Phosphorescence 319 



Stone did not burn the skin " because being so fine, it has not the 

 strength to make the impression upon the nerves." The reason the 

 stone could imbibe and emit light for years was because " this little 

 fire rarifies and exalts other Sulphurs in the inside of the Stone, 

 which take the place of those that are lost." 



" The Stone takes the light of the colour of the fire which was 

 used in the calcination, because its Sulphur is tinctured with this 

 colour, . . . when the stone has lost its properties a new calcination 

 rarifies and exalts the sulphur which remains." 



Lemery held that the luminescence appeared in a vacuum because 



the sulphureous parts of the Stone being of a fineness proportioned to 

 the fire of light, there is no need of Air to light them, nor to preserve 

 them burning: For if the light pass and preserve itself in a vacuum, it 

 can also set on fire a very subtile Sulphur, and preserve it burning. But 

 if this reason does not please, and that you think Air absolutely neces- 

 sary for burning the Bolognian Stone, you may find as much as is needful 

 in that which we call a vacuum, since it is impossible entirely to pump 

 the air out of a vessel of glass or crystal, but there will always remain a 

 little, do what you can: and this little quantity of air is sufficient for 

 lighting so fine a Sulphur. 



Lemery then compared the Bolognian stone with the phosphorus 

 of urine which does require air to luminesce and also burns the 

 fingers and decided that the latter " cannot be set on fire by light 

 alone, because its Sulphur is too gross to be burnt by so fine a fire 

 as it [light] is: There must be a pair of Bellows such as the Air is, 

 to put the saline and sulphineous parts of the Phosphorus in motion 

 that by rubbing violently upon one another, they may take fire . . . 

 for this there must be a great disposition to motion in the parts of 

 the matter." On the other hand the Bolognian stone has such 

 exalted sulphur " and so well purified from the grosser parts that 

 it has no need of any other motion than that of the light to set it 

 on fire; its Sulphur will not take fire at night, because then there is 

 nothing which can light it: All the Air in the world is not capable 

 to move its parts so swiftly as is necessary to inflame it; they are 

 too subtile to receive any impression from it." Such statements 

 give an excellent idea of the thought of a French chemist at the 

 time. 



The views of French physicists are also of interest. Although 

 Descartes did not mention the Bolognian phosphor, both Jacques 

 Rohault (1671) and Antoine Le Grand (1680) wrote concerning it. 

 Rohault gave the following explanation in his Trait e cle Physique, 

 the English edition of John Clark (1723) . 



