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science is given by Dr. Priestly, which will, hereafter, afford you much entertainment and interesting instruction. To-morrow we shall enter into the practical part of the subject : and I doubt not that the experiments in this part of science will be as interesting as those in any other which you have been studying. The electric light, exhibited in different forms; the various signs of attraction and repulsion acting on all bodies; the electric shock, and the explosion of the battery, will give you pleasure, and excite your admiration,

CONVERSATION XXVIII.

of Electric Attraction and Repulsion-Of Electries

and Conductors.

TUTOR. You must for a little time, that is, till we exhibit before you experiments to prove it, take it for granted that the earth, and all bodies with which we are acquainted, contain a certain quantity of exceedingly elastic and penetrating fluid, which philosophers call the electric fluid.

Charles. You say a certain quantity: is it limited ?

Tutor. Like other bodies, it undoubtedly has its limits ; this glass will hold a certain quantity of water, but if I attempt to pour into it more than that quantity, a

T

VOL. III.

part will flow over. So it is with the electric fluid: there is a certain quantity which belongs to all bodies, and this is called their natural quantity, and so long as a body contains neither more nor less than this quantity, no sensible effect is produced.

James. Has this table electricity in it?

Tutor. Yes, and so has the inkstand, and every thing else in the room ; and if I were to take proper means to put more into it than it now has, and you were to put your knuckle to it, it would throw it out in the shape of sparks.

James. I should like to see this done.

Charles. But what would happen if you should take away some of its natural quan

tity ?

Tutor. Why then, if you presented any part of your body to the table, as your knuckle, a spark would go from you to the table.

James. But, perhaps, Charles might not have more than his natural share, and in that case he could not spare any.

Tutor. True ; but to provide for this, the earth on which he stands would lend him a little to make up for what he parted with to the table.

James. This must be an amusing study; I think I shall like it better than any of the others.

Tutor. Take care that you do not pay for the amusement before we have done.

Here is a glass tube about eighteen inches long, and perhaps an inch or more in diameter ; I rub it up and down quickly in my hand, which is dry and warm, and now I will present it to these fragments of paper, thread, and gold-leaf : you see they all move to it. That is called electrical attraction.

Charles. They jump back again now, and now they return to the glass.

Tutor. They are, in fact, alternately attracted and repelled, and this will last several minutes if the glass be strongly excited. I will rub it again, present your knuckle to it in several parts one after another.

James. What is that snapping? I feel likewise something like the pricking of a pin.

Tutor. The snapping is occasioned by little sparks which come from the tube to your knuckle, and these give the sensation of pain.

Let us go into a dark room, and repeat the experiment.

Charles. The sparks are evident enough now, but I do not know where they can come from.

Tutor. The air and every thing is full of the fluid which appears in the shape of sparks; and, whatever be the cause, which I do not attempt to explain, the rubbing of the glass with the hand collects it from the air, and having now more than its natural share, it parts with it to you, or to me, or to any body else that may be near enough to receive it.

James. Will any other substance besides the hand, excite the tube?

Tutor. Yes, many others, and these, in this science, are called the rubbers; and the glass

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