Bucharest, 3 October 2005: A Foucault Pendulum and an Allais Pendulum Watched Through a Partial Eclipse

This short French-language note in the Proceedings of the Romanian Academy, Series A (volume 7, number 2/2006, received 31 May 2006), reports a search for the Allais Effect during a partial solar eclipse using both a long Foucault pendulum and a copy of the short ball-borne pendulum that Maurice Allais himself used. Its authors, Ieronim Mihăilă, Nicolae Marcov and Varujan Pambuccian of the University of Bucharest's Faculty of Mathematics and Informatics, dedicate it to Allais and conclude that the effect "was confirmed" once more.

Where the instrument came from

The note explains that nobody observing the 11 August 1999 eclipse had a Paraconical Pendulum, so the Bucharest group had relied on a Foucault pendulum then. At a Paris colloquium on pendulum anomalies held on 28 September 2001, a proposal was made to build two Allais pendulums in Romania, one at the Suceava Planetarium and one at the University of Bucharest. The idea was to observe the slow periodic drift of the swing plane continuously and simultaneously at both sites, echoing Allais's paired Saint-Germain and Bougival runs of 1958. Both pendulums were built to Allais's plans and installed in 2002. Mihăilă refined the Bucharest one between 2002 and 2004, and the acknowledgements credit Guy Berthault with funding it.

The authors also draw a distinction worth keeping. They call the eclipse anomaly the Allais effect in the "restricted" sense, and the periodic azimuth variation Allais found in his continuous 1954–1960 observations the effect in the "broad" sense. They also cite a criterion from Allais's 1999 memoir for NASA, based on the ratio of length to the square of amplitude, which they say favours a short pendulum for showing the effect.

The two pendulums

The Foucault pendulum hung in a stairwell of the faculty, the same one used for the 1999 and 31 May 2003 eclipses; the Allais pendulum stood in an adjacent laboratory. Each pendulum was released by burning a thread, and its swing plane was read on a graduated alidade that the authors say gives azimuth to about a tenth of a degree. The oscillation period was measured only for the Foucault pendulum, and the authors say the stairwell was kept closed, with its temperature gradient checked periodically, while those period determinations were made.

One procedural choice departs from Allais. He relaunched his pendulum in the last azimuth it had reached, chaining the readings; the Bucharest team instead relaunched every time from the same azimuth, 70°, with the support held fixed and the same ball throughout.

What was reported

In Bucharest the eclipse was partial: it began at 11h 15m local time (8h 15m UT), peaked at 12h 32m with the Sun 41° high and 37% covered, and ended at 13h 51m.

For the Foucault pendulum the expected turning rate at Bucharest's latitude (44°25') is 10.527° per hour. The team compares observed azimuths every five minutes with a straight line at that rate. The observed plane falls behind from 11h 20m onwards, the lag reaches about 1.1° (its largest tabulated value is −1.2° at 12h 55m) and stays near that level until roughly 13h 30m, then shrinks back to zero by about 14h 50m. The authors say this matches their own 1999 and 2003 results, Allais's 1954 and 1959 eclipse records, and the amplitude of the broad-sense effect in his 1958 paired runs.

For the Allais pendulum the quantity is how far the plane turned in each 15-minute run, against a Foucault-only expectation of 2.63°. Before and well after the eclipse the readings range from 2.5° to 2.9°. Around the eclipse maximum three runs give 2.0°, 2.2° and 2.0° (starting 11h 45m, 12h 05m and 12h 25m), and the run ending at 13h gives 2.4°. A further reading of 2.0° in the run ending at 14h was discarded because the ball had shifted slightly on its plate; the ball was recentred before later releases.

What the evidence does and does not show

The reported dips line up with the eclipse on both instruments. Even so, the note itself leaves several things unestablished:

• One partial eclipse at one site. The intended second instrument at Suceava is not reported for this eclipse, and no simultaneous record from another place is given.
• No error analysis. The only uncertainty given is the roughly 0.1° error in reading an azimuth; it says nothing about how much the 15-minute rate scatters from run to run. There is no statistical treatment and no comparison with non-eclipse days for the azimuth. The note says the Foucault period was also measured on the Sunday and Tuesday around the eclipse, but those results are not presented.
• A small sample. The Allais-pendulum anomaly rests on three readings. The authors set aside a 2.0° reading at 14h, equal to the eclipse minimum, because the ball had moved on its plate. That shows how sensitive the readings are to the mounting, and that excluding values was a judgement the authors made; Table 3 still lists the discarded value.
• The Airy correction is not applied. The authors note that elliptical swinging adds its own rotation (the Airy effect), and they tabulate the ellipse axes for the Foucault pendulum, with minor semi-axes up to 2.5 mm whose sense of rotation reverses during the run. Their comparison line, however, is the plain Foucault rate, and the size of the Airy contribution is not worked out.
• A recovery that goes undiscussed. For the cumulative Foucault lag to return to zero by 14h 50m, the plane must have turned faster than the Foucault rate after the eclipse. The note does not comment on this.
• A changed protocol. Releasing from a fixed azimuth makes this a variant of Allais's method rather than an exact repeat.

Place in the dossier

This 3 October 2005 note is separate from the Romanian report on the 2006 annular eclipse listed in Allais Effect Claims vs. Evidence: Positive Reports, Negative Results and the Unpublished NASA Study. It adds a first-hand data table to the positive side of that ledger. It gives no statistical treatment, and it does not test any of the conventional explanations reviewed in Duif's 2004 Review: Can Ordinary Physics Explain the Eclipse Pendulum and Gravimeter Anomalies?.

Reference

Mihăilă, I., Marcov, N., Pambuccian, V. "Sur le mouvement du pendule de Foucault et du pendule d'Allais lors de l'éclipse de Soleil du 3 octobre 2005." Proceedings of the Romanian Academy, Series A, 7(2), 2006.