HYDROGRAPHY. j,_ 



We cannot as said already expect with certitude that there should be a great deal of vegetable 

 plankton, because we have met with plenty of oxygen. This is a natural consequence of the fact 

 that a long time can elapse from the moment that the surface-water is supersaturated with atmospheric 

 air, until again it assumes its normal saturation. We have seen from the foregoing that this state 

 of matters, in so far as the nitrogen is concerned, is of great importance, and there is no reason to 

 suppose that there should be any material difference in the behaviour of the oxygen than in that of 

 the nitrogen, when the question is about giving up the atmospheric air absorbed by the water, 

 or, more properly spoken, the air which the water contains in surplus according to the law of 

 absorption. 



We are therefore fully justisfied in expecting that/— e is determined, not only by the 

 plankton found in the water at the moment of investigation, but also by the plankton 

 that has been in the water for some time before the investigation took place. The longer 

 the time that has elapsed since the plankton disappeared, or was replaced by new plankton, the less the 

 influence of it will be. If then for inst. we find a certain value ior f— c, but not the plankton corre- 

 sponding to this value, we may draw the conclusion that such plankton has been at this place 

 shortly before, that is to say, within a space of time, which, on the basis of the experiences 

 gathered from the determinations of nitrogen, we may estimate to be at the most a few (3—4) weeks. 



To form an idea of the generation of oxygen that is the result of the assimilation of carbonic 

 acid and respiration of vital diatoms, as well as of the consumption of oxygen that is due to the 

 respiration alone, I made up my mind to make the following experiment on board, at which the 

 botanist of the expedition Mr. Ostenfeld, M. A. assisted me with great willingness. 



At a place where there was plenty of diatom plankton, the fishing was carried on with a small 

 horizontal net made of mill-gauze Nr. 20. The plankton that was fished up, was filtered through 

 another net with so large openings that the diatoms just could make their way through it, by which 

 process they were separated from all larger, specially animal organisms. The diatoms that had got 

 through, were now percolated through a very tight net, and those that had come through this net 

 were deposited in ioo ccm of sea-water in a measuring glass, care being taken, that the depositing was 

 complete. Half of the contents of the measuring-glass was poured into a bottle holding 1 litre, which 

 was filled immediately with sea-water and corked, but a very fine opening was left at the cork to 

 avoid an increase or a diminishing of the pressure inside the bottle. This latter was made of perfectly 

 bright and transparent glass. The other half of the contents of the measuring bottle was, under 

 observance of the same measures, placed in a similar bottle, entirely wrapped up in tin-foil. Two 

 similar bottles, the one with, and the other without tin-foil, were filled with the same kind of water 

 as that filled on the two first bottles, but still without diatoms. All four bottles were placed in a 

 basket and submerged into the sea, close below the surface. Here the bottles were turned several 

 times, and after they had remained in the water some time, they were hauled up and analysed imme- 

 diately afterwards. To prevent diatoms from getting into the air-analysis-apparatus, the end of the 

 suction-tube was covered with a piece of silk network, similar to that used for the filtration and the 

 fishing-net. The weather was cloudy, and the sun was shining brightly now and then during the 



