On Light. 19 
TABLE continued. 
Colour an Intensity of 
the Light. 
Names of the Minerals.|Colour of the Minerals, 
Corundum, 
Anatase, 
Tungstate of lime, 
Quartz, 
Amethyst, 
Obsidian, 
Mesotype from Au- 
vergne, 
Glassy actinolite, 
Ruby silver, 
Muriate of silver, 
Carbonate of copper, 
Green telesie, 
Brown, 
Dark, 
Yellowish-white, 
Bright. 
Reddish-yellow. [coal. 
Brilliant like a burning 
Very faint. 
Faint. 
Pretty bright; dirty 
[blue. 
The phosphorescence of 
these nine minerals] Very faint. 
was observed in the|Little specks. 
pistol barrel. Rather bright. 
Blue. 
Very faint. 
Pale blue, and pretty 
: Pega : bright. 
The phosphorescence of anatase is entirely different from that 
of the other minerals. It appears suddenly like a flame, and is 
soon over. Dr, Brewster found, in opposition to what Mr.Wedg- 
wood had stated, that exposure of green fluor spar to the heat of 
a common fire in a crucible for half an ‘hour, entirely deprived it 
of phosphorescence. Though he placed one fragment for se- 
veral days in the beams of a summer sun, and even exposed it 
to the bright light near the focus of a burning glass, he could 
not succeed in obtaining from it the slightest indication of phos- 
phorescence. The light emitted i combustion belongs to the 
same head. The phosphoric light of minerals has the same pro- 
perties as the direct light of the sun, according to Dr. Brewster. 
4. Light emitted from bodies in consequence of the action of 
extraneous light. ‘To this section we refer solar phosphori. The 
most powerful of these is the artificial compound of Canton. If 
we mix three parts of calcined oyster shells in powder, with one 
of flowers of sulphur, and, ramming the mixture into a crucible, 
ignite it for half an hour, we shall find that the bright parts will, 
on exposure to the sunbeam, or to the common day-light, or to 
aa electrical explosion, acquire the faculty of shining in the dark, 
so as to illuminate the dial of a watch, and make its figures le- 
gible, It will, indeed, after a while, cease to shine; but if we 
keep the powder in a well corked phial, a new exposure to the 
sunbeam will restore the luminescence. Oyster shells, stratified 
with sulphur, in a crucible and ignited, yield a more powerful 
phosphorescent substance than the powder. It also must be 
kept in a close phial. When the electric discharge is transmitted 
along the surfaces of certain bodies, or a little above them, a 
somewhat durable phosphorescence is occasioned, which probably 
belongs to this division, 
C2 Sul- 
