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Disse Formler gjælde strengt taget kun for det Til- 
fælde, at man har retliniede, æquidistante Isobarer og jevn 
Bevegelse. Af Kartet, Pl. XXXI, vil man se, at disse 
Betingelser temmelig nær tilfredsstilles for store Strækninger 
af Nordhavet. Centrifugalkraften, der nærmest skulde 
blive virksom i Østhavet, bliver ringe, da Vindens Hastig- 
hed paa de respective Steder ikke er stor. Da, som senere 
skal vises, Vindens Virkning ikke overalt directe kan over- 
føres paa Havets Bevægelse, bliver den exacte Bestemmelse 
af Vindens Retning og Hastighed af mindre Betydning. 
Jeg har derfor anvendt de ovenstaaende Formler uden 
Modification. 
Gradienten er taget af Isobarerne paa Kartet PI. 
XXXI. Ved Hjelp af Tversnit, lagte lodret paa Isobarerne, 
eller i Gradientens Retning, i hvilke 10 mm i vertical Ret- 
ning forestillede en Lufttrykforskjel af 1mm, og Grund- 
linien havde Kartets Maalestok, bestemtes Beliggenheden af 
Isobaren for hver Tiendedel Millimeter og indtegnedes 1 
Arbejdskartet. Dernæst construeredes paa Millimeterpapir 
en Skala, der med Argument (i horizontal Retning): Af- 
stand paa Kartet gav som Function (i vertical Retning, 
Gradient af 1 mm = Ordinat paa 100 mm.): den tilsva- 
rende Gradient. Da Gradientens Storrelse er omvendt 
proportional med Isobarernes indbyrdes Afstand, havde 
denne Skala Form af en ligesidet Hyperbel. Ved at ud- 
maale paa Kartet Afstanden mellem Isobarerne for en 
Lufttrykforskjel af 1 mm, der svarer til det Punkt, for 
hvilket man vil beregne Vindens Retning og Hastighed 
(10 Gange Afstanden mellem Isobarerne for 0.1 mm), af- 
sætte denne Afstand som Abscisse paa Skalaen, og søge 
Størrelsen af den dertil svarende Ordinat, finder man i 
denne den søgte Størrelse af Gradienten. 
Størrelsen 0, Massen af en Kubikmeter Luft, bestem- 
mes paa følgende Maade. Ved det absolute Lufttryk 
760 mm, O° og Normaltyngden vejer et Kilogram tor Luft? 
1.293052 Kilogram. Sættes Normaltyngden (45° Bredde, 
Havets Overflade) efter Listing til 9.806165 bliver Massen 
af en Kubikmeter Luft under de anforte Forhold 
1.293052 
= == = (ile 
å = gg — SL 
Er det absolute Lufttryk 6 mm, Luftens Temperatur 
£0 C., og indeholder den Vanddamp af e mm Tryk, bliver 
b—0.3779 e 1 a 
mm ico omeerg © 
b-—0.3779 e 
At . 
“ (G sin @ G cos a 
oO oO 
S S 
“= asm — | 
These formule apply in a strict sense only for recti- 
linear, equidistant isobars and a uniform motion. From 
the map, Pl. XX XI, we see that full compliance with such 
conditions is nearly found for extensive tracts of the North 
Ocean. 
exert its chief influence 
Centrifugal force, which might be assumed to 
in the Barents’ Sea, is but 
trifling, the wind having no great velocity in the respective 
localities. But since, as will subsequently appear, the effect 
of the wind cannot be everywhere transferred direct to 
the motion of the sea, the exact determination of the wind’s 
direction and velocity is of less moment. I have therefore 
applied the above-given formule without modification. 
The gradient has been taken from the isobars in the 
map, Pl. XX XI. 
perpendicular to the isobars, or in the direction of the 
By means of transverse sections, laid 
gradient, in which 10 mm. in a vertical direction repre- 
sented a difference in atmospheric pressure of I mm. and in 
which the scale of the base was that of the map, the position 
of the isobar was determined for every tenth of a millimetre 
and marked off in the working-map. I then constructed on 
ruled paper a. scale, which, with argument (horizontal 
direction): distance on map, gave as function (vertical 
direction, gradient of I mm. = ordinate of 100 mm.): the 
corresponding gradient. The magnitude of the gradient being 
inversely proportional to the respective distances between 
the isobars, this scale had the form of an equilateral hyp- 
erbola. By measuring out on the map the distance between 
the isobars for a difference in pressure of I mm., that cor- 
responds to the point for which the direction and velocity 
of the wind has to be computed (10 times the distance 
between the isobars for 0.1 mm.), then setting off this distance 
as an abscissa on the scale and seeking the magnitude of 
the corresponding ordinate, we shall find therein the required 
value of the gradient. 
The quantity 0, or the mass of a cubic metre of air, 
was determined in the following manner. At the absolute 
pressure 760 mm., 0°, and the normal gravity, one kilogramme 
of dry air! weighs 1.293052 kilogramme. Now, if we put 
the normal gravity (lat. 45°, sea-level), according to Lis- 
ting, at 9.89665, the mass of a cubic metre of air under 
the said conditions will be — 
1.293052 
0 = zm = ( 
S 0.806165 
Assuming the absolute pressure at ) mm., the temper- 
ature of the air at #°C., and the latter to contain aqueous 
vapour of e mm. pressure, then 
— 0.047366. a 
273 b—0.3779 e 
760 BIB at HS kG 
1 0. J. Broch. Poids du litre Vair atmosphérique. Travaux et mémoires du comité international des poids et mesures. 
15* 
