PHILOSOPHICAL TKANSACTIONS. 
I. The Bakeeian Lectuee. — On the Absor^ption and Badiation of Heat by Gases and 
Vapour's, and on the Physical Connexion of Badiation, Absorption, and Conduction. 
By John Tyndall, Esp, F.B.8., Member of the Academies and Societies of Holland, 
Geneva, Gottingen, Zurich, Halle, Marburg, Breslau, la Societe Philomathigue of 
Paris, &c. ; Professor of Natural Philosophy in the Boyal Institution, and in the 
Government School of Mines. 
Eeceived January 10, — Eead February 7, 1861. 
The researches on glaciers which I have had the honour of submitting from time to 
time to the notice of the Boyal Society, directed my attention in a special manner to the 
observations and speculations of De Saussuee, Foueiee, M. Pouillet, and Mr. Hop- 
kins, 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 exceedingly limited. So far as 
my knowledge extends, the literature of the subject may be stated in a few words. 
From experiments Avith his admirable thermo-electric apparatus, AIelloni inferred 
that for a distance of 18 or 20 feet the absorption of radiant heat by atmospheric air is 
perfectly insensible*. 
With a delicate apparatus of the same kind. Dr. Feanz of Berlin found that the air 
contained in a tube 3 feet long absorbed 3 ’5 4 per cent, of the heat sent through it from 
an Argand lamp ; that is to say, calling the number of rays which passed through the 
exhausted tube 100, the number which passed when the tube was filled with air was 
only OGAGf. 
In the sequel I shall refer to circumstances which induce me to conclude that the 
* La Thermochrose, p. 136. t Poggendoeit’s Annalen, vol. xciv. p. 342. 
MDCCCLXI. R 
