108 SOLAR FHO&PIIOIII. 



quest of some alchemical secret was induced to calcine a parcel of 

 Bolognian spar (a sub-species of heavy spar or native sulphat of ba- 

 ryte), which he had procured from Monte Paterno, in the neigh, 

 bourhood of the city; and observed, that whenever this substance, 

 thus prepared, was placed in a dark room, after having been ex- 

 posed to the sun, it continued to emit faint rays of li^ht for some 

 hours afterwards. 



In consequence of this interesting discovery, the Bolognianspar 

 came into considerable demand among natural philosophers, and 

 the curious in general, so that the best way of preparing it was 

 found an object of some pecuniary importance. This seems to 

 have been hit upon by the family of Zagoni, who supplied all Eu- 

 rope with Bolognian phosphorus, till the discovery of more power, 

 ful phosphoric put an end to their monopoly. Margraaf, some 

 jears afterwards, proved that other species of sulphated bar) te 

 might, under particular management, be made to produce a simi. 

 lar effect. 



In the year 1677, nearly half a century after the discovery of 

 the Bolognian phosphorus, G. A. Baldwin, a native of Misnia, 

 observed, that if nitrat of lime were evaporated to dryness, and 

 then formed into a compact mass by fusion at a red heat, it would 

 exhibit the same property of imbibing and emitting light as the 

 former, only somewhat inferior in degree : hence this preparation 

 obtained the name of Baldwin's phosphorus. 



lu 1730, M. du Fay, who is justly celebrated for his electrical 

 researches, directed his attention to this subject, and observed, that 

 all earthy substances, susceptible of calcination, either by mere 

 fire, or when assisted by the previous action of nitrous acid, 

 possessed the property of becoming more or less luminous when 

 calcined and exposed for a short time to the light : that the most 

 perfect of these phosphor! were limestones, and other kinds of 

 carbonated lime, gypsum, and particularly the topaz ; and that 

 some diamonds were also observed to be luminous by simple expo, 

 sure to the sun's rays, without being previously ignited ; while 

 flint, sand, jasper, agate, and rock crystal, were inphospho. 

 rescent. 



Not long after, M. Beccaria discovered that a great variety of 

 other bodies were convertible into phosphor!, by exposure to the 

 mere light of the sun ; not only the varieties of carburet and sul. 

 phat of lime, but organic animal remains 3 and geodes lined with 



