650 Messrs. K. Honda and S. Shimizu on the 



If the time of vibration of the table alone is observed and 

 then the time of vibration of the table with a body of known 

 moment of inertia placed on it, the moment of inertia of the 

 table can be calculated. It is only necessary then, in deter- 

 mining the moment of inertia of a body about a given axis, to 

 place it on the table in such a position that the given axis 

 coincides with the fixed axis of vibration, and again determine 

 the time of vibration. 



Laws connecting the moments of inertia of a body about 

 different axes can be easily verified with this table, e. g., the 

 law that " the moment of inertia of a body about any axis is 

 equal to its moment of inertia about a parallel axis through its 

 centre of gravity together with the moment of inertia of the 

 whole mass collected at its centre of gravity about the given 

 axis," can be verified by varying the distance of the body 

 from the axis of vibration. 



LXVIII. The Wiedemann Effect In Ferromagnetic Substances. 

 By K. Honda and 8. Shimizu*. 



[Plate XVI.] 



THE Wiedemann effect in iron and nickel is so well known 

 that it is superfluous to enter into the details of the 

 phenomenon. The experiments by G. Wiedemann f, C. G. 

 Knott J, Prof. H. Nagaoka and one of us§, show that so 

 long as the longitudinal field is not strong, the direction of 

 twist in iron coincides with that of a circular field, if this 



direction is right-handedly related to that of the longitudinal 

 © •/ © 



field ; they also show that in nickel the direction of twist is 

 opposite to that of iron in weak fields. The direction of twist 

 is reversed when either the circular or the longitudinal field 

 changes its direction. The Wiedemann effect in nickel steels 

 of different percentages was recently studied by Prof. Nagaoka 

 and one of us, and it was found that the twist is the same as 

 that of iron. The effect of tension on the Wiedemann effect 

 in iron and nickel was examined by C. G. Knott, who found 

 that tension diminishes the twist in these metals. 



The present paper consists of two parts ; firstly, we deal 

 with the influence of tension on the Wiedemann effect in 

 nickel steels, and secondly, with the same effect in ferro- 



* Communicated by the Authors. 



t G. Wiedemann, Pogg. Ann. ciii. p. 571 (1858) ; cvi. p. 161 (1859) ; 

 Electricitat, iii. p. 797. 



X Knott, Trans. Roy. Soc. Edinb. xxxii. (1), p. 193 (1882-83) ; xxxv. 

 (2) p. 377 (1889) ; xxxvi. (2) p. 485 (1891). 



§ Nagaoka and Honda, Jour. Coll, Sci, xiii. p. 263 (1900). 



