Note 4 — Chapter VI
Reading edition
The principle of "Great Circle Sailing," which now guides the navigator to the Indian Ocean, must be studied in connection with this chapter. "For every degree the ship changes her longitude south of the Line she sails a shorter distance along the great circle than on any other curve; for on the parallel of 60° thirty miles corresponds to a distance of sixty at the equator."—ROBERTSON'S Theory of Great Circle Sailing: Bell and Daldy.