19 



Anvendelse i Soen. Betingelser for ilens heldige Anven- 

 delse er et bredt Fartoj. en let Styring, roligt Vejr og 

 tilstrækkelig Tid. samt fremfor ali en saadan Plads for In- 

 strumentet, at de med samme tåpne Bestemmelser af In- 

 klination og Intensitet harmonerer. 



Det er saaledes kun Misvisnings-Observationerne, der 

 have ledet til brugbare Resultater. 



Forend jeg gaar over til at beskrive den i Soen an- 

 vendte Fremgangsmaade og give de beregnede Resultater. 

 maa jeg først omtale Resultaterne af de < >bservationer, som 

 gjordes i Huso til Bestemmelse af Kompassets Deviation. 



Den 13de Juni 1876 svang jeg Skibet paa Huso 

 Havn for at bestemme Kompassets Deviation. Svingningen 

 udførtes ved Trosser, fastgjorte i Land. For hver anlagt 

 Kurs (16 forskjellige Streger). paa hvilke der observeredes, 

 pejledes med Kompasset Varden paa Poldetind. Samtidig 

 observerede paa Teltpladsen i Land Prof. Mohn, paa givet 

 Signal. Magnetometret til Bestemmelse af den absolute 

 Deklination. Fra Teltpladsen var. som ovenfor Side 8 an- 

 ført, Azimut af Yarden paa Poldetind X 48" 7. '5 E. Da 

 Fartojet (Standard Kompasset ombord) under Svingningen 

 laa meget nær i Vertikalplanet mellem Teltpladsen og 

 Poldetind. bliver Azimut af Poldetind for Standard-Kom- 

 , passet ombord X 48. "1 E. Poldetinds Afstand fra Huso 

 er 10 Kvartmil, saa at en Forrvkning lodret paa Sigte- 

 linen mellem begge Steder af 0."1 svarer til 32.4 Meter, 

 en Afstand. der er meget større end Forrykningen af Kom- 

 passets Plads under Svingningen. 



Trækkes Azimut af Poldetind — 48." 1 — fra Pej- 

 lingen af Poldetind. faar man det sande Azimut af Koin- 

 pasnaalens Xordende eller den devierende Misvisning. Den 

 følgende Tabel indeholder Observationerne og de deraf be- 

 regnede Værdier for devierende Misvisning. 



superable obstacles to the use of the Fox circle at sea. 

 The conditions for successful observation with the instru- 

 ment are a vessel broad in the beam and easy to steer, 

 calm weather aud sufticient time, and above all such a 

 position for the instrument as will admit of satisfactory 

 agreement in its determinations of inclination and intensity. 



Hence. the only observations attended with trust- 

 worthy results. were those tåken to tind the declination. 



Before proceeding to describe the method adopted at 

 sea and give the computed results. I must first set forth 

 the results of the observations tåken at Huso for deter- 

 mining the deviation of the compass. 



( >n the 13th of June. 1876. I swung the ship in 

 Huso harbour. by means of hawsers, to obtain the devia- 

 tion of the compass. For evéry course by compass (16 

 different points) on which I ohserved, the bearing of the 

 Poldetind signal was tåken with the compass. Professor. 

 Mohn. at a given signal, simultaneously observing the mag- 

 netometer in the tent on shore. to determine the absolute 

 declination. As previously stated. page 8. the azimuth of 

 the Poldetind signal from the tent was N. 48" 7. '5 E. 

 Xow. as the ship (standard compass on board) lay when 

 swinging very nearly in the vertical plane between the tent 

 and Poldetind. the azimuth of Poldetind for the standard 

 compass on board will be X. 48. "1 E. The distance of 

 Poldetind from Husø is 10 miles; and hence a change in 

 position of 0.°1 perpendicular to the line of vision between 

 both places. corresponds to 32.4 metres. a distance much 

 greater than is that corresponding to the change in the 

 position of the compass during the swinging of the ship. 



If the azimuth of Poldetind — 48. "1 — be subtracted 

 from the bearing of Poldetind. we get the true azimuth of 

 the north end of the compass-needle . or the deviating 

 variation. In the following Table are given the observa- 

 tions. and the valnes computed from them, for deviating 

 variation. 



3* 



