Radiation of Heat by Gases and Vapours. 181 



posing the quantity of gas first introduced to be so inconsiderable 

 that the number of rays extinguished by it is a vanishing quan- 

 tity compared with the total number capable of absorption, we 

 might reasonably expect that in this case a double quantity of 

 gas would produce a double effect, a treble quantity a treble 

 effect, or in general terms, that the absorption would, for a time, 

 be proportional to the density 



To test this idea, a portion of the apparatus, which was pur- 

 posely omitted in the description already given, was made use 

 of. O 0, Plate III., is a graduated glass tube, the end of which 

 dips into the basin of water B. The tube can be stopped above 

 by means of the stopcock r : d d is a tube containing fragments 

 of chloride of calcium. The tube being first filled with 

 water to the cock r, had this water displaced by olefiant gas ; 

 and afterwards the tube S S', and the entire space between the 

 cock r and the experimental tube, was exhausted. The cock n 

 being now closed and r 1 left open, the cock r at the top of the 

 tube was carefully turned on and the gas permitted to 

 enter the tube S S' with extreme slowness. The water rose in 

 0, each of whose smallest divisions represents a volume of j^th 

 of a cubic inch. Successive measures of this capacity were 

 admitted into the tube and the absorption in each case deter- 

 mined. 



In the following Table the first column contains the quantity 

 of gas admitted into the tube ; the second contains the corre- 

 sponding deflection, which, within the limits of the Table, ex- 

 presses the absorption; the third column contains the absorp- 

 tion, calculated on the supposition that it is proportional to the 

 density. 



Table II — Olefiant Gas. 



Absorption, 



Measures of gas. 



Observed. 



Calculated. 



1 



2-2 



22 



2 



4-5 



4-4 



3 



&6 



&6 



4 



8-8 



8-8 



5 



110 



110 



6 



120 



132 



7 



14-8 



154 



8 



16-8 



17-6 



9 



19-8 



19-8 



10 



22-0 



220 



11 



24-0 



242 



12 



25-4 



26-4 



13 



29-0 



28-6 



14 



30-2 



29-8 



15 



33-5 



33-0 



