3(50 H. XAGAOKA AXD K. HONDA; 



tended by the numerous researches of Dr. C. G. Knott.° It is mach 

 to be regretted that the magnetization was not uniform in his experi- 

 ments, and that consequently the change of volume could not be 

 expressed as a function of the magnetization. If the field within 

 the magnetized body be not uniform, then there will be internal 

 forces A, B, C, according lo Kirchhoff, and the discussion will 

 thereby be rendered very tedious. As (he length of the magne- 

 tizing coil is not given in Dr. Knott's experiments, it is rather 

 difficult to estimate the mean field strength ; but as the length of the 

 magnet was about 46 cm., while the field strength at the distance 

 of 21.9 cm. from the centre of the coil was 0.937 from that at the 

 middle, it would appear that the field at the ends of the magnet 

 was widely different from the mean value. The discussion of the 

 result is rendered doubly difficult by the influence of the steel or 

 brass cap for fixing the capillary tube to the hollow cylinder. 

 Such inconvenience will disappear if the change ot volume 

 of the magnet itself be observed, as is easily possible, if sufficient 

 precautions be taken in the arrangement of the measuring ap- 

 paratus. 



These circumstances show that the question regarding the 

 changé of volume by magnetization is by no means settled ; and as 

 almost all theories of magnetostriction make the strain in ferromao- 

 netics depend on the intensity of magnetization and that of the 

 magnetizing force, we have examined the alteration of the volume 

 as functions of these two quantities. 



The change of volume was determined by means of a 

 dilatometer. The specimen to be tested was placed in a glass tube 

 provided with a capillary neck (Fig. 1.). The upper part of the 



1). Knott, Transactions of Boy. Soc, Edinburgh, 33» 527, 1896. 



