1 1 



always that the clepth bas not perceptibly increased, and that no special influences of current 

 have been at work. 



Almost all our trawlings or dredgings were preceded by a sounding. The various depths 

 indicated on the charts were not often trusted to. In the East-Indian Archipelago it is neyer 

 very safe to do so, unless there are reliable landmarks, by which the soundings of earlier and 

 later dates can be localised beyond dispute. Owing to the many inaccuracies in existing charts 

 and the unavoidable incorrectness of locajisation arising therefrom, it is quite within the range 

 of possibility to imagine that one has reached the point where a previous sounding was taken, 

 while in reality one has come to quite another place; and a difference of a few miles may 

 make a great difference in the depth of the sea floor. As an example we may take Station i 77 'j, 

 were a depth of 1633 metres was registered only three miles away from the place, where the 

 chart registered 121 1 metres of mud floor; the clepth during the dredging therefore, gradually 

 decreased to 1300 metres. This place also brought some curious sediments to light. 



The Station 271, situated immediately West of the Aru islands may serve as an example 

 of a dredging in which the indications of the chart were followed with good results. We steamed 

 from our sounding place, where we had found a depth of 1788 metres, in an E. N. E. direction, 

 steering towards the point where the "Challenger" had founcl a depth of 1536 metres. The rope 

 was stopped at 2240 metres and the net touched ground at a depth of about 1600 metres. 

 When the dredging was concluded the depth had decreased to 1520 metres. 



The greatest depth at which a successful haul was made, was registered at 4391 metres 

 (6 November, Station 223). About 800 kilogrammes of mud were brought to the surface. It 

 was a heavy strain on the capstan, but on the whole the operation was successful. One of the 

 booms of the trawl, a tube 2 l j i inch in diameter of 6 millimetres thickness of metal was entirely 

 collapsed and split owing to the enormous pressure of the water. This was caused by the tube 

 being air- and water-tight with iron caps fixed on the ends. 



The large vertical nets were also worked from the dredge-rope. To insure their going 

 straight clown to the bottom, the lower part, below the reservoir was weighted with a ballast 

 of 20 kilogrammes, and just above the swivel joint a weight of 30 kilogrammes was fastened 

 to the rope. The letting out of those nets was at a rate of from 30 to 32 metres, the hauling 

 in at a rate of 1 5 or 16 metres per minute. At moderate depths we fished sometimes with the 

 vertical net. which was provided with an electric lamp connected with the ship's conductor. 



The quantitative Plankton-net was worked by the rope of the depth registerer, on the 

 poop of the ship. 



For the fishing with closed nets we used our Le Blanc sounding-machine. It was provided 

 for this purpose with a separate heavier barrel round which 600 metres of steel rope of 6 

 millimetres diameter was wound. As the weight of this rope was so much greater than that of 

 the sounding line, two stronger springs were added to the stopper to be used with this rope. But 

 as the constant changing about of the springs was awkward, the necessary extra pressure on the 

 footreel was procured in a much simpler manner by a handspike pressing on the lever of the reel. 



t) For stations see List of stations in: Siboga-Expeditie I. Max Webeh : Introduction et desciiption de 1'expédition. 



