Geoscience Reference
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lawsuit, and the son loyally agreed to sell his instruments to pay off the family debt.
This setback proved his first stroke of fortune. His instruments were purchased by
Jérôme Lalande. In this way he came into contact with Lalande who sent him the
proofs of his topic on astronomy. In 1772 Lalande procured for Méchain a job as
hydrographer at the naval map archives in Versailles. The archives were transferred
to Paris and Méchain began to draw up military maps of Germany and northern
Italy. He also became active as an astronomical observer and eventually discovered
several comets as well as several nebulae now known best by their listing in
Messier's Catalogue. In 1785 he became the editor of the
Connaissance de Temps
,
the French nautical almanac.
In 1787 Méchain had been one part of an Anglo-French team measuring the dif-
ference of longitude between Greenwich and Paris. His work with traditional sur-
veying instruments was duplicated by Cassini and Legendre using Borda's new
repeating circle and proved the superiority of the new device (although it took two
people to work it). It was also a matter of pride that the repeating circle, invented
and constructed by their countrymen, proved to be as accurate as the theodolite
used by the English team and constructed by the acknowledged English master
instrument-builder, Jesse Ramsden.
AUTHORIZATION TO BEGIN the new survey of the Paris Meridian arrived in
June 1792 and Delambre immediately began preparatory work. Within two months
he had established bases in Paris and was ready for the first night measurements.
He sent an assistant, Michel Lefrançais de Lalande (Lalande's nephew) to the high
point in Montmartre with instructions to light a signal on 10 August, 1792 on which
he could sight his measuring telescope. There was no signal to be seen. What had
gone wrong? Once again the Revolution had come between the scientists and their
work. What had happened was the following.
The Revolutionary government had been cohabiting uneasily with King Louis
XVI. His position was, to say the least, difficult, but had he been a wiser man or more
surefooted politically, France might have turned out to be a constitutional monarchy
like Britain rather than the republic it became. Ultimately it was the King who pro-
voked the crisis, turning progressively for support to foreign relatives including those
of his wife Marie-Antoinette, known as “
l'Autrichienne
” (the Austrian woman), and
particularly Leopold II of Austria, Marie-Antoinette's brother. Reluctant to take part
in the ceremonies and proclamations which consolidated the new constitution, King
Louis XVI and the royal family plotted escape. The King played it cool, participating
in normal kingly business up to the last minute. On 19 June 1791, in the Tuileries
Palace, he even received the Committee on Weights and Measures - Borda, Cassini,
Coulomb, Lavoisier, Legendre and others. He exchanged pleasantries with Cassini,
and then asked him: “M. Cassini, I have been told that you will measure the Paris
Meridian again. Your father and grandfather already did this before you. Do you think
you can do it better than they did?” Cassini replied, “Sire, I would not boast of it if I
had not a great advantage over them. The instruments my father and grandfather used
only gave the measure of an angle to within 15 arc seconds. The Chevalier de Borda
has devised an instrument that will measure angles to one arc second. This will be to
