76 
PEOFESSOR TYNDALL ON THE ABSORPTION AND 
Nitrous oxide on entering caused the needle to swing in a direction which indicated 
the heating of the gas ; the limit of its excursion was 28°, after which it slowly sunk to 0°. 
The pump was now worked ; the propulsion of the first portions of the gas from the 
tube was so much work done by the residue. That residue became consequently chilled ; 
into it the face of the pile adjacent poured its heat, and a swing of the needle on the 
negative side of 0° was the consequence. The limit of the excursion was 20°. 
Olefiant gas, operated on in the same manner, produced on entering the tube a swing 
of 67°, showing radiation; and on pumping out, a swing of 41°, showing absorption. 
After the pumping out of the gas, and without introducing a fresh quantity, dry air was 
again admitted ; the swing produced by the dynamic radiation of the residue of the gas 
(0-2 of an inch intension) was 59°. On pumping out very qidckly, the dynamic absorp- 
tion produced a deflection of nearly 40°. 
A little of the vapour of sulphuric ether was admitted into the tube ; on the admis- 
sion of dry air afterwards the needle swung from 0° to 61°; on pumping out, the needle 
ran up to 40° on the opposite side. 
These and other experiments, which I confess gratified me exceedingly, showed that, 
without resorting to any source of heat external to the gaseous body itself, its radiation 
and absorption might be determined with extreme accuracy, and the reciprocity of both 
phenomena rendered strikingly clear. In fact, at this very time 1 had been devising an 
elaborate apparatus for the purpose of examining the radiation of gases and vapours, 
with a 'view to comparing it Avith their absorption ; but no such apparatus would have 
giA'en me results equal in accuracy to those placed within reach by the discovery of 
dynamic radiation and absorption. 
The following Table is the record of a series of experiments in connexion with this 
subject. The vapour in each case was admitted till the mercury column fell half an 
inch, and dry air was admitted afterwards. 
Table IV. — Dynamic Kadiation and Absorption of Vapours. 
Deflections. 
Radiation. 
Absorption. 
Bisulphide of carbon . 
O 
... 14 
O 
6 
Iodide of methyl 
. . . 19-5 
8 
Benzol 
... 30 
14 
Iodide of ethyl . 
... 34 
15-5 
Methylic alcohol 
... 36 
Chloride of amyl 
... 41 
23 
Amylene 
... 48 
Alcohol 
... 50 
27-5 
Sulphuric ether . . 
... 64 
34 
Formic ether . . . 
. . . 68-5 
38 
Acetic ether . . . 
... 70 
43 
