es laid down in the Eighth Series of these
Researches.

1123. Guided by these principles I was led to the construction of a voltaic
trough, in which the coppers, passing round both surfaces of the zincs, as
in Wollaston's construction, should not be separated from each other except
by an intervening thickness of paper, or in some other way, so as to
prevent metallic contact, and should thus constitute an instrument compact,
powerful, economical, and easy of use. On examining, however, what had been
done before, I found that the new trough was in all essential respects the
same as that invented and described by Dr. Hare, Professor in the
University of Pennsylvania, to whom I have great pleasure in referring it.

1124. Dr. Hare has fully described his trough[A]. In it the contiguous
copper plates are separated by thin veneers of wood, and the acid is poured
on to, or off, the plates by a quarter revolution of an axis, to which both
the trough containing the plates, and another trough to collect and hold
the liquid, are fixed. This arrangement I have found the most convenient of
any, and have therefore adopted it. My zinc plates were cut from rolled
metal, and when soldered to the copper plates had the form delineated, fig.
1. These were then bent over a gauge into the form fig. 2, and when packed
in the wooden box constructed to receive them, were arranged as in fig.
3[B], little plugs of cork being used to keep the zinc plates from touching
the copper plates, and a single or double thickness of cartridge paper
being interposed between the contiguous surfaces of copper to prevent them
from coming in contact. Such was the facility afforded by this arrangement,
that a trough of forty pairs of plates could be unpacked in five minutes,
and repacked again in half an hour; and the whole series was not more than
fifteen inches in length.

[Illustration: Fig. 1.]

[Illustration: Fig. 2.]

[Illustration: Fig. 3.]

[A] Philosophical Magazine, 1824, vol. lxiii. p. 241; or Silliman's
Journal, vol. vii. See also a previous paper by Dr. Hare, Annals of
Philosophy, 1821, vol. i. p. 329, in which he speaks of the
non-necessity of insulation between the coppers.

[B] The papers between the coppers are, for the sake of distinctness,
omitted in the figure.

1125. This trough, of forty pairs of plates three inches square, was
compared, as to the ignition of a platina wire, the discharge between
points of charcoal, the sh