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. V 



n when the pin is thrust through the cords and the 

 electricity turned on? 



