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 VII. 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 в to the conductor, to take sparks from it.-But first shut the window-shutters.

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 experiment 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 H, 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 elec trified 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

brought near any conducting substance, it will fly to it in luminous streams.

Ex. 9. Place a drop of water on the conductor, and work the machine, the drop will afford a long spark, assume a conical figure, and carry some of the water with it.

Ex. 10. On this wire I have fixed a piece of sealing-wax, and having fixed the wire into the end of the conductor, I will light the wax, and the moment the machine is worked, the wax will fly off in the finest filaments imaginable.

Ex. 11. I will wrap some cotton-wool round one of the knobs of my dischargingrod, and fill the wool with finely bruised resin: I now discharge a Leyden jar, or a battery, in the common way, and the wool is instantly in a blaze. The covered knob must touch the knob of the jar, and the discharge should be effected as quickly as possible.

You will remember that the electric fluid always chooses the nearest road, and the

best conductors to travel by; in proof of which take the following experiment :

Ex. 12. With this chain I make a sort of w, (Plate VII. Fig. 15.) the wire w touches the outside of a charged jar, and the wire x, is brought to the knob of the jar, and in the dark a brilliant w is visible. But if

the wire w is contined to m, the electric fluid takes a shorter road to x, and, of course, only half of the w is seen, viz. that part marked mzy: but if, instead of the wire w m, a dry stick be laid in its place, the electric matter will prefer a longer circuit, rather than go through a bad conductor, and the whole w will be illuminated.

Ex. 13. Here is a two ounce-phial, half full of sallad-oil, through the cork is passed a piece of slender wire, the end of which, within the phial, is so bent as to touch the glass just below the surface of the oil. I place my thumb opposite the point of the wire in the bottle, and in that position take a spark from the charged conductor. You observe that the spark, to get to my thumb, has actually perforated the glass.