Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
mærket to diametralt staaende Nulpunkter (Indexer), o g
Beslaget h skal være saaledes placeret, at naar Pejlskiven
nedsættes i dette med sine to Tapper i i, saa skal Linjen
mellem de to Nulstreger paa det faste Tverstykke g være
parallel med Skibets Diametralplan. Om en tyndere
Fortsættelse af Tappen a bevæger sig Diopterlinealen k med
sine Dioptere, og kan fæstes i en hvilkensomhelst Vinkel
med g ved Hjælp af Skruen l.
Pejlingen foregik altsaa saaledes: En Observatør
passede Styringen og aflæste nøjagtig anlagt Kurs i
Observa-tionsøjeblikket. en anden havde Kronometret og
Notice-bogen. og en tredie stod ved Pejlskiven. Naar Skibet gik
støt, uden Giringer, og Kompasnaalen var i Ro. pejltes
Solen enten direkte eller, naar den var højere paa Himlen,
ved Hjælp af Skyggen af den vertikale Traad og
Diameterstregen paa Linealen k. Naar clisse var nøjagtig overet,
raabtes "Nu!" og Kronometrets Visende noteredes; derefter
opgaves anlagt Kurs, der ligeledes noteredes, og Ringen /
drejedes saaledes, at den samme Kursstreg kom overet med
Nulpunktet paa g. Inddelingen paa Ringen havde da
nøjagtig samme Stilling til Diametralplanet som Inddelingen
paa Kompasrosen havde i det Øjeblik, da der blev raabt
"Nu", hvorpaa Pejlingen aflæstes paa Ringen i Aabningen
og ligeud for Diameterstregen paa Linealen k, som om den
var aflæst direkte paa Kompasrosen. Dersom Linealen k
under en forlig eller agterlig Pejling dækker Nulstregen,
benyttes de to Hjælpestreger, der er anbragte et vist Antal
Grader til Siden af den egentlige Nulstreg.
Kronometrets Stand for sand Tid ombord bestemtes
enten efter dets Stand for Greenwich Tid og Skibets
beregnede Længde eller, naar Dagstiden var gunstig, det er
Solen ikke for nær Meridianen, ved at tage nogle Solhøjder
og deraf beregne Solens Timevinkel.
Af den saaledes fundne Uhrkorrektion, den efter
Kronometret noterede Tid. Bredden og Solens Deklination
beregnedes Solens Azimut. Forskjellen mellem Solens
sande Azimut og Pejlingen af Solen gav de til de
forskjellige anlagte Kurser svarende Værdier for den devierende
Misvisning. Efter den ovenbeskrevne grafiske Methode
bestemtes derpaa Middeltallet af de ækvidstante Værdier for
denne, hvilket antoges som den sande Misvisning.
De følgende Tabeller indeholder Observationerne og
de deraf udledede Resultater, t = Klokkeslettet efter sand
Soltid, S Pejling af Solen, a Solens Azimut.
screwed a cross-piece, g. marked with two diametrically
opposite zero-points (indices), and the frame h must be so
placed that, on inserting into it the dumb-card with its
two pivots i i, the line between the two zero-points on the
fixed cross-piece q will be parallel to the middle fore and aft line
of the ship. On a thinner continuation of the pivot a
moves-a cross-piece, k, with sight-vanes, which admits of being
fixed at any required angle with g by means of the screw /.
The bearings were taken accordingly as follows: —
One observer looked to the steering, and read off the exact
compass course at the moment of observation, another had
charge of the chronometer and noted the time, and a third
observed the azimuth dumb-card. Now, when the ship kept
steady on her course without yawing, and with the
compass-needle at rest, the bearing of the sun was taken either
direct or, for greater altitudes, by the shadow of the
vertical wire and the diameter-line on the cross-piece k. The
moment the shadow of the thread and the line were exactly
coincident, observer No. 3 called out to his colleague with
the chronometer, who noted and entered the time, after
which the direction of the ship’s head by the compass was
given, and entered in the note-book, the ring f being then
moved in such manner that the division corresponding to
the direction of the ship’s head by compass was made
coincident with the zero-point 011 the cross-piece g. Hence,
the division-lines on the ring had precisely the same
position relative to the midship line as the division-lines on the
compass-card at the moment observer No 3 called out. and
the bearing was then read off through the open space in
the centrepiece k, the extremities of the diameter-line being
the index, exactly as though it had been read off direct
from the compass-card. Should the piece k when taking
a bearing in or near the direction of the fore and aft
midship line cover the zero-point, recourse is in that case
had to the two lines drawn a certain number of degrees
from the true zero-point, one on either side.
The error of the chronometer on apparent time 011
board was found either from its error on Greenwich time
and the ship’s computed longitude, or, at a favourable hour
of the day, i. e. with the sun not too near the meridian,
by taking a few solar altitudes and computing the
hour-angle of the sun.
From the error of the chronometer thus determined,
the observed chronometer-time, the latitude, and the sun’s
declination, was computed the azimuth of the sun. The
difference between the true azimuth and the bearing of the
sun gave the values for deviating variation corresponding
to the different compass courses. By the diagramatic
method described above was found the mean of the
equidistant values for the deviating variation, which we assumed
to be the true declination.
In the following Tables are set forth the observations
and their computed results: † signifies apparent time: S,
bearing of sun; a, azimuth of sun.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
