152 THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



ton's phosphorus, etc., which were made to glow by ex- 

 posure to a Leyden spark, were placed. But it made no 

 difference in the light whether the magnetism was on 

 or not. 



It was also found that the electric spark from a con- 

 tact-breaker would communicate phosphorescence to all 

 the various bodies in use in these experiments, and that 

 up to a certain point the intensity of the light increased 

 with the number of sparks received. 



Phosphorescence is not communicable from one body 

 to another. Having provided two polished plates of 

 fluor-spar, one of them was made to glow by an electric 

 spark, and the other was immediately put upon it. No 

 communication of phosphorescence took place ; the sec- 

 ond piece remained perfectly dark. 



Some authors state that fluor-spar does not become 

 phosphorescent by exposure to the sun ; but this re- 

 mark does not apply to all varieties of it. Thus some 

 chlorophane, which had been ignited in a glass tube till 

 it had ceased to shine, was pulverized and again ignit- 

 ed in a platinum crucible. It emitted an emerald light. 

 A slip of wood was now put on it to screen a part of 

 its surface, and it was exposed to the sun for a few 

 minutes. On ignition, it shone again finely, with a green 

 light, the shadow of the wood being beautifully depict- 

 ed. The same having been repeated a great many 

 times, it appeared that the phosphorescence at last be- 

 gan to decrease, perhaps by frequent ignition causing a 

 change. 



A screen of yellow glass intervening between the sun 

 and some powdered chlorophane prevented phosphores- 

 cence, but it took place through a plate of polished fluor- 

 spar. When the light of an electric spark was used in- 

 stead of the sunshine in this experiment, the fluor-spar 

 prevented phosphorescence. 



