MEMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. 135 



of Seville, speaking of the "lightning-stone," says, "Si 

 sub clivo positus fuerit fulgorem rapit sidereum." That 

 condition is previous exposure to light. 



The discovery of the elementary substance now known 

 as phosphorus drew the attention of the cultivators of 

 natural science to this singular property, and under the 

 names of sun-stones, light magnets, noctilucas, etc., vari- 

 ous shining bodies were introduced. But the first truly 

 scientific examination of the subject was made by Boyle, 

 on the occasion of observing that a certain diamond be- 

 longing to Mr. Clayton, and subsequently purchased by 

 Charles II., emitted li^ht in the dark. Though he does 



O O 



not seem to have been aware of it, the fact itself was not 

 new, for the alchemist Albertus Magnus says in the thir- 

 teenth century that he had seen a diamond which glowed 

 when it was put into warm water. A diamond rubbed 

 upon gold becomes beautifully luminous; as Bernouilli 

 remarks, it shines like a burning coal excited by the bel- 

 lows. 



A diamond rubbed upon gold emitting light! the 

 imaginary or intrinsic value of the substances employed 

 adds to the glory of the phenomenon. A light, too, that 

 cannot be extinguished by water, and yet so ethereal and 

 pure that it can set nothing on fire. Here certainly were 

 facts of interest enough to excite the philosophers of the 

 last century. 



The chief points ascertained by Boyle respecting the 

 diamond were that it shone by friction with various 

 bodies, and at the same time displayed electrical devel- 

 opment ; that it also glowed when warmed by a candle, 

 the fire, a hot iron, or even when placed on the skin. 

 Under the latter circumstances it exhibited no electricity, 

 being unable to attract a hair held near to it. He also 

 found that it would shine under water, various acid or 

 alkaline liquids, or when covered with saliva, and that 



