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FREY PETER, LETTER TO FREY DIEGO, 28TH DECEMBER, 1589
Pages 33

Page 23. He describes the current methods of navigation generally, and in particular of deadreckoning, which consisted in estimating the length and direction of your day’s run according to the observed speed of the ship and her course by compass-bearing, allowing as well as you could for drift and lee-way. Until the days of the chronometer it was the mariner’s only means of “guessing”—Stevens has the right word-at your longitude; and as even the log was not invented till somewhere round 1620 and you took your speed by throwing a chip or some such light matter overboard at a certain point in the bows and noting how long it took to drift to another certain point further aft; as the existence of currents was mostly imperfectly ascertained and their speed and set scarcely at all, and as the crank ships made almost as much lee-way as headway on most points of sailing, it was a lucky deadreckoning that gave you a land-fall within a day or a hundred miles of your calculations. Small wonder that the early navigators watched every sea-beast, every bird, every scrap of floating weed. To us it seems that they must have smelt their way from land to land.