ELECTRICITY. OPPOSITE ELECTRICITIES. 23 



its being first observed in excited amber, which the Greeks 

 called electron. 



A rod of glass may be excited in the same manner by 

 rubbing with silk. But in this case the electricity is of a 

 different kind. 



74. Take a smooth piece of iron or brass, or any other 

 metal, and hang it up by silk threads so .that it shall not 

 touch or be near to any thing, and fasten to it several 

 pith balls hung to the end of cotton threads. Rub the* 

 piece of metal with a rod of excited amber or sealing 

 wax, and, immediately, electricity is excited, and the pith 

 balls are repelled, and fly from each other and from the 

 metal as far as they can go. Bring the rod of amber or 

 wax near to the balls, and they will be repelled and avoid 

 it. But if you bring a rod of excited glass near them, 

 they will be attracted, and will fly towards it. The elec 

 tricity excited in the glass is of an opposite kind to that 

 excited in the amber, and the opposite electricities attract 

 each other. 



75. Touch the metal with a finger, and the little balls 

 immediately fall together again. The electricity is dis 

 charged through the finger. 



76. Something similar is supposed to take place with 

 vapor. When water is turned into vapor by the sun s 

 heat, it forms little hollow bubbles or vesicles, which 

 repel each other in consequence of being electrified by 

 evaporation. Any thing which draws off the electricity 

 of a cloud of such vapor causes the little vesicles to 

 collapse, and rush together, and form drops of rain. 



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