The Allais effect is a claimed anomalous precession

Precession

Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...

 of the plane of oscillation of a pendulum

Pendulum

A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

 during a solar eclipse

Solar eclipse

As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

. It has been speculated to be unexplained by standard physical models of gravitation

Gravitation

Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...

, but recent mainstream physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

 publications tend rather to posit conventional explanations for the reported observations.

The effect was first reported in 1954 by Maurice Allais

Maurice Allais

Maurice Félix Charles Allais was a French economist, and was the 1988 winner of the Nobel Memorial Prize in Economics "for his pioneering contributions to the theory of markets and efficient utilization of resources."...

, a French

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 polymath

Polymath

A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...

 who went on to win the Nobel Prize in Economics. He reported another observation of the effect during a 1959 solar eclipse.

Prof. Allais’s explanation for this and other anomalies is that space evinces certain anisotropic

Anisotropy

Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...

 characteristics, which he ascribes to motion through an aether

Luminiferous aether

In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light....

 which is partially entrained by planetary bodies. He has presented this hypothesis in his 1997 French

French language

French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

 book L’Anisotropie de l’espace.

Exotic explanations for Allais and related effects have not gained significant traction amongst mainstream scientists.

Subsequent observations

A recently published observation of what was initially claimed to be a possibly related anomalous gravitational effect (claimed variation of terrestrial gravitation as measured by a sensitive gravimeter

Gravimeter

A gravimeter or gravitometer is an instrument used in gravimetry for measuring the local gravitational field of the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant downward acceleration of gravity, which varies by about 0.5% over the surface of the Earth...

) was by Wang et al. in 2000, for an experiment carried out in 1997 in a remote region of China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 during a total solar eclipse. Further observations which the same team performed in 2001 and 2002 during solar eclipses in Zambia

Zambia

Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....

 and Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 appear to have yielded much weaker evidence of similar anomalies. However, the same authors later (2002 and 2003) published papers explaining that their observations could be explained by conventional phenomena such as temperature and pressure change caused by the eclipse. In their 2002 paper, they posited a more conventional explanation based on temperature changes causing ground tilting, but they suggested that this explanation was unlikely. In their 2003 paper (Flandern and Yang, 2003), on the other hand, the authors argued that atmospheric motion induced by temperature changes was both plausible and sufficient to explain the observed anomaly.

Another anomalous effect during a solar eclipse, an increase in the period of a torsion pendulum, was reported by Saxl

Erwin Saxl

Erwin Joseph Saxl was a physicist and inventor. He was born in Vienna in 1904 and received his Ph.D. there in 1927. In the late 1920s he emigrated to the United States. In 1935 he founded the Saxl Instrument Company, which designed and manufactured tension meters for use in the textile...

 and Allen

Mildred Allen

Mildred Allen was an American physicist.-Early life and education:Mildred Allen was born in Sharon, Massachusetts to MIT professor C. Frank Allen and Caroline Hadley Allen. She had one younger sister, Margaret Allen Anderson.Allen graduated from Vassar College in 1916 with Phi Beta Kappa honors...

 in 1970, but subsequent attempts to replicate this experiment (under different eclipse geometries and with much smaller pendulum bobs) failed to observe any effect (Kuusela, 1991; Jun, 1991). Jeverdan in Romania

Romania

Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

 claimed to have observed anomalous pendulum behavior during a solar eclipse in 1961 (Jeverdan, 1981) – decrease of the period by about 1 part in 2000 – the so-called ‘Jeverdan effect’, but his report was not published in a mainstream English

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

-language scientific journal

Scientific journal

In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...

.

A recent published article on the topic in a mainstream scientific journal (Flandern, 2003) concludes that there have been "no unambiguous detections [of an Allais effect] within the past 30 years when consciousness of the importance of [experimental] controls was more widespread." This paper also suggests a mechanism that might cause slight gravitational variations during an eclipse (high speed high-altitude winds). They point out that "the gravitation anomaly discussed here is about a factor of 100,000 too small to explain the Allais excess pendulum precession… during eclipses" and from this conclude that the original Allais anomaly was due to merely poor controls.

A possible but yet controversial explanation is the so-called van Flandern-Yang hypothesis

Van Flandern-Yang hypothesis

The van Flandern-Yang hypothesis is the theory attempting to explain theunusual anomalies of about 7 m/s2 observed in theSolar eclipse of March 9, 1997. This hypothesis conjectures that the gravity anomalies are due to a travelling density spot in the upper atmosphere caused by the cooling during...

 by van Flandern and Yang's article, which conjecture the effect is due to the gravitational effect of an increased density spot in the upper atmosphere created by cooling during the solar eclipse.

A self-published review article by Chris Duif, which surveys the field of gravitational anomalies in general, concludes that the question remains open, and that such investigations should be pursued, in view of their relatively inexpensive nature and the enormous implications if genuine anomalies are actually confirmed – but the article has not undergone any peer review

Peer review

Peer review is a process of self-regulation by a profession or a process of evaluation involving qualified individuals within the relevant field. Peer review methods are employed to maintain standards, improve performance and provide credibility...

.

Eight gravimeters and two pendulums were deployed across six monitoring sites in China for the solar eclipse of July 22, 2009. It is hoped that this effort will resolve the uncertainties surrounding this problem.

An automated Foucault pendulum was used by H.R. Salva and found no evidence for a precession change of the pendulum's oscillation plane (<0.3 degree / hour) during the Solar eclipse of July 11, 2010

Solar eclipse of July 11, 2010

The total solar eclipse of July 11, 2010, occurred over the southern Pacific Ocean. -Visibility:The eclipse was one of the most remote in recorded history...

.