82 Prof. Tyndall on the Absorption and Radiation 



shown to possess 970 times the absorptive energy of atmospheric 

 air, while it was shown to be probable that, when pressures of 

 y\jth of an atmosphere were compared, the absorption of defiant 

 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 opake 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 expe- 

 riment. 



The third paper * of the series to which I have referred was 

 devoted to the examination of one particular vapour, which, on 

 account of its universal diffusion, possesses an interest of its own 

 — I mean of course the vapour of water. In this paper I con- 

 sidered all the objections which had been urged against my 

 results up to the time when the paper was written ; I replied to 

 each of them by definite experiments, removing them one by 

 one, and finally placing, as I believe, beyond the pale of reason- 

 able doubt the action of the aqueous vapour of our atmosphere. 

 In this third paper, moreover, the facts established by experi- 

 ment are applied to the explanation of various atmospheric phe- 

 nomena. 



I have now the honour to lay before the Royal Society a fourth 

 memoir, containing an account of further researches. Hitherto 

 I have confined my self to experiments on radiation through gases 

 and vapours which were introduced in succession into the same 

 experimental tube, the heat being thus permitted to pass through 

 the same thickness of different gases. A portion of the present 

 inquiry is devoted to the examination of the transmission of 

 radiant heat through different thicknesses of the same gaseous 

 body. The brass tube with which my former experiments were 

 conducted is composed of several pieces, which are screwed 

 together when the tube is to be used as a whole ; but the pieces 

 may be dismounted and used separately, a series of lengths 

 being thus attainable, varying from 2*8 inches to 49*4 inches. 

 I wished, however, to operate upon gaseous strata much thinner 

 than the thinnest of these ; and for this purpose a special appa- 

 ratus was devised, and with much time and trouble rendered 

 at length practically effective. 



The apparatus is^ sketched in fig. 1. C is the source of heat, 



which consists of a plate of copper against the back of which a 



steady sheet of flame is caused to play. The plate of copper 



forms one end of the chamber F (the " front chamber M of my 



* Phil. Trans. December 1862; and Phil. Mag. July 1863. 



