16 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
to change in volume under the action of the magnet, so neither would any other gas 
or vapour do so, but that all the individuals belonging to this great class of bodies 
would be alike in that respect. In connection with this conclusion I may state, 
that I have on former occasions, and more lately, endeavoured to ascertain, by the 
use of very delicate apparatus and powerful electro-magnets, whether any change 
was produced in the volume of such fluids as water, alcohol and solution of sulphate 
of iron, but could observe no effect of the kind, and I do not believe in its existence. 
Still more recently, and in reference to the class of solid bodies, I have submitted iron 
as a magnetic metal, and bismuth as a diamagnetic body, to the same examination ; 
the metals were employed both in the state of solid cylinders and of filings or frag- 
ments. The cylinders were put into glass tubes and the partieles into glass bottles ; 
gauges, like those described (2732.), were applied to them, and that part of the con- 
taining vessel which v/as not filled with metal, was occupied, in one set of experi- 
ments, by air, and in another by alcohol, yet in no case could the least change in the 
volume of the iron or bismuth be observed, however powerful the magnetic force to 
which they were submitted. 
2753. One other result of a repulsive force seemed possible even in cases when, 
according to a former supposition (2751.), the tendency to expand equatorially might 
be compensated by an equal amount of tendency to contract in the axial direction, 
namely, that of the production of currents outwards or equatorially, i. e. in lines per- 
pendicular to the magnetic axis, where pointed poles or the hour-glass core, already 
described, were used, and of other currents setting in towards that line along the in- 
clined surfaces of the polar terminations ; in some degree like those occurring so power- 
fully, and traced so readily when flame or hot air is observed in air, or when a stream 
of one gas is observed in another gas*. 
2754. When however the gas occupying the whole of the magnetic field was uniform 
in nature and alike in temperature, not the slightest trace of sueh currents as these 
could be observed. It is not easy to devise unexceptionable tests of such motions, 
because visible bodies introduced into such a magnetic field to test the movements of 
the air there, are themselves diamagnetic; and if they form a little isolated cloud, 
are moved together and away as a diamagnetic body would be ; but when the whole 
field was occupied pretty equally by very light particles of dust or lycopodium, and 
the magnet in powerful action, no signs of currents in the air were visible. Further, 
when a faint stream of diffuse cold smoke from a taper spark -f- was allowed to fall 
or rise a little on one side of the axial line, it was determined outwards and equato- 
rially ; but though it went outwards with the most force when equidistant from the 
two conical poles, or their representative parts in the double iron core (2738.), still 
when it was made to pass near to one side, it continued to go outwards and equato- 
rially, even when, from its eiose vicinity to the iron surface, it had as it were to move 
* Philosophical Magazine, 1847, vol. xxxi. pp. 402, 404, 409. t P- 
