374 



ELEMENTARY LESSONS ON [CHAP. x. 



end of the axis. This armature differs from the earlier 

 simple longitudinal armature of Siemens only in the 



Fig. 151. 



multiplication and arrangement of its parts, the four- 

 fold division giving a current which is practically con- 

 tinuous. The commutator consists of a metallic tube 

 split into eight parts, different segments being connected 

 with each other through the separate coils of the arma- 

 ture. Against the commutator press a pair of metallic 

 brushes or springs, as contact pieces, which touch oppo- 

 site sides at points on the right and on y the left, and 

 so lead away into the circuit the current generated 

 in the coils of the rotating " armature. Suppose the 

 lines -of- force in the field to run vertically downwards, 1 



1 Their exact direction is not exactly this when the generator is working, 

 as the magnetic force due to the currents in the coils, which is nearly 



