Well, it could have been a rotary switch-a small,round ceramic base,covered with a brass lid,with a small brown bakelite knob.Or it could've been two small buttons on a more-or-less normal appearing light switch plate,or even a modern-appearing switch. There were several styles out at the time. I'd go with the dual pushbutton type.(relatives of mine lived in a house back in the '70's that had its original mid-30's wiring and it had the dual-pushbutton type).