MAGNABRIDGE
Electromagnetic Drawbridge Works
Cog-carts roll the slate line toward four gaps. Each gap's drawbridge is held by an
electromagnet — keys 1–4 cycle it:
LAY — plate down: iron carts roll across.
PULL — plate up, coil energised: brass carts are yanked over.
Wrong state and the cart drops into the void. Mind the plate travel time — traffic never stops.