Electroluminescence 287 



linson dated July 1 1, 1747, spoke of the " wonderful effect of pointed 

 bodies in drawing off the electrical fire ... in the dark you will 

 see, sometimes at a foot distance and more, a light gather upon it 

 (electrified point) like that of a fire-fly or glow-worm." The expres- 

 sion " electric fire " was highly descriptive, not merely from the 

 appearance but because the discharges actually burnt the flesh. 



In France, the study of electricity was quite the vogue, carried on 

 chiefly by Nollet and Jallabert. Abbe Nollet, friend of Dufay and 

 instructor of the royal family, carried out experiments of many 

 kinds, among them observations on the appearance of the electric 

 light in vacuo. Like others he noticed that the light was much more 

 diffuse and unbroken in the absence of air. If the end of a conductor 

 from the electrical machine was inserted in an exhausted glass vessel, 

 the vessel became full of light whenever his hand was brought near 

 and much brighter when his hand was spread over the glass, an 

 effect due to the conduction of electricity through the residual gas 

 toward the body of the investigator, as shown in figure 25, from 

 the Italian edition (1755) of Recueil des Letters sur I'Electricite 

 cles Corps (Paris, 1753) by Nollet. 



Nollet included in his studies the effects of electricity on plants 

 and animals. He also helped to refute the extravagent claims of 

 electrical cures, which had been reported by Dr. Privati in Italy in 

 1747. His early ideas on electricity are summarized in two books, 

 Essai sur Electricite des Corps (Paris, 1747) and Recherches sur les 

 Causes Particulieres des Phenomenes £lectriques (Paris, 1749). 

 Later studies are contained in his Legons de Physique Experi- 

 mentale, vol. 6 (Paris, 1764) . 



The second French worker was Jean Louis Jallabert (1712-1768) , 

 professor of philosophy and mathematics at Geneva. In his Experi- 

 ences sur Electricite, published at Geneva in 1748, he devoted 

 seventy pages to the electric light, summing up all knowledge of the 

 subject available in his time. 



WILLIAM WATSON AND ELECTRICITY IN VACUO 



Fortunately there were physicians in the mid-eighteenth century 

 with true scientific interest, unwilling to be carried away by specula- 

 tion on electricity and the human body. One of these was Dr. Wil- 

 liam Watson (1715-1787), also a botanist, whose electrical experi- 

 ments became so famous they were observed by royalty at his home 

 in Aldersgate. He had studied electrical discharges in air in 1747 

 and their behavior in a vacuum was described in a paper entitled, 

 " An Account of the Phenomena of Electricity in Vacuo with some 

 Observations thereupon," published in the Philosophical Transac- 



