The shape of the earth

I.S. Glass

in Nicolas-Louis De La Caille, Astronomer and Geodesist

Published in print December 2012 | ISBN: 9780199668403
Published online January 2013 | e-ISBN: 9780191749315 | DOI:
The shape of the earth

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Having accomplished the astronomical aim of his visit to the Cape, La Caille decided to make the first measurement of the earth's radius in the southern hemisphere. The Swartland plains, north of Cape Town and overlooked by conveniently placed mountains, were ideal for this purpose. Aided by slaves, he laid out a precise baseline of 12605 metres length employing measuring rods brought from Paris. This was used to calibrate the baseline of two large triangles with vertices at his observatory in Cape town and near the present village of Aurora. The latitudes of the end stations were measured using a zenith sector. The radius of the earth at 33 degrees south was found to be comparable to that at 45 degrees north in France, implying that the planet was somewhat pear-shaped.

Keywords: Swartland; radius of earth; arc of meridian; geodesy; pear-shaped earth; Piketberg; Riebeeck Kasteel; Kapokberg

Chapter.  6576 words.  Illustrated.

Subjects: History of Science and Technology

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