QUESTIONS 501 



SUMMARY 



Certain substances may be made to take on the properties 

 of loadstone and to become magnets. A magnet has a 

 positive and a negative pole. The dipping needle and the 

 mariner's compass are applications of magnetic properties. 



There are two kinds of electrical charges, positive and 

 negative. Electricity may be generated by friction, but to 

 be of practical service it must flow continuously as a current. 

 Lightning is an electrical discharge. Currents of electricity 

 may be generated by means of voltaic cells, and these cur- 

 rents may be conducted by wires. There are many practi- 

 cal applications of electricity, as in electroplating, incandes- 

 cent lamps, welding, flatirons, electric bells, the electric 

 telephone, and the electric telegraph. 



Michael Faraday made the greatest electrical discovery 

 when he found that a magnet if thrust quickly into a coil 

 of wire generates a momentary current in one direction, 

 and if withdrawn generates a momentary current in* the 

 opposite direction. This discovery made possible the in- 

 vention of the electric dynamo and the electric motor. 



Recent experiments indicate that atoms of matter con- 

 tain electricity, and that the negative electricity in them 

 exists in the form of exceedingly minute particles called elec- 

 trons. A current of electricity is supposed to be a stream of 



these electrons. 



QUESTIONS 



Where have you ever seen magnetism employed to man's ad- 

 vantage ? 



What is the relation between lightning and electricity ? 



With what simple electrical devices are you familiar ? 



In how many different ways do you know electricity to have 

 been applied for your benefit ? 



Describe four electrical machines or appliances which you con- 

 sider of particular value. 



