Electricity 



241 



IMG. 136. A, the "fuse gap" and B, the "nail plug." 



in a new fuse. The next three experiments will help 

 you to understand fuses. 



Experiment 72. On the lower wire leading to the electric 

 lamp in the laboratory you will find a " gap," a place where 

 the wire ends in a piece of a knife switch, and then begins 

 again about an inch away in another piece of the switch, as 

 shown in Figure 136. There must be some kind of wire or 

 metal that will conduct electricity across this gap. But the 

 gap is there to prevent as much electricity from flowing 

 through as might flow through copper wire. So never put 

 copper wire across this gap. If you do, you will have to 

 pay for the other fuses which may blow out. Always keep 

 a piece of fuse wire stretched across the gap. Fuse v. 

 a soft leadlike wire, which melts as soon as too much elec- 

 tricity passes through it. 



Unscrew the lamp, and into the socket where it was, 

 screw the plug with the two nails sticking out of it. Turn 

 the electricity on. Does anything happen? Turn the 

 electricity off. Now touch the heads of the two nails to- 

 gether, or connect them with a piece of any metal, and turn 



