RADIATION OP HEAT BY OASEOHS MATTER. 
73 
tension is about 6, and at O’l of an inch tension would probably not exceed 1 ; hence, 
at O'l of an inch tension, bisulphide of carbon has probably 15 times the absorbent 
power of bromine ; but bisulphide of carbon is the feeblest of the compound vapours 
that I have yet discovered. The strongest of these, boracic ether, has, according to the 
above estimate, and at the tension stated, more than 600 times the absorbing energy of the 
strongly coloured bromine. 
The whole of the numbers in the above Table are referred to atmospheric air as 
unity ; OT of an inch of bisulphide of carbon vapour, for example, absorbs 15 times as 
much as a whole atmosphere of air. Let us compare, for an instant, the action of 
boracic ether with that of air. We arrive at an approximate comparison in this way. 
The absorption of the tenth of an inch of boracic ether is something more than that of a 
whole inch of methylic alcohol ; by diminishing the quantity of methylic alcohol to one- 
tenth, we reduce its absorption from 590 to 109. The absorption of one-tenth of an inch 
of boracic ether is 620°; suppose it to diminish in the proportion above found for me- 
thylic alcohol, we should have for 0-01 of an inch of boracic ether an absorption of 111 ; 
that is to say, for - g - oVo ^^ of atmosphere of boracic ether, we should have an absorp- 
tion 111 times that of a whole atmosphere of oxygen, nitrogen, hydrogen, or atmo- 
spheric air. 
With the transparent elementary gases it is impossible to measure directly the absorp- 
tion of OT of an inch ; but assuming, as before, that up to an absorption of 1 the effect 
is proportional to the quantity of gas present, the absorption of each of the elementary 
gases, at a tension of OT of an inch, would be about 0‘0033; hence the absorption of 
boracic ether of OT of an inch tension is to that of air at the same tension as 
620 : 0-0033, 
V'hich ti'ouhl give to the ether an energy 186,000 times that of air. 
I have already spoken of the blackness of ammonia at 30 inches tension. Eeferring 
to Table I., its absorption is found to be 1195. In the last Table the vapour of acetic 
ether, possessing only one-thirtietli of the tension of the ammonia, produces apparently 
the same effect; its absorption is also 1195. Such facts give one entirely new ideas 
of the capabilities of matter, and our wonder will not be diminished by the results to be 
recorded further on. 
With both gases and vapours we find that it does not follow that a gas which produces 
a larger effect than another at one tension should surpass that other at all tensions. 
Some gases start from a lower level than others, but finally attain an equal, or even a 
greater elevation. If their absorptions were represented by curves plotted from the 
same datum-line, these curves would in some cases approach, and in some cases cross 
each other. At a tension of 1 inch, for example, carbonic acid has more than double 
the absorptive power of carbonic oxide, whereas at a tension of 30 inches they are 
equal : indeed some of my experiments show carbonic oxide to have the advantage. On 
the 22nd of October, for example, I found the deflection produced by 2 inches of car- 
bonic oxide to be 15°, while that of 2 inches of carbonic acid was 38°. The two gases 
MDCCCLXII. 
L 
