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mserket to diametralt staaende Nulpunkter (Indexer), og
Beslaget h skal vsere saaledes placeret, at naar Pejlskiven
nedsaettes i dette med sine to Tapper ii, saa skal Linjen
.mellem de. to Nulstreger paa det faste Tverstykke g vsere
parallel med Skibets Diametralplan. Om en tyndere Fort-
ssettelse af Tappen a bevaeger sig Diopterlinealen k med
sine Dioptere, og kan faestes i en bvilkensomhelst Vinkel
med g ved Hjaelp af Skruen l.
• Pejlingen foregik altsaa saaledes: En Observator pas-
sede Styringen. og aflaeste nojagti'g anlagt Kurs i Qbserva-
tionsojeblikkot. en anden havde Kronometret og Notice-
bogen, og en tredie stod ved Pejlskiven. Naar Skibet gik
stot, uden Giringer, og Kompasnaalen var i Ro. pejltes
Solen enten direkte eller, naar den var bojere paa Himlen,
ved Hjaelp af Skyggen af den vertikale Traad og Diameter-
stregen paa Linealen k. Naar disse yar uojagtig overet,
raabtes “Nu!” og Kronometrets Visende noteredes; derefter
opgaves anlagt Kurs. der ligeledes jioteredes, og Ringen /
drejedes saaledes, at den samme Kursstreg kom overet med
Nulpuuktet paa g. Inddelingen paa Ringen havde da noj-
agtig samme Stilling til Diametralplanet som Inddelingen
paa Kompasrosen havde i det 0jeblik, da der blev raabt
“Nu”, hvorpaa Pejlingen aflsestes paa Ringen i Aabningen
og ligeud for Diameterstregen paa Linealen 1c, som om den
var aflaest direkfe paa Kompasrosen. Dersom Linealen k
under en forlig eller agterlig Pejling .dsekker Nulstregen.
benyttes de to Hjaelpestreger, der er anbragte etvist Antal
Grader til Siden af den egentlige Nulstreg.
Kronometrets Stand for sand Tid ombord bestemtes
enten efter dets Stand for Greenwich Tid og Skibets be-
.regnede Laengde eller, naar Dagstiden var gunstig, det er
Solen ikke for naer Meridianen, ved at tage nogle Solhojder
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 forskjel-
lige anlagte Kurser svarende Vaerdier for den devierende
Misvisning. Efter den ov-enbeskrevne grafiske Methode be- •
stemtes derpaa Middeltallet af de aekvidstante Yaerdier for.
denne, hvilket antoges som den sande Misvisning.
. De folgende Tabeller indeholder Observationerne og
de deraf udledede Resultater. t = Ivlokkeslettet efter sand .
Soltid, 8 Pejling af Solen, a Solens Azimut.
scfewed 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 g 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 l.
The bearings were taken accordingly as follows: —
One observer looked to the steering, and read off the exact
compass bourse 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 withofit yawing, and with the com-
pass-needle at rest, the bearing of the sun was taken either
direct or, for greater altitudes, by the shadow of the ver-
tical wire and the diameter-line on the cross-piece lc. 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 coin-
cident with the zero-point on the cross-piece g. Hence,
the division-lines on the ring had precisely the same posi-
tion 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 on
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 meridiaft,
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 equi-
distant 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: t signifies apparent time; S,
bearing of sun; a, azimuth of sun.
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