Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
125
Jordrotationen. Et Exempel vil bedst oplyse dette. Vi
vælge et Punkt i Østhavet, hvor baade Strømbanernes
Krumning og Strømmens Hastighed er betydelig, nemlig ved
.Spidsbergens Sydkup. Centrifugalkraftens Størrelse er
R’
naar K er Krumningsradien for Banen. Kaldes den
Held-ningsvinkel, Centrifugalkraften vil frembringe, tf, saa har man
rotation of the earth. This will best be shown by an
example. Let us take a point in the Barents Sea where
both the curvature of the course of the current and its
velocity is considerable, viz., off South Cape Spitzbergen.
The value of the centrifugal force is assuming 11 to be
lx
the radius of curvature of the course. Now, calling the angle
of inclination which the centrifugal force will produce /’,
we have
& ’ (J R
I vort Exempel liar man u = 0.13 m. p. S., <j — 9.826
og R — 50000 Meter, og deraf if = 0".0071. Paa samme
Sted bliver ij 0".3785 og altsaa if = ’ •
Den Flade, Havets Overflade vilde indtage i Forhold
til Niveaufladen, som Følge af de normale Vindes
Virkning, kalder jeg Vind-Fladen. Dens Bestemmelse har
jeg udfort paa følgende Maade.
Vindfladen er i Pl. XXXIII fremstillet ved Linier,
der gaa gjennem de Punkter, hvis vortiealo Afstand fra
Niveaufladen gjennem Axen A B er den samme. . Disse
Ligehøjde-Linier repræsentere ogsaa Linier for ligestor
Trykhøjde, ganske som Isobarerne i Meteorologien. Da vi
som virkende Kræfter antage alene Tyngden og Afbøjningen
ved Jordrotationen, og se bort fra Friction, Træghed og
Centrifugalkraft, maa, ligesom i Atmosfæren Luftens
Bevægelse i dette Tilfælde gaar langs med Isobarerne, lodret
paa Gradienten, med en Afbøjningsvinkel af 90°, Vandets
Bewegelse folge Ligehøjde-Linierne. Da Vandets
Bevægelse maa følge Kystliniens Retning, bliver den første
Be-tingelsesligning, at en og samme Ligehøjde-Linie maa falde
sammen med en og samme sammenhængende Kystlinie.
Den Ligehøjde-Linie, som vi have ved Norges Vestkyst,
maa vi ogsaa have paa den ene Side ved Finmarkens
Kyst, ved Ruslands Nordkyst og ved Novaja Semlja, paa
den anden Side ved Skagerak, Jyllands Vestkyst,
Tysklands Nordsøkyst, Hollands og Belgiens Kyster, Frankrigs
Kyst og de britiske Øers Kyster.
De Ligehøjde-Linier, som betegnes ved Islands,
Spidsborgens og Grønlands Kyster, kunne tilhøre et lavere eller
højere Niveau end den Linie, som betegnes ved Europas.
For at tinde Niveauet ved Fastlandets Kyster,
opsøges et rent Strømprofil, der staar lodret paa Strøm
banerne. Et saadant have vi fra A til Norges Kyst ved den
1)5. Breddegrad. Som man ser af PI. XXXII, er i dette
Strømhastigheden paa det nærmeste proportional med
Afstanden fra A.
Sættes Strømhastigheden eller Tangenten til
Heldnings-vinkelen proportional med Afstanden fra A, bliver
Overfladens Gjennemsnit med et verticalt Plan en Parabel, hvis
Toppunkt er i A. og hvis Axe er vertical opad. Kaldes
Afstanden fra A for Yindtladens verticale Ordinat i denne
’ g R’
In our example, u = 0.13 m. per see., ♂ = 9.826, and
E= 50000 metres, wherefore if = 0".007l. At the same
place
: 0".3785. and hence if —
53
The surface which the sea would assume relative to
the surface of level consequent on the effect of the
normal winds, I call the Wind-Surface. Its determination I
have effected in the following manner.
The wind-surface is represented Pl. XXXIII, by
lines passing through the points whose vertical distance
from the surface of level through the axis A B is the
same. These lines of equal height also represent lines
of an equal height of pressure, precisely as do the
isobars in meteorology. Now, since gravity and the deviation
arising from the rotation of the earth are the only forces
to which we pay regard, putting aside friction, inertia, and
centrifugal force, the motion of the water must — as in the
atmosphere the motion of the air under a like supposition
is along the isobars, perpendicular to the gradient, with
a deviation of 90° — obviously follow the lines of equal height.
As the motion of the water cannot but take the direction of
the coastal line, the first equation of condition will be, that
one and the same line of equal height must coincide with
one and the same continuous coast-line. The line of equal
height passing along the West Coast of Norway, we shall
also have on the one side along the coast of Finmark, the
north coast of Russia, and the coast of Novaja Semlja, on
the other side along the Skagerak, the west coast of
Jutland, the North-Sea coast ol’ Germany, the coasts of
Holland and Belgium, the coast of France, and the coasts
of the British Islands.
The lines of equal height indicated by the coasts of
Iceland, Spitzbergen, and Greenland, may lie at a lower
or a higher level than does the line indicated by those of
Europe.
In order to find the level at the coasts of the continent,
a clear cross-section, cutting the stream-lines at right angles,
must be sought out. Such a section we have from A to the
coast of Norway, on the 65th parallel of latitude. As will
be seen from Pl. XXXII, the current-velocity in this
section is very nearly proportional to the distance from A.
Putting the current-velocity, or the tangent to the
angle of inclination proportional to the distance from A,
the section of the surface by a vertical plane will be a
parabola having its vertex in A and its axis pointing
vertically upwards. Now, calling x the distance from yl; the
<< prev. page << föreg. sida << >> nästa sida >> next page >>
