MBMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. 



4. TV photpliorescence accompanied with a development 

 of electricity ? 



It has been stated already that the experimenters of 

 the last century paid a good deal of attention to this 

 point. Du Fay established the fact that though in many 

 cases of phosphorescence there is a development of elec- 

 tricity, there are many others in which the light seems 

 to be wholly unattended by any disturbance of that 

 kind. 



I have repeated some of these experiments, and with 

 the same result, proper care being taken to avoid fric- 

 tion and other obvious causes of electrical excitement. 

 Thus a flat piece of chlorophane, phosphorescing power- 

 fully, was put on the cap of a very delicate gold-leaf 

 electroscope, but no disturbance whatever was percep- 

 tible. 



A large crystal of fluor-spar was made to phosphoresce 

 brilliantly along a line about half an inch in length by 

 passing the spark of a Leyden-jar between two blunt 

 iron wires, the ends of which were that distance apart, 

 and resting on the face of the crystal. Over this line of 

 blue light, which was pretty sharply marked, and which 

 lasted for several minutes, a fine hair was held. This 

 would have been readily attracted and repelled by the 

 feeblest excitation of sealing-wax, but in this case it 

 wholly failed to yield any indication whatsoever. 



In connection with the foregoing experiments, I may 

 mention some miscellaneous facts. Some attempts' were 

 made to determine whether phosphorescent bodies in 

 the field of a powerful electro-magnet would exhibit any 

 change of property. Six Grove's pairs were caused to 

 magnetize a good electro-magnet ; the power they could 

 give to it would enable the keeper to support about 

 half a ton. Between its polar pieces chlorophane, Can- 



