120 History of Luminescence 



larly, ^vho looked on water as the chief constituent of matter, might 

 be expected to notice bioluminescences because of experiments on 

 juices of the body, or from the study of gases, but such is not the 

 case. His description of the flint stone, which might be a natural 

 phosphor, will be described in Chapter VHI. 



During the last third of the seventeenth century, several new lumi- 

 nescent materials were recognized, three of them the result of chemi- 

 cal experiments. In 1669 a substance was prepared which played 

 an all important part in the theories of animal luminescence until 

 after the middle of the nineteenth century. This was the element 

 phosphorus, isolated by Hennig Brand (or Brandt) . The announce- 

 ment caused great excitement in the intellectual world. Such men 

 as Kunkel, Krafft, Leibnitz, and Boyle were stimulated to rediscover 

 the original secret. Details of its history are given in Chapter XH 

 on Chemiluminescence. 



Another chemical discovery of the same period was the second 

 substance capable of storing light, a preparation of Christolph 

 Adolph Baldewein (1632-1682) , the phosphorus balduinus or her- 

 meticus, probably an impure calcium nitrate. Prepared in 1675, 

 Baldewein's phosphor created a renewed interest in luminescence 

 and started the search for additional examples. The title page of 

 his book is reproduced as figure 8. 



As a result, three more types of luminescence, all considered in 

 separate chapters, were to be recognized before the end of the cen- 

 tury. Knowledge of artificial electroluminescence in tubes may be 

 said to have started when Jean Picard (1620-1682) , in 1675, noticed 

 the greenish light emitted from the vacuum of a mercury barometer 

 when shaken. It was later studied by many savants, including 

 Johann Bernoulli (1667-1748) in 1700 and by Francis Hauksbee 

 (died 1713) in 1704 to 1708. Often referred to as the mercurial 

 phosphor, its connection with electricity became apparent early in 

 the eighteenth century, 



Thermoluminescence was recognized as an entity in 1676 by 

 Johann Sigismund Elsholtz's (1623-1688) observation that certain 

 varieties of fluorspar would luminesce on warming slightly. The 

 material, an impure calcium fluoride, was called phosphorus smarag- 

 dinus or the thermal phosphor. Thus by 1676, the principal phos- 

 phori were the Bolonian phosphor, the Baldeweinian phosphor, 

 phosphorus mirabilis, and phosphorus smaragdinus. This circum- 

 stance led to the publication of De Phosphoris Qiiatuor (1676) by 

 Elscholtz, and an account in the Phil. Trans. (1676) by Heinrich 

 Oldenburg (1626-1678) entitled, " Four Sorts of Factitious Shining 

 Substances." 



