Miles and metres

Nautical miles and metres were both originally defined in the same way: each of them was the distance on the surface of the earth subtended by a particular angle. For nautical miles, the angle is a minute of arc; for the metre, it is 1/40,000,000 of a turn.

I was idly wondering about the history of this way of defining a unit of length, and how it led to these two particular units, and what (if any) influence they had on each other. The In Our Time episode on Pierre-Simon Laplace briefly discussed his involvement in the definition of the metric system in revolutionary France, which nudged me to actually do some reading.

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