CHAPTER XVI 

 FRICTIONAL OR STATIC ELECTRICITY 



217. Nature of Current. When certain bodies, such as 

 leather belting and pulleys, paper and steel plates, or cotton 

 and steel rolls, are rubbed together, sparks are frequently 

 produced. This kind of electricity is called frictional or 

 static, and is quite dangerous because of its liability to cause 

 a fire. Frictional electricity acts in many ways like magnet- 

 ism. To illustrate: A magnetized body has at least two 

 poles which are unlike and the magnetism appears more or 

 less concentrated. In like manner, when a body which is 

 rubbed becomes electrified, it shows two different kinds of 

 electricity. For instance, if a sheet of glazed paper is 

 rubbed vigorously with a smooth pencil and then placed 

 over a small piece of paper, the sheet attracts the small 

 piece, showing that the bit of paper has a different electri- 

 fication from that of the sheet. When two different sub- 

 stances are rubbed or passed over one another quickly, one 

 becomes charged positively with electricity, while the other 

 is negatively or oppositely charged. 



218. Leyden Jar. Static electricity may easily be drawn off 

 and bottled up in what is called a Leyden jar. This is a glass jar 

 (Fig. 82) three-quarters of the surface of which is coated inside and 

 outside with tin-foil. A brass rod with a knob at the end goes 

 through the cork and into the jar until it touches the inside coating 

 of tin-foil. If the knob of this jar be held about half an inch from 

 the conductor of an electrical machine, sparks will pass for some 



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