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Tætliedsfladens Form, det er dens vertieale
Coordinator over Niveaufladen, beregnes saaledes. Efter Formelen
pMt = 54.0438 -f- 53.23 p’ — 1.02783)
beregnes Trykket, i Atmosfærer, af Vandsøjlen paa 300
Favnes Højde, regnet fra Overfladen af, for en Række
Stationer i Nordhavet. Ved de Stationer, hvor Dybden er
mindre end 300 Favne, har jeg tænkt mig et Ror lagt
langs Bunden fra Stationens Vertical til det nærmeste
Punkt i 300 Favnes Dyb og taget i dette, efter
Tversnit-tene Pl. XXXIX XLI,den midlere Tæthed for Lagene
mellem 300 Favne og 200 Favne, mellem 200 Favne og
100 Fv. o.s.v. De saaledes extrapolerede Værdier ere i
Tabellerne Side 130—143 merkede med en Stjerne. Paa
denne Maade har jeg ført Tæthodstladen ind til Kysterne.
De saaledes beregnede Værdier for Trykket af en
Vandsøjle af 300 Favnes Højde blive af forskjellig Størrelse,
-lo større —, desto større Tryk. Til Grundplan for
Tæt-hedsfladon har jeg taget Niveaufladen gjennem Overfladen
paa et Sted, hvor det beregnede Tryk i 300 Favnes Dyb
er 54.0438 Atmosfærer. Trykket i de andre Stationer er dels
større, dels mindre end dette. Da nu Trykket i
Grændsefladen skal være constant 54.(3438 Atmosfærer i alle
Stationer, saa betegner et mindre Tryk end dette, at
Vandsøjlen paa 300 Favne er for kort til at frembringe tiet
Tryk, som Grændsefladen skal have. Til de 300 Favnes
Højde maa lægges en Vandsøjle at en saadan Højde, at
dennes Tryk er ligt det manglende. Overfladen kommer
altsaa over 300 Favne højere end Grændsefladen.
Ligesaa betegner en større Værdi af pm end 54.6438
Atmosfærer, at den tilsvarende Vandsøjle er for tung. Den
maa forkortes saameget, at dens Tryk bliver 54.6438 Atm.,
det er, der maa fradrages den en liden Vandsøjle, hvis
Tryk er p^a — 54.6438. Overfladen kommer saaledes at
ligge mindre end 300 Favne over Grændsefladen. Da
Afstanden mellem Grændsefladen og Niveaufladen for
Overfladen i Station 247 er 300 Favne, vil i første Tilfælde
Tæthcdsfladen ligge højere, i sidste Til fjelde lavere end
Ni-veaufladen gjennem Overfladen i Station 247. Den til
Tryk-forskjellen svarende Højdeforskjel findes af Formelen
i( t _ a„ S., (1 —ß eos 2(f ) (l -f bli) f h
’ 1 — i, P
1
■ (IP . l-’JP
a„ S„’ 1 -j-bh 1 — ß eos 2 ç
’l -,;p
r = 1.82877 Meter, faar man
.Ih iltoz.-’f, dp.
1 — ß eos 2 <(
The form of the surface of density, i. e., its vertical
co-ordinates above the surface of level, was computed as
follows. According to the formula
pM„ = 54.6438 + 53.23 (2 — 1.02783),
the pressure is computed, in atmospheres, of the column
of water of a height of 300 fathoms, reckoned from the
surface, for a series of Stations in the North Ocean. At
the Stations where the depth is less than 300 fathoms, I
have supposed a tube laid down along the bottom from
the vertical of the Station to the nearest point at a depth of
300 fathoms, and have taken in the said tube, from the
transverse sections Pl. XXXIX to Pl. XLI, the mean density
for the strata between 300 and 200 fathoms, between 200
and 100 fathoms, etc. These extrapolated values are marked
with an asterisk in the Tables, page 139 to 143. In this
way I have carried the surface of density up to the coasts.
The values thus computed for the pressure of a column
of water 300 fathoms in height will of course be different.
The greater 2:’. the greater the pressure. As the base for the
surface of density. I have taken the surface of level through
the top-surface, in a locality where the computed
pressure at a depth of 300 fathoms is 54.6438 atmospheres.
The pressure at the other Stations is partly greater, partly
less. Now, since the pressure at the limiting surface has
to be 54.6438 atmospheres at all Stations, a pressure less
than this will indicate that the column of water of a depth of
300 fathoms is too short to produce the pressure which the
limiting surface requires. To the height of 300 fathoms
must be added a column of water of such a height that
its pressure will equal that which is wanting. The
surface of the sea must accordingly lie more than 300 fathoms
above the limiting surface. In like manner, a value of p:M,
greater than 54.6438 atmospheres indicates that the
corresponding column of water is too heavy. It must, therefore,
be shortened to such an extent as will make its pressure
54.5438 atmospheres, i. e., from off it has to be taken a short
column of water whose pressure is p.MI — 54.6438. The
surface will accordingly lie less than 300 fathoms above the
limiting surface. As the distance between the limiting surface
and the surface of level for the top-surface at the
Station 247 is 300 fathoms, the surface of density must
in the former case lie higher, in the latter case lower than
the surface of level passing through the top-surface at
Station 247. The difference in height corresponding to the
difference in pressure is found from the formula
dp =
whence (I h =
a. .S.I 1 —eos 2(f) <1 4 I’ll)
ilh.
I - ,,p
dp I -.j. 1
ff,, i>’„ 14-hh I — [1 eos 2 //
- till
For 300 fathoms »S’,, , ’ = 1.0805: ami as 1
1 — p
fathom = 1.82877 metre, we get
... 10.(127
.III in metres = , , , it p.
1 > eos 2 .1
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