The
British nation, as the leading maritime power of the world, was
naturally interested in the discovery of a method by which the
longitude could be found at sea. As most of my hearers are
probably aware, there was, for many years, a standing offer by the
British government, of ten thousand pounds for the discovery of a
practical and sufficiently accurate method of attaining this
object. If I am rightly informed, the requirement was that a ship
should be able to determine the Greenwich time within two minutes,
after being six months at sea. When the office of Astronomer Royal
was established in 1765, the duty of the incumbent was declared to
be "to apply himself with the most exact care and diligence to the
rectifying the Tables of the Motions of the Heavens, and the
places of the Fixed Stars in order to find out the so much desired
Longitude at Sea for the perfecting the Art of Navigation."
About the middle of the last century the lunar tables were so far
improved that Dr. Maskelyne considered them available for
attaining this long-wished-for object. The method which I think
was then, for the first time, proposed was the now familiar one of
lunar distances. Several trials of the method were made by
accomplished gentlemen who considered that nothing was wanting to
make it practical at sea but a Nautical Ephemeris.
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