47 



vægt ved 17' .") C< Disse Observatioher bleve dog selv 

 paa de to sidste Togter ikke anstillede [-.samme Udstræk- 

 ning som Egenvægtsbestemmelserne, der ogsaa oprindelig 

 vare bestemte til i første Række :it tjene som Maal for 

 den samlede Saltgehalt. 



Expeditiouen var for Egenvægtsbestemmelser forsynet 



mrd flere Sæt Glasaræometre fra Dr. Kuchler i Ilmenau. 



17" 5 

 indrettede til at vise Sovandets Egenvæsrt ved -t-= — s- 1 , saa- ' 



17 ° o 



ledes at et Sæt viste Egenvægter fra 1 til 1.007, et andet 

 fra L.006 til L.013, et tredié fra 1.012 til 1.019, et fjerde 

 fra L.018 til 1.025 og et femte fra 1.024 til 1,031. Aræo- 

 metrene vare inddelte i Delstreger af \ r ærdi 0.0002, medens 

 Afstanden mellem disse Delstreger paa Scalaen beløb sig 

 til meget liiiT 1.5 mm , saaledes at man maatte kunne aflæse 

 uden stor Feil det Ste Decimal. Under Aflæsningen af 

 Vandprøvernes specitiske Vægt anbragtes disse i en i dob- 

 belt Slingrebøile ophængt Glascylinder, hvis indre Diameter 

 belob sig til omtrent det tredobbelte af Aræometrets Cor- 

 pus, hvorefter dette omhyggeligt renset og aftørret ned- 

 dykkedes i Vædsken og tillodes at svømme frit i nogen 

 Tid. indtil det bavde antaget \ "åndets Temperatur. Aflæs- 

 ningen foretoges nu langs den undre Band af Vædskens 

 Xiveau. idet samtidig Våndets Temperatur iagttoges paa et 

 controlleret Tbermometer. inddelt i Delstreger af Værdi 

 0.°2. 



Paa Grand af det af Expeditiouen benyttede Damp- 

 skibs fortrinlige Egenskaber som Søskib voldte disse Obser- 

 vationer i nogenlunde roligt Veir ingensomhelst Vanskelig- 

 lieder. selv naar Kursen sattes ret mod Vinden, bvorimod 

 Skibets Duvning i meget haardt Veir altid ytrede sig i 

 mærkbare om end smaa Bevægelser hos Aræometret. Hvor 

 Vandprøverne opjtoges i saa uroligt Veir. at Bestemmelsen 

 paa Grund deraf kunde medføre forøget Usikkerbed. bleve 

 de altid hensatte nogle Dage. indtil de kunde undersoges 

 under mere gunstige Vilkaar. 



Disse saaledes atlæste 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 reduceréde til 

 den fælles Normaltemperatur 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 tiere Videnskabsmænd udforte Be- 

 stemmelser af Søvandets Volumforandring med Temperaturen 

 Midlerne til at beregne disse, idet baade Hjibbard -. L. F. 



1 Naar her som ofte senere brages Betegningsmaaden Egenvægl ved 

 f 

 yj, da menes dermed Egenvægl ved t" i Forhold til destilleret Vand 



af T" som Enhed. Alle Temperaturangivelser i denne Afhandling ere 

 udtryjcte i. Grader Celsius. 



-' Maury's Såiling Directions 1858, — 1 — 2.\'. 



Expedition. K those amounts in cubic centimetres corres- 

 ponding to 1 M of the solution of silvef, and 8 the specific 

 gravity of the standard sample at L7° 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- 

 ;ill\ agreednpon, the total amount of salt was to bechiefl] 

 computed. 



For performing specific gravity determinations, the Ex- 

 pedition bad been supplied by Dr. Kiichler of Ilmenau 

 with divers sets of glass areometers, adapted to show the 



17' .") 

 specific gravity of sea- water at — — - 1 , one set indicatine 



.li" o 



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 off 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 Hoat 



freely lor 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 tifths 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 tb'e wind; pitching. however. 

 was found to have a distinctly disturbing efféct 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 ouce. were stored for a few days. till the weather 

 had improved. 



These readings of specific gravity have, however. atwo- 

 fold need of correction. arising on the one hand from the 

 very different temperatures at which the specific gravities 

 were read. involving the necessity of their reduction by 

 proper corrections to the normal temperature 17" 5, and 

 on the other, the constant error of the areometer, which 

 bas 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 voliime of 

 sea-water varies with the temperature. Hubbard, 2 L. F. 



1 The expression, specific gravity at =5-, signifiea specific 'gravity at 



t". with distilled water of 2"° as the unit of comparison. All statements 

 of temperature in this Memoir are given in degrees Celsius. 



-' Maury's Såiling Directions, 1858, 1. p. 237. 



