omena were obtained together. Thus,
a magnet was made, a galvanometer deflected, and, perhaps, a wire heated
by one single discharge of the electric force of the animal. When the
shock is strong, it is like that of a large Leyden battery charged to a
low degree, or that of a good voltaic battery of, perhaps, one hundred
or more pairs of plates, of which the circuit is completed for a moment
only.

I endeavoured by experiment to form some idea of the quantity of
electricity, and came to the conclusion that a single medium discharge
of the fish is at least equal to the electricity of a Leyden battery of
fifteen jars, containing 3,500 square inches of glass coated on both
sides, charged to its highest degree. This conclusion is in perfect
accordance with the degree of deflection which the discharge can produce
in a galvanometer needle, and also with the amount of chemical
decomposition produced in the electrolysing experiments.

The gymnotus frequently gives a double and even a triple shock, with
scarcely a sensible interval between each discharge.

As at the moment of shock the anterior parts are positive and the
posterior negative, it may be concluded that there is a current from the
former to the latter through every part of the water which surrounds the
animal, to a considerable distance from its body. The shock which is
felt, therefore, when the hands are in the most favourable position is
the effect of a very small portion only of the electricity which the
animal discharges at the moment, by far the largest portion passing
through the surrounding water.

This enormous external current must be accompanied by some effect within
the fish _equivalent_ to a current, the direction of which is from the
tail towards the head, and equal to the sum of _all these external_
forces. Whether the process of evolving or exciting the electricity
within the fish includes the production of the internal current, which
is not necessarily so quick and momentary as the external one, we cannot
at present say; but at the time of the shock the animal does not
apparently feel the electric sensation which he causes in those around
him.

The gymnotus can stun and kill fish which are in very various relations
to its own body. The extent of surface which the fish that is about to
be struck offers to the water conducting the electricity increases the
effect of the shock, and the larger the fish, accordingly, the greater
must be the shock to w