35 
on the Production of Light from Bodies . 
bodies, dropt, in moderately fine powder, into a flask contain- 
ing a small quantity of boiling oil at the bottom, emit a copi- 
ous flash of light as soon as the powder touches the surface of 
the oil ; when the particles of the body have lain at the bottom 
of the heated fluid for about a minute, they become but faintly 
luminous ; if the flask be then agitated so as to raise some of 
these particles out of the oil, and lodge them on its sides, they 
suddenly rekindle into the same brightness as at first, and pre- 
serve this re-assumed livstre for some time ; and even after being 
again washed down into the oil, they may be readily dis- 
tinguished from the particles which have remained at the bot- 
tom. This experiment is extremely beautiful, and is not at all 
obstructed by the faint light of the oil ; it succeeds best with 
the stinking blue fluor of Derbyshire. 
Powdered marble, and probably every other body, when 
spread upon the heater, in the receiver of an air-pump, is 
equally luminous during the exhaustion and re-admission of 
the air. 
Bodies are by far most luminous the first time they are 
heated, but cannot, perhaps, be entirely deprived of this pro- 
perty by any number of heatings, nor by any degree of heat. 
Chalk, fluor, and feldspat, give out a very faint light on the 
heater, after having been exposed to a smart red heat in an 
open crucible, in small quantities, and kept frequently stirred 
for several hours ; the feldspat was equally luminous when laid 
hot upon the heater, or first cooled, and then laid on. Chalk 
and fluor were not tried in this particular. A bit of glass, melted 
in a heat of 120° of my father's thermometer, and as soon as 
it is cold reduced to powder, gives out light on being thrown 
upon the heater below redness. 
F 2 
