ABSTRACT
The terrestrial globe, familiar in model form from earliest geography lessons, rotates about its axis, an imaginary line passing through the two poles and the Earth's centre. Latitude at a point on a spherical Earth is measured by the angle of an arc of the circular meridian between the point and the equator north or southwards respectively in the two hemispheres. Isaac newton postulated that, were two channels to be bored, one from a pole to the centre of the Earth, the other from a point on the equator to meet it at the centre, then, if the channels were imagined as filled with a liquid, the liquid would be in equilibrium and at rest to an earthbound observer. Uncertainties due to atmospheric refraction alone would be destructive to any accuracy when measuring so far from the vertical, particularly in using Riccioli's method or use of the horizon at sea.
