on the Production of Light from Bodies. 41 
fusion, and being then much harder than loaf sugar or borax, 
both which are luminous from moderate attrition, gives no 
light, though rubbed with much violence *. 
If two pieces of glass or quartz be strongly rubbed against 
each other, and then applied to the fine down of a feather, the 
down is not sensibly affected ; if the same glass be rubbed on 
woollen cloth, and placed near the feather, the down is imme- 
diately attracted. 
Rock crystal, quartz, feldspat, white unglazed earthen ware, 
Derbyshire black marble, and probably all phosphorescent 
bodies, insoluble in water, give out their light on rubbing 
them under water, as copiously as in air. Hard white sugar, 
from the outside of the loaf, gives out its light when rubbed 
in oil. Bodies seem equally luminous in atmospheric, pure, 
fixed, and inflammable, air. 
All hard earthy bodies emit a peculiar smell on attrition. 
The most remarkable for this property are chert, quartz, feld- 
spat, biscuit earthen ware, and rock crystal : this smell does 
not differ much in kind, though it does considerably in inten- 
sity. Many of the softer bodies yield the same smell, but 
in a less degree, and, probably, none are entirely without it. 
It appears to be strongest where the friction is greatest : it 
* The Count de Razoumowski has investigated the luminous property of bodies 
in a way which appears to me very unfavourable for the discovery of their true lights. 
He rubbed, not one piece against another of the same body, but, all of them against 
quartz or glass : he finds several metals luminous from this treatment, and at- 
tempts to draw some curious conclusions from the colour of their lights. I tried these 
metals in his own way, and found that no light was emitted except when the violence of 
the blow shattered the quartz or glass ; a piece of the indurated alum will excite light 
from rock crystal, by breaking its surface, but this is the light of the fragments of the 
crystal rubbing on each other, and not of the alum. 
MDCCXCII. G 
