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21
2den Differents af Rækken, hvilken, fraregnet de
uundgaae-lige mindre Variationer i Udlobshastigheden, viste sig at
være paa det nærmeste constant. Med denne anden
Differents beregnedes Størrelsen af Tidsintervallet for Udløbet
af det sidste observerede Hundredefavnemærke til det næste
Mærke, inden hvilket 100 Favne-Interval altsaa Loddet
kom i Bund. Ved Hjælp af dette Tal og den mellem
Ud-løbsøjeblikket for det sidst observerede Hundrefavnemærke
og Øjeblikket for „Bund" forløbne Tid beregnedes ved
simpel Proportion, hvor mange Favne der vare udløbne mellem
de tilsvarende Øjeblikke. Denne Længde, tillagt Xurneret
for sidste observerede Mærke, bliver Lodskuddet eller Dybden.
Som Exempel anføres her et Uddrag af
Locldejour-nalen, der tillige viser dennes Indretning.
was calculated from the first, and the figures thus obtained,
if we except all minor variations in velocity, proved very
nearly constant. From the second difference was
computed the interval that would have elapsed, had the depth
been sufficient, ere the slip of bunting next in succession
to that last run off could have entered the water, and
within which the lead had accordingly reached the bottom.
Then, with the figure thus found and that denoting the
time between the moment when the last slip of bunting
reached the water and that at which the lead struck the
bottom, was computed, by simple proportion, the odd
number of fathoms, which, added to the length on the slip last
run off the reel, gave the true sounding, or depth.
The following is an extract from the
sounding-journal, showing its mode of arrangement.
Date 1877 June, 20th.
Lat. . . . 67° 40’5 N.
Long.. . . 6° 42’ E.
Temp, of Air 5° 9
Do. of Sea 6° 8
Depth . . 709 Fathoms.
Bottom . . Brown Clay.
Character . Good.
No. 129.
Klokkeslet . . 4A 30m p. m.
Vind.... NE.
Styrke ... 3
Vejr .... Skyet.
Sø .... NE. 4
Vægt . . . 112 Pd.
Dato 1877 Juni 20
Bredde . 67° 40’.5 N.
Længde . 6° 42’ E. Greenw.
Lufttemperatur 5°.9
Overflade do. 6.8
Dybde . . . 709 e Fv.
Bund . . . Brun Ler
Karakter . . Godt.
Favne. Tid. Interval. _,dc" Diff.
T. M. S. M. S. See.
Lad gaa 4 46 30
100 47 .41 x 2
200 48 51 1 30 17
300 50 24 ’ 12
400 52 6 1 13
1 oo
oOO o4 1 9 3 8
600 56 4 2 q 6
700 58 13 a
1-0 lo
Bund 58 28
No. 129.
Time .... 4.30 p. m.
"Wind . . . . NE.
Force .... 3
Weather . . . Cloudy
Sea .... NE. 4
Weight . . .112 pounds
Fathoms. Time. Interval. 2nd Diff.
h. m. s. m- s- s-
0 4 46 30 _
100 4 47 41
200 4 48 54 ^ 2
300 4 50 24 J ^ 17
400 4 52 (5 .. 12
500 4 54 1 2 °3 13
600 4 56 4 9 g 8
700 4 58 13 " 6
Bottom. 4 58 28 °
For Intervallet 700 til 800 Favne beregnes
Udlobs-tiden til 2" 9’ + 6’ = 2" 15’ = 135’. Altsaa faaes
Proportionen :
135’: 100 Favne = 15’: 11 Favne.
Efter dette skulde Dybden være 711 Favne. Ved
Udmaa-ling af det Stykke af Lodliuen, der var i Vandet i det
Øieblik. Loddet slog i Bund, over 700 Favne, efter den
nedenfor beskrevne Methode, fandtes 9 Favne, altsaa
Dybden 709 Favne, som opført i Loddejournalen.
Nøjagtigheden af Tidsintervalmethoclen beror, som man
ser. ganske paa den Grad af Jevnhed i Bevægelsen, som
kan tilvejebringes ved Bremsningen. Resultatet tiltrænger
derfor en Kontrol ved andre Methoder, saaledes som det
stadig blev gjort paa vor Expedition. Ved at sammenligne
Resultaterne af de forskjellige Methoder viser det sig, at
Tidsintervalmethoden næsten altid giver for store Tal.
Now, the interval from 700 to 800 fathoms is found
to be 2in 9s 6s = 2m los = 135s; and hence
135s : 100 fathoms : : 15s : 11 fathoms.
This would make the depth 711 fathoms. Measuring by
the method described below the part of the line which, in
addition to the 700 fathoms, had run out when the lead
struck the bottom, we get 9 fathoms, and thus a depth of
709 fathoms, the depth entered in the sounding-journal.
As regards the accuracy of the method of
computation by time-intervals, it is obvious that this must be
wholly dependent upon the degree of uniformity attainable
in braking. The results will have in each case to be tested
by some other method; and this was invariably done on
the Norwegian Expedition. On comparing together the
results of the different methods, the figures obtained
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