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vation. Med et almindeligt Lommeur, der slaar 5 Slag
i 2 Secunder, for det venstre Øre, og Yindmaaleren i højre
Haand trykker Iagttageren paa Knappen h og tæller i
samme Øjeblik 0. Naar han har talt 75 Slag af Uret, ere
30 Secunder forløbne, og Knappen slippes. Instrumentet
bringes ind i Bestiklugaren og aflæses.
Med Hensyn til Instrumentets Construction bemerkes
forøvrigt Følgende. Korset, der bærer Halvkuglerne, er
fæstet til Verticalaxen med en Skrue, der ved en Fjeder,
som griber i et Indsnit i denne, er hindret fra at skrue
sig løs. En liden cylindrisk Kappe lige under denne Skrue
drejer sig rundt med Axen og hindrer Regndraaber fra at
komme ned langs Axen. Halvkuglerne ere fæstede til
Armene med sterke Skruer, saa at de ikke let kunne løsne
og blæse bort, og holdes tillige af dem i den rette Stilling
og Afstand. Tæller verket er indesluttet i en Metalkasse,
der paa Forsiden har en Dør med et lidet Vindu, gjennem
hvilket Aflæsningen paa Skiven kan ske, uden at Kassen
behøver at aabnes. Ved at aabne Døren kan man med
Lethed komme til de enkelte Dele af Verket for at rense
eller smøre dein. I Bunden af Kassen er en firkantet
Aabning, netop stor nok til den fornødne Bevægelse af
Armen e f, hvilken herved er reguleret til de bestemte
Grændser til begge Sider. Den øverste Del af Haandtaget
er en hul Metalcylinder, i hvilken den nederste Del af
Armen e f med Knappen h bevæger sig. I denne Cylinder
er Træhaandtaget indskruet og lukker saaledes forneden for
Tællerverket.
Instrumentets Frictionscoejfitient bestemtes, saa ofte
der var Anledning dertil, ved i ganske stille Vejr at lade
Vindmaaleren registrere den ombord følte Vindhastighed,
medens Skibets Hastighed observeredes efter Vandloggen,
som nedenfor skal beskrives. Ved disse Bestemmelser maa
man passe nøje paa, at Luften under Registreringen er
aldeles rolig. Et Kjendetegn herpaa er, at Søens Overflade
ikke viser den mindste Krusning. Men dette Tegn maa
være af nogen Varighed, for at man skal være sikker, thi
de første Vindpust gaa henover Søens Spejl uden synlig
Virkning. Kommer Vindpustene fra Siden, har man et
sikkert Merke deri, at Røgen fra Skorstenen ikke viser
nøjagtig ret agterover.
Iagttagelserne til Bestemmelse af Frictionscoefficienten
vare følgende.
1877.
Datum. I Kvartmil i Timen. Og- Meter ]>r. Secund. Vindmaaler. Meter
Frictions-jir. fecund. Coefficient.
Juni 15 7-7 4.0 2-5 + 1-5
r 30 7-* 3-7 2.1 1.6
n r. 7-3 3-8 2.2 1.6
Juli 15 7.0 3-6 1-7 1-9
Middel...............1.65
Den norske Nordhavsexpedition. H. Mohn: Meteorologi.
taken out on deck and held up ready for observation.
Holding to his left ear an ordinary watch (5 beats in 2
seconds), and having in his right hand the anemometer, the
observer presses the button h, counting as he does so 0.
Having counted 75 beats of the watch, 30 seconds will
have elapsed, and the thumb is removed from the button.
The instrument is then taken into the deck-house and the
reading made.
With regard to the construction of the instrument,
the following additional remarks are appended: — The
crossbars supporting the cups are fixed to the vertical axis by
means of a screw, which a spring, that fits into an incision
in the latter, prevents from screwing itself loose. A small
cylindrical collar, placed immediately beneath this screw,
revolves with the axis, and prevents drops of rain from
trickling down it. The cups are fastened to the arms with
strong screws, to prevent them from loosening and blowing
away, as also to keep them in the right position and at the
right distance. The wheelwork is adjusted in a metal case,
having in front a door with a small window, through which
the reading on the dial can be made without the necessity
of opening the case. On opening the door, the wheelwork
can be easily got at, to be cleaned or oiled when required.
In the bottom of the case there is a rectangular opening, just
sufficiently large to admit of the free motion of the arm
e f, which is accordingly kept on both sides within the
proper limits. The upper part of the handle consists of a
hollow metal cylinder, in which moves the lower part of
the arm e / with the button h. Into this cylinder is
screwed the wooden handle, closing in accordingly the
wheelwork from below.
The friction-coefficient of the anemometer was
determined as frequently as opportunity offered, by registering
in perfectly calm weather the velocity of the wind as felt
on board, the rate of the ship being simultaneously taken
from the water-log, to be described in .the sequel. When
performing these determinations, the greatest care must be
taken to ascertain that the air is quite calm during
registration. A good proof is afforded by not even the faintest
breath of air curling the surface of the sea. But this sign
must be of some duration, to give perfect certainty, since
the first puffs of wind pass over the surface of the sea
without producing the slightest visible effect. When the
puffs of wind are on the beam, the observer has a sure
sign in the smoke from the funnel not passing straight aft.
The observations for determining the friction-coefficient
of the anemometer were as follows: —
1877.
Date. Log. Naut. Miles Metres an Hour, j per Second. Anemc Metres per Second. meter.
Friction-Coefficient.
June 15 7-7 4.0 2-5 + 1.5
* 30 7-2 3-7 2.1 1.6
„ „ 7-3 3-8 2.2 1.6
July 15 7.0 3-6 1-7 1.9
Mean................1.65
2
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