containing the rarer gas being apparently driven away, and the
greater the difference between the densities of the two gases,
the greater was the energy of this action.

And now observe his mode of reaching a material magnetic zero.
When a bubble of nitrogen was exposed in air in the magnetic field,
on the supervention of the power, the bubble retreated from the magnet.
A less acute observer would have set nitrogen down as diamagnetic;
but Faraday knew that retreat, in a medium composed in part of oxygen,
might be due to the attraction of the latter gas, instead of to the
repulsion of the gas immersed in it. But if nitrogen be really
diamagnetic, then a bubble or bulb filled with the dense gas will
overcome one filled with the rarer gas. From the cross-piece of his
torsion-balance he suspended his bulbs of nitrogen, at equal distances
from the magnetic axis, and found that the rarefaction, or the
condensation of the gas in either of the bulbs had not the slightest
influence. When the magnetic force was developed, the bulbs
remained in their first position, even when one was filled with
nitrogen, and the other as far as possible exhausted. Nitrogen,
in fact, acted 'like space itself'; it was neither magnetic nor
diamagnetic.

He cannot conveniently compare the paramagnetic force of oxygen with
iron, in consequence of the exceeding magnetic intensity of the
latter substance; but he does compare it with the sulphate of iron,
and finds that, bulk for bulk, oxygen is equally magnetic with a
solution of this substance in water 'containing seventeen times the
weight of the oxygen in crystallized proto-sulphate of iron, or 3.4
times its weight of metallic iron in that state of combination.'
By its capability to deflect a fine glass fibre, he finds that the