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Art. VIIL On the Variation of the Compass, observed in the 

 late Voyage of Discovery to the North Pole, under 

 Captain Buchan, and on the Errors in Longitude, pro- 

 duced by the action of Iron in Ships upon Chronometers. 

 By George Fisher, Esq. 



[Communicated by the Atithort] 



DURING the voyage the variation of the compass, as may 

 be conceived, was an object of constant attention with the 

 officers of the expedition. The powerful attraction exerted by 

 the iron in the ship on the needle, renders the determination of 

 the variation at sea a problem of the greatest difficulty and un- 

 certainty. The ships were but little time in a high latitude be- 

 fore we were convinced of this ; from the great increase of dip, 

 the binnacle compasses were often so sluggish as to refuse to 

 traverse, and, therefore, beftame useless ; recourse was therefore 

 had to those of lighter and better construction. 



On the first of June a point of land on the north-west coast of 

 Spitzbergen was seen, and observed to bear S.E. the ship being 

 at the time on the larboard tack, and her head in the direction 

 of E. ; but on putting her on the other tack, the same point of 

 land bore S,, the ship's head being then in the direction N. by 

 W,, making a difference in the bearings observed in each tack of 

 no less than four points, or 45°. Several other compasses were 

 likewise tried, and were affected in a similar manner with those 

 in the binnacle. Jennings' patent Insulating Compass was also 

 tried ; this compass, which certainly appears to resist the action 

 of iron not magnetical, was, however, not less affected than the 

 others, and continued so throughout the voyage, 



Mr. Wales, who accompanied Captain Cook, appears to have 

 been the first to notice the singular effect the position of the 

 ship's head had on the needle ; and Captain Flinders, in his 

 Voyage round the World, has afforded us many valuable obser- 

 vations on this subject ; his conclusion, however, appears some- 

 what premature, he observes : — ^That the error produced by an 

 alteration in the position of the ship's head, varies as the sine of 

 the angle contained between the magnetic meridian and the 

 direction of the ship's head. 



Vol. IX. G 



