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IV.
Piezometret som Dybdemaaler.
Vandets Sammentrykkelighed.
IV.
The Piezometer as a Depth-Meter.
Compressibility of Water.
Paa Nordhavs-Expeditionens 2. Togt i 1877 anvendtes
et Piezometer, og paa det sidste Togt i 1878 3 Piezometre,
der ved Lodningerne vare fastgjorte paa Lodlinen sammen
med Dybvandsthermometrene, et Par Favne over Lodderne
(og Vandhenter). Kun et af disse Piezometre har ved
nærmere Eftersyn vist sig paalidelig^ Ved grafisk at
opstille Piezometeraflæsningerne som Function af Lodskuddene
give cle to Instrumenter uregelmæssige Curver, medens det
trodie giver, paa Smaaafvigelser nær, en continuerlig,
ganske svagt krummet Linie.
Piezometrenes Construction. De vare
construerede efter Angivelse af J. Y. Buchanan,
Challenger-Expeditio-nens Chemiker, af Casella i London. Reservoiret stod opad,
og Capillarroret med sin nedre, aabne, Ende i en kugleformet
Kop med Kviksølv, der med en kort Kautschukslange
holdtes fast til Capillarroret. En tynd Glasstang, rørformet,
anbragt mellem Roret og Slangen, skaffede det ydre Tryk
Adgang til Kviksølvet i KoppenInstrumentets
Constanter vare mig opgivne af Hr. Buchanan, der havde bestemt
dem ved Vejninger af Piez o metret, dels tomt, dels fyldt
med destilleret Vand til forskjellige Merker. Paa
Capillarroret er en Millimeterskala indridset. Det indre er fyldt
med luftfrit destilleret Vand. En magnetisk Glas-Index
med Haar til Fjedring markerer Kviksølvets Stand i
Capillarroret, ligesom paa Miller-Casellas Dybvandsthermometre.
Ved de to Piezometre, hvis Angivelser ikke have vist sig
brugelige, har rimeligvis Indexen siddet for lost.
Piezometrets Stand ved forskjellige
Temperaturer. Før Rejsen, i 1878, blev Piezometret, No. 321(>9,
On the second cruise of the North-Atlantic Expedition,
in 1877, a piezometer was employed, and on the last cruise,
in 1878, three piezometers were in use, which, when
having to take a sounding, we made fast to the line, along
with tin* deep-sea thermometers, a few fathoms above the
weights (and the water-bottle). Only one of these
piezometers proved on closer inspection trustworthy. By laying
down on a diagram the readings of the piezometers as
function of the depths, two of the instruments were found
to give irregular curves, whereas the third gave, with but
trifling deviations, a continuous, faintly-curved line.
Construction of the Piezometers. — These instruments
were made by Casella of London, in accordance with
directions from J. Y. Buchanan, Chemist to the "Challenger"
Expedition. The bulb is uppermost, and the capillary
tube has its lower open end dipped into a globular-shaped
cup tilled with mercury, which a short piece of india-rubber
tubing keeps attached to the capillary tube. A slender
glass rod (tubular), inserted between this tube and the
rubber-tubing, affords the outer pressure admission to the
mercury in the cup.1 The constants of the instrument I
had from Mr. Buchanan, who determined them by
weighing the piezometer, when empty and when filled up to
different scale-divisions with distilled water. On the capillary
tube, a millimetre-scale has been etched in. The internal
volume contains distilled air-free water. A magnetic glass
index, with a hair acting as a spring, marks the reading
of the mercury in the capillary tube, as with the
Miller-Casella deep-sea thermometers. The two piezometers whose
indications did not prove reliable, had in all probability the
index too loose.
Heading of Piezometer at different Temperatures. —
Previous to the cruise in 1878, piezometer No. 32109 was
So Side 10.
See page 10.
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