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 Ed. 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 ' Encyclopaedia 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." 



