284 History of Luminescence 



The growing interest in electricity again focussed attention on the 

 barometer light. Although Hauksbee demonstrated for all practical 

 purposes that the mercurial phosphor was similar to his light in 

 rubbed globes and electrical in nature, perhaps the final proof may 

 be said to have come from Christian Friedrich Ludolff, an M. D. of 

 Berlin. He showed in 1745 that a barometer, when shaken to pro- 

 duce light, actually became charged and would attract threads. In 

 the same year, a letter from a Mr. Abraham Trembly, F. R. S., to 

 the President of the Royal Society, Martin Folkes, Esq., was pub- 

 lished in the Phil. Trans. (1745) , " Concerning the light caused by 

 Quicksilver shaken in a glass Tube, proceeding from Electricity." 

 In this letter from The Hague, February 4, 1745, Trembly said 

 that " Mr. Allamand *^ continues here very successfully his Experi- 

 ments upon Electricity " and had empowered him to report that 

 the light of mercury is due to friction as it runs on the glass and 

 electrifies it. A bit of feather down in the tube is attracted to the 

 mercury. Hence the barometer light should not properly be called a 

 phosphorus. Trembly also saw Mr. Musschenbroek at Leyden with 

 " an exhausted Globe of Glass, which, when rubbed with the Hand, 

 seemed all fill'd with a very bright Fire." 



In addition to the electric fire and the electric light, there was 

 also the " electric wind," which had been observed by Hauksbee. 

 This effect is due to electrified air (ions) repelled by the charge on 

 a point. They set the air in motion with sufficient velocity to move a 

 candle flame. It was well shown in a striking experiment of Johann 

 Carl Wilcke*^ (1732-1796), reported by Priestley (1769:292) in 

 his book on Electricity. 



Mr. Wilcke put English phosphorous upon a pointed body, which in 

 the dark, rendered the whole visible; and when he suspended this pointed 

 body perpendicularly, the phosphoreal vapours were seen to ascend; but 

 upon electrifying it, as it hung in the same direction, the vapours were 

 carried downwards, and formed a very long cone, extending out of the 

 middle of the cone of electric light, which was seen perfectly distinct 

 from it. When the electrification was discontinued, the phosphoreal 

 vapour ascended as at first. 



It is apparent that an electrical age of wonderful luminous effects 

 had arrived. Priestley related that by the use of several simultane- 

 ously rotating glass globes or tubes and good insulation, it became 



*^J. N. S. Allamand (1713-1787), a professor of philosophy and natural history in 

 the University of Leyden. 



** Wilcke's experiments were published in the Svenska V etenskapakademiens Hand- 

 lingar, and in the book De electricitatibus contrariis, a Disputatio inauguralis physica, 

 Rostok, 1757. 



