SOME WAYS OF PRODUCING ELECTRICITY 177 



that two bodies with like charges repel each other, while two 

 bodies with unlike charges attract each other and a body 

 with either charge will attract a neutral body. 



Conductors and Insulators. Soon after 1600, men 

 tried to electrify many substances. They decided that 

 metals could not be 

 electrified. In trying 

 to electrify a metal, 

 they held it in one 

 hand and rubbed it 

 with fur, silk, or flan- 

 nel, and in no case did 

 they get any result. 

 It was not until after 

 1700 that some one 

 held a stick of dry 

 wood which had a 

 metal on its end and 

 rubbed the metal with 

 fur. The metal re- 

 ceived a charge of electricity which was easily detected. 

 In earlier trials all the electricity produced in the metal by 

 rubbing was given off or conducted from the metal to the 

 hand which in turn conducted it away. This experiment 

 showed that in relation to electricity, bodies are separated 

 into two classes, conductors and nonconductors or insulators. 

 It was this property of some materials to conduct electric- 

 ity that gave Benjamin Franklin the opportunity to get 

 sparks from his kite string during the thunderstorm, and 

 suggested to him that lightning rods would protect build- 

 ings by carrying up streams of electricity from the earth 

 to the cloud above, or from the cloud down to the earth. 

 The charge on the cloud may be so reduced in this way 

 that the possibility of a huge flash to the earth through 

 the building is greatly reduced. 



H. & W. SCI. I 13 



U. S. Forest Service 



Lightning results from a discharge of electricity 



between two oppositely charged bodies. Do 



electrons play any part in lightning ? 



