Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
4
Forsøg, som Directøren for det fysiske
Central-Observato-rium i St. Petersburg, Prof. H. Wild, dersteds har ladet
udføre, at denne Regel ikke er gyldig, var det af Vigtighed
at faa bestemt Størrelsen af de Fejl, som den antagne
Forudsætning indførte i Resultaterne. Dette er lykkets, da en
af de i St. Petersburg prøvede Vindmaalere er construeret
nøjagtig efter samme Model som den af os anvendte.1 Ved
den af Dohrandt som "Elektrisk registrerende No. 4"
betegnede Vindmaaler er nemlig opgivet Længden af Armene
r = 0.m1551 og Diameter af Halvkuglerne 0.m1044.
Endvidere er for dette Instrument fundet Forholdet mellem
Vindens og Kuglecentrernes Hastighed at være 2.5293,
istedetfor 3. Vind vejen, der svarer til en Omdrejning af
Verticalaxen, er altsaa 2itr X 2.5293, eller, ved vort
Instrument 2» X 0.1538 X 2.5293, det er 2.m445. Ti
Omdrejninger af Axen eller 1 Delstregsinterval paa nederste
Hjul bliver saaledes 24.ffl45. Den ældre Regel giver 29.m0.
Instrumentets Frictionscoefficient, eller den mindste
Vindhastighed, som er istand til at dreje Instrumentet
rundt, kunde jeg bestemme paa følgende Maade. Den 1ste
Juni 1876, i Sognefjorden, ganske stille Vejr, fandtes den
Distance, Fartøjet havde udløbet i 16 Minuter, efter
ud-merkede Pejlinger og Kartet, at være 3900 Meter. Dette
giver en Hastighed af 3900 : 960 eller 4.062 Meter pr.
Se-cund. I det samme Tidsrum registrerede Vindmaaleren,
frit opstillet som ved Observation, 99.9 Dele af nederste
Skive. Hertil svarer en Vindvej af 99.9 X 24.m45 eller
2442."6, altsaa en Hastighed af 2442.m6 : 960 eller 2.544
Meter pr. Secund. Fartøjets Hastighed gjennem Luften
eller den ombord følte Vindhastighed var altsaa 4.m062 pr.
Secund, medens Vindmaaleren angav kun 2.m544 pr. See.
Dennes Frictionscoefficient er saaledes 4.062—2.544 eller
1.518 Meter pr. Secund, og Vindens Hastighed findes af
Formelen
v - 1.518 + 2.5293 k,
hvor k er Kuglecentrernes Hastighed i Meter pr. Secund.
Er det Antal Delstreger paa nederste Skive, der er
registreret i 30 Secunder, n, bliver den tilsvarende Vindvej
i 30 Secunder 24.45 n og Vindhastigheden 24.45 ~ eller
0.815 n Meter pr. Secund. Formelen for Vindhastigheden
bliver da
v = 1.518 + 0.815 n.
Antages Vindhastigheden lig 3 Gange Kuglecentrernes
Hastighed, faar man Vindvejen for en Omdrejning af
Verticalaxen lig 3 X 2 nr, for 10 Omdrejninger eller 1
Delstregsinterval paa nederste Skive 30 X 2 nr eller 29.ra0.
vestigations of Professor H. Wild, Director of the Central
Physical Observatory of St. Petersburg; and hence it was
obviously of importance to determine the amount of the error which
from that source might enter into the results. In this I
happily succeeded, one of the anemometers tested in St.
Petersburg having been constructed on precisely the same
model as that used on our Expedition.1 The instrument,
termed by Mr. Dohrandt "electrically registering No. 4,"
has the length of the arms r = 0.m1551, and the diameter
of the cups = 0.m1044. Moreover, for this instrument, the
ratio of the velocity of the wind to that of the cup centres
was found to be 2.5293, and not 3, as previously assumed.
The distance run by the wind during one revolution of the
vertical axis of the anemometer, is therefore 2 nr X 2.5293,
or, for our instrument. 2 n X 0.1538 X 2.5293, i.e.
2.m445. Ten revolutions of the axis zz one division of the
first dial = 24.m45. The original rule gives 29.m0.
The friction coefficient of the anemometer, or the
smallest velocity of the wind capable of making the
instrument revolve, was determined by the following experiment.
On the 1st of June, 1876, in the Sogne Fjord, the air
being quite calm, the ship’s distance run in sixteen minutes,
as determined by excellent land bearings and the map, was
3900 metres. This gives a rate of Jjvjp or 4.062 metres
per second. In the same interval the anemometer registered,
freely exposed, 99.9 divisions of the first dial. To this
number corresponds a distance run by the wind of 99.9 X
2442.m6
24.m45, or 2442.m6, — hence a mean rate of , ’ , or
960
2.544 metres per second. The true velocity of the wind as
felt on board was consequently 4.m062 per second, whereas
the anemometer registered only 2.m544 per second. The
friction coefficient of the instrument is accordingly 4.m062
— 2.544, or 1.518 metres per second; and the velocity of
the wind may be expressed by the formula
v = 1.518 •+ 2.5293 k,
in which k is the velocity of the cup centres in metres per
second.
If the number of divisions of the first dial registered
in 3U seconds — n, the corresponding distance run by the wind
in 30 seconds must be 24.45 n, and the velocity of the wind
24.45 or 0.815 n metres per second. Hence, the
formula for the velocity of the wind will be —
v = 1.518 + 0.815 n.
Assuming the velocity of the wind to be three times
that of the cup centres, the distance run by the wind
during one revolution of the vertical axis would be 3 X 2 nr,
and during ten revolutions, or one division of the first dial,
1 F. Dohrandt. Bestimmung der Anemometer-Constanten.
Repcr-orium für Meteorologie. T. IV, No. 5.
1 F. Dohrandt. Bestimmung der Anemometer-Constanten.
Reper-torium für Meteorologie, Vol. IV, No. :">.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
