Before the time of Bradley, who
commenced work at the Greenwich Observatory about 1750, the
observations were so far from accurate that they are now of no use
whatever, unless in exceptional cases. Even Bradley's observations
are in many cases far less accurate than those made now. In
consequence, we have not heretofore had a sufficiently extended
series of observations to form an entirely satisfactory theory of
the celestial motions.
As a consequence of the several difficulties and drawbacks, when
the computation of our ephemeris was started, in the year 1849,
there were no tables which could be regarded as really
satisfactory in use. In the British Nautical Almanac the places of
the moon were derived from the tables of Burckhardt published in
the year 1812. You will understand, in a case like this, no
observations subsequent to the issue of the tables are made use
of; the place of the moon of any day, hour, and minute of
Greenwich time, mean time, was precisely what Burckhardt would
have computed nearly a half a century before. Of the tables of the
larger planets the latest were those of Bouvard, published in
1812, while the places of Venus were from tables published by
Lindenau in 1810.
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