Travel Reference
In-Depth Information
Bougainville and his contemporaries, therefore, had to rely on
the
other
method for calculating longitude. It was more complicated.
It required careful handling of instruments and several mathemat-
ical calculations. It was also less accurate. But those experts who
preferred this method (and the superiority of calculations based on
chronometers was by no means proved in the 1760s) believed that
it could be perfected and simplified. The astronomical calculation of
longitude aimed at measuring the difference in time between dif-
ferent points on the earth's surface by comparing the occurrence
of constant astronomical phenomena such as the angular distance
between the moon and various other heavenly bodies. The marine
navigator - given a clear sky and a deck that was not pitching too vi-
olently - had to take regular readings with instruments of varying
sophistication. Then he had to consult his almanac, which gave him
corresponding measurements in London or Paris or some other
European fixed point for every day of the year. The arithmetic ne-
cessary to convert all these data into a single, accurate measurement
of the angle of longitude was not simple and was certainly beyond
many mariners. However, the astronomical method, like the mech-
anical method, was being improved. In 1766 the British Astronomer
Royal, Nevil Maskelyne, published the
Nautical Almanac
which
provided a new set of lunar tables and instructions for their use.
Equipped with these, an accurate set of readings and more than a
smattering of mathematics a naval officer could calculate longitude
in about a quarter of an hour. But there were still many points in
the process at which human error could insinuate itself. What was
needed, in Bougainville's opinion, was to take an expert to sea and
entrust all measurements and calculations to him.
Thus it was that Pierre Antoine Veóron, a young astronomer,
boarded the expedition's flagship,
Boudeuse,
equipped with all the
latest instruments. During the voyage he took thousands of readings
with quadrant, octant and megameter - devices of varying sophist-
