Electroluminescence 289 



changes in the light effects noted when the hand was brought near 

 the glass. 



^Vatson was so imbued ^vith the connection of electricity and fire 

 that he asked (1746, 1747) the question whether electricity was not 

 elementary fire which merely appeared in different forms, and 

 whether an electrical machine is not a " fire-pump," as Guericke's or 

 Boyle's machine is an " air pump." He related that he inclined to 

 the opinion of Homberg, Lemery the Younger, s'Gravesande, and 

 Boerhaave, " who held fire to be an original, a distinct principle, 

 formed by the Creator himself, than to those of our illustrious 

 Countrymen, Bacon, Boyle and Newton, who conceived it to be 

 mechanically producible from other bodies. Must we not be very 

 cautious how we connect the elementary fire, which we see issue 

 from a man, with the vital flame and calidum innatum of the An- 

 cients; when we find that as much of this fire is producible from a 

 dead animal as from a living one, if both are especially replete with 

 fluids? " The Copley Medal of the Royal Society was awarded 

 Watson in 1745 for his earlier discoveries incorporated in his book 

 (1746). 



WILSON, SMEATON, AND CANTON 



The next study of the electric light was similar to that of Hauks- 

 bee and had to do with evacuated vessels revolved on a lathe and 

 rubbed by hand. The experiments were made by Mr. Smeaton ^* 

 at the request of Benjamin Wilson (1708-1788) , Secretary of the 

 Royal Society, later a student of phosphors. If the air within was 

 rarified five hundred times, " a considerable quantity of lambent 

 flame, variegated with all the coulours of the rainbow, appeared 

 within the glass, under the hand." This light was steady but " when 

 a little air was let in it appeared more vivid and in greater quantity; 

 but was not so steady." With more air " streams of bluish light 

 seemed to issue from under his hand," sometimes in the form of 

 trees or moss." With more air the coruscations within became less 

 and then vanished and when full of air no light appeared inside but 

 only a dim light on the outside of the glass where rubbed by the 

 hand. 



The effects of different gas pressures were clearly recognized in 

 the Smeaton-Wilson experiments, and the attempt to obtain higher 

 and higher vacua, as exemplified by Watson's use of the double 

 barometer of Lord Charles Cavendish, has continued imtil the 

 present day. The reward came in the next century with the dis- 



^*See Priestley, History of electricity, 301, 1767. 



^° The Abb6 Nollet referred to " aigrettes lumineuses." 



