Suppose now we should undertake to use the same flasher and the same lamp on a 220-volt current. This might push more current through than the small wire could carry. It might melt, or its insulation might burn off before _a_ made contact with _b_; if not the lamp would certainly burn out after the contact. If we undertook to operate with this flasher several 32-candle-power lamps instead of one upon the 110-volt circuit, the result would be the same, for in that case the resistance would be reduced and, therefore, a greater current would pass than the wire could carry without undue heating. [Illustration: Fig. 86] The boys were at first troubled to see how increasing the number of lamps in a circuit would decrease the resistance in that circuit. Fig. 86 was drawn to explain the matter. The lamps _l_, _l_, _l_, etc., are connected _in parallel_. Each lamp makes an independent connection from one feed wire to the other. The flasher _a_ acts as a switch to close the circuit for the whole. Now if we think of these wires as pipes to conduct water we would say that water flows from _D_ to _E_ through ten pipes more readily than through one. It would meet with only one tenth as much resistance. The result would be the same, if we should substitute for the ten pipes one pipe ten times as large in cross section. So it is with wires which are conducting electricity. Introduce two in parallel, and you allow twice as much current to pass by reducing the resistance to one half. Ten parallel conductors reduce the resistance to one tenth and allow ten times as much current to pass. [Illustration: Fig. 87] It is to be noticed that this flasher is an automatic switch which is opened or closed according to temperature. Remove the fine wire from _a_ and we have precisely the device which regulated the temperature in our electric incubator. Suppose the "thermostat" (as it is called in that case) is placed within the egg chamber which is to be kept at 103 degrees. A screw in the metal strip _c_ underneath the end of _a_ may be set so that it will normally touch _a_. Suppose now the brass strip is underneath the strip of iron in _a_. As the hot plate warms up the egg chamber, the brass will expand more than the iron, and the bar will curve upward and break the connection with _c_. As soon as the current stops the temperature of the chamber begins to fall, and the bar curves downward again until connection is made. This device is capable of adjustment so as to keep the temperature constantly at 103 degrees or any other desired degree. The device is in use for scores of different purposes, including the regulation of temperature in school rooms.