228 



HEXKY A. EOWLAXD 



inside of the rings. In the Siemens pattern the coils are around the 

 ends of the armature. In a section of the Gramme ring (Fig. 8), the 

 outside portion of the wire (a) is active, since the lines of force follow 

 the core and the outside of the ring around; but the lines of force do 

 not go through the core of the ring, so that the inside portion (6) is 

 dead, so that we can say nearly half the wire is dead wire. In the 

 Siemens armature one cannot see immediately how much dead wire 

 there will be, because it depends upon the length of the armature. The 

 wire is wound around in that way (Fig. 9), and this portion (a a) is 

 active, and this portion (6 &) is dead. If the armature is very thick we 

 would have more dead wire than when it is simply long. I cannot say 

 which has the more dead wire, but I dare say the Gramme has more 



I 1 I I 



J 4_l 



i 1 i 1 i 



FIG. 9. 



than the Siemens. Furthermore, either in the Gramme ring or the 

 Siemens armature (Fig. 10) we have the lines of force running across 

 here (arrows) ; that portion is active ; but these portions (a a) in between 

 the poles are dead, and when the armature revolves we have the lines 

 of force turning around, and I think that would add more dead wire. 

 I believe an attempt has been made to throw out these coils. 



There is no necessity to go further. As I have said, the efficiency of 

 the circuit depends upon the ratio of the resistance of the armature to 

 the resistance of the wires, and therefore, as far as this point is con- 

 cerned, any machine can be made as efficient as one pleases by putting 

 in greater and greater external resistance. But as the magnet remains 

 the same, we would find a point where the efficiency as a whole would 

 not increase for an increase of external resistance, but would actually 

 diminish. There are other things to be taken account of, such as losses 



