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Skrue uden Ende drejer Hjulet b, der har 28 Tænder.
Concentrisk med b og fast i dette er Drevet c, der har 8
Tænder. Dette drejer igjen det store Hjul eller Skiven a,
som har 80 Tænder. Følgelig svarer 10 Omdrejninger af
b til 1 Omdrejning af a. 28 Omdrejninger af Yerticalaxen
give en Omdrejning af b. 280 Omdrejninger af
Yerticalaxen give 10 Omdrejninger af & og 1 Omdrejning af a.
Sættes altsaa n — 280, have vi
v = f + 0.08216 X 280 = / + 23.00.
Skiven a er nu inddelt ved radiale Streger paa
Randen i 23 ligestore Dele. og hver Del mellem disse ved
Punkter i Femtedele, saa at Tiendedele med Lethed kunne
aflæses. Dersom Viseren i, der staar fast paa a’s
Omdrej-ningsaxe, viser paa 0 før Registreringen, vil den, efter en
Registreringstid af 30 Secunder, ligefrem angive Værdien
af 0.08216 n eller v—f, eller med andre Ord
Vindhastigheden minus Frictionscoefficienten, udtrykt i Meter pr.
Se-cund. For at faa den sande Vindhastighed, behøver man
følgelig kun at stille Skivefi saaledes, at Viseren staar paa
0, lade Instrumentet, udsat for Vinden, registrere i 30
Secunder, aflæse hvad Viseren peger paa og dertil lægge
Frictionscoefficienten.
Registreringen i et bestemt Tidsrum iverksættes paa
følgende Maade. Hjulene a, b og c dreje sig om faste
Axer, der sidde paa Armen e f. Denne er bevægelig, idet
den ved sin øvre Ende, ved e, kan drejes om en i
Instrumentets Bagvæg fastgjort horizontal Axe, medens dens
nederste Del trækkes stadig tilhøjre (i Retning af Pilen
Fig. 6) af en Metalfjeder g. Naar derfor Instrumentet
ikke registrerer, griber Hjulet b ikke ind i Gjængerne paa
Skruen uden Ende paa Verticalaxen, men denne drejer sig
ganske frit med Halvkuglekorset. Iagttageren tager
Instrumentet i Haanden, som Fig. 5 viser, med Tommelfingeren
paa Knappen h, men uden at trykke paa denne, og løfter
det i Vejret med Axen vertical. Halvkuglerne gaa nu frit
rundt med Vinden-. I det Øjeblik Uret viser 0 Secunder,
trykker han Knappen ind. Armen e f med de tre Hjul
flyttes ind mod Verticalaxen, Tænderne paa Hjulet b gribe
ind i Skruen paa denne, Hjulene b, c, og a sættes i
Bevægelse : Registreringen "begynder. Den fortsættes, idet
Knappen h holdes trykket ind, i 30 Secunder. Naar denne Tid
er forløben, slippes Tommelfingeren løs fra Knappen h,
Fjederen virker og flytter b fra Skruen uden Ende, og
Registreringen standser. . ^
Tandhjulet d har et dobbelt Øjemed. Naar
Registreringen standser, gribe Tænderne paa Hjulet b ind i
Tænderne paa d og dette virker som en Stopper eller Bremse
til at holde Tællerverket fast, saa at Aflæsningen kan
foretages senere og hvorsomhelst. Ved at dreje paa Knappen
s paa Bagsiden af Yderkassen (Fig. 7) drejer man ogsaa
Hjulet d og Iagttageren kan saaledes, uden at aabne
Kassen, dreje Hjulene b, c og a og bringe Viseren til at pege
paa 0.
Som man ser, er Instrumentets Construction saadan,
at det med Lethed kan bruges ogsaa om Natten. Med
Knappen s stilles, f. Ex. inde i Bestiklugaren, Viseren paa
0. Instrumentet tages ud og holdes op færdigt til Obser-
axis turns the wheel b, which has 28 teeth. Concentric
with & is a cogwheel c. with 8 teeth, which turns the large
wheel or disk a, furnished with 80 teeth. Consequently.
10 revolutions of b Correspond to one revolution of a; 28
revolutions of the vertical axis correspond to one revolution
of b, 280 revolutions of the vertical axis Jo 10 revolutions
of-6 and one revolution of a. Hence, putting n — 280,
we have
v = f -f 0.08216 X 280 = J + 23.00.
The dial a is accordingly divided by radial lines on
its limb into 23 equal parts, and each part by dots into
fifths, so that tenths can easily be read off. If the hand,
or index, i, which is fixed to the axis of a, points to zero
before registration, it will, after an interval of 30 seconds,
indicate the value 0.08216 n, or v—f, that is the
velocity of the wind minus the friction coefficient, expressed in
metres per second. In order to get the true velocity of
the wind, we have, therefore, only to place the dial so that
the index points to zero; let the instrument, exposed to
the wind, register for 30 seconds; and then read off the
indication of the hand, adding to this number the value
of the friction coefficient.
The registration in a definite interval of time is
per-formed as follows. The wheels a, b, and c have their axles
fixed to the arm e f. This arm is moveable, turning as it
does at the upper end. at e, about a pivot in the hind
part of the instrument, whereas its lower end is constantly
drawn to the right (in the direction of the arrow, Fig. 6)
by the metallic springy. When, therefore, the instrument
is not registering, the teeth of the wheel b do not bite in
the endless screw on the vertical axis; both are quite free
and revolve with the cups. The observer takes the
instrument by the handle, with his thumb resting lightly on the
button h (as shown in Fig. 5), and then raises the
instrument, with its axis in a vertical position. The cups now
revolve freely with the wind. At 0 seconds by the
observer’s watch, he presses the button inwards, the arm e f with
the three wheels is moved towards the vertical axis, the
teeth of the wheel b bite in the endless screw, b, c, and a
are put in motion, and the registration begins. It is
continued for 30 seconds, the button h being kept pressed in.
After the expiration of this interval, the observer removes
his thumb from the button h, the spring acts, removes b
from the endless screw, and the registration stops.
The toothed wheel d serves two purposes. On
stopping registration, the teeth of the wheel b bite into the
teeth of the wheel d, which acts as a stopper or break,
and keeps the wheelwork steady, so that the reading of
the dial may be made at any time or place afterwards.
On turning the button s at the back of the outer case
(Fig. 7), the wheel d is also turned with it, and the
observer can thus, without opening the case, turn the wheels b,
c, and a, and adjust the index to zero.
As will be seen, the construction of the instrument
is such as to admit of its being used with facility at night.
By means of the button s, for example, the index is
adjusted in the Deck-house to zero. The instrument is then
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