HYDROGRAPHY. j.- 



As to the greater part of the stations, it appears that a low surface-temperature is attended 

 with a great supersaturation with nitrogen, in consequence of which, it would not be unlikely to sup- 

 pose that such a supersaturation was a feature characteristic to a cold stratum of water. That this 

 assumption cannot be upheld, and that it is not the temperature itself or the nature 

 of the water, but, on the contrary, the variation of temperature that has the domi- 

 nant influence here, manifests itself sufficiently by the observations made at the stations 59 and 60. 

 The temperatures are very low (i°7, i°7), btit the supersaturation only amounts to 06 and o-6 ccm re- 

 spectively, nor has the heating, according to the chart, been specially great at these stations. (For 

 station 59 it is 2°8. At station 60 20 fathoms (38 metres), a temperature of 2°i is put down, which, 

 however, may be due to observational errors). It is not unlikely that this is indicative of a melting 

 of ice having taken place recently, and this agrees very well with the fact of the observations at the 

 stations having been taken in the month of May, and that the water had such a low temperature. 

 That the above-mentioned assumption cannot hold good, appears even more distinctly, if we cast a 

 glance at the observations at station 94, where the surface-temperature is 2°5, the heating o°o, and 

 the supersaturation abt. o*oo ccm . Finally we shall come to the same conclusion, if we look at the obser- 

 vations at station 133, which has a high surface-temperature, namely io°8, the heating 2°2, and the 

 supersaturation abt. o-6o ccm . 



I shall direct the attention to another circumstance, which may be the cause of supersatura- 

 tion. Supposing for inst. that 1 litre of sea-water with a temperature of — 2 , and a salinity of 30%o, 

 was mixed with another litre of sea-water that had a temperature of 12° and a salinity of 35 °/ o0 , and 

 that both species of water, before the process of mixture took place, were saturated with nitrogen, 

 the result of this operation would be that the mixture approximatively would get a temperature of 5 

 and a salinity of 32-5 %o> and, according to the observations of Hambcrg, nearly contain a quantity 

 of air (16-07 + 11*62): 2 = I3*845 ccm per litre. According to Hamberg, the mixture shall contain only 

 I 3'535 ccm to be saturated, so that according to this, it will be supersaturated with o*3i ccm . We dare 

 not, however, take it for granted that a process of mixture will take place in the sea, between water 

 with so great differences of temperature as assumed in the example, and the supersaturation caused 

 by the mixture will therefore hardly exceed about 20 cc,n . 



We may therefore, in so far as the surface-water is concerned, set up the thesis: 

 That the supersaturation of the water with nitrogen is due to a heating, and that 

 the extent of the supersaturation is dependent on the rapidity with which the 

 heating is taking place. 



If furthermore we take it for granted that a rapid heating has the effect of causing a great 

 supersaturation, we may through this be able to judge of the influence the height of baro- 

 meter has on the gases contained in the water, and that such an influence really is exercising 

 its power, we may beforehand consider as a fact. The question is then whether it can be left out of 

 consideration or not. That is to say: can a specially high or low height of barometer remain unaltered 

 over the same water during a space of time that cannot be left out of consideration when comparing 

 it with the time during which the water is heated to about 2° or 3 ? It can be seen, namely, that 

 the difference between the temperature measured and the temperature of absorption can rise to that 



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