Once, as a child, I visited the Franklin Institute in Philadelphia. In a room devoted to clocks and clockwork, I was mesmerized by an erratically moving miniature tetherball: Beside a vertical 4-inch rod, a tiny ball hanging by a fine chain from a swinging arm was being flung in an arc. The ball and chain wound up around the rod, unwound, and then the ball was flung around again to wind up, unwind . . .

One 19th-century novelty clock used such a tetherball, rather than a pendulum, to regulate its ticks. It wasn't particularly accurate, but it was unique and entertaining, and that's why a tetherball was in the Franklin Institute in 1957. In 1998, by then a confirmed Burner, I recalled my visit and thought, "Yes! Really big, and on fire. I have to build one."