1870, p. 12 ; Trans- 

 actions, clxiii. pp. 622-4. Having elsewhere shown that the lunar 

 radiation consists of a small quantity of reflected heat and a compara- 

 tively large quantity of heat emitted from its soil, Lord Rosse compares 



