350 Mr. Q. Cook : An Experimental Determination 



Thus the magnetization of different gases can be satis- 

 factorily explained by the theory of Professors K. Honda 

 and J. Okubo by introducing certain assumptions, not only 

 qualitatively but also quantitatively. 



In conclusion I wish to express my deepest obligation to 

 Professor K. Honda, under whose suggestion and constant 

 guidance the present investigation was carried out. I also 

 wish to express my hearty thanks to Professors M. Ogawa 

 and M. Katayama, of the Department of Chemistry, for 

 their valuable suggestions and criticisms in the work. My 

 thanks are also due to Messrs. N. Yamada and K. Shikata 

 who kindly helped me in the preparation of pure gases in 

 the early part of the present research. 



Physical Institute 



of the University, Sendai, 



April 26, 1919. 



XXX. An Experimental Determination of the Inertia of a 

 Sphere moving in a Fluid. By Gilbert Cook, Af.Sc, 

 A.MJnst.C.E* 



IT has been shown by Stokes t that when a solid body is in 

 motion in a frictionless fluid of infinite extent, the 

 effect of the fluid pressure is equivalent to an increase in the 

 inertia of the body. The effect is manifest only in cases of 

 accelerated or retarded motion, and has a direct application 

 to the dynamical theory of the oscillating mine, which the 

 writer had occasion to study during the war. 



The only cases for which the magnitude of the increase of 

 inertia hns been determined analytically are those of the 

 cylinder of infinite length moving at right angles to its axis, 

 and of the ellipsoid of revolution, including the sphere. The 

 case of the sphere, in which the increase of inertia is found 

 to be one-half of the mass of fluid displaced, is one which 

 lends itself readily to experimental verification. 



The experiment was carried out in a tank 15 feet in 

 diameter and 30 feet in depth. The spherical body consisted 

 of a mine-case 38*2 ins. in diameter ballasted in such a 

 manner that its weight in water was approximately one 

 pound, the displacement being 1080 lb. ' It was allowed to 

 fall freely through the water under the influence of gravity. 

 The motion was recorded by means of an instrument designed 



* Communicated by Prof. J. E. Petavel, F.R.S. 



f Trans. Camb. Phil. Soc, vol. viii. (1843) ; ' Collected Papers," vol. i. 

 p. 17. 



