166 History of Luminescence 



stances, deflagration of sulphur, solution in acids of metals, abundant 

 with phlogiston. Included in this category are the fires that arise 

 from heat of fermentation,^" luminous vapors of fish, or meats cooked 

 or spoiled, vapors of stagnant waters,-" feux foUets, defined as little 

 fires that play in the air, " etoiles filantes " and other " pareils 

 meteores," perhaps also the pyrophore of Hoffman. (6) Phosphores 

 produced by the union of a strong acid with pure phlogiston, which 

 results in a true sulphur, although all sulphurs or all unions of acid 

 and phlogiston are not phosphores. The Phosphore de Kunkel, 

 known also as " phosphore d'urine " or " le soufre phosphorique," 

 is " un soufre parfait," composed of phlogiston and a particular acid. 



ENCYCLOPEDIA BRITANNICA 



The first edition of the Encyclopedia Britannica (1768-1771) , in 

 three volumes, contains practically nothing on luminescence but the 

 second edition of ten volumes (1777-1784) makes up for the pre- 

 vious deficiency. The long article on electricity contains much on 

 the " electric light " or electroluminescence, while the article on 

 " light " is full of various luminescences. The discussion was taken 

 almost entirely from Priestley's book. Vision, Light and Colours 

 (1772) , to be considered in a later section on Priestley and his 

 contemporaries. 



This general survey of encyclopedias of the eighteenth century 

 reveals that the authors had excellent knowledge of the recognized 

 luminescences of their time. The different varieties are all men- 

 tioned but the explanations are understandably influenced by the 

 nationality and the period of the writer. Public instruction on 

 " cold light " was by no means neglected in the " Age of Enlighten- 

 ment." 



Textbooks of Chemistry and Physics 



The various textbooks of chemistry and physics must rank in 

 importance with encyclopedias for the diffusion of luminescence 

 knowledge. Since light is primarily a physical subject and fire a 

 chemical problem, in treating luminescences the distinction between 

 chemistry and physics breaks down. Since luminous phenomena 

 were sometimes thought of as fire and sometimes as light, they are to 

 be found in both chemical and physical treatises. 



It will be recalled that throughout the eighteenth century New- 

 ton's views became predominant, replacing the Cartesian conception 

 of the universe. Light was almost universally accepted as a cor- 



^° Possibly a reference to the mist observed over manure piles and marshes. 



