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No. 74: Mar-Apr 1991

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Solar eclipse affects a pendulum -- again!

The period of a Foucault pendulum located at Jassy University, Romania, was carefully monitored during the solar eclipse of February 15, 1961. The pendulum's length was 25.008 meters; its spherical bob weighed 5.5 kilograms. The eclipse commenced at 8h 49m 3s and terminated at 11h 16m 50s. Observations are recorded in the table below left:

TimePeriod (sec)
Effects of a solar eclipse upon a paraconical pendulum
Effects of a solar eclipse upon a paraconical pendulum. (After M.F.C. Allais).

If the above effect of the eclipse on the pendulum period is not strange enough, consider what happened at 10:08, in the chart, above right.

"At that moment a surprising fact occurred, the pendulum produced a perturbation by describing an ellipse whose major axis deviated in relation to the initial plane by approximately 15�. The eccentricity of the ellipse was 0.18. At the end of the eclipse the pendulum continued to maintain the elliptical oscillation, but the major axis approached increasingly to its initial plane."

(Jeverdan, G.T., et al; "Experiments Using the Foucault Pendulum during the Solar Eclipse of 15 February, 1961,"Biblical Astronomer. 1:18, Winter 1981.)

See also "Preliminary data about the behavior of a Foucault pendulum during the sun eclipse from 15 february 1961", by G. T. Jeverdan, Gh. Ilie Rusu and V. I. Antonescu. Published in Romanian as "Date preliminare asupra comportarii unui pendul Foucault in timpul eclipsei de soare de la 15 februarie 1961", Analele Stiintifice ale Universitatii "Al. I. Cuza" of Iasi, section I, tom VII, anul 1961, Fasc.2, p. 457.

See also: M. Allais, French Academy of Sciences: C.R.A.S. (1959) 245, 1875; 245, 2001; 244, 2469; 245, 2467; 245; 2170; in English in Aero/Space Engineering, September and October, 1959 (18, (9) and (10). See also: E. Saxl And M Allen, Phys. Rev. D3; 823, 1971. See also: Decrypting the Eclipse at http://www.science.nasa.gov/newhome/headlines/ast06aug99_1.htm.

Comment. Such observations are naturally hard to accept. The result obtained by Allais (1954) concerning the shift of the oscillation plane of the pendulum during eclipse was observed again by G. Jeverdan in 1961 and then later in 1970 was observed again by Allen and Saxl (1971). Moreover, in 1961, Jeverdan also observed an decrease of the medium value for the period of the Foucault pendulum during the eclipse, and therefore an increase in the gravitational acceleration, not reported before by Allais in his work from 1954.

Details may be found in ASX6 in our catalog: The Sun and Solar System Debris. Ordering information here.

From Science Frontiers #74, MAR-APR 1991. � 1991-2000 William R. Corliss