PHOSPHORESCENCE. 



gatello seems to have done, but sent both the mi- 

 neral and the substance produced from it, to the 

 princes and learned men of the day, thereby con- 

 tributing more than any other person to make 

 known this singular discovery. 



The stone discovered by Cascariolo is now 

 known as Barytine, or Heavy-spar (sulphate of 

 baryta). By heating it with charcoal he had trans- 

 formed it into sulphur et of barium, a substance 

 which has the curious property of shining in the 

 dark, after it has been exposed for some time to 

 the rays of the sun. 



Many years after its discovery, the German che- 

 mist Marggraf found an easy and certain method 

 of preparing it, by making into a paste with water 

 a mixture of pulverized barytine and flour, and 

 submitting the whole to heat in a closed crucible. 

 The sulphuret thus produced is placed in a well- 

 corked glass jar, or made into stars, which shine 

 marvellously in the dark after they have been ex- 

 posed to the sun for a short time. 



Such is the history of the discovery of the sub- 

 stance first known to be phosphorescent by inso- 

 lation. For many years it has been sold in the 

 streets of Bologna as a curiosity, under the name 

 of Solar Phosphorus, or the Bologna Stone. Marg- 

 graf showed that other minerals, other varieties of 

 heavy-spar, were capable of furnishing similar 

 "light magnets" or "luminous stones," and at 



