The next electrical fish we are to mention is the Torpedo; a genus of
fishes belonging to the order of Chondropterygia; the species of this
genus are remarkable and numerous; but we must content ourselves with
the sixth species, called the _electrical ray_, or _cramp fish_, or
Torpedo. The head and body, which are indistinct, are nearly round, the
ventral fins form on each side the quarter of a circle, the two dorsal
fins are placed on a trunk of the tail, which is round, the caudal fin
is broad and abrupt. The eyes are small, and placed near each other;
behind each is a round spiracle with six small cutaneous rags on their
inner circumference.—The mouth is small, and the teeth are minute and
spicular.
These fish have been taken in Torbay, off Pembroke, near Waterford in
Ireland, and many other parts of Europe, with a trawl, and sometimes
with a bait; they commonly lie about forty fathoms deep. The food of the
Torpedo is fish.—For an anatomical description we refer the curious
reader to one given by Mr. Hunter, in the Philosophical Transactions,
vol. 63.
The electrical properties of this fish are remarkable; for a long time
they were considered as fabulous; but the fact having been ascertained
beyond the possibility of doubt, it was endeavoured to be accounted for,
by a variety of ingenious though unsatisfactory arguments. But when the
phenomena of electricity began to be better understood, considerable
light was thrown upon the subject; and Mr. Walsh at last, not only
explained the phenomena which generally attend it, on the known
principles of electricity, but actually contrived an artificial fish, by
which a shock very similar to that of the natural one can be given.
The electrical power of the Torpedo is conducted by the same substances
as conduct common electric matter, and is interrupted also by the same
non-conductors: but its shock will not pass over the least interception
of the circuit, not even if a chain be used. This singular fact was also
imitated by Mr. Walsh with his artificial Torpedo.
It has not been in our power to obtain a particular account of this
artificial Torpedo of Mr. Walsh.—But we know that one may be formed in
the following manner.
Let a number of small thin laminæ of talc, commonly called isinglass, or
thin sash glass, coated in the usual way, be joined together in the same
manner as in the battery. Let these be placed in the body of an
artificial fish resembling the Torpedo.—Let them then be charged, and on
being touched, the same phenomena which accompany the real Torpedo will
ensue; except that the shock of this will not be impeded by a small
interruption in the circuit. Similar effects may also be produced, by
means of a large battery weakly charged and furnished with Lane’s
electrometer.
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