204 History of Luminescence 



Substanzen, wenn sie sich verwesung nahern mit Riicksich auf das 

 Leuchten lebender Geschopfe." The other sections dealt with (I) 

 phosphorescence of natural and artificial preparations, inorganic 

 and organic, after exposure to light (i. e„ phosphors) ; (II) the phos- 

 phorescence of bodies as a result of rise in temperature, including 

 both phosphorus and heated oils; (IV) luminescence by mechanical 

 means such as fracture and friction, and (V) luminescence from 

 chemical mixtures of various kinds. Heinrich included not only 

 the work of his predecessors, but his own experiments, and in a final 

 series of papers (1820) answered the criticisms leveled against his 

 book. 



Space does not permit a detailed resume of Heinrich's views. His 

 classification of luminescences is quite modern, generally correspond- 

 ing to the divisions of his book, except that he grouped luminescences 

 from rise in temperature, according as the heating came from the 

 outside, as in thermoluminescence, or from internal heat due to 

 chemical mixture, solution, fermentation, etc. Heinrich attempted 

 to show that all bodies which luminesced contained acid. By irradia- 

 tion, warming, or friction, the material was to a certain extent 

 decomposed, some acid separated out, and since the acid contained 

 " light substance," part of the light ^vas freed. For example, he held 

 that because many diamonds phosphoresce they must contain car- 

 bonic acid, and since ice is phosphorescent it " has more acid prin- 

 ciple than water." Indeed, one might think that Heinrich had 

 taken over almost completely the acid theory of J. G. Lehmann, 

 who argued so vigorously in 1750 that all light resulted from acid 

 (see Chapter V under Tracts and Theses on Luminescence) . 



A great deal of attention was paid to phosphorescent wood, shining 

 fish and flesh, the general light of the sea, the luminescence of marine 

 animals, insects and men, both dead and living, classed together as 

 spontaneous decompositions. 



Heinrich grouped larger sea animals into three classes— naked 

 worms, crustaceans, and fish. The first luminesce only when alive, 

 the second both alive and dead, and the third only when dead. He 

 inquired how this could be, since they live in the same element 

 and eat the same material on which the formation of a light-sub- 

 stance must depend, for Heinrich declared emphatically there must 

 be a " Leuchtstoff." He made a detailed comparison of animal and 

 vegetable phosphorescence and came to the conclusion that both 

 are fundamentally alike and due to combustion of a luminous ma- 

 terial—the plant combustion weak but more noticeable than the 

 animal. He held that phosphorus in combination with hydrogen 

 and nitrogen was concerned in the burning, since phosphorus was 



