Francis Hauksbee, Robert Symmer 79 



such a manner that the electricity could not escape to 

 earth. He advised the use of silk threads, as owing to 

 their thinness they were likely not to conduct so well. 

 This proved to be successful, not for the reason given 

 but because silk is an excellent non-conductor. Besides 

 silk, other substances like glass and resins were recognized as 

 insulators, and the range of experimentation was thereby 

 much enlarged. 



There was at the time considerable confusion owing to 

 the capricious manner in which electrical forces showed 

 themselves, sometimes by attraction and sometimes by 

 repulsion. No progress could be made in this respect until 

 Dufay, a Captain in the French army, showed in the year 

 1733 that these apparently contradictory effects could be 

 explained by assuming the existence of two kinds of elec- 

 tricity, which he called vitreous and resinous, terms which 

 in our own time Lord Kelvin used in preference to the more 

 common nomenclature of positive and negative electricity. 

 Dufay's experiments attracted little attention, and Franklin, 

 two years later, formed independently a theory, which 

 admitted only one kind, but distinguished between an excess 

 and defect of that kind. Bodies were called positively and 

 negatively electrified according as they contained an excess 

 or deficiency. 



Another Fellow of the Royal Society, Robert Symmer, 

 also apparently unaware of Dufay's work, revived in 1759 

 the theory of two separate kinds of electricity with opposite 

 properties, and he was for some time supposed to be its first 

 originator. He did much to promote clear and definite 

 notions on electrical matters and the merit of his investigations 

 cannot be called in question. Though the controversies 

 between the followers of Franklin and those of Dufay and 

 Symmer lasted until quite recent times, they could not lead 

 to any substantial result because there is no fundamental 

 difference between the two views. Both emphasize the 

 distinction between two opposite electrical states, and our 

 preference for one or other alternative depends mainly on 

 the ideas which we unconsciously attach to forms of expression 

 which suggest more than they are intended to do. As a 

 matter of convenience, we may think of positive and negative 



