RADIATION OF HEAT BY GASES AND VAPOURS. 
13 
promptly closed. The galvanometric deflection consequent on the partial cutting off of 
the calorific rays was then noted ; a second quantity of the vapour, sufficient to depress 
the gauge another inch, was then admitted, and in this way the absorptions of five suc- 
cessive measures, each possessing within the tube 1 inch of tension, were determined. 
In the following Table the first column contains the tensions in inches, the second 
the deflection due to each, and the third the amount of heat absorbed, expressed in 
the units already referred to. For the purpose of comparison, I have placed the corre- 
sponding absorption of olefiant gas in the fourth column. 
Table III. — Sulphuric Ether. 
Tensions 
in inches. 
Deflections. 
Absorption. 
Corresponding absorption 
by oleliant gas. 
I 
64-8 
214 
90 
2 
70-0 
282 
123 
3 
72-0 
315 
142 
4 
73-0 
330 
154 
5 
73-0 
330 
163 
For these tensions the absorption of radiant heat by the vapour of sulphuric ether is 
more than twice the absorption of olefiant gas. We also observe, that in the case of the 
former the successive absorptions approximate more quickly to a ratio of equality. In 
fact the absorption produced by 4 inches of the vapour was sensibly the same as that 
produced by 5. 
But reflections similar to those which we have already applied to olefiant gas are also 
applicable to ether. Supposing we make our unit-measure small enough, the number of 
rays first destroyed will vanish in comparison with the total number, and for a time the 
fact will probably manifest itself that the absorption is directly proportional to the 
density. To examine whether this is the case, the other portion of the apparatus, 
omitted in the general description, was made use of. K is a small flask with a brass 
cap, wliich is closely screwed on to the stopcock c'. Between the cocks c' and c, which 
latter is connected with the experimental tube, is the chamber M, the capacity of whicli 
was accurately determined. The flask /r was partially filled with ether, and the air above 
the liquid removed. The stopcock c' being shut off and c turned on, the tube S S' and 
the chamber M are exhausted. The cock c is now shut off, and c' being turned on, the 
chamber M becomes filled with pure ether vapour. By turning c' off and c on, this quan- 
tity of vapour is allowed to diffuse itself through the experimental tube, and its absorp- 
tion determined ; successive measures are thus sent into the tube, and the effect pro- 
duced by each is noted. Measures of various capacities were made use of, according to 
the requirements of the vapours examined. 
In the first series of experiments made with this apparatus, I omitted to remove the 
air from the space above the liquid ; each measure therefore sent in to the tube was a 
mixture of vapour and air. This diminished the effect of the former; but the pro- 
