Researches in Electricity 113 



thus stored. Simple mechanical devices operated by 

 the Hauksbee machine, such as the electric chimes and 

 the tourniquet, there were already, but Franklin's motors 

 were no mere modifications of these. The first, called 

 the electric jack, was driven by the attractive and repel- 

 lant forces of two oppositely charged Leyden jars. 

 These were placed diametrically opposite and just out- 

 side the periphery of a wheel having some thirty spokes 

 of glass at the ends of which brass thimbles were 

 mounted. The wheel revolved upon a vertical axis and 

 the thimbles were successively attracted, charged and 

 repelled as they passed each jar. The power developed 

 was considerable, being sufficient to maintain a speed of 

 twelve or fifteen turns a minute even when loaded with 

 one hundred Spanish dollars. Franklin deemed it ca- 

 pable of carrying a large fowl " with a motion fit for 

 roasting " if set up before a fire.^ 



The other motor, Franklin's self-moving wheel, was 

 a condenser consisting of a circular glass plate coated on 

 both faces and mounted to revolve upon a vertical shaft. 

 Equidistant around the rim of this disk were leaden bul- 

 lets connected alternately with the coatings. Surround- 

 ing the revolving plate were glass columns supporting 

 insulated brass thimbles and these attracted, were charged 

 by and then repelled each passing bullet as the wheel 



'Franklin: Electricity. Fourth edition — 1769, p. 31. 

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