Phosphorescence and Colour by Electricity. 277 



were increased : for, unless the intense heat at the interrup- 

 tion of the circuit were avoided, it would destroy the phospho- 

 rescence which might be produced by the vivid light and con- 

 tinuous current. 



Portions of calcined oyster and scollop-shells were sub- 

 mitted to the voltaic light from points of charcoal attached to 

 the extremities of a voltaic battery in good action, of a hundred 

 pairs of four-inch plates ; the discharge being repeatedly in- 

 termitted, so as to resemble a series of ordinary sparks, guard- 

 ing against the elevation of the temperature of the tube and 

 the inclosed fragments. After ten minutes' exposure, they 

 seemed to have acquired phosphorescence through the glass ; 

 for, when heated, they appeared faintly luminous. 



Common calcined purple fluor did not appear affected by 

 close proximity to the voltaic discharge. 



Calcined oyster-shell powder, exposing a large surface to 

 the direct light, was phosphorescent when heated. 



Calcined purple fluor was placed in a tube, the voltaic dis- 

 charge likewise effected in the tube over and through the frag- 

 ments, which were thus influenced by the voltaic discharge and 

 currents, from charcoal and from metal poles, but no phos- 

 phorescence appeared when the substance was heated. 



A silver capsule, forming the termination of one pole, was 

 strewed with calcined fluor spar ; the charcoal extremity of the 

 other pole traversed the metal plate, causing sparks and silent 

 discharges to pass repeatedly through the portions of mineral ; 

 but the fluor was not luminous when heated. 



Calcined scollop-shell, by the same arrangement, was ren- 

 dered phosphorescent upon the subsequent application of heat. 



So that there are great differences with respect to the induc- 

 tion of phosphorescence in these bodies by ordinary and by 

 voltaic electricity. 



On the Colouration of Fluor Spars by the Action of Electricity. 



It was announced in the former communication, that certain 

 fluor spars, rendered white by calcination, became coloured 

 after they had been electrified a distinct blue colour appear- 

 ing upon specimens which originally were deep purple. As 

 the cause of colour in these minerals has often been a subject 



