Reaction of Dynamo, Field and Armature

A principle of the dynamo current generator, discovered by Soren Hjorth of Denmark. When the armature is first rotated it moves in a field due to the residual magnetism of the field magnet core. This field is very weak, and a slight current only is produced. This pa ing in part or in whole through the field magnet cores slightly strengthens the field, whose increased strength reacts on the armature increasing its current, which again strengthens the field. In this way the current very soon reaches its full strength as due to its speed of rotation. The operation is sometimes termed building up. Sometimes, when there is but a trace of residual magnetism, it is very hard to start a dynamo.