128 THE LAST CRUISE OF THE CARNEGIE 



At this station we are to reach down five thousand meters, 

 so it will be necessary to repeat the bottle-series twice. The 

 "short-series" will consist of nine bottles lowered to 5, 25, 50, 

 75, 100, 200, 300, 400, 500 meters respectively, while one bottle 

 is reversed at the surface. As the greatest difference in tempera- 

 ture and chemical salts occurs near the surface, the intervals are 

 fairly short there. But in the "deep-series," which is sent down 

 later, the bottles are spaced 500 meters apart. The strain on 

 the wire would be far too great were we to lower twenty bottles 

 at once. 



During this time Seiwell has put out the plankton-nets. These 

 are lowered in series, much as the bottles; but onlv three are used. 

 One goes to 100 meters; another to 50 meters; and the third to 

 the surface. Microscopic life in the sea is chiefly concentrated 

 near the surface because sunlight does not penetrate water very 

 far. All animals depend on plants for food, directly or indirectly, 

 and of course it is sunlight which is utilized as a source of energy 

 by plants such as diatoms. 



Ten minutes are allowed for the lowered Nansen bottles to 

 take up the temperature of their surroundings. Captain Ault 

 now drops a brass "messenger" down the wire to reverse the first 

 bottle in the series. As each bottle tips over, its own messenger 

 is freed to proceed to the next bottle, and so on down the line. 

 It takes from ten to forty minutes for the messenger to reach the 

 lowest bottle. When they are inverted in this way, the valves 

 automatically imprison a sample of water from the desired depth. 

 Also, the mercury capillary of the thermometer separates in such 

 a way that the temperature of that level can be read off on deck, 

 no matter what temperatures are encountered on the way to the 

 surface. 



It is not possible to raise the bottle-series until the bottom- 

 sampler has struck. With depths like five thousand meters this 

 may take an hour. When the signal is given that the piano-wire 

 is slack, Leyer ceases to pay out, Erickson reads the meter-wheel, 

 and Captain Ault measures the vertical angle made by the wire. 

 From these readings the depth can be calculated. Soule has 

 meanwhile made an echo-sounding to check this value. 



