324 History of Luminescence 



are corpuscles of different sizes (red large and violet small) thrown 

 off by the light source. For example, a phosphor calcined in a fire 

 with considerable green light receives the green sized corpuscles in 

 its pores, which thereby take and conserve exactly the size charac- 

 teristic of green. Thus the phosphor is comparable to a sieve that 

 allows only certain sized grains to pass. When the phosphor is 

 exposed to the light of day, it is only the green corpuscles, of the 

 proper size to fit its pores, which are absorbed. Or, if one supposes 

 that daylight merely sets in movement the sulphurs of the phosphor 

 and they ignite, these sulphurs directly represent in their confor- 

 mation {monies) the figtue, the size, and the degree of movement 

 which the fire of calcination has communicated to them and which 

 is partly conserved. That is why, if one transports this stone or 

 rather this sponge of light from daylight to obscurity, it appears 

 like a green coal for some minutes. 



Cohausen also looked upon the calcination of the natural stone 

 as producing a certain texture, but instead of referring the lumi- 

 nescence to movement of sulphur, he regarded the emitted light as 

 something connected with the air or the aether. The calcined ma- 

 terial was able to hold the air (aether) in such a way that it could 

 vibrate in the same manner that light in air itself was believed to 

 vibrate. 



Bartholomeo Beccari and Co-workers 



Work on the Bolognian phosphor was continued by the Italians, 

 Jacopo Bartholomeo Beccari-'* (1682-1766), a physician and pro- 

 fessor of physics at the Institute of Sciences and Arts at Bologna, 

 and Francesco Maria Zanotti (1692-1777) ,-^ later president of the 

 University of Bologna. This work had the support of Count Mar- 

 sigli, whose book (1698) has already been mentioned, and Domenico 

 Maria Gusmano Galeati (1686-1775) , a physician and also professor 

 of physics at the Institute of Bologna. The study was started in 1711 

 but not published until much later (Zanotti, 1748) . 



Many of their experiments at the Bolognian Institute were quanti- 

 tative, designed to determine the relation between the intensity, 

 duration, and color of the exciting light and corresponding quali- 

 ties of the emitted light. Only a very short exposure, one second, 

 was sufficient to excite a luminescence which lasted thirty minutes. 



^' J. B. Beccari, De adamente aliisque rebus in phosphororum numerum referendis, 

 Comment. Bonon. II, 1:274-303, 1745. Cojnment. Bonon. XII, 2 (2) : 136-179, 1746; 

 2 (3): 498-519, 1747. See the English translation in Phil. Trans. 44:81-91, 1746, and 

 the appendix to B. Wilson's book (1775) . A French translation will be found in the 

 Collection academique etranger 10: 525-545 and 594-600, 1775. 



■2^ F. M. Zanottus, De lapide bononiensi. Comment. Bonon. 1: 181-205, 1748. 



