The C. G. S. or fundamental unit of force. It is the force which can
impart an acceleration of one centimeter per second to a mass of one
gram in one second. It is equal to about 1/981 the weight of a gram,
this weight varying with the latitude.

A dynamo in which the rotation of a conductor effects a continuous
increase in the number of lines cut, by the device of arranging one part
of the conductor to slide on or around the magnet. (S. P. Thomson.)
Faraday’s disc is the earliest machine of this type.

A dynamo in which the inductive or armature coils were carried at the
ends of the prongs of a gigantic tuning fork, and were there maintained
in vibration opposite the field magnets. It was invented by T. A.
Edison, but never was used.

A dynamo whose field magnet is excited by a single coil. Several such
have been constructed, with different shapes of field magnet cores, in
order to obtain a proper distribution of poles.

A dynamo whose field is wound in shunt with the external circuit. Two
leads are taken from the brushes; one goes around the field magnets to
excite them; the other is the external circuit.
In such a dynamo the lowering of resistance on the outer circuit takes
current from the field and lowers the electro-motive force of the
machine. Short [...]

A dynamo whose armature, field winding, and external circuit are all in
series.
In such a dynamo short circuiting or lowering the resistance of the
external circuit strengthens the field, increases the electro-motive
force and current strength and may injure the winding by heating the
wire, and melting the insulation.

A dynamo whose field magnets are excited by a separate current
generator, such as a dynamo or even a battery. Alternating current
dynamos are often of this construction. Direct current dynamos are not
generally so. The term is the opposite of self-exciting.

A dynamo in which the field magnet coils are entirely disconnected from
the main circuit, and in which current for the field is supplied by
special coils carried for the purpose by the same armature, or by a
special one, in either case a special commutator being provided to
collect the current.

A dynamo which excites its own field. The majority of dynamos are of
this construction. Others, especially alternating current machines, are
separately excited, the field magnets being supplied with current from a
separate dynamo or current generator.

Dynamos can be coupled exactly like batteries and with about the same
general results. An instance of series coupling would be given by the
dynamos in the three wire system when no current is passing through the
neutral wire, and when the lamps on each side of it are lighted in equal
number.