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How were ocean depths measured before echo sounding was developed?

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Before the development of echo sounding, ocean depths were measured using a technique known as sounding by lead line.12

In this method, a rope or cable marked in fathoms—units of approximately six feet—was weighted with a lead sinker and cast overboard. The surveyor would measure the length of the line paid out once the weight reached the seafloor. To gain additional information about the environment, the bottom of the lead weight was often hollowed out and filled with grease to collect a physical sample of the ocean floor.12

This process was notoriously tedious and slow, particularly in deep waters. Furthermore, it was frequently inaccurate because subsurface currents or the movement of the vessel could deflect the line, preventing it from traveling straight to the bottom and resulting in a single-point measurement rather than a continuous record of seafloor topography.12