til 3 mm. paa Skalaen. Naar Instrumentet er i Dybet, vir- 
ker Havvandets Tryk til at sammentrykke Glasset, det 
rene Vand i Røret og Kviksølvet. Ved en vis Temperatur 
vil da Kviksølvtoppen O vise paa højere Tal (mindre 
Temperatur) end 1 Luften, da Vandets Sammentrykkelig- 
hed er den overvejende. For hver 100 Favnes Dybde er 
den heraf flydende positive Temperaturcorrection 09.15 eller 
0.4 mm. paa Skalaen. I Havet, hvor Temperaturen 1 Rege- 
len synker med Dybden, vil saaledes Aflæsningen af In- 
dexens nedre Ende, omgjort til Temperatur og corrigeret 
for Virkningen af Trykket, give den søgte Temperatur i 
Dybet. — Forøvrigt har Hr. Buchanan vist,! at et Kvik- 
sølvpiezometer 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 Kviksolvtoppen 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- 
vandsthermometre, saavel med Hensyn til Antal som God- 
hed, end de foregaaende Aar. Hos Casella anskaffedes 
tre Index-Thermometre, der, efter Hr. Buchanans Model, 
deri vare forskjellige fra de ældre Miller-Casella-Thermo- 
metre, at Graderne paa Minimumsiden vare betydelig læn- 
gere (1° C = 6 mm.) 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 
09.03 til 09.04. Disse tre Thermometre “Casella-Buchanan” 
ere 1 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-Dybvandsthermometer, der registre- 
rer Temperaturen ved at Instrumentet vendes om og som, 
indesluttet i et sterkt Glasrør, er upaavirket af det ydre 
Tryk. En Beskrivelse af Instrumentet, i den Form, 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. 
Å We @ Sb VGB 
A variation in temperature of 1° C corresponds very nearly 
to 5 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 mer- 
cury, O, will point to higher figures (a lower temperature) 
than in the atmosphere, the compressibility of water pre- 
For 100 depth, the 
positive temperature-correction thus amounts to 0915, or 
0.4 mm. on the scale. 
dominating. every fathoms of 
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 cor- 
rected for the influence of pressure, gives the deep-sea 
temperature sought to be determined. For the rest, Mr. 
Buchanan has shown! that a mercury-piezometer of this 
can of tem- 
perature, even should the temperature increase with the 
depth at a 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 
construction give a correct determination 
slow 
will be greater and raise it to higher figures, so that the 
index can 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 
both as regards number and excellence, 
From Mr. Casella had been 
procured three index-thermometers, which, on Mr. Bu- 
chanan’s model, differed from the original Miller-Casella 
thermometers , 
than the two previous years. 
thermometers in the degrees on the minimum-side being 
considerably wider (19°C = 6mm.), 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 of 
reading amounted only from 0°.03 to 0°.04. These three 
*Casella-Buchanan” thermometers will be indicated by the 
figures 46, 48, and 49. 
In the spring of 1878, I had a piece of singular good 
fortune, viz., to become acquainted, from a technical journal 
mean error a single 
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 unin- 
fluenced 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 
eruise in 1878. They will be indicated by the figures 
89 and 91. 
1 Thid. p. 163. o% 
