276 Dr. Draper on the Use of a Secondary Wire as a 



wire ^, and a third, in which a wire j 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. 



This increase of tension follows the increase of the length 

 of the wire, as the following measures show. 



Table C. 



Ex. 



1. 



2. 

 3. 

 4. 

 5. 



Current from a single pair of plates 



— — a long wire introduced 



a second ditto, added 



third 



fourth . , 



Quantity. 



Tension. 



Thus, by successively increasing the aggregate length of the 

 discharging wire, the tension continually increased, com- 

 mencing at '4-177, and finally becoming '8333. Similar ex- 

 periments with other wires gave similar results. 



Now is this remarkable rise of tension due to a momentum 

 which the current acquires on the wire? Or does it arise 

 from the fact, that the wire acts simply as an obstacle, react- 

 ing thereby on the electromotoric plates, the increase of ten- 

 sion being due to them, not it? This is easily determined; for 

 if the rise of tension be due to the plates and not to the wire, 

 a short vyire, slender enough to obstruct the current to the 

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



This expei'iment, the result of which leads to the true 

 theory of voltaic combinations, I shall carefully describe. 



I took a copper wire, 46 feet long and y g inch in diameter, 

 and found that it stopped a certain portion of the current 

 coming from a single pair of plates. The micrometer 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 micrometer was 

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

 now the long wire being introduced, and the slender one taken 

 away, the needle came again to zero. But I suppose, if the 

 long wire had impressed more tension on the current than 

 the slender one, either by momentum or otherwise, more 

 electricity should have passed the secondary wire when it 

 was used, which is not the case. 



