dinary conditions a person is able to turn the generator handle at
the rate of about two hundred revolutions a minute, and as the ratio
of gearing is about five to one, this results in about one thousand
revolutions per minute of the generator, and, therefore, in a
current of about one thousand cycles per minute, this varying
widely according to the person who is doing the turning.

[Illustration: HOWARD OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCO
An All-Concrete Building Serving the District South of
Market Street.]

The end plates which support the bearings for the armature are usually
extended upwardly, as shown in Fig. 72, so as to afford bearings for
the crank shaft. The crank shaft carries a large spur gear which
meshes with a pinion in the end of the armature shaft, so that the
user may cause the armature to revolve rapidly. The construction shown
in Fig. 72 is typical of that of a modern magneto generator, it being
understood that the permanent magnets are removed for clearness of
illustration.

Fig. 73 is a view of a completely assembled generator such as is used
for service requiring a comparatively heavy output. Other types of
generators having two, three, or four permanent magnets instead of
five, as shown in this figure, are also standard.

[Illustration: Fig. 73. Five-Bar Generator]

Referring again to Fig. 69, it will be remembered that one end of the
armature winding shown diagrammatically in that figure, is terminated
in the pin _5_, while the other terminates in the pin _7_. When the
armature is assembled in the frame of the generator it is evident that
the frame itself is in metallic connection with one end of the
armature winding, since the pin _5_ is in metallic contact with the
armature casting and this is in contact with the frame of the
generator through the bearings. The frame of the machine is,
therefore, one terminal of the generator. When the generator is
assembled a spring of one form or another always rests against the
terminal pin _7_ of the armature so as to form a terminal for the
armature winding of such a nature as to permit the armature to rotate
freely. Such spring, therefore, forms the other terminal of the
generator.

Automatic Shunt. Under nearly all conditions of practice it is
desirable to have the generator automatically perform some switching
function when it is operated. As an example, when the generator is
connected so that its armature is in series in a telephon