i5» 



HYDROGRAPHY. 



whole of the time the experiment was made. The results of the analyses, after the indicated periods 

 had elapsed, were as follows: 



I. bottle without diatoms, without tin-foil 

 II. — with — — — 



III. — — — with — 



IV. — without — — — 



Diatoms generate in the dark 

 — — light 



Time elapsed | 



between the j ccm . C0 2 ! can. iV 2 

 preparation I 



and the P er Litre per Litre 



analyses 



ccm. Oi 

 per Litre 



«/i hour 



2 hours 20 m. 



4 hours 



6 hours 



4 hours 

 2 hours 20 m. 



660 



17-60 



4-19 



6-53 



-2-38 

 4 11-03 



100 2 

 W+O2 



34'4 

 59' 2 

 25-9 

 34-6 



In consequence of analysis IV only being a repetition of analysis I, we might expect to find 

 the same amount - of nitrogen. The great difference in the quantities of nitrogen (o-23 ccm ) which has 

 appeared in the results of the two analyses, is perhaps due to observational errors, and I am therefore 

 led to be believe that it has been caused by the decautations. The difference in the quantities of 

 oxygen, in so far as these two analyses are concerned, is a mere trifle in comparison with the altera- 

 tions that took place at the two other experiments. 



It wall be seen that the difference in the quantity of oxygen in both cases (diatoms in the 

 dark and diatoms exposed to the light), is greater than the difference in the quantity of carbonic-acid- 

 Nearly the whole of the large volume of oxygen found at analysis II, had remained in a dissolved 

 state in the water, and only a few bubbles of air, which could not amount to man}- hundreds of 

 cubic-centimetres, were disengaged on the faces of the bottle, but in consequence of this, the amount 

 of oxygen stated is even too small. The number of diatoms used for this experiment, must be sup- 

 posed to have been about 300 times as large in the bottles as the number of diatoms in the same 

 volume of water in the sea. This statement is, however, in a high degree unreliable, as it is impos- 

 sible to know how great an error is made, when we consider it as given that the volume of 

 water that is passing through the net is equal to the product of the opening of the net, and the 

 distance the net is carried through the water. 



The experiment shows, however, that it would be entirely wrong to ignore the in- 

 fluence of the living plankton on the quantity of oxygen in the sea, nay not even 

 on that at the surface, and the volume of oxygen absorbed by the plants at their 

 respiration is very small in comparison with the quantity that is eliminated when 

 they are exposed to the light 



If we look at the stations in the table of the gas-analyses at which animal plankton has been 

 specially predominant, we find, as a rule, that a negative value for _/— c corresponds to such 

 a large quantity of animal plankton, that is to say, an incomplete saturation. This 

 is for inst the case at stations 59, 62, 68, 74, 75, and 97. Stations 96, 125, 133 make an exception to 

 this rule. As to station 96, we cannot draw any reliable conclusions from the observations made therei 



