32 Rev. Mr Scoresby's Observatiofis on the 



outward, instead of two and a half, and three homeward, in or- 

 der that some sort of agreement might be found between the 

 reckoning and the actual- place of the ship. The total effect of 

 the deviation on a passage from Spitzbergen to England com- 

 monly amounts to 4° or 6° of Longitude ; and almost all stran- 

 gers to that navigation, unprovided with chronometers, instead 

 of making^Shetland, the place at which the whalers aim, fall 

 upon or near the coast of Norway, 160 or 180 miles distant. 

 Even Captain Phipps, on his return from his Polar discovery, 

 committed this error ; but its cause was then unknown. 



This error was usually attributed to the operation of an east- 

 erly current, — but it undoubtedly belongs in a great degree, if 

 not entirely, to the deviation. 



The ship Baffin, which I recently commanded in the Green- 

 land fishery, possessed a very large and uncommon measure of 

 local attraction. The first intimation which we had of this dan- 

 gerous influence, was on passing on a north-easterly course to 

 the eastward of the Faroe Islands. In one day''s run, during a 

 gale of wind, the difference of latitude, as found by observation, 

 was less by almost a degree than that determined by calcula- 

 tion,— an error which, if ascribed entirely to the local attraction 

 on the course steered, would have indicated a quantity of devia- 

 tion amounting to nearly two points ! Though this amount, 

 however, was subsequently found to be considerably in excess, 

 yet the absolute quantity in a high latitude, where the dip of 

 the needle was about 80°, proved to be 17° on a S. S VV. course 1 

 The dangerous influence of such a deviation will be readily ap- 

 preciated by a simple example. 



Suppose the Baffin to have sailed with a fair wind 100 leagues 

 on a S. S W. course, per compass [the variation being, say, 42° 

 W.], and then back again 100 leagues on a N. N E. course, 

 per compass, it is evident that, if there were no deviation, or ^ 

 other cause of error, she would return exactly to the point from 

 whence she started. But, in consequence of the deviation only, 

 her actual position would prove to be 123 miles to the eastward, 

 and 55 miles to the nor ih ward of the place from whence she set 

 out — the deviation, as above, being 17° southerly when steering 

 S. S W., and 8^° easterly, as also determined by observation, 

 when steering N. N E. 



