CHAPTER XV 

 ELECTRICITY 



Strange as it may seem, a scientist does not have to 

 know all about a form of energy to use it. If he discovers 

 how it acts or how it is produced he can apply this knowl- 

 edge in ways to render great service to mankind Elec- 

 tricity is a striking illustration. 



Each of us can name ways in which electricity benefits 

 us. We know it as one of the most useful forms of energy. 

 Yet no scientist knows what it is. In a way it is as mys- 

 terious to us as it was to the Greeks who began to. won- 

 der about it many centuries ago. 



We can easily produce electricity. We can make it by 

 stroking a cat's fur, or by combing our hair, or by placing 

 certain metal strips in a jar of acid and water, or we can 

 transform the energy of water into electricity. The scien- 

 tist knows how electricity behaves, how to measure it, 

 how to control it, and how to transport it to distant 

 points where it will be useful. We should all become 

 better acquainted with this great force that is playing a 

 larger part in our lives each day. We are living in an 

 electric age. 



The exact nature of electricity is not fully known. That it 

 is a form of energy no one doubts. Like water and air, it will flow 

 and exert pressure under the proper conditions. Upon these 

 two properties depends its great value in doing work for the 

 benefit of man. Although from the remotest ages electricity in 

 the form of lightning and the northern lights has been observed 

 by man with interest and wonder, it is only in comparatively 

 recent times that he has learned how to harness electricity and 

 make it serve him in many varied fields. 



Static Electricity. Static means stationary. Static electric- 

 ity means electricity held or confined in comparatively close limits. 

 Unconfined electricity is current, or flowing, electricity. Thales, 

 a Greek, noticed that when amber was rubbed it had the property 

 of attracting to itself light bodies, such as dry bits of paper and 

 pith balls. This attracting force of static electricity differs from 



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