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til 3 mm. paa Skalaen. Naar Instrumentet er i Dybet,
virker Havvandets Tryk til at sammentrykke Glasset, det
rene Vand i Röret og Kviksølvet. Ved en vis Temperatur
vil da Kviksølvtoppen C vise paa højere Tal (mindre
Temperatur) end i Luften, da Vandets
Sammentrykkelighed er den overvejende. For hver 100 Favnes Dybde er
den heraf flydende positive Temperaturcorreetion 0°.15 eller
0.4 mm. paa Skalaen. I Havet, hvor Temperaturen i
Regelen synker med Dybden, vil saaledes Aflæsningen af
In-dexens nedre Ende, omgjort til Temperatur og corrigeret
for Virkningen af Trykket, give den søgtt Temperatur i
Dybet. Forøvrigt har Hr. Buchanan vist,1 at et
Kvik-søl vpiezometer af denne Art kan give en rigtig
Tempera-turbestemmelse, selv naar Temperaturen stiger svagt med
Dybden. En Temperaturtilvæxt med Dybden af mindre
end 0°.15 pr. 100 Favne vil paa vort Instrument, som
man ser, bringe Kviksølvtoppen C til at vise paa lavere
Tal, men Virkningen af Trykket vil være sterkere til at
bringe den paa højere Tal, saaat Indexen vil kunne skydes
opad og registrere Toppens Stand. Instrumentets
Tryk-Correction var mig opgivet af Hr. Buchanan. Den blev
i 1878 bestemt af mig paa Expeditionen, som nedenfor
nærmere omtalt.
I 1878 var jeg betydelig bedre udrustet med
Dyb-vandstherinometre, saavel med Hensyn til Antal som
Godhed, end de foregaaende Aar. Hos Casella anskaffedes
tre Index-Tliermometre, der, efter Hr. Buchanans Model,
deri vare forskjellige fra de ældre*
Miller-Casclla-Thermo-metre, at Graderne paa Minimumsiden vare betydelig
længere (1° C = 0 111111.) og at der paa selve
Thermometer-røret var indætset en Millimeterskala, der benyttedes til
den egentlige Aflæsning, medens Gradskalaen ved Siden af
Røret tjente til Control. Værdien af Millimeterskalaens
Delstreger bestemtes ved Sammenligning med
Normalther-mometret. Middelfejlen af en enkelt Aflæsning var kun
0°.03 til 0°.04. Disse tre Thermometre "Casella-Buchanan"
ere i det Følgende betegnede ved Tallene 46, 48 og 49.
Et. stort Held var det, at jeg Vaaren 1878 gjennem
en technisk Journal, som en for vor Expedition varmt
interesseret Ven viste mig, blev bekjendt med Negretti &
Zambra’s nye Kviksølv-Dybvandsthernioineter, der
registrerer Temperaturen ved at Instrumentet vendes om og som,
indesluttet i et sterkt Glasrør, er u paa vir kot af det ydre
Tryk. En Beskrivelse af Instrumentet, i den Fonn, hvori vi
brugte det (med Trækasse) findes i "Nature" for 25. Juli
1878. Af dette Instrument anvendtes to Stykker stadig i
1878. De ere i det Følgende betegnede ved Tallene 89
og 91.
A variation in temperature of 1° C corresponds very nearly
to 3 mm. on the scale. When lowered in the deep, the
pressure of the sea-water acts on the instrument so as to
compress alike the glass, the pure water in the tube, and the
mercury. At a given temperature, the top of the
mercury, C, will point to higher figures (a lower temperature)
than in the atmosphere, the compressibility of water
lire-dominating. For every 100 fathoms of depth, the
positive temperature-correction thus amounts to 0". 15, or
0.4 liim. on the scale. In the sea, where the temperature,
as a rule, decreases with the depth, the reading of the
lower end of the index, converted to temperature and
corrected for the influence of pressure, gives the deep-sea
temperature sought to be determined. For the rest, Mr.
Buchanan lias shown1 that a mercury-piezometer of this
construction can give a correct determination of
temperature, even should the temperature increase with the
depth at a slow rate. An increase of the temperature
with depth of less than 0°.15 per 100 fathoms, will, as
appears, with our instrument cause the top of the mercury,
C, to indicate lower figures; but the effect of the pressure
will be greater and raise it to higher figures, so that the
index cail be pushed up and register the height of the
mercury. The pressure-correction of the instrument was
given me by Mr. Buchanan. In 1878, I determined it
myself on the Expedition, as stated more in detail below.
In 1878, I was much better provided with deep-sea
thermometers, both as regards number and excellence,
than the two previous years. From Mr. Casella had been
procured three index-thermometers, which, on Mr.
Buchanan’s model, differed from the original Miller-Casella
thermometers in the degrees on the minimum-side being
considerably wider (1° C — 6111111.), and also in having on
the tube of the thermometer itself a millimetre-scale etched
in, which was used for the final reading-off, whereas
the scale of degrees, at the side of the tube, served
the purpose of control. The value of the
millimetre-scale’s divisions was determined by comparison with the
Standard-Thermometer. The mean error of a single
reading amounted only from 0°.03 to 0°.04. These three
"Casella-Buchanan" thermometers will be indicated by the
figures 46, 48, and 49.
I11 the spring of 1878, I had a piece of singular good
fortune, viz., to become acquainted, from a technical journal
shown me by a friend who interested himself warmly in
the Norwegian Expedition, with Negretti and Zambra’s
new mercury deep-sea thermometer, which registers the
temperature by the instrument turning over, and which,
enclosed within a strong glass tube, remains wholly
uninfluenced by the outer’ pressure. A description of the
instrument having the form in which we used it (with a
wooden frame), will be found in "Nature" for 25 July 1878.
Two of these instruments were in constant use during the
cruise in 1878. They will be indicated by the figures
89 and 91.
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