It was not until Harrison’s chronometer became generally available in the 1770s that the third of these preconditions was fulfilled. This brilliant invention made it possible for cartographers to fix longitude precisely, something that the Sumerians, the Ancient Egyptians, the Greeks and the Romans, and indeed all other known civilizations before the eighteenth century were supposedly unable to do. It is therefore surprising and unsettling to come across vastly older maps which give latitudes and longitudes with modern precision.
