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CHAPTHR, I. 
PHOSPHORESCENCE AFTER INSOLATION. 
SEVERAL substances manifest the strange property 
of emitting ight when they are placed in darkness, 
after having been exposed for some time to the 
direct rays of the sun. In some cases avery short 
exposure to sunlight is sufficient to excite the 
manifestation of this remarkable property, and in 
others the direct rays of the sun are not necessary : 
it suffices that the substance experimented upon 
be exposed to the dull hght of a cloudy day. To 
this phenomenon the denomination of Phosphores- 
cence after msolation has been given. 
The substances which possess this property in 
the highest degree are the Bologna stone, or solar 
phosphorus, certain varieties of fluor-spar and 
carbonate of lime, some fossils, calcined shells or 
pearls, phosphate of lime, arseniate of lime, etc. 
Many diamonds shine with brilliancy in the dark 
if they have previously undergone an exposure of 
some seconds? duration only to solar ight. But 
