CHAP. VIL] MAGNETO-ELECTRIC MACHINES. 665 



In 1871 M. Jamin communicated to the French Academy of 

 Sciences a short note by M. Gramme on a magneto-electric machine 

 which gave electrical, currents always in the same direction by the 

 revolution of an electro-magnetic ring between the poles of a per- 

 manent magnet. The construction of the electro-magnetic or ring 

 armature in Gramme's machine differs in some mechanical details 

 from that of the transversal electro- magnet of Pacinotti, and the 

 serious mistake of applying the rubbers which carry off the current 

 at the wrong place is avoided. We must therefore regard the Gramme 

 machine as the first effective magneto-electric machine constructed to 

 give continuous currents all flowing in the same direction. 



The construction of the ring armature in Gramme's machine will 

 be readilv understood from. Fig. 435, in which it is represented in 



FIG. 485. Gramme armature. 







different stages of its construction, so as to show the manner in which 

 the principal parts are connected. At A a section of the iron ring 

 itself is shown, composed of a bundle of iron wires ; at B B the helices, 

 or bobbins, are seen both in section and detached; and at E K the form 

 is shown of one of the insulated copper conductors, to which the 

 contiguous ends of the wires of the helices are attached, and from 

 which the current is drawn off by means of rubbers or brushes formed 

 of flexible bundles of copper wire. These brushes are so applied at 

 the neutral positions of the ring that they begin to touch one of the 

 conductors, R, before they have left the preceding one. In this way 

 no actual break or interruption occurs in the current. The permanent 



