Electroluminescence 281 



by Dalibard and Delor in France and by Franklin himself in 

 America. 



THE RISE OF ELECTRICAL KNOWLEDGE 



After Hauksbee's experiments, striking as they were, little inquiry 

 into electricity occurred until the late seventeen-twenties. The ob- 

 servations were chiefly concerned with attraction and repulsion but 

 the fact that bodies which were rubbed emitted sparks and showed 

 luminosity drew more and more attention to the electric light and 

 electric fire, which became accepted accompaniments of electrical 

 effects. ^^ The principal investigators of the early eighteenth-century 

 were three: Stephen Gray (died 1736) , a pensioner at the Charter 

 House, who rediscovered *° conduction in 1729 and showed that 

 metals could be electrified if insulated, otherwise they conduct away 

 the " electric virtue " as fast as excited; Charles Francois de Cisternay 

 Dufay (1698-1739) , who rediscovered induction and declared (1733) 

 that there two kinds of electricity, vitreous and resinous; and Jean 

 Theophile Desaguliers (1683-1744) , who continued the study of 

 metals, calling them conductors. Desaguliers won many medals and 

 prizes between 1734 and 1742 but added nothing to luminescence 

 knowledge. The idea of " electric effluvia " about the electrified 

 body changed to an " electric fluid " which might move, and Gil- 

 bert's idea of electrics and anelectrics changed to that of insulators 

 and conductors. 



All these men worked before the discovery of the electric phial 

 or Leyden jar in 1745. The electrical machine was still Hauksbee's 

 globe, or a tube, usually of glass,*^ revolved and rubbed by hand. It 

 was found that all substances could be made electric (i. e., electri- 

 fied) , if insulated, especially when heated, and a number of experi- 

 ments involved the electrification of chunks of beef, chickens or 

 small boys suspended on silk cords. Gray's and Dufay's demonstra- 

 tion of the possibility of conducting the " electric virtue " to some 

 very distant place by wet threads or metal connections was of great 

 practical advantage. The fact that Dufay's discovery of vitreous and 

 resinous electricity was by Franklin to be identified respectively 

 with an excess (plus) and a deficiency (minus) of electricity and 

 referred to as positive (vitreous) and negative (resinous) , did not 

 detract from its importance. 



8»See P. T. Riess, Die Lehre von der Reibungselectricitat 2: 124-170, Berlin, 1853, 

 for a detailed history of light phenomena. 



*° Von Guericke had observed conduction along a linen cord six feet long in the 

 sixteen sixties. 



" The glass disk was used by Martin Planta in 1755 and by Jesse Ramsden (1735- 

 1800) of London in 1768. 



