Mi^asure of the relative Tension of Electric Currents. 275 



all these cases the measured numbers were absolutely the 

 same as before. Therefore there is no change impressed on 

 a thermal current, either in relation to quantity or tension, 

 by making it pass along a coiled wire, or by acting on it with 

 a magnet or a bar of soft iron. 



(c.) The same experiments wei'e made with a hydro-electric 

 current, and they gave the same results. 



{d.) The above-mentioned [b) thermal current was passed 

 along one of the wires of a double helix, and through the 

 other wire a hydro-current was passed, from a single pair of 

 plates; but the tension and quantity remained the same as be- 

 fore. On sending a current of still greater intensity, viz. from 

 a voltaic series of five pair of plates, the same result was still 

 obtained ; the hydro-current had power enough to decompose 

 water. 



(e.) On altering the polar communications, and thereby 

 changing the course of the current, no change whatever in the 

 primary current, either as to quantity or tension, was ob- 

 served. 



It is well known, that by using a long wire as a discharger 

 of a single pair of plates, a spark will be obtained of a much 

 more brilliant character than when the current passes through 

 a shorter wire; it is upon this fact that the flat spiral ribbon 

 coil is constructed. Many electricians have supposed that the 

 results obtained by this beautiful contrivance were partly due 

 to the inducing action of the successive spires, but chiefly to 

 a long and easy conducting channel being open to the cur- 

 rent, which gathers momentum in its passage. I have al- 

 ready shown that there is no permanent action of induction in 

 the case of a coiled wire, — an observation applying equally to 

 an elongated helix and to a flat spiral. Let us now determine 

 whether the increased tension is due to momentum. 



A copper wire, 46 feet long and -^-^ inch in diameter, being 

 arranged as the discharger of a single pair of plates, a bril- 

 liant spark was seen to pass; but with a wire of the same dia- 

 meter and a foot long, the spark was barely perceptible. The 

 quantity and tension in each case was now determined. 



Table B. 



Hence, by the use of a long wire we greatly increase the ten- 

 sion of an electric current. A second experiment, in which a 



T2 



