HEAT AND LIGHT FROM ELECTRIC CURRENTS 203 



is more than one branch through which the electricity may 

 pass. It may be compared to the stream of water about an 

 island in a river. Part of the water flows around one side of 

 the island, and the remainder goes around the other side, but 

 the two streams join lower in the channel and become one. 

 If there are several islands in the stream at this point we 

 might imagine a current of water broken up into numerous 



FIG. 100. Demonstration of series and parallel connections 



The strength of current (amperes) is read from the ammeter on the left, the 



electrical pressure (volts) from the voltmeter on the right. The sign lamps 



shown are rated at eleven volts. The electric toaster is made of high-resistance 



wire or ribbon 



small streams about the islands, but the total quantity above 

 and below remaining the same. This is exactly what occurs 

 in the parallel circuits of an ordinary residence. There are 

 many branches of the electric circuit in the various rooms, 

 but all the electricity that goes into these branches from the 

 main wire on one side flows out on a wire connected to the 

 other side of the circuit. Practically all incandescent lamps, 

 electric bells, and buzzers are arranged in parallel. The great 

 advantage of the parallel circuit is that one electrical appliance 

 may be operated independently of any other device (fig. 99). 



