Thermoluminescence 371 



ous marbles, chalk, and ruby powder with a red to orange lumi- 

 nescence, diamond and sea shells with a white luminescence. Quartz, 

 iceland spar, and white porcelain also showed a white luminescence. 



Some of these materials were luminescent " by attrition " but the 

 order of brightness was not the same. The duration of the thermo- 

 luminescence was very variable. In general, the experiments indi- 

 cated a certain parallel between thermoluminescence and tribolumi- 

 nescence but it was far from exact. 



Wedgwood also found salts of various kinds and some organic 

 materials— paper, linen, wool, wood, waxes, and oils— to be lumi- 

 nescent on heating.*' This effect was no doubt in some cases an 

 actual combustion, as M. van Marum (1776, 1782) had observed 

 the luminescence of oils when heated. At a time when combustion 

 was not thoroughly understood, the similarity of diverse phenomena 

 made interpretation difficult. Wedgwood himself called the light 

 "some sort of inflammation," and Dessaignes (1809, 1810) and 

 C. B. J. Williams (1835) showed that no light appears in absence 

 of air (see Chapter XIII) . 



Nineteenth-Century Contributions 



It will be noted that the previous work had been mostly descrip- 

 tions of new thermophosphors, with some experimentation. The 

 trend continued in the early nineteenth century. Rene Just Haiiy 

 (1743-1822), the eminent French mineralogist and discoverer of 

 piezoelectricity (in 1782) , tested systematically a large number of 

 minerals on a hot plate. Among them about a dozen showed marked 

 thermoluminescence. The list is contained in his Traite de Miner- 

 alogie (1801). Dessaignes (1809, 1810) , Heinrich ( 1 8 1 2) , and Grot- 

 thus (1815) added more examples. 



By far the most important contributions were made by the last 

 three men, who used their findings as a basis for the theories of 

 phosphorescence which have been described in Chapter VIII. Like 

 others, Dessaignes held that almost all organic and inorganic bodies 

 would luminesce when scattered as powder on a hot plate at 256° C. 

 The nature of the plate made no difference. However, most of the 

 organic substances which he tested required air and the light was 

 actually a burning. His study of heat and light excitation led him 

 to the idea that in the material there was a phosphoric fluid of an 

 electrical nature, which was set into vibration by moderate heating 

 but destroyed by strong heating. 



' Brugnatelli (1800; in Italian, 1797) noticed that ground sugar, cotton, feathers, 

 wool, and camphor would " luminesce " on a hot plate. 



