. Fig. 21. 56-lb. stream-line lead, with bar attached. Fig. 22. Ball-bearing swivel for use with trawls, dredges and large tow-nets. be too frail for our purpose and others of heavy cast gunmetal were substituted. These proved satisfactory, but later were replaced by an ordinary Ekman reversing bottle adapted to fit on wires of large calibre. The bottle serves equally well and has the added advantage that it provides a water sample as well as the temperature. In placing such instruments as these on a long length of towed wire rope, a stop should be used and the instrument attached above it wit
. Fig. 21. 56-lb. stream-line lead, with bar attached. Fig. 22. Ball-bearing swivel for use with trawls, dredges and large tow-nets. be too frail for our purpose and others of heavy cast gunmetal were substituted. These proved satisfactory, but later were replaced by an ordinary Ekman reversing bottle adapted to fit on wires of large calibre. The bottle serves equally well and has the added advantage that it provides a water sample as well as the temperature. In placing such instruments as these on a long length of towed wire rope, a stop should be used and the instrument attached above it with a loose-fitting clamp, so that it will not revolve as the rope twists and untwists. The thermometer type of gauge will, of course, only record the depth at the moment when the messenger arrives, and for biological work it 1 For description of the method see Ruppin, Wtss. Meeresuntersuch. Kiel, Helgoland, Abt. Kiel, neue Folge, ix, p. 182, 1906, and Brennecke, Ann. Hydrographie, 41, p. 363, 1913, and 42, p. 34, 1914.
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