Which unit of measurement was originally defined as one minute of arc along a meridian of the Earth?
Minute and second of arc arcsecond on a 10 m class telescope. Minutes (′) and seconds (″) of arc are also used in cartography and navigation. At sea level one minute of arc along the equator or a meridian (indeed, any great circle) equals exactly one geographical mile along the Earth's equator or approximately one nautical mile (1852 meters, or ≈1.15078 statute miles). A second of arc, one sixtieth of this amount, is roughly 30 meters or 100 feet. The exact distance varies along meridian arcs because the figure of the Earth is slightly oblate (bulges a third of a percent at the equator). Positions
History of the metric system astronomer, published the book "Observationes diametrorum solis et lunae apparentium" 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. The milliare would be defined as a minute of arc along a meridian and would be divided into 10 centuria, the centuria into 10 decuria and so on, successive units being the virga, virgula, decima, centesima, and the millesima. Mouton used Riccioli's estimate that one degree of arc was 321,185 Bolognese feet, and his own experiments showed that a pendulum of length one