292 MECHANICAL ELECTRICITY. 



produced a current of 2^° to 5°. But on using a 

 disconnected turning tool to the same side, and 

 near the wire, the current was still 2|° to 5° ; and 

 yet the tool could have induced a current of 30° 

 or 40°. On increasing the pressure of the wire 

 against the cylinder, current 6° to 9°. On using 

 the turning tool as before, no increase of current 

 could be perceived. Yet, on applying a lighted 

 taper at the junction of the wire to the cylinder, 

 current 35°. 



The turning tool does not, therefore, augment 

 the heat of surface of the disc, so as by heat 

 to produce a current of thermo-electricity. 



Exp. 44. Attached the two galvanometer wires 

 to the piece of Bismuth used in the experiments 

 for the production of thermo electricity, one at 

 each end. Rubbed one extremity of the Bismuth 

 with force against the revolving copper disc, for 

 one minute, and yet no current was indicated, 

 which would have been the case, if the heat 

 developed by friction in these cases had been the 

 source of development of the fluid. For instantly 

 on applying the same end to the flame of a spirit 

 lamp, the galvanometer began to deflect. Re- 

 peated the experiment with like results. And on 



