348 
PROFESSOR TYNDALL’S CONTRIBUTIONS TO MOLECULAR PHYSICS. 
more transparent, in comparison with sulphuric ether, does formic ether become. Thus 
what I have called its complexity tells upon the vibrating periods of the formic ether ; 
the atom of oxygen which it possesses in excess of sulphuric ether renders it more 
sluggish as a vibrator. Experiments made with a source of 212° Fahr. establish more 
decidedly the preponderance of the formic ether for vibrations of slow period. 
Table XVI. — Radiation through Vapours. Source, 
Leslie’s cube, coated with lamp- 
black. Temperature, 212 c 
’ Fahr. 
Name of vapour. 
Absorption. 
Bisulphide of Carbon . . . 
. 6-4 
Iodide of Methyl .... 
. 18-4 
Chloroform 
. 19-5 
Sulphuric Ether .... 
. 54-8 
Formic Ether 
. 60-9 
For heat issuing from this source, the absorption by formic ether is 6T per cent, in 
excess of that by sulphuric. 
Deeming the result worthy of rigid confirmation, 
obtained the following deflections : — 
I repeated the experiments, and 
Table XVII. 
Name of vapour. 
Deflections. 
Bisulphide of Carbon . . . 
. 9 3 
Iodide of Methyl .... 
. 25-0 
Chloroform 
. 26-5 
Iodide of Ethyl 
. 34-0 
Benzol 
. 35*5 
Amylene 
. 46*8 
Sulphuric Ether . . . . 
. 47*31 
Sulphuric Ether . . . . 
. 47*7) 
Formic Ether 
. 49*7) 
Formic Ether 
. 49-9) 
Acetic Ether 
. 51-4 
When the absorptions were calculated from these deflections, the absorption of formic 
ether was found to be 6*3 per cent, in advance of that of sulphuric. 
But in both Tables XVI. and XVII. we notice another case of reversal. In all the 
experiments with the platinum spiral recorded in Table XV., chloroform showed itself 
less energetic as an absorber than iodide of methyl ; but in Tables XVI. and XVII. 
chloroform shows itself to be decidedly the more powerful of the two. Cases of this 
kind have, in my estimation, a peculiar significance, and I therefore take care to verify 
them. The experiments with all the vapours were therefore repeated, with the follow- 
ing results : — 
