360 



HOW ELECTRICITY IS CONTROLLED 



How electricity is led about in the home. - Although 

 electricity has become a valuable servant and a cheap 

 one where water power is available, yet it is a dangerous 

 servant as well. We have often heard of fires that were 

 caused by crossed wires making a " short circuit " or by 



accidents from electric 

 wires of heating devices, 

 or of people shocked to 

 death by receiving a 

 charge of electricity in 

 their body. We know 

 that the wires which 

 carry electricity must be 

 carefully guarded by a 

 layer of what we call in- 

 sulating material, that is, 

 something that will not 

 readily conduct the elec- 

 tricity. We have all 

 learned enough about 

 the conduction of heat to 



know that some materials are good and some are poor con- 

 ductors. Likewise certain metals will conduct electricity, 

 while other substances, like rubber, will not conduct it, 

 hence the latter are used in insulation. 



Current electricity. If we rub wax rapidly with a 

 piece of woolen cloth we can electrify it. The wax is then 

 said to be charged with electricity. A charged body such 

 as this, is one in which electricity is at rest. To be sure, 

 the amount in the wax is very, very small, but if we were to 

 connect two oppositely charged bodies, negative and posi- 

 tive, with a good conductor, such as a metal wire, elec- 



The sal ammoniac cell. 



