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This piece of leaf brass is called the electric fish, one end is a sort of obtuse angle, the other is acute : if the large end be presented towards an electrified conductor, it will fix to it, and, from its wavering motion, it will appear to be animated.

This property of attaction and repulsion has led to many inventions of instruments called electrometers.

James. Is not an electrometer a machine to measure the strength of the electricity?

Tutor. Yes; and this is one of the most simple (Plate vil. Fig. 5.,) and it depends entirely upon the repulsion which takes place between two bodies in a state of electrifica. tion. It consists of a light rod and a pithball, hanging parallel to the stem, but turning on the centre of a semicircle, so as to keep close to its graduated limb. This is to be placed in a hole a on the conductor 1, and according as the conductor is more or less electrified, the ball will fly farther from the stem.

Charles. If the circular part be marked with degrees, you may ascertain, I suppose,

pretty accurately, the strength of any given charge.

Tutor. Yes, you may; but you see how fast the air carries away the electricity, it scarcely remains a single moment in the place to which it was repelled. Two pithballs may be suspended parallel to one another, on silken threads, and applied to any part of an electrical machine, and they will, by their repulsion, serve for an electrometer, for they will repel one another the more, as the machine acts more powerfully.

Fames. Has this any advantage over the other?

Tutor. It serves to show whether the electricity be negative or positive ; for if it be positive, by applying an excited stick of sealing-wax, the threads will fall together again ; but if it be negative, excited sealingwax, or resin, or sulphur, or even a rod of glass, the polish of which is taken off, will make them recede farther.

We have now perhaps said enough respecting electrical attraction and repulsion, at least for the present; I wish you, how

ever, to commit the following results to your memory.

(1.) Bodies that are electrified positively repel each other.

(2.) Bodies that are electrified negatively repel each other.

Charles. Do you mean, that if two bodies have either more or less of the electric, fluid than their natural share, they will repel each other if brought sufficiently near?

Tutor. That is exactly what I mean.

(3.) Bodies electrified by contrary powers; that is, two bodies, one having more, and the other less, than its natural share, attract each other very strongly.

(4.) Bodies that are electrified attract light substances which are not electrified.

These are facts which, I trust have been made evident to your senses.

To-morrow we will decribe what is usually called the Leyden phial.

CONVERSATION XXXIII.

Of the Leyden Phial or Jar.

TUTOR. I will take away the wires and the ball from the conductor, and then remove the conductor an inch or two farther from the cylinder. If the machine acts strongly, bring an insulated pith-ball, that is, you know, one hanging on silk, to the end of the conductor, nearest to the glass cylinder.

Charles. It is immediately attracted.

Tutor. Carry it to the other end of the conductor, and see what happens.

Charles. It is attracted again ; but I thought it would have been repelled.

Tutor. Then as the ball was electrified before, and is still attracted, you are sure that the electricity of the two ends of the conductor are of different names; that is, one is plus, and the other minus.

James. Which is the positive, and which is the negative end?

Tutor. That end of the conductor which is nearest to the cylinder, becomes possessed of an electricity different from that of the cylinder itself.

James Do you mean that if the cylinder is positively electrified, the end of the conductor next to it is electrified negative

ly?

Tutor. I do: and this you may see by holding an insulated pith-ball between them.

Charles. Yes, it is now very evident, for the ball fetches and carries as we have seen it before.

Tutor. What you have seen with regard to the conductor, is equally true with re• spect to non-conducting bodies. Here is a common glass tumbler: if I throw within

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