A historical review, starting with the existence of the horizon at sea, proceeding to various studies of the Earth's size and shape, and leading to the attempt by Columbus to reach India by sailing westward. A related unit, also included in this lesson plan . ... This lesson plan supplements: "The Round Earth and Christopher Columbus" section #8, on disk Scolumb.htm , on the web . ... Understand why the Earth is round (see optional discussion at the end of this lesson plan).] ...