Geoscience Reference
In-Depth Information
Some of the expedition's mountain-top measurements were the highest scientific
measurements made up to that time. On one mountain, Rucu Pichincha (15,413 feet
high, 4.7 km), they were shocked to see that the barometer stood 300 mm below the
normal height of 760 mm of mercury, the lowest atmospheric pressure that anyone
had ever observed. It was little wonder then that on the ascent they suffered vomiting
and fainting, what we know today as altitude sickness, due to lack of oxygen in the
rarefied air. This mountain defeated their geodesic measurements and after 23 days
they retreated to a lower altitude to complete their telescopic observations of other
distant peaks. The highest altitude at which they worked was on Mount Corazon at
15,794 feet (4.8 km), whose altitude they measured to within a few toises (say 10
meters). This is the same height as Mont Blanc, first climbed in August 1786, 50
years later. On Mount Corazon their “clothes, eyebrows and beards were covered
with icicles,” and it was little wonder that the members of the expedition were
amused when, a few months later, they received a letter from their colleagues in
France expressing concern that, so close to the equator, they must be “suffering too
much from the heat.”
Each expedition observed natural phenomena, as well as the geodetic measure-
ments that were the initial objective of their trip such as optical phenomena in mists
and fogs, like haloes around the Sun (describing for the first time the
Ulloa Halo
or
Bouguer Halo
), Inca ruins, volcanoes, trees, animals, and birds. Bouguer in
particular made observations of the period of a pendulum in the mountains, and he
discovered for the first time the influence of the density of local rocks on the Earth's
gravity; the difference between gravity at a given place and the mean is still called
the
Bouguer anomaly
.
The lives of the expedition members were not completely uncomfortable. In
Riobamba, for example, they were royally entertained as distinguished visitors from
Europe, especially by the Peruvian women who were keen to learn the latest dance
steps from France. La Condamine was especially charmed by the musical abilities of
the oldest daughter of the family of Don Joseph Davalos. However, he was shy because
he had facial scars from smallpox that he felt were disfiguring, and she had the sole
ambition to become a nun. Needless to say, their relationship did not develop.
In Tarqui they were amused by a native festival; the members had observed the
astronomers crouching at the eyepiece of a telescope observing the Sun to deter-
mine time to measure the latitude and longitude of one end of their meridian line.
La Condamine wrote:
It must have been for them an impenetrable mystery, to see a man on his knees at the base
of a quadrant, head facing upwards in an uncomfortable position, holding a lens in one
hand and with the other turning a screw at the foot of the instrument, and alternately
carrying the lens to his eye and to the divisions to examine the plumb line and from time
to time running to check the minutes and seconds on the pendulum and jotting some num-
bers down on a piece of paper and once again resuming the first position. None of our
movements had escaped the observations of our spectators and when we least expected it
they produced on stage large quadrants made of painted paper and cardboard which were
quite good copies, and we watched as each of us was mimicked mercilessly. This was done
in such an amusing manner that I must admit to not having seen anything quite so pleasant
during the years of our trip.
