RADIATION OR HEAT BY GASEOUS AND LIQUID MATTER. 211 
Table XV. — Olefiant Gas. 
Length of Chambers. 
Sum of Absorptions. 
Absorption of Sum. 
12-2 
37-2 
124-8 
76-3 
15-4 
34*0 
131-8 
77-1 
108 
29-6 
138-2 
77-0 
23-8 
25-6 
139-4 
77-6 
36-3 
13-1 
133-1 
78-8 
Means 133-4 
77-3 
The conclusion that the sum of the absorptions is greater than the absorption of the 
sum is here amply verified. The Tables also show that the ratio of the sum of the 
absorptions to the absorption of the sum is practically constant for all the gases. 
Dividing the first mean by the second in the respective cases, we have the following 
quotients : — 
Carbonic oxide T70 
Carbonic acid 1-72 
Nitrous oxide 1*61 
Olefiant gas (mean of both) T68 
The sum of the absorptions ought to be a maximum when the two chambers are of 
equal length. Supposing them to be unequal, one being in excess of half the length of 
the tube, let us consider the action of this excess singly. Placed after the half-length, it 
receives the rays which have already traversed that half ; placed after the shorter length, 
it receives the rays which have traversed the shorter length. In the former case, there- 
fore, the excess will absorb less than in the latter, because the rays in the former case 
have been more thoroughly sifted before the heat reaches the excess. From this it 
is clear that, as regards absorption, more is gained by attaching the excess to the short 
length of the tube than to the half-length ; in other words, the sum of the absorptions, 
when the tube is divided into two equal parts, is a maximum. This reasoning is approxi- 
mately verified by the experiments. Supposing, moreover, one of the lengths constantly 
to diminish, we thus constantly approach the limit when the sum of the absorptions and 
the absorption of the sum are equal to each other, the former being then a minimum. 
The effect of proximity to this limit is exhibited in the first experiment in each of the 
series ; here the lengths of the compartments are very unequal, and the sum of the 
absorptions is, in general, a minimum. 
After the absorption by the permanent gases had been in this way examined, I passed 
on to the examination of vapours. They were all used at a common pressure of 05 of 
an inch of mercury, or about ^th of an atmosphere. The liquid which yielded the 
vapour was enclosed in the flasks described in my previous memoirs, and the pure 
vapour was allowed to enter the respective compartments of the experimental tube 
without the slightest ebullition. The following series of Tables contains the results thus 
obtained. 
