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V. On the Absorption and Radiation of Heat by Gaseous and Liquid Matter. — Fourth 
Memoir. Ry John Tyndall, F.R.S., Member of the Academies and Societies of 
Holland, Geneva, Gottingen, Zurich, Halle, Marburg, Breslau, Upsala , la Societe 
Philomathique of Paris, Cam. Phil. Soc. &c . ; Professor of Natural Philosophy in 
the Royal Institution. 
Received June 18,— Read June 18, 1863. 
§ 1 - 
The Royal Society has already done me the honour of publishing in the Philoso- 
phical Transactions three memoirs on the relations of radiant heat to the gaseous form of 
matter. In the first of these memoirs* it was shown that for heat emanating from the 
blackened surface of a cube filled with boiling water, a class of bodies which had been 
previously regarded as equally, and indeed, as far as laboratory experiments went, per- 
fectly diathermic, exhibited vast differences both as regards radiation and absorption. 
At the common tension of one atmosphere the absorptive energy of olefiant gas, for 
example, was found to be 290 times that of air, while when lower pressures were 
employed the ratio was still greater. The reciprocity of absorption and radiation on 
the part of gases was also experimentally established in this first investigation. 
In the second inquiry f I employed a different and more powerful source of heat, my 
desire being to bring out with still greater decision the differences which revealed them- 
selves in the first investigation. By carefully purifying the transparent elementary 
gases, and thus reducing the action upon radiant heat, the difference between them 
and the more strongly acting compound gases was greatly augmented. In this second 
inquiry, for example, olefiant gas at a pressure of one atmosphere was shown to possess 
970 times the absorptive energy of atmospheric air, while it was shown to be probable 
that when pressures of -g^th of an atmosphere were compared, the absorption of olefiant 
gas was nearly 8000 times that of air. A column of ammoniacal gas, moreover, 3 feet 
long, was found sensibly impervious to the heat employed in the inquiry, while the 
vapours of many of the volatile liquids were proved to be still more opaque to radiant 
heat than even the most powerfully acting permanent gases. In this second investigation, 
the discovery of dynamic radiation and absorption is also announced and illustrated, and 
the action of odours and of ozone on radiant heat is made the subject of experiment. 
* Philosophical Transactions, February 1861 ; and Philosophical Magazine, September 1861. 
f Philosophical Transactions, January 1862 ; and Philosophical Magazine, October 1862. 
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