Phosphorescence 333 



Camillo Galvani 



Shortly after Wilson's (1775) book appeared, a general account 

 of the Bolognian stone was published at Bologna by Camillo Gal- 

 vani, Delia Pietra Fosforica Bolognese (Bologna, 1780) , dedicated 

 to six " Agl' Illustrissimi ed Eccelsi Signori Senatori Assunti dello 

 Studio Di Bologna," mostly counts and marquises. 



In the twelve chapters of the ninety-one-page book, the history, 

 color, shape, internal structure, and analysis, etc., of the Bolognian 

 stone are described in considerable detail, and a comparison made 

 with other phosphors. Beccari and his co-workers are particularly 

 referred to and ten pages of experiments reported. Galvani ended 

 with various reflections on the subjects presented. On the whole 

 the book is a good resume of contemporary knowledge, although 

 John Canton and Benjamin Wilson are not mentioned. 



Excitation of Phosphorescence by Spectral Colors 



The discovery of the new phosphor of John Canton in 1768, and 

 the ease with which it could be prepared from oyster shells, started 

 a wave of research on these substances which revolved about three 

 principal questions: (1) the color of phosphorescence after exposure 

 to different colored lights; (2) excitation by electric discharges; (3) 

 whether the light was the result of combustion. Study of the rela- 

 tion between the color of the exciting light and that of the phosphor 

 was largely initiated by an incorrect report. In 1771, Father Gio- 

 vanni Battista Beccaria (1716-1781) of Turin (no relation to Jacopo 

 Bartholomeo Beccari of Bologna) ivhose principal interest was elec- 

 tricity, wrote a letter to Canton, published in the Philosophical 

 Transactions, in which he claimed that Canton's phosphorus, illumi- 

 nated under red, yellow, and green glasses, would luminesce with 

 red, yellow, and green light. This finding was contrary to the pre- 

 vious work of Zucchi (1652) and Zanotti (1748) on the Bononian 

 phosphor, and, as we have seen, differed from the results of Ben- 

 jamin Wilson (1775) on oyster shell phosphors. 



Since the publication of the Beccaria note, a large number of 

 investigators working with a variety of phosphors have mostly con- 

 cluded that phosphors behave as if the light they emit depends on 

 an inherent peculiarity of the phosphor rather than on the excit- 

 ing light. However, interpretation is often difficult because of the 

 intensity of phosphor luminescence in different colors. The Jesuit, 

 Joseph Edler von Herbert (1725-1794) , professor of physics at 

 Vienna and canon of St. Stephan, discussed the matter in his book 

 on fire, De Igne, etc. (1773) . Herbert regarded fire and light as the 



