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

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this curve crosses the time axis is the right ascension of the apex of the motion. This occurs at seventeen hours. The declination of the apex is determined from the amplitude of the curve and the cosine of the latitude of the observatory, and is equal to +68°. Figure 7 shows, at the bottom, the average diurnal variation in the azimuth

Fig. 7

(the broken line) as compared with the theoretical variation shown by the smooth curve. The upper part of Figure 7 shows, in the broken line, the average diurnal variation in the observed magnitude of the effect, while the smooth curve shows the theoretical variation. If this is due to an ether drift, the sidereal time of minimum magnitude is the right ascension of the apex. This is seventeen hours, in agreement with the right ascension obtained from the azimuth curve. The declination of the apex is dependent upon the minimum and maximum values of the effect and upon the latitude of the ob-



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,