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20
er af Vigtighed for Nøjagtigheden af den følgende
Beregning af Dybden. Det Stykke af Lodlinen, der er mellem
Rullen og Fodblokken, maa altid have en passende
Stramning, saaat Linen ikke under Bevægelsen slaar Bugter, der
kunde bringe deif til at kaste sig 0111 en eller anden
frenestaaende Gjenstand og derved foraarsage Havarier eller en
pludselig Standsning af Lodlinens Bevægelse. Denne
Bremsning fordrer derfor baade Opmerksomhed. Kraft og Øvelse.
I 1877 forsøgte jeg en mekanisk Bremse paa Rullen,
men den viste sig upraktisk og anvendtes kun nogle Gange.
Naar Skibet løfter sig paa Søen, rives Linen af Rullen
med stor Kraft, og naar det atter sænker sig. formindskes
Loddets Drag, ja ophæves undertiden næsten for et
Øjeblik. Disse uafladelige Forandringer føles strax, naar man
bremser med Haand, og med nogen Øvelse vænner man sig
til at bremse netop det nødvendige, men med den
mekaniske Bremse viste det sig ugjørligt at følge Forandringerne,
der ikke føltes gjennem Apparatet.
Ved Dybder, der ikke oversteg 900 til 1000 Favne,
mærkedes bedst, at Loddet slog i Bund, derved, at man
lod Linen løbe ganske lost gjennem Haanden, og man følte
da en pludselig Aftagen i Udløbshastigheden. Man kunde
ogsaa tydelig se det derved, at Linen mellem Fodblokken
og Rullen lagde sig pludselig flad ned paa Dækket.
Saasnart over 700 Favne var ude, var den Bremsning, der
udfordredes for at holde Linen stram, kun ringe. 1 nogle
faa Tilfælder, i hvilke der blev loddet paa 1100 til 1200
Favne meel Rørlod alene, viste det sig, at det ikke var
muligt at iagttage det Øjeblik, da Loddet kom i Bund.
Linen vedblev at løbe ud paa Grund af sin egen Vægt
med en Hastighed, der ikke var synligt forskjellig fra den
Hastighed, hvormed den løb med Loddet som Tillægsvægt.
Under saadanne Omstændigheder loddedes om igjen med
Baillie-Maskine, dersom det ansaaes fornødent at faa et
nøjagtigt Lodskud. Med Rørlod og Wilies Vandhenter
sammen "kunde der faaes gode Lodskud paa over 1100 Favne,
som et Forsøg paa Station 247 viste. Her gav nemlig
Baillie-Maskinen 1120 Favne, medens Rørlod med
Vand-henter gav 1124 Favne.
Bestemmelse af Dybden. Da Lodlinen for de større
Dyb kun var mærket for hver 100 Favne, maatte det
nøjagtige Favnetal søges ved særegne Observationer og
Beregninger. Den fra først af brugte Fremgangsmaade var
følgende. I det Øjeblik, Loddet gik i Vandet, og naar et
Hundrede-Favne-Mærke gik i Vandet, raabtes „Nu" og
Klokkeslettet noteredes i Loddejournalen paa nærmeste
Sekund. Forat give Noteringerne større Sikkerhed,
varskoedes af Folkene ved Rullen altid i Forvejen „Mærke",
naar et af Mærkerne gik af Rullen. I det Øjeblik Loddet
var i Bund, raabtes „Bund" og det tilsvarende Klokkeslet
noteredes. Af Rækken af de under hverandre noterede
Klokkeslet toges første Differents. Disse Tal stige med
Dybden, idet Udløbshastigheden aftager med Længden af
den gjennem Vandet løbende Lodline. Dernæst beregnedes
presented in Fig. 14. The two men with leather gloves
endeavoured, by pressing upon the reel, to keep the motion
as uniform as possible, this being an essential condition
for accurately computing the depth. When veering, the
line between the reel and the leading-block must be kept
sufficiently taut, to prevent its running out in bights,
that might catch on some projecting object, and thus
occasion damage, or possibly a sudden stoppage of the
line. Hence, skilful braking requires care, practice, and
physical strength. In 1877 I tried a mechanical brake; it
proved, however, inefficient, and was used only a few times.
When the vessel heaves, the line is run off the reel with
great violence, and on her plunging into the trough of a
sea, the drag of the lead becomes greatly diminished, nay,
for a moment may be taken off altogether. These constant
alternations are instantly felt when the braking is done by
hand; and with some little practice, the brakesmen can
calculate to a nicety the needful amount of pressure,
whereas with the mechanical brake we found it impossible to
follow the changes, which could not be felt through the
machine.
In depths not exeeding 900 or 1000 fathoms, the best
way of determining the exact moment when the lead struck
the bottom, was to let the line run loosely through the
hand, when a sudden disminisliment of velocity would be felt.
Nay, it could be distinctly seen, the line between the
leading-block and the reel becoming all at once slack and
dropping down on the deck. Having veered to a depth
of 700 fathoms, there was no great need of braking to keep
the line taut on the remainder of the downward journey.
In some few instances, when sounding in from 1100 to 1200
fathoms with the tube-lead alone, we found it impossible
to tell exactly when the lead touched the bottom. The
line went on running out by its own weight only, and
moreover. with a velocity that did not sensibly differ from that
given it by the additional weight of the lead. Hence, when
accuracy of measurement was the chief desideratum, we had
to sound again, and with the Baillie machine Sent down
along with Wille’s water-bottle, the tube-lead gave good
results, as shown at Station 247. Here, the Baillie machine
indicated a depth of 1120 fathoms, and the tube-lead used
with Wille’s water-bottle, 1124.
Determination of Depth. — The line for deep-sea
soundings being graduated into hundreds of fathoms, the exact
depth had in each case to be computed from special
observations. Our mode of procedure was, at first, as follows:
-The moment the lead entered the water, as also one of the
slips of bunting on the line, an officer called out, and
the time to a second was entered in the sounding-journal.
To attain greater accuracy, the brakesmen had to give
timely notice for every slip of bunting run ofl’ the reel; the
instant the lead struck the bottom, the officer gave the
word, and the time was. entered in the journal. From the
series of entries was computed the first difference,’ or set of
intervals. These figures increase with the depth, the
velocity diminishing with the length of the line running out
through the water. The second difference of the series
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