80 



TENSION RISES WITH LENGTH OF WIRE, 



of induction in the case of a coiled wire, an observation applying equally to an elon- 

 gated helix and to a flat spiral. Let us now determine whether the increased tension 

 is due to momentum. 



279. A copper wire 46 feet long and T V inch in diameter being arranged as the 

 discharger of a single pair of plates, a brilliant spark was seen to pass ; but with a wire 

 of the same diameter and a foot long, the spark was barely perceptible. The quantity 

 and tension in each case were now determined. 



TABLE B. 



Hence, by the use of a long wire, we greatly increase the tension of an electric current. 

 A second experiment, in which a wire i, and a third, in which a wire of an inch in 

 diameter, were used, gave analogous results. In neither of these cases, however, did 

 the tension rise so high as in the former ; it was lower as the diameter of the wire was 

 greater. ! 



280. This increase of tension follows the increase of the length of the wire, as the 

 following measures show. 



TABLE C. 



Thus, by successively increasing the aggregate length of the discharging wire, the ten- 

 sion continually increased, commencing at -4177, and finally becoming -8333. Similar 

 experiments with other wires gave similar results. 



281. Now is this remarkable rise of tension due to a momentum which the current 

 acquires on the wire 1 Or does it arise from the fact, that the wire acts simply as an 

 obstacle, reacting thereby on the electromotoric plates, the increase of tension being 

 due to them, not it 1 This is easily determined ; for if the rise of tension be due to the 

 plates and not to the wire, a short wire, slender enough to obstruct the current to the 

 same extent, ought to act equally as well as the long wire. 



282. This experiment, the result of which leads to the true theory of voltaic combi- 

 nations, I shall carefully describe. 



283. I took a copper wire 46 feet long and T V inch in diameter, and found that it 

 stopped a certain portion of the current coming from a single pair of plates. The mi- 

 crometer of the balance was now turned, and the needle brought accurately to zero. 

 Then I cut off from another slender copper wire such a length (2 feet 10 inches) as 

 to obstruct the current to the same extent as the long wire, the needle being brought, 

 when it was interposed in the path of the current, to zero. The secondary coil was 

 now introduced ; it of course stopped off a certain portion of the current ; but the mi- 

 crometer was again adjusted, until the needle was brought to zero. And now the long 



