Electroluminescence 301 



to the temperature gradient, potential drop, kind and pressure of 

 gas, etc., in the tube. Since Plucker had presumed that the light of 

 Geissler tubes was the result of temperature rise, rather than a 

 purely electrical effect, the temperature of different regions of the 

 tube assumed particular importance. It was studied by both the 

 father, G. Wiedemann (1876), and the son, E. Wiedemann (1878- 

 1880) , in one of the latter 's first investigations of luminescence. 



The phrase, " conduction of electricity through gases," has be- 

 come almost synonymous with the name of J. J. Thomson (1856- 

 1940), whose book (1903) of that title has summed up knowledge 

 of the many complex phenomena to be observed. It has served to 

 obscure an earlier work, Recent Researches in Electricity and Mag- 

 netism (Oxford, 1893) , which was intended as a sequel to Clerk- 

 Maxwell's treatise (1873) on these subjects. In Thomson's book 

 (1893) , Chapter II (pp. 53-207) deals with the " Passage of Elec- 

 tricity Through Gases," a general account of the many luminescent 

 and other phenomena which occupied the principal attention of 

 physicists of the period. A similar work Elektrische Lichterschein- 

 ungen, was published by Otto Lehmann (1855-1922) in Germany 

 in 1898, to be followed by Die Elektrizatdt in Gasen (1902) of 

 Johannes Stark, a Nobel prize winner in 1919. Knowledge of elec- 

 troluminescence before the more modern approach made possible 

 by quantum theory is well covered in these works. 



AFTERGLOW IN GASES 



In some of Becquerel's tubes containing only rarified gas, it was 

 noticed that a persistent light '^^^ was visible, not due to phospho- 

 rescence or electrification of the glass. ^"^ It was later determined by 



1898; G. Granquist, 1898; H. Hertz, 1883; A. Herz, 1895; W. Hittorf, 1869-1884; M. 

 Hoffmann, 1897; C. Kirn, 1894; O. Lehman, 1895; C. A. Mebius, 1896; B. Nebel, 

 1885; A. Paalzow and F. Neesen, 1895; J. Puluj, 1880-1882; A. Schuster, 1884, 1890; 

 G. Seguy, 1898; C. A. Skinner, 1899, 1900; W. Spottiswoode and J. E. Moulton, 1880; 

 F. Stenger, 1885; J. J. Thomson, 1886-1895; J. Trowbridge and T. W. Richards, 1897; 

 E. Wiedemann and H. Ebert, 1888; E. Wiedemann and G. C. Schmidt, 1898; G. 

 Wiedemann, 1876; G. Wiedemann and R. Riihlmann, 1872; R. W. Wood, 1896. 



"^ It is interesting to note that Michael Faraday (1857) described " the persistent 

 appearance of a lightning flash " which appeared as a Y in the clouds and lasted a 

 second or more. The form was not an impression on the eye, as it did not move with 

 the eye but remained fixed in the cloud. Faraday asked, " What is the cause of this 

 effect? The most probable guess seems to me to be, that it is due to a highly exalted 

 phosphorescent condition of the particles of cloud, along or through which, the elec- 

 tric discharge has passed; and perhaps an experiment might find means of realizing 

 it in some degree. I believe that like luminous traces have been observed upon sugar 

 and some other bodies when the electric discharge has been made over them." Perhaps 

 this is the first record of a persistent luminescence of gases. 



»» See E. Becquerel, Ann. Chim. et Phys., ser. 3, 57: 40-124, 1859; also P. Riess, 



