Searching for the Ether
There are some special observational difficulties in this second method. If it were possible to observe a star laying exactly in the direction of the celestial North Pole, the observation would be quite simple. However, if the star is not exactly in the direction of the pole, its zenithal distance will depend on the sidereal time of the observation. This classical large effect would have, therefore, a period of one sidereal day and would interfere with any attempt to measure any influence due to the motion through the ether with a period of one sidereal day. Other interfering effects, such as temperature changes, vary with a period of about one solar day, and they are very large and irregular. For those reasons, Courvoisier gave up the attempt of finding the amplitude of the sidereal day effect, and only computed the half sidereal day effect. It was impossible, therefore, to find all parameters, and he assumed a value of 40° for the declination, and computed the speed and right ascension of the motion of the Earth relative to the ether. Dropping out the component corresponding to the period of one sidereal day, he obtained the following equation:
Az = - (lMXv/c^.sin2<|) (const. - cos2D.cos2(9-4)] (12)
Fig. 8. Esclangon’s coupled mirror device for measuring the motion of the Earth through the ether (a), and a graphical representation of his results (b), showing the observed angular fluctuations as a function of sidereal time.
Roberto Martins Searching for the Ether DIO 17
Fig. 9. According to Courvoisier, the Lorentz contraction of the Earth and of optical instruments could have a small observable influence on astronomical observations and terrestrial experiments.
Using the data he had already obtained from 1914 to 1917, and combining those results with other measurements he made in 1921-1922 and 1925-1926, with the same instrument, Courvoisier obtained the following result:
A = 74° ± 3°; [D = +40°]; v = 587 ± 48 km/s
He also analyzed measurements that had been obtained in routine observations at the Paris observatory, in the period 1899-1901. All those series of observations exhibited similar variations with a period of 12 sidereal hours. Assuming a value of 40° for the declination, he obtained the following results:
A = 70° ± 11°; [D = +40°]; v = 810 ± 166 km/s
Afterwards Courvoisier also computed the motion of the Earth using measurements from Breslau (1923-1925 and 1933-1935) and from München (1927-1931). Taking into account all the observations, he obtained the following final result:
A = 65° ± 10°; [D = +40°]; v = 574 ± 97 km/s