Edgar Allan Poe paired a pendulum with menace.

In some circles, the pendulum and its swing have been accorded special, even occult powers. Many believe that the pendulum's mesmerizing motion induces hypnosis. Others say the steady sweep, followed by stillness, enables fortune telling.

Roch Preite operates Pendulum Hypnotic Solutions in Old Bethpage, N.Y. A slow arcing pendulum can be hypnotic for several reasons, he said.

"The thing that catches one's eye, I think, is the consistency and rhythmic nature of the swing," he said. "Its smoothness is alluring and it can be comforting. It harkens back to the beat of your own mother's heart while you were still in the womb."

Legend credits a teenager bored during Mass in a cathedral in Pisa, Italy, with first noticing the characteristics later associated with the pendulum.

Of course, Galileo was no ordinary teen.

As the story goes, while cathedral-bound, he noticed that a chandelier swinging overhead "took as many beats to complete an arc when hardly moving as when it was swinging wildly." (Years later, Galileo's support for the heretical theory that the Earth orbits the sun really steamed the Catholic Church.)

Indiana University physics professor Roger Newton, apparently no kin to Isaac, wrote in "Galileo's Pendulum" that the principle of the pendulum's swing, as identified by Galileo in the 1580s, "marks a simple yet fundamental system in nature, one that ties the rhythm of time to the very existence of matter in the universe."

The period for a pendulum's single swing -- how long it takes for the pendulum to go back and forth once -- is tied to the length of the pendulum and the force of gravity. Because gravity is a constant, "the only thing that affects the period of a pendulum is the length of the pendulum," according to howstuffworks.com.

But Galileo did not invent the pendulum clock. Dutch mathematician-astronomer Christiaan Huygens recognized how the pendulum's swing could be tied to timekeeping. Historians say he invented the pendulum clock in 1656.

For grandfather clocks, the pendulum's steady swing -- together with descending weights or springs, gravity and attachment to gears -- provides the steady "tak, tick" for the clock's second hand.

Time ticks forward and the grandfather clock chimes, sounds that can startle and pester a restive overnight guest or charm owners accustomed to the clock's striking accompaniment to their lives.

Preite said he believes the pendulum "masses all its potential energy and stops for a millisecond before it begins to swing back."

"If ever we could harness that energy and manipulate time itself," he said, "a pendulum would no doubt hold the key to those secrets."