MECHANICAL ELECTRICITY. 287 



Exp. 34. May 2. A copper disc rubbed by 

 a rod of Bismuth, current produced vibrating to 

 30° stationary at 15° towards the Bismuth from 

 the copper. 



Exp. 35. A rod of zinc against the same copper 

 the edges of the disc being made sharp, 2\° to- 

 wards the copper, with a good cutting edge, 4° 

 constant. The zinc by this means being well cut. 

 Repeated 4°. Zinc robbing copper as in Exp. 31. 



Exp. 36. A piece of iron made sharp with filing, 

 when used with a large copper disc, 3^ inches 

 in diameter, gave a current of 8° stationary, while 

 the edge remained good and removed shavings, 

 from the iron towards the copper, iron positive. 



Exp. 37. Employed a piece of rod copper^ in 

 friction against the revolving copper disc, and not 

 the least indication of current was observed. 



Exp. 38. Silver thus employed against the 

 copper disc, gave a slight current of 1° from the 

 silver towards the disc. 



Exp. 39. With a steel tool, a constant current 

 of 2^° towards the copper. 



