In discharging electrical jars, the elec tricity goes in the greatest quantity through the best conductors, and by the shortest course. Thus, if a chain and a wire, communicating with the outer coat ing, be presented to the knob of a jar, the greater part of the charge will pass by the wire, and very little by the chain, which is a worse conductor, by reason of its discontinuation at every link. When the discharge is made by the chain only, sparks are seen at every link, which is a proof that they are not in contact ; and as the chain must be stretched by a con siderable force before the sparks cease to appear on the discharge, it follows, that there is a repulsive power in bodies, by which they are prevented from coming into contact, unless by means of a certain force.
By accurate experiments, it appears, that the force of the electric shock is weakened, that is, its effects are diminish ed, by using a conductor of great length in making the discharge. Dr. Watson, and other gentlemen of eminence in the philosophical world, were at the pains of making experiments of the same kind, but much more accurate. They found, by means of wire insulated on baked wood, that the electric shock was trans mitted instantaneously through the length of 12,276 feet.
When any animal or substance is to be subjected to the shock, it is done by means of two chains, one of which con nects one extremity of the animal or sub stance with the outer coating, and the other being made to touch the other ex tremity, is applied to the knob of the in ner coating, to make the discharge. The animal or substance thus forming a part of the circuit, receives the whole shock. The strong shock of a battery will melt wire of the seventieth of an inch in dia meter, and wires of less diameters are frequently blown away and dispersed; and the effect is the same with equal quantities of electricity, whether the in tensity be greater or less, within certain extended limits. Gunpowder may be
fired by a charge of three square feet : the method is, to put it into a quill, and thrust a wire into each end, so as not to meet, and then make these wires a part of the circuit. A less charge will serve, if iron filings be mixed with the gunpow der. Alcohol, ether, or a mixture of com mon air and hydrogen, may also be fired by the same means, or even by the spark from the conductor.
If the ball of a thermometer be placed in a strong current of electricity, the mercury or spirit will rise many de grees.
If a thin bottle be exhausted of air by means of the air-pump, it will receive a considerable charge by applying its bot tom to the electrified prime conductor, during which time the electric matter will pass through the vacuum between the hand and the inner surface of that part of the glass which is nearest the prime conductor. This appearance is ex ceedingly beautiful in the dark, especially if the bottle he of a considerable length. It exactly resembles those lights which appear in the northern sky, and are call ed streamers, or the aurora borealis. If one hand be applied to the part of the bottle which was applied to the conduc tor, while the other remains at the neck, the shock will be felt, at which instant the natural state of the inner surface is restored by a flash, which is seen per vading the vacuum between the two hands.