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

determined the relevant parameters from an analysis of the Leyden data, using the method of minimum squares. He obtained an effect corresponding to a speed of about 800 km/s in the direction of the Auriga constellation. This speed is, of course, much larger than the orbital speed of the Earth. Courvoisier interpreted it as due to the motion of the whole solar system through the ether. A few years later, Courvoisier obtained new data, using the same method (direct versus reflected direction). Using the vertical circle of the Babelsberg observatory, he made a long series of observations (1921-1922) that led to results similar to those that had been obtained from the Leyden observations.

After obtaining his first positive result, Courvoisier attempted to find other independent methods of measuring the speed of the Earth (or the solar system) relative to the ether. He conjectured that the Lorentz contraction of the Earth and of optical instruments could have some small observable influence on astronomical observations. According to Courvoisier, the motion of the Earth relative to the ether produces a contraction that transforms its spherical shape into an ellipsoid with the smaller axis in the direction of its motion. The surface of the ellipsoid, at each point, was supposed to be perpendicular to the local gravitational field. As the Earth rotates, each place on the surface of the Earth passes through different points of the ellipsoid, and the angle between the axis of the Earth and the local vertical direction should undergo a periodical change.

Of course, it is impossible to measure the angle between the local vertical and the axis of rotation of the Earth. However, since the direction of this axis is fairly constant relative to the fixed stars (for short time periods), it is possible to choose a star very close to the North celestial pole and to measure its distance to the zenith (that is, the local vertical direction). This angle, according to Courvoisier's theory, should undergo a periodical change, as a function of the sidereal time.

As a matter of fact, Courvoisier had already measured the position of a star very close to the North pole, in a long series of observations from 1914 to 1917, using the Babelsberg Observatory vertical circle.11 Those measurements were very accurate and were evenly distributed as regards the sidereal time of the observations. They were therefore suitable for looking for the influence of the Lorentz contraction on astronomical measurements.

As in the former case, Courvoisier first plotted the zenithal distances of the star against sidereal time, and found a regular fluctuation of the angle. He

11 Leopold Courvoisier, “Zenitdistanzbeobachtungen der Polarissima am Vertikalkreise der Stemwarte Berlin-Babelsberg”. Astronomische S'achnchlen. ccviii (1919), 349-64. He made this series of measurements as routine observations to ascertain the latitude of the Babelsberg observatory. The method used by Courvoisier is very precise, and was recently used for the determination of the azimuth of a transit instrument in Brazil: Ramachrisna Teixeira and Paulo Benevides Soares, “Absolute azimuth determination”, Astronomy and astrophysics, clxv (1986), 251-3.

Roberto Martins Searching for the Ether DIO 17

then developed an equation to account for the effect, analyzed the data using the minimum square method, and obtained his second measurement of the velocity of the Earth relative to the ether. The speed obtained in this case was about 700 km/s, in the direction of the constellation of Perseus (not very far from Auriga). Courvoisier regarded the agreement of those two earliest results as satisfactory, and this led him to further researches. There was a delay of 5 years between Courvoisier’s first positive results and his next publication on the subject.12 In this period he accumulated a series of positive results by different methods, obtained the equations required for the analysis of his data, and devised new methods for measuring the absolute speed of the Earth. This delay shows that Courvoisier was careful enough to resist publishing preliminary results before he was able to amass a large amount of evidence for his claim.

The method of the moving mirror

Courvoisier derived equations13 that related the relevant measurements to the parameters of the motion of the Earth relative to the ether.14 The main parameters that appear in his equations (Fig. 2) are:

c = the speed of light relative to the ether = 300,000 km/s

v = speed of the Earth (or the solar system) relative to the ether

A = right ascension of the apex of the absolute motion

D = declination of the apex of the absolute motion

a = North local component of v/c

P = Zenith local component of v/c

y = West local component of v/c

<|) = latitude of the terrestrial observatory

9 = sidereal time of measurement

A straightforward geometrical analysis shows that the components of v/c are:

a = (v/c) [cos <|) sin D - sin <|) cos D cos (0—^4)] (1)

P = (v/c) [sin <|) sin D + cos <|) cos D cos (9-v4)] (2)

12 Leopold Courvoisier, “Bestimmungsversuche der Erdbewegung relativ zum Lichtäther”, Astronomische Nachrichten, ccxxvi (1926), 241-64.

13 Courvoisier never published the details of his derivations - he only presented his main assumptions, a few steps and the final results. In all relevant cases, however, I have been able to confirm that his equations do follow from his assumptions.

14 Courvoisier, “Bestimmungsversuche der Erdbewegung relativ zum Lichtäther” (ref. 12).