[Electric engineering.] . have a higher efficiency. The armature M is ofthe ring, open-circuit type, and its general construction isthe same as that of the older style armature with a numberof improvements in the mechanical details and method ofinsulation. The connections are also slightly different inorder to adapt the armature to a four-pole field. Instead ofconnecting diametrically opposite coils in series, as in atwo-pole machine, four coils situated one-quarter of a cir-cumference from one another are connected in series andthe terminals brought out to the commutator segments. The field i
[Electric engineering.] . have a higher efficiency. The armature M is ofthe ring, open-circuit type, and its general construction isthe same as that of the older style armature with a numberof improvements in the mechanical details and method ofinsulation. The connections are also slightly different inorder to adapt the armature to a four-pole field. Instead ofconnecting diametrically opposite coils in series, as in atwo-pole machine, four coils situated one-quarter of a cir-cumference from one another are connected in series andthe terminals brought out to the commutator segments. The field is the same in some respects as that on the oldmachine, but there are four poles on each side of the arma-ture instead of two. On each side the poles are alternately § 19 ELECTRIC LIGHTING. 19 north and south, but poles directly opposite each other areof the same polarity. For example, in Fig. 13, poles A, Aare alike and of one polarity, while B, B are also alike butof opposite polarity to A, A. In placing and connecting. Fig. 13. the field coils, the instructions sent out by the makersshould be followed carefully, and it is always a good plan tosend current through the coils and test the polarity with acompass before starting up the machine. 23. The other chief point of difference between the new-style and old-style Brush machine lies in the old regulator was entirely separate from the dynamo 20 ELECTRIC LIGHTING. § 19 and took the form of a carbon resistance connected inshunt across the terminals of the field. This resistancewas made of a pile of carbon plates that were pressedtogether by a lever pulled by a magnet connected in seriesin the circuit. If the current increased, the magnet pulledon the lever and pressed the plates together, thereby lower-ing the resistance in shunt with the field. This allowed agreater proportion of the current to flow past the fieldwindings, thus cutting down their magnetizing power, low-ering the voltage, and bringing the main cu
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