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Linen ind, hvorved Thermometret vendtes, Kviksølvtraaden
splittedes og registrerede Temperaturen, og Haglene rullede
ned i den anden Ende, der nu blev den tungere, og tjente
til at sikre Instrumentet mod en ny Omvending. Til sin
Accomodation behøver dette Thermometer kun 3 Minuter,
men det er en nødvendig Betingelse, at det i denne Tid
staar lodret eller næsten lodret med Kuglen nedad. Dette
tinder Sted, naar Trækassen har Opdrift i Vandet. Denne
Egenskab have Trækasserne, naar de ikke have været
udsatte for sterkere Vandtryk. Men naar Trækasserne havde
været paa større Dyb end et Par Hundrede Favne, viste
Erfaring mig, at de mistede sin Flydeevne. Herom
overbeviste jeg mig ved directe. Forsøg. Naar en Trækasse
kommer under et større Vandtryk, driver dette den i
Træcellerne indesluttede Luft, der giver Træet dets
Flydeevne, ud, og Kassen mister sin Opdrift. En saadan
Kasse vil, naar Lodlinen standser, strax vende sig om og
registrere Thermometrets Temperatur. Hvorvidt denne
eiden samme som det omgivende Vands, beror paa
Omstændighederne. Dersom Temperaturen i Havets Dyb ikke
forandrer sig eller kun forandrer sig ganske langsomt paa
det Stykke, Thermometret gjennemløber i de sidste
Minuter, vil dette kunne registrere den søgte Temperatur. Det
er lier at bemerke, at Accomodationen foregaar forholdsvis
hurtig under Thermometrets nedadgaaentle Bevægelse. Da
det var umuligt at faa gjort nye Trækasser til hvert
Dyb-lodskud, ere vore Bundtemperaturer, der væsentlig bero
paa de Negretti-Zambra’ske Thermometry, bestemte efter
det her fremsatte Princip og kunde derfor muligens være
lidt for højt angivne. Der er imidlertid, som nedenfor
skal vises, saa god Overensstemmelse mellem den ved
Ne-gretti & Zambra’s Vendethermometre gjorte Bestemmelse af
Trykcoefficienten tør Buchanans Kviksølvpiezometer og den
af Buchanan selv opgivne, at Virkningen af Forskjellen
mellem begge paa 2000 Favnes Dyb ikke gaar op til mere
end 0°.l, og Kviksølvpiezometret antyder endog en
Correction i modsat Retning af den som ovenfor er antydet.
En anden Control haves i de Bestemmelser af
Indexther-niometrenes Trykcorrectioner, der ere udførte i Dybet
under den atlantiske Strøm, jevnførte med dem, der ere
udførte i Polarstrømmen. I den første aftager
Temperaturen raskere mod Dybet end i den sidste. De nævnte
Bestemmelser ere gjorte med Negretti & Zambra’s
Vendethermometre som Normal, og give, som Resultat for 2000
Favnes Dyb, i Gjennemsnit —0°.31 for den varme Strøm
og —0.°21 for Polarstrønimen. Dette peger i Retning af en
mindre fuldstændig Accomodation i Polarstrønimen end i
Dybet under den varme Strøm, et Forhold, der strider
imod det virkelige, og saaledes kun tjener til at bestyrke
Antagelsen af en fuldstændig Accomodation. Herom se
yderligere nedenfor.
we hauled in the line, whereby the thermometer turned
over, the thread of mercury broke and registered the
temperature, and the shot rolled down to the other end, which
now became the heavier, and thus kept the instrument
from turning over again. For aecomodation, this
thermometer requires a space of 3 minutes; but it is a
necessary condition that during this time the instrument shall
keep perpendicular, with the bulb downwards. Ami such
will not fail to be the case provided the wooden frame
has the necessary buoyancy in the water. This property
the frame is found to have, should it not have been
exposed to any considerable pressure of water. But when
the wooden cases had been lowered to some depth,
for instance more than 200 fathoms, they lost their
buoyancy. Of this I obtained proof by direct experiment.
When one of such wooden cases has to sustain a great
pressure of water, this expels the air in the pores of the
wood, which gives the latter its buoyancy, and the case loses
the property of floating. A frame in this condition will, on
the stoppage of the sounding-line, immediately turn over and
register the temperature of the thermometer. Meanwhile,
whether it be the same as that of the surrounding water,
depends upon circumstances. Provided the temperature in
the depths of the sea do not vary, or vary but very
slowly in the strata passed through by the thermometer
during the last few minutes previous to stopping, the
instrument will be able to register the temperature sought to
be measured. I must remark here, that the accomodation
proceeds quickly on the downward passage of the
thermometer. As new wooden frames could not possibly be
got ready for every deep-sea sounding, our bottom-tempeiy
atures, which ultimately depend on Negretti & Zambra’s
inverting-thermometers and are determined on the
principle here laid down, may therefore, possibly, have been
given a trifle too high. Yet there is, as will be shown
farther on, such excellent agreement between the
determination of the coefficient of pressure for Buchanan’s
mercury-piezometer computed from Negretti & Zambra’s
inverting-thermometers and that given by Buchanan
himself, that the effect of the difference at a depth of 2000
fathoms does not amount to more than 0.°1; and the
mercury-piezometer indicates even a correction of an opposite
character to that suggested above. Another mode of control
lies in the determinations of the index-thermometers’
pressure-corrections — which are made in the deep under the
Atlantic Current — as compared with those made in the
Polar Current. In the former current, the temperature
diminishes more rapidly with the depth than in the latter.
The said determinations are performed with Negretti &
Zambra’s inverting-thermometer as standard, and give an
average result, for a depth of 2000 fathoms, of —0.°31
for the Warm Current and of —0".2l for the Polar Current.
This points towards a less perfect accomodation in the
Polar Current than in the depths beneath the Warm
Current — in direct opposition to fact, which thus
tends to confirm our assuming a perfect accomodation. —
Respecting this subject, see further on.
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