318 
PROFESSOR TYNDALL ON THE ACTION OF FREE MOLECULES ON 
the atomic periods of the transparent vapours synchronise best with the slower oscilla¬ 
tions, the absorptions in A are considerably higher than those in B. Under C are the 
absorptions when the source was a moderate limelight, produced by coal gas and oxygen. 
Under D are the absorptions when the source was the limelight, with its heat gathered 
up and sent through the experimental tube by a concave mirror, while under E are the 
absorptions of the heat of the incandescent spiral aided by a rocksalt lens. The 
absorptions in D and E are somewhat less than those in C, because the path of the 
rays was diminished, through the reduction of internal reflection by the mirror and lens. 
With the foregoing results, obtained with the brass experimental tube polished 
within, where the greater portion of the heat reaching the pile had undergone reflec¬ 
tion, are now to be compared those obtained with the silvered tube, where internal 
reflection was wholly avoided. 
Table IY. 
Wide silvered tube with no reflection. 
L 
L 
M 
M 
L 
A 
B 
C 
D 
E 
Spiral 
Spiral 
Lime 
Lime 
Lime 
(dark). 
(bright). 
(bright). 
(moderate). 
(dull red) 
Bisulphide of Carbon .... 
4-0 
1-8 
T5 
1*5 
3*3 
Chloroform. 
5-6 
3-0 
3-5 
4*3 
6-0 
Benzol. 
7-0 
5-1 
4 - 4 
6*o 
8-0 
Iodide of Methyl. 
7-5 
5-9 
5*0 
6-5 
9*2 
Iodide of Ethyl. 
Ilf 
7-6 
6-8 
8*5 
11-2 
Amylene. 
15'0 
11*8 
8‘8 
120 
173 
Sulphuric Ether. 
21-2 
17T 
12-5 
15-0 
25*0 
Acetic Ether. 
26-0 
20-0 
16-3 
24-0 
32*0 
Formic Ether. 
27-0 
21-0 
17-0 
25-0 
34*0 
The vapour pressures here were those given in Table TIT. Column A contains the 
absorptions measured when the source of heat was a spiral under incandescence, aided 
by a rocksalt lens. B contains the absorptions measured with the same arrangement, 
the spiral being raised to bright redness. As usual the heat of lowest refrangibility is 
most absorbed. C contains the absorptions of a tolerably intense limelight aided by 
the silvered mirror. E> the absorptions of the same light with its intensity reduced, 
while E contains the absorptions of the rays from a lime cylinder heated to dull 
redness by a steady flame of hydrogen, burning in air, and aided by a rocksalt lens. 
Here, then, where no trace of reflected heat is sent to the pile, we have substantially 
the same results as those obtained when by far the greater portion of the heat reaching 
the pile had undergone reflection. The agreement shows that the films, the action of 
which had been posited, but never proved, are, in regard to this action, what I always 
knew them to be, imaginary. 
