282 History of Luminescence 



Stephen Gray's first paper on electricity, which appeared in 1720, 

 had to do with the light observed when electric bodies (feathers, 

 hair, linen, wool, etc.) are drawn through the fingers. Later (1735) 

 with an electrical machine. Gray repeated some experiments of 

 Dufay and described ^^ corona and brush discharges. He observed 

 at night, 



suspending the Iron Rod on the Silk Lines; then applying one end of 

 the tube to one End of the Rod, not only that End had a Light upon it, 

 but there proceeded a Light at the same Time from the other, extend- 

 ing in the Form of a Cone, whose Vertex was the End of the Rod, and 

 we could plainly see that it consisted of Threads, or Rays of Light, 

 diverging from the Point of the Rod, and the exterior rays being incur- 

 vated. This light is attended by a small hissing Noise; every stroke we 

 give the Tube, causes the light to appear. 



He obtained the same effects with wood and other material. Like 

 Dr. Wall, Gray concluded " this Electrick Fire . . . seems to be of 

 the same Nature with that of Thunder and Lightning." 



Dufay had long been a student of the phosphorescence of minerals 

 and precious stones, after exposure to light or on warming (see 

 Chap. VIII and IX) . He used the electrolimiinescence of amber 

 rubbed with a cloth as a standard light to tell if his eyes were dark 

 adapted. Since Dufay did not work with vacua, he contributed little 

 to the subject of electroluminescence, but he stated ^^ that the writ- 

 ings of Hauksbee and Gray " put him upon the subject and furnish'd 

 me with the Hints " that led to discoveries. Dufay was highly solicit- 

 ous of Gray's feelings concerning his entry in the field of electricity. 



Dufay's (1723) early work on the barometer light contains no 

 mention of electric phenomena. Later experiments on electrification 

 of various objects and living animals, including himself, helped to 

 identify the light observed on living things, the ignis lambens, with 

 electricity, although Dufay made no special point of the resemblance. 

 In these experiments he noticed the crackling noise and the minute 

 sparks and added: ^^ " But it is otherwise if the Experiment be 

 made with the Carkass of an Animal, for then one perceives only, 

 if it be in the Dark, a still uniform Light, without Snappings or 

 Sparks." The fancied difference between living and dead was of 

 course only a reflection of certain conditions of the experiment. 

 Dufay repeated many of Gray's experiments, increasing the distance 

 to which electric effects could be conducted, and had as a willing 

 assistant the Abbe Nollet, who later greatly extended electrical 



"S. Gray, Phil. Trans. 39: 16-24, 166-170, 1735. 



*' Dufay, Phil. Trans. 38:258-266, 1733, a letter containing a good resume of the 

 French experiments. See J. G. Doppelmayr (1744) in German. 



