Messrs. H. Nagaoka and K. Honda on Magnetostriction. 275 



It will be shown later on that the minuteness of the effect 

 of compression on the magnetization of iron and nickel leads 

 to an important conclusion in the theory of magnetostriction. 

 Effect of Transverse Stress on the Magnetization of an Iron 

 Tube. — Lord Kelvin *, in his series of experiments on the 

 electrodynamic qualities of metals, investigated the effect of 

 transverse stress on the magnetization of an iron tube by 

 subjecting the inner surface of a gun-barrel to hydrostatic 

 pressure. In our experiment it was of no small importance 

 to try similar experiments with iron, to decide whether the 

 minute change produced by all-sided pressure was also 

 characteristic of the effect of transverse stress produced by 

 pressure on the external surface of an iron or nickel tube. 



To the extremities of a hollow iron cylinder (external 

 diameter 0*93() cm., internal diameter 0*400 cm., length 

 25 cm.) were soldered two thick brass caps in the manner 

 shown in the annexed diagram (fig. 4), and placed in the 

 compressing-vessel above described. By pumping in water 

 to the vessel, the iron tube was subjected to pressure 

 on its external surface alone, and the change of ^ ' 

 magnetization tested in the manner above described. ||§|| 

 It was soon noticed that the effect was enormously 

 large and opposite to that of all-sided pressure. 

 By keeping the pressure constant, the difference in 

 magnetization when the tube was in the strained 

 and unstrained state was determined for different 

 fields ; the curves of the change in magnetization 

 thus obtained for pressures of 50_, 150, and 250 

 atmospheres are shown in fig. 18 (PI. II.). 



The present experiment is just the reverse of Lord Kelvin's, 

 and the inspection of the figures (fig. 18) will show that the 

 result is just the reverse. With increase of the magnetizing 

 force there is increase of magnetization till it reaches a 

 maximum, thence to diminish in stronger fields. As the 

 pressure is increased, the decrease of magnetization after 

 once reaching a critical value is so great that the magnetiza- 

 tion in strong fields is less than in the unstrained condition. 

 The result is thus in close agreement with Lord Kelvin's 

 anticipation that the effects of positive pressure will be 

 opposite to the effects of negative pressure. 



These experiments show that the application of stress so as 

 to produce no shear affects the magnetization of iron and 

 nickel only very slightly; but the remarkable change in 

 magnetization produced by tensional or compressional stress 



* Kelvin, Phil. Trans, clii. p. 64 (1878) ; Mathematical and Physical 

 Papers, ii. p. 370 (1884). 



