MECHANICAL ELECTRICITY. 291 



to produce this uncertainty, which subjects them 

 to the government of the earth's polarity. 



Is the current induced by mechanical opera- 

 tions, simply thermo Electric or not ? 



Exp. 42. Immersed the lower half of the 

 Bismuth cylinder in water at 55°. By turning it 

 with a steel tool about one minute, (the water 

 revolving around the cylinder the whole period,) 

 a current was constantly maintained, at length 

 from 35° to 40°, fine turnings being produced. 



The water, 9 oz. and 2 drs. in which the Bismuth 

 disc was immersed, and which would derive 

 the principal part of the heat from the whole 

 process, being heated only to 57" or 2°,* and the 

 tool immersed in a like quantity of water, was 

 found to increase it only half a degree. 



Exp. 43. A conducting wire, made to press 

 against the revolving Bismuth disc slightly, 



* Observe, the turnings alone which were made, would, as 

 will be hereafter shown, heat the water nearly to this amount, 

 and the tool would in this instance heat the water more than 

 the disc. Therefore the heat derived from the disc would be 

 less than \°. 



