Sounding device with steel cable (Kelvin & Hughes, London), beginning of last century. Early bathymetric measurements or "soundings" were made by lowering a weighted line over the side of a boat and measuring the length of line output when the weight hit bottom. The sounding device in figure has a metal drum housing 500 m of steel cable with a 10 kg weight at the end. The drum is rotated manually using crank handles and is equipped with brakes and counter to record the length of the cable lowered into the water. The instrument is mounted on a cast iron support, designed to be fixed to a boat. A device similar to this was used to prepare the first bathymetric map of Lake Maggiore in 1887 published by Istituto Idrografico della Marina (I.I.M.).