The Headmaster's Resonance Dial

At the center of the circular solar stands a heavy pedestal of dark mahogany, topped with a rotating brass ring surrounding a core of translucent quartz. Four crystalline lenses, colored ruby, sapphire, emerald, and topaz, are set into the ring at the cardinal points. The air smells faintly of ozone and old leather, while a soft hum resonates from the pedestal, causing nearby loose papers to flutter as if in a gentle breeze. When the ring is turned, the central quartz pulses with a light that matches whichever lens is currently aligned with a north-facing brass arrow fixed to the floor.