134 ■ PHILOSOPHICAL TRANSACTIONS. [aNNO IJQl. 



is often very strong when no light is emitted. Rock crystal, quartz, feldspat, 

 white biscuit earthen-ware, and probably all such hard bodies, produce this smell 

 under water. Quartz stones, violently rubbed on each other for a few minutes 

 in a cup of water, communicate this smell, and a peculiar taste, to the water. 

 The taste is probably derived from an impalpable powder, which floats in the 

 water for many days. 



Derbyshire black marble, and the stinking blue fluor, give out, on attrition, a 

 strong smell peculiar to themselves, both in air and water ; they lose this pro- 

 perty by being once made red-hot. Quartz produces the smell equally strong in 

 fixed, pure, and common air. 



Mr. W. having now stated all the facts relative to phosphorescent bodies 

 which he had as yet been able to discover, offers a few reflections, tending to 

 show, that heat is the probable cause of the light produced from bodies by attri- 

 tion. It is easy to see why bodies emit light instantly when rubbed ; for they 

 often send out sparks as soon as the attrition commences, which proves that par- 

 ticles in their surfaces are instantly heated to redness by attrition. Since hard 

 bodies may be heated to redness by attrition, we have an excellent method of 

 discovering the lights they give out at that temperature, which could not be 

 effected by sprinkling their powders on a red-hot heater, as the light of the 

 powder would be mixed with that of the heater. In some cases of attrition, 

 bodies are raised to a temperature beyond visible red heat. The corner of an 

 angular piece of window-glass being applied to the circumference of a revolving 

 wheel of fine grit, part of its mass is worn away ; but a larger portion, lying 

 just above the abraded part, is heated to redness. Now, as all the heat which is 

 there collected, and a great deal more, which is carried away in the abraded 

 part, and conducted off by the air, and by the glass lying up to the red-hot 

 portion, has once occupied a smaller space in the part worn away ; it follows, 

 that the abraded portion, or aggregate of heated surfaces, has been heated to a 

 degree exceeding redness, by all the heat remaining in the red-hot paj-t, and by 

 the quantity of heat conducted off by the air and the adjacent glass ; and, con- 

 sequently, that each surface has been heated by the attrition to a degree as much 

 exceeding redness. 



After all, it remains entirely problematical, in what manner heat operates to 

 produce light from bodies: the air does not seem to have any concern in its pro- 

 duction, as bodies are equally luminous in almost all kinds of air, and when im- 

 mersed in liquids. The phosphorism of sugar is probably of a different kind 

 from that of the earthy class ; for though so soft and friable a substance, it 

 produces its light very copiously on gentle attrition. In speaking ot the attri- 

 tion of bodies on the stone wheel, Mr. W. has said that they became red-hot 



