According to Newton's theory, the centrifugal force of the Earth's spin should result in a slight flattening at the poles and a bulging at the equator, which would make the planet slightly oblate. That meant that the length of a degree wouldn't be the same in Italy as it was in Scotland. Specifically, the length would shorten as you moved away from the poles.
It think he has the sign wrong. If the Earth is oblate, the length of a degree is shortest at the poles and longest at the equator. NO, OK, I understand it now. Let's take the latitude to be the angle of a normal to the surface. Then, because the surface is flattened at the pole, you need to travel a little further for it to rotate by a degree at the pole than at the equator.
