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45
Der er Tegn til. at de større Vindhastigheder gjøre
ep for liden, og de mindre ep for stor, saaledes som man
kunde vente. Allerede en Vindhastighed af 6m pr. Secund
skulde gjøre ep 0.mm14 for liden, en Vindhastighed, der er
lavere end den gjennemsnitlige i alle 3 Expeditionsaar. Det
synes ikke, herefter at dømme, at Thermometrene have
manglet det nødvendige Luftdrag. Medens saaledes denne
Iagttagelse taler til Gunst for Nøjagtigheden af vore
Lufttemperaturer, faa vore Fugtighedsbestemmelser finde sig i
at være underkastede Virkningen af Psychrometrets
Ufuldkommenhed. Denne Virkning har dog paa Søen vistnok
mindre at betyde, da den relative Fugtighed altid er stor.
De i Observatiohstabellerne givne Værdier af
Vanddampenes Tryk og den relative Fugtighed ere beregnede efter
Psychrometeriagttagelserne ved Hjelp af Jelinek’s Tabeller.
I 1876 og 1877 havde jeg, som allerede nævnt, et
lignende Thermometerhus, som det under Fokkestaget,
opstillet paa Agterdækket lige ved Roret. Da
Thermometrene i dette viste overensstemmende med de forud i alle
Tilfælder med Undtagelse af, naar Vinden var ret forind og
hele Skibets Varme strømmede agterover, bleve
Thermometrene agterud ikke aflæste til de regulære Observationstider,
og i 1878 vare de ikke opstillede.
I 1876 havde jeg opstillet et Thermometerhus med
Psychrometer, af den af Meteorological Office i London
benyttede Model, paa Forkant af Hytten om Bagbord lige
ved den Plads (Fig. 2, y), hvor man tog Vandets
Temperatur. Dette Instrument viste en smuk
Overensstemmelse med det under Fokkestaget hængende, naar det var
i Skygge, men skinnede Solen det mindste paa Kassen,
viste Thermometrene for højt. Da jeg ingen Anledning
havde til at anbringe Skjærme mod Solen, blev Instrumentet
ikke opstillet de følgende Aar.
There are indications to the effect, that with greater
wind-velocities ep is too small, and with smaller wind-velocities
too large, which was indeed to be expected. Even with a
velocity of 6m per second, ep should be 0.mm14 too small — a
velocity lower than the mean for all three cruises of the
Expedition. Hence, judging from this circumstance, the
thermometers would not appear to have lacked the requisite
draught of air. Thus, while this result argues in favour
of the accuracy with which the temperature of the air was
determined, we must, as regards our determinations of
humidity be content to take them subject to the influence
exerted by the imperfection of the psychrometer. This
influence, however, at sea is of minor importance, the relative
humidity being invariably great.
The values given in the Tables for the force of vapour
and relative humidity were computed, according to Jelinek’s
Tables, from the observations taken with the psychrometer.
In 1876 and 1877, I had, as previonsly stated, a
ther-mometer-case similar to that under the fore stay mounted
close to the rudder. The thermometer in the said case
having always indicated the same temperature as those
under the fore stay, save when the wind came right ahead
and the whole heat of the ship was carried aft, they were
not read off at the regular hours of observation, and in
1878 they were not mounted.
In 1876, I set up a thermometer screen with a
psychrometer, the identical model adopted by the
Meteorological Office in London, on the fore bulkhead of the
roundhouse (port side of the vessel), in immediate proximity to
the place (see Fig. 2, y) where the temperature of the
sea-water was taken. This instrument exhibited a
remarkable agreement with that suspended under the fore stay,
when in the shade, but if the sun shone ever so little on
the case, the thermometers indicated too high a temperature.
Being without the necessary means of screening off the sun,
the instrument was not set up the following year.
4. Skyernes Form noteredes paa samme Maade som
ved det meteorologiske Instituts Land-Stationer. (Howards
Betegnelser).
5. Skydækkets Størrelse noteredes efter den
sædvanlige Scala: 0 zz klart, 10 = overskyet.
6. Nedbørens Slags noteredes for hver Time i en
særskilt Rubrik, med specielle Betegnelser for dens Sterke.
Desuden noteredes i Anmerkningsrubrikken Nedbør,
som faldt mellem Observationstiderne.
4. The Form of the Clouds was noted in the same
manner as at the Land Stations of the Meteorological
Institute (Howard’s Nomenclature).
5. The Amount of Cloud was noted according to
the usual scale: 0 = clear, 10 = overcast.
6. The Nature of the Precipitation was noted every
hour, and entered in a separate column, with special symbols
to indicate its force.
Moreover, the nature of the precipitation that fell
between the hours of observation was noted in the column
for General Remarks.
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