THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JANUARY 1881. 



I. On the Absorption of dark Heat-rays by Gases and Vapours. 

 By Ernst Lecher and Joseph Pernter*. 



[Plate I.] 



MAGNUS and Tyndall, who, as is well known, have in- 

 vestigated (the latter through a long series of years) 

 the absorption of radiant heat by gases and vapours, arrived, 

 on some points, at very different results. Other investigators 

 also have devoted time and trouble to this investigation, and 

 in particular to the absorption of heat-rays by aqueous vapour, 

 without being able to arrive at any final decision. 



The difficulty of the observations in question, perhaps on few 

 other questions of experimental physics so great as on this, 

 hardly permits the employment of a method entirely free from 

 objection; hence the explanation of the fact that hardly ever 

 do we meet with such differences, and even contradictions, as 

 here. Thus, for example, Tyndall f finds that a layer of pure 

 dry air of 1*22 metre thickness transmits all the rays of heat 

 given off by a source of heat at 100° O.J Magnus §, on 



* Translated from a separate impression, communicated by the Author, 

 from the Sitzb. der k. Akad. der Wissensch. in Wien, July 1880. 



t Tyndall, ' Contributions to Molecular Physics in the Domain of 

 Eadiant Heat' (London, Longman, Green and Co., 1872.) We cite 

 this work whenever possible for the investigations of Tyndall, since he 

 has himself carefully collected all his different researches on the subject 

 in this work. 



% Loc. cit. p. 19. § Pogg. Ann. cxii, 



Phil. Mag. S. 5. Vol. 11. No. 65. Jan. 1881. B 



