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XXIII. Studies on Magnetism, By E. Bouty, Professor of 

 Physics at the Lycee of Rheims, 

 [Concluded from p. 98.] 



III. On the Breaking of Magnetized Needles. 



IT has long been known that when a magnet is broken the 

 fragments possess magnetic properties ; but I do not think 

 that up to the present any one has set himself to deter- 

 mine the laws which govern the formation of breakage-magnets. 

 In the act of fracture of a magnet we shall distinguish the 

 fact of the separation of the parts (with its consequences, such 

 as would be presented in the case of the simple disjunction of 

 the same parts juxtaposed*, not welded, in the primitive mag- 

 net) from the mechanical fact of the breaking. I purpose, in 

 the first place, to ascertain if this mechanical fact modifies in 

 any way the magnetic state of the fragments. The following 

 are the experiments I have made on this subject. 



1. The proper effect of the Rupture. 



A regular magnetized needle is obtained by passing a freshly 

 tempered steel needle through a spiral traversed by a current. 

 If we break this needle in the middle, two cases may present 

 themselves : — 



1st. If the needle is tempered hard enough to break between 

 the fingers like glass, the two halves will be magnets possessing 

 the same magnetic moment, as was to be expected by reason of 

 symmetry. 



2nd. If the needle is tempered soft, so as to bend several 

 times in opposite directions before breaking, the two halves 

 possess unequal magnetic moments, in an apparently arbitrary 

 manner. 



In the first place this difference must be accounted for. For 

 that purpose I take a needle slightly tempered and regular. I 

 grasp it by the middle between two plates of lead so that one of 

 the halves remains immovable during the breaking, while the 

 other, seized with the hand, is submitted to flexions in opposite 

 directions till rupture takes place. It is found that the half 

 which was submitted to the flexions possesses a lower magnetic 

 moment than that of the half which was nipped, and so much 

 the more as the breaking was more difficult. 



* When two pieces of steel are united by two equal plane faces, the parts 

 opposed to each other are in reality separated by a lamina of air, the thick- 

 ness of which is very great in proportion to the distance of two magnetic 

 molecules. The thing in question here is perfect juxtaposition, such as 

 exists between the different portions of a coherent solid. 



