|| This St. Louis motor with the electromagnet supplying
the magnetic field is unmarked, and does not appear to have been made by
Knott, Welch or Central Scientific. The electromagnet can be connected
in parallel or in series with the armature.
However, the motor can also be run as a generator or a
magneto. It can be connected to a galvanometer and twisted slowly with
the fingers to show the direct (but pulsating) nature of the output EMF.
It can also be equipped with slip rings to produce an alternating output.
The bar magnets may be swung away when the armature is being rotated to
show the dependence of the output on the strength of the magnetic field.