Foucault Pendulum



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:

Historical Reception
The Popular and Scientific Reception of the Foucault Pendulum in the United States by Michael F. Conlin, Ph.D. Full Text Link

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:

p.185

p.193

The work goes on at length on the public controversy surrounding the experiment.

Systematic Error
Prof. A.C. Longden of Knox College found that the pendulum was subject to mechanical errors and bias. From "On the Irregularities of Motion of the Foucault Pendulum" in the April 1919 edition of The Physical Review we read:

Non-Uniform Variation
In Earth Not a Globe Samuel Birley Rowbotham informs us that the variation of the pendulum is often non-uniform and unpredictable:

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:

From The Romance of Science (8-10) we read:

Museum Exhibit Devices
We read the following from an installation guide:

http://www.academypendulums.com/pdf/Mark2FoucaultInstallation.pdf (Archive)

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".

Dr. Schoepffer
Dr. Schoepffer, an eye-witness of the experiment, says:

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.

https://www.southpolestation.com/trivia/00s/southpolefoucault.html (Archive)

Mach's Principle
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."

External links:

 * Amir D. Aczel, Pendulum: Léon Foucault and the triumph of science


 * Foucault Pendulum chapter in Earth Not a Globe by Samuel Birley Rowbotham


 * The Romance of Science by Lady Blount and Zetetes