go Mr . T. Wedgwood's Experiments and Observations 
distinguished himself by many curious experiments made with 
it ; he found that his phosphorus might be made to shine by- 
heating it, after it had ceased to be luminous of itself, but that 
the same heat would have this effect for a certain time only. 
Heat has been observed by several of these philosophers to pro- 
mote the emission, and to shorten the duration, of the light of 
phosphor i. 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 to- 
gether. Pott extended this discovery to all pure flints and 
crystals, and to porcelain. Keysler found glacies marise to be 
luminous when heated. M. de la Metfierie has observed some 
neutral salts and calcareous earths to be luminous in the same 
way. The Count de Razoumowski, in a Memoir of the Phy- 
sical Society of Lausanne, shews 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 upon one another ; he finds quartz to give out its 
light under water. 
This brief account includes, as far as I am able to collect, 
the chief discoveries which have been made concerning lumi- 
nous bodies. I was led to make the following experiments 
from observing the light which proceeds from two quartz 
pebbles rubbed against each other : I searched for this property 
in many other bodies with success, but met with two soft 
stones, which did not afford any light upon the most violent 
attrition. Conceiving that heat might probably be the cause 
of the light emitted by quartz from attrition, I attributed this 
failure to a want of sufficient hardness in these friable stones for 
producing the necessary heat. Accordingly, sprinkling some 
