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98
Jan Mayen. For 1878 Aars Vedkommende maatte
Grupperingen tildels blive noget forskjellig for de forskjellige
Elementer, idet der i enkelte af de forsøgte Grupper ikke
viste sig Spor af nogen rimelig Periode. De Hensyn, som
ligge til Grund for de valgte Grupper, skulle paa sit Sted
blive forklarede.
. I hver af de valgte Grupper er der kun medtaget
hele Observationsdage, det vil sige saadanne, paa hvilke
der er blevet observeret alle 24 Timer i Døgnet, regnet
fra Midnat til Midnat.
Førend de valgte Gruppers Middeltal for de enkelte
Klokkeslet ere anvendte til Beregningen af Formlerne for
de daglige Perioder, ere de blevne corrigerede for
Virkningen af de uperiodiske Variationer og den aarlige
Forandring samt Stedforandring af Observationspunktet (Skibet).
Da hver Gruppe i Regelen udgjøres af flere mindre, adskilte
fra hinanden ved de Dage, Expeditionen laa i Havn, ere disse
Correctioner beregnede først særskilt for hver af de mindre
sammenhængende Afdelinger, og deres Medium, Hensyn taget
til Dagenes Antal, anbragt ved de større Gruppers Me(Jier.
Med Hensyn til Methodens Anvendelse henvises til H. Wild,
Die Temperaturverhältnisse des Russischen Reiches.1 Erste
Hälfte. Side 9, og til de under hver Gruppe nedenfor
givne Oplysninger.
Som ovenfor i denne Afhandling (Side 40) nævnt,
udførtes de timevise Observationer efter Skibsuret, der stilledes
paa 12 hver Middag sand Tid. Ved Skibets Sejlads
vestover eller østover svarede saaledes Observationstiderne ikke
ganske til sand Tid paa Skibets paaværende Plads.
Afvigelserne, der voxe med Tiden, naaede sin største Værdi
den næste Dags Middag, forudsat, som Tilfældet uden
mange Undtagelser — Se Kartet over Vøringens Route —
var, at i Mellemtiden Længden var alene voxet eller aftaget.
At indføre nogen Correction af de beregnede
Middeltal for Observationsklokkeslettene for at bringe dem i
Overensstemmelse med den sande Tid paa Stedet kunde vistnok
lade sig gjøre ved Interpolation mellem Værdierne for de
enkelte Timer. Men en saadan Fremgangsmaade vilde neppe
lønne Umagen. I ethvert Tilfælde bliver man afhængig af
den Variation, som selve Skibets Stedforandring medfører.
Betragter man de daglige Perioder, som resultere af vore
Beregninger, saa ser man, at det mest fremtrædende Træk
er Amplitudernes Lidenhed. De absolute Værdiers
Variation med Tiden indenfor den daglige Periode bliver
saaledes kun ringe, og en mindre Fejl i Klokkeslettet har liden
eller ingen praktisk Betydning ligeoverfor Observationens
absolute Nøjagtighed. Hertil kommer endvidere, som jeg
nedenfor for hver Gruppe skal vise, at Fejlen i
Klokkeslettet for de enkelte Observationer compenseres næsten
aldeles fuldstændigt ved den Omstændighed, at Summen af
1 Supplementband zum Repertorium für Meteorologie. St.
Petersburg 1877. ,
other those taken within the Greenland Polar current and
during the stay of the Expedition at the Island of Jan
Mayen. As regards 1878, this grouping had to be varied
for the different elements, some of the groups I tried to
form not having exhibited even traces of an admissible
period. The various reasons that affected me in forming
the groups, will be explained in the sequel.
For each of the groups selected, none but whole
"observation days" have been taken, that is to say, such on
which we observed every hour of the four and twenty, from
midnight to midnight.
Before applying the mean values of the groups for
each individual hour to compute the formulæ for the diurnal
periods, they were corrected for the effect of the non-periodic
variation, as also for the annual change and the change in
the place of observation (ship’s position). Each group
comprising as a rule several smaller ones, separated one
from the other by the interval passed by the Expedition
in harbour, these corrections were first computed separately
for each of the smaller continuous sections, and their mean —.
regard being had to the number of days — applied to the
means of the greater groups. With respect to the
application of the method, the reader is referred to H. Wild.
Die Temperaturverhältnisse des Russischen Reiches,1 Erste
Hälfte, p. 9. and likewise to the information given under
each group in the sequel.
As previously stated in this Memoir (p. 46), the hourly
observations were taken by the ship’s clock, which every
day at noon was set to apparent solar time. Hence, with
the vessel steaming westward or eastward, the hours of
observation did not correspond exactly with apparent time on
board. The difference, continually increasing, reached its
maximum the next day at noon, provided, as was actually
the case without many exceptions, — see Plate showing
the track of the Vøringen, — that in the meantime the
longitude had only increased or diminished.
To introduce a correction of the computed means for
the hours of observation, in order to make the latter
correspond with the apparent time of the ship’s position, might
indeed be effected by means of interpolation between the
values for the different hours. But this would hardly be
worth the trouble. In any case, the results would still be
affected by the variation involved in the change of position
of the ship herself. If we regard the diurnal periods resulting
from our computations, the most salient feature is found
to be the smallness of the amplitudes of variation. Hence,
the hourly variation of the absolute values within the diurnal
period will be but trifling, and a slight error in the hour
for the different observations is of little or no practical
importance as compared with the absolute accuracy of the
observations. And moreover, as will be shown below for
each group, the error in the hour of the different
observations is almost wholly compensated by the sum of the
1 Supplementband zum Repertorium fiir Meteorologie. St.
Petersburg 1877.
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