558 



I have confined myself throughout to that branch of the calculus 

 wherein the functions treated of are arranged according to powers of 

 TT ; that wherein they are arranged according to powers of has been 

 already more fully discussed by Mr. Russell. 



III. ez On the Absorption and Radiation of Heat by Gaseous 

 Matter." Second Memoir. By JOHN TYNDALL, Esq., 

 F.R.S. Received January 9, 1862. 



(Abstract.) 



Resuming with a new apparatus his experiments on the influence 

 of chemical combination on the absorption and radiation of heat by 

 gases, the author in the present investigation first examines the de- 

 portment of chlorine as compared with hydrochloric acid, and of 

 bromine as compared with hydrobromic acid, and finds that the 

 act of combination, which in each of these two cases notably dimi- 

 nishes the density of the gas, and renders the coloured gas perfectly 

 transparent to light, renders it more opake for obscure heat. He 

 also draws attention to the fact that sulphur, which is partially 

 opake to light, is transparent to 54 per cent, of the rays issuing 

 from a source of 100 C., while its compound, heavy spar, which is 

 sensibly transparent to light, is quite opake to the rays from a 

 source of 100 C. He demonstrates, in confirmation of Melloni, the 

 transparency of lampblack in thin layers, and shows how irrecon- 

 cileable its deportment to radiant heat is with the idea generally 

 prevalent at the present day, that lampblack absorbs heat of all kinds 

 with the same intensity. 



He has repeated all his experiments with gases, using a different 

 source of heat, and finds the result still more pronounced than 

 formerly, that the compound gases far transcend the elementary ones 

 in absorptive power. Taking air as unity, ammonia at 30 inches 

 tension is 1 1 95, this latter figure representing all the heat that issued 

 from the source. A layer of ammonia 3 feet long is perfectly black 

 to heat emanating from an obscure source. The coloured gases 

 chlorine and bromine, though much superior in absorptive power to 

 the transparent elementary gases, are exceeded in this respect by 

 every compound gas that has been hitherto examined. When instead 



