Graeme
Corvus wrote:

You had the roughly pear-shaped geoid in mind? Ie. a sphere, flattened

somewhat at the equator by the Earth's spin into a hardly perceptible oblate-shape, and further modified into something thicker below the equator than above [1] when you get into the details?

Yep, that's it. It wasn't until the 1950's that we really knew what the earth was shaped like. Until around 200 BC, it was considered flat. Though wrong, this answer was, in a sense, NEARLY right, considering that the curvature of the earth is only about 8 inches to the mile, and the measuring isntruments of the time were rather crude.

Then the ancient Greeks decided that it was round. But that was wrong too, and we moved to the idea that it was an oblate spheroid. Only that wasn't *quite* right either, since we found out in the 50's that the bulge was slightly bigger (and by slightly, I mean measured in *yards*, not miles) south of the equator.