Properties of the Alloys of Cast-iron and Aluminium. 619 



The coefficients of expansion of these crystals are probably 

 different from the coefficient of expansion 'of the surrounding 

 matrix; and since solidification takes place at a high tempe- 

 rature, the material of the specimens would, at ordinary 

 temperatures, be in a strained condition. 



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The effect of repeated heating and cooling would gradually 

 produce disintegration. 



Let us assume that the change in the magnetic condition 

 due to this breaking down of the material of the specimen is, 

 to a first approximation, equivalent to the introduction of an 

 air-gap in the magnetic circuit. 



If this were the case, the actual magnetic force in the spe- 

 cimen would be less than that due to the magnetizing-current 

 alone. 



Let us assume that, after a certain number of heatings, 

 the only change going on is due to disintegration, and that 

 the actual force in the specimen can be represented approxi- 

 mately by the expression (H — KB) (as would be the case 

 with a split ring), where H= the magnetic force due to the 

 spiral alone, and K is some constant depending upon the 

 number and size of the gaps in the specimen (due to disinte- 

 gration). If then H l5 H 2 be the values of H on the two 

 curves I and II (fig 4) corresponding to a given value of B, 

 we should, on the above assumption, have the relation 



Hx-KjB-^Hj-KaB, 



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