Ships emerge on the horizon
Ships at sea appear to rise up from the waves on the horizon due to the curvature of the Earth.
It is possible to tell that the earth is round without using technology. You just have to look at the shadow of the earth on the moon during a lunar eclipse.
During the partial phases of a lunar eclipse, the shadow of Earth can be seen on the surface of the Moon. It clearly casts a circular shape. This proves that the earth must be round.
The reason the shadow on the moon is round could be because the earth is a flat disc.
(P1) If the earth is round then there would be a round shadow on the moon during a lunar eclipse (P2) There is a round shadow on the moon during a lunar eclipse (P3) Therefore the earth is round
Reject (P3) Therefore the earth is round
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