452 Prof. Beeiz on the Influence of Magnetization 



in regard to the changes which the resistance of an iron wire expe- 

 riences during magnetization. From the first two processes, which 

 are in fact identical, the conclusion must be drawn that the re- 

 sistance is diminished by magnetization ; for the contact between 

 the molecules in the direction of the length becomes closer, and 

 the entire length diminishes ; by the third process the contact is 

 closer indeed, but the bar becomes longer and thinner ; thus 

 there may be either an increase or a decrease in the resistance, 

 according as one or the other action predominates. The fourth 

 action must necessarily increase the resistance ; in the fifth there 

 appears no reason why the resistance which it produces should 

 be altered either in one direction or the other. 



The experiments of Wartmann*, Moussonf, and EdlundJ 

 have not shown any change in resistance during magnetization, 

 while Thomson § observed an increase of resistance in the direction 

 of the magnetic axis, and a diminution in a direction at right angles 

 thereto. In discussing these discordant results, Wiedemann || 

 has suggested that in many of Thomson's experiments it was 

 possible that the attraction of the poles had exerted a purely 

 mechanical pull on the iron between them, by which it would be 

 extended in an axial, but drawn together in an equatorial direc- 

 tion ; and I must confess that in reference to the other experi- 

 ments of the same observer I had from the first a suspicion that 

 the alteration in resistance is an entirely secondary phenomenon, 

 produced by the alteration in the length of the bars. It is true 

 that the increase in resistance which Thomson observed is so 

 considerable that it cannot be directly explained on Ohm's law 

 from that alteration in length, not even if we remember that 

 such an alteration in length must be accompanied by a diminu- 

 tion of the section if the volume remains constant ; and neither 

 Joule nor Wertheim nor Buff has been able to show that there is 

 any change in volume. Yet Mousson's experiments, in. which 

 wires were stretched by weights, showed such an unlooked-for 

 increase in resistance, that its chief reason must be sought in the 

 removal of the molecules from each other. Experiments which I 

 have made on the alteration in length and in resistance have 

 shown that my supposition was not correct. 



The bars whose lengths were to be measured were fastened at 

 one end in a horizontal position, and were supported in several 

 places by easily moveable rollers. From the free end of the bar 

 a string passed which was coiled round a vertical steel axis, then 

 passed over a pulley, and was stretched by a weight. On the 



* Arch, des Sc. Phys. vol. xiii. p. 35. f Ibid. vol. xxxi. p. 111. 



X Poggendorff's Annalen, vol. xciii. p. 315. 



§ Phil. Trans. 1856, p. 315. 



|| LehrbucJi des Galvanismus } vol. ii. p. 466. 





