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være uforholdsmæssig store, eu Anskuelse, som ved de
senere Undersøgelser fuldstændig er bleven modbevist.
Rigtignok er det paa den engelske Challengerexpedition
iagttaget. at de i den hede Zone fra Havbunden optagne
Vandprøver ved at henstaa nogen Tid vise
Overmætningsphæno-mener, men dette vil jo ikke være vanskeligt at forklare,
naar man erindrer, at Vandet i de store Dyb selv i
Æqva-toregnene er meget nær iskoldt. Det følger nemlig af sig
selv. at de til en saa lav Temperatur svarende
Luftmængder ikke kunne holdes opløste, naar Vandprøverne ved
længere Tids Henstand antager de tropiske Egnes høie
Lufttemperatur. Stærkest taler cle paa den norske Expedition
udførte Luftbestemmelser for. at Tryktilvæxten med
Dybden ikke kan have nogen Indflydelse paa Mængden af den
i Søvandet opløste Luft. Tager man nemlig Middelet af
Dybder, Temperaturer og Kvælstofmængder for alle de fra
Puncter under Overfladen stammende Vandprøver, hvori
der paa denne Expedition er foretaget Luftbestemmelser,
erholder man til et Middeldyb 693 Favne (1267 Meter) en
Middeltemperatur — 0.° 05 og en midlere Kvælstofgehalt
13.99 CC. per Litre, det vil sige, Vandet i Dybet
indeholder gjennemsnitlig næsten 0.5 CC. Kvælstof mindre, end
det ved sin Temperatur vilde kunne holde opløst under en
Atmosphæres Tryk.
Naar man erindrer, at Trykket i Havdybene ikke
dreier sig om Atmosphærer men om Hundreder af
Atmo-sphærer. saa maatte man dog vente, at dets Indflydelse
(om det havde nogen) vilde give sig tilkjende ved
Uregelmæssigheder af paa viselig Størrelse, og man er, da dette
ikke i mindste Maade er Tilfældet, berettiget til den
Slutning, at Trykket ikke besidder nogen Evue til i mærkbar
Grad at ophobe Luftmængderne i de store Dyb. Paa den
anden Side maa det fornuftigvis antages, at Vandet i de
dybere liggende Lag ikke kan afgive noget af sin Luft. da
det jo paa Grund af det der herskende Tryk vil kunne
holde opløst overveiende større Mængder end de, der
nogensinde ere forefundne.
Den rimeligste Slutning af de senere Tiders
Observationer over clisse Gjenstande vil saaledes være den. at en
Vandprøve, saalænge den befinder sig under Overfladen,
uforandret vil beholde den samme Luftmængde eller
rigtigere Kvælstofmængde1, som den havde absorberet, da den
sidste Gang befandt sig i Overfladen udsat for Luftens frie
Indvirkning.
Nu er den Luftmængde, som Søvandet absorberer af
Atmosphæren, hovedsagelig afhængig af Vandets Temperatur,
idet Barometerstandens Variationer ligeoverfor større
Temperature! iflereutser kun har en underordnet Betydning. Heraf
følger, at de Vandmasser, der have absorberet siu
Luftmængde under varmere Himmelstrøg,. maa være forholdsvis
1 Den absorberede Surstofmæ’ftgde er Aemlig i nogen Grad
afhængig af Dyrelivet og andre Tilfældigheder, saaledes at det her
ligesom i den tidligere Afhandling vil være det Rigtigste at anvende
Kvælstofmængden som Maal for den samlede Luftmængde.
vailing there, has been wholly’ refuted by the results of
later observations. True, the samples of water obtained
at great depths within the tropics on the ’Challenger’
Expedition were found to exhibit the phenomena of
super-saturation when allowed to stand over some time; this,
however, is easily explained, if we call to mind that the
water at great depths, even in equatorial regions, has a
temperature but little above zero. Heuce it naturally
fol-lows% that the quantity of air corresponding to so low a
temperature cannot be retained on the samples of water
having stood over sufficiently long to acquire the high
temperature of the atmosphere in tropical climates. The
air-determinations performed on the Norwegian Expedition
afford the strongest proof of the fact, that the increase of
pressure with the depth does not exert any appreciable
influence on the proportion of air in sea-water. Now. if
we compute the mean depth, temperature, and amount of
nitrogen for all the samples of water from below the
surface examined for air-determinations, the result will .be as
follows: mean depth 693 fathoms (1267 metres); mean
temperature — 0.°05; mean amount of nitrogen 13.99cc
per litre, which shows that in the depths of the ocean the
proportion of nitrogen averages 0.5cc less than could be
absorbed by sea-water of the temperature prevailing there
with the pressure of oue atmosphere.
If we call to mind that the pressure in the depths
of the sea is not computed even by tens, but by hundreds
of atmospheres, its influence, if any, must surely, oue would
imagine, occasion irregularities of appreciable magnitude: and
we may therefore safely, conclude, since no such disturbance
can be detected, that pressure does not perceptibly increase
the amount of air at great depths. On the other hand, there
is every reason to infer, that the water in the lower strata,
owing to the immense pressure, cannot part with any of
its air, the quantity actually absorbed never being even
approximately so great as such a pressure would enable it
to retain.
From the latest observations throwing light on this
question, we may therefore reasonably infer, that all
sea-water below the surface retains undiminished the quantity
of air, or rather of nitrogen,1 which it absorbed when last
at the surface, in direct contact with the atmosphere.
Now, the quantity of air absorbed by sea-water is
mainly dependent on the temperature of the latter, the
rise or fall of the barometer, as compared with
considerable differences in temperature, beiug in this case of but
little moment. Hence it follows, that the proportion of air
absorbed by sea-water in warm climates is small compared
1 The amount of oxygen absorbed by sea-water depending to a
certain extent on the presence of animal life and other accidental
causes, the amount of nitrogen may, with greater precision, be
assumed to represent the total amount of air — a standard of
measurement adopted in the preceeding Memoir.
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