IV. 
Piezometret som Dybdemaaler. 
Vandets Sammentrykkelighed. 
Paa Nordhavs-Expeditionens 2. Togt i 1877 anvendtes 
et Piezometer, og paa det sidste Togt 1 1878 3 Piezometre, 
der ved Lodningerne vare fastgjorte paa Lodlinen sammen 
med Dybvandsthermometrene, et Par Favne over Lodderne 
(og Vandhenter Kun et af Piezometre har 
nærmere Eftersyn vist sig paalideligt. Ved grafisk at op- 
stille Piezometeraflæsningerne som Function af Lodskuddene 
disse ved 
give de to Instrumenter uregelmæssige Curver, medens det 
tredie giver, paa Smaaafvigelser nær, en continuerlig, gan- 
ske svagt krummet Linie. 
Piezometrenes Construction. De vare construe- 
rede efter Angivelse af J. Y. Buchanan, Challenger-Expeditio- 
nens Chemiker, af Casella i London. Reservoiret stod opad, 
og Capillarrøret 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 Røret og Slangen, skaffede det ydre Tryk 
Adgang til Kviksølvet i Koppen". Instrumentets Constan- 
ter vare mig opgivne at Hr. Buchanan, der havde bestemt 
dem ved Vejninger af Piezometret, dels tomt, dels fyldt 
med destilleret Vand til forskjellige Merker. Paa Capillar- 
røret er en Millimeterskala indridset. Det indre er fyldt 
med luftfrit destilleret Vand. En magnetisk Glas-Index 
med Haar til Fjedring markerer Kviksølvets Stand i Capil- 
larrøret, ligesom paa Miller-Casellas Dybvandsthermometre. 
Ved de to Piezometre, hvis Angivelser ikke have vist sig 
brugelige, har rimeligvis Indexen siddet for løst. 
Piezometrets Stand ved forskjellige Tempe- 
raturer. Før Rejsen, 1 1878, blev Piezometret, No. 32109, 
" Se Side 10. 
IV. 
The Piezometer as a Depth-Meter. 
Compressibility of Water. 
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 hav- 
ing to take a sounding, we made fast to the line, along 
with the deep-sea thermometers, a few fathoms above the 
weights (and the water-bottle). 
meters proved on closer inspection trustworthy. 
Only one of these piezo- 
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 di- 
rections 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 filled 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.* The constants of the instrument I 
had from Mr. Buchanan, who determined them by weigh- 
ing the piezometer, when empty and when filled up to dift- 
On the capillary 
The internal 
A magnetic glass 
erent scale-divisions with distilled water. 
tube, a millimetre-scale has been etched in. 
volume contains distilled air-free water. 
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. 
Reading of Piezometer at different Temperatures. — Pre- 
vious to the cruise in 1878, piezometer No. 32109 was 
' See page 10. 
