| HYPERBOLIC SLOT displays
an aspect of mathematics which is positively arresting. A flat vertical
plane made of plastic is mounted on a table top; there is a curve
cut into the plastic sheet. Next to the plastic sheet stands a straight
stick which is mounted on a vertical rod. The stick, even though
it is straight, swings cleanly through the radically curved slot
in the plastic. Graphics explain why this is so, and describe the
nature of the curve.