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DAYTON C. MILLER
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
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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
CONFERENCE ON MICHELSON-MORLEY EXPERIMENT 363
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-