) 



ORNi^X^ 



NO. 6.] COMPASS ON BOARD. 77 



E. Determination of Declination and Deviation by Compass 



on Board. 



Observer: Lieutenant Scott-Hansen, when not otherwise stated. 



Some meteorological observations and observations of northern lights having been referred 

 to the meridian of the compass on board, the following list will be of importance for reducing 

 the directions to the true meridian. In some few cases the bearing of the celestial object was 

 taken directly with the steering compass on deck which could, for this purpose, be provided 

 with a diopter, but when the rigging was in the way, which was generally the case, the bearing 

 was taken with the azimuth-dial on the bridge, the ship's course being read off simultaneously 

 on the compass. After the ship's enclosure in the ice, the compass-box was generally tapped 

 after the first reading; the numbers here given are the means of the readings after tapping 

 when this produced a sensible difference. 



The abbreviations used in the column "Bearing" are the following: 



S. B. Starboard Bow. S. Q. Starboard Quarter. 



P. B. Port Bow. P. Q. Port Quarter. 



It will be remembered that the angles on the bow and the quarter are counted from the 

 stem and the stern respectively. 



The correction of the watch to the chronometer will, in all cases, be found in List 

 A or B. 



The resulting sum of magnetic declination and local deviation is given here at once, 

 together with the latitude and longitude. When the results of the regular magnetical observations 

 are known, there will probably be no difficulty in separating the deviation, in which case these 

 observations will furnish further material for the determination of the declination. They are 

 also of interest in showing the gradual change in the ship's direction. After the enclosure in 

 the ice, the angles on the compass are counted continually from north through east. The same 

 is also the case for the few bearings taken directly by compass. 



After 1895, August 22, only one observation of this kind was taken, but a supplementing 

 record of the ship's course will be found in the following section. 



As to the observations taken at sea in 1893 (before September 22), they are of less interest, 

 but are nevertheless reproduced here as furnishing the material for the determination of deviation, 

 mentioned in the introduction. The three divisions, marked by spaces between the lines, corres- 

 pond to the three periods there mentioned. It should be observed that the latitudes and longi- 

 tudes given for this part of the observations are only approximate; as the definitive calculation 

 of the astronomical observations taken at sea could not be effected without application of the 

 dead-reckoning, which again required a knowledge of the deviation, preliminary values of latitude 

 and clock error must be used for these observations by compass. The values here given are 

 those actually employed in the calculation. The inaccuracy thus introduced is smaller than the 

 accidental errors necessarily inherent to observations of this kind in high latitudes, the results 

 of which must in all cases be subject to an adjustment. 



Any case of special uncertainty is indicated by the sign : 



