cely or not at all
affected.

The assertion of Bernoulli and others, that the absolute force of the
artificial magnet increases in the ratio of its superficies, stands
corrected in the far more accurate experiments of Coulomb (published in
his Treatise on Magnetism), which proves that the increase takes place (in
a far greater degree) in the ratio of its length. The same naturalist even
found means to determine that the directing powers of the needle, which he
had measured by help of his _balance de tortion_, stand to the length of
the needle in such a ratio as that, provided only the length of the needle
is from forty to fifty times its diameter, the momenta of these directing
powers will increase in the very same direct proportion as the length is
increased. Nor is this all that may be deduced from the experiment last
mentioned. If only the magnet be strong enough, it will show likewise that
magnetism _seeks_ the length. The proof is contained in the remarkable
fact, that the iron interposed between the magnet and the magnetic needle
_breadthways_ constantly acquires its two opposite poles at both ends
_lengthways_. Though the preceding experiments are abundantly sufficient
to prove the position, yet the following deserves mention for the
beautiful clearness of its evidence. If the magnetic power is determined
exclusively by length, it is to be expected that it will manifest no
force, where the piece of iron is of such a shape that no one dimension
predominates. Bring a _cube_ of iron near the magnetic needle and it will
not exert the slightest degree of power beyond what belongs to it as mere
iron. By the perfect equality of the dimensions, the magnetism of the
earth appears, as it were, perplexed and doubtful. Now, then attach a
second cube of iron to the first, and the instantaneous act of the iron on
the magnetic needle will make it manifest that with the length thus given,
the magnetic influence is given at the same moment.

That electricity, on the other hand, does not act in length merely, is
clear, from the fact that every electric body is electric over its whole
surface. But that electricity acts both in length and breadth, and _only_
in length and breadth, and not in depth; in short, that the (so-called)
electrical fluid in an electrified body spreads over the whole surface of
that body without penetrating it, or tending _ad intra_, may be proved by
direct experiment. Take a cylinder of wood, and bore an ind