214 Mr W. S. HARRIS on the Heat excited in 



the electrometer E was only affected by as much of the charge 

 as could not pass immediately in the direction of the small wire. 

 When, therefore, the conducting power of the latter was caused 

 to vary, either by change of temperature, size, or quality, such 

 variation was simultaneously shewn by the elevation or depres- 

 sion of the fluid along the graduated scale of the electrometer, 

 and of these changes the instrument seemed to be most deli- 

 cately sensible. 



13. (g) It does not appear to be of any consequence, how the 

 heat is derived by which the conducting power becomes dimi- 

 nished ; thus, when the wire m n was caused to transmit the 

 charge of a second battery of sufficient power to heat it some- 

 what considerably, the same result ensued. This was very 

 pleasingly shewn by the following arrangement: Two electro- 

 meters, A and B, Fig. 5, being placed in the circuit tr'rn't, and 

 the elevation of the fluid observed in each : one of them, A, was 

 connected with a second battery C, and in such way, that the 

 wire in the electrometer A might exclusively transmit the 

 charge of this second battery, as well as that of the first *. In 

 this instance, the elevation of the fluid in A was increased, whilst 

 that in B was decreased ; so that the two electrometers A and B 

 appeared to vibrate as if delicately balanced, the slightest change 

 in the one being accompanied by an opposite change in the 

 other. 



14. It may be inferred from the foregoing experiments, that 

 the indications of the electrometer (2) may be always taken as a 

 measure of the variations in the action of a voltaic combination, 

 provided we employ a wire in the bulb above a certain diameter ; 

 and that the limit to the diameter of such a wire, in any given 

 case, may be determined experimentally by observing the action 



* This can be readily managed by one particular arrangement of the connecting 

 wires, which admits of the two batteries operating separately. 



