1881.] 



Molecular Magnetism. 



215 



from magnetism and through which an electric current has never 

 passed. I mention this negative experiment in order to prove that all 

 the effects I shall mention are obtained only through the magnetism 

 of the wire. If now I pass an electric current for an instant through 

 this same wire, its molecules are instantly polarised. I have never 

 yet been able to restore the wire to its original condition, and the 

 magnetisation induced by the passage of a current is far more powerful 

 and more persistent in soft iron than tempered steel. This maybe due, 

 however, to the fact that in tempered or softened steel we find traces 

 only of a current during to the rotation by torsion of its molecules, 

 some two to three degrees of sonometer, whilst iron gives constantly 

 a current of 70 sonometric degrees.* 



In order to obtain these currents, we must give a slight torsion of 5° 

 or 10° to and fro through the zero point. We then have a current 

 during the motion of the index to the right, and a contrary current in 

 moving the index to the left. If we use a galvanometer, we must time 

 these movements with the oscillations of the needle ; but with the 

 telephone it gives out continuous sounds for either movement, the 

 interruptions being only those caused by the rheotome. The direction 

 of the current has no influence on the result ; either positive to the 

 free arm or index or negative gives equal sounds, but at the moment 

 of reversal of the current a peculiar loud click is heard, due to the 

 rapid change or rotation of the polarisation of its molecules, and this 

 peculiarly loud momentary click is heard equally as well in steel as in 

 iron, proving that it is equally polarised by the current, but that its 

 molecular rigidity prevents rotation by torsion. We can imitate in 

 some degree the rigidity of steel by giving the iron wire several per- 

 manent twists. The current due to elastic torsion is then reduced 

 from 70° to 40°, in consequence of the mechanical strain of the twists 

 remaining a constant; and a weakening of the current is also remarked 

 if with a fresh wire we pass in torsion its limit of elasticity. 



If a new soft iron wire of 2 millims. (giving no traces of a current 

 by torsion) has passed through it a momentary current of electricity, 

 and the wire is then observed free from the current itself, it will be 

 found to be almost as strongly polarised as when the current was con- 

 stantly on, giving by torsion a constant of 50 sonometric degrees. If, 

 instead of passing a current through this new wire, I magnetise it 

 strongly by a permanent magnet or coil, the longitudinal magnetism 

 gives also 70° of current for the first torsion, but weakens rapidly, so 

 that in a few contrary torsions only traces of a current remain, and we 

 find also its longitudinal magnetism almost entirely dissipated. Thus 

 there is this remarkable difference, that, whilst it is almost impossible to 

 free the wire from the influence produced by a current, the longitudinal 

 magnetism yields at once to a few torsions. We may, however, trans- 

 * 0'8 of a Daniell batter j. 



VOL. XXXII. Q 



