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

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report was presented. Chase,1 working at Harvard University, increased the accuracy of his measurements about three times. Even taking into account the factor 1/5 mentioned above, his new apparatus could have detected an ether-drift velocity of 3 km/sec. Within this accuracy his results were negative, thus giving strong support to the theory of relativity. The most accurate and recent work of Piccard’s was carried out by him, jointly with E. Stahel,2 on the summit of the Rigi in Switzerland (altitude, 1800 m). The same self-recording interferometer with thermostatic temperature control was used. The results were completely negative, the ether drift being only one-fortieth part of that expected according to Miller.]


[Dr. Walter S. Adams, director of the Observatory, opened the discussion, expressing his hope that Professor Lorentz and Professor Michelson would give their opinions in regard to the considerations of Righi and Hedrick.]

Professor H. A. Lorentz: I feel somewhat guilty in regard to the work of Righi. It was a long time ago that I read his papers, and I do not remember their contents very well, as I have been busy with quite different things these last years. I should have read them again of course for this meeting. But this good intention could not be materialized because of my being entertained so much by the people of Pasadena. After having heard Mr. Hedrick’s report, I intend, however, to study these questions again very carefully in relation to Mr. Miller’s experiment. Further, the considerations of Brylinski must be taken up again. Offhand, I can only say that the results of Mr. Hedrick are in contradiction with those which I presented yesterday. Until today I felt myself quite satisfied with the considerations which are based on Fermat’s principle. After Mr. Hedrick’s report, however, I shall have to reconsider these questions carefully. According to Mr. Hedrick’s results it appears, indeed, that the result to be expected in the Michelson-Morley experiment may be numerically different from that which we ordinarily expect on the basis of the classical theory. The numerical value of the second-

1 Physical Review, 30, 516, 1927.

2 Die Naturwissenschaften, 16, 25, 1928.



order effect would be different from that which Michelson calculated. My procedure seems to me still to be the easiest and most straightforward one. Still it must be found out where the discrepancy between the two ways lies. In case a method other than Fermat’s is chosen, one has to do considerable work. One must distinguish, for instance, very carefully between the rays of light and the normals to the wave trains. Another difficult point is involved in the treatment of the reflection from moving mirrors. Fermat’s principle, of which I have made use, gives in any case a much simpler treatment. But as there exists a discrepancy between the results obtained by the two methods, I intend to go through the detailed calculations as soon as possible. In the meantime I still hope, of course, that my general considerations are right.

I should now like to make some remarks on Mr. Miller’s experiment. It seems to me that there is a serious problem connected with the effect which is periodic for a full turn of the apparatus and which is discarded by Mr. Miller, who emphasizes the importance of the half-period effect (periodic with half-turns of the apparatus) in regard to the question of an ether drift. In many cases the full-period effect is much larger than the half-period effect. According to Mr. Miller, the full-period effect is dependent on the width of the fringes and would become zero for infinitely wide fringes.

Although Mr. Miller says that he was able to eliminate this effect to a great extent in his Cleveland measurements, and that it is to be explained easily by the experimental arrangement, I should like to understand its cause somewhat more clearly. Speaking now for a moment as an adherent of the relativity theory, I should contend that no such effect whatever could exist. Indeed, a rotation of the entire apparatus as a whole, the source of light included, should not give any shift at all from the standpoint of relativity. No effect would be expected were the earth and the apparatus at rest. According to Einstein, then, the same absence of an effect is to be expected for the moving earth. The full-period effect is thus in contradiction with the theory of relativity and of main importance. If then Mr. Miller has found some systematic effects whose existence cannot be denied, it is also important to know the cause for the full-period effect.