THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Art. XLI. — The Invisible Solar and Lunar Spectrum ;* by 

 S. P. Langley. With Plates IX, X. 



The following investigation has been made from studies at 

 the Allegheny Observatory, but it is proper to state that the 

 provision of the very special apparatus used, is due to the lib- 

 erality of a citizen of Pittsburgh, who has desired that his name 

 should not be mentioned. 



This paper is an abstract of a forthcoming memoir, which 

 will eventually appear in the fourth volume of the publications 

 of the United States Academy of Sciences, to which the reader 

 is referred for fuller details. 



Ever since the writer first f investigated the infra-red of the 

 solar spectrum to the extent of about three microns, he has as- 

 sumed, from all analogy, the probable existence of solar heat of 

 still greater wave-lengths, which, however, he has not till lately 

 been able to experimentally demonstrate, so that there has been 

 a doubt whether such waves were emitted by the sun after ab- 

 sorption by its own atmosphere, or whether they existed pre- 



* As the writer has already presented to the National Academy a memoir (read 

 October 17, 1884, Memoirs Nat. Acad, of Sci., vol. iii,) on the heat of the moon, in 

 which he spoke of investigations still in progress on it, it should be said that 

 these are not yet published, and that they are only given here so far as is neces- 

 sary in explanation of certain anomalies in the infra-red solar heat-spectrum, 

 which forms the principal subject of the present paper. 



f Compies Rendus de l'Institut de France, September 11, 1882. Amer. Jour. 

 Science, March, 1883. 



Am. Jour. Sci.— Third Series, Vol. XXXVI, No. 216.— Dec, 1888. 

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