Electricity 



243 



hot, it melts in two. It has enough resistance to make 

 it hot as soon as too many amperes flow through ; and 

 it has such a low melting point that as soon as it gets 

 hot it melts in two, or blows out. This breaks the cir- 

 cuit, of course, so that no more electricity can flow. 

 In this way the fuse protects houses from catching fire 

 through short circuits. 



Unfortunately, however, the fuse is almost no pro- 

 tection against an electric arc. The copper vapor 

 through which the electricity passes in an arc has enough 

 resistance to keep the amperage (current) low; so the 

 arc may not blow out the fuse at all. But if it were not 

 for fuses, there would be about as much danger of houses 



FIG. 137. What will happen when the pin is thrust through the cords and the 

 electricity turned on? 



