to determine molecular arrangement; in the present instance the
magnetic analysis is opposed by the force of diffusion, which is
also very strong comparatively. The same remark applies to, and is
illustrated by, another experiment subsequently executed by Faraday.
Water is diamagnetic, sulphate of iron is strongly magnetic.
He enclosed 'a dilute solution of sulphate of iron in a tube,
and placed the lower end of the tube between the poles of a powerful
horseshoe magnet for days together,' but he could produce
'no concentration of the solution in the part near the magnet.'
Here also the diffusibility of the salt was too powerful for the
force brought against it.

The experiment last referred to is recorded in a paper presented to
the Royal Society on the 2nd August, 1850, in which he pursues the
investigation of the magnetism of gases. Newton's observations on
soap-bubbles were often referred to by Faraday. His delight in a
soap-bubble was like that of a boy, and he often introduced them
into his lectures, causing them, when filled with air, to float on
invisible seas of carbonic acid, and otherwise employing them as a
means of illustration. He now finds them exceedingly useful in his
experiments on the magnetic condition of gases. A bubble of air in
a magnetic field occupied by air was unaffected, save through the
feeble repulsion of its envelope. A bubble of nitrogen, on the
contrary, was repelled from the magnetic axis with a force far
surpassing that of a bubble of air. The deportment of oxygen in air
'was very impressive, the bubble being pulled inward or towards the
axial line, sharply and suddenly, as if the oxygen were highly
magnetic.'

He next labours to establish the true magnetic zero, a problem not