82 Mr. Pearsall on the Effects of 



and likewise introduced into the tube ; after several discharges 

 had been made, most of the splinters had acquired a blue tint ; 

 when heated they evolved a strong light of a pale yellow colour. 



Larger pieces electrified, assumed a blue tint, giving also a 

 blue light when heated ; but when these pieces were crushed 

 into small fragments, electrified in the tube, and then heated, 

 they evolved a pale yellow light, as in the preceding experi- 

 ment. 



In some instances, however, fragments gave a light, at first 

 blue, afterwards changing to a straw colour ; but in every repe- 

 tition the colour and intensity of the light differed according 

 to the size of the specimen, as in the above examples. 



The blue tint caused by electricity seemed to be superficial, 

 or nearly so; for when some coloured portions were broken, 

 they were colourless in the interior, but tinted upon the external 

 edges. 



The colourless parts were not phosphorescent, while the 

 coloured and exterior parts were. So that it is probable that 

 the phosphorescent property is also conferred principally upon 

 the superficies, which may be the cause of the differently- sized 

 pieces evolving differently-coloured light. 



To avoid any fallacy from the transfer of metal from the 

 wires, and its oxidation by the electrical explosions, experi- 

 ments were repeated, and the discharges were made from 

 platinum points, with the same resulting blue colour as before. 



Other substances were then examined, which, however, pro- 

 duced nothing immediately bearing upon the preceding experi- 

 ments, excepting, however, that it was found that, by passing 

 twelve discharges through a diamond, it afterwards evolved a 

 pale blue light when heated ; it had been made red-hot previous 

 to electrization, but without effect. 



Two other diamonds gave no light when heated, until from 

 twelve to twenty discharges had been made over them, when 

 they, also, gave a pale blue light by heat. 



Diamonds probably vary in respect to this property ; for a 

 cut diamond gave no light, neither could any be imparted to 

 it by electricity; whilst, on the contrary, another diamond 

 was found slightly phosphorescent by heat, shewing feebly a 

 pale bluish light ; and this specimen, when electrified and again 

 heated, gave a stronger blue light than any other diamond. 



