Reference to the work of Roger Bacon has not been made, because of the doubts surrounding it.
[CHAPTER VI]
COLUMBUS, COPERNICUS, GALILEO AND OTHERS
Long before the Christian era the Chinese used pivoted magnetic needles to indicate absolute direction to them; but that they possessed or had invented the mariner's compass, there is considerable doubt. The history of the invention of the mariner's compass has not yet been written. It is not known when, or where, or by whom it was invented.
It is well-known, however, that the mariner's compass was in use in the Mediterranean Sea in the early part of the fifteenth century A. D. Guided by it, the navigators of that day pushed far out from land.
The first great navigational feat that followed the invention of the compass was that performed by the Portuguese, Bartholomew Dias, who conceived the idea of reaching India by going around Africa, and sailed down the west coast of Africa as far as its southern end, later called the Cape of Good Hope. It was a tremendous undertaking, and it had tremendous results; for it demonstrated the possibilities of great ocean voyages, proved that the road to India was very long, and led to the expedition of Columbus, six years later. It was also a great invention, both in brilliancy of conception and excellence of execution, although Dias did not reach India.
The second great navigational feat was performed by Christopher Columbus in 1492. Before that time it was conceded by most men of learning and reflection that the earth was spherical; and it was realized that, if it was spherical, it might be possible by sailing to the westward to reach India, the goal of all commercial expeditions in that day. Columbus is not to be credited with the first conception of that possibility.
Portuguese Voyages and Possessions