The Art of Navigation

...subtlety that with a round instrument, no larger than the palm of the hand, which we call an Astrolabe, one can measure the curvature of the heavens: which is so great that the understanding of man cannot easily comprehend it. Also that with the said instrument one can take the height of the Sun, making its light pass through a very small and fine opening The "pertuis" refers to the small holes in the vanes or pinnules of the astrolabe used to sight celestial bodies. (even though the Sun is many times larger than all the earth and the sea); and that one may know how far it is removed from or near to us. Similarly, one can take the height of the stars, and this teaches and guides us, so that there is not the error of a single point.

Who could also describe the subtlety of the Compass (or sea needle), which is so excellent, that with a little paper (like half the hand) and with certain marked lines (which signify the winds), and a little iron (from which is fashioned an instrument, which moves by itself through the sole natural power that a stone The "stone" refers to a lodestone, a naturally magnetic piece of magnetite used to "touch" and magnetize the iron compass needle. gives and influences it) by its own movement, and without anyone touching it, shows where the East and the West are, the North and the South, and likewise all the thirty-two winds of navigation. It does not teach them only in one spot, but in all places of this world; and so surely that by it all those who navigate are directed.

Secondly, the certainty of this art is so great that it seems the understanding of one or many men could not have been sufficient to ordain it, if God, by special grace, had not provided for it and given understanding to men for this purpose: as can be proven hereafter. Let us suppose the case that a pilot navigating the sea is overtaken by a great and furious storm, three hundred leagues in the open sea, and that by day there is a heavy fog, and the night is so dark that one cannot see the hand before one’s eyes; or that the said pilot, being at the stern of his ship, cannot see the prow, or barely the mast, and that the said ship turns