On the general Causes of the Ocean-Currents. 31 



drown up higher towards the surface; nevertheless the saltness there is 

 very variable. Farther on in the Kattegat, as I have already mentioned, 

 the saltness rises to 2, and in the Skagerack to 2.5 " „ and in the Nor- 

 thern corners of the Skagerack sinks again to about 2 "/„ in consequence 

 of the copious discharge from the Norwegian rivers. 



If the level of the North-Sea was constant and the discharge from 

 the rivers continued unvariable, and there were no other disturbing cau- 

 ses, the water-strata throughout the whole system would arrange tliem- 

 self in an imchangeable manner, dependent on the areas of the sections 

 of the basins and the channels that connect them. The sp. gravity 

 of the flowing water-strata, would then not, in my opinion, be the dri- 

 ving force for the streams, but it wmiLl he the decisive cause of dif- 

 ferences of level, assumed by the surface-strata all the way from Lin- 

 desnaes to Torneå. These differences, causing the surface-stream, would 

 of course be greater between ditl'ercnt basins of the system, than between 

 different points within the same basin. How great then is it possible 

 for these dift'erences to be? Between the North-Sea and Bottenhaf 

 no level can be assumed at a greater depth than 23 mètres, without its 

 being interrupted by land: hence the difference of level, due exclusively 

 to specific gravity, between the North-Sea and the Northern extremit}^ of 

 the Bothnian sea, cannot exceed 0.54(1 mètres, assuming the sp. gravities 

 of the waters to be respectively 1.0270 and 1.003; whence we obtain for 

 the w'hole distance an incline of only one in more than three millions '). 



The course of the streams within the above described system 

 of waters is however disturbed by several causes. I have already shown. 



') From the .above mentioned part of the Bottenhaf, i. e. from Sundswall to 

 Levanger in Throndhjemsfjord, tlic Swedish Geological Bureau, in 1869 and 1870, 

 caused a line to be levelled by Mr. A. Böhtzell, the Engineer, the details of which 

 measurements were published in the »Kungl. Svenska Vetenskaps-Akademiens För- 

 handlingar» for 1871. On this occasion it was endeavoured to carry the work to 

 such a point of accuracy, as to control the statement concerning the relative levels 

 of the Atlantic and the Bottenhaf. The water-level in Throndhjemsfjord at the mean 

 between ebb and Hood was then foiuid to be 0.725 met. lower than that of the Bot- 

 tenhaf at Sundswall. As however tin,' two extremities of the line thus determined, 

 have not yet been directly compared with the mean state of the water in the two 

 seas, a strict conclusion can not be drawn from this levelling relative to the question 

 here agitated. Nevertheless the result exhibits a remarkable agreement with that de- 

 duced from the specific weight of the waters, an agreement, Avhich deserves a some- 

 what greater consideration from the circumstance, that the extremities of the line le- 

 velled were determined at just the same season of the year. 



