Conference on the Michelson-Morley experiment held at the Mount Wilson observatory Pasadena, California February 4 and 5, 1927

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it seems necessary to assume that, in effect, the earth drags the ether so that the apparent relative motion at the point of observation is reduced from 200, or more, to 10 km/sec., and further that this drag also displaces the apparent azimuth of the motion about 6o° to the west of north. It is possible that the westerly deflection is influenced by the trend of the Mount Wilson range of mountains from southeast to northwest. The reduction of the indicated velocity of 200 km/sec., or more, to the observed value of 10 km/sec. may be explained by the theory of the Lorentz-FitzGerald contraction without assuming a drag of the ether. This contraction may or may not depend upon the physical properties of the solid, and it may or may not be exactly proportional to the square of the relative velocities of the earth and the ether. A very slight departure of the contraction from the amount calculated by Lorentz would account for the observed effect.

The values of the quantities defining the absolute motion of the solar system as obtained from these ether-drift observations are in general agreement with the results obtained by other methods. The recent study of proper motions of stars by Ralph Wilson, of the Dudley Observatory, and of the radial motions of the stars by Campbell and Moore, of the Lick Observatory, gives the apex of the sun’s way in the constellation Hercules with a right ascension of 270° and a declination of about +30°, with a velocity of about 19 km/sec. Dr. G. Strömberg, of the Mount Wilson Observatory, from a study of globular clusters and spiral nebulae, finds evidence of a motion of the solar system toward a point having a right ascension of 307° and a declination of +56°, with a velocity of 300 km/sec. Lundmark, studying the spiral nebulae, finds evidence of a motion having a velocity of 400 km/sec. The various determinations of the motion of the solar system are all in the same general direction and lie within a circle having a radius of 20°. Our assumed velocity of 200 km/sec. is simply a lower limit; it might equally well be 300 or 400 km/sec. The first assumption therefore seems to offer no difficulty. The location of the apex in the constellation Draco, at right ascension 2550 and declination +68°, is within 6° of the pole of the ecliptic, that is, the indicated motion of the solar system is almost perpendicular to the plane of the ecliptic. The sun’s axis of rotation



points to within 120 of this apex. One cannot help wondering whether there may be some dynamic significance in these facts.

The argument now being presented can be demonstrated only by means of observations extending over the whole twenty-four hours of the day, in order to determine the exact form of the daily variation in magnitude and azimuth of the effect, and by means of observations made at different times of year, in order to prove that the effect is dependent on sidereal time. The earlier observations of 1887 and 1905 are not sufficiently numerous and are not distributed throughout the day in such a manner as to make it possible to calculate the direction of the drift. These earlier observations were made for the purpose of detecting the earth’s orbital motion and consequently were made at two selected times of day, such that at one time the magnitude of this particular effect would be a maximum and at the other time it would be zero; or, two times of day were chosen in which the azimuth of the orbital component of motion would have very different values. Furthermore, until the year 1925 the experiments have never been carried out at intervals of six months. The reason that a second set of experiments has not been made after this interval before is simply that in no instance has the expected effect been found in a first set.

The observations made at Cleveland by Michelson and Morley in 1887, and later repeated by Morley and Miller, have just been recomputed on the present hypo thesis; while the earlier observations are not sufficient to determine the direction of the drift, they are nevertheless shown to be entirely consistent with the conclusions drawn from the Mount Wilson experiments. Or, to state the converse, the present result wholly confirms the earlier experiments of Michelson and Morley, giving no evidence of the effect of the earth’s orbital motion. In addition to this, the recent experiments, by a thorough study of the residual effects, have shown that there is a systematic cosmical effect as of a true ether drift. This conclusion introduces a new question, “Why is the magnitude of the effect less than would be expected on the classical theories and why is the direction of the effect at Mount Wilson deflected to the westward?” This question certainly is no more difficult than are many others now awaiting solution.