(ss PHOSPHORESCENCE. 
2. Phosphorescence caused by increase of temperature by 
heating, as in the case of the Diamond, Fluorspar, Topaz, and some 
other minerals, e g., silicates. 
3. Phosphorescence due to mechanical stress, such as by friction, 
percussion, cleavage. Many substances respond to one or other of 
these influences, such as quartz crystals and pebbles, sugar, card- 
board. A very good general illustration of this kind of phosphor- 
escence is afforded by sharply tearing one of those products of art 
and science known as a paper collar. 
4. Phosphorescence, as the result of electricity, shewn by 
shells, minerals, jewels. This kind of phosphorescence can take 
place just as well in vacuo. 
5 Phosphorescence, following what is called Insolation, or the 
exposure of substances to direct sunlight or a strong source of 
artificial light, shewn by sulphides and phosphates of the alkaline 
earths. Examples—luminous paint (mainly calcium sulphide), paper, 
silk, sugar, amber, the teeth. The rays which cause the strongest 
effects of this kind are situated in that part of the spectrum called 
the ultra-violet rays akin in their nature to those which cause the 
beautiful phenomenon in some liquids known as fluorescence, e.g., 
quinine in solution, paraffin, esculin, &c. Phenomena of this kind 
may be also caused by rays in the region beyond the red, influencing 
eosine and chlorophyll, &c. 
Besides the ordinary sources of phosphorescence in living and 
non-living matter, the following cases are on record :— 
Wood rotting in a fairly dry place. 
Phosphorescence at a point where a branch had been broken off 
a tree. 
Luminous fungi. 
Phosphorescence on the surface of coal workings, said to have 
been seen with dazzling effect in a coal mine in the vicinity 
of Dresden. 
