10(3 



OBSERVATIONS ON SPONTANEOUS LIGHT. 



Latent light is HI. The imhibed Held, after behw in a latent State, it excited 

 excluded from , _>,, • ,, . ~ TT 



Canton's phof- an(i rendered luminous by the Agency of Heat. 



Exp. 7. Some fmall pieces of the phofphorus, after having 

 been illuminated, were depofited in the laboratory ; when the 

 light by degrees faded away, and became totally invifiblc. 

 They were kept in this dark ftate for the fpace often days, 

 and then placed one after another upon a heated bar of iron, 

 as in the laft experiment, upon which they quickly became 

 exceedingly luminous. 



From an experiment made by the ingenious Mr. Canton, 

 I obferve, that fome of his phofphorus, contained in glafs 

 balls hermetically fealed, and heated in the above manner, 

 gave a confiderable degree of light, after it had been kept in 

 a ftate of darknefs more than fix months. Phil. Tranf. Vol. 

 LVIII. page 342. 



§ 2. 



The Effects of Cold on imbibed Light, 



. « 



EXPERIMENT. 



Coldextinguifh- About 15 grains of the phofphorus were put into a half- 



of Canton's ce P n * a *> containing two drams of cold pump water, that 



phofphorus, &c. had been deprived of its air by boiling. The phial was then 



corked, and expofed for fome time to folar light, whereby 



the phofphorus became finely illuminated. In this flate, it 



was immediately put into a frigorific mixture, compofed of 



fnow and fea fait, and retained there about 30 or 40 minutes, 



when it was taken out, and the light found to be totally ex- 



tinguifhed. The phial was then placed in fome water, at 



about 60° temperature, and the light gradually revived, and 



became as brilliant as before it had been expofed to the cold. 



This experiment was frequently repeated, and always with 



the fame refult, 



I cannot but remark, that in the courfe of experiments on 

 this fubjeci, the fuperior power of folar over that of fponta- 

 neous light w^s very apparent. For, the firft trials being 

 made in fmall phials, containing only atmofpheric air with the 

 phofphorus, the light was with fome difficulty totally extin^ 

 guiihed ; and, after the phials were taken out of the frigorific 



mixture^ 



