User:Egil/Sandbox/Gabriel Mouton

Gabriel Mouton (1618–1694) was a French abbot and scientist. He was a doctor of theology from Lyon, but was also interested in mathematics and astronomy.

His 1670 book, the Observationes diametrorum solis et lunae apparentium, came to form the basis of what was to become the metric system hundred years later. Based on the measurements of the size of the Earth conducted by Riccioli of Bologna (at 321,815 Bologna feet to the degree), Mouton proposed a decimal system of measurement based on the circumference of the Earth, explaining the advantages of a system based on nature.

His suggestion was a unit, milliare, that was defined as a minute of arc along a meridian. The base unit would be the virga, 1/1000 of this, corresponding to 64.4 Bologna inches, or ~2.04 m. This was reasonably close to then current unit of length, the Parisian toise (~1.95 m), which was meant to make acceptance of the new unit easier. For practical reasons, Mouton suggested that the actual standard be based on pendulum movement, so that a pendulum located in Lyon of length one virgula (1/10 virga) would change direction 3959.2 times in half an hour. Using a 45° latitude g of 9.80665 this corresponds to ~20.538 cm.

His ideas attracted interest at the time, and were supported by Jean Picard as well as Huygens in 1673, and also studied at Royal Society in London. In 1673, Leibniz independently made proposals similar to those of Mouton.

By todays measures, his milliare corresponds directly to a nautical mile, and his virga would by definition have been 1.852 m.