156 PETTERSSON OCH EKMAN, SKAGERACKS OCH KATTEGATS HYDROGRAEI. 



rection. Wi have found such points of divergence in the current at the entrance to the 

 Kattegat: off Hållö on the Swedish coast; south of Fredriksva3rn, and W. of Lindesnses 

 and Lister. The last and most remarkable point of divergence in the Baltic streani (at 

 least in the summei-)') seems to be at the 62nd and the 63rd parallels on the Norwegian 

 coast off Cape Stadt, where the Norwegian channel opens into the deep basin of the 

 northern Atlantic in a manner very much resembling the embouchure of the deep channel 

 of the Kattegat into the basin of the Skagerack. 



The splitting of the Baltic stream into one westerly and one easterly branch, which 

 according to our observations took place at the mouth of the Kattegat from the 12th to 

 the 13 of February (see plate II) has also very much resemblance to the singular formation 

 of the surface waters, in the summer, represented on plate IX (after Herr Tornges' chart 

 in part III (Chemistry) of the reports of the Norwegian North- Atlantic expedition 1876 

 — 78), at Lat. 62° — 64° W. of Norway. At every such place that part of the stream 

 which turns westward soon löses itself in the surrounding sea and gives birth to a series 

 of water-strata of increasing saltness owing to mixture with the surrounding seawater, while 

 -the remaining eastern part of the stream shows a tendency to increase in saltness. Besides 

 another phenomenon of still greater importance takes place. That part of the original 

 stream which disappears after turning to the West also löses its velocity and energy ot 

 motion. This is transferred into work i. e. into under-currents and side-currents of 

 that kind which F. L. Ekman observed at the estuary of Göta Elf. On plate VIII 

 we have traced two diagrams representing a section along the estuary of that river from 

 the town of Gothenburg to the outer part of the Dana fjord. The upper figure shows 

 the state of things in July 1876, when Ekman first investigated this raatter, the second 

 section 11 shows the results of our investigations in February 1891. On both occasions 

 there was found to be an undercurrent of salt water from the open sea entering the river 

 below the outflowing fresh water. Ekman has shewn that this will always be the case 

 where fresher water flows out into a part of the ocean. The lower side of the outflow- 

 ing body of fresh water compels, by means of friction, the adjoining layer of seawater 

 to partake of its motion and in order to replace those particles which are carried away 

 and mixed up with the overlapping fresh water-stratum a new supply of salt water i'ises 

 from the depth and moves inwards and upwards in the opposite direction to that of the 

 upper current. These undercurrents Ekman named reaction streams. The vis movendi of 

 such a current is the kinetic energy stored up in the Avaters of the upper layers, which 

 gradually disappears as they proceed farther out into the open sea and is transformed 

 into movement of the deeper water-strata in the opposite direction. 



We had the opportunity of studying the effect of the western branch of the Baltic 

 stream N. of the SkaAv in producing reaction-currents from the depths of the Skagerack. 

 In order to explain this we must dwell a little upon the atmospheric conditions which 

 prevailed at the beginning of February 1890. After a stormy period of westerly winds 

 at the close of January and the first days of February, an anticyclonic maximum was 

 established över the Scandinavian peninsula about the 8th of February accompanied by 



') Since we do not know Ijow far to the north the oiitlying branches of the Baltic curreijt reach in 

 the winter. 



