THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1861. 



XXIII. On the Absorption and Radiation of Heat by Gases and 

 Vapours, and on the Physical Connexion of Radiation, Absorp- 

 tion, and Conduction. — The Bakerian Lecture. By John 



Tyndall Esq., F.R.S. %c* 



[With a Plate.] 

 § 1. r |^HE researches on glaciers which I have had the honour 

 A of submitting from time to time to the notice of the 

 Royal Society, directed my attention in a special manner to the 

 observations and speculations of De Saussure, Fourier, M. Pouil- 

 let, and Mr. Hopkins, on the transmission of solar and terrestrial 

 heat through the earth's atmosphere. This gave practical effect 

 to a desire which I had previously entertained to make the 

 mutual action of radiant heat and gases of all kinds the subject 

 of an experimental inquiry. 



Our acquaintance with this department of Physics is exceed- 

 ingly limited. So far as my knowledge extends, the literature 

 of the subject may be stated in a few words. 



From experiments with his admirable thermo-electric appa- 

 ratus, Melloni inferred that for a distance of 1 8 or 20 feet the 

 absorption of radiant heat by atmospheric air is perfectly insen- 

 sible f. 



With a delicate apparatus of the same kind, Dr. Franz of 

 Berlin found that the air contained in a tube 3 feet long ab- 

 sorbed 3*54 per cent, of the heat sent through it from an Ar- 

 gand lamp ; that is to say, calling the number of rays which 

 through the exhausted tube 100, the number which 

 when the tube was filled with air was only 96*46 J. 



* From the Philosophical Transactions, Part I. for 1861, having been 

 read at the Royal Society February 7, 1861. 



t La Thermochrose, p. 136. X Pogg. Ann. vol. xciv. p. 342. 



Phil. Mag. S. 4. Vol. 22. No. 146. Sept. 1861. N 



