University of Pavia, that the electricity was not in the animal
but generated by the contact of the two dissimilar metals and the
moisture of the flesh. Going a step further, in the year 1800 he
invented a new source of electricity on this principle, which is
known as "Volta's pile." It consists of plates or discs of zinc
and copper separated by a wafer of cloth moistened with acidulated
water. When the zinc and copper are joined externally by a wire, a
CURRENT of electricity is found in the wire One pair of plates
with the liquid between makes a "couple" or element; and two or
more, built one above another in the same order of zinc, copper,
zinc, copper, make the pile. The extreme zinc and copper plates,
when joined by a wire, are found to deliver a current.

This form of the voltaic, or, as it is sometimes called, galvanic
battery, has given place to the "cell" shown in figure II, where
the two plates Z C are immersed in acidulated water within the
vessel, and connected outside by the wire W. The zinc plate has a
positive and the copper a negative charge. The positive current
flows from the zinc to the copper inside the cell and from the
copper to the zinc outside the cell, as shown by the arrows. It
thus makes a complete round, which is called the voltaic
"circuit," and if the circuit is broken anywhere it will not flow
at all. The positive electricity of the zinc appears to traverse
the liquid to the copper, from which it flows through the wire to
the zinc. The effect is that the end of the wire attached to the
copper is positive (+), and called the positive "pole" or
electrode, while the end attached to the zinc is negative (-), and
called the negative pole or electrode. "A simple and easy way to
avoid confusion as to the direction of the current, is to remember
that the POSITIVE current flows FROM the COPPER TO the ZINC at the