54 



by weights attached to their lower ends. The torsion was measured 

 by observing the image of a scale reflected in a mirror fastened to 

 the lower end of the wire. 



When the south pole of the magnetized wire was uppermost, and 

 the current descends, the lower end of the wire, as seen from above, 

 twists in the direction of the motion of the hands of a watch. A 

 change in the direction of either the transmitted or the magnetizing 

 current changes the direction of the torsion. 



As long as the magnetizing current remains constant, the torsion 

 increases with the intensity of the transmitted current till it reaches 

 a maximum. 



When the intensity of the magnetizing current increases, the trans- 

 mitted current remaining unchanged, the torsion diminishes. 



The torsion of the wire is nearly independent of the weight by 

 which it is stretched, as long as the intensities of the magnetizing 

 and the transmitted current remain invariable. 



3. The same torsion is produced when a voltaic current is trans- 

 mitted through iron wires which have been for some time suspended 

 vertically, and thus magnetized by the magnetism of the earth, or 

 which have acquired permanent magnetism in any other manner. 



4. A voltaic current being transmitted through an iron wire sus- 

 pended in the axis of a spiral, if a weak current be afterwards trans- 

 mitted through the helix, the wire will twist in the same direction as 

 if the current had been transmitted first through the spiral and after- 

 wards through the wire. The torsion increases with the intensity of 

 the magnetizing current till it attains a maximum. On increasing 

 further the intensity of the magnetizing current, the torsion diminishes. 



5. If an iron wire be suspended in the axis of a helix, and tem- 

 porarily magnetized, the intensity of the temporary magnetism will 

 be weakened on transmitting a voltaic current through the wire. 



On interrupting the current through the wire, the temporary mag- 

 netism of the wire will be increased. If the circuit be completed 

 repeatedly, whatever be the direction in which the current is trans- 

 mitted through the wire, the temporary magnetism will diminish, 

 and on interrupting the current will resume its original intensity. 



6. If a voltaic current be transmitted through the iron wire after 

 the magnetizing current has been interrupted, its permanent mag- 

 netism will be weakened. 



