PEOrESSOE TYNDALL ON THE ABSOEPTION AND 
No bubbling of the liquid was in any case permitted. The vapour entered silently and 
without the slightest commotion, and when the mercurial column was depressed to the 
extent required, the cock S was promptly turned off. 
The energy with which the needle moves the moment a strong vapour enters is so 
extraordinary, that I was compelled to remove the stops which arrested the swing of the 
needle at 90°, lest the shock against them should derange the equilibrated magnetism of 
the astatic pair. The needle often swung far beyond a quadrant ; and after it had come 
finally and permanently to rest, its position was observed in the following manner : — 
The dial of the galvanometer being well illuminated, a looking-glass was placed behind 
the instrument, at such an angle that when looked at horizontally the image cf the dial 
was clearly seen. This image was observed by an excellent telescope, fixed at a distance 
of 11 feet from the galvanometer. Attached to the needle, and in continuation of it, 
was a bit of glass fibre of extreme fineness, which ranged over the graduated circle, and 
by means of it a very small fraction of a degree could be easily read off. I resorted to 
the expedient of obseiudirg from a distance, because I found that the approach of my 
person, perhaps through the diamagnetic action of my own body, had a sensible effect 
upon the needle of my instrument, which, I believe, surpasses in delicacy any hitherto 
constructed. 
The 'permanent deflection of the needle was noted in all these experiments, and the 
value of the deflection, expressed in terms of one of the lower degrees of the galvano- 
meter, was obtained from a table of calibration. To spare unnecessary labour, I omit 
the deflections in the following Table, and give the absorptions only produced by the 
vapoiu's mentioned, at OT, 0‘5, and I’O inch of tension. 
Table III. 
Tensions. 
A 
Name of substance. 
O'l inch. 
0 5 inch. 
I'O inch. 
Bisulphide of carbon . . 
. 15 
47 
62 
Iodide of methyl 
. 35 
147 
242 
Benzol 
. 66 
182 
267 
Chloroform 
. 85 
182 
236 
Methylic alcohol 
. 109 
390 
590 
Iodide of ethyl 
. 158 
290 
390 
Amylene 
. 182 
535 
823 
Sulphuric ether 
. 300 
710 
870 
Alcohol 
. 325 
622 
Formic ether 
. 480 
870 
1075 
Acetic ether 
. 590 
980 
1195 
Propionate of ethyl .... 
. 596 
970 
Boracic ether 
. 620 
Let us compare some of the results of this Table of transparent vapours with the action 
of the highly coloured vapour of bromine. The absorption of bromine vapour at 1 inch 
