Electroluminescence 297 



One of the leaders in this field was Julius Pliicker (1801-1868) , pro- 

 fessor of mathematics and physics at the University of Bonn. His 

 early work, beginning in 1826, was purely mathematical, but later, 

 in 1847, he turned to the study of magnetism and particularly 

 (1851) the magnetic relations of gases at atmospheric pressure. No 

 interest could have been better chosen for discovery of the extra- 

 ordinary phenomena which turned out to be connected with the 

 emission of cathode rays. His paper of 1858 had to do with the 

 action of the magnet on electrical discharges in Torricellian vacua 

 (1858) and continued with the stratifications and dark bands and 

 the spectra (1859-1863) emitted. The first investigations were ob- 

 servational, but the Pliicker and Hittorf (1865) paper contains 

 plates of the spectra of various gases. 



The influence of a magnet ^^ on luminescence of a gas in vacuum 

 tubes appears to have been first (1849) observed by August Arthur 

 de la Rive (1801-1873) , a professor at the Academy in Geneva, in 

 connection with his theory of the aurora borealis, although the dis- 

 covery of magnetic effects in a rarefied gas is usually attributed to 

 Pliicker (1858) . Certainly the results of Pliicker's experiments were 

 far reaching and led to the important research on cathode rays de- 

 scribed in Chapter XII. When Pliicker's papers appeared, de la 

 Rive (1858) called attention to his earlier work and very actively 

 continued (1858-1872) the study of luminous phenomena in rare- 

 fied gases. J. W. Hittorff's series of papers on electrical conductivity 

 of gases began in 1869 and lasted until 1884. It was entitled, Ueber 

 Elektricitatsleitung der Gase, but contained much more than the 

 title would indicate. E. Becquerel (1859, 1869) carried out many 

 experiments with solids sealed in glass tubes containing rarefied gas 

 through which electric discharges were passed, although he was prin- 

 cipally engaged in mapping the spectra of phosphorescent and fluo- 

 rescent substances in his phosphorescope. For phosphors, E. Bec- 

 querel, and for gases, J. Pliicker may be considered the pioneers in 

 spectral research on luminescence. V. S. M. Van der Willigen (1858, 

 1859) was another early worker, whose original paper in Dutch 

 contained a plate of gas spectra. 



At about the same time John Peter Gassiot (1797-1878), a mer- 

 chant in London, was investigating (during the years 1858 to 1862) 

 the form of the electric discharge in partial vacua, particularly the 

 dark spaces and stratification. De la Rive and Gassiot wrote a joint 



^' Others who studied the effect of a magnet on electroluminescence in a rarefied 

 gas are W. Hittorf (1869) , A. Treve (1870) , A. J. Angstrom (1871) , L. Daniel (1870) , 

 A. Secci (1870), de la Rive and E. Sarasin (1872), J. Chautard (1874-1876), and E. 

 Van Aubel (1898) . 



