Early in the 15th c. the introduction of the mariner's compass rendered the seaman independent of sun and stars—an incalculable gain, as •e_s soon shown in the ocean voyages of Columbus, Cabot, and others. In 1492 Columbus rendered navigation more secure by the discovery of the variation of the compass. Between that and 1514 the "oross-staff" began to be used; a rude instrument for ascertaining the angle between the moon and a fixed star, with the consequent longitude. Early in the 16th c., tables of declination and ascension became common. In 1537 Nnfiez (Nonius), a Portuguese, invented various methods of computing the rhumb-lines and sailing on the great circle. In 1.545 the two first treatises on systematic navigation appeared in Spain, one by Pedro do 3ledina, the other by Martin Cortes. These works were speedily translated into French, Dutch, English, etc., and for many years served as the text-books of practical navigation. Towards the end of the century, Bourne in England, and Stevin in Hol land, improved the astronomical portion of the art, while the introduction of time-pieces and the log (q.v.) rendered the computation of distance more easy.
It would be tedious to enumerate the successive improvements by which the science of navigation has been brought to its present high perfection; but as conspicuous points in the history of the art, the following stand out; The invention of Mercator's chart in 1569; the formation by Wright of tables of meridional parts, 1597; Davis's quadrant, about 1600; the application of logarithms to nautical calculations, 1620, by Edmund Gunter; the introduction of middle-latitude sailing in 1623; the measure of a degree on the meridian. by Richard Norwood, in 1631. Hadlev's quadrant, a century later, rendered observations.easier and more ,accurate; while lIarrison's chronometers (77f4), rendered the computation of longitude a matter of comparatively small difficulty. Bond, and Norwood were the authors of scientific navigation, and their science is now mode available in practice by means of the Nautical Almanac, published annually by the British admiralty. The more important points of the science of navigation are noticed under such heads as DEAD-RECKONING, LATITUDE AND LONGITUDE, GREAT CIECLE SAILING, SAILINGS, etc.