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

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servatory. The computed value is about +69°, agreeing with that obtained from the azimuth curve. As far as instrumental considerations are concerned, the azimuth and magnitude are independent of each other; it is only when they are produced by the same cause that there is any necessary connection between them. The agreement of the calculated and observed effects for both magnitude and azimuth surely points to a real, cosmical cause. The result cannot be considered as a “null” effect; neither can it be due to instrumental or local disturbances.

The fact that the direction and magnitude of the observed ether drift are independent of local time and are constant with respect to sidereal time implies that the effect of the earth’s orbital motion is imperceptible in the observations. The present experiments show no effect of the orbital motion, and hence they are no more consistent with the old theory of a stagnant ether than were the experiments of Michelson and Morley. In order to account for the absence of the orbital effect, it is assumed that the constant motion of the earth in space is more than 200 km/sec., but that for some unexplained reason the relative motion of the earth and the ether in the interferometer at Mount Wilson is reduced to 10 km/sec.; under those conditions a component motion equal to the earth’s orbital motion would produce an effect on the resultant which is just below the limit of the smallest quantity which can be measured by the present interferometer. It is for this reason that it is concluded that the velocity of the motion of the solar system is at least 200 km/sec., and it may be much greater.

Several critics seem to be under the impression that the earlier Cleveland observations gave a real zero effect and that it is claimed that the present positive effect is due to the greater elevation at Mount Wilson. This is not true. The numerical values of the positive effect at Cleveland and at Mount Wilson are so nearly equal that with the observations now available (those at Cleveland being relatively few in number) it is impossible to state that there is any effect due to altitude. If there is any influence of altitude, it is certainly small; further observations at Cleveland are now being made to determine this matter.

In order to account for these effects as the result of an ether drift,


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