Roberto De Andrade Martins. Searching for the Ether: Leopold Courvoiser’s Attempts to Measure the Absolute Velocity of the Solar System // DIO, vol. 17, december 2011

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Roberto Martins

Searching for the Ether

DIO 17

The estimated error of the speed amounted to about 25%. The errors of the right ascension and declination amounted to about 1/15 of the full circle. Between 1921 and 1922 Courvoisier repeated the Leyden measurements, but with a slight change of method. Instead of a meridian circle he used a Wanschaff vertical circle that enabled him to make measurements of the stars at any time during the night. Therefore his measurements were not limited to two sidereal times for each star.

From 4 June to 14 December 1921 he made a series of 142 measurements of the polar star BD +89.3°, and from 18 March to 23 May 1922 he made further 64 determinations of z-z'. From those measurements Courvoisier obtained:

A = 93° ± 7°; D = +27° ± 12°; v = 652 ± 71 km/s

The estimated relative error of the speed was reduced to about 10% and the errors of the right ascension and declination amounted to less than 1/30 of the full circle.

Courvoisier’s work called the attention of a French astronomer, the director of the Strasbourg observatory, Ernest Esclangon, who repeated those measurements.18 He confirmed the existence of a systematic effect of the same order of magnitude, and computed the values oL4=69° andD=44° Esclangon did not publish the estimated errors of his evaluation, nor the estimated speed of the Earth.

Other evaluations were later obtained by Courvoisier using measurements made at München (1930-1931) and Breslau (1933-1935), with the following results:


Breslau ( 1 )

Breslau (2)

A = 73° ± 6°

D = +40° (estimated)19 v = 889 ± 93 km/s

A = 92° ± 12°

D = +44° ± 25° v = 927 ± 200 km/s

A = 80° ± 4°

D = +30° ± 10° v = 700 ± 60 km/s

The results obtained in the second Breslau series presented the smallest errors.

In 1945, after his retirement, Courvoisier made a final series of observations from Basel. He obtained the following results:

A = 60° ± 14°; D = +40° (estimated); v = 656 ± 157 km/s

18 Ernest Esclangon, “Sur la dyssimétrie mécanique et optique de l'espace en rapport avec le mouvement absolu de la Terre”, Comptes rendus de l'academie des sciences de Paris, clxxxii (1926), 921-3.

19 In some of his analysis, Courvoisier found that the effect with one sidereal day period was not clearly noticeable. In those cases, he assumed the value of 40° for the declination, and computed the right ascension and speed of the Earth.

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Roberto Martins Searching for the Ether DIO 17

If we compare all the series of measurements, we notice that the right ascension varied between 60° and 104° (more than the estimated errors); the declination varied between 39° and 44° (within the estimated errors);20 and the speed varied between 652 and 927 km/s (within estimated errors). Notice that it is very hard to explain away Courvoisier's results as due to instrument errors, because the observed effect varied with periods of one sidereal day and half sidereal day. All common causes of error (gravity changes, temperature changes, etc.) would vary with periods of one (or half) solar day. Tidal influences due to the Moon would have periods that could also be easily distinguished from the effects predicted by Courvoisier. Besides that, the data used by Courvoisier was obtained with different instruments at different places, and covered a time span of 80 years. The results presented by Courvoisier are therefore highly impressive and cannot be dismissed lightly.

Courvoisier's device for measuring the absolute speed of the earth

In the first method used by Courvoisier, the stars work as mere point-like light sources. There is nothing peculiarly “astronomical” in the observed effect because, according to Courvoisier's theory, this was ascribed to the “principle of the moving mirror”. Therefore, similar effects should occur for terrestrial light sources, too.

Accordingly, Courvoisier was led to build a new instrument: an optical device for measuring absolute motion (Fig. 6).21 He used two small telescopes that were placed in an underground room where the temperature was fairly constant. Both telescopes pointed obliquely (zenithal distance = 60°) to a mercury mirror that was placed between them. They were mounted in a vertical plane in the East-West direction. One of the telescopes had a small electric light close to its reticule, and this was the light source that was observed from the second telescope. Both telescopes were first adjusted so that it was possible to see the reflection of the illuminated reticule of the first telescope from the second telescope. They were then fastened in those directions. Of course, the angles of the telescopes with the local vertical were sensibly equal. The experiment did not try to measure any difference between those angles. It attempted to detect small periodical changes of the position of the image of the first telescope reticule as observed from the second one. The apparent motion of

20 The slight variations of the values found for the declination led Courvoisier to assume this value as known, as remarked above (note 18), in all cases when it was impossible to compute A, D and v/c.

21 Leopold Courvoisier, “Bestimmungsversuche der Erdbewegung relativ zum Lichtäther II”, Astronomische Nachrichten, ccxxx (1927), 425-32; idem, “Über die Translationsbewegung der Erde im Lichtäther”, Physikalische Zeitschrift, xxviii (1927), 674-80.

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