PROFESSOR TYNDALL’S CONTRIBUTIONS TO MOLECULAR PHYSICS. 
347 
Table XV. — Absorption of heat by Vapours. Tension 0 - 5 of an inch. 
Name of vapour. 
Source, platinum spiral. 

Barely visible. 
Bright red. 
White hot. 
Near fusion. 
Bisulphide of Carbon 
. 6-5 
4-7 
2-9 
2-5 
Chloroform . . 
. 9-1 
6-3 
5-6 
3-9 
Iodide of Methyl 
. 12-5 
9-6 
7-8 
Iodide of Ethyl . . 
. 21-0 
17-7 
12-8 
Benzol 
. 26-3 
20-6 
16-5 
Amylene .... 
. 35-8 
27-5 
22-7 
Sulphuric Ether . 
. 43-4 
31-4 
25-9 
23-7 
Formic Ether . . . 
. 45-2 
31-9 
25-1 
21-3 
Acetic Ether . . . 
. 49-6 
34-6 
27-2 
The gradual augmentation of penetrative power as the temperature is augmented is 
here very manifest. By raising the spiral from a barely visible heat to an intense white 
heat, we reduce the absorption, in the cases of bisulphide of carbon and chloroform, to 
less than one-half. At barely visible redness, moreover, 56’6 and 54’8 per 100 get 
through sulphuric and formic ether respectively ; while, of the intensely white-hot spiral, 
76-3 and 78-7 per 100 pass through the same vapours. By augmenting the tempera- 
ture of solid platinum, we introduce into the radiation waves of shorter period, which, 
being in discord with the periods of the vapours, get more easily through them. 
What becomes of the more slowly recurrent vibrations as the more rapid ones are 
introduced \ Do the latter take the place of the former 1 This question is answered 
by experiments made with an opaque solution of iodine, and with lampblack. As the 
temperature of the platinum spiral increases from a dark heat to the most intense white 
heat, the absolute quantity transmitted through both these bodies steadily augments. 
But this heat is wholly obscure, for both the solution and the lampblack intercept all 
the luminous heat. Hence the conclusion that the augmentation of temperature which 
introduces the shorter waves augments at the same time the amplitude of the longer 
ones, and hence also the inference that a body like the sun must of necessity include in 
its radiation waves of the same period as those emitted by obscure bodies. 
§8. 
Eunning the eye along the numbers which express the absorptions of sulphuric and 
formic ether in Table XV., we find that, for the lowest heat, the absorption of the latter 
exceeds that of the former; for a bright red heat they are nearly equal, but the formic still 
retains a slight predominance ; at a white heat, however, the sulphuric slips in advance, 
and at the heat near fusion its predominance is decided. I have tested this result in 
various ways, and by multiplied experiments, and placed it beyond doubt. We may at 
once infer from it that the capacity of the molecule of formic ether to enter into rapid 
vibration is less than that of sulphuric. By augmenting the temperature of the spiral 
we produce vibrations of quicker periods, and the more of these that are introduced, the 
