James. Is this the case also with the other electrical fishes?

Tutor. The gymnotus possesses all the electric properties of the torpedo, but in a very superior degree. This fish has been called the electrical eel, on account of its resemblance to the common eel. It is found in the large rivers of South America.

Charles. Are these fishes able to injure others by this power?

Tutor. If small fishes are put into the water in which the gymnotus is kept, it will first stun, or perhaps kill them, and if the animal be hungry, it will then devour them. But fishes stunned by the gymnotus may be recovered, by being speedily removed into another vessel of water.

The gymnotus is said to be possessed of a new kind of sense, by which it knows whether bodies, which are brought near him, are conductors or not.

Charles. Then it possesses the same knowledge by instinct which philosophers have gained by experiment.

Tutor. True, The following experiment, among others, is very decisive on this point.

Ex. The extremities of two wires were dipped into the water of the vessel in which the animal was kept; they were then bent, extended a great way, and terminated in two separate glasses full of water. These wires, being suppored by non-conductors, at a considerable distance from each other, the circuit was incomplete: but if a person put the fingers of both hands into the glasses in which the wires terminated, then the circuit was complete. While the circuit was incomplete, the fish never went near the extremities of the wires, as if desirous of giving the shock; but the moment the circuit was completed, either by a person, or any other conductor, the gymnotus immediately went towards the wires, and gave the shock, though the completion of the circuit was out of his sight.

James. How do they catch these kind of fish; the men would, probably, let them go on receiving the shock?

Tutor.

In this way the property was,

perhaps, first discovered. The gymnotus, as well as the others, may be touched, without any risk of the shock, with wax or with glass; but if it be touched with the naked finger, or with a metal, or a gold ring, the shock is felt up the arm.

Charles. Does the silurus electricus produce the same effects as the others?

Tutor. This fish is found in some rivers in Africa, and it is known to possess the property of giving the shock, but no other particulars have been detailed respecting it.

With regard to the torpedo, its power of giving the benumbing sensation was known to the ancients, and from this it probably took its name.-In Fermin's Natural History of Surinam is some account of the trembling-eel, which Dr. Priestley conjectures to be different from the gymnotus: it lives in marshy places, from whence it cannot be taken, except when it is intoxicated. It cannot be touched with the hand, or with a stick, without feeling a terrible shock. If trod upon with shoes, the legs and thighs are affected in a similar manner.

CONVERSATION XLIII.

General Summary of Electricity, with Experiments.

TUTOR. You now understand what electricity is ?

Charles. Yes, it is a fluid which seems to pervade all substances, and when undisturbed, it remains in a state of equilibrium.

James. And that certain portion which every body is supposed to contain, is called its natural share.

Tutor. When a body is possessed of more, or retains less, than its natural share, it is said to be charged or electrified.

Charles. If it possess more than its natural share, it is said to be positively electri

fied; but if it contain less than its natural share, it is said to be negatively electrified.

Tutor. Does it not sometimes happen, that the same substance is both positively and negatively electrified at the same time?

James. Yes: the Leyden jar is a striking instance of this, in which, if the inside contain more than its natural share, the outside will contain less than its natural quantity.

Tutor. What is the distinction between conductors and non-conductors of electricity?

Charles. The electric fluid passes freely through the former, but the latter oppose its passage.

Tutor. You know that electricity is excited in the greatest quantities, by the friction of conducting and non-conducting substances against each other.

Ex. Rub two pieces of sealing-wax, or two pieces of glass together, and only a very small portion of electricity can be obtained; therefore the rubber of a machine should be a conducting substance, and not insulated. Ff

VOL. III.