384 Dr Brewster on the Phosphorescence of Minerals. 
heat^ or by attrition, or by simple pressure ; but he does not 
appear to have noticed the same property in other minerals. 
Although the developement of light in decayed wood, in ani- 
mal bodies, and in artificial phosphori, was studied with much 
attention in the 17th and 18th centuries, yet little attention 
seems to have been paid to the phosphorescence of heated 
minerals. Fluor-spar, and one or two other substances, had been 
accidentally found to emit light, when placed upon a hot iron; 
but the subject had never been investigated with care, till the 
year 1792, when Mr Thomas Wedgwood laid before the Royal 
Society, his Experiments and observations on the production 
of light from different bodies by heat, and by attrition^ The 
general method which he employed was, to reduce the body 
to a moderately fine powder, and to sprinkle it by small por- 
tions at a time, on a thick plate of iron, or mass of burnt lu- 
ting, made of sand and clay, heated just below visible redness, 
and removed into a perfectly dark place.” By this means, he 
found the following minerals to be luminous by heat. 
Fluor-spar of various kinds. 
Marbles of various kinds. 
Red feldspar from Saxony. 
Diamond. 
Oriental ruby. 
Iceland spar. 
Steatite from Cornwall. 
Black Hint. 
Rock-crystal from E. Indies. 
White asbestos. 
Red irony mica. 
Alabaster. 
The Abbe Hauy •[*, who availed himself with singular success 
of the physical properties of minerals, has employed their phos- 
phorescence as a distinguishing character. Like Mr Wedgwood, 
he developed it, by throwing the mineral, when reduced to pow- 
der, upon a hot iron, and in this way he found it only in the 
following substances : 
Fluor spar. 
Iceland spar. 
Arragonite. 
Phosphate of Lime. 
Grammatite, 
Carbonate of Barytes. 
Carbonate of Strontites, 
Harmotome. 
Dipyre. 
Wernerite. 
» Phil. Trans, 1792, vol. 82. p. 28. 270. 
Traite de Mineralogies Par. 1801, vol. i,”p. 235. 273. 
