f iron. By this arrangement the resistance to
the conduction of the electricity was diminished and a greater quantity
made to circulate around the iron from the same battery. The second
method of producing a similar result consisted in increasing the number
of elements of the battery, or, in other words, the projectile force of
the electricity, which enabled it to pass through an increased number of
turns of wire, and thus, by increasing the length of the wire, to
develop the maximum power of the iron.

[Illustration: Fig. 6]

To test these principles on a larger scale, the experimental magnet was
constructed, which is shown in Fig. 6. In this a number of compound
helices were placed on the same bar, their ends left projecting, and so
numbered that they could be all united into one long helix, or variously
combined in sets of lesser length.

From a series of experiments with this and other magnets it was proved
that, in order to produce the greatest amount of magnetism from a
battery of a single cup, a number of helices is required; but when a
compound battery is used, then one long wire must be employed, making
many turns around the iron, the length of wire and consequently the
number of turns being commensurate with the projectile power of the
battery.

In describing the results of my experiments, the terms _intensity_ and
_quantity_ magnets were introduced to avoid circumlocution, and were
intended to be used merely in a technical sense. By the _intensity_
magnet I designated a piece of soft iron, so surrounded with wire that
its magnetic power could be called into operation by an _intensity_
battery, and by a _quantity_ magnet, a piece of iron so surrounded by a
number of separate coils, that its magnetism could be fully developed by
a _quantity_ battery.

I was the first to point out this connection of the two kinds of the
battery with the two forms of the magnet, in my paper in _Silliman's
Journal_, January, 1831, and clearly to state that when magnetism was to
be developed by means of a compound battery, one long coil was to be
employed, and when the maximum effect was to be produced by a single
battery, a number of single strands were to be used.

These steps in the advance of electro-magnetism, though small, were such
as to interest and astonish the scientific world. With the same battery
used by Mr. Sturgeon, at least a hundred times more magnetism was
produced than could have been obtained by his exper