RESEARCHES ON MAGNETOSTRICTION. 355 



longitudinal compression by Ewing and Chree. 2) Unlike nil these 

 effects, the change wrought by hydrostatic pressure is of a 

 different order of magnitude, as remarked by Tomlinson. Without 

 special arrangement for detecting a minute change in magnetiza- 

 tion, we can not well measure the change produced by pressure on 

 all sides. 



In a paper on the effect of magnetic stress in magnétostriction,^ 

 Mr. E. T. Jones and one of us have pointed out the importance of 

 investigating the relation of magnetization to hydrostatic pressure in 

 deciding the intricate question of magnetostriction. Mr. Jones 4) has, 

 however, found out that it is unnecessary to take up experiments on 

 hydrostatic pressure, inasmuch as the quantity which is required to 

 settle the question can be deduced by means of simple experiments on 

 the effect of longitudinal pull on a ferromagnetic wire. 



In the present investigation our attention bas not been confined 

 to the question of magnetic stress, and we have been able, after several 

 fruitless attempts, to establish the fact that the effect of hydrostatic 

 pressure is not immeasurably small, but that there is a remarkable 

 reciprocal relation between the volume change by magnetization and 

 the change of magnetization by compression. 



In order to settle the question of magnetostriction, we have 

 measured the change of length and the effect of longitudinal pull on the 

 magnetization of iron and nickel. From the different combinations of 

 these effects, we can calculate the coefficients h' and h" introduced by 

 Kirchhof!'. We are thus enabled to examine the effect of stress from 

 the strains caused by magnetization, and vice versa. 



1). Ewing, Phil. Trau*. 179, 333, 1888. 



2). Chree, „ „ 13t, 329, 1890. 



3). Xagaoka a. T. Jones. Phil. Mag. May, 1896. 



4). T. Jones, Phil. Tran*. 139, 189, 1897. 



