ELECTRICITY FOR ENGINEERS 77
In order to start generation a small wire may be
attached to one of the terminals of the dynamo and
the other end brought in contact with the other ter-
minal for a fraction of a second or the shortest possible
instant. If the circuit happens to be arranged some-
what as shown in the figure, the plug may be inserted
so that the dynamo is started through only one lamp.
When this lamp is burning properly the plugs may be
suddenly withdrawn and the current will now force
itself through the other lamps. This process is known
as "jumping in" and should be used only in an emer-
gency, as much damage may be caused, especially if a
dynamo is already running a large number of lamps
and is then "jumped into" a bad circuit. This is also
often done, but is just as dangerous as it would be to
attempt to start a heavy steam engine by opening up
the throttle valve with a quick jerk.
Constant current dynamos are always equipped with
automatic regulators and before the dynamo is started
special attention must be given the regulator to see
that it is in proper working order.
Often it may be desirable and even necessary to run
two dynamos in series, as, for instance, if a circuit has
been extended beyond the capacity of one machine.
In such a case the regulator of one machine is cut out
and that machine set to operate at about its highest
electromotive force, and the variations are taken care
of by the other dynamo.
The Brush System. The brush arc dynamo is quite
distinct from other constant current dynamos in general
We shall therefore give the following descrip-
tion of it taken from literature furnished by the Gen-
eral Electric Company.
The brush arc generator is of the open coil type, the
