Mach's Principle as an Explanation for Rotation
Match's Principle explains that if the earth was still and the all the stars went around the Earth then the gravitational pull of the stars would pull the pendulum. As Mach said "The universe is not twice given, with an earth at rest and an earth in motion; but only once, with its relative motions alone determinable. It is accordingly, not permitted us to say how things would be if the earth did not rotate."
See this passage in the book 'Pendulum' by Simon Winchester: http://books.google.com/books?id=kvGt2OlUnQ4C&pg=PA207&lpg=PA207&dq=mach's+principle+foucault+pendulum&source=web&ots=wCVb9hZqLj&sig=gcTdN3juHCNp1flqN6836GBYGoM&hl=en
Variation by latitude according to Earth not a Globe
Summarily, the line of the pendula must be 25 meters in length to get the minimum effect, and so by necessity, Leon Focault's original experiments between latitudes were conducted outside hung from a tree exposed to the elements. Dr. Rowbotham finds that the variations of the pendulum by latitude are caused entirely by the contraction and expansion of its line due to temperature variations upon the earth's surface in relation to the nearness of the Sun. These variations match up perfectly with the official published results of Focault's experiments.