Electroluminescence 283 



knowledge by his own experiments and became an opponent of 

 Franklin's theories. 



The ideas of the time are well expressed in Petrus van Musschen- 

 broek's (1692-1761) Elemeiita Physicae, published in 1754. In Chap- 

 ter XVII, " On electrical bodies," he took the position ** that elec- 

 tricity " depends on some subtile exhalations, emitted by cold or 

 hot bodies, but chiefly by hot ones, after they have been rubbed 

 violently for a good while. . . . These effluvia are discoverable even 

 by our senses . . . they even shine in the dark. . . . The electrical 

 virtue continues in vacuo and can run along a string 1256 feet long." 



Like Dufay, Desaguliers was also solicitous of Gray's feelings, and 

 did not publish until after Gray's death in 1736. His many experi- 

 ments between 1739 and 1742 were not concerned with vacua and 

 hence contributed little to knowledge of the electric light. He 

 pointed out the ability of water films to conduct and the necessity 

 of dryness for success in electrical experiments, a condition which 

 made many of the striking luminous effects possible. 



After the period of Gray, Dufay, and Desaguliers, many isolated 

 experiments kept the " electric fire " and the " electric light " in the 

 public eye. The names of Ludolff, Winckler, Allemand, Wilke, 

 Bose, Hansen, Grummert, Franklin, van Musschenbroek, Nollet, 

 Beccaria, Watson, and Jallabert are associated with this electric era, 

 characterized by public demonstrations of striking effects and a belief 

 in the therapeutic value of electrical treatment. Even John Wesley ^^ 

 (1702-1791) , founder of the Methodist Church, advocated electrical 

 cures. 



Among the interesting discoveries of the 1740's was the ability 

 of electric fire to inflame the ethereal liquor or " phlogiston of 

 Frobenius " *" (ether) , the vapor of spirits of wine, and hydrogen, 

 prepared by the action of acid on iron. Credit for these observations 

 goes to Dr. Christian Friedrich Ludolff (1707-1763) of Berlin in 

 1744 and to Dr. Johann Heinrich Winckler (1703-1770) of Leipzig, 

 also noted for introducing a cushion of leather for rubbing the globe, 

 instead of the hand, thereby greatly improving the electrical ma- 

 chine. Dr. Watson later (1745) confirmed them and Mr. Bose 

 (1744) even fired gunpowder and described the feat in latin verse. *^ 



**From the translation by John Colson, Elements of natural philosophy, London, 

 1744. 



*^ John Wesley, The desideratum, or electricity made plain and useful, London, 1760. 



*®Sigismund August Frobenius (died 1741), a German living in London, prepared 

 ether and published on it in the Phil. Trans, for 1730. Valerius Cordus is said to have 

 discovered ether in 1535. 



*'' Die Elektrizitdt, nach ihre Entdeckung und Fortgang mit poetischer Feder 

 entworffen, Wittenberg, 1744. Also W. Watson, Phil. Trans. 43: 483, 1745. 



