Measure of the relative Tension of Electric Currents. 277 



Again, I took a copper wire, 242 feet long and y^ inch in 

 diameter, and adjusted to it a fine iron wire as before: the 

 extremities of this wire were tinned ; it was 12^ inches long. 

 Either of these wires being used as a discharger, brought the 

 needle to the same point of the scale. On using the secondary 

 wire and the long wire together, I adjusted the needle accu- 

 rately to zero, and then passing the current through the fine 

 wire and secondary wire, it came again to zero. And this was 

 repeated often, and so near was the adjustment, that when an 

 assistant turned first one and then the other wire on, it could 

 not be told which was in action, or whether the current had 

 come along the long or the short wire. A long wire there- 

 fore impresses no sort of change on a current, but merely 

 serves as an obstacle ; for in the first case we had one wire 

 sixteen times longer than the other, and in this we have a 

 wire more than 230 longer than the one with which it is 

 compared, yet the tension has increased only to the same 

 amount in both. 



And the same results were obtained by the voltameter. 



The current that flows in a simple closed voltaic circle may 

 be resisted in two ways: 1st, the length of the wire connect- 

 ing the plates may be increased, as in the foregoing experi- 

 ments ; 2nd, the connecting wire remaining of constant length, 

 the distance of the plates may be increased : the result is the 

 same in both cases, a rise of tension. 



Table D. 



So that, whether we obstruct the current by lengthening 

 the connecting wire, or by increasing the distance of the plates, 

 the general effect is the same, the tension immediately rises; 

 that increase of tension being due to the plates themselves, 

 and not to the channel of conduction. This brings us to the 

 third proposition : — 



" That there are two different methods of accomplishing 

 these disturbances, and thereby of raising the elastic force of 

 a current. 1st, That tension may be augmented by the sacri- 

 fice of quantity ; Volta's plan of a reduplicated series, and 

 Henry's ribbon coil in its condition of equilibrium, being ex- 

 amples : 2nd, By the introduction of new affinities in the ex- 



