The Foucault Pendulum is a famous experiment which is alleged to give simple, direct evidence of the earth's rotation. Introduced in the 1851, Léon Foucault claimed that the swinging rotational motions were proof the earth's rotation. The pendulum swings back and forth, and over time, slowly seems to rotate over its arena or "pit". It is explained that the earth is rotating beneath the pendulum. Today Foucault Pendulums are popular displays in science museums and universities.
A common criticism of the Foucault Pendulum is to point out that when the pendulum experiment has been recreated and put into motion, the pendulum has often been seen to rotate in excess, in shortness, or in an opposite direction from the direction it should have traveled according to theory. At times it does not rotate at all. Those scientists who have repeated the experiment have freely admitted that “it was difficult to avoid giving the pendulum some slight lateral bias at starting.”
In the unmotorized Foucault Pendulum experiment the pendulum is, as we will read below, generally inconsistent in its movements. Because of air resistance and the impossibility of perpetual motion, the unmotorized pendulum will only move for a short while before needing to be reset. In motorized Foucault Pendulums, as seen in museum exhibits, it is the repetitive machinery which imparts the repeating lateral bias that creates the regular results seen for the museum's visitors.
Thus, the experiment is entirely invalid as a demonstration of diurnal rotation. That a pendulum on a line can rotate as it swings back and fourth has more to do with the initial conditions which set it into motion than the supposed rotation of the earth.
Lady Blount provides the following in The Romance of Science:
“ 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! ”
History professor Michael Conlin gives us a historical account of the Foucault Pendulum and its reception. We read that, although the Foucault Pendulum was publicly supported by Royal Astronomer George Airy and others, it was privately rejected:
“ In private correspondence, Airy had repeatedly dismissed the Foucault pendulum experiment as a "fraud." He regarded the latitude-dependent formula for the period of the apparent precession of the pendulum as a "mathematical curiosity having no application whatever to the soi-disant experiment." Attending no demonstrations, Airy based his conclusion on oral accounts of the experiment. Concurring with Airy, Powell accepted the theory but held that as a "practical question" the experiment was "doubtless open to every kind of doubt." After learning of successful demonstrations by British scientists, Airy conducted his own experiments. Although it was possible to conduct the experiment properly, he concluded that the "difficulty of starting a free pendulum, so as to make it vibrate at first in a plane, is extremely great."
Although Airy and Powell kept their opinions private, popular journals learned of their rejection of the experiment. Linking Airy's and Powell's doubts to recent unsuccessful popular demonstrations of the experiment, these journals questioned the validity of the Foucault pendulum. The London Literary Gazette recommended caution to those who would attempt the experiment because "persons unqualified by previous habits of research and accurate investigation" had failed. The Literary Gazette knew of several exhibitions "in which, to the horror of the spectators, the earth has been shown to turn the wrong way." The Illustrated London News expressed similar reservations, observing that the "experiment is now giving rise to much controversy, and it is hard to conceive that there is not some fallacy lurking at the bottom of it." ”
“ In Newark C. Dowden, a correspondent of the AAAS [American Association for the Advancement of Science], conducted an unsuccessful repetition in July. In an article for Appletons' Mechanics' and Engineers' Journal, Dowden explained that scientists had "jumped to a hasty and premature conclusion" in asserting that a vibrating pendulum could provide a visible proof of the earth's rotation because of two "unjustifiable" assumptions:t hat friction at the point of suspension was nothing and that the pendulum could vibrate independently of the earth's motion Dr. William Kitchell, a member of the AAAS, and two other gentlemen repeated the experiment with a pendulum thirty feet in length at the New Jersey Art-Union Gallery in Newark. After numerous trials made over several days, they reported to the Newark Advertiser that the result was "invariably ELLIPTICAL MOTION!" While it might have been theoretically possible to take sufficient precautions to repeat the experiment successfully, they "reluctantly" concluded that air resistance and the impossibility of bringing the pendulum completely to rest before starting were "insuperable obstacles to its practical performance. "After consultation with Dowden, Kitchell reasoned that Foucault's demonstration at the Pantheon and subsequent American exhibitions must have been "vitiated" by "unobserved errors." They boldly proposed another method to demonstrate the earth's motion with a pendulum by measuring the deviance between the calculated motion and the observed motion of the apsides of the ellipse. They hoped that Strong would determine the angular motion of the ellipse of a given pendulum so that they might perform the experiment. Assuring them that the Foucault pendulum demonstrated the earth's rotation, Strong offered to repeat the experiment for doubters. Dowden remained unconvinced, believing that he had a "positive duty" to reject the Foucault pendulum because its "advocates cannot agree among themselves," its proofs were "impossible," and its workings "absolutely absurd."2 ”
The work goes on at length on the public controversy surrounding the experiment.
In Earth Not a Globe Samuel Birley Rowbotham informs us that the variation of the pendulum is often non-uniform and unpredictable:
“ 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? ”
The Wrong Direction
The Foucault Pendulum is often seen to move in the wrong direction entirely. See the following from A Hundred Proofs The Earth is Not a Globe:
“ 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. ”
From The Romance of Science (8-10) we read:
“ 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. ”
Museum Exhibit Devices
We read the following from an installation guide:
“ Pay close attention to the photo beams alignment. This adjustment can effect the Ball’s precession around the pit. It may require a couple of days to determine if precession is operating properly. Precession is a function of the Earths rotation. ”
We are instructed to spend several days adjusting the alignment of the photo beams, which affects the pendulum's precession, an element which is supposedly a function of the earth's rotation, until we have determined that the "precession is operating properly".
South Pole Pendulum
In 2001 a Foucault pendulum device was installed at the "South Pole" in the stairwell of a newly constructed research station. It has been claimed that this verified Foucault’s theory. However, excerpts from the report show that adjustments had to be made to obtain the desired results.
“ A hole was drilled through a length of 2×4 through which the pendulum’s wire was fixed in such a way that it would have freedom of movement in all directions. The 2×4 was then fixed to the top of the stairwell and the wire suspended down into the stairwell. ”
“ There was no mechanism for keeping the pendulum swinging and the amplitude decayed within a couple of hours so it had to be restarted periodically over the 24 hour period.
...Our first attempt with the pendulum showed the Earth spinning backward from what was expected. We didn’t notice this at first because we’re all from the Northern Hemisphere and are accustomed to the earth spinning in an anticlockwise direction. We then realized that from our frame of reference the earth should be spinning clockwise so we had to modify the pendulum.
...Our second attempt showed the earth rotating in the proper direction but at an angular velocity twice what is expected (ire., 12 hour days instead of 24). We suspected some kind of government conspiracy but decided to make a further modification and try it again.
...It was difficult to make the pendulum swing in a plane instead of an ellipse. After several attempts with various techniques of holding the bob and dropping it we always got some kind of ellipse instead of a plane. This adds to our error because it is more difficult to locate and mark the pendulum arc’s apex. A way to do it is to suspended the bob by tying it off with a piece of string and letting it settle, then burn through the string. The bob would then drop without any outside force and swing in a plane. Since it is against the Antarctica Treaty to have any open flames at the South Pole we could not do this. After much practice Mike Town got very adept at dropping the bob so that it arced in a plane. ”
One alternative explanation that has been suggested by those who do accept the Foucault Pendulum is Mach's Principle. 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."