64 VARIATION OF THE COMPASS, 



Are two magnetic poles sufficient to explain all the 

 phenomena of the variation of the compass, or are we 

 under the necessity of assuming more ? Formerly 

 Professor Hansteen placed a north-east magnetic 

 pole inlat. 85 49' North, long. 101 30' East. . 



Movement of the Magnetic Pole. 



The magnetic pole does not move under a parallel 

 of latitude ; it does not move in a curve or straight line 

 under a meridian ; it does not move in any line on 

 any side of the pole of the earth ; and consequent its 

 movement must be in some unknown and very 

 eccentric curve round the pole of the earth. 



No satisfactory theory of the variation of the com- 

 pass can be established, but on the supposition that 

 the earth is not solid. 



In the most elevated regions of the earth's atmos- 

 phere hitherto attained by man, the magnetic needle 

 remains as strongly polarized as at the surface of the 

 earth. 



It was obvious in Captain Parry's third voyage, 

 that since 1819, the magnetic pole had moved consi- 

 derably to the east. 



Professor Hansteen's Theory supposes a motion 

 eastward of eleven minutes (1 1') every year. 



Neutralization of the Attraction of the 

 /Ship's Iron. * 



Place the centre of a small circular iron plate in 

 the line of no attraction (of the ship's iron), and at a 

 proper distance behind and below the pivot of the 

 compass needle, (which must be ascertained and fixed 

 before the ship leaves port,) and the needle will not 

 only remain active and vigorous in the polar regions, 

 but will continue to point to the correct magnetic 

 meridian, uninfluenced by the attraction of the ship's 

 iron in every part of the world. 



* Usually called Deviation. 



