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32
Søbarometret alle 3 Expeditionsaar. Naar Fai’tøjet havde
inde hele sin Kul- og Vandbeholdning, var Barometrets
Kapsel 1™ over Hav-Niveauet. Eftersom disse Beholdninger
forbrugtes, løftede Fartøjet sig indtil 0.m5 i Vandet.
Barometerkapselens Højde over Havfladen var saaledes
gjennemsnitlig l.m25, og Barometerhøjdens Reduction til
Havfladen. der i Observationstabellerne er anbragt ved samme,
er sat til + 0."™13.
I 1876 havde Expeditionen paa Rejsen til og fra
Island stadig meget uroligt Vejr. Barometret var under disse
Omstændigheder vanskeligt at observere, da det. navnlig
naar Fartøjet satte, pumpede betydeligt. For at faa en
brugbar Observation, maatte Iagttageren passe paa at
opsøge den højeste og laveste Stand under Pumpningen og
tage Middel af disse. Denne Observationsmethode tog
imidlertid uforholdsmæssig lang Tid. At Observationerne dog
have lykkets, derpaa tyder den regelmæssige Curve for den
daglige Variation, som udkommer for 1876 og navnlig dennes
Lighed med Curverne fra de to følgende Aar.
Efter Expeditionens Tilbagekomst til Bergen i 1876
sammenlignede jeg Søbarometret Adie 1493 med 2
Barometre, hvis Correctioner vare bestemte ved det meteorologiske
Institut i Christiania. For det ene, Rejsebarometret
Ne-gretti & Zambra No. 649, fandtes i Maj 1876 Correctionen
= + O."""^, September 21—30 Correctionen = -f 0.mra12,
Middel Corr. ’ = -f- 0.’"ffl15. For det andet,
Stationsbaro-meter Adie No. 1511, fandtes i Marts 1876 Correctionen
— 0.ram34. Tages Medium af disse 2 Barometre,
corri-gerede med disse Correctioner. som Normal, give
Sammenligningerne i Bergen, der udførtes paa Observatoriet,
følgende Resultat.
1876. Lufttryk (Pressure). Corr. for Adie 1493.
Sept. 4 755-4",m — 0.45"""
,. 5 740.3 — 0.60 Bar. sterkt faldende (Bar. falling rapidly).
•r 7 742.6 —0.45
v 8 744.4 —0.31
Middel (Mean) 745.7 — 0.44 (MF = + o.o8""".)
For the mean, the observation taken on the 5th of
September has been given half weight.
The correction of the marine barometer had
accordingly kept unchanged from the commencement of the cruise
in 1876 to its termination. The comparisons undertaken
in September do not afford particularly forcible indications
that the correction for 740mm should be less than for 755mm.
Readings of the barometer under 750mffl did not occur
frequently in 1876.
I Middelet er Observationen den 5te September givet
halv Vægt.
Søbarometrets Correction har saaledes holdt sig
constant fra Rejsens Begyndelse til dens Ende i 1876.
Sammenligningerne i September vise ikke synderlig sterke Tegn
til, at Correctionen skulde være mindre ved 740""" end ved
755mm. Barometerhøjder under 750""" forekomme ikke
hyppigt i 1876.
(Fig. 4. x) the marine barometer retained on each of the
three cruises of the Expedition. When the vessel had
taken in her full complement of coal and water, the cistern
of the barometer reached lm above the sea-level. As the
said complement diminished, the vessel gradually rose 0.m5
in the water. The height of the cistern of the barometer
above the sea-level was accordingly on an average l.m25.
and the reduction of the observations of the barometer to
the sea-surface is put at + 0.mm13. The observations
given in the Tables include this correction.
In 1876, the Expedition encountered exceedingly
boisterous weather on the whole of the passage to and from
Iceland. Hence the barometer under these circumstances
was difficult to observe, since, in particular when the vessel
pitched, it pumped considerably. In order to obtain a
trustworthy observation, the highest and lowest extremes
reached during the pumping had to be noted as carefully
as possible, and the mean of the two taken. This mode
of observation was, however, necessarily troublesome and
protracted. That the observations notwithstanding proved
successful, may be inferred from the regularity of the curve
resulting for the diurnal variation for 1876, and more
especially from its conformity with the curves constructed
for the two following years.
After the return of the Expedition to Bergen in 1876,
I compared the marine barometer Adie No. 1493 with two
barometers for which the corrections had been determined at
the Meteorological Institute in Christiania. For one of these
instruments, a mountain barometer, Negretti & Zambra. No.
649, the correction in May 1876 was found = 0.mm18,
in September (21—30) = 0.mm12; the mean correction
being = -j- 0.mm15. For the other instrument, a station
barometer. Adie No. 1511, the correction in March 1876
was found = — 0.ram34. Taking the mean of these two
barometers, reduced with the said corrections, the
comparisons in Bergen, made at the Observatory, gave the
following result: —
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