Foucault wrote that after about a half hour, the eye can pick up that the room has rotated such that the pendulum does not appear to be traveling in the same path. He suggested that a fixed point be drawn beneath the bob so the appearance could be seen in smaller increments of time.
The pins that form a circle beneath the bob of the pendulum serve the purpose that Foucault suggested (the Foucault pendulum at the Franklin Institute has 90 pins). The pins are surprisingly light-weight. As the pendulum swings, it passes through a path that contains the pins. As the earth rotates, the building rotates. Throughout the day, the pins are knocked down by the swinging pendulum. One could tell what time it is based on the number of pins knocked over. However, a Foucault pendulum is not a very accurate time piece. |
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Last Modified: Wednesday, 01-Mar-2000 00:30:05 EST |