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Tutor. Not in the case of shocks, unless the coverings be very thick: but when sparks are to be taken, then the person from whom they are drawn must be insulated, and the clothes should be stripped off the part affected.

James. For what disorders are the shocks and sparks chiefly used?

Tutor. Shocks have been found useful in paralytic disorders; in contractions of the nerves; in sprains, and in many other cases; but great attention is necessary in regulating the force of the shock, because, instead of advantage, mischief may occur if it be too violent.

Charles. Is there less danger with sparks?

Tutor. Yes; for unless it be in very tender parts, as the eye, there is no great risk in taking sparks and they have proved very effectual in removing many complaints.

The celebrated Mr. Ferguson was seized, at Bristol, with a violent sore throat, so as to prevent him from swallowing any thing: he caused sparks to be taken from the part

affected, and in the course of an hour he could eat and drink without pain.

This is an excellent method in cases of deafness, ear-ache, tooth-ache, swellings inside the mouth, &c.

James. Would not strong sparks injure the ear?

Tutor. They might; and therefore the electric fluid is usually drawn with a pointed piece of wood, to which it comes in a stream, or when sparks are taken, a very small brass ball is used, because, in proportion to the size of the ball, is the size of the spark

CONVERSATION XLII.

Of Animal Electricity: of the Torpedo; of the Gymnotus Electricus, and of the Silurus Electricus.

TUTOR. There are three kinds of fish which have been discovered that are possessed of the singular property of giving shocks very similar to those experienced by means of the Leyden jar.

Charles. I should like much to see them: are they easily obtained?

Tutor. No, they are not: they are called the torpedo, the gymnotus electricus, and the silurus electricus.

James. Are they all of the same species? Tutor. No: the torpedo is a flat fish, seldom twenty inches long, and is common

in various parts of the sea coast of Europe. The electric organs of this fish are placed on each side of the gills, where they fill up the whole thickness of the animal, from the lower to the upper surface, and are covered by the common skin of the body.

Charles. Can you lay hold of the fish by any other part of the body with impunity?

Tutor. Not altogether so for if it be touched with one hand, it generally communicates a very slight shock; but if it be touched with both hands at the same time, one being applied to the under, and the other to the upper surface of the body, a shock will be received similar to that which is occasioned by the Leyden jar.

James. Will not the shock be felt if both

hands be put on one of the electrical organs

at the same time?

per

Tutor. No: and this shows that the upand lower surfaces of the electric organs are in opposite states of electricity, answering to the positive and negative sides of a Leyden phial.

Charles. Are the same substances conductors of the electric power of the torpedo, by which artificial electricity is conducted?

Tutor. Yes, they are: and if the fish, instead of being touched by the hands, be touched by conducting substances as metals, the shock will be communicated through them. The circuit may also be formed by several persons joining hands, and the shock will be felt by them all at the same time. But the shock will not pass where there is the smallest interruption; it will not even be conducted through a chain.

James. Can you get sparks from it?

Tutor. No spark was ever obtained from the torpedo, nor could electric repulsion and attraction be produced by it.

Charles. Is it known how the power is accumulated?

Tutor. It seems to depend on the will of the animal, for each effort is accompanied with a depression of its eyes, and it probably makes use of it as a means of self-defence.

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