183 
en spids Vinkel @ med Gradienten, skulde man regne med 
Formelen 
EE RE ae, 
SEA 
I dette Tilfælde vil Bevægelsen kunne blive accelere- 
rende. Men det er at merke, at den’ for en Del er op- 
stigende, modvirkes altsaa af Tyngden. I det Tilfælde, at 
Bevægelsen foregaar paa skraa mod Isobarerne, fra det 
lavere mod det højere Tryk, vil den kunne blive retarderende, 
men her har den en nedstigende Component og understøt- 
tes saaledes af Tyngden. Endvidere sees, at de forskjellige 
Slags Bevægelser langs Isobathen jevnlig afvexle hverandre, 
og Vandets Continuitet vil regulere Bevægelsen saaledes, at 
den ogsaa her nærmer sig til at blive continuerlig og over- 
ensstemmende med den, der følger af Formelen Side 176 
med «@ = 90°. 
Isobarsystemet for 300 Faynes Dyb er væsentlig 
det samme som Vindfladens. Vi faa saaledes 1 dette Dyb 
den samme Fordeling af Hastighederne, som er beskrevet 
under Vindfladens Beskrivelse. Værdien af Gradienten for 
Afstanden mellem to lsobarer er den samme 1 begge Til- 
felder. Den Omstændighed, at Vandet 1 300 Favnes Dyb 
er noget tungere end i Overfladen, gjør Hastighederne 1 
Dybet forholdsvis mindre, dog kun i Forholdet 1.027 : 1.080 
eller 0.9971, det er 0.3 Procent mindre. Man kan derfor 
godt benytte Skalaen paa Pl. XLIIT til at udmaale Ha- 
stighederne. 
Ved at sammenligne Karterne Pl. X LITT og Pl. XLIV 
ser man, at Stromhastighederne i Overfladen ere idethele- 
taget betydelig større end i 300 Favnes Dyb. Forskjellen 
er netop de Hastigheder, der svare til Tæthedsfladen. Thi 
Vindfladens Ordinater Pl. XXXIIT og XLIV ere Strømfla- 
dens (Pl. XLITT) minus Tæthedsfladens (Pl. XLII). 
Der, hvor Vandet i 300 Faynes Dyb passerer over 
Wyville Thomson-Ryggen, angiver Kartet en Hastighed af 
0.1 m. p. 8. (6 Kvm. 1 24”, 0.21 Kym. i 1”). D. Steven- 
son angiver,! at en Hastighed af Strømmen i en Elv af 
3 Tommer pr. Secund (0.170 Mil pr. Time) vil netop be- 
gynde at virke paa fint Ler, medens en Hastighed af 6 Tom- 
mer pr. Secund (0.34 Mil pr. Time) vil løfte fint Sand. 
Mellem disse Hastigheder ligger den af mig beregnede 
Strømhastighed. Denne skulde saaledes være tilstrækkelig 
til at transportere lettere Bundmateriale fra Ryggen ind i 
Færø-Shetland-Renden. J. Murray siger?: “At der over 
Ryggen stryger saavel sterke Tidevandsstromme som den 
stadige Strom mod Nordost, fremgaar af den Omstændig- 
hed, at ingen Aflagring af fint Material faar Lov til at legge 
sig paa den, og af de Sandkorn og Smaastene, der ere 
spredte over Havbunden imod Nordost. Over Ryggen viser 
' A. Geikie, Text-Book of Geology, 1882, S. 368. 
*  Eneyclopædia Britannica S. 594. 
a direction forming an acute angle, «. with the gradient, 
the computation should be made with the formula 
G45 Ap COS &X 
SVA ko 
motion 
w= 10.333 
the can become accelerated. 
Meanwhile, we must bear in mind that to some extent it 
Should 
the motion proceed obliquely to the isobars, from the lower 
to the higher pressure, it may become retarded, but then 
it has a descending component, and is thus assisted by 
Moreover, it appears that the different kinds of 
In this case 
is ascending, and therefore counteracted by gravity. 
gravity. 
motion proceeding along the isobath continually vary, and 
the continuity of the water will regulate the motion, so 
that here too it shall tend to become continuous, and to 
accord with that resulting from the formula, p. 176, with 
= BO, 
The isobar-system, for a depth of 300 fathoms, is in 
all essential particulars the same as that of the wind- 
surface. Hence, at this depth we get the same distrib- 
ution of velocity as set forth in the description of the 
wind-surface. The value of the gradient for the distance 
between any two isobars is the same in either case. The 
circumstance, that at a depth of 300 fathoms the water is 
somewhat heavier than at the surface, entails in the 
deep comparatively reduced velocities — but only in the 
ratio of 1.027 : 1.030 or 0.9971, 1. e., 0.8 per ‘cent less. 
We may therefore, without apprehension, make use of the 
scale given in Pl. XLIIT for measuring the velocity. 
If we compare the maps Pl. XLIIT and Pl. XLIV, it 
will appear that the current-velocities at the surface, taken 
on the whole, are considerably greater than at a depth of 
300 fathoms. The difference applies exclusively to the 
velocities resulting from the surface of density. For the 
ordinates of the wind-surface (Pl. XX XIII and Pl. XLIV) 
are those of the current-surface (Pl. XLIIL) minus those 
of the surtace of density (Pl. XLII). 
Where, at a depth of 300 fathoms, the water passes 
over the Wyville-Thomson Ridge, the map gives a velocity 
of 0.1 m. per sec. (5 naut. miles in 24 hours = 0.21 naut. 
mile in 1 hour). Mr. D. Stevenson states! that a river-cur- 
rent with a velocity of 3inches per second (0.170 mile an 
hour) will just begin to work on fine clay, whereas a ve- 
locity of 6 inches per second (0.34 mile an hour) will lift 
fine sand. Between these two velocities les the current- 
velocity I have computed. The latter should accordingly 
be sufficient to transport lighter bottom-materials from off 
the ridge into the Færoe-Shetland Channel. Mr. J. Mur- 
ray says:? “That the Wyville-Thomson Ridge is swept 
by strong tidal currents as well as by the steady flow to 
the north-east is shown by the fact that no fine deposit is 
allowed to accumulate on it, and by the particles of sand 
and gravel from the ridge which are spread over the sea-bottom 
1 A. Geikie, Text-Book of Geology, 1882, p. 368. 
2 
Encyclopedia Britannica, p. 594. 
