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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of the earths 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 earths 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 αMag and δMag indicate the values obtained from the magnitude curves, while αAz and δAz 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.







Feb. 8

18h 0m

18h 0m

18h 0m

6h 0m

Apr. 1

15 15

16 10

15 42

3 42

Aug. 1

15 45

16 10

15 57

3 57

Sep. 15

17 5

17 0

17 3

5 5

Table II. Declination of apex.





Feb. 8

79 35′

75 19′

77 27′

Apr. 1

78 25

75 12

76 48

Aug. 1

67 30

62 4

64 47

Sep. 15

61 40

62 28

62 4

Table III. Velocities and displacements.



λ = 5700A

Feb. 8

9.3 km /sec.


Apr. 1



Aug. 1



Sep. 15



In this work the calculations proceed directly from the actual observations, without any presumptions as to the result. All of the original observations have been included in the calculation, without any omissions and without the assignment of weights. No corrections of any kind have been applied to the observed quantities. This procedure has been adopted as the only safe one in the first search for a hitherto unidentified effect. The present results strikingly illustrate the correctness of this method, as it now appears that the forty-six years of delay in finding the effect of the orbital motion of the earth in the ether-drift observations has been due to the efforts to verify certain predictions of the so-called classical theories and to the influence of traditional points of view.

Absolute Motion of the Solar System and The Earths Orbital Motion Determined

Northern apex of the solar motion rejected

As already explained, the interferometer determines the line in which the motion of the earth with respect to the ether takes place but does not determine the direction of motion in this line. The results of the observations given in Tables I and II indicate either an apex located near the north pole of the ecliptic or one diametrically opposite, near the south pole of the ecliptic. The choice between the two possible directions of motion is determined by the consistency of the results in satisfying the original observations taken as a whole and in connection with known phenomena. The studies of the proper motions and of the motions in the line of sight of stars in our own cluster have shown that the solar system is moving with respect to the nearby stars towards an apex located in the constellation Hercules, about 42 from the northern one of the two apexes indicated by the interferometer observations, the velocity of this motion being about nineteen kilometers per second. This circumstance seemed confirmatory of an absolute motion towards the north and the northern apex was chosen for further study of the problem.

Upon the completion of the observations for three epochs at Mount Wilson, corresponding to April 1, August 1, and September 15, 1925, a study of the results was made upon the pre

sumption of a northern apex. Various trial solutions were checked with the parallelogram apparatus, Fig. 18, and finally by a partial least squares solution, for the determination of the velocity of the cosmic motion. The effects which should be characteristic of the several epochs because of the varying direction of the orbital motion could not be identified in the corresponding curves of observation, indicating that the orbital component is probably much smaller than the cosmic component. The curves for the three epochs were simply averaged and it was found that when plotted in relation to local civil time, the curves are in such phase relations that they nearly neutralize each other; the average effect for the three epochs thus plotted is very small and unsystematic. The curves of observation were then plotted with respect to sidereal time and a very striking consistency of their principal characteristics was shown to exist, not only among the three curves for azimuth and those for magnitude, but, what was more impressive, there was a consistency between the two sets of curves, as though they were related to a common cause. The average of the curves, on sidereal time, showed conclusively that the observed effect is dependent upon sidereal time and is independent of diurnal and seasonal changes of temperature and other terrestrial causes and that it is a cosmical phenomenon. The results of this study were presented as the address of the President of the American Physical Society at the meeting in Kansas City, on December 29,

1925.13 The conclusion stated that there is a positive, systematic ether-drift effect, corresponding to a constant relative motion of the earth and the ether, which at Mount Wilson has an apparent velocity of ten kilometers per second; and that the variations in the direction and magnitude of indicated motion are exactly such as would be produced by a constant motion of the solar system in space towards an apex, near the north pole of the ecliptic, having a right ascension of 171/2 hours and a declination of +65. On the hypothesis of the Stokes ether concept, that the ether is partially entrained by matter moving through it, it was suggested that the observed velocity of ten kilometers per second might be only a fraction of the absolute velocity;

13 D. C. Miller, Science 63, 433 (1926).

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