226 Common Science 



packed with earth ; but since water pipes go down deep 

 and the earth is already packed around them, the most 



FIG. 127. The ground can be used in place of a wire to complete the circuit. 



convenient way to ground a circuit is to connect the wire 

 that should go into the ground with the water pipe. 

 The next experiment, the grounding of a circuit, should 

 be done by the class with the help of the teacher. 



Experiment 68. Caution: Keep the switches turned off 

 throughout this experiment. 1 



(a) Put a piece of fuse wire across the fuse gap. Screw 

 the plug with nails in it into the lamp socket. Connect 

 the bare end of a piece of insulated wire to the water faucet 

 and touch the other end to one nail of the plug. If nothing 

 happens, touch it to the other nail instead. The electricity 

 has gone down into the ground through the water pipe, in- 

 stead of into the other wire. The ground carries the elec- 

 tricity back to the dynamo just as a wire would. 



(b) Put a new piece of fuse wire across the gap. Keep 

 switches turned of. Touch the brass disk at the bottom of 

 an electric lamp to the nail which worked, and touch the 

 wire from the faucet to the other brass part of the lamp 

 (Fig. 129). What happens ? 



Caution: Under no circumstances allow the switch to be 

 turned on while you are doing any part of this experiment. 



1 All through this chapter it is assumed that the electrical apparatus 

 described in the appendix is being used. In this apparatus all the 

 switches are on one wire, the other wire being alive even when the 

 switches are turned off. 



