how is this system associated with clocks?
Christiaan Huygens's pendulum marking the seconds gave rise to proposals to use its length as a standard unit
History of the metric system
In 1656, Dutch scientist Christiaan Huygens invented the pendulum clock, with its pendulum marking the seconds. This gave rise to proposals to use its length as a standard unit. 
who ruled france when the metric system was established Ancien Régime
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History of the metric system [SEP] Clocks and pendulums
In 1656, Dutch scientist Christiaan Huygens invented the pendulum clock, with its pendulum marking the seconds. This gave rise to proposals to use its length as a standard unit. But it became apparent that the pendulum lengths of calibrated clocks in different locations varied (due to local variations in the acceleration due to gravity), and this was not a good solution. A more uniform standard was needed. In 1670, Gabriel Mouton, a French abbot and astronomer, published the book "Observationes diametrorum solis et lunae apparentium" ("Observations of the apparent diameters of the Sun and Moon") in which he proposed a decimal system of measurement of length for use by scientists in international communication, to be based on the dimensions of the Earth.