338 



Dr. Tyndall on the Polarity of Bismuth, 



whenever the bar reached the limit of its swing, and closing it 

 when the bar crossed the axial line, the action could be increased 

 to such a degree as to cause the bar to make an entire rotation 

 round the axis of suspension. This result is diametrically opposed 

 to the above conclusion — here again the bismuth bar behavea 

 like a bar of iron. 



15. These experiments seem fully to bear out the theory ad- 

 vanced by M. von Feilitzsch in his letter to Mr. Faraday*. He 

 endeavours to account for diamagnetic action on the hypothesis 

 that its polarity is the same as that of iron ; " only with this dif- 

 ference, that in a bar of magnetic substance the intensity of the 

 distribution over the molecules ina^eases from the ends to the 

 middle, while in a bar of diamagnetic substance it decreases from 

 the ends to the middle.^' So far as I can see, however, the rea- 

 soning of M. von Feilitzsch necessitates the assumption, that in 

 the self-same molecule the poles are of unequal values, that the 

 intensity of the one is greater than that of the other, an assump- 

 tion which will find some difficulty of access into the speculations 

 of most physicists. A peculiar directive action might be readily 

 brought about by the distribution of magnetism assumed by 

 M. von Feilitzsch ; but up to the present time I see no way of 

 reconciling the repulsion of the total mass of a piece of bismuth 

 with the idea of a polarity similar to that of iron. 



16. During these inquiries, an observation of Mr. Faraday 

 perpetually recurred to me. " It appeared to me,^^ he writes f, 

 " that many of the results which had been supposed to indicate 

 a polar condition were only consequences of the law that diamag- 

 netic bodies tend to go from stronger towards weaker places of 

 action.^' The question here arose, whether the various actions 



Fig. 1. 



observed might not be 

 explained by reference 

 to the change effected 

 in the magnetic field 

 when it is intersected by 

 an electric cun*ent. The 

 distribution of magnetic 

 intensity between the 

 poles will perhaps be 

 rendered most clear by 

 means of a diagi*am. 

 Let AB represent the 

 distance between the 

 polar faces ; plotting the 

 intensity at every point 

 in AB as an ordinate from that point, the line which unites the 

 ends of all these ordinates will express the magnetic distribution. 

 ♦ Fhil. Mag., S. 4. vol. i. p. 46. f Ibid., S. 3. vol. xxxvii. p. 89. 



