When the maritime history of the eighteenth century is under discussion it is usual to stress the limitations imposed by the inability of navigators to determine their longitude. It is generally assumed that since the advent of the Davis Quadrant or back-staff the latitude could be observed with considerable accuracy, and that with the compass in a wooden hull and with the more accurate graduation of the log-line as shown by Norwood, the dead reckoning should, over short periods of time, be reasonably reliable.