82 Prof. Draper on the Phosphorescence of Bodies. 



In consequence of this theft, Kunkel succeeded in discovering 

 what the substance was, and made kuo\ni the method of its pre- 

 paration. 



The particular condition under which these preparations shine 

 in the dark was very quickly perceived to be the same as the old 

 authors had recognised. Isidore of Seville, speaking of the 

 " lightning-stone," says, " si sub divo positus fuerit fulgorem 

 rapit sidereum." That condition is previous exposure to the 

 light. 



The discovery of the substance now known as phosphorus, 

 drew the attention of the cultivators of natural science to this 

 singular property; and under the names of sunstones, light- 

 magnets, noctilucas, &c., various shining bodies were inti'oduced. 

 But the iu'st truly scientific examination of the whole subject was 

 made by Mr. Boyle, on the occasion of observing that a certain 

 diamond belonging to Mr. Clayton, and subsequently purchased 

 by Charles II., emitted light in the dark. Though he does not 

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

 the alchemist, Albertu.s Magnus, says, in the thirteenth century, 

 that he had seen a diamond which glowed when it was put into 

 wann water. A diamond rubbed upon gold becomes beautifully 

 luminoiis ; as Bernouilli remarks, it shines like a burning coal 

 excited by the bellows. 



A diamond rubbed upon gold emitting light ! the imaginary 

 or intrinsic value of the substances employed adds to the gloiy 

 of the phsenomenon. A light, too, that cannot be extinguished 

 by water, and yet so jethereal 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 Mr. Boyle respecting the dia- 

 mond were, that it shone by friction with various bodies, and at 

 the same time displayed electrical development ; but that it also 

 glowed when warmed by a candle, the fii-e, a hot iron, or even 

 when placed on the skin ; and under these circumstances exhi- 

 bited no electricity, being unable to attract a hair held near it. 

 He also foimd that it would shine under water, various acid or 

 alkaline liquids, or when covered -with saliva, and that the glow 

 was increased when put into hot water. 



These results evidently led to the conclusion, that though 

 mider certain circumstances the light was accompanied by elec- 

 trical development, as when friction had been used, there was no 

 necessary connexion between the two properties. The gem would 

 shine without the least trace of attractive power. 



Eai'ly in the last century two diff"erent hypotheses were intro- 

 ducedfor the explanation of these various cases of phosphorescence. 



1st. That phosphorescent bodies act like sponges to the light. 



