180 Prof. Tyndall on the Absorption and 



could add to the conclusiveness of the proofs just furnished, that 

 the case is one of true calorific absorption*. 



§ 6. Having thus established in a general way the absorptive 

 power of defiant gas, the question arises, " What is the relation 

 which subsists between the density of the gas and the quantity 

 of heat extinguished ?" 



I sought at first to answer this question in the following way : — 

 An ordinary mercurial gauge was attached to the air-pump; the 

 experimental tube being exhausted, and the needle of the galva- 

 nometer at zero, olefiant gas was admitted until it depressed the 

 mercurial column 1 inch, the consequent deflection being noted ; 

 the gas was then admitted until a depression of 2 inches was ob- 

 served, and thus the absorption effected by gas of 1, 2, 3, and 

 more inches tension was determined. In the following Table 

 the first column contains the tensions in inches, the second the 

 deflections, and the third the absorption equivalent to each de- 

 flection. 



Table I. — Olefiant Gas. 



Tensions in inches. 



Deflections. 



Absorption. 



1 



o 



56 



90 



2 



58-2 



1.23 



3 



59-3, 



142 



4 



60-0 



157 



5 



605 



168 



6 



61-0 



177 



7 



61-4 



182 



8 



617 



186 



9 



62-0 



190 



10 



62-2 



192 



20 



66-0 



227 



No definite relation between the density of the gas and its 

 absorption is here exhibited. We see that an augmentation of 

 the density seven times about doubles the amount of the absorp- 

 tion; while gas of 20 inches tension effects only 2i times the 

 absorption of gas possessing 1 inch of tension. 



But here the following reflections suggest themselves : — It is 

 evident that olefiant gas of 1 inch tension, producing so large a 

 deflection as 56°, must extinguish a large proportion of the rays 

 which are capable of being absorbed by the gas, and hence the 

 succeeding measures having a less and less amount of heat to 

 act upon must produce a continually smaller effect. But sup- 



* It is evident that the old mode of experiment might be applied to this 

 gas. Indeed, several of the solids examined by Melloni are inferior to it in 

 absorptive power. Had time permitted, I should have checked my results 

 by experiments made in the usual way; this I intend to do od a future 

 occasion. 



