The Nineteenth Century 221 



latent image on silver chloride photographic paper, when an engrav- 

 ing previously exposed to sunlight was laid on the paper. Phipson 

 believed the effect was " owing to the action of light alone; no 

 chemical agent whatever, to which such a phenomenon might be 

 attributed, entered into these experiments." However, later experi- 

 ments -^ have indicated that chemical action rather than invisible 

 radiation is usually responsible for photographic effects. 



It is surprising to find that after the treatise of E. Becquerel in 

 1867, if the lists of fluorescent compounds are excepted, no general 

 book on phosphorescence or fluorescence appeared in any language 

 until the next century." This lack was finally filled by one of the 

 huge German compilations in physics, the great Handbuch der Spec- 

 troscopie of Heinrich Kayser (1853-1940), for many years professor 

 of physics at the University of Bonn. The five volumes were pub- 

 lished between 1900 and 1912, and covered most phenomena con- 

 nected with light. Volume 4 (1908) contained 289 pages on phos- 

 phorescence by Kayser himself and 373 pages on fluorescence by 

 H. Konen, a really comprehensive historical and factual survey 

 which served to summarize the knowledge of all inorganic lumines- 

 cences in the pre-quantum period. 



in review 



The principal advances in knowledge of inorganic luminescence, 

 or better, luminescence not connected with living organisms, may 

 be stated briefly as (1) recognition of fluorescence as a true light 

 emission; (2) discovery of radioluminescence excited by elementary 

 particles and X-rays; (3) recognition of many chemiluminescences 

 of organic compounds in solution; (4) invention of the phosphoro- 

 scope; (5) accurate measurement of the spectral distribution of 

 luminescence emission, and (6) clarification of the relation between 

 the emitted and the exciting light in the case of fluorescence and 

 phosphorescence; (7) collection of accurate information on various 

 factors (temperature, pressure, impurities, etc.) which affect vari- 

 ous luminescences; (8) development of theories of luminescence 

 based on energy changes and well established thermodynamic prin- 

 ciples. More specific observations might have been considered, for 



"See W. J. Russell, Proc. Roy. Soc. 61: 424-433, 1897, and G. L. Keenan, Chem. Rev. 

 3: 95-111, 1926. 



^^ Many articles were of book length, for example E. Wiedemann's Zur Mechanik 

 des Leuchtens, Aim. d. Physik 37: 177-148, 1889, and the series by E. Lommel, Ober 

 Fluorescenz, in the Annalen der Physik (1871-1880) . The principal work on chemi- 

 luminescence, triboluminescence, and crystalloluminescence was the 112-page article 

 of Max Trautz, Studien iiber Chemilumineszenz, published in the Zeitschrift fiir physi- 

 kalische Chemie for 1905. 



