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Charles. If water is a good conductor, how is it that the charge did not run through it without breaking the tube?

Tutor. The electric fluid, like common fire, converts the water into a highly elastic vapour, which occupying very suddenly à much larger space than the water, bursts the tube before it can effect any means of

escape.

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CONVERSATION XXXVII.

Of the Electric Spark, and Miscellaneous Experiments.

TUTOR. I wish you to observe some facts connected with the electric spark. By means of the wire inserted in this ball, I fix it to the end of the conductor, and bring either another brass ball, or my knuckle to it, and if the machine act pretty powerfully, a long crooked, brilliant spark, will pass between the two balls, or between the knuckle and ball. If the conductor is negative, it receives the spark from the body ; but if it is positive, the ball or the knuckle receives the spark from the conductor.

Charles. Does the size of the spark depend at all on the size of the conductor?

Tutor. The longest and largest sparks are obtained from a large conductor, provided the machine act very powerfully. When the quantity of electricity is small, the spark is straight; but when it is strong, and capable of striking at a greater distance, it assumes what is called a zig-zag direction.

James. If the electric fluid is fire, why does not the spark, which excites a painful sensation, burn me, when I receive it on my hand ?

Tutor. Ex. 1. I have shown you that the charge from a battery will make iron wire red-hot, and inflame gunpowder. Now stand on the stool with glass legs, and hold the chain from the conductor with one hand.

Do you, Charles, hold this spoon, which contains some spirit of wine, to your brother, while I turn the machine, and a spark taken from his knuckle, if large, will set fire to the spirit.

Charles. It has indeed. Did you do nothing with the spirit?

Tutor. I only made the silver spoon pretty warm before I put the spirit into it.

Ex. 2. If a ball of box-wood be placed on the conductor instead of the brass ball, a spark taken from it will be of a fine red colour.

Ex. 3. An ivory ball placed on the conductor will be rendered very beautiful and luminous if a strong spark be taken through its centre.

Ex. 4. Sparks taken over a piece of silver leather appear of a green colour, and over gilt leather of a red colour.

Ex. 5. Here is a glass tube (Plate vir. Fig. 13.) round which, at small distances from each other, pieces of tin foil are pasted in a spiral form, from end to end : this tube is enclosed in a larger one, fitted with brass cups at each end, which are connected with the tin foil of the inner tube. I hold one end a in my hand, and while one of you turn the machine, I will present the other end B to the conductor, to take sparks from it. But first shut the window-shutters. VOL. III

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Charles. This is a very beautiful experiment.

Tutor. The beauty of it consists in the distance which is left between the pieces of tin foil, and by increasing the number of these distances, the brilliancy is very much heightened.

Ex. 6. The following is another expe. riment of the same kind. Here is a word, with which you are acquainted (Plate VIII. Fig. 14.) made on glass, by means of tinfoil pasted on glass, fixed in a frame of baked wood. I hold the frame in my hand at , and present the ball G to the conductor, and at every considerable spark the word is beautifully illuminated.

Ex. 7. A piece of sponge filled with water, and hung to a conductor, when electrified in a dark room,

exhibits a beautiful appearance.

Ex. 8. This bottle is charged: if I bring the brass knob that stands out of it, to a basin of water which is insulated, it will attract a drop; and, on the removal of the bottle, it will assume a conical shape, and if

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