Questions about changing the speed of a toy motor. - echoplex motor.jpg (0/1)

This one should be easy for most of you. My question is, what type
(rating, voltage, amp) of variable resistor or other component should
I use to connect to an old toy motor (see pic) that would allow me to
manually change it's speed? My first attempt was to connect a dimmer
switch (from a light fixture) between one of the leeds and the power
source (a.c. plug from outlet). Even with the dimmer rotated to it's
max position the motor did not spin. The specs on the label of the
motor read as follows: V.115     Hz.60     A. .25     RPM 1550

Thanks in advance, Bill.