378 ELEMENTARY LESSONS ON [CHAP. x. 



A continuous current will therefore be generated in an 

 external wire, making contact at F and F by means of 

 brushes, for as each successive coil moves up towards 

 the brushes the induced current in it increases in 

 strength, partly because of the increased inductive action 

 in itself, partly because the coils on each side of this 

 position are sending their induced currents also toward 

 that point. 



Fig. 153 shows the arrangements of the little Gramme 

 machine, 21 inches high, suitable for producing an 

 electric light when driven by a 2^ horse-power engine. 

 Above and below are opposite pairs of powerful electro- 

 magnets, whose iron pole -pieces project forwards and 

 almost embrace the central ring -armature, which, with 

 the commutator, is fixed to the horizontal spindle. 



411. In Brush's dynamo-electric generator, a ring- 

 armature is also used, but it differs somewhat from that 

 of Gramme's machine in detail, the iron ring being 

 enlarged with protruding cheeks, with spaces between in 

 which the coils are wound, the coils themselves being 

 also somewhat differently joined. The " Brush " machine 

 has found almost as great favour in America as the 

 " Gramme " in Europe. In another new machine, de- 

 vised by De Meritens, a rotating ring-armature, resemb- 

 ling those of Paccinotti and Brush, moves in front of 

 fixed permanent steel magnets. This machine gives 

 powerful alternating currents. Alternating current- 

 machines have also been devised by Lontin, Gramme, 

 and Siemens, for use in particular systems of electric 

 lighting. 



All and any of the continuous-current magneto-electric 

 and dynamo-electric machines can be used as electro- 

 motors, the armature rotating with considerable power 

 when a current from an independent source is led into 

 the machine. 



