AE 
161 
Axen til et Punkt, der ligger nærmere Randen, og med at 
Tæthedsforskjellerne ere mindre i Dybet og som Følge 
deraf ogsaa Gradienterne i de nedre Lag, vil man komme 
til den Slutning, at Gjennemsnitshastigheden 1 de nedre 
Lag er betydelig mindre end i de øvre Lag. Vi føres 
saaledes snart op paa mindre Dybder for Grændsefladen. 
Allerede et Forhold mellem Hastighederne som 2 til I 
rykker den op til 474 Favne og som 3 til 1 til 349 Favne. 
Et sterkere Forhold mellem Hastighederne har forholdsvis 
mindre Indflydelse paa Grændsefladens Dybde, naar vi komme 
op til 300 Favne, der svarer til et Forhold af V:v = 3.622: 1. 
Nærmere kunne vi ikke komme til Løsningen ad 
denne Vej. Vi maa derfor se os om efter andre Kjende- 
merker og undersøge, om der i Bevægelsens Retning kunde 
være saadanne at finde. Her møder den Vanskelighed, at 
Bevægelsen i Havet hovedsagelig er bestemt af Vindene, 
hvis Virkning overgaar og overdækker Tæthedens. At ud- 
skille den sidste bliver vistnok i de fleste Tilfælder umuligt. 
Dens Spor lade sig dog nok paavise, navnlig turde her 
henpeges paa Isothermernes Sænkning i Havets Midte og 
Opstigning ved Renderne, der er saa fremtrædende 1 Snit- 
tene Pl. X til XIII. I Projectionssnittet Pl. X XVI se 
vi ogsaa, paa Norges Kystbanker, den sterkeste Sammen- 
trengning af Isothermerne ved noget over 300 Faynes Dyb, 
et Fænomen, der vidner om, at her lider det varme Vand 
i de øvre Lag, der drives frem af Vinden, en sterk! Afkjo- 
ling fra koldt Vand, der stiger op fra Dybet langs Bun- 
dens Skraaning. Her turde altsaa vere et Parti, der 
svarer til Punktet N i Fig. 2. 
I Færø-Shetland-Renden, navnlig i dens nordvestlige 
Halvdel (Snittene I, IT, III, IV og VI, Pl. IX), ligger 
iskoldt Vand under varmt Vand. Det varme Vand føres 
af de sydvestlige Vinde ind fra Atlanterhavet mod Nord- 
ost. Det iskolde Vand har sin Rod i Nordhavets Dyb 
østenfor Island og Færøerne; det maa komme ind langs 
Rendens Nordside fra Nordost mod Sydvest. Her have vi 
altsaa modsatte Bevægelser 1 de øvre og 1 de nedre Lag. 
Grændsen mellem disse ligger omtrent paa 800 Faynes Dyb; 
thi indtil dette Dyb rækker det varme Atlanterhavsvand 
paa Wyville Thomson-Ryggen. 
Jo højere Grændsefladen lægges, desto mindre Vægt 
tillægges Tæthedernes Ulighed som strømfrembringende 
Kraft. Thi jo mindre megtigt det øvre Lag bliver, desto 
mindre vil Forskjellen i de verticale Vandsøjlers Vægt 
blive, desto mindre de deraf flydende Uligheder i Trykket. 
Man er saaledes muligens paa den sikkre Side, naar man 
lægger Grændsefladen noget højt, fremfor i en større Dybde. 
Under disse Omstændigheder har jeg maattet gjøre et 
Valg indenfor de af Sandsynlighedshensyn optrukne Grændser. 
Jeg sætter Grændsefladens Dybde til 800 Favne. 
Den norske Nordhavsexpedition. H. Mohn: 
Nordbavets Dybder, Temperatur og Strømninger. 
surface they increase from the axis to a point nearer 
the margin, and that the differences of density are less 
in the deep, and consequently also the gradients in the 
lower strata, shall arrive at the result that the 
average velocity in the lower strata is considerably less 
than in the upper. We are thus soon brought up to less 
depths for the limiting surface. Even a ratio of the veloci- 
ties of 2 to 1 will raise it to 474 fathoms, and of 3: to 1 
to 349 fathoms. A greater ratio of the velocities has 
comparatively less influence on the depth of the limiting 
surface when raised to 300 fathoms, which corresponds 
to a proportion of V:v=3.622: 1. 
we 
A nearer solution we cannot arrive at in this way. 
We must, therefore, seek other criterions, and investigate 
if such are to be found in the direction of the motion. 
Here, however, we meet with the difficulty that in the 
sea the motion is chiefly determined by the winds, the 
effect of which exceeds and conceals that of the density. 
To separate the latter will no doubt in most cases prove 
impossible. Still, its traces will possibly admit of being 
detected; here, more especially, we may call attention to 
the dipping down of the isotherms in the middle of the 
sea and their rise at the margins, so conspicuous in the 
sections Pl, X to Pl. XIII. In the projected section, 
Pl. XXVI, we also see, on the Norwegian coast banks, 
the greatest crowding of the isotherms in a depth of some- 
what over 300 fathoms, a phenomenon clearly proving 
that here the warm water in the upper strata, driven for- 
ward by the wind, undergoes a considerable cooling from cold 
water, which ascends from the deep along the slope of 
the bottom. Here, accordingly, may be a part of the sea- 
bed corresponding to the point N in fig. 2. 
In the Færoe-Shetland Channel, more especially through- 
out its north-western half (Sections I, IT, ITI, IV, and VI, 
Pl. IX), ice-cold water extends under warm water. The 
warm water is carried by the south-westerly winds from 
the Atlantic Ocean towards the north-east. The ice-cold 
water has its source in the deep of the North Ocean, east of 
Iceland and the Feroes; it must find an entrance along 
the north side of the channel, from the north-east to the 
south-west. Here, we have accordingly opposite motions 
in the upper and in the lower strata. The dividing plane 
between the two lies at a depth of about 300 fathoms; for 
to that depth the warm Atlantic water reaches down on 
the Wyville-Thomson Ridge. 
The higher we place the limiting surface, the less 
importance we attach to the differences of density as a cur- 
rent-producing force. For the less deep the upper stratum, 
the less will be the difference of weight of the vertical 
columns of water, and the less the differences of pressure 
arising from them. Hence, we are possibly on the safe 
side in placing the limiting surface somewhat high, rather 
than at a comparatively great depth. 
Under these circumstances, I was compelled to choose 
within the limits of probability. 1 take the depth of the 
limiting surface at 300 fathoms. 
21 
