The Eighteenth Century 157 



fessor of physics, medicine, anatomy, and chemistry and later became 

 its president. He was associated with Domenico Maria Gusmano 

 Galeati (1686-1775) , Giuseppe Monti (1682-1760) , and Francesco 

 Zanotti (1692-1777) . The experiments of these men were similar 

 to those of Dufay, and greatly extended the materials known to be 

 phosphors. They included such organic substances as paper, natural 

 plant products, and dried animal parts, although the luminescence 

 might not last longer than a second or two after exposure to sun- 

 light. The work was quite new and fascinating; details will be found 

 in Chapter VIII on phosphorescence. 



Apart from the discovery that so many common substances are 

 luminescent, a chief interest in Beccari derives from the classifica- 

 tion of luminescences which he adopted in the two papers which 

 appeared in 1744 and 1747. His views are well expressed in the 

 opening paragraph of a translation by B. Wilson (1776) , entitled: 

 An Account of a Great Number of Phosphori Discovered by J. B. 

 Beccari. 



1. Of bodies that give light in the dark there are several kinds. For 

 some bodies throw out light spontaneously, and others upon being 

 excited. And of the former kind some shine with a natural light as 

 glow-worms, dates [i. e., Pholas], and a good many aquaticks: others 

 enjoy an adventitious light, as rotten woods and the flesh of some quad- 

 rupeds and birds. These are not naturally phosphori, but owe that prop- 

 erty to some particular cause; which generally is putrefaction, and some- 

 times an insensible change introduced into the natural constitution of 

 the parts. 



2. The other kind of bodies which become phosphori upon being 

 excited, or are at least assisted by that means, may be distributed into 

 different species, according to the different modes of excitation. These 

 modes are attrition, heat, the free admission of the air, and lastly, being 

 exposed to the external light. 



Here we have practically a modern classification of luminescence by 

 method of excitation, as if the words triboluminescence, thermo- 

 luminescence, chemiluminescence and photoluminescence were used. 

 Beccari 's monograph deals entirely with the latter, excitation by 

 exposure to light. He related that there were not sufficient samples 

 of the Bolognian stone to supply the demand since the secret of 

 preparation was mostly kept in a few prominent families, and phi- 

 losophers were glad when Baldwyn prepared his phosphor from 

 chalk and spirit of nitre. ^ 



* The work of Beccari and others of the early eighteenth century had focused atten- 

 tion on the extraordinarily large number of luminous materials. At the same time 

 there was a growing interest in electricity. It seemed logical to regard " phosphores " 



