The ordinary proofs of the sphericity of the earth are: (1) It can be
circumnavigated; (2) the appearance of a vessel at sea always indicates
a nearer convexity of the earth’s surface; (3) the sea-horizon is always
depressed equally in all directions when viewed from an elevation; (4)
the elevation of the pole star increases as we travel northwards from
the equator; (5) the shadow of the earth on the moon during a lunar
eclipse is spherical.