Hogwarts had a clock tower. Whenever its enormous pendulum swung, it made the sound of machinery turning. Yet the Foucault pendulum beneath the Pantheon's dome made no sound at all.
This enormous simple-pendulum apparatus stood on a circular slab of marble, above which sat a transparent table. It was said that, to reduce interference from external forces, the steel cable's suspension mechanism had been specially treated to prevent factors such as friction from affecting the experimental data.
It was the same when people played with an Ouija Board. Perhaps devils and Satan had not come to meddle, but one of the companions playing the game had secretly tampered with it.
In the ignorant ages of the past, all manner of "magic" performances often appeared. One famous trick involved having a boy climb into a basket while people outside thrust swords into it, making blood seep out. Then, after the "magician" recited an incantation, the boy crawled out alive.
To modern people, it was nothing more than a magic show, but people at the time believed it wholeheartedly, thinking the magician truly possessed magic.
The principle of the Foucault pendulum came from inertia, Newton's First Law: all objects not acted upon by external force would continue in straight-line motion. In 1851, when Foucault burned through the thread binding the copper ball, it did not leave a straight trail in the sand tray below. Instead, as though drawing a flower, it traced a complex pattern.
This experiment had ensured that no other forces could interfere, and so people reached a conclusion: the Earth truly rotated on its axis. Humans could not feel the Earth's rotation because their sense of uniform motion depended on changes in their relative position to other objects. When the trees outside a car window moved backward, one felt