The investigation was
facilitated by the circumstance that a diligent observer had recently
compiled elaborate star maps for certain tracts of the heavens lying
in a sufficiently wide zone on both sides of the equator. These maps
were as yet only partially complete, but it happened that Hora. XXI.,
which included the very spot which Le Verrier's results referred to,
had been just issued. Dr. Galle had thus before his, eyes a chart of
all the stars which were visible in that part of the heavens at the
time when the map was made. The advantage of such an assistance to
the search could hardly be over-estimated. It at once gave the
astronomer another method of recognising the planet besides that
afforded by its possible possession of a disc. For as the planet was
a moving body, it would not have been in the same place relatively to
the stars at the time when the map was constructed, as it occupied
some years later when the search was being made. If the body should
be situated in the spot which Le Verrier's calculations indicated in
the autumn of 1846, then it might be regarded as certain that it
would not be found in that same place on a map drawn some years
previously.
The search to be undertaken consisted in a comparison made point by
point between the bodies shown on the map, and those stars in the sky
which Dr.
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