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

Courvoisier made two series of observations: 22-24 October and 22-25 November 1922. He noticed that temperature changes affected the position of the telescope, and that this influence had to be taken into account. From the uncorrected observed measurements he computed the following values:

A = 74° ± 10°; D = +67° ± 13°; v = 920 ± 73 km/s

Applying a temperature correction, he obtained the following results:

A = 98° ± 7°; D = +25° ± 11°; v = 500 ± 47 km/s

This experiment was repeated by August Kopff, of the Heidelberg observatory, from 10 to 29 June 1923. As in the case of Courvoisier's experiment, there was a strong effect due to temperature changes (temperature varied between +6°C and +17°C). Courvoisier analyzed Kopff s data assuming the values A = 75° andD = +40°. After applying temperature corrections, he obtained a speed of 753 ± 57 km/s.

Other methods

Courvoisier also attempted to detect the motion of the Earth relative to the ether by other methods. He regarded the positive result of the nadir observation method as a confirmation of his hypothesis that the Lorentz’s contraction produced an observable periodical change of the local vertical. He soon devised other ways of observing such an effect.

Plumb line motion

One of the instruments he used was a plumb line attached to one of the columns of the Babelsberg observatory. The main body of the plumb line was a metallic rod, 95 cm long. At its lower end there was a mark that was illuminated and projected upon a wall. It was possible to observe deflections of about 0.05" of the direction of the plumb line, in the East-West direction.24 Measurements made in 1925 with this instrument led to a speed of the Earth of about 400 km/s, assuming A = 75° and D = +40°. In 1931 Courvoisier improved this instrument observing the motion of its tip with the aid of a microscope (Fig. 10). Now he was able to compute the three parameters of the Earth's motion, obtaining:

A = 64° ± 6°; D = +50° ± 9°; v = 367 ± 29 km/s

24 Leopold Courvoisier, “Ableitung der Bahngeschwindigkeit der Erde aus der auf Grund der Lorentz-Kontraktion (Zeigerstabversuch) betimmten Absolutbewegung”,

Astronomische Nachrichten, ccxlvii (1932), 105-18.


Roberto Martins Searching for the Ether DIO 17


Fig. 10. Courvoisier’s plumb line apparatus for measuring oscillations of the local gravitational vertical due to Lorentz contraction.

Similar observations were made by Esclangon, with the help of Andre-Louis Danjon, using two horizontal pendulums with perpendicular motions.25 One of the pendulums lead to .4=69°; for the second pendulum, .4=52°. Esclangon did not provide other information and did not attempt to compute the speed of the Earth.

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