102 HYDROGRAPHY. 



chart Temperature & salinity have been indicated at every determination for the sake of perspicuity, 

 except at such places, where the determinations are so close to one another that there is no room for 

 the ciphers. Thus between o (o) and ioo fathoms (188 m.) is only noted salinity and temperature at 

 50 fathoms (94 m), even if there be more determinations. Among the curves drawn, the blue are 

 isotherms, the red ones isohalines drawn according to the interpolation curves on the plates IV — XIX, 

 and the signification of a curve is, as a rule, marked on it The o° isotherms are drawn with a thicker 

 blue line than the other isotherms. In so far as regards those isotherms and isohalines that have been 

 drawn, this principally depended on whether they offered any interest and could be drawn with toler- 

 able exactness. The depths are, in the same manner as under the curves, indicated in Danish fathoms 

 and metres. 100 fathoms (188 metres) is represented by a centimeter. 



TEMPERATURE AND SALINITY IN THE DEPTH. 



The ideal we should try to attain by hydrographic investigations, is to be able to give an 

 account of what the condition of a certain area of the sea is at any time. By means of such a voyage 

 as the Ingolf expedition, we can certainly acquire ample information of the state of the sea at many 

 places and at different periods, and by this our knowledge of it has no doubt been greatly increased, 

 as we may take it for granted that in the course of time the condition of the sea has been subject 

 only to changes of such little importance, that they need not to be taken into consideration. Still it 

 is to be observed, that this assumption only can find application on the great depths. As, however, 

 it is necessary for us to have a basis to work on, we choose, as we know of no better, this assump- 

 tion as the most simple. 



To be able to account for the state of the water at a certain place, we must be capable of 

 stating its chemical & physical properties as well as its motion. We have chosen temperature, 

 and the amounts of chlorine, nitrogen, and oxygen (and perhaps flora and fauna) as representatives for 

 the chemical and physical properties as the variations of these qualities are best fit for determinations, 

 and at any rate partly may be attributed to simple and well known causes. 



The motion of the water has upon the whole not been measured directly anywhere, and even 

 if such a thing had been the case, we could not from the motion which the water had at the moment 

 of observation, draw any reliable conclusion concerning the resultant motion for any great length of time. 

 It is specially this which offers interest, and we must therefore to the best of our ability draw con- 

 clusions on the basis of the observed chemical and physical properties. 



If we look at the curves on the plates IV — XIX, it will be seen at once that they nearly all 

 may be ranged txnder one of the two principal types. One is characterised by the fact of its 

 temperature being rather high (in comparison with the other), and that it is principally 

 decreasing with the depth. The salinity does not vary much, and it is above 35.00, as 

 a rule decreasing with the depth. s(^j increases gradually with the depth, and varies 



