136 THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



the glow was increased when the gem was put into hot 

 water. 



These results led to the conclusion that though under 

 certain circumstances the light was accompanied by elec- 

 trical development, as when friction had been used, there 

 was no necessary connection between the two properties. 

 The gem would shine without the least trace of attract- 

 ive power. 



(Among substances endowed with this property, one 

 of the best was discovered about a century ago by Can- 

 ton. Still known as Canton's phosphorus, it is easily 

 made by burning oyster-shells in an open fire until they 

 have become white ; then, having pulverized them with 

 about a quarter of their weight of flowers of sulphur, 

 they are once more brought to a dull red heat in a cru- 

 cible. This completes the preparation. A convenient 

 mode of using the substance is to provide a piece of tin 

 plate-two or three inches square, brush over one side of 

 it with gum or glue water, then dust upon it from a fine 

 sieve some of the powdered phosphorus. In this manner 

 a uniform white surface is procured, well adapted for 

 experiments. 



If on such a surface a key or other opaque object be 

 laid, and it then be exposed for a moment to daylight, 

 on carrying it into a dark room and removing the key, 

 a spectral shadow will be seen, depicted in black, and its 

 contour marked out by the brilliantly glowing phos- 

 phorus surrounding it. After continuing to shine for 

 some minutes, the light gradually fades, and finally be- 

 comes extinct. If, this having been accomplished, the 

 phosphorized plate be put away in a box or drawer 

 where not a ray of light can reach it, and kept therein 

 for days or even weeks, on exposing it in a dark room, 

 on a plate of warm metal, the phantom shadow will 

 emerge, perhaps even more strongly than at first. 



