Phosphorescence 331 



havior of oyster-shell phosphors prepared by his own method. 

 Wilson not only translated Beccari's articles but wrote a treatise of 

 his own, A Series of New Experiments Relating to Phosphori and 

 the Prismatic Colours they Exhibit in the Dark (London, 1775). 

 This treatise dealt entirely with phosphors excited by sunlight; no 

 bioluminescences were mentioned. Using the same experimental 

 procedure, Wilson confirmed much of Beccari's work. He observed 

 the bright phosphorescence of paper, especially when hot or slightly 

 browned (but not when charred) , toasted bread, linen, cotton, gum 

 arable, gum copal, sugar, joiners glue, some kinds of bone and hair, 

 feathers, and shells. He noted that paper wet with hot water and 

 hot oil would phosphoresce and the oil itself gave off light, but the 

 most interesting observation had to do with sugar pressed into paper 

 by a hot iron, which Wilson found to phosphoresce with a green 

 color. 



Many minerals and gems would also phosphoresce, as Dufay had 

 shown, but Wilson was disappointed that the 200-grain diamond of 

 Lord Pigot showed no phosphorescence, although a smaller yellow 

 diamond was very bright. He was particularly interested in the 

 discovery that oyster shells previously dissolved in nitric acid and 

 calcined in a crucible with copper, gave all the colors of the rain- 

 bow when exposed to sunlight and examined in a dark room. Wilson 

 tried many such experiments, calcining oyster shells with various 

 metals, alkaline salts, neutral salts, inflammable bodies like oils, and 

 phosphorus, in some cases obtaining material that phosphoresced 

 with light of many colors, in other cases only red or only green 

 phosphorescence. 



He observed that steel added to the shells gave better results (i. e., 

 more prismatic phosphorescent colors) than iron, and concluded 

 that steel, since it was made from iron by heating over charcoal, 

 which abounds in phlogiston, must have imparted that phlogiston 

 to the oyster shells. He in fact believed that " prismatic colours . . . 

 depend upon that inflammable principle [phlogiston] which the 

 shells received in consequence of its being disengaged by the force 

 of the fire, from the bodies they were in contact with in the cruci- 

 ble." Later Wilson discovered that mere heating of oyster shells 

 over a " sea-coal " fire without adding anything would result in ma- 

 terial exhibiting beautiful prismatic phosphorescent colors and had 

 to admit that chance played a considerable part in his experiments. 



Wilson's idea of light emission was connected with his study of 

 excitation by different colored lights and was strongly influenced 

 by the phlogiston theory, which was still in vogue at that time. 

 Since every luminescence color appeared under red (or green, blue. 



