Was it not the case that the direction of swing was
unaffected by the earth's rotation, and so it's line
of oscillation seemed to swing around in a circle?

Walt Davidson wrote in message
...
When I worked at the Science Museum in the mid 1960s, one of my duties
was to start the Foucault Pendulum at 2 pm on a Sunday afternoon. Its
purpose was to demonstrate and measure the effect of the earth's
rotation on the direction of swing of the pendulum.