314 History of Luminescence 



After dinner, I enquired of a priest and Dr. Montalbano, to whom I 

 brought recom'endations from Rome . . . the composition of the lapis 

 illuminabilis, or phosphorus. He shew'd me their property (for he had 

 several) , being to retain ye light of the sun for some competent time, by 

 a kind of imbibition, by a particular way of calcination. Some of these 

 presented a blew colour like the flame of brimstone, others like coals 

 of a kitchen fire. 



Evelyn's statement thus confirms the fact that the luminescence was 

 of different colors. 



The light of the stone was accepted as a fact by Sir Thomas 

 Browne (1605-1682) in the second edition of his Pseudodoxia Epi- 

 demica (1650), although he regarded the stories of luminous gems 

 as vulgar errors. John Ray (1628-1705) in 1663, when at Bologna, 

 actually visited Signor Gioseppi Bucemi, a chymist, who prepared 

 the Bononian stone or " Lapis phosphorus," which, " if exposed a 

 while to the illiuninated air, will imbibe the light, so that with- 

 drawn into a dark room, and there look'd upon, it will appear like a 

 burning coal; but in a short time gradually loses its shining, till 

 again exposed to the light." ^* No samples were taken to England, 

 as an anonymous note ^^ appeared in the Philosophical Transactions 

 of the Royal Society (No. 21) in 1666, regretting the fact that prepa- 

 ration of the Bononian stone had apparently been lost. 



The most important discovery of the mid-century came from one 

 of the Italian workers, Nicolai Zucchi (1586-1670) , a teacher of 

 mathematics at the Collegio Romano in Rome. His large book, 

 Optica Philosophia, from Lugduni in 1652, included pages on the 

 Bolognian phosphor, as well as many experiments on light in gen- 

 eral. He not only showed that the Bolognian stone luminesced more 

 intensely the stronger the light to which it was exposed, but also 

 that the color of the luminescence was the same whether exposed to 

 white light or whether the white light had passed through glasses of 

 red, yellow, or green color. From this he concluded that the light is 

 not merely absorbed as such, but " rather it excites and unites with 

 a spiritous substance contained in the stone, and when the illumina- 

 tion has ceased, this substance gradually dissipates and becomes 

 unsuitable for exhibiting a visible glow." ^^ Although Zucchi's expla- 

 nation is a little difficult to understand, it has the germ of truth in 

 it as indicating that the light absorbed is not the same as the light 

 emitted. His experiment was a very important one, not repeated 



^* Travels through the Low Countries, by John Ray, 1673. 



^^ Possibly by R. Boyle, as he wished to study the effects of a vacuum on the light. 

 See Phil. Trans. 2: 581-600. 1668. 



^* Modified from a translation of Mrs. Annemarie Holborn. 



