The "Challenger" was provided with a most complete and liberal organization for the purpose; she had powerful deck engines for hauling in the dredge, workrooms, laboratories and libraries for investigating the results on the spot, and a staff of competent naturalists to undertake such investigations and to superintend the packing and preservation of the specimens reserved for future study. Since the "Challenger" expedition the use of wire rope has enabled far smaller vessels to undertake deep sea work. The "Challenger," however, may be said to have established the practicability of dredging at any known depth. _Operating Dredges and Trawls in deep Seas._--Dredging operations from large vessels in deep seas present numerous difficulties. The great weight of the ship makes her motion, whether of progress or rolling, irresistible to the dredge. The latter tends to jump, therefore, which both lowers its efficiency and causes it to exert a sudden strain on the dredge rope. The efficiency or evenness of dredging was secured, therefore, by the special device of fastening a heavy weight some 200 or 300 fathoms from the dredge end of the dredge rope. This was either lowered with the dredge or sent down after by means of a "messenger," a ring of rope fixed round, but running freely on, the dredge rope. The latter plan was used on the "Challenger"; the weights were six 28 lb. leads in canvas covers: their descent was arrested by a toggle or wooden cross-bar previously attached to the rope at the desired point. When, however, the rope used is of wire this front weight is unnecessary.