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99. Besides its magnetic and heating effects, the current has also the power of decomposing compound substances, under certain conditions. Suppose, for instance, that the poles of a battery, instead of being brought together, are plunged into a vessel of water, decomposition will at once begin, and small bubbles of oxygen will rise from the positive pole, while small bubbles of hydrogen will make their appearance at the negative. If the two gases are collected together in a vessel, they may be exploded, and if collected separately, it may be proved by the ordinary tests, that the one is oxygen and the other hydrogen.

100. We have now described very shortly the magnetic, the heating, and the chemical effects of currents; it remains for us to describe the effects of currents upon one another.

In the first place, suppose that we have two wires which are parallel to one another, and carry currents going in the same direction; and let us further suppose that these wires are capable of moving, then it is found that they will attract one another. If, however, the wires, although parallel, convey currents going in opposite directions, they will then repel one another. A good way of showing this experimentally is to cause two circular currents to float on water. If these currents both go