ased upon his own great
discovery of magneto-electric currents. The effect is a most singular
one. A weight of several pounds of copper may be set spinning between
the electro-magnetic poles; the excitement of the magnet instantly stops
the rotation. Though nothing is apparent to the eye, the copper, if
moved in the excited magnetic field, appears to move through a viscous
fluid; while, when a flat piece of the metal is caused to pass to and
fro like a saw between the poles, the sawing of the magnetic field
resembles the cutting through of cheese or butter.[1] This virtual
friction of the magnetic field is so strong, that copper, by its rapid
rotation between the poles, might probably be fused. We may easily
dismiss this experiment by saying that the heat is due to the electric
currents excited in the copper. But so long as we are unable to reply
to the question, 'What is an electric current?' the explanation is only
provisional. For my own part, I look with profound interest and hope on
the strange action here referred to.

Faraday's thoughts ran intuitively into experimental combinations,
so that subjects whose capacity for experimental treatment would, to
ordinary minds, seem to be exhausted in a moment, were shown by him to
be all but inexhaustible. He has now an object in view, the first step
towards which is the proof that the principle of Archimedes is true of
magnetism. He forms magnetic solutions of various degrees of strength,
places them between the poles of his magnet, and suspends in the
solutions various magnetic bodies. He proves that when the solution
is stronger than the body plunged in it, the body, though magnetic,
is repelled; and when an elongated piece of it is surrounded by the
solution, it sets, like a diamagnetic body, equatorially between the
excited poles. The same body when suspended in a solution of weaker
magnetic power than itself, is attracted as a whole, while an elongated
portion of it sets axially.

And now theoretic questions rush in upon him. Is this new force a true
repulsion, or is it merely a differential attraction? Might not the
apparent repulsion of diamagnetic bodies be really due to the greater
attraction of the medium by which they are surrounded? He tries the
rarefaction of air, but finds the effect insensible. He is averse to
ascribing a capacity of attraction to space, or to any hypothetical
medium supposed to fill space. He therefore inclines, but still with
caution, t