The Eighteenth Century 179 



was forced to use the great encyclopedias discussed in a previous 

 section, or special cyclopedias such as the Dictionnaire d'Histoire 

 Naturelle (1769). A later work, the Dictionnaire Raisonne Uni- 

 versel d'Histoire Naturelle (1791) of J. C. Valmont-Bomare (1731- 

 1807) contained excellent information on " Mer lumineuse," " Porte- 

 lumiere," or " Mouches luisantes." 



The nearest approach to a general work on luminescence in the 

 middle of the century was a doctor's thesis entitled, De Noctilucis, 

 a Dissertatio Philosophica Inauguralis, by Johannes Albertus Mel- 

 chior, Franequerae (Franeker) , 1742, under the direction of W. G. 

 Muys. Melchior followed the classification used at the start of the 

 century and divided his thesis into two sections, " De Noctilucis 

 Artificialibus " (36 pages) and " De Noctilucis Naturalibus " (25 

 pages) . In connection with the artificial phosphors, the ideas of 

 Desaguliers, Newton, 'sGravesande, Hauksbee, Boyle, Boerhaave, 

 Descartes, Bernoulli, Dufay, Hamelio,^° Homberg, and Lemery were 

 presented, while views on natural phosphors, i. e., living organisms 

 and precious stones, came from Boyle, Clark, Lemery, Beale, Waller, 

 de la Voie and Auzout, Vossio (on the cucuyo) , Dufay, Josephus 

 (on the Baaras) , Pliny, and Aelian. 



Another thesis, a Dissertatio Inauguralis Chymico-medica, of forty 

 pages, was by Nicholas Ludolphus Marheinecken, entitled, De 

 Phosphoris (Jena, 1744) . Although rotten wood and insects were 

 mentioned, the chief interest of the author was inorganic lumi- 

 nescence, with most of the classical work reviewed and nothing new 

 added. 



Finally, the thirty-six-page pamphlet of Johann Gottlob Lehmann 

 (died 1767) , Ahhandlung von Phosphoris, etc. (Dresden und Leip- 

 zig, 1750) , gives a short account of a wide variety of luminescences. 

 Lehmann was a Bergrath in Berlin until 1761 and later a professor 

 of chemistry and director of the Royal Museum in St. Petersburg. 

 This work on various phosphors was one of his earliest publications. 

 It professed to give the preparation and uses of phosphors as well as 

 remarks on fire and light and his theory of the origin of the lumi- 

 nescence. Lehmann's later writing had to do mostly with minerals 

 but his treatment of luminescences was not very good. They were 

 divided into the natural and the artificial, the latter either prepared 

 chemically, or lighting by mechanical manipulation, which Leh- 

 mann realized was electrical in nature in the case of mercury shaken 

 in a glass tube. 



^*Jean Baptiste Duhamel (1624-1705), French astronomer and secretary of the 

 Academie des Sciences, who wrote a history of the Academy (1698) and a treatise on 

 the old and new philosophy (1678) , in Latin. 



