'Eratosthanesdid a famous experiment on measuring the
angle of the sun at noon in Alexandria, Egypt, and in Syrene. Finding the
difference in the angles and knowing the distance between the two points,
the circumference can be calculated. He calculated the circumference in
stadia, which we do not know the conversion to our present day measure.
If you travel north or south a signigicant distance, you will see a
different set of stars at night. This will not happen on a flat surface'
