SOUNDING

operation of ascertaining depth of water, for navigation, cable laying, and scientific purposes. For small depths s. is done by lowering a weight attached to a rope marked in fathoms. In deep s’s machines are used, wire taking the place of rope. From the reel the wire pa es over a wheel which registers the amount run out, an automatic brake stopping the reel when bottom is reached. In haling in the wire, sudden tensions caused by movements of the ship are relieved by an automatic compensating device. At great depths the weights are not recovered, but are slipped by a contrivance which also brings up a specimen of the bottem. Self-registering thermometers are fixed to the wire at intervals. A device has been perfected by which sound waves are utilized to indicate the depth of the ocean at any point at which s’s are taken.