St. Louis Motors
   The St. Louis (Laboratory) Motor was described in an article of the same name in the October 1909 issue of School Science and Mathematics. The author was S. A. Douglass of Soldon High School in St. Louis, Missouri; presumably he taught physics at the high school. He noted that the motor was the "outgrowth of a long series of experiments conducted by the physics teachers of the St. Louis high schools." The key idea was that the parts were all out in the open so that the students could see the rotating armature, the commutator and the source of the magnetic field. The latter could be supplied by either a pair of bar magnets or an electromagnet. These two configurations are shown by the two St. Louis motors below, both from the Greenslade Collection.
   With the bar magnets in place the effect of changing the magnetic field can be observed by swinging the poles in and out. The operation of the commutator can be studied by moving the bar holding the brushes back and forth to apply the magnetic torque early or late. The motor with the bar magnets is a Milvay model, made by the Chicago Apparatus Company. In the 1929 catalogue, the basic motor is listed at $4.00, and an electromagnet was an extra $1.25.
   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. 

  The St. Louis Motor below is in the Greenslade Collection and was made by the firm of C.H. Stoelting of Chicago. It is shown, in a slightly differnt form, in the 1912 Stoelting catalogue, where the copy reads: "The original of the ... dissectible motor was designed by one of the experts in our laboratory while teaching in one of the St. Louis high schools, but it has since been remodeled in accordance with suggestions by a number of teachers in the St. Louis high schools ... it has now been used for over two years in the shop and laboratories of the St. Louis and other high schools." This model has both DC and AC armatures, with the latter used to "show alternating current effect with [a] D'Arsonval galvanometer." The total cost was $3.65.
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