ADVANCE IN NAUTICAL SCIENCE 63 lateen rig. The caravel marks an early stage of the development of square into side sails which added much to the tacking power of ships, and enabled them to put the wind to its full use on ocean voyages. Prince Henry adopted the caravel as his model for distant explorations and developed its navigating qualities. Cadamosto, although a Venetian, declared that the Portuguese caravels craft of fifty tons increasing in the sixteenth century to two hundred were the best sailing ships afloat. The rudeness of the nautical instruments and of the nautical science of the time was a hindrance to Prince Henry scarcely less serious than the imperfec- tions in the rig and build of his ships. The magnetic needle had been to some extent utilized by Italian sail- ors in the twelfth century. But the early forms of the mariner's compass were too rough to be trusted on long voyages. Brunetto Latini (the tutor of Dante), who visited Roger Bacon at Oxford, probably in 1258, de- clared that its discovery " must remain concealed until other times, because no master-mariner dares to use it, lest he should fall under a supposition of his being a magician. Nor would even the sailors venture them- selves out to sea under his command, if he took with him an instrument which carries so great an appearance of being constructed under the influence of some in- fernal spirit." An advance was made during the following century, but the Portuguese historian Barros records with refer- ence to one of Prince Henry's early expeditions, that
