The people were reported to be civilised and good seamen, though unacquainted with the use of the compass, while south of them were savage cannibals, and still more to the south-west another civilised people, who built large cities and temples, but offered up human victims in them.

There seems to be here a dim knowledge of the Mexicans.
The great difficulty in maritime discovery, both for the ancients and the men of the Middle Ages, was the necessity of keeping close to the shore.

It is true they might guide themselves by the sun during the day, and by the pole-star at night, but if once the sky was overcast, they would become entirely at a loss for their bearings.

Hence the discovery of the polar tendency of the magnetic needle was a necessary prelude to any extended voyages away from land.

This appears to have been known to the Chinese from quite ancient times, and utilised on their junks as early as the eleventh century.