10 



that in all cases the ratio between the 

 electromotive forces of the two machines 

 remains the same, namely, — -(4-) Of 



two machines containing the same 

 amount of material, the one which is 

 wound to give alternating currents will 

 therefore produce about two and a quar- 

 ter times the electromotive force of that 

 wound for continuous current. Since 

 the halves of the armature-conductor in 

 a direct-current machine are grouped in 

 parallel, the strength of current, which 

 such a machine gives when the current 

 density is the same as in the armature of 

 an alternator of equal dimensions, is 

 twice that of the latter, so that the out- 

 put of the alternator will only be about 

 12 per cent, greater than that of a direct- 

 current dynamo of equal weight. This 

 result, it should be remembered, has 

 been obtained on the basis of the fchi 

 of alternators as found in text-books, 

 whilst neglecting self-inductions, dis- 

 tortions of field, and other disturbing 

 elements; and, before it can be accepted 



