"In 1862 Professor Hubbard began a series of observations of [a]
Lyrae at the Washington Observatory with the prime vertical transit
instrument, for the purpose of determining the constants of
aberration and nutation and the parallax of the star. The methods of
observation and reduction were conformed to those used with such
success by W. Struve. After Hubbard's death the series was continued
by Professors Newcomb, Hall, and Harkness until the beginning of
1867. Professor Hall describes these observations as the most
accurate determinations of declination ever made at the Naval
Observatory. The probable error of a declination from a single
transit was +-0".141, and judging from the accidental errors, the
series ought to give trustworthy results. Upon reducing them,
however, it was found that some abnormal source of error existed,
which resulted in anomalous values of the aberration-constant in the
different years, and a negative parallax in all. A careful
verification of the processes of reduction failed to discover the
cause of the trouble, and Professor Hall says that the results must
stand as printed, and that probably some annual disturbance in the
observations or the instrument occurred, which will never be
explained, and which renders all deductions from them uncertain. The
trouble could not be connected with personal equation, the anomalies
remaining when the observations of the four observers who took part
were separately treated. Nor, as Professor Hall points out, will the
theoretical ten-month period in the latitude furnish the explanation.

"It is manifest, however, that if the 427-day period exists, its
effect ought to appear distinctly in declination-measurements of such
high degree of excellence as these presumably were, and, as I hope
satisfactorily to show, actually are. When this variation is taken
into account the observations will unquestionably vindicate the high
expectations entertained with regard to them by the accomplished and
skilful astronomers who designed and carried them out."

[Sidenote: Direction of revolution of Pole.]

[Sidenote: Example of results.]

From this general account I am excluding technical details and figures,
and unfortunately a great deal is thereby lost. We lose the sense of
conviction which the long rows of accordan