394 History of Luminescence 



instead of " reflect," he would have solved the fluorescence prob- 

 lem nearly two hundred years before the classic work of Stokes. 

 For that whole period the emission and the reflection of light from 

 surfaces was to remain in confusion. 



Edme Mariotte {ca. 1620-1684) , the mathematician and physicist 

 of Dijon, was another who compared the blue color of " lignum 

 nephriticum " to that of air containing smoke, thus continuing the 

 confusion between scattering and emission of light. His discussion 

 will be found in De la Nature des Couleurs, published in (Euvres 

 de Mariotte (Leiden, 1717) . 



Eighteenth-Century Observations 



The phenomena exhibited by lignum nephriticum were also ob- 

 served by a few other early workers like Christian Wolf (1679-1754) 

 in Experimenta Physica (1721-23) , and new liquids were found to 

 behave in a similar way, petroleum by Peter van Musschenbroek 



(1734) , blue and red sandalwood. Quassia wood (bitter wood) tinc- 

 ture and horse-chestnut bark tincture (aesculin) by K. W. Nose 



(1780) . However, there was little progress in explanation, although 

 another experimental attempt was made by Christian Ernst Wiinsch 



(1744-1828) , recorded in his book, Versuche und Beobachtung ilber 

 die Farben des Licht (Leipsig, 1792) . He studied the transmitted 

 and reflected light of lingnum nephriticum solution when illumi- 

 nated by light of different spectral tints, but his colors were so im- 

 pure that little can be concluded from the work. The term " fluores- 

 cence " had not yet been coined and the whole subject lay dormant 

 during the eighteenth century, 



Brewster, Herschel, and Stokes 



At the beginning of the nineteenth century, a material in the 

 solid state, fluorspar, was to play an important part in the explana- 

 tion of bicolored solutions, and was in fact to supply the name 

 " fluorescence " to the phenomenon. Fluorspar was known to ex- 

 hibit thermoluminescence and phosphorescence, even tribolumines- 

 cence, and many mineralogists, particularly the celebrated Abbe 

 Rene Just Haiiy (1743-1822) , professor of mineralogy in the Musee 

 d'Histoire Naturel in Paris, observed and commented (1801) on 

 the fact that the color of the mineral was different by reflected and 

 transmitted light. Haiiy attempted to explain the effect as an exam- 

 ple of the color of thin films. Somewhat later, John Herschel (1792- 

 1871), the famous astronomer, in his Treatise on Light (1828) at 

 first adopted the same point of view, but in 1845 introduced a new 



