350 PROFESSOR TYNDALL’S CONTRIBUTIONS TO MOLECULAR PHYSICS. 
Were it essential to my purpose, I should certainly be able to make even the small 
differences which here show themselves to disappear. But the agreement is such as to 
place the reliability of the experiments beyond doubt. It will be seen that , contrary to the 
results obtained with a white-hot spiral, in all three cases , where a blackened cube of boil- 
ing water was the source, chloroform exceeds iodide of methyl, and formic ether exceeds 
sulphuric in absorbent power. To confirm the demonstration, I once more resorted to 
the white-hot spiral, and obtained the following results : — 
Table XXI. — Radiation through Vapours. Source, white-hot platinum spiral. 
Name of vapour. 
Deflection. 
Absorption. 
Chloroform . . . 
... 9-8 
4-5 
Chloroform . . . 
... 9-5 
4*5 
Iodide of Methyl . 
. . . 16-0 
7-3 
Iodide of Methyl . 
. . . 15-8 
7-3 
Formic Ether . . 
. . . 42-1 
24-2 
Formic Ether . . 
. . . 42-3 
24-5 
Sulphuric Ether . 
. . . 43-6 
26-3 
Sulphuric Ether . 
. . . 43-5 
26*2 
Total heat . . . 
. . . 70-9 
100-0 
Here chloroform retreats once more 
behind iodide of methyl, and formic ether behind 
sulphuric. 
The^ positions of sulphuric and formic ether are reversed within the range of the 
experiments made with the platinum 
spiral, but this is not the 
case with the chloroform 
and the iodide of methyl. Even when the spiral was at a barely visible heat, the iodide 
was decidedly the most opaque of the two ; the same result was obtained with a spiral 
heated under redness, as proved by the following figures : — 
Name of vapour. 
Deflection. 
Absorption. 
Chloroform . . 
... 8-5 
12-14 
Chloroform . 
... 8-5 
12-14 
Iodide of Methyl . 
. . . 10-0 
14-28 
Iodide of Methyl . 
. . . 10-0 
14-28 
Total heat . . . 
. . . 47-3 
100-0 
Here the iodide is still predominant. Is it, then, a question of temperature merely 1 
or is there a special flux emitted by the lampblack, to which chloroform is particularly 
opaque 1 In other words, is there a special accord between the rates of vibration of 
lampblack and chloroform 1 To answer this question I operated thus : — The platinum 
spiral was heated by only two cells, and the strength of this current was lowered by the 
introduction of resistance. When decidedly below a red heat, the spiral was plunged 
into boiling water. Bubbles of steam issued from it, proving that its temperature was 
