prior to the Introduction of the Potentials. 39 



the eighteenth century it was generally compared to an envelop- 

 ing atmosphere. " The electricity which a non-electric of great 

 length (for example, a hempen string 800 or 900 feet long) 

 receives, runs from one end to the other in a sphere of electrical 

 Effluvia" says Desaguliers in 1740 ^and a report of the French 

 Academy in 1733 says :f " Around an electrified body there is 

 formed a vortex of exceedingly fine matter in a state of agitation,, 

 which urges towards the body such light substances as lie 

 within its sphere of activity. The existence of this vortex is 

 more than a mere conjecture ; for when an electrified body i& 

 brought close to the face it causes a sensation like that of 

 encountering a cobweb. "J 



The report from which this is quoted was prepared in 

 connexion with the discoveries of Charles-Francois du Fay 

 (b. 1698, d. 1739), superintendent of gardens to the King of 

 France. Du Fay accounted for the behaviour of gold leaf when 

 brought near to an electrified glass tube by supposing that at 

 first the vortex of the tube envelopes the gold-leaf, and so attracts 

 it towards the tube. But when contact occurs, the gold-leaf 

 acquires the electric virtue, and so becomes surrounded by a 

 vortex of its own. The two vortices, striving to extend in 

 contrary senses, repel each other, and the vortex of the tube, 

 being the stronger, drives away that of the gold-leaf. " It is 

 then certain/' says du Fay,H " that bodies which have become 

 electric by contact are repelled by those which have rendered 

 them electric ; but are they repelled likewise by other electrified 

 bodies of all kinds ? And do electrified bodies differ from each 

 other in no respect save their intensity of electrification ? An 

 examination of this matter has led me to a discovery which I 

 should never have foreseen, and of which I believe no one 

 hitherto has had the least idea." 



* Phil. Trans, xli., p. 636. t Hist, de 1'Acad., 1733, p. 6. 



t This observation had been made first by Hawksbee at the beginning of the 

 century. 



Mem. de 1'Acad. des Sciences, 1733, pp. 23, 73, 233, 457 ; 1734, pp. 341, 

 503; 1737, p. 86 ; Phil. Trans, xxxviii. (1734), p. 258. 



|| Mem. de 1'Acad., 1733, p. 464. 



