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of tensions of 30 inches we compare tensions of 1 inch, the differences 

 between the gases come out still more strikingly. At this tension, 

 for example, the absorption of sulphurous acid is eight thousand times 

 that of air. 



The author also records a new and extensive series of experiments 

 on the absorption of radiant heat by vapours. The least energetic, 

 as before, he finds to be bisulphide of carbon, the most energetic 

 boracic ether. He shows that the absorption of the latter vapour, 

 which is quite transparent, is, at 0*1 of an inch of tension, 600 times 

 the absorption of the densely coloured vapour of bromine, while in 

 all probability it is 186,000 times that of air. 



The author was led by a series of perplexing experiments, which 

 are fully described in the memoir, to the solution of the following 

 remarkable and at first sight utterly paradoxical problem, " To 

 determine the absorption and radiation of a oas or vapour without 

 any source of heat external to the gaseous body itself." 



When air enters a vacuum, it is heated by the arrest of its mo- 

 tion : when a vessel containing air is exhausted by an air-pump, 

 chilling is produced by the application of a portion of the heat of 

 the air to generate vis viva. Let us call the heating in the first case 

 dynamic heating, and the chilling in the second case dynamic chilling. 

 Let us further call the radiation of a gas which has been heated 

 dynamically, dynamic radiation, and the absorption by a gas which has 

 been chilled dynamically, dynamic absorption. A thermo-electric pile 

 being placed at the end of the experimental tube, and the latter being 

 exhausted, the gas to be examined is permitted to enter : the gas is 

 heated, and if it possess any sensible radiative power, the pile will 

 receive its radiation and the galvanometer connected with the pile 

 will declare it. 



Proceeding in this way with gases, the author found that the ra- 

 diation thus manifested, and which was sometimes so intense as to 

 urge the needle of the galvanometer through an arc of more than 

 sixty degrees, followed the exact order of the absorptions which he 

 had already determined. After the heat of the radiating column of 

 gas had wasted itself by radiation, the air-pump was worked at a 

 certain rate ; the rarefied gas within the tube became chilled, and the 

 face of the pile turned towards the chilled gas became corre- 

 spondingly lowered in temperature. The dynamic absorptions of 



