194 GENERAL SCIENCE 



body conducts the electricity away as fast as it is made. 

 With non-conductors such as glass, the charge remains 

 where it is developed. In the commercial use of electricity 

 both conductors and insulators are of great value. 



Experiment 55. Support one end of a metal rod on an elec- 

 troscope and the other end on an insulating stand (Figure 163). 

 Bring a charged body near the end of the rod. The divergence 



of the leaves of the 

 electroscope shows 

 that the charge has 

 been carried by the 

 rod to the electro- 

 scope. The rod is 

 a conductor of elec- 

 tricity. Test the 

 conductivity of 

 FIG. 163. other substances. 



Theory of Electricity. To study the theory of elec- 

 tricity we must introduce the reader to a new and very 

 interesting physical character, the electron. All the 

 atoms of all substances are known to contain both posi- 

 tive and negative electricity. The negative electricity 

 exists in the form of electrons or particles of negative 

 electricity. The positive electricity probably exists as 

 the center or nucleus around which these little particles 

 of negative electricity are grouped. They cling together 

 by reason of having opposite or unlike charges, the posi- 

 tive charge just equaling the sum of the charges of the 

 little electrons. We are most concerned with these nega- 

 tive particles or electrons at present, for they have a 

 very important part in our everyday life. If a piece of 

 woolen cloth is rubbed on a piece of hard rubber, some 

 of these electrons are brushed from their places on the 

 atoms of the piece of cloth and collect on the piece of 



