Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/59

 the eighteenth century it was generally compared to an enveloping 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: "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 is brought close to the face it causes a sensation like that of encountering a cobweb."

The report from which this is quoted was prepared in connexion with the discoveries of Charles-François 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, "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."