AFTER INSOLATION. 17 
for instance, with sugar, dry chalk, and many 
other substances. 
Among bodies slightly phosphorescent after in- 
solation, we may name melted potash and soda, 
dry nitrate of lime, and chloride of calcium, sul- 
phate of potash, sulphate of soda, arragonite, calc- 
spar, dolomite, carbonate of strontia, carbonate of 
baryta, different calcareous earths, phosphates of 
lime, sulphate of baryta, sulphate of strontia, etc. 
According to Kd. Becquerel, other substances 
are phosphorescent after insolation, but in order to 
observe it we must remain some time in a dark 
room, and then, by means of a hole in the shutter, 
expose the body experimented upon to the light, 
at the same time keeping the eyes closed until the 
hole in the shutter is shut again. By experiment- 
ing in this manner, many substances are seen to 
be phosphorescent for a few seconds after insola- 
tion; amongst others numerous minerals, salts, 
organic substances such as paper, gum, sugar, 
teeth, etc. 
Long before Becquerel, however, we find in the 
article ‘Phosphorus,” of the ‘Hneyclopeedia Perth- 
ensis,’ it has been found “that almost all terres- 
trial bodies, upon being exposed to light, will ap- 
pear luminous for a little while in the dark, metals 
only excepted.” 
