Electroluminescence 271 



a magnetic terella, such as had been previously studied by Gilbert. 

 These experiments were made in the early sixteen sixties and ob- 

 served by the physician, Adviser to the King, and Lieutenant of 

 Police from Lyons, Balthasar de Monconys,^* but not published by 

 von Guericke until 1672.^^ 



Von Guericke not only heard the electric noise and saw the elec- 

 tric light but discovered most of the fundamental phenomena of 

 static electricity in so simple a form that later workers are usually 

 thought of in connection with the concepts. Conduction and induc- 

 tion were clearly observed by von Guericke although the former is 

 usually credited to Gray in 1729 and the latter to Dufay in 1733. 



Luminescence from rubbing the well-known electric, amber, must 

 have been noticed by many persons, although the effect appears not 

 to have been recorded until the paper of W. Wall (1708) . One of 

 the important early observations of electroluminescence was that of 

 Robert Boyle (1663) on a diamond which " being rubbed upon 

 my clothes as is usual for the exciting of amber, wax and other elec- 

 trical bodies, it did in the dark manifestly shine." Some of the 

 light in this case was undoubtedly due to electrical discharge but 

 complicated by phosphorescence and thermoluminescence, charac- 

 teristics of certain kinds of diamonds (see Chapter X) . 



After the sulphur ball and the diamond, the next instance of 

 artificial electric light to be described was the luminous barometer, 

 which came to be known as the mercurial phosphor, although it 

 was not recognized that the phenomenon was connected with elec- 

 tricity until some years later. 



THE BAROMETER LIGHT OR THE MERCURIAL PHOSPHOR 



Two pupils of Galileo, Evangelista Toricelli (1608-1647) and 

 Vincenzo Viviani (1622-1703), constructed the mercury barometer 

 in 1643, thereby contributing to science an instrument of universal 

 importance in research. During the latter part of the seventeenth 

 century, every laboratory had its barometer. Some thirty years after 

 its invention, in 1675, Jean Picard (1620-1682) , a French priest 

 and one of the famous group of astronomers at the newly established 

 Paris observatory, noticed a glow above the mercury in his barometer 

 when carried about in a dark room, and duly reported this obser- 

 vation in a note in the second volume of the Memoires de I'Academie 



^* B. de Monconys, Journal des voyages, 3 parts, Lyons, 1665. 



^^ Experimenta nova (ut vocantur) magdeburgica de vacuo spatio, Amsterdam, 

 1672. German translation in Ostiuald's Klassiker, No. 59. Kaspar Schott (1608-1666) 

 repeated many of von Guericke's experiments and published them as Mechanica 

 hydraulico-pneumatica in 1657. 



