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3
Da alene den sidste Methode tillader Anvendelsen af
nøjagtigere Maaleapparater og derved i Regelen vil kunne
give ulige større Nøjagtighed end den første, blev den
vedtaget til Brug paa vor Expedition.
Vindens Retning ombord observeredes efter Compasset.
Dette, et Admiralitets Standard-Compas, stod paa
Hyttedækket, foran Rattet, ved c, Fig. 2. Staaende i Læ af
Compasset, kunde man, med alle Vindretninger, der ikke
gik over det agtenfor staaende Bestikhus k — hvilket ikke
existerede i 1876 — efter Følelsen af Tindens Virkning
paa Ansigtet bestemme dens Retning og projicere samme
paa Compasrosen med en Nøjagtighed, der svarer til
omtrent en halv Streg eller 5 Grader. Ellers havde man til
Vejledning og til Kontrol saavel Røgen af Skorstenen som
Retningen af en paa Fortoppen hejst Vager, hvis Vinkel
med Diametralplanet let lod sig bestemme og hvis Retning
derigjennem kunde overføres til Compasset. Vageren, der
brugtes i 1877 og 1878, var 1.4 Meter lang. se Fig. 1,
og kunde saaledes observeres med Lethed fra Compasset
af. I 1876 anvendtes ofte en liden Vimpel paa en Stage
paa Forkant af Hyttedækket.
Vindens Hastiglied ombord observeredes med et
Robinsons Anemometer. Iagttageren valgte en Plads paa
Hyttedækket, hvor Instrumentet var mest udsat for Vindens
Virkning. I Regelen var dette paa Forkant af Hytten,
men med Vinden agtenfor tvers stod han paa den luv
Lodde-bro (l Fig. 2). Vindmaaleren holdtes i Haanden, saa højt
som muligt, og med Omdrejningsaxen vertical.
Registreringen af dens Bevægelse varede i Regelen 30 Secunder.
I 1876 brugtes en engelsk Vindmaaler. der i sin Tid
var sendt fra Admiral Fitz Roy til den norske Fyrdirectør.
Den havde 5 Skiver, hver inddelte paa Randen i 10 Dele.
Skiverne drejede sig om horizontale Tapper, som vare
stillede verticalt over hverandre. Armenes Længde, fra
Omdrejningsaxens Centrum til Centrum af Halvkuglerne, var
0.1538 Meter og Halvkuglernes Diameter var 0.1046 Meter.
Ved Observation lod man i Regelen Instrumentet dreje sig
frit rundt af Vinden, noterede, idet Uret viste 0 Secunder,
Aflæsningen af Viseren paa det nederste Hjul, og derpaa
Aflæsningen af samme, naar Uret viste 30 Secunder. Ved
svage Vinde lod man ofte Registreringen vare 1. l’/g eller
2 Minuter. Undertiden, naar Vinden var sterk, stillede
Iagttageren, ved at dreje Korset rundt, Viseren paa
nederste Hjul paa 0. I det Øjeblik, Registreringen begyndte,
løftedes Instrumentet hurtigt op i Vejret, og naar de 30
Secunder vare forløbne, førtes det hurtigt ned igjen og
standsedes, hvorpaa Viserens Stand aflæstes. Undertiden
brugtes et Timeglas i Stedet for Ur.
De Observationer, som gjordes med dette Instrument,
ere beregnede efter den tidligere antagne Regel, at Vindens
Hastighed er 3 Gange saa stor som Halvkuglecentrernes
Hastighed. Efterat det er bleven paavist, navnlig ved de
As the latter method only will admit of using
apparatus for actual measurement, and as a rule, therefore,
gives far superior results to the former, it was exclusively
adopted on the Norwegian Expedition.
The Wind’s Direction on board was observed by the
compass — an Admiralty standard compass, mounted (Fig.
2 c) on the spar deck, immediately in front of the wheel.
Standing to leeward of the compass, from whichever
quarter the wind might blow, provided only it did not come
straight aft over the deck-house h (put up in 1877), the
observer could, by turning his face to the wind, tell the
direction in which it was blowing, and project that direction
on the compass-card with an accuracy corresponding to about
half a point, or five degrees. There was, too, the smoke
from the funnel to act as a guide, and a vane at the
fore-topmast head, the direction of which —. the angle
subtending between it and the fore and aft line of the ship being
easily determined — could be transferred to the compass.
This vane — adopted in 1877 and 1878 — was 1.4 metre
in length (see Fig. 1), and could therefore be easily observed
from the compass. In 1876, a small pennant attached to
the top of a pole on the fore part of the deck of the
roundhouse, was frequently made use of.
The Velocity of the Wind on board was measured with
a Robinson’s anemometer. The observer chose a position
on the deck of the roundhouse in which the instrument
would be most exposed to the wind. This was generally on the
fore part of the deck of the roundhouse; but with the wind abaft
the beam, the observer stood on the windward sounding-bridge
(I, Fig. 2). The anemometer was held in the hand, as high
as possible, with its axis in a vertical position. The
registering of its motion lasted as a rule 30 seconds.
The anemometer used on the first cruise, in 1876,
was an English instrument, sent many years ago by
Admiral Fitz Roy to the Director of Norwegian Lighthouses.
It had five dials, each divided on the limb into ten equal
parts. The dials revolved on horizontal pivots, arranged
vertically one above the other. The length of the arms
from the centre of revolution to the centres of the cups
was 0.1538 metre, and the diameter of the cups 0.1046
metre. When taking an observation, the instrument was
as a rule allowed to revolve freely with the wind, the
indication of the hand of the lowest dial being first read off"
at 0 seconds of the observer’s watch, and then exactly 30
seconds after. In a gentle breeze the registering was
frequently protracted for the space of l1^ or 2 minutes.
Sometimes, when it was blowing hard, the observer would,
by turning round the cross, adjust the hand of the lowest
dial to zero. On commencing the registering, the instrument
was lifted quickly up, and, at the expiration of 30 seconds,
brought quickly down and stopped, after which the
indication of the hand was read off. Now and then an
hourglass was substituted for a watch.
The observations taken with this anemometer have
been computed on the assumption that the velocity of the
wind was three times that of the cup centres. Meanwhile,
this assumption is not admissible, as appears from the in-
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