ced, the corrections applied to
existing tables rendered it more accurate than any other. Since that
time, the introduction into foreign ephemerides of the improved tables
of Le Verrier have rendered them, on the whole, rather more accurate
than our own. In one direction, however, our ephemeris will hereafter
be far ahead of all others. I mean in its positions of the fixed stars.
This portion of it is of particular importance to us, owing to the
extent to which our government is engaged in the determination of
positions on this continent, and especially in our western territories.
Although the places of the stars are determined far more easily than
those of the planets, the discussion of star positions has been in
almost as backward a state as planetary positions. The errors of old
observers have crept in and been continued through two generations of
astronomers. A systematic attempt has been made to correct the places
of the stars for all systematic errors of this kind, and the work of
preparing a catalogue of stars which shall be completely adapted to the
determination of time and longitude, both in the fixed observatory and
in the field, is now approaching completion. The catalogue cannot be
sufficiently complete to give places of the stars for determining the
latitude by the zenith telescope, because for such a purpose a much
greater number of stars is necessary than can be incorporated in the
ephemeris.

From what I have said, it will be seen that the astronomical tables, in
general, do not satisfy the scientific condition of completely
representing observations to the last degree of accuracy. Few, I think,
have an idea how unsystematically work of this kind has hitherto been
performed. Until very lately the tables we have possessed have been the
work of one man here, another there, and another one somewhere else,
each using different methods and different data. The result of this is
that there is nothing uniform and systematic among them, and that they
have every range of precision. This is no doubt due in part to the fact
that the construction of such tables, founded on the mass of
observation hitherto made, is entirely beyond the power of any one man.
What is wanted is a number of men of different degrees of capacity, all
co-operating on a uniform system, so as to obtain a uniform result,
like the astronomers in a large observatory. The Greenwich Observatory
presents an example of co-operative work of this class