A look at how water depth is measured via lead and echo soundings to prevent ships running aground.
Item title reads - Invisible roadways of the sea.
L/S of observation towers along the coastline of America. M/S of people standing on them and looking through binoculars. M/S of a lighthouse. M/S of men carrying out water surveys on the beach. M/S of a small boat making lead soundings in shallower waters. M/S of a boat in Alaska carrying out echo soundings in deep water. M/S of a diagram showing how the echo soundings work to measure the depth via an oscillator and fathometer. Various good shots of a ship grounded near rocks.