Phosphorescence and Colour by Electricity. 271 



20th Discharge both colours deeper, the light remains longer. 



40th the colours are very rich, purple inclining to red towards the 



lust. 

 100 explosions rendered the green tint very vivid and yellower, the purple was 



increased to intense richness. 



1 60 discharges gave intense light nearly white when heated, succeeded by 

 brilliant green, rich purple, of long duration; then yellow, and tints of 

 violet. 



This portion has been heated and electrified above fifteen 

 times, the shocks and the temperature being very variable and 

 intense, but the substance does not seem to have undergone 

 any deterioration in its capacity for producing phosphoric 

 light. 



The fact of the communication and restoration of phospho- 

 rescence may be regarded as established by the examples 

 adduced. 



The following tabular view will show the permanence of the 

 property so communicated. The minerals selected are the 

 FLUORS enumerated in the preceding table : they were calcined, 

 electrified, and divided into two portions ; one of which was 

 exposed to sunlight in glass tubes ; the other was wrapt in 

 papers, and kept in darkness. 



The portions were heated after they had been exposed to, 

 or secluded from daylight during the following periods : 



N After 21 days After 21 days in Portions kept in the dark 



in Light. Darkness. for three months. 



1. Very faint purple I Good light, green and pur- ( Yellow, ending with bright pur-> 

 light ......... \ pie ................. \ pie, good light. 



Strong yellow andj Pale yellow, green, violet, ~\ Tints of yellow, orange, pale- 

 greenish colour. \ a.nd purple^ strong light/ green, and purple. 



" d ' ribt 



6. Yellow and orange Yellow ............... Strong light, yellow and orange. 



7 - 



8. Yellow light, cori-l a , ,. , , , .. 



fined to spots. . J Stron g h gH P ale S*>w G and violet. 



9. No light ....... Chiefly feeble purple light Fleeting tints of purple. 



T2 



