ROTATING A DIELECTRIC IN A MAGNETIC FIKLD. 



125 



.it S. SM liinl lln- oil -in : 'l|. i.t' til-- siirl-K I tin- :i\lf til!'- fct) ilv r,,l .li.Mi in ll,,- 



magnetic field could not affect the potential of the outside coating (/C of the ebonite 

 cylinder. 



The magnetic field was produced by a solenoid 16 centims. long, 5';} centims. 

 inside, and 15 centims. outside diameter, having 95'5 turns per centim. The axle 

 was supported by hard-steel cones, on which it turned, which were carried by a 

 heavy cast-steel mounting. Fig. 2 shows the mounting of the cylinder and solenoid 

 drawn to scale, and fig. 3 is a vertical section perpendicular to the axis of the 

 cylinder. 



Fig. 3. A, phosphor bronze axle ; BB, elwnite cylinder; KF, brushes ; \V\V, water jacket ; 

 SS, solenoid ; CC, steel base. Dotted linu = pillar supporting Injuring. 



The steel cones were bored through as shown, and connected to an oil reservoir 

 (see fig. 4) about 2 feet above the level of the bearings. Oil was thus supplied 

 under pressure at the axis of the bearings, and the lubrication was so good that even 

 when running continuously at 200 revolutions per second the bearing! did not 

 get hot. 



The sliding contact or brush at E, tig. 2, was supported by a brass rod carried at 

 each end by ebonite plates screwed to the frame of the solenoid. The rod could 

 rotate freelv in holes in the ebonite, and at K' a small lever was attached to it, the 



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weight of which kept the brush pressed against the rotating cylinder. The brush 

 was formed of about 15 thin brass wires soldered side by side at right angles to the 

 brass rod. 



A similar brush arrangement at K, fig. 2, was carried by a brass tube passing 

 through the ebonite plate K', and was kept pressed against the rotating tube by a 

 small lever at K', pulled down by a spiral spring. 



