VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. l^Q^ 



these philosophers to promote the emission, and to shorten the duration, of the 

 light of phosphori. Fluor has been long known to give a fine bright light when 

 heated. D. Hoffman discovered that red blende and feldspat were luminous 

 when pieces of either were rubbed together. Pott extended this discovery to all 

 pure flints and crystals, and to porcelain. Keysler found glacies mariae to be lu- 

 minous when heated. M de la Metherie has observed some neutral salts and cal- 

 careous earths to be luminous in the same way. The Count de Razoumowski, in 

 a Memoir of the Physical Society of Lausanne, shows that quartz and glass give 

 out light, when struck by almost any hard body, and that some few other bodies 

 are luminous, when pieces of the same kind are rubbed on one another; he finds 

 quartz to give out its light under water. 



Mr. W. was led to make the following experiments from observing the light 

 which proceeds from 2 quartz pebbles rubbed against each other : he searched 

 for this property in many other bodies with success, but met with two soft 

 stones, which did not afford any light on the most violent attrition. Con- 

 ceiving that heat might probably be the cause of the light emitted by quartz 

 from attrition, he attributed this failure to a want of sufiicient hardness in these 

 friable stones for producing the necessary heat. Accordingly, sprinkling some 

 of their powder on a plate of iron nearly red-hot, he observed it emitting a con- 

 siderable light. Extending this mode of trial, he found that the phosphorism of 

 almost all bodies might be made apparent either by heat or by attrition ; he 

 therefore divided the subject of this paper into 2 parts. 1. On the light pro- 

 duced by heat — 2. On the light produced by attrition. 



1 . The best general method of producing the light by heat is, to reduce the 

 body to a moderately fine powder, and to sprinkle it, by small portions at a time, 

 on a thick plate of iron, or mass of burnt luting made of sand and clay, heated 

 just below visible redness, and removed into a perfectly dark place. The follow- 

 ing is a list of such bodies as he found to be luminous by this treatment, ar- 

 ranged according to the apparent intensity of their light. 



1. Bluefluor, from Derbyshire, giving out a fetid smell on attrition. 



2. Black and grey marbles, and fetid white marbles, from Derbyshire. 

 Common blue fluor, from Derbyshire. Red feldspat, from Saxony. 



3. Diamond. Oriental ruby. Aerated barytes, from Chorley, in Lanca- 

 shire. Common whiting. Iceland spar. Sea shells. Moorstone, from Corn- 

 wall. White fluor, from Derbyshire. 



4. Pure calcareous earth, precipitated from an acid solution. Pure argillaceous 

 earth (of alum.) Pure siliceous earth. Pure new earth, from Sydney Cove. 

 Common magnesia. Vitriolated barytes, from Scotland. Steatites, from Corn- 

 wall. Alabaster. Porcelain clay of Cornwall. Mother of pearl. Black flint. 

 Hard white marble. Rock crystal, from the East-Indies. White quartz. Por- 



VOL. XVII. S 



