104 EtECTEIC LIGHT. 



Argillaceous electric light from the explosion. But a slate used in this 

 genus. neighbourhood, brought from Colly Weston, in Northamp- 



tonshire, and which effervesces with acids, is by far the most 

 beautiful. When the shock is taken above the centre of a 

 piece some inches square, not only the part immediately be- 

 low the rods is luminous, but the surface of the slate appears 

 bespangled with very minute brilliant points to some distance 

 from its centre; and when the points of the dischargers rest 

 upon the surface of the slate, these minute spangles are de- 

 tached, and scattered about the table in a luminous state. 

 The track of light between the rods continues phosphores- 

 cent several minutes. 



Hone stone, of a dirty greyish colour, gave a good spark, 

 and was phosphoric by the explosion. 



Fuller's Earth gave a good bright spark, but was very 

 slightly luminous, except in the track the fluid left in its 

 passage from one rod to the other. 



Reddle gave no spark, but a purple stream, attended with 

 avery sharp hissing sound. It was rather more luminous 

 than Fuller's Earth. 



Armenian Bole affords a spark, which is ramified upon its 

 surface. It is not luminous by the electric explosion; even 

 when the points of the dischargers rest upon it, no track of 

 light is visible ; but several minute fragments are shivered 

 irora its surface. 



Terra Sigillitica of the shops gives a spark, and is phos- 

 phoric after the explosion. 



Basalt gives sparks which are radiated upon its surface, 

 but not ramified as in Chlorite and micaceous Schist. It was 

 phosphoric only in the track formed by resting the dis- 

 chargers upon it. 



Bricks of various kinds afforded small purple sparks, of 

 a bright red colour on the surface. They were very slightly 

 luminous by the explosion ; but afforded a bright track of 

 light between the points of the dischargers when they rested 

 upon them. 



Tiles of different kinds afforded similar results to the 

 bricks, except that most of the tiles were rather mare 

 luminous than the bricks, when the electric explosion was 

 made above them, especially a yellow tile, with a redish 

 tinge in the fracture, which, from its greater phosphores- 



