I2 2 HYDROGRAPHY. 



be the cause of the formation of the transitional layer. During the summer time the ice-water is 

 heated, but the rays of the sun do not get far down in the water, before they are, as it were, completely 

 absorbed, so that it is only a very thin surface-layer which is heated directly by the rays of the sun. 

 This heating has, moreover, the effect of reducing the specific gravity of the ice-water, which 

 involves great difficulties with respect to a process of mixture between the surface-water and the water 

 below this latter. At any rate, a mixture must take place, as water from o to 10 fathoms (o — 19 M.) 

 only alters its temperature and salinity slightly, and as we can take it for granted that the rays 

 of heat do not make their way so far down, before they, get almost completely absorbed. 



The motion of the waves caused by a moderate breeze, will hardly produce any mixture. It 

 is therefore likely to be supposed that the mixture takes place when it is blowing a gale of wind. If 

 this assumption be correct, we must expect to find a high temperature at the surface when 

 it has been fine weather for some time, while, on the other hand, a gale of wind 

 must have the effect of reducing the temperature at the surface considerably, as, 

 in that case, the warmest surface layer, perhaps not 1 fathom (2 M.) thick, will be mixed with colder 

 water from a depth of 10 fathoms (19 M.). The process of mixture must be most energetic near 

 the surface, and it will therefore have the effect of making the temperature near the surface vary 

 slowly. It will appear afterwards, that these possibilities agree with the reality. If, on the contrary, 

 the heat should be transmitted downwards by conduction only, the variation of temperature near the 

 source of heat — this is synonymous with the surface — would grow rapidly, and afterwards decrease 

 towards the depth. 



It will be seen from the curves of temperature that there is a turning-point on the first 

 down-going part of the curves. The depth at which this turning-point appears, we must therefore 

 regard as the limit, above which the heat, upon the whole, is transmitted downwards by processes of 

 mixture in the water, while below this limit it is principally transmitted downwards by conduction. 

 We have thus by the position of the turning-point, a kind of mark that shows at 

 how great a depth the beating of the waves can have a disturbing effect on the 

 stratification of the bodies of water. 



The assumption that the sections XV, XVI and XVII are situated in a Polar Current, running 

 southerly along the east-coast of Iceland, is fully accounted for by all the peculiarities found in these 

 sections. The Polar Current carries with it in a southerly direction the warm but not 

 very salt water which is found on the eastern side of the north coast of Iceland, and 

 the presence of this water makes itself known thereby, that in all three sections, it forces the isoha- 

 line 34 - oo down close to the coast, and, that in the depth and close to the land, there is found i° nay 

 even 2 isotherms, which are not to be found again at a great distance from the main land. 



This warm water is pressing itself in among the regular under and upper-layer, and as it is 

 warmer than these two layers, and, moreover, enclosed by them, it will be cooled successively, and 

 the more so, the longer it has been in contact with the cold stratum of water. Owing to this, it 

 must be supposed that its temperature is decreasing to the southward, which just proves to be the 

 case. The maximum-temperature caused by this water in the deep close inshore, is sinking from 

 station 123 |3 C 5 at a depth of 50 fathoms (94 M.)| through the stations 121 |2°o at a depth of 75 fath- 



