372 



H. XAGAOKA AND K. HONDA; 



Fie. 4 



hydrostatic pressure. In our experiment, it was of no small importance 

 to try similar experiments with iron, in order 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 

 0.47 cm., internal diameter 0.20 cm.) were soldered two thick brass 

 caps as shown in 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 lateral 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 the magnetization, when the tube was in 

 the strained and unstrained state, Avas determined for 

 different fields ; the curves of the change in magnetization thus 

 obtained for pressures of 50. 150 and 250 atmospheric pressures are 

 shown in Fig 21. 



The présent experiment is just the reverse of Lord Kelvin's, 1} and 

 the inspection of the figures will show that the result is also 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 field is increased, the decrease of magnetiza- 

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

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



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

 tion that the effects of positive pressure will be opposite to the effects 



1). Kelvin, Phil. Trans. 152 \\ 6l, 1878; Mathematical and Physical Papers, II. p. 370, 



