Messrs* M. Nagnoka and It. Honda on Magnetostriction. 26 k 5 



of his successors. It is beyond doubt that the change of 

 volume was very minute, and there was sufficient evidence 

 that the elongation in the direction of magnetization is 

 accompanied by contraction in the direction perpendicular 

 to it. 



The elaborate researches of Cantone*on the strain of ferrc- 

 magnetic ovoids are not free from the fault above mentioned. 

 The major axis of the ovoid was 16' 7 times that of the minor, 

 so that the demagnetizing factor — 0'1134. As his results 

 are given in terms of the magnetizing current and the 

 moment of the magnet, we have thought it advisable to re- 

 calculate the result in magnetizing force H (= H — NI, 

 where H stauds for the magnetizing force in the coil) and 

 I. The following table gives (Jantone's determination of the 

 intensity of magnetization : — 



H . 



H. 



I. 



135 



20 



102 



26-7 



3-8 



202 



38-1 



44 



293 



51-6 



6-8 



397 



585 



75 



450 



It will be seen from the above table that on account of the 

 great demagnetizing factor the magnetizing force was less than 



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8 C.G.S. units although the field in the coil was nearly 60. 



Cantone observed no alteration of volume in an iron ovoid 

 even with a magnetizing current of 12 amperes ; but it is 

 quite probable that the intensity of magnetization, as well as 

 that of magnetizing force, was insufficient to produce appre- 

 ciable change, 



On account of the small susceptibility of nickel f, the effect 

 of the great demagnetizing factor in Cantone's nickel ovoid 

 was not so marked as in iron. So far as we are aware, he was 

 the first to notice the diminution of volume in nickel by mag- 

 netization. Although his measurements with dilatometer 

 filled with water and with alcohol are widely different, it is 

 beyond doubt that the readings with alcohol are the more 

 reliable for reasons which will be afterwards given. His 

 calculation of Kirchhoff's coefficients k' and k" based on the 

 measurement of the change of length and of volume in nickel 

 by magnetization throw much light on the theory of magneto- 

 striction. 



* Cantone, Mem. d. R. Accad. dei Lincei, vol. vi. p. 487 (1890). 

 t Cantone, Rendiconti d. R. Accad. d. Lincei, vol. vi. p. 252 (1890). 





