270 Messrs. H. Nagaoka and K. Honda on Magnetostriction* 



These changes are plotted against H and I in fig. 7 (PL I.) 



It will be seen from these curves that the length-change 



. . . 

 produced in the ovoid or in the nickel rod is similar to 



that obtained by one of ns, and described in the papers 

 above c^ted. The determinations are in close agreement with 

 the results of Bidwell and several other investigators. The 

 inspection of these figures for nickel shows a striking re- 

 semblance between similar curves for the change of volume 

 in the same metal. The behaviour in iron is different as 

 regards the change of length and that of volume. 



§ 2. Effects of Hydrostatic and Transverse Pressures on the 

 Magnetization of Iron and Nickel. 



The remarkable effect produced by longitudinal pull or 

 compression on the magnetization of ferro-magnetic bodies 

 premised the outcome of a similar result by the application 

 of hydrostatic pressure, as shown by the experiments of 

 Wassmuth"*. No such marked influence of compression was 

 observed, but a minute change in the reading of the magneto- 

 meter showed that the effect was not immeasurably small. It 

 was only by special arrangement that the nature of the change 

 was clearly made out. 



The hydrostatic pressure was given by means of Cailletet's 

 pump used for liquefying gases. The pump was provided 

 with Ducretet manometer indicating pressure up to 300 

 atmospheres. These indications, on being gauged by mea- 

 suring the volume of dry air, showed wide difference from the 

 actual pressure, the relation between the change of volume 

 and pressure being taken from Natterer and Ainagat's 

 determinations. One end of a seamless copper tube 4* 7 metres 

 long and of 3 millim. internal, 7 millitn. external diameter 

 was attached to the pump ; by pumping water into the tube 

 pressure was communicated to a vessel containing iron or 

 nickel which is to be compressed. 



The ovoid or rod, which was to be examined under dif- 

 ferent pressures, was enclosed in a short brass tube T (fig. 2) 

 (internal diameter 1*1 centim., external diameter 2 centim., 

 length 31 centim.) filled with water. The tube fitted loosely 

 in the maonetizino-coil. The lower end of the ovoid was 

 placed in a conical hole bored in the end screw fitting into 

 the main tube T. To prevent dislocation of the ovoid and to 

 keep it always vertical, the upper end was loosely placed in a 

 triangular hole in the brass plate A in the manner already 

 described in the determination of the change of volume. The 

 neck of the vessel consisted of a smaller brass tube provided 

 * Wassniuth, loc. cit. 



