672 M. Wartmann's First Memoir 



20. In order to unite all the desirable demonstrations of the 

 exactness of these results, I have repeated with the same wire 

 and under similar circumstances, some experiments on its 

 conductibility as a function of its length, the wire and the 

 thermo-electric rheometer being alone in the circuit. I ob- 

 tained, as it was easy to foresee, values which agree with the 

 formula of M. Ohm*. Thus the remark (16.) is established. 

 § III. Induction of a constant "wire by fwo "wires, one of nsohich 



is variable. 



21. Proceeding from the facts above related, similar results 

 for the simultaneous induction of two inductor currents on a 

 wire placed symmetrically between them, were to be expected. 

 The subject divided itself naturally into six cases, which were 

 examined. Calling the currents induced at the time of the 

 closing of the circuit direct currents, those which are induced 

 at the time of its rupture inverse currents, these six cases are 

 characterized as follows : — 



a. The two inductors are equal and traversed by direct 

 currents in the same direction. 



b. The two inductors are equal and traversed by direct 

 currents in contrary directions. 



c. The two inductors are unequal and traversed by direct 

 currents in contrary directions. 



d. The two inductors are unequal and traversed by direct 

 currents in contrary directions. 



e. The two inductors are equal and traversed, one by a 

 direct current, the other simultaneously by an inverse current. 



f The two inductors are unequal and traversed, one by a 

 direct current, the other by an inverse simultaneous current. 



22. First case. — Different precautions are requisite in the 

 arrangement of the apparatus, in order not to bring any per- 

 turbating force into play. 1 found that the current of ten 

 pairs, in passing through the two wires of the small helix, 

 heated them rapidly. On the other hand, the great conduc- 

 tibility of the wires of the great helix causing each of them, 

 taken separately, to be sufficient even to discharge the current 

 of twenty pairs, the deviations of the hydro-electric rheometer 

 united to the induced wire remained the same, whether the 

 two inducing wires or a single wire were employed. The ar- 

 rangement which I found to succeed the best, consisted in 

 mounting two piles of ten pairs, and making the current pass 

 from the one into the first inductor wire, that of the other 



♦ Die Galvanische Kette Mathematisch bcarbeitet, p 36. " Des Travaux 

 et des Opinions des Allemands sur la Pile Voltaique," Archives de I'Elec- 

 tricite, vol. i. pages 36 and 46. [Ohm's investigation here referred to will 

 be found in Scientific Memoibs, vol. ii. p. 401.] 



