H.M.S. Challenger Dredging and Sounding Equipment-Shown on the decks of H.M.S. Challenger is the dredging and sounding equipment used by the Royal Society in the first charting of the map of the world under the seas. The equipment included instruments for taking soundings, bottom samples and undersea temperatures; winches and a donkey engine; 144 miles of sounding wire; sinkers, nets and dredges. The Royal Navy crew held H.M.S. challenger steady at each site with her steam engines, enabling scientists to take a standard series of observations which included the total depth of water, the temperature at various depths, the atmospheric and meteorological conditions, the direction and rate of the current on the ocean surface and occasionally of the currents at different depths. All soundings and sampling from depths were hoisted by the 18-horsepower donkey steam engine, using the main yard arm as a boom over the side. Sounding to determine depths was carried out in shallow water under 1,000 fathoms with a light conventional lead which had a small compartment for obtaining a bottom sample. For greater depths, a different device was developed which had detachable weights of 300 pounds. This was the forerunner of the modern corer which took a sample of the bottom in a tube.