THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



AUGUST 1864. 



X. On the Absorption and Radiation of Heat by Gaseous and 

 Liquid Matter. — Fourth Memoir. By John Tyndall, 

 F.R.S., %c.* 



THE Royal Society has already done me the honour of pub- 

 lishing in the Philosophical Transactions three memoirs 

 on the relations of radiant heat to the gaseous form of matter. 

 In the first of these memoirs f it was shown that for heat ema- 

 nating 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 radia- 

 tion 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 em- 

 ployed the ratio was still greater. The reciprocity of absorption 

 and radiation on the part of gases was also experimentally esta- 

 blished in this first investigation. 



In the second inquiry J I employed a different and more 

 powerful source of heat, my desire being to bring out with still 

 greater decision the differences which revealed themselves in the 

 first investigation. By carefully purifying the transparent ele- 

 mentary gases, and thus reducing the action upon radiant heat, 

 the difference between them and the more strongly acting com- 

 pound gases was greatly augmented. In this second inquiry, 

 for example, olefiant gas at a pressure of one atmosphere was 



* From the Philosophical Transactions, Part II. 1864, having been read 

 at the Royal Society June 18, 1863. 



t Phil. Trans. February 1861 ; and Phil. Mag. September 1861. 



t Phil. Trans. January 1862; and Phil. Mag. October 1862. 

 Phil. Mag. S. 4. Vol. 28. No. 187. Aug. 1864. G 



