Of course such tables did not possess
astronomical accuracy. At that time, in the case of the moon,
completely new tables were constructed from the results reached by
Professor Airy in his reduction of the Greenwich observations of
the moon from 1750 to 1830. These were constructed under the
direction of Professor Pierce and represented the places of the
moon with far greater accuracy than the older tables of
Burckhardt. For the larger planets corrections were applied to the
older tables to make them more nearly represent observations
before new ones were constructed. These corrections, however, have
not proved satisfactory, not being founded on sufficiently
thorough investigations. Indeed, the operation of correcting
tables by observation, as we would correct the dead-reckoning of a
ship, is a makeshift, the result of which must always be somewhat
uncertain, and it tends to destroy that unity which is an
essential element of the astronomical ephemeris designed for
permanent future use. The result of introducing them, while no
doubt an improvement on the old tables, has not been all that
should be desired. The general lack of unity in the tables
hitherto employed is such that I can only state what has been done
by mentioning each planet in detail.
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