Various systems and theories appear to have prevailed among the ancients respecting the figure and motion of the earth; some justly enough supposing it to be a ball or sphere, suspended in infinite space, while others conceived it to be a flat surface, floating upon and surrounded by an interminable ocean.  The just conceptions of some ancient philosophers, respecting the spherical figure of the earth, and its diurnal motion around its own axis, were superseded by others of a more popular nature, and forgotten for many ages.  Lactantius and Augustine, two fathers of the catholic church, unfortunately adopted the idea of the earth being a flat surface, infinitely extending downwards; grounding this false notion upon a mistaken interpretation of the holy scriptures, or rather seeking assistance from them in support of their own unphilosophical conceptions.  So strongly had this false opinion taken possession of the minds of men, in our European world, even after the revival of learning in the west, that Galileo was imprisoned by the holy inquisitors at Rome for asserting the sphericity of the earth, and the doctrine of antipodes, and had to redeem his liberty and life, by writing a refutation of that heretical doctrine, which satisfied the inquisitors, yet convinced the world of its truth.

Columbus assuredly grounded his grand discovery of America upon the knowledge of the earth being a sphere; and had not the new western world intervened, his voyage had probably been the first circumnavigation.  In modern times, an idea has been advanced that Columbus only retraced the steps of some former navigator, having seen certain parts of the grand division of the world which he discovered, already delineated on a globe.  It were improper to enter upon a refutation of this idle calumny on the present occasion; yet it is easy to conceive, that the possessor of that globe, may have rudely added the reported discoveries of Columbus, to the more ancient delineations.  At all events, Columbus was the first person who conceived the bold idea that it was practicable to sail round the globe.  From the spherical figure of the earth, then universally believed by astronomers and cosmographers, in spite of the church, he inferred that the ancient hemisphere or continent then known, must of necessity be balanced by an equiponderant and opposite continent.  And, as the Portuguese had discovered an extensive track by sailing to the eastwards, he concluded that the opposite or most easterly coast of that country might certainly be attained, and by a nearer path, by crossing the Atlantic to the westwards.  The result of this profound conception, by the discovery of America, has been already detailed in the Second Book of this collection; and we now proceed in this Fourth Book to detail the various steps of other navigators, in prosecution of this grand design of surrounding the globe, in which many curious and interesting discoveries have been made, and by which geographical knowledge and practical navigation have been brought to great degrees of perfection.