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Consequently, as unlike poles attract and like repel, the soft iron is attracted by the inducing pole much as a pithball is attracted by an electric charge.
Machines of this sort have been made with plates 7 feet in diameter, and yielding sparks nearly 2 feet long. The properties of the "electric fire," as it was now called, were chiefly investigated by Dufay. To refine on the primitive experiment let us replace the shreds by a pithball hung from a support by a silk thread, as in figure 2.
In such a case, of course, the car would fly toward the object, whatever it might be, like a pithball or a feather, attracted to the knob of an electrical machine. In this way, considerable danger was occasionally encountered, and a few accidents could not be avoided. Fortunately, however, such cases were rare.
It appears from these facts that electricity has the power of disturbing or decomposing the neutral state of a neighbouring conductor, and attracting the unlike while it repels the like induced charge. Hence, too, it is that the electrified amber or sealing-wax is able to attract a light straw or pithball.
We have said that all bodies yield electricity under the friction of dissimilar bodies; but this cannot be proved for every body by simply holding it in one hand and rubbing it with the excitor, as may be done in the case of glass. For instance, if we take a brass rod in the hand and apply the rubber vigorously, it will fail to attract the pithball, for there is no trace of electricity upon it.
If we allow the pithball to touch the glass rod it will steal some of the electricity on the rod, and we shall now find the ball REPELLED by the rod, as illustrated in figure 4. Then, if we withdraw the rod and bring forward the handkerchief, we shall find the ball ATTRACTED by it. Evidently, therefore, the electricity of the handkerchief is of a different kind from that of the rod.
When a message was to be sent over this early telegraphic line an electric discharge was passed through the particular wire representing the letter of the alphabet to be sent; this discharge, reaching the other end, caused a pithball to be repelled and thus laboriously, letter by letter, the message was transmitted.
The experiments of figures 1, 2, and 3 have also shown us that when the pithball is charged with the positive electricity of the glass rod it is REPELLED by the like charge upon the rod, and ATTRACTED by the negative or unlike charge on the handkerchief.
This can be proved by suspending a magnetic needle like a pithball, and approaching another towards it, as illustrated in figure 26, where the north pole N attracts the south S. Obviously there are two opposite kinds of magnetic poles, as of electricity, which always appear together, and like magnetic poles repel, unlike magnetic poles attract each other.
By producing, with the aid of the electrical generator contained in this car, an enormous charge of electricity, Mr. Edison was able to counterbalance, and a trifle more than counterbalance, the attraction of the earth, and thus cause the car to fly off from the earth as an electrified pithball flies from the prime conductor.
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