198 



DISCOVERY REPORTS 



after each operation. Parts of the clock-work were of steel and would rapidly have been 

 destroyed if continual care had not been taken. 



For depths below 1500 m. the only gauge used was of the reversing thermometer 

 type^. If carefully calibrated beforehand a pair of thermometers, one protected against 

 pressure and the other unprotected, will give a more reliable indication of depth than 

 can be obtained by any other means. The thermometers were made by Richter and 

 Wiese of Berlin, and were used at first in simple reversing frames supplied by the 

 makers. These frames, though doubtless strong enough for vertical work, proved to 





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. 



