Page:Incandescent electric lighting- A practical description of the Edison system.djvu/70

 have to manipulate our field-resistance boxes so as to permit more current to, How around the field-magnets, thus increasing our current and raising our pressure to the proper point.

This is continued until the number of lamps in circuit nearly equal the capacity of the pair of dynamos in operation, when two others are started, and are permitted to get up to the proper speed before they are connected with the general circuit; for the pressure of the current from any dynamo varies with its speed; and should a dynamo be connected to the general circuit before it had attained the necessary speed to give its current the proper pressure, the current from the dynamos already in operation would pass through it and cause its armature to rotate without producing any current; on the contrary, it would absorb an amount of current proportional to the power

necessary to turn its armature, and whatever that armature might be connected with by belting,—this condition is known as making a motor of a dynamo.