4 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 sulphuret 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 mso- 
lation. or 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- 
oraf showed that other minerals, other varieties of | 
heavy-spar, were capable of furnishing similar 
“light magnets”? or ‘luminous stones,” and at 
