Geoscience Reference
In-Depth Information
Chapter 7
Past its Prime
The Paris Observatory (Fig. 6) was the first national observatory and dates from
1667. The Greenwich Observatory (
Fig. 34
) followed closely (Malin and Stott
1984, Howse 1997), originating with a suggestion by a Frenchman to Louise de
Keroulle (1649-1734), Duchess of Portsmouth, who whispered it into the ear of
King Charles II. The Frenchman, Le Sieur de St Pierre, about whom nothing certain
is known except this reference which originated from the first Astronomer Royal
John Flamsteed, claimed that he had solved the answer to the determination of
longitude but in truth his suggestion was plagiarized, as I shall explain.
To know where a ship was it was necessary to make observations of the positions
of the stars and relate them to calculations of the orientation of the Earth at the time
the observations were made. There were no accurate enough clocks, though, so
astronomers sought clocks among the stars. Cassini's solution, as we have seen, was
to use eclipses of the satellites of Jupiter, but it was not practical to use the long tele-
scopes of the time to observe the satellites of Jupiter from the sailing ship's heaving
deck. As an alternative, Le Sieur de St Pierre suggested that the motion of the Moon
be used because the position of the Moon could be calculated relative to the fixed stars
and you could deduce time if you measured its position,. This was the method of lunar
distances first proposed in 1514 by Johann Werner, a German astronomer who edited
an edition of
Ptolemy's Geography
, and put forward the principle in a footnote:
Therefore the geographer goes to one of the given places and from there observes, by
means of this observational rod [an instrument that measures angles] at any known
moment, the distance between the Moon and one of the fixed stars...
Le Sieur de St Pierre tried to promulgate his idea in France where it received a
cool reception, perhaps because the Paris observers were already developing the
method which used Jupiter's satellites. He went to England to sell his idea and called
on Louise de Keroulle, partly because she was his compatriot and was then the mistress
of King Charles II, bearing him a son in 1672. This meeting resulted in King
Charles's appointment of a commission to advise him on how to find longitude.
The commission, which included John Flamsteed (1646-1719), agreed that the
method was sound in principle, but in practice neither the positions of the stars or the
motion of the Moon were known accurately enough nor was there an instrument that
could measure to the required accuracy. King Charles decided to attack these problems
