Brass tube, lashed to a hemp rope, which is tied to a galvanised cast iron sinker weight, for Ocean depth sounding machine, used for marine vessel navigation

Brass tube, containing a glass tube, which has a brass cap at one end and open at the other end, containing traces of silver chromate and / or silver chloride, lashed to a hemp rope - which is tied to a galvanised cast iron sinker weight hollowed at base, for Ocean depth sounding machine, used for marine vessel navigation, patented by Sir William Baron Kelvin Thomson, British, 1876 and made by James White, Glasgow, Scotland, 1876