Since the strength of any magnet depends on the number of ampere turns in its field winding, reducing or increasing the number of turns will respectively reduce or increase the field strength, the current being kept constant. =Ques. What is the objection to this method?= Ans. This arrangement is undesirable for magnets of large size, because of the tendency to flashing at the contacts of the regulating switch. [Illustration: FIG. 193.--Shunt wound dynamo for parallel circuit incandescent lighting, and for mill and factory power. The coils of the field magnet form a shunt to the main circuit; they consist of many turns of fine wire and consequently absorb only a small fraction of the current induced in the armature. The characteristic of the shunt dynamo is that it gives practically constant voltage for all loads within its range. If overloaded the pressure will drop and the machine cease to generate current.] =The Shunt Dynamo.=--The shunt wound dynamo differs from the series wound machine, in that an independent circuit is used for exciting its field magnet. This circuit is composed of a large number of turns of fine insulated copper wire, which is wound round the field magnets and connected to the brushes, so as to form a shunt or “by pass” to the brushes and external circuit, as shown in fig. 193. Two paths are thus presented to the current as it leaves the armature, between which it divides in the inverse ratio of the resistance. One part of the current flows through the magnetizing coils, and the other portion through the external circuit. In all well designed shunt dynamos, the resistance of the shunt circuit is always very great, as compared with the resistance of the armature and external circuit, the strength of the current flowing in the shunt coils being very small even in the largest machines. =Ques. For what service is the shunt dynamo adapted?= Ans. It is used for constant voltage circuits, as in incandescent lighting. =Ques. In the operation of a shunt dynamo what is its characteristic feature?= Ans. The voltage at the dynamo remains practically unchanged, and the current varies according to the load. =Ques. Does the voltage remain constant for all loads?= Ans. There is a certain maximum load current that the shunt dynamo is capable of supplying at constant voltage; beyond this, the voltage will decrease, the machine finally demagnetizing itself, and ceasing to generate current. =Ques. Why does the voltage not remain constant for all loads?= Ans. Because there is a drop in the voltage in forcing the current through the armature windings which increases with the load. =Ques. What is the usual method of regulation for shunt dynamos?= Ans. The method of varying the current through the field coils by means of a rheostat inserted in series with the field winding as shown in fig. 194.