122 Dr. J. A. Ewing and Mr. L. H. Walter. [Jan. 11, 



provided on the interior with two long wedge-shaped pole-pieces, 

 M, M, the current to the winding being supplied through brushes 



bearing against insulated rings below. The magnet is made to revolve 

 by an electro-motor, the best speed being about five to eight revolu- 

 tions per second, but the electro-magnet may be replaced by a 



