408 History of Luminescence 



dorff's Annalen between 1852 and 1861. The final section deals 

 with uses of fluorescence, such as the detection of ultraviolet light 

 in various spectra, and testing light which is not safe to use in a 

 photographic dark room, since the fluorescence-exciting and the 

 photochemically-active rays are essentially identical. He noted that 

 invisible writing with quinine or aesculin solutions can be photo- 

 graphed as a result of their fluorescence, and uranium glass used in 

 a microscope to reduce the annoyance experienced from the intense 

 blue light of the sky. On the whole, Pisco covered the subject quite 

 thoroughly for 1861, but he could not foresee the widespread appli- 

 cations of the present day. 



The book of E. Becquerel, La Lumiere, ses Causes et ses Effets 

 (Paris, 1867) , contains much information on fluorescence, although 

 he used the term phosphorescence, rather than fluorescence, for the 

 light emission. Becquerel's later work was presented as original 

 papers. 



Despite the attention to theory and to interpretation of results by 

 Lommel, his extensive research of the last third of the century was 

 not brought together in book form. With the exception of K. 

 Noack's (1887) list of fluorescent substances and a few articles in 

 textbooks of physics " or on light, no book devoted to fluorescence 

 appeared between E. Becquerel's La Lumiere (1867) and Konen's 

 article, "Fluorescence" (1908), previously mentioned. Heinrich 

 Mathias Konen (born 1874) was a professor of physics in the Uni- 

 versity of Munster i W., later at Bonn. His thesis, " t)ber die 

 Spectren des Jod " (1898) , as well as later publications dealt mostly 

 with spectra and theoretical optics. His monumental review (373 

 pages) in H. Kayser's, Handbuch der Spectroscopie, makes a fitting 

 companion on " Fluorescence " to Kayser's own 239-page article on 

 " Phosphorescence " in the same volume. 



With the development of " black light," using filters which pass 

 ultraviolet light and absorb the visible, largely perfected through 

 the efforts of Robert Wood at the time of the First World War, 

 fluorescence may be said to have come into its own. The term 

 became a household word as a result of fluorescent effects in the 

 theatre and in advertising. Secret invisible writing, which fluoresced 

 in black light, was used in World War I, and aroused great curiosity 

 afterwards. Fluorescence became important in biological research 

 and in medicine for detection of disease. The development of physi- 

 cal and chemical theories concerning the excitation of atoms and 



^^ In Adolph Wiillner's Lehrbuch der Experimentalphysik (4th ed., 1883) , the 

 fourth volume. Die Lehre von der Strahlung, contains twenty-four pages on fluores- 

 cence and eleven pages on phosphorescence. 



