47 
vægt ved 17° 5 ('. Disse Obsorvationer bleve dog selv 
paa de to sidste Togtcr ikke anstilledc i samme Udstræk- 
ning som Egenvægtsbestemmelserne, der ogsaa oprindelig 
vare bestemte til i første Række at tjene som Maal for 
den samlede Saltgehalt. 
Expeditionen var for Egenvægtsbestemmelser forsynet 
med flere Sæt Glasaræometre fra Dr. Kiichler i Ilmenau, 
li 7° 5 
indrettede til at vise Søvandets Egen vægt ved ^ iV h saa- 
ledes at et Sæt viste Egenvægter fra 1 til 1.007. et andet 
fra 1.006 til 1.013, et tredie fra 1.012 til 1.019, et fjerde 
fra 1.018 til 1.025 og et femte fra 1.024 til 1.031. Aræo- 
metrene vare inddelte i Delstreger af Yærdi 0.0002, medens 
Afstanden mellém disse Delstreger paa Scalaen beløb sig 
til meget nær 1.5""", saaledes at man raaatte kunne aflæse 
udeii stor Feil det 5te Decimal. Under Aflæsningen af 
Vandprø vernes specifiske Vægt anbragtes disse i en i dob- 
belt Slingrebøile opbængt Glascylinder, hvis indre Diameter 
belob sig til ointreut det tredobbelte af Aræometrets Cor- 
pus. hvorefter dette 
dvkkedes i Vædsken 
omhyggeligt renset og 
aftorret ned- 
og tillodes at svømme frit i nogen 
Tid. indtil det liavde antaget Vandets Temperatur. Aflæs- 
ningen foretoges nu langs den undre Rand af Vædskens 
Niveau, idet samtidig Vandets Temperatur iagttoges paa et 
controlleret Thermometer, inddelt i Delstreger af Værdi 
0 . " 2 . 
Paa Grund af det af Expeditionen benyttede Damp- 
skibs fortrinlige Egenskaber som Soskib voldte disse Obser- 
vationer i nogenlunde roligt Veir ingensomhelst Vanskelig- 
heder, selv naar Kursen sattes ret mod Vinden, hvorimod 
Skibets Duvning i meget liaardt Veir altid ytrede sig i 
mærkbare om end smaa Bevægelser hos Aræometret. Hvor 
Vandproverne optoges i saa uroligt Veir, at Bestemmelsen 
paa Grund deraf kunde medføre forøgct Usikkerhed, bleve 
de altid hensatte nogle Dage, indtil de kunde undersøges 
under mere gunstige Villen ar. 
Disse saaledes aflæste Egenvægter maa imidlertid i 2 
Henseender forbedres, idet man paa den ene Side maa an- 
vende passende Correctioner for at faa de ved meget for- 
skjellige Temperaturer aflæste Egenvægter reducerede til 
den fælles Nor malte mperatur 17.° 5, og paa den anden Side 
maa befrie dem for Aræometrenes constante Feil. 
Hvad for det Første Correctionerne for Temperaturen 
angaar. da give de af flere Videnskabsmænd udførte Be- 
stemmelser af Søvandets Volumforandring med Temperaturen 
Midlerne til at beregne disse, idet baade Hubbard s , L. F. 
Expedition, Å those amounts in cubic centimetres corres- 
ponding to l w of the solution of silver, and S the specific 
gravity of the standard sample at 17" 5 C. These obser- 
vations. however, were not instituted even on the two last 
voyages to the same extent as those based on determina- 
tions of specific gravity, the method by which, as origin- 
ally agreed upon, the total amount of salt was to bo chiefly 
computed. 
For performing specific gravity determinations, the Ex- 
pedition had been supplied by Dr. Kiichler of Ilmenau 
with divers sets of glass areometers, adapted to show the 
1 7 ' 5 
specific gravity of sea-water at ^ one set indicating 
specific gravities from 1 to 1.007. another from 1.006 to 
1.013, a third from 1.012 to 1.019, a fourth from 1.018 
to 1.025, and a fifth from 1.024 to 1.031. The areometers 
were graduated in degrees of 0.0002, the interspaces on 
the scale measuring however very nearly 1.5"""; and hence 
you could read oft' with comparative accuracy to the fifth 
decimal. When about to read the specific gravity, the 
samples of water were poured into a glass cylinder sus- 
pended in gimbals, the inner diameter of the cylinder being 
triple that of the areometer, which, carefully wiped and 
dried, was immersed in the fluid and suffered to float 
freely for some time till of the same temperature as the 
water. The specific gravity was now read in the ordinary 
way, the temperature of the water, as shown by a tested 
thermometer graduated in fifths of a degree Centigrade, 
being simultaneously observed. 
The steamer selected for the Expedition being an 
excellent sea-boat, these observations were attended with 
no difficulty whatever in moderately fair weather, even 
when steaming dead against the wind; pitching, however, 
was found to have a distinctly disturbing effect on the 
areometer, and therefore all samples of water drawn when 
it was in any way violent, so as to give reason for appre- 
hending greater uncertainty in the determinations if per- 
formed at once, were stored for a few days, till the weather 
had improved. 
These readings of specific gravity have, however, a two- 
fold need of correction, arising on the one hand from the 
very different temperatures at which the specific gravities 
were read, involving the t necessity of their reduction by 
proper corrections to the normal, temperature 17" 5, and 
on the other, the constant error of the areometer, which 
has also to be eliminated. 
As regards the corrections for temperature, these 
may be computed by the determinations performed by di- 
vers men of science of the extent to which the volume of 
sea-water varies with the temperature, Hubbard,* L. F. 
1 Naar her so in ofte senere brugea Bctcgningsmaaden Egenvægt ved 
<° ’ 
, da menes dermed Egenvægt ved t° i Forhold til destillerct Vand 
af T" som Enhed. Alle Ttfmperaturangivelser i denne AflmiuMing ere 
udtrykte i Grader Celsius. 
a Maury’s Sailing Directions 1858, — 1 — 237. 
1 The expression, specific gravity at ? , 0 ) signifies specific gravity at 
t ° , with distilled water of T° as the unit of comparison. All statements 
of temperature in this Memoir are given in degrees Celsius. 
1 Maury's Sailing Directions, 1858, 1 , p. 237. 
