266 Messrs. H. Nagaoka and K. Honda on Magnetostriction. 



Our knowledge of the change of internal volume in iron, 

 steel, and nickel tubes in the magnetizing field has been 

 largely extended by the numerous researches of Dr. C. G. 

 Knott *. It is much to be regretted that the magnetization 

 was not uniform in his experiments, and consequently the 

 change of volume could not be expressed as a function of 

 the magnetization. The discussion of his results is rendered 

 doubly intricate by the influence of the steel or brass cap for 

 fixing the capillary tube to the hollow cylinder. Such incon- 

 venience will disappear if the change of volume of the magnet 

 itself be observed, as is easily possible if sufficient precaution 

 be taken in the arrangement of the measuring apparatus. 



These circumstances show that the question regarding the 

 change of volume by magnetization is by no means settled ; 

 as almost all theories of magnetostriction make the strain in 

 ferromagnetics depend on the intensity of magnetization and 

 that of magnetizing force, we have examined the alteration of 

 volume as functions of these two quantities. 



The change of volume was determined by means of a dila- 

 tometer. The specimen to be tested was placed in a glass 

 tube provided with a capillary neck (fig. 1). B shows the 

 upper part of the capillary tube (0*215 mm. radius) with 

 reservoir for filling the dilatometer with liquid. In supporting 

 1he ovoid in the tube, care was taken not to let it touch the 

 sealed end of the glass tube. Two circular brass rings (a, a') 

 were inserted into the tube, and made to fit tightly against 

 the wall of the dilatometer. A brass plate of the form given 

 at A was soldered to the ring at S. The ends of the ovoid 

 were then placed loosely in the triangular holes. The ovoid 

 wns thus supported in the central line of the dilatometer 

 without touching the glass tube. A similar arrangement was 

 employed for supporting the nickel rod within the dilatometer. 



To prevent rusting of iron, the dilatometer was filled with 

 very dilute solution of caustic soda nearly up to the neck. 

 The capillary tube and a small portion of the main tube near 

 the neck contained ether. When the dilatometer was all 

 filled with water or petroleum, the indication of the volume- 

 change was very irregular, as fine drops of the liquid stuck 

 to the wall of the capillary tube and as the liquid was not 

 sufficiently mobile. Cantone f had also similar experience in 

 measuring the volume-change of the nickel ovoid. It would 

 have been easier to fill the dilatometer ail with ether, but 



* Knott, Proc. Roy. Soc. Edinburgh, vol. xix. p. 249 (1892) ; vol. xx. 

 pp. 290, 295, 334 (1893-1895) ; Trans. Roy. Soc. Edinburgh, vol. xxxviii. 

 p. 527 (1896). 



t Cantone, Ice. cit. 





