Plato's Mistake (cont.)
By Nick Kollerstrom, PhD
EarthMeasure
A couple of millennia roll by, and gradually the size of the Earth starts to be known; whereby the subject of geodetic metrology can arise: this examined indications that the ancient units of measure had originally come from the size of the Earth. (The endeavour to define the metre geodetically, around 1800, in terms of a polar meridian passing through Paris, such that a Great Circle around the Earth would be 40,000 km, was nearly right, it turned out to be 40,008.6 km.) The British Platonist philosopher John Michell gained especial insight into this endeavour, and he wrote:
The Greek foot is the most obviously geodetic of all units. In the earth's meridian circumference … there are 129,600,000 Greek feet. 1,296,000 is the number of seconds in the 360 degrees of a circle... [6]
The Urnumber has here reappeared  but neither John Michell nor any of the other Earthmetrologists (if we want to call them that) twigged that early mathematics had in fact come across this big number, or that it once had a central meaning.
What we might call the
mainsequence of British Earthgeodesy books  Nicholson, Men
and Measures (1912), Berriman Historical Metrology (1956),
Ivimy The Sphinx and the Megaliths (1976), and Michell Ancient
Metrology (1981) – all made a similar comment upon the
Greek foot as being the primary, geodetic unit: and found themselves
having to burden their readers with the hardtobelieve concept that
some culture way back in prehistory had divided up the Earth’s
circumference into degrees, minutes and seconds: ‘possibly the
circumference was rated 60^{4} units in remote antiquity,’
opined Berriman (p.19). Both Nicholson and Ivimy discussed how the
Greeks had inherited a base60 system of length measure even though
this was foreign to their maths: ‘At least sixty centuries ago
the Chaldean astronomers had divided the circumference of the Earth,
and of circles generally, into 360 degrees (that is 60 x 60) each of
60 parts.’ (Nicholson p.15, see also Ivimy p.55)
All of these authors
postulated a definition of the ancient Greek foot comparable to that
of the nautical mile in the 19^{th} century, such that there
would be 6000 Greek feet in a
nautical mile. To quote Wiki (N.Mile),
'Both the Imperial and US definitions of the nautical mile were based on the Clarke (1866) spheroid: specifically, they were different approximations to the length of one minute of arc along a great circle of a hypothetical sphere having the same surface area as the Clarke spheroid.'
It was agreed to define the Nautical Mile as 6080 feet.
Endnotes
