HYDROGRAPHY. IQ , 



but little from place to place at the same depth. Water in possession of these properties, 

 will in the following be called Atlantic-Ocean-Water; as it is so with the temperature and 

 salinity of the water in the Atlantic, and in the seas that have been explored, we shall hardly meet 

 with water in possession of the aforesaid properties, but that it is found in or originates from the 

 Atlantic. 



The second of the two aforesaid principal types distinguishes itself by its throughout low 

 temperature, as well as by a minimum of temperature in or near the surface, and 

 below this minimum of temperature a maximum of temperature, from which the 

 temperature is decreasing gradually towards the "bottom. The salinity is throughout 

 lower than in the first of these principal types, and it is specially low at the surface. 

 In general there is a maximum of salinity near the surface, underneath this a minimum, and finally 

 a maximum lying still farther down. s(j) is near the surface greatly increasing with the 

 depth (still it is to be observed that the curve sometimes is bent downwards); in greater depths 

 s /-) grows more slowly, but it will as a rule be greater than in Atlantic-Ocean-Water at a correspond- 

 ing depth. When the depth is great, s(— ) will generally decrease in the lowermost strata. It should 

 be remembered, however, that s(jj does not mean the specific gravity of the sea-water in situ, as 

 the specific gravity — with a few exceptions in the ice-water at the surface — is increasing when the 

 depth is getting larger. 



By the foregoing will be seen, that in so far as the North Atlantic is concerned, temperature 

 as well as salinity varies with the depth. If not the water was in a constant motion, these differences 

 would gradually [disappear, and this motion must, on the basis of the aforesaid assumption, take place 

 in such a manner that it is just able to maintain the state of matters for the time being. Owing to 

 this, an upper stratum of warm and salt water must therefore be added, and it is a well known fact 

 that this is the case with the whole of the Atlantic draught that is coming from the southward. 

 Water in possession of the last named properties, must therefore be added to the upper strata to 

 maintain the lower temperature and smaller degree of salinity. The simplest manner in which this 

 addition could be effected, would be that the water during the winter time adopted a lower temperature, 

 and, on account of the more abundant rain-fall, a smaller degree of salinity, so that, on account of the 

 cooling, its specific gravity would be increased, and thus make it sink to the bottom. It will be seen, 

 however, by further reflection, that the addition cannot take place in this manner in the whole of 

 the north eastern part of the Atlantic, for, while in this part of the Atlantic, the minimum of the tempe- 

 rature of the surface water hardly goes below 6°, the temperature of the water at a depth of more 

 than 600 fathom (1130 m.) will as a rule be below 6°, and in the larger depths even come down to 2°. 

 The cold water at the bottom cannot therefore be surface-water cooled on the spot, 

 but it must have been added by horizontal currents in the depth. 



It is quite a different thing with the seas north of the Faroe-Iceland- and Greenland ridge, in 

 which we have a cold fresh layer of water on top of a warmer and Salter one. As the formation of 

 ice in the Polar-seas prevents the fresh water — that is making its way to these seas from rivers as 



