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work. The electric fluid passes from the conductor to the inside of all the jars, till it is charged sufficiently high for the

purpose. be used when you come to make experiments with a battery, for fear of an accident, either to yourself, or to spectators.

Great caution, however, must

Charles. Would a shock from this be attended with any bad consequences?

serious accidents

may

Tutor. Yes : very happen from the electricity accumulated in a large battery, and even with a battery such as is represented in the plate, which is one of the smallest made; a shock may be given, which, if passed through the head, or other vital parts of the body, may be attended with very mischievous effects. James. How do you know when the battery is properly charged?

Tutor. The quadrant electrometer (Plate VII. Fig. 5.) is the best guide, and this may be fixed either on the conductor, or upon one of the rods of the battery. But if it is fixed on the battery, the stem of it should

be of a good length, not less than twelve or fifteen inches.

Charles. How high will the index stand when the battery is charged?

Tutor. It will seldom rise so high as 90°, because a machine, under the most favourable circumstances, cannot charge a battery so high, in proportion, as a single jar. You may reckon that a battery is well charged when the index rises as high as 60o, or between that and 70o.

James. Is there no danger of breaking the jars when the battery is very highly charged?

Tutor. Yes, there is; and if one jar be cracked, it is impossible to charge the others, till the broken one be removed. To prevent accidents, it is recommended, not to discharge a battery through a good conductor, except the circuit is at least five feet long. Charles. Do you mean the wire should be so long?

Tutor. Yes, if you pass the charge through that; but you may carry it through any conductor.

Before a battery be used, the uncoated part of the jars must be made perfectly clean and dry, the smallest particles of dust will carry away the electric fluid. And af ter an explosion, always connect the wire from the hook, with the ball, to prevent any residuum from remaining.

CONVERSATION XXXV.

Experiments made with the Electrical Battery."

TUTOR. I will now show you some experiments with this large battery. To perform these in perfect safety, I must beg you to stand a good distance from it: this will prevent accidents.

Example 1. I take this quire of writingpaper, and place it against the hook or wire that comes out of the box; and when the battery is charged I put one ball of the discharging-rod to a knob of one of the wires F, and bring the other knob to that part of the paper that stands against

the wire, proceeding from the box. You see what a hole it has made through every sheet of the paper. Smell the paper where the perforation is.

Charles. It smells like sulphur.

Tutor. Or more like phosphorus. You observe, in this experiment, that the electric fluid passed from the inside of the jars through the conducting rod and paper, to the outside.

James. Why did it not pass through the paper, in the same manner as it passed the brass discharging rod, in which it made. no hole?

Tutor. Paper is a non-conducting substance, but brass is a conductor: through the latter it passes without any resistance, and in its endeavour to get to the inside of the box, it burst the paper as you see. The same thing would have happened had there been twice or thrice as much paper. The electric fluid of a single jar will pierce through many sheets of paper.

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