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trykket for det absolute Lufttryk, eller N (1 —0.002Ö9 eos 2 y), hvor
f er Observationsstedets Bredde. Med andre Ord, den normale
Barometerhøjde (den til 0° og Normalbarometret reducerede
Kviksølvhøjde) skulde, for at bringes i Overensstemmelse med
Aneroidbarometrets Angivelser, corrigeres med den af Observationsstedets Bredde
afhængige Tyngdecorrection, — N X 0.002f>9 eos 2 y, en Størrelse,
der paa vore Bredder altid er positiv og voxer med Bredden.
Undladelsen af at tage det nævnte Hensyn har imidlertid ikke medført
nogen Fejl af praktisk Betydning i Reductionen af Expeditionens
Barometerhøjder, da de udførte Sammenligninger mellem begge
Instrumenter ere blevne behandlede i Grupper, indenfor hvilke
Obser-vation8stedernes Bredde ikke varierer inden vide Grænser. I 1877
var den midlere Bredde af de Steder, hvor Sammenligningerne
mellem Kviksølv- og Aneroidbarometret foretoges, (18.° 1. Den
gjennemsnitlige Forskjel mellem Tyngdecorrectionen ved en enkelt
Sammenligning og ved denne Bredde er, uden Hensyn til Fortegn, 0.mm0(i6
og den største forekommende Forskjel er —O. """21 (04° Bredde) og
+ 0.""13 (paa 71° Bredde, ved Jan Mayen). I 1878 ere de
tilsvarende Tal for Aneroidbarometer A : 73.°6, ± 0.«"05ß, — 0."""l2 (70.°6)
og + 0.mra14 (77.°9), og for Aneroidbarometer B: 78.°4, ±0."•"•027,
— 0.nmll (74.°6) og + 0."»"04 (80.°0). Det vil sees, at disse Værdier
for Middelafvigelsen gruppere sig i samme Orden som de ovenfor
fundne Værdier af den sandsynlige Fejl af en enkelt Sammenligning
mellem Aneroid- og Kviksølvbarometer (0.17, 0.14 og 0.11). Det er
derfor sandsynligt, at de sidste vilde kunne formindskes noget ved
Indførelsen af Tyngdecorrectionen. Ved Rejser, hvor Barometrene
sammenlignes under forskjellige Bredder, bør, naar der er
Spørgsmaal om en større Nøjagtighed, altid Tyngdecorrectionen tages med
i Beregningen, en Fremgangsmaade, der overhovedet anbefaler sig
ved sin rationelle Begrundelse, og som det er at haabe vil vinde
gjennemgaaende Indgang i den meteorologiske Praxis.
barometer, should be substituted the expression for absolute pressure,
or N (1 — 0.00259 eos 2 y>), in which f signifies the latitude of the
place of observation. In other words, the normal height of the
barometer (the height of the mercury, reduced to 0° and to the standard
barometer) should, to make it correspond with the indications of the
Aneroid, be corrected with the gravity correction (— N X 0.00259 eos 2 <p),
which is dependent on the latitude of the place of observation, and
which, in our latitudes, is always positive and increases with the
latitude. Meanwhile, this omission has not given rise to any error
of practical importance in the reduction of the readings of the
barometer noted on the Expedition, since the comparisons between both
instruments have been treated in groups, within which the latitude
of the places of observation does not vary to any considerable extent.
In 1877, the mean latitude of the localities in which I made the
comparisons between the mercury and the Aneroid barometers, was
68.°1. The average difference between the gravity corrections for a
single comparison and for the said latitude, is, without regard to sign,
+ 0."""0()(i, and the greatest differences that occurred are — 0."""21
(64° N. lat.) and +0.""»13 (71° N. lat., ofl’ the Island of Jan Mayen).
In 1878, the corresponding figures for the Aneroid barometer A are
as follows: 73.°(i, ± 0.mm0r>6, — 0.ram12 (70.°6), and + 0."""14 (77.°9),
and for the Aneroid barometer B, 78-°4, ± 0.Mm027, — 0."""11 (74.°6)
and 0.mm04 (80.°0). It will be seen that these values for the mean
deviation are ranged in the same order as the values, given above,
of the probable error of a single comparison between the Aneroid
and the mercury barometer (0.17, 0.14, and 0.11). Hence, it is
probable that the latter might be somewhat diminished by introducing the
correction for gravity. On voyages during which the barometers are
compared in different latitudes, the correction for gravity should, when
greater accuracy is desirable, be taken into account, a mode of
procedure manifestly the most rational, and which, it is to be hoped,
will in future be generally adopted in meteorological practice.
3. Luftens Temperatur og Fugtighed.
Ombord i et mindre Dampskib er det ingen let Sag
at finde en passende Plads for et Thermometer, der skal
angive den rigtige Lufttemperatur. Den første Dag, vi
vare under Damp, den 1ste Juni 1876, paa Vejen fra
Bergen til Sognefjorden, en klar Solskinsdag, gik jeg med
et Slyngethermometer rundt Skibets Dæk for at prøve alle
mulige Steder som Plads for Thermometrene. Resultatet
blev den følgende Ordning, der viste sig meget
tilfredsstillende.
Begge Thermometre, det tørre og det vaade,
opstilledes i et Hus af bronzeret Kobberblik, paa lignende Maade
som ved det norske meteorologiske Instituts Stationer.
Kobberhuset (Fig. 10) var 57 Cm. højt, 22 Cm. bredt og 15
Cm. dybt. Det havde pyramideformet Tag med Skorsten,
Jalousier over hele Bagvæggen, over hele Døren (der vises
lukket op i Figuren) og nedentil, i Højde med
Thermo-metrenes Kugler, paa begge Siderne og paa Forsiden samt i
Bunden. Thermometrene stode meget frit inde i dette Hus,
idet de oventil gik gjennem Huller i en Tverbjelke af Træ,
og nedentil hvilede i Bøjler af tyk Messingtraad, der vare
indskruede i den midt efter Huset staaende verticale
Træ-bjelke. I den nederste Del af Huset hang ved den Væg,
der var nærmest det vaade Thermometer, en Kop med Vand,
hvorfra en Væge sugede Vand til det vaade Thermometer.
3. Temperature and Humidity of the Air.
On board a comparatively small steamer, it is no easy
matter to find a good place for mounting a thermometer
that has to indicate the true temperature of the air. The
first day we were under steam, June 1st 1876, on our
passage from Bergen to the Sognefjord, in bright sunshiny
weather, I made the tour of the ship’s deck with a sling
thermometer, to try every available place in which the
thermometers might be mounted. The result was the following
arrangement, which proved in every respect satisfactory.
Both thermometers, the dry and the wet, were set
up in a bronzed copper case, in the manner adopted at
the Stations of the Norwegian Meteorological Institute.
The copper case (Fig. 10) was 57cm high, 22cm broad, and
15cm deep. It had a pyramidical - shaped roof, provided
with a funnel, louvres across the whole of the hind wall,
across the door (open in the figure), and below, on a level
with the bulbs of the thermometers, on both sides, and
in front, as also at the bottom. Within this case the
thermometers had an exceedingly free position, passing as they
did, above, through holes in a cross-piece of wood, and
being supported below in rings of thick brass wire, screwed
into the vertical cross-piece stretching through the middle
of the case. In the lower part of the case, suspended near
the wall nearest to the wet thermometer, hung a cup filled
with watar, from which a wick sucked up the fluid to the
wet thermometer.
Den norske Nordhavsexpedition. H. Mohn: Meteorologi.
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