g(S Mr. T. Wedgwood’s Experiments and Observations 
Ouartz, from the same original piece, is equally luminous 
when the powder is directly thrown upon the heater — when 
it is previously made red hot, and then cooled and thrown on 
— or when a fragment of some size has been made red hot, then 
pounded and thrown on. 
For the most part, the softest bodies require the least heat 
to become luminous ; marble, chalk, fluor, &c. give a faint 
light when sprinkled on melted tin just becoming solid. As the 
temperature of the heater is raised, they continue to give out 
more and more light. 
Vitriols of iron, copper, and zink, previously exsiccated, 
when thrown on earthen ware or metal made nearly red hot, 
give minute flashes of light of momentary duration, such as 
appear from some of the metallic precipitates, particularly 
zink, on a similar treatment ; with this difference, however, 
that the light of most of the precipitates is of a reddish hue. 
The light of the metals is white, and exactly similar to that 
of some earths. 
White paper, when dipped in a solution of sal ammoniac, 
and slowly dried, becomes black upon the heater, and then 
gives out much less light than common paper. 
If a lump, of the size of a small bean, of fluor, marble, feld- 
spat, or any of the most phosphorescent bodies, be laid upon the 
heater, the light proceeds gradually upwards from the part in 
contact with the heater, till the whole mass is thoroughly illu- 
minated ; if the same piece be heated a second time, it is much 
less luminous; nor, if it be broken, are the fragments at all 
more luminous, either then, or after having been exposed for 
a month to the light and sunshine. 
A little boiling oil at the bottom of a glass flask, when 
