NON-EXPANSION OF GASEOUS BODIES BY MAGNETISM. 
13 
pected that the continuation of the iron throng-hoot would prevent any diminution 
of its length, from the pressure of the poles (2734.), and that the diamagnetic pheno- 
mena would be abundantly produced in the parts from whence the iron had been 
removed. The latter was found to be the fact, for flame, smoke, bismuth and other 
diamagnetic matter, when placed there, passed equatorially very freely. 
2/39. A copper tube, 2-5 inches long, made of metal OT of an inch thick, was fitted 
to the iron, so that when in its place it should occupy the position represented (fig. 3), 
and could easily be made perfectly gas-tight by a little soft cement. In this way it 
formed an annular air-chamber round the iron, which, when measured, was found to 
have a capacity of rather more than 2 cubic inches, and included the most intense 
part of the magnetic field. Three stopcocks were fitted into this copper jacket, by 
two of which gas was passed into and out of the chamber, and the third was appro- 
priated to the pressure-gauge as before. Whilst naked, this apparatus could not be 
used, because of its ever-varying temperature, and the consequent disturbance and 
ejectment of the fluid in the gauge; but when clothed in three thicknesses of flannel 
its temperature was perfectly steady; and by the further use of wooden keys to turn 
the cocks the apparatus became unexceptionable. 
2740. Before proceeding to employ this apparatus with different gases, and in order 
to obtain some idea of what might be expected by comparing one gas with another, 
I made a preliminary experiment, dependent on the relative specific gravities of air 
and hydrogen, of the following nature. It is easy to diffuse a trace of ammonia- 
through the air of ajar, by putting a little paper wetted with a strong solution into 
it* ; and it is equally easy to send a jet of hydrogen, containing the smallest portion 
of muriatic acid gas, by a horizontal tube into the ammoniated air. When this is done, 
the course of the light hydrogen in the heavy air is rendered very distinctly visible; 
and it is seen, on leaving the horizontal tube, to turn at once upwards and to ascend 
rapidly, becoming wire-drawn in its course, in consequence of its small specific gravity 
compared to air. 
2741 . Two hemispherical iron pole terminations, associated with the great magnet, 
were then placed in contact with each othei', so that they might be surrounded either 
by air or oxygen-^, and the jet of hydrogen, delivering at the rate of 6 cubic inches per 
minute, was placed exactly beneath the axial line, in the centre of the magnetic field. 
When there was no magnetic force employed the hydrogen rose vertically, breaking 
against the points where the hemispherical poles touched ; but when the magnetic- 
power vms on, the stream of hydrogen divided into two parts, moving right and left, 
and ascended in two streams at a distance from the point of contact. Now this divi- 
sion took place at a certain distance helow the axial line ; and at that point, notwith- 
standing the ascensive power of hydrogen in air or oxygen, it was constrained to go 
horizontally by the apparently repulsive power of the magnetic force, and did not in 
its further course approach nearer to the axial line, but formed a curve concentric 
* Plulosophicai Magazine, 1847, vol. xxxi. p. 415, f Ibid. pp. 413, 414. 
