which, according to his calculations, the planet must actually be
found. And now for an episode in this history which will be
celebrated so long as science shall endure. It is nothing less than
the telescopic confirmation of the existence of this new planet,
which had previously been indicated only by mathematical
calculation. Le Verrier had not himself the instruments necessary
for studying the heavens, nor did he possess the skill of the
practical astronomer. He, therefore, wrote to Dr. Galle, of the
Observatory at Berlin, requesting him to undertake a telescopic
search for the new planet in the vicinity which the mathematical
calculation had indicated for the whereabouts of the planet at that
particular time. Le Verrier added that he thought the planet ought
to admit of being recognised by the possession of a disc sufficiently
definite to mark the distinction between it and the surrounding
stars.

It was the 23rd September, 1846, when the request from Le Verrier
reached the Berlin Observatory, and the night was clear, so that the
memorable search was made on the same evening. 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