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LX. Considerations on Permanent Magnetism. 

 %M. F. Osmond*. 



IRON possesses at least two molecular states, a and |8. a. is 

 soft iron, that is iron which has been annealed and cooled 

 slowly. It changes into /3 during heating, at a certain critical 

 temperature, and in part preserves this state during cooling, 

 the more so the quicker the cooling and the larger the pro- 

 portion of carbon, manganese, and tungsten that it contains. 

 Some /3 iron is also produced during cold hammering. Iron 

 deposited electrically is also of the /3 variety. 



A bar of steel, allowance being made for the carburets 

 and other compounds simply in mixture, can then be looked 

 upon as an intimate mixture of a iron and /3 iron in rela- 

 tive proportions, which can change from point to point but 

 are determinate at any point. That being so, let us con- 

 sider /3 as forming in a steel bar a porous framework, not 

 changing under the influence of currents and of magnets. 

 On the other hand, let us look upon a. as composed of particles 

 polarizable under such influences. (The actual mobility of 

 such particles, admitted by Hughes, appears from the sounds 

 and changes of volume which take place during magneti- 

 zation.) The particles a so polarized will form so many small 

 elementary magnets, which the magnetizing force has dis- 

 placed from their former normal position of equilibrium, and 

 which tend to take up this position again so soon as the ex- 

 ternal force ceases to act. 



But in presence of the rigid network of iron /3 these po- 

 larized particles a are conceived as catching in the pores of 

 the /3 structure, and immovable in this position, thus resulting 

 in a permanent magnet. The temporary magnetism and the 

 permanent magnetism determined by the action of a certain 

 magnetizing force at a point of a bar will be therefore a func- 

 tion of the relation -=r at this point. 

 P 



As an attempt to represent these ideas graphically, let 

 there be a square, A X Y, of which the side represents 100 



parts. Every line m n parallel to the axis of Y meeting in p 

 the diagonal OA represents a steel containing j^- of iron a, 

 ^ of iron ft. 



At saturation the temporary magnetism, or rather the sum 



* Communicated by the Physical Society : read April 18, 1890. 



