Mr. T. Wedgwood's Experiments and Observations, &c. 29 
calcined in a particular manner, it acquired the remarkable pro- 
perty of absorbing the light of the sun, of retaining it for some 
time, and of emitting it in the dark : subsequent experimenters 
found it to do the same with the light of a candle. In 1663, 
Mr. Boyle observed a particular diamond to give out a light 
almost equal to that of a glow-worm, when heated, rubbed, 
or pressed ; and investigated very fully the nature of the light 
of dead fish, flesh meat, and rotten wood. In 1677, Baldwin 
of Misnia discovered, in the residuum of a distillation of chalk 
and nitrous acid, a phosphorus similar in its properties to the 
Bolognian, but not possessing the phosphoric virtue in so emi- 
nent a degree. In 1705, Mr. Francis Hawkesbee found that 
glass rubbed on glass, in common air, in the vacuum of an air- 
pump, or under water, <£ exhibited a considerable light." In 
1724, M. du Fay discovered that almost all substances which 
could be reduced to a calx by fire only, or after solution in the 
nitrous acid, absorbed and emitted light like the phosphorus of 
Cascariolo and of Baldwin ; and that some diamonds, eme- 
ralds, and many other precious stones emitted light in the dark, 
after being exposed to the rays of the sun. About the same 
time, Beccaria of Turin found almost every body in nature to 
be luminous after a similar exposure : he added, too, this very 
important discovery ; that an artificial phosphorus, exposed to 
the light in a coloured glass vial, emits, in the dark, rays of the 
identical colour of the vial. Mr. Margraaf, by an analysis of 
the Bolognian stone, shews that it contains vitriolic acid united 
to calcareous earth, and that all gypseous stones treated like 
the Bolognian, provided they are pure from iron, become phos- 
phorescent. About the year 1764, Mr. Canton made a phos- 
phorus of sulphur and oyster-shells calcined together, and 
