50 



Krængning 20 ". 



Angle of Heel 20°. 



Observere! Fart. 



(Observed Speed.) 



Kvartmil i Timen. 

 (Miles an Sour.) 



r' 



Virkelig Fart. 



(Actual Speed.) 



x = 

 Corr. I >ift'. f. 1 Kvartmil. 



(Corr.) 1 1 1! (f. for 1 Mile.) 



1) Kvartmil i Timen 



(Mill 9 "'i II, ,u r | 



+ 1'" 



Corr. 



X = — 1" 



( 'cirr. 



12.0 



g.O 

 6.0 



4-0 



3-o 



2.5 

 2.2 

 2.177 

 1.0 



0.03 

 0.03 

 0.03 

 0.03 

 0.03 

 0.03 

 0.03 

 0.03 



Man ser, at Krængningsfejlen, selv med en saa stor 

 Krængning som 20°, for de større Farter kun udgjør Brøk- 

 dele af en Knobs Fart. Svinger Fartøjet om et Punkt i 

 eller nær Vandliniens Flade, er Krængningsfejlene i ethvert 

 Tilfælde meget smaa. 



Anderledes stiller Forholdet sig, dersom Stigerøret ikke 

 staar midtskibs. Der kommer da under Krængning en ny 

 Korrektion til, som bliver positiv for Krængning til den ene 

 Side og negativ tor Krængning til den anden, og hvis Stør- 

 relse voxer med Stigerørets Afstand fra Diametralplanet 



Etter vor Erfaring viste Vandloggen sig særdeles hen- 

 sigtsmæssig og holdtes med største Lethed i Orden. Et 

 Blik ned i Maskinskylightet var nok til at observere Skibets 

 Fart i Øjeblikket Maskinisten kunde under Skrabning og 

 Trawling holde Skibet gaaende med den befalede Fart. Til 

 Reduktion af de observerede Vindretninger og Vindhastig- 

 heder til sande kræves Skibets Hastighed i Observations- 

 øjeblikket. Denne observeredes paa Vandloggen, der saa- 

 ledes er et udmærket nautisk-meteorologisk Apparat. 



Astronomiske Observationer. Da Expeditionen ferde- 

 des paa høje nordlige Bredder om Sommeren, var der ikke 

 Tale om at observere andre Himmellegemer end Solen til 

 Bestemmelse af Skibets paaværende Plads. Observationerne 

 gjordes med ilere Sextanter, der altid var godt verificerede, 

 og hvis Indexfejl stadig blev kontrolleret. Sammenlignende 

 t >bservationer med forskjellige Sextanter gav altid godt 

 overensstemmende Resultater. Observationspladsen var i 

 Regelen Hyttedækkel 1 Solobservationernes Udførelse og 

 Beregning deltog, formlen jeg selv og Skibsotticiererne 

 Petersen og Grieg, Professor Mohn og Hr. Tornøe. Sol- 

 højder maaltes til alle Dagstider, naar der var Anledning. 

 I 1878 iagttoges oftere Midnatsolen. De1 var kun yderst 

 faa Dage, paa hvilke der manglede Observationer. 



It is evident that, with greater speed, the error in- 

 volved in heeling, even at an angle of 20°, will amount to 

 only a fraction of a mile. And if the point about which 

 the vessel turus lie in or near the plane of the water-line, 

 the error will be generally very small. 



The case, however, is different in the eveut of the 

 upper tube not being amidships. Another eorrection, posi- 

 tive with a heel to the one side, negative with a heel to the 

 other. will then be needed for computing the speed, and 

 the effect of the heeling will increase witb the distanee of 

 the upper tube from amidships. 



So far as our experience went. we bad every reason 

 to be satisfied witb the water-log; it answered exeellently, 

 and was easy to keep in order. A glance down the engine- 

 room skylight sufficed to tell the ship's speed. Hence, in 

 dredging or trawling the engineer could keep the vessel at 

 the exaet rate required. For reducing observations of the 

 wind's direction and velocity to their true valne, the speed 

 of the vessel at the moment of observation has to be found. 

 Now, this we took from the water-log. which aceordingly 

 proved an excellent instrument for meteorological work 

 at sea. 



Astronomien! Observations. — The North Atlantic Ex- 

 pedition having to cruise in high northern latitudes during 

 the summer season, observations of other celestial bodies 

 than the sun for determining the ship's position were of 

 course out of the question. The altitudes were tåken 

 with several sextants, accurately verified; the index-error, 

 too, being determined for eacb separate observation. The 

 results of comparative observations with different sextants 

 never failed to exhibit satisfactory agreement. Our post of 

 observation was, as a rule, the roof of the roundhbuse. Besides 

 mvself and the sliips oltieers. Mr. Petersen and Mr. < < rieg. Pro- 

 fessor Mohn and Mr. Tomoe also assisted in taking the observa- 

 tions and computing their results. Solar altitudes were tåken 

 at all hours of the dav: nav. on the last cruise, in 1878. we 



