Until the last few hundred years, people believed that
the earth was flat.
In the 6th century B.C., Aristarchus proposed
that the earth was actually a spinning ball that rotated once daily, but
hardly anyone believed him.
It was not until 1543, when Copernicus presented the idea again with his theory that the earth revolves around the sun annually, that the idea began to find acceptance. Even then, people were skeptical, wanting some way to prove this in a way they could see.
One idea was to drop a stone down a mine shaft. The theory was that there should be a noticeable deflection from where the stone was released to where it landed. However, the depth of the shaft was so small in comparison to the radius of the earth that the test was inconclusive.
Another idea was to shoot a projectile straight along a north/south direction. Would it show a deflection? Again, the flight of the projectile was too short; its time in the air was too short to show conclusive proof.