Phosphorescence 335 



stances (some of which were given him by J. B. Beccari of Bologna) 

 in the electric light, i. e., the electric spark, before 1753. He found 

 that those bodies which retain the solar light in greatest degree, also 

 retain the electric light, for example the well-known phosphors and 

 also paper and sugar. Beccaria wrote: " A full discharge of my 

 usual coated plate, sent through powdered sugar, produced the 

 beautiful light of a copious luminous flower, and left as it were a 

 Glory ^^ of light around the place which drew the sparks. I also 

 found that a like Glory remained imprinted on the surface of a 

 very fine dry linen cloth." 



Joseph Priestley, in his book on electricity (1769: 244) , has com- 

 mented on some later experiments of a Mr. Lane, as follows: 



That electric light is more subtle and penetrating, if one may say so, 

 than light produced in any other way is manifest from several experi- 

 ments, particularly the remarkable one of Mr. Hawkesbee; but none 

 prove it so clearly as some made by the ingenious Mr. Lane, who gives 

 me leave to mention these: 



When he had, for some different purpose, made the electric shock 

 pass over the surface of a piece of marble, in the dark; he observed, that 

 the part over which the fire had passed was luminous, and retained that 

 appearance for some time. No such effect of the electric shock having 

 ever been observed before, he repeated the experiment with a great 

 variety of circumstances, and found it always answered with all calcarious 

 substances, whether animal or mineral, and especially if they had been 

 burnt into a lime. And, as far as he had tried, many more substances 

 would retain this light than would not do it; among others several vege- 

 table substances would do it, particularly white paper. Tiles, and brick 

 were luminous, but not tobacco-pipe clay, though well burnt. 



That gypseous substances, when calcined, were luminous, appeared 

 from bits of images made of plaister of Paris; and of this class, he says, 

 is the famous Bolognian stone. But many bodies, he found, were lumi- 

 nous after the electric stroke, which were not apparently so, when ex- 

 posed to the rays of the sun. 



He made these curious experiments by placing the chains, or wires 

 that led from the conductor to the outward coating of his jar, within one, 

 two, or three inches (according to the strength of the charge) from one 

 another, on the surface of the body to be tried, and discharging a shock 

 through them. If the stone was thin, he found, that if one chain was 

 placed at the top, and the other at the bottom, it would appear luminous 

 on both sides after the explosion. 



Mr. Canton, to whom these experiments were communicated, clearly 

 proved, that it was the light only that the substances retained, and noth- 

 ing peculiar to electricity; and, moreover, after frequent trials, discovered 



*' A splendid luminous appearance around heads of saints or the Virgin Mary or 

 God. 



