den for den Norske Nordhavs-Expedition vedtagne Plan 
var indtaget meteorologiske Iagttagelser paa Havet, 
omfattende Vindens Retning, Styrke og Hastighed, Luftens 
Tryk, Temperatur og Fugtighed, Skyernes Art og Mængde, 
Nedbørens Art og Mængde, Søgangens Retning og Styrke, 
Havoverfladens Temperatur, og andre lejlighedsvis forekom- 
mende Fænomener. Iagttagelserne, udførte hver Time gjen- - 
nem hele Døgnet, antoges at kunne tjene dels til Bestem- 
melse af de meteorologiske Elementers daglige Periode i 
Sommermaanederne paa et hidtil i denne Henseende ikke 
udforsket Strøg af Verdenshavet, dels til Oplysning om 
Vejrforholdene sammesteds, naynlig ved Indførelse i synop- 
tiske Karter. Forsøgsvis skulde anstilles Iagttagelser over 
Havvandets Fordunstning. 
De meteorologiske Iagttagelser paa Expeditionen bleve 
ken) te) ke) 
organiserede af mig, og som Deltager i samme paa alle 
dens Togter havde jeg dagligt Tilsyn med deres Udførelse. 
I denne Afhandling skal jeg først beskrive de an- 
vendte Instrumenter og deres Brug samt Ilagttagelsernes 
Reduction, for hvert af de meteorologiske Elementer sær- 
skilt. Dernæst skal jeg give, i Tabelform, de reducerede 
Tagttagelser, og til Slutning de Resultater, der ere udledede 
af disse. Som Tillæg skal jeg meddele mine Iagttagelser 
over Havvandets Fordunstning. 
I. Vind. 
Ombord i et Skib, der er i Fart, og navnlig paa et 
Dampskib, foles Vinden i en Retning og af en Hastighed, 
der i Regelen begge ere forskjellige fra den virkelige Retning 
og Hastighed af Vinden. For at kunne finde den sande 
Vindretning og Vindhastighed maa man derfor enten directe 
observere Vindens Virkning paa Søens Overflade, eller man 
maa ved Observation bestemme Vindens Retning og Hastig- 
hed, saaledes som den fornemmes ombord, og ved Bereg- 
ning, idet man tillige har iagttaget Skibets Retning og 
Hastighed, af disse Data søge at komme til Resultatet. 
Den norske Nordhavsexpedition. H. Mohn: Meteorologi. 
he Scheme of Work for the Norwegian North-Atlantic 
Expedition included Meteorological Observations at 
Sea, comprising the direction, force, and velocity of the 
wind, the pressure, temperature, and humidity of the atmo- 
sphere, the form and amount of cloud, the nature and 
amount of the precipitation, the direction and state of the 
sea, the temperature of the sea-surface, and phenomena of 
occasional occurrence. Such observations, taken every hour 
of the twenty-four, would serve, it was believed, partly to 
determine the diurnal period of the meteorological elements 
during the summer months throughout a tract of ocean till 
then unexplored, and partly to elucidate questions bearing 
on the weather in that region of the North-Atlantic, the 
results being inserted in synoptical charts. Moreover, ex- 
periments were to be made on the evaporation of sea- 
water. 
The meteorological work was planned and organized 
by myself; and haying accompanied the Expedition as a 
member on each of its three cruises, I had daily oppor- 
tunity of superintending the observations. 
In this Memoir, I shall first describe the instruments 
employed and the mode of using them, as also the reduc- 
tion of the observations, — separately for each of the 
meteorological elements; I shall then tabulate the reduced 
values, and finally set forth the results deduced therefrom. 
An Appendix will contain my observations on the evapora- 
tion of sea-water. 
I. Wind. 
The direction and velocity of the wind as felt on 
board a ship in motion, more particularly a steamer, are 
as a rule both found to differ from the true direction and 
velocity. In order, therefore, to find the true direction 
and velocity of the wind, we must either observe the effect 
of the latter on the surface of the sea, or determine its 
direction and velocity as felt on board, and then, the direc- 
tion and rate of the vessel having been observed, compute 
the true result. 
