244 Common Science 



being set on fire by short circuits as by arcs. Perhaps 

 there would be more danger, because short circuits are 

 the more common. 



Experiment 73. Put a new piece of fuse wire across the 

 fuse gap. Leave the "nail plug" screwed in the socket. 

 Use a piece of flexible lamp cord the kind that is made of 

 two strands of wire twisted together (see Fig. 137). Fasten 

 one bared end of each wire around each nail of the "nail 

 plug." See that the other ends of the lamp cord are not 

 touching each other. Turn on the electricity. Does any- 

 thing happen? Turn off the electricity. Now put a pin 

 straight through the middle of the two wires. Turn on the 

 electricity again. What happens? 



There is not much resistance in the pin, and so it 

 allows the electricity to rush through it. People some- 

 times cause fuses to blow out by pinning pictures to elec- 

 tric lamp wires or by pinning the wires up out of the way. 



A short circuit an " easy circuit." You always get 

 a short circuit when you give electricity an easy way to 

 get from one wire to the other. But you get no current 

 unless you give it some way to pass from one wire to 

 the other, thus completing the circuit. Therefore you 

 should always complete the circuit through something 

 which resists the flow of electricity, like an electric lamp, 

 a heater, or an iron. Remember this and you will have 

 the key to an understanding of the practical use of elec- 

 tricity. 



The term " short circuit " is a little confusing, in that 

 electricity may have to go a longer way to be short 

 circuited than to pass through some resistance, such as 

 a lamp. Really a short circuit should be called an 

 " easy circuit " or something like that, to indicate that 



