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James. What next is to be done if I wish to electrify my knee, for instance?

Tutor. All you have to do is to bring the balls of the discharging-rod close to your knee, one on the one side, and the other on the opposite side.

Charles. And at every discharge of the Leyden jar, the superabundant electricity from withinside will pass from the knob at A to the knob B, and will pass through the wire and the knee, in its way to the outside of the jar, to restore to both sides an equilibrium.

James. But if it happen that a part of the body, as an arm, is to be electrified, how is it to be done, because in that case I cannot use both my hands in conducting the wires ?

Tutor. Then you may seek the assistance of a friend, who will, by means of two instruments, called directors, be able to conduct the fluid to any part of the body whatever.

Charles. What are directors ?
Tutor. A director consists of a knob-

bed brass wire, which, by means of a brass cap, is ce mented to a glass handle. So the operator holding these directors by the extremities of the glass handle, brings the balls, to which the wires or chains are attached, into contact with the extremities of that part of the body of the patient through which the shock is to be sent. If I feel rheumatic pains between my elbow and wrist, and a person hold one director at the elbow and another about the wrist, the shocks will pass through, and probably will be found useful in removing the complaint.

James. Is it necessary to stand on the glass-footed stool to have this operation performed?

Tutor. By no means: when shocks are administered, the person who receives them may stand as he pleases, either on the stool, or on the ground; the electric fuid taking the nearest passage, will always find the other knob of the other director, which leads to the outside of the jar.

Charles. Is it necessary to make the body bare?

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 Gymno

tus 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 t'ie Leyden jar.

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

Tutor. No, they are not : they are call. ed 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

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