miCTIONAL ELECTRICITY. 199 



hands. The first ball was repelled by the glass ; it will be 

 attracted ly the sealing-ivax. The second ball was repelled 

 by the sealing-wax; it will be attracted ly the glass. 

 These experiments clearly show that the electricity 

 developed on glass is different in kind from that 

 developed on sealing-wax. They exhibit opposite 

 forces to a third electrified body, each attracting what the 

 other repels. 



327. The Two Electricities Named. As the 



two kinds of electricity are opposite in character, they 

 have received names that indicate opposition. The elec- 

 tricity developed on glass by rubbing it with silk is 

 called positive or + ; that developed on sealing-wax 

 by rubbing it with flannel is called negative or . 

 The terms vitreous and resinous respectively were formerly 

 used. 



328. Only Two Kinds of Electricity. By 



repeating the experiments of 326 with other substances, 

 it is found that all electrified bodies act like either the 

 glass or the sealing-wax. 



329. The Law of Electric Action. By the 



experiments already performed, we have made evident the 

 fact that two bodies charged with like electricities 

 repel each other ; two bodies charged with opposite 

 electricities attract each other. 



330. The Test for Either Kind of Electricity. 



When the pith ball was attracted by the rubbed glass it became, 

 during the time of contact, charged with the + electricity of the 

 glass ; hence it was repelled. When it was attracted by the rubbed 

 sealing-wax it became, during the time of contact, charged with the 

 electricity of the wax ; then it was repelled. But either the wax 

 or the glass attracted the uncharged pith ball. We must therefore 



