The Focault Pendulum is a famous experiment alleged to give simple, direct evidence of the earth's rotation. Introduced in the 1851, Léon Foucault claimed that the motions were proof the earth's diurnal rotation. Today Foucault Pendulums are popular displays in science museums and universities.
Lady Blount provides a summary of the Foucault Pendulum experiment:
“This pendulum, modern scientists tell us, affords a visible proof that we are living on a whirling globe, which, according to a ‘work on science’ now before me, is spinning upon its so-called axis at the rate of over 1,000 miles an hour at the equator; and, in addition to other motions, is rushing on an everlasting tour round the sun (the diameter of which is said to be 813,000 miles, and its weight 354,936 times greater than the earth from which it is said to be about 93,000,000 miles distant,) at the rate of over 1,000 miles per minute. Now to prove that the earth really has these motions a pendulum is suspended at the show; the showman sets motion, and bids the gaping world of thoughtless men and women to ‘behold a proof’ that we are living on a whirling globe which is rushing away through space!”
—The Romance of Science, Lady Blount
Samuel Birley Rowbotham informs us that the variation of the pendulum is often non-uniform:
“First, when a pendulum, constructed according to the plan of M. Foucault, is allowed to vibrate, its plane of vibration is often variable – not always. The variation when it does occur, is not uniform – is not always the same in the same place; nor always the same either in its rate or velocity, or in its direction. It cannot therefore be taken as evidence; for that which is inconstant cannot be used in favor of or against any given proposition. It therefore is not evidence and proves nothing! Secondly, if the plane of vibration is observed to change, where is the connection between such change and the supposed motion of the Earth? What principle of reasoning guides the experimenter to the conclusion that it is the Earth which moves underneath the pendulum, and not the pendulum which moves over the Earth? What logical right or necessity forces one conclusion in preference to the other? Thirdly, why was not the peculiar arrangement of the point of suspension of the pendulum specially considered, in regard to its possible influence upon the plane of oscillation? Was it not known, or was it overlooked, or was it, in the climax of theoretical revelry, ignored that a ‘ball-and-socket’ joint is one which facilitates circular motion more readily than any other?”
—Earth Not a Globe, Samuel Birley Rowbotham
Dr. Samuel Birley Rowbotham further discusses the Foucault Pendulum and its movements in Chapter 14, Section 8 of Earth Not a Globe. Rowbotham provides additional insight in Chapter 14, Section 21.
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 pendula 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 similarly with the official published results of Focault's experiments.
The Wrong Direction
The Focault Pendulum is often seen to move in the wrong direction entirely. See the following quotes:
“Astronomers have made experiments with pendulums which have been suspended from the interior of high buildings, and have exulted over the idea of being able to prove the rotation of the Earth on its ‘axis,’ by the varying direction taken by the pendulum over a prepared table underneath – asserting that the table moved round under the pendulum, instead of the pendulum shifting and oscillating in different directions over the table! But, since it has been found that, as often as not, the pendulum went round the wrong way for the ‘rotation’ theory, chagrin has taken the place of exultation, and we have a proof of the failure of astronomers in their efforts to substantiate their theory.”
—100 Proofs the Earth is Not a Globe, William Carpenter
“We believe, with all due deference to the pendulum, and its proprietor, that it proves nothing but the craftiness of the inventor; and we can only describe the show and showman as deceptions. A thing so childish as this ‘pendulum proof’ that it can only be described as one of the most simple and ridiculous attempts to gull the public that has ever been conceived. It has been said that the pendulum experiment proves the rotation of the earth, but this is quite impossible, for one pendulum turns one way; and sometimes, another pendulum turns in the opposite direction. Now we ask does the earth rotate in opposite directions at different places at one and the same time? We should like to know. Perhaps the experimenters will kindly enlighten us on this point … If the earth had the terrible motions attributed to it, there would be some sensible effects of such motions. But we neither feel the motion, see it, nor hear it. And how people can stand watching the pendulum vibrate, and think that they are seeing a proof of the motions of the earth, almost passes comprehension. They are, however, brought up to believe it, and it is thought to be ‘scientific’ to believe what the astronomers teach.”
—The Romance of Science (8-10), Lady Blount
As an alternative explanation, Mach'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."