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rounded by radial coils c. The yoke- 

 rings y are of cast-iron and the magnet- 

 cores of wrought or cast-iron with pole- 

 shoes of rectangular shape. This arrange- 

 ment has been adopted with a view to 

 obtain, on the outside of the armature, as 

 large a ratio as possible between the 

 pitch and length of field. For the same 

 purpose, and to reduce leakage, the pole- 

 shoes are tapered on the inside. The 

 importance of securely supporting the 

 armature- wires is well known, and there 

 is hardly any good continuous-current 

 dynamo now made, in which this 

 mechanical detail does not receive careful 

 attention. In alternators, a strong 

 mechanical fastening of the wires on the 

 armature is, however, of even greater 

 importance. The mechanical strain to 

 which the wire is subjected depends, not 

 on the mean current and electromotive 

 force at which the machine is rated, but 

 on their maximum values. Now the 

 maximum value of the periodic current 

 is about 40 per cent, greater than the 

 mean value, and the same is the case with 



