Thanks for giving me research for the next few days. I did not realize the difference. I was thinking of a dimmer switch, similar to ones that are installed in homes to control lighting and fans. I am still uncertain if it is actually a rheostat or an autotransformer. I have always heard them called rheostats.
I love learning and AC is one of my weak areas, so thanks for pointing this out. I did find a formula for figuring out the pulley size and rpms.
Drive Pulley diameter / driven pulley diameter * input RPM = Output RPM