Prof. Wartmann on Electric Induction, 551 



application of heat diminishes the conductibility of the metals 

 which I have employed, it may be imagined that the hetero- 

 geneous wire, the solder of which was raised from 116° to 

 140°, according to circumstances, would no longer leave 'i 

 passage, except for an imperceptible fraction of the current.'^ 

 cv69. Leaving the circuit of one of the pairs invariable, that 

 Of the other was modified by insensible degrees (as the rheo- 

 stat allows of conveniently), by shortening the whole length 

 of its additional wire 11 metres, or by adding it to it, which 

 nearly destroyed its own current. The course of the needle 

 of the rheometer never indicated other than a progressive in- 

 crease or diminution of deviation, and proved the preponde- 

 rating influence of one current over the other, or their mu- 

 tual neutralization, on account of their equality in opposite 

 directions. qi sq ii'.^- 



70. The experiment was repeated, sending the two currents 

 in the same direction by the wire of the rheometer. It gave 

 an analogous result, that is to say, t/ie most complete abse?tce of 

 intei'mittence in the progress of the needle for a constantly in- 

 creasing addition or subtraction of the additional wire. '^ ^f'^ 



71. I have made other trials with hydro-electric piles (6)^ 

 employing Breguet's thermometer (5, c) as a means of metf^ 

 suring. Two of Daniell's pairs were connected with that in- 

 strument by means of two very equal brass conductors, No. 4<. 

 On establishing a second circuit with two other similar wires, 

 so that the current, issuing from the same poles, should tra- 

 verse the thermometer in an inverse direction to the first, 

 the needle retuined to its zero of departure and remained 

 there. In order to be sure that this neutralization was not 

 apparent only and attributable to the circumstance that the 

 double circuit sufficed for the complete discharge of the bat- 

 tery outside the spiral, I repeated the experiment with four 

 steel wires No. 1, forming a double circuit, a much worse 

 conductor than that of the brass wires, and with ten pairs in- 

 stead of two. The result was the same. -wjoc> r ja;; 



72. The following objections might perhaps b#~^l^d 

 against the method of direct and continuous currents :—^^ ''^' 



a. It is advisable to employ a common source instead bf 

 two similar electrical sources. In the phaenomena of luminous 

 or calorific interference, the bundles which destroy one^'' 

 other are derived from the same radiation. " ''^'** 



b. On the undulatory hypothesis of electricity, the circum- 

 stance that the vibrations must traverse a part of a circuit (the 

 wire of the rheostat) the diameter of which is diminished, 

 might prevent the possibility of their ulterior interference with 

 a current the vibrations of which have not undergone a like 

 modifiication 



