202 Dr. C. Fromme on the Magnetism of Steel Bars, 



The harder the steel, the feebler is the magnetizing force at 

 which residual magnetism enters. 



This result was to be expected beforehand, according to the 

 representation which the theory of rotataWe molecular mag- 

 nets gives of the process of magnetization. 



The molecular forces oppose the placing of the molecules 

 in positions of magnetic equilibrium when the molecules 

 are acted on by magnetizing forces ; but, inasmuch as they 

 have themselves undergone a change by the rotation of the 

 molecules, they also resist the rotation of the latter back to 

 their unmagnetic positions, and keep them fixed in certain 

 magnetic ones after the force has ceased to operate. Now, as 

 the molecular forces are more intense in the harder sort of 

 steel than in the softer, the temporary magnetization turns out 

 less in the former ; and, on the contrary, the residual mag- 

 netism is greater, because the molecular forces are more altered 

 on the rotation of the molecules. 



That with the more-elongated ellipsoids residual magnetism 

 commences earlier than with the less-elongated ones receives 

 its explanation from this — that in the former, with an equal 

 external magnetizing force, the sum of the forces acting on 

 each molecular magnet is greater. The greater the longitu- 

 dinal dimension of a body in comparison with its transverse 

 dimension, the more of that part of the reciprocal action of 

 the molecular magnets which is opposed to the external mag- 

 netizing force vanishes, while at the same time that which 

 supports it and acts in the same direction is increased. 



On the other hand, between the values of the argument K 

 no definite relation appears to subsist. We may infer that 

 residual magnetism enters at the same value of the argument 

 K of the magnetization-function in differently elongated ellip- 

 soids, at least of the same sort of steel. Only I. 5 shows a 

 considerably greater value of the argument ; on this see § 9. 



Since, however, in such investigations a limit is always 

 reached at which a normal variability of the quantities to be 

 measured becomes quite concealed by the unavoidable errors 

 of observation, the proposition, that the limit of the residual 

 magnetism corresponds to a finite value of the magnetizing 

 force, must be qualified by adding that, with further refine- 

 ment of our means of observation, this limit will be removed 

 more and more towards zero, and perhaps at length vanish 

 entirely. With this qualification, the results obtained may 

 serve as an experimental confirmation of Maxwell's theory of 

 residual magnetism. Meanwhile I will just mention here that 

 the theory obtains another important argument in its favour 

 through the results of experiments to be hereafter commnni- 



