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

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nent of the motion of the earth and is the absolute motion of the solar system as a whole; this cosmic motion of the earth has a velocity of 208 kilometers per second and is directed to the apex having a right ascension of 4 hours and 54 minutes and a declination of 70 33′.

The location of the apex thus determined is in the constellation Dorado, the Sword-Fish, and is about 20 south of the star Canopus, the second brightest star in the heavens. It is in the midst of the famous Great Magellanic Cloud of stars. The apex is only about 7 from the pole of the ecliptic and only 6 from the pole of the invariable plane of the solar system; thus the indicated motion of the solar system is almost perpendicular to the invariable plane. This suggests that the solar system might be thought of as a dynamic disk which is being pulled through a resisting medium, and which therefore sets itself perpendicular to the line of motion.

The fact that the sun is moving towards the southern apex with a velocity of 208 kilometers per second and at the same time is apparently moving, with respect to the near-by stars, in the opposite direction towards the constellation Hercules with a velocity of 19 kilometers per second, indicates that the group of stars as a whole is moving towards the southern apex with a velocity of 227 kilometers per second.

Reduced velocity and displaced azimuth are unexplained

The direction of the earths motion in space has been determined by assuming that the motion is projected onto the plane of the interferometer and by observing the variations produced in the projected component by the rotation of the earth on its axis and by the revolution around the sun. The velocity of the motion has been obtained by comparison with effects presumed to be produced by the known orbital velocity of the earth. The evaluation of the observed effect is based on the presumption that it is a second order effect and that the ether is wholly stagnant and undisturbed by the motion of the earth through it. There are found to be two facts of observation which are wholly unexplained on this simple theory.

The displacement of the interference fringes has always been less than was expected, indi

cating a reduced velocity of relative motion, as though the ether through which the interferometer is being carried by the earths motion were not absolutely at rest. When the values of the velocity of the earths motion as calculated from the results of this investigation are compared with the velocities observed in the interferometer, there is obtained a quantitative measure of the factor of reduction which has so far remained inexplicable. Table V shows the maximum observed resultant velocities, from Table III, together with the calculated resultant velocities in the plane of the interferometer and the factor of reduction, k, for each epoch. The value of k which leads to results most concordant with the actual observations for all epochs is

Fig. 25. Chart showing the observed displacement of the axis of azimuth of the ether-drift.

Table V. Cosmical velocities.





Feb. 8

9.3 km/sec.

195.2 km/sec.


Apr. 1




Aug. 1




Sep. 15




Value adopted for calculations, k=0.0514

k = 0.0514 and this one value has been used in the calculations for the theoretical curves. However, until the physical nature of this reduction factor is understood, it need not be assumed that it should be constant for all epochs. It is assumed that the cosmic component and the orbital component are both reduced in the same proportion.

In accordance with the simple theory, the direction of the cosmic motion should swing back and forth across the north and south line once in each sidereal day, because of the rotation of the earth on its axis. When the observed azimuth of motion is charted, the resulting curve of directions crosses its own axis twice in each day, as shown in Fig. 25, but this axis is variously displaced from the meridian. For the February epoch the axis is displaced 10 to the west of north; for April the displacement is 40 east; for August 10 east, and for September 55 east.

Validity of the solution

Every suspected cause of disturbance having been eliminated, and an adequate method of

Fig. 26. The observed and calculated velocity and azimuth of ether-drift for the four epochs of observation, plotted with relation to sidereal time.

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