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The obliquity of the ecliptic, as deduced from the early observations by the Greenwich quadrant, compared with the present obliquity, gives the diminution for an interval of nearly sixty years, with almost sufficient accuracy to state with some confidence the mass of Venus; but to obtain this point with certainty, the present obliquity, deduced from a mean of the observations of different astronomers, should be used. Upon this subject the author alludes to the opinion of astronomers, that observations of the winter solstice have given a less obliquity than those of the summer solstice,—an opinion sustained by the observations of Maskelyne, Arago, and Pond, but questioned by Bessel and Bradley. Dr. Brinkley refers this difference to some unknown modification of refraction; he has observed that at the winter solstice the irregularity of refraction for the sun is greater than for the stars at the same zenith-distance. He points out the necessity of paying attention to the observations at the winter solstice, and gives a table, exhibiting the mean obliquity reduced to January 1813. Dr. Brinkley next alludes to the maximum of the aberration of light, which appears from his observations of last year to be 20"·80.

abstracts of the papers printed in the philosophical transactions of the royal society of london

The results of observations made at the observatory of Trinity College, Dublin, for determining the obliquity of the ecliptic, and the maximum of the aberration of light