10 JACOBI OX THE APPLICATION' OF ELECTRO-M AGXETISM 



currents generated by the same movement ; but such a state can 

 never occur to magnetism at rest. 



There is probably also another state of equilibrium w hich may 

 be attributed in part to magneto-electric currents. In the nume- 

 rous experiments which I have made, I remarked, conformably 

 to M. Ohm's formula, that the action of a voltaic current is much 

 more constant when a rather long conducting wire is employed. 

 I communicated some time back to Professor Moser of Konigs- 

 berg, the idea, that under similar conditions the action of a pair 

 ought to be of higher constancy, if long conducting wire be wound 

 spirally round a soft iron bar, than when this same wire is ex- 

 tended or inverted on itself. The usual decrease in the energy 

 of the battery would give rise to a magneto-electric current of 

 the same direction as the voltaic current, and serving partly to 

 re-establish this latter. I tried this delicate experiment, but have 

 not yet been able to anixe at incontestable results. I shall re- 

 commence these researches, which appeal' to me to be of im- 

 portance for the validity of the theory, and fertile in its prac- 

 tical applications. 



The following experiment, which I owe in part to Professor 

 Moser, appears to me to throw a great hght on the intimate na- 

 ture of magnetism. The helix of one ai'm of the horse-shoe 

 (Art. 9) was brought into contact with a voltaic pair, while 

 the helix of the other arm could be united to the multiplier of a 

 very sensible galvanometer. This latter circuit being completed, 

 there is, as is well known, a very energetic deviation of the 

 needle, as soon as the voltaic circuit is completed or interrupted. 

 But after the establishment of the voltaic circuit, if 4 to 5, or 

 even 7 seconds, are allowed to elapse before completing the mag- 

 neto-electric circuit, there will still be a sensible deviation of the 

 needle. The same observation may be made, but in an inverse 

 manner, if the voltaic circuit be interrupted some seconds pre- 

 A'ious to the establishment of the magneto-electric circuit. The 

 deviation weakened in proportion to the length of time which has 

 elapsed between the two operations. These etfects are much 

 more decided, if an armature be connected with the extremities 

 of the magnet*, and are ])robably still more so when a soft iron 

 ring is employed. 



* I have just noticed in the Gth part of PoggendorfF's Aniialen, that Professor 

 Magnus, of Berlin, has made a series of analogous experiments. 



