Searching for the Ether
The first series comprised 489 observations, and the second series only 67 observations. From the first series, Courvoisier computed the following values:
A = 70° ± 6°; D = +33° ± 11°; v = 493 ± 54 km/s
From the second series, he obtained the results:
A = 22° ± 6°; D = +72° ± 11°; v = 606 ± 45 km/s
Of course, the results obtained from the first series of measurements seemed more reliable than those from the second series, and they exhibited a closer agreement with former measurements.
Notice that, although those measurements attempted to detect the same kind of effects as the astronomical observations - that is, a difference between angle of incidence and angle of reflection in a moving mirror - the star observations used the North-South direction, and the cave experiments employed the East-West direction. The equations were different, and nevertheless Courvoisier obtained a nice agreement between the new device and the former results.
The double mirror experiments
In 1928 Courvoisier built another device to measure the speed of the Earth using the principle of the moving mirror. Instead of using two telescopes, he used a single telescope, with two perpendicular mirrors in front of its objective (Fig. 7).22 The body of the telescope was placed in a horizontal position. The mirrors were adjusted so that it was possible to observe the reflected image of the thread micrometer of the telescope in close coincidence with the real micrometer thread. He predicted that the relative position of the image and the thread should undergo periodic fluctuations, and computed the predicted effect.
From April to June 1928 Courvoisier obtained a series of 53 measurements, both in the North-South and in the East-West directions, and he computed the following values:
A = 74° ± 1°; D = +36° ± 1°; v = 496 ± 10 km/s
22 Leopold Courvoisier, “Bestimmungsversuche der Erdbewegung relativ zum Lichtäther III”, Astronomische Nachrichten, ccxxxiv (1928), 137-44.
Roberto Martins Searching for the Ether
Fig. 7. Courvoisier’s coupled mirror device for measuring the motion of the Earth through the ether.
Courvoisier’s new experiment was probably suggested by a similar arrangement that had been used by Esclangon in 192 7.23 The French astronomer used two mirrors, but light underwent three reflections (Fig. 8). The maximum effect occurred at 3 h or 15 h sidereal time, corresponding to A = 45° or 225\ Esclangon did not compute the speed of the Earth through the ether - indeed, he did not even provide a definite interpretation of the phenomenon.
The second method: Lorentz contraction
As described above, Courvoisier's second attempt to measure the absolute velocity of the Earth was grounded upon his analysis of the Lorentz contraction of the Earth (Fig. 9). In this case, Courvoisier supposed that the local vertical would undergo a change, due to the Lorentz contraction of the Earth, and this change would be observable as a periodical fluctuation in the angle between the North Pole and the zenith, as a function of the sidereal time.
Courvoisier's theoretical analysis led him to predict that the variation of the zenithal distance Az of a star close to the North Pole would obey the approximate relation:
Az = Vi ap (11)
23 Ernest Esclangon, “Sur la dissymétrie optique de l'espace et les lois de la réflexion", Comptes rendus de Yacadémie des sciences de Paris, clxxxv (1927), 1593-5 ; idem, “Sur l'existence d'une dissymétrie optique de l'espace", Journal des observateurs, xi (1928), 49-63.