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

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tances through which the light travels in glass in Michelson’s experiment are comparatively so small, and that practically they cannot give rise to any difficulty at all. For all these reasons I think that the theory which I presented is general, and, at tjie same time of exact applicability to the actual instrument. In any case, I intend to study all the recent work such as Mr. Hedrick’s.

Dr. G. Strömberg: It is often said that the sun’s motion “in space” is 20 km/sec. toward the point a = 270°, ô=+30°. This expression is quite inadequate and means that the sun’s motion referred to the brighter stars is of this magnitude and direction. Referred to distant objects, this velocity is much greater. The sun’s velocity relative to the system of globular star clusters is about 300 km/sec. in the direction a = 320°, 5= +65°, and relative to the spiral nebulae it may be even larger, although in about the same direction.

As the bigger reference frame is, presumably, the more fundamental, the higher velocity may also be of more fundamental nature.

And this is just what has been found to be the case. The sun’s motion as referred to different classes of objects in our neighborhood is quite different, and the general rule has been established that the higher the internal velocity dispersion in a group, the larger is the sun’s motion relative to this group. Practically all celestial objects can be arranged in a sequence with increasing velocity dispersion, and moving with different velocity along a certain axis. This sequence terminates with the globular clusters, and a quadratic relationship exists between group motion along a certain axis and the velocity dispersion along the same axis. This phenomenon can, at least formally, be explained as the effect of a velocity restriction in a fundamental reference frame in which the globular star clusters are statistically at rest.

Recent studies of the velocities of giant M stars have completely confirmed this hypothesis. In fact, it has been found possible to represent the velocity distribution along this fundamental axis in a much more satisfactory way by one disposable constant, in addition to this fundamental velocity vector, than by four arbitrary constants, as in the prevalent methods.

In stellar motions we have to introduce a fundamental velocity vector of 300 km/sec. in the direction mentioned in order to secure



order and regularity. This implies the existence of a “fundamental” reference frame, or “medium,” or “ether,” whatever we prefer to call it. The introduction of such a conception has been of great value in the study of stellar motions.

Professor H. Bateman: The Michelson-Morley experiment maybe regarded as a test of the laws of reflection by a moving mirror. For the general case in which the source of light is moving relative to the earth, the question resolves itself into two: (i) Is the image of a moving point source of light a single moving point source of light as in the classical electromagnetic theory? (2) Are the spacetime co-ordinates of a point source and its image connected by the relations ,

x' = x—- 2C (x — ut) t' — t—(x — ut) , c2 — u2 v J c2 — u2 v J

yr = y zf = z (u = velocity of mirror) ,

of the classical electromagnetic theory and the theory of relativity?

On the assumption that the first question is to be answered in the affirmative, various modifications of the equations connecting the space-time co-ordinates of a point source and its image might be tried on the arrangements of mirrors in the Michelson-Morley experiment. The interference fringes may in each case be regarded as the fringes produced by light coming directly from certain image sources and traveling in accordance with certain assumed laws of propagation which are also under test. The general problem is still more complicated by the contraction of the apparatus. The first question of the sharpness of the image of a point source which is moving relative to the mirror is difficult to settle experimentally on account of the lack of point sources of light moving at a high speed and at some distance from the earth. The velocity of a shooting star may be forty-five miles a second, but this is probably too small for the production of lack of sharpness in the image.

Director Adams closed the conference, thanking all the speakers for their contributions.

Carnegie Institution of Washington Mount Wilson Observatory April 1928