112 Nichols: Franklin's 



earlier experiments of von Kleist, Gralath and Winkler, 

 he appears to have had no knowledge — the scientific 

 attention of all Europe had been focused for more than 

 a year, but it remained for Franklin to demonstrate ex- 

 plicitly that the inside and outside of a jar are oppositely 

 charged and that the charges reside in the dielectric and 

 not in the coatings. He also showed that a jar cannot 

 be discharged by contact with either coating separately, 

 but only by providing a conducting circuit between 

 them; that a jar cannot be charged without grounding 

 one coating or in some way removing from one coating 

 a charge equal but opposite in sign to that introduced 

 into the other, and that a jar may be charged by the 

 outer coating provided the inner meantime be grounded. 



He devised the cascade arrangement by which a num- 

 ber of jars can be charged or discharged in series and 

 made condensers of glass plates with coatings of lead — 

 such as are still known as Franklin plates. In this, as 

 he himself soon learned, he had, however, been antici- 

 pated by both Smeaton and Bevis in England. He also 

 magnetized and demagnetized steel needles and even re- 

 versed their polarity by means of the discharge current 

 from his condensers. 



Having established to his satisfaction the principles 

 of action of Leyden jars, Franklin, in whom the inven- 

 tive spirit was native and irrepressible, constructed two 

 forms of electric motor driven by means of the energy 



