Equivalent Shell of a Circular Current. 139 



The similarity of the expression obtained for the Total 

 Stress Energy with the Kinetic Energy of the aether produce.! 

 by motion of a charged sphere is noteworthy. 



§ 4. Tlie Magnetic Analogue. 



The magnetic analogue of the circular electric current 

 was experimentally tried. A flywheel with a rim of circular 

 cross-section mounted on " single-ball ? ' bearings was ma£- 

 netized by an electric current so as to have its north pole at 

 the two ends of the axle, the south pole being distributed 



Two brushes 



mainly along the axis of the circular rim. 



Fi<r. 3. 



made contact with the two sides of the flywheel, and a 

 circuit was completed through a sensitive dead-beat galvano- 

 meter. The deflexion increased with the speed of rotation 

 and with the "magnetic current " threaded by the circuit, 

 increasing to a maximum when the contact was near the 

 neutral line of the rotating magnet and decreasing to zero 

 when the contact was made with the centre of the screw- 

 heads. The deflexion reversed in direction with reversal of 

 the " magnetic current." 



The current may no doubt be explained from ordinary 



