Miller D.C. The Ether-Drift Experiment and the Determination of the Absolute Motion of the Earth // Reviews of modern physics, Vol.5, July 1933

Fig. 22. Single observations and average curves for the ether-drift effect at Mount Wilson in 1925-1926.

of the earth’s absolute motion, characteristic of the particular epoch. There are four curves showing the average azimuth of the ether-drift effect throughout a sidereal day, for the four epochs; each of these curves determines the right ascension and declination of the apex of the earth’s absolute motion. In all, there are four determinations of the velocity of motion as projected on the plane of the interferometer, one for each epoch, and eight independent determinations of the apex of the motion, two for each epoch.

These observations are to be reduced according to the principles explained in the preceding sections, to determine the positions of the apexes of the resultant motions for the four epochs. From each curve for the magnitude of the effect are to be obtained the numerical values of the maximum and minimum ordinates and the sidereal time of the minimum; from each curve for the azimuth of the effect are to be obtained the maximum oscillation of the azimuth and the two sidereal times when the curve crosses its axis.

The reduction of the observations involves the latitude of the location of the interferometer. The observations here recorded were made at the Mount Wilson Observatory in latitude +34° 13'.

It is at once evident from the character of the curves of observation, Fig. 22, that the declination of the apex is greater than the complement of the latitude of the observatory; this is indicated by the fact that the departure of the azimuth curve from its axis is always less than 90° and by the fact that the magnitude curve shows only a single maximum and a single minimum. This determines the choice of the alternate formulae of calculation. The study of the conditions with the models leads to the same conclusion. Furthermore, the earlier calculations of these observations included the consideration of an apex with a declination smaller than the complement of the latitude, always leading to inconsistent results. Thus the apex is known to be circumpolar in its astronomical relations.

It may be noted that both the direction and the velocity of the ether drift should change from epoch to epoch because the effect is the resultant of the constant cosmic motion of the

earth and of the changing orbital motion and these changes should be systematic and characteristic of the epoch, as will be explained later.

Final results of observation

Tables I and II give the right ascensions and declinations of the apexes of the observed motion of the earth for the four epochs and for the two alternative directions. In the tables α–Mag and δ–Mag indicate the values obtained from the magnitude curves, while α–Az and δ–Az are obtained from the azimuth curves.

Table I. Right ascension of apex.

The curves of observation, Fig. 22, give directly the values of the maximum velocity of relative motion of the earth and ether, as observed in the plane of the interferometer, for the four epochs; these velocities are given in Table III. The table also shows the displacements of the interference fringes, in terms of a fringe-width, which would be produced in the interferometer used in these experiments, by the observed velocities of ether drift.

The three tables contain all of the data provided by the three hundred and sixteen sets of observations made at Mount Wilson in 1925 and 1926, for the solution of the ether-drift problem.

Table II. Declination of apex.

Table III. Velocities and displacements.