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

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to mechanical harmonic analysis for the purpose of determining the azimuth and magnitude of the drift. In this work all the original observations have been used, without any omissions and without the assignment of weights; furthermore, there are no corrections of any kind to be applied to the observed values. The results of the analyses are finally charted in such a way as to show the variation in the azimuth of the drift throughout the day of twenty-four hours for each epoch, and the variation in magnitude is similarly charted.

[The observations of 1925 were described and the details of the results were shown by means of lantern-slide diagrams. A similar report constituted the address of the President of the American Physical Society read at Kansas City on December 29, 1925. This address is printed in full in Science, 63, 433-443, April 30, 1926.]

A calculation based only on the observations of 1925 was made to determine the absolute motion of the earth. The result of this, as reported at the Kansas City meeting, indicated that the solar system is moving toward an apex in the constellation Draco with a velocity which is in excess of 200 km/sec. In order to confirm the Kansas City report, a set of observations consisting of 2020 turns of the interferometer was made at Mount Wilson, corresponding to the epoch February 10, 1926. A complete calculation has now been made, including the observations of both 1925 and 1926, which leads to the following conclusion: The ether-drift experiments at Mount Wilson show, first, that there is a systematic displacement of the interference fringes of the interferometer corresponding to a constant relative motion of the earth and the ether at this observatory of 10 km/sec., with a probable error of 0.5 km/sec.; and, second, that the variations in the direction and magnitude of the indicated motion are just such as would be produced by a constant motion of the solar system in space, with a velocity of 200 km/sec., or more, toward an apex in the constellation Draco, near the pole of the ecliptic, which has a right ascension of 2550 (17 hours) and a declination of +68°; and, third, that the axis across which the observed azimuth of drift fluctuates, because of the rotation of the earth on its axis, points in a northwesterly direction, whereas the simple theory indicates that this axis should coincide with the north and south meridian.



The arguments which have led to these conclusions may be illustrated by means of Figures 6 and 7. In the lower part of Figure 6 the four light-line curves represent the average azimuths for the four epochs of observation, plotted with respect to Mount Wilson local or civil time. The curves all have the values for midnight on the



Fig. 6

ordinate for zero hours and the noon values on the ordinate for twelve hours, etc. The heavy curve represents the average of the four sets of observations and is clearly seen to be irregular and nearly zero in value. In the upper part of Figure 6, the four azimuth curves are plotted against sidereal time. The heavy-line curve representing the average is clearly a periodic curve. If the effect is due to a motion of the earth through space, the sidereal time at which