Suppose anything happened to the first lamp, which stopped the current from jumping through it. There would be no path for the current to travel farther, and, consequently, all the lights would go out. To get over this difficulty there is sometimes used what is called a "shunt," which only acts when the lamp will not light. This shunt carries the current round the lamp to the other wire, so that it may travel on and light up the other lamps. WIRES FOR INCANDESCENT LAMPS The wiring for incandescent lamps is carried out in an entirely different way, which you can see by comparing Fig. 25 A with Fig. 25 which shows the wiring for arc-lamps. [Illustration: Fig. 25 A] This is called connecting in "multiple arc." You will notice that the two wires running out from the dynamo (which are called the main wires) do not form one continuous loop as in the arc-light system, but that a smaller wire is attached to one of the main wires and then connected with the screw-ring in the lamp-socket; then another wire is connected with the button in the socket and afterward to the other main wire. Every lamp forms an independent path through which the current can travel back to the dynamo. Now, if we turn one of these incandescent lamps out, we simply shut off one of these paths and the electricity travels through the other lamps, and, if we wish, we can turn out all the lamps but one and there will still be a way for the electricity to go back to the dynamo. In the arc-lamps we must have a very high number of volts pressure, because the electricity has only one path, and it all has to pass through the first and other lamps till it comes to the last one. In the incandescent light the electricity has as many paths as there are lamps, so we only need to keep _one_ certain _pressure_ in volts in the main wires all the time. This pressure is _even_ all the way through the main wires, and, therefore, it is ready to light a lamp the instant it is turned on, because, as you have seen, electricity will always get back to the dynamo if there is a possible chance, and the lamp opens a path. The volts pressure used to operate any number of incandescent lamps is altogether very much less than for a number of arc-lights. For example, in the Edison system the pressure (sometimes called "electromotive force") is only about 110 volts, which is very mild and not at all dangerous. This electromotive force would be _the same_ if there were _one lamp or ten thousand_ lighted. While this Edison current would not hurt any one, you should remember that it is much the better plan not to touch _any_ electric-light wires until you have learned a great deal more on this subject.