Radiation of Heat by Gaseous Matter, 277 



Initials. Absorption . 



J. T 56 



R. C 62 



J. T 56 



R. C. . , 59 



In all cases R. C, who is the smallest and least robust man 

 of the three, appeared to have the advantage. I will only add a 

 few results obtained on the 6th of October, the quantity of air 

 expired on the occasion depressing the mercurial column 5 inches. 



Initials. Absorption. 



J. T 335 



R. C 35 



R. C. After half a glass of Trinity Audit Ale . 41 



Again 35 



After a teaspoonful of brandy .... 35 

 After chewing and swallowing a small 



quantity of onion ....... 40 



After taking the ale and brandy my assistant washed his mouth 

 and gargled his throat several times with cold w^ater. I give 

 these results merely as illustrative of one of the numerous appli- 

 cations of the apparatus. In all the experiments the tube re- 

 mained perfectly transparent throughout, and, on pumping, the 

 needle in each case returned accurately to zero. 



§ 3. In my last paper I brought the fact somewhat promi- 

 nently forward that the elementary bodies which I had then 

 examined were far less hostile to the passage of the longer 

 undulations than the compound ones ; and I founded at the 

 time certain theoretic considerations on this fact*. I w r as desi- 

 rous this year to extend the experiments to one or two of the 

 coloured gases and vapours, and on the 20th of September 

 resumed my experiments on chlorine. This gas is itself highly 

 coloured, and of a specific gravity of 2*45 ; one of its compounds, 

 hydrochloric acid, is quite transparent, and of specific gravity of 

 only 1*26. Does the act of combination with hydrogen which 

 renders chlorine gas more transparent to light render it also 

 more transparent to heat ? Chlorine prepared from hydrochloric 

 acid and peroxide of manganese, and dried by passing it through 

 sulphuric acid, was admitted into the tube till it depressed the 

 mercury gauge 21 inches ; the absorption of the gas was ex- 

 pressed by the number 44. 



Hydrochloric acid was admitted till it depressed the gauge 

 19 inches ; the absorption was 68. This experiment indicates 

 that transparency to light and opacity to heat accompany the 

 same act of chemical union. 



* Phil. Mag. vol. xxii. p. 169. 



