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Tutor. Yes ; and by drawing out the wires, the balls may be separated to any distance less than the length of the ivory. The figure - (Plate vir. Fig. 12.) represents a press, which may be substituted in the place of the table e D. It consists of two flat pieces of mahogany, which may

be brought together by screws.

James. Then instead of tying the slips of glass together in Example 4, you might have done it better by making use of the

press ?

Tutor. I might; but I was willing to show you how the thing might be done, if no such apparatus as this were at hand. The use of the table and press, which, in fact, always go together, is for keeping, steady all descriptions of bodies through which the charge of a single jar, or any number of which a battery consists, is to be conveyed. We will now proceed with the experiments.

Example 6. I will take the knobs from the wires of the universal dischar


ger, and having laid a piece of very dry writing paper on the table E, I place the points of the wires at an inch or from one another ; then, by connecting one of the rings c with the outside wire or hook of the battery, and bringing the discharging-rod from the other ring c to one of the knobs of the battery, you will see that the paper will be torn to pieces.

Example 7. The experiment which I am now going to make, you must never attempt by yourselves: I put a little gunpowder in the tube of a quill, open at both ends, and insert the pointed extremities of the 'two wires in it, so as to be within a quarter of an inch or less from each other. I now send the charge of the battery through it, and the gunpowder, you see, is instantly inflamed.

Example 8. Here is a very slender wire, not a hundredth part of an inch in diameter, which I connect with the wires of the discharger, and send the charge

of a battery through it, which will completely melt it, and you now perceive the little globules of iron instead of the thin wire.

Charles. . Will other wires besides iron be melted in the same manner?

Tutor. Yes, if the battery be large enough, and the wires, sufficiently thin, the experiment will succeed with them all : even with a single jar, if it be pretty large, very slender wire may be fused. But the charges of batteries have been used to determine the different conducting powers of the several metals.

James. If the charge is not strong enough to melt the wire, will it make it red hot?

Tutor. It will : and when the experiment is properly done, the course of the fluid may be discerned by its effects : for if the wire is about three inches long, it will be seen that the end of it, which is connected with the inside of the battery, is red-hot first, and the redness proceeds towards the other.

Charles. That is a clear proof that the superabundant electricity accumulated in the inside is carried to the outside of the jars.

Tutor. Example 9. We have in the present volume discussed the subject of magnetism: and we may here observe that by discharging the battery through a small sewing needle, it will become magnetic, that is, if the needle be accurately suspended on a small piece of cork in a basin of water, one end will, of itself, point to the north, and the other to the south.

Example 10. I will lay this chain on a sheet of writing-paper, and send the charge of the battery through the chain ; and you will see black marks will be left on the

paper in those places where the rings of the chain touch each other.

Example 11. Place a small piece of very dry wood between the balls uf the universal dischargers so that the fibres of

the wood may be in the direction of the wires, and pass the charge of the battery through them, the wood will be torn in pieces. The points of the wires being run into the wood, and the shock passed through them, will effect the same thing.

Example 12. Here is a glass tube, open at both ends, six inches long, and a quarter of an inch in diameter. These pieces of cork, with wires in them, exactly fit the ends of the tube. I put in one cork, and fill the tube with water, then put the other cork in, and push the wires so that they nearly touch, and pass the charge of the battery through them, you see the tube is broken, and the water dispersed in every direction.*

* To prevent accidents, a wire cage, such as is used in some experiments on the air-pump, should be put over the tube before the discharge is made young persons should not attempt this experiment by themselves.

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