On the Influence of Magnetization on Iron Bars. 451 



vora fattened for human food must be derived from other sub- 

 stances than fatty matter in the food. 



2. That when fattening animals are fed upon their most ap- 

 propriate food, much of their stored-up fat must be produced 

 from the carbo-hydrates it supplies. 



3. That nitrogenous substance may also serve as a source of 

 fat, more especially when it is in excess and the supply of 

 available non-nitrogenous constituents is relatively defective. 



LXII. On the Influence of Magnetization on the Length and the 

 Resistance of Iron Bars. By W. Beetz*. 



"Vl/'IEDEMANNf and Buff J have both expressed opinions as 

 ■ to the molecular actions which occasion a lengthening in 

 an iron bar when it is magnetized. From these actions we may 

 expect on the one part a lengthening, on the other part a short- 

 ening of the bar. For it may be supposed — 



(1) On the theory of magnetic fluids, that a shortening of 

 the bar occurs in consequence of the mutual attraction of mole- 

 cules which have become magnetic. 



(2) On Ampere's theory, that the parallel currents attract 

 each other, whereby the bars are shortened. 



(3) That the molecular magnets set with their long axis pa- 

 rallel to the axis of the bar, and thus produce a lengthening of 

 the bar, — a view which De la Rive§ has expressed, and to which 

 Tyndall || and Buff adhere. 



(4) That, by magnetizing, a mechanical pull is exerted on some 

 parts of the bar, which lengthens it, as was observed by Wer- 

 theim^T. 



(5) That the bar was previously twisted or bent, and that 

 magnetization stretches it by removing this. 



In fact, both a lengthening and a shortening action have been 

 observed in the magnetization of iron bars : Joule**, Wertheim, 

 and Buff have undoubtedly shown a lengthening, and Tyndall ft 

 has even demonstrated it by a lecture-experiment; Joule has 

 further shown that, instead of a lengthening, there is a shortening 

 if the bars or wires are under a strong strain. 

 From the supposed molecular actions, conclusions may be drawn 



* Translated from PoggendorfFs Annalen for June 1866. 



t Lehrbuch des Galvanismus, vol. ii. p.457- 



X Liebig's Annalen, Supplementary volume iii. p. 136. 



§ Ann. de Chim. et de Phys. ser. 3. vol. xxvi. p. 158. 



|| Cosmos, vol. xxiv.p. 719. 



IT PoggendorfFs Annalen, vol. Ixxvii. p. 43. 



** Phil. Mag. S. 3. vol. xxx. p. 1Q. tt Cosmos, vol. xxiv. p. 718. 



2G2 



