Phosphorescence 365 



of his colleague at Erlangen, Gerhart C. Schmidt appeared over the 

 years 1878 to 1907. In 1901, Wiedemann prepared a pamphlet of 

 twenty-eight pages, Ueber Luminescence, which was published by 

 the University of Erlangen in a Festschrift seiner Koniglichen Hoheit 

 des Prinzregenten Luipold von Bayern ziim achtzigsten Geburtstage. 

 This more or less popular presentation was a rare departure from his 

 usually technical publications. 



With the turn of the century, the electron and the quantum 

 became the most important concepts in the theory of light and 

 views on luminescence changed completely, taking the direction 

 discussed in the previous section on the photoelectric effect and 

 phosphorescence. 



It must not be supposed that the hypothesis of Wiedemann and 

 Schmidt contained the last word on phosphorescence. In the first 

 decade of the twentieth century, approach to the scientific study of 

 phosphorescence (and fluorescence) was pioneered by Robert Wood 

 (1868-1955), Edward L. Nichols (1854-1937) and Ernest Merritt 

 (1865-1948) in the United States, and by J. Stark (born 1874) and 

 Peter Pringsheim in Germany, while P. Lenard (1862-1947) and 

 V. Klatt continued their important work. These men introduced 

 new theories, in which the electron played an all important role, 

 and a host of later workers continued phosphorescence study until, 

 by 1955, at least sixty books (including published symposia) have 

 dealt with this fascinating subject. 



