Forsøg, som Directøren for det fysiske Central-Observato- 
rium'1 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 For- 
udsætning 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. Ved 
den af Dohrandt som “Elektrisk registrerende No. 4” be- 
tegnede Vindmaaler er nemlig opgivet Længden af Armene 
y = 0.71551 og Diameter af Halvkuglerne = 0.71044. 
Endvidere er for dette Instrument fundet Forholdet mellem 
Vindens og Kuglecentrernes Hastighed at vere 2.5293, 
istedetfor 3. Vindvejen, der svarer til en Omdrejning af 
Verticalaxen, er altsaa 2ar 2.5293, eller, ved vort 
Instrument 277 Xx 0.1538 x 2.5293, det er 2.7445. Ti 
Omdrejninger af Axen eller I Delstregsinterval paa nederste 
Hjul bliver saaledes 24.”45. Den ældre Regel giver 29.”0. 
Instrumentets Frictionscoefficient, eller den mindste 
Vindhastighed, som er istand til at dreje Instrumentet 
rundt, kunde jeg bestemme paa følgende Maade. Den Iste 
Juni 1876, i Sognefjorden, ganske stille Vejr, fandtes den 
Distance, Fartøjet havde udløbet i 16 Mmuter, 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."45 eller 
2442.”6, altsaa en Hastighed af 2442.76: 960 eller 2.544 
Meter pr. Secund. Fartgjets Hastighed gjennem Luften 
eller den ombord følte Vindhastighed var altsaa 4.”062 pr. 
Secund, medens Vindmaaleren angav kun 2.”544 pr. Sec. 
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 &, 
hvor k er Kuglecentrernes Hastighed i Meter pr. Secund. 
Er det Antal Delstreger paa nederste Skive, der er 
registreret i 80 Secunder, n, bliver den tilsvarende Vindvej 
i 80 Secunder 24.45 n og Vindhastigheden 24.45 3 eller 
0.815 m Meter pr. Secund. Formelen for Vindhastigheden 
bliver da 
oO = NÆNG ae 0.815 n. 
Antages Vindhastigheden lig 3 Gange Kuglecentrernes 
Hastighed, faar man Vindvejen for en Omdrejning af Ver- 
ticalaxen lig 3 & 2 wr, for 10 Omdrejninger, eller 1 Del- 
stregsinterval paa nederste Skive 30 x 277 eller 29.0. 
? F. Dohrandt. Bestimmung der Anemometer-Constanten. Reper- 
orium fir Meteorologie. T. IV, No. 5. 
 24."45, or 2442."6, — hence a mean rate of - 
vestigations of Professor H. Wild, Director of the Central 
Physical Observatory of St. Petersburg; and hence it was obvi- 
ously 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. Pe- 
tersburg having been constructed on precisely the same 
model as that used on our Expedition." The instrument, 
termed by Mr. Dohrandt “electrically registermg No. 4,” 
has the length of the arms y = 0.71551, and the diameter 
of the cups = 0.71044, 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 ver- 
tical axis of the anemometer, is therefore 27r X 2.5293, 
or, for our instrument, 27 X 0.1588 x 2.5293, 1.e. 
2.”445. Ten revolutions of the axis = one division of the 
first dial = 24.”45, he original rule gives 29.70, 
The friction coefficient of the anemometer, or the 
smallest velocity of the wind capable of making the instru- 
ment revolve, was determined by the following experiment. 
On the Ist 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 
960’ 
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 
, 2442.6 
DEG 
2.544 metres per second. The true velocity of the wind as 
felt on board was consequently 4.7062 per second, whereas 
the anemometer registered only 2.”544 per second. The 
friction coefficient of the instrument is accordingly 4.”062 
— 2.544, or 1.518 metres per second; and the velocity of 
the wind may be expressed by the formula 
3900 metres. This gives a rate of or 4.062 metres 
or 
v = 1.518 + 2.5293 &, 
in which Æ is the velocity of the cup centres in metres per 
second, 
If the number of divisions of the first dial registered 
in 30 seconds = n, the corresponding distance run by the wind 
in 80 seconds must be 24.45 nm, and the velocity of the wind 
x @ 
24.45 30) 
mula for the velocity of the wind will be — 
or 0.815 nm metres per second. Hence, the for- 
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 zr, 
and during ten revolutions, or one division of the first dial, 
1 F. Dohrandt. Bestimmung der Anemometer-Constanten. Reper- 
torium fiir Meteorologie, Vol. IV, No. 5. 
