In the same way I can make holes all round

the phial.

Charles. Would the experiment succeed with water instead of oil?

Tutor. No, it would not.

James. At any rate we see the course of the electric fluid in this experiment, for the spark comes from the conductor down the wire, and through the glass to the thumb. Tutor. Its direction is, however, better shown in this way.

Ex. 14. At that end of the conductor which is farthest from the machine, I fix a brass wire, about six inches long, having a small brass ball on its extremity. To this ball, when the machine is at work, I hold the flame of a wax taper.

Charles. The flame is evidently blown from the ball, in the direction of the electric fluid: it has a similar effect to the blast of a pair of bellows.

Ex. 15. I will fix a pointed wire upon the prime conductor, with the point outward, and another like wire upon the insulated rubber. Shut the window-shutter,

and I will work the machine: now observe the points of the two wires.

James. They both are illuminated, but differently. The point on the conductor sends out a sort of brush of fire, but that on the rubber is illuminated with a star.

Tutor. You see then the difference between the positive and negative electricity.

CONVERSATION XXXVIII.

Miscellaneous Experiments-Of the ElectrophorusOf the Electrometer, and the Thunder House.

TUTOR. I shall proceed this morning with some other experiments on the electrical machine.

Ex. 1. Here are two wires, one of which is connected with the outside of this charged Leyden jar, the other is so bent as easily to touch the knob of the jar. The two straight ends I bring within the distance of the tenth of an inch of one another, and press them down with my thumb, and in this position, having darkened the room, I discharged the jar. Do you look upon my thumb.

Charles. It was so transparent that I think I even saw the bone of the thumb.But did it not hurt you very much?

Tutor. With attention, you might observe the principal blood vessels, I believe; and the only inconvenience that I felt was a sort of tremour in my thumb, which is by no means painful. Had the wires been at double the distance, the shock would have probably made my thumb the circuit, which must have caused a more powerful and unpleasant sensation, but being so close, the electric fluid leaped from one wire to the other, and during this passage it illuminated my thumb, but did not go through it.

Ex. 2. If, instead of my thumb, a dẹcanter full of water, having a flat bottom, were placed on the wires, and the discharge made, the whole of the water will be beautifully illuminated.

Ex. 3. This small pewter bucket is full of water, and I suspend it from the prime conductor, and put in a glass syphon, with a bore so narrow that the water will hardly drop out See what will happen when I

work the machine; but first make the room

dark.

James. It runs now in a full stream, or rather in several streams, all of which are illuminated.

Tutor. Ex. 4. If the knob a (Plate vIII. Fig. 16.) communicate with the outside of a charged Leyden jar, and the knob b with the inside coating, and each be held about two inches from the lighted candle x, and opposite to one another, the flame will spread towards each, and a discharge will be made through it: this shows the conducting power of flame.

This instrument (Plate VIII. Fig. 17.) which consists of two circular plates, of which the largest B is about fifteen inches in diameter, and the other A fourteen inches, is called an electrophorus. The under plate B is made of glass, or sealing-wax, or of any other non-conducting substance: I have made one with a mixture of pitch and chalk boiled together. The upper plate A is sometimes made of brass, and sometimes of tin plate, but this is of wood, covered very