APP. N° IX.] MACNETICAL OBSERVATIONS. 548 



the true meridian, different from what is observed by a com- 

 pass on shore ; the north point of the compass being con- 

 stantly drawn towards the focus of attraction, which appears 

 to be a south pole in north dip; and the south point being at- 

 tracted in south dip, where the focus of attraction becomes a 

 north pole. 



a. The phenomenon of a ship appearing to lie nearer the 

 wind v.'hen beating to the northward, with the wind at 

 north, than tt^hen beating to the southward, with a 

 southerly wind, was obser^''ed by my father at least 

 20 years ago, which phenomenon he attributed to the 

 *' attraction of t3ie ship upon the compass ;" and ever 

 since the jesx 1805, I have been in the habit of al- 

 lowing only ^ to 2| points variation on the passage 

 outward to Xa-reenland, -with a northerly or north-eas- 

 terly course, but generally three points variation on 

 the homeward passage w^ien the course steered was 

 S. VV . or S. W. b. W. Without this difference of al- 

 lowance, a Greenland ship outward bound will be ge- 

 nerally found to be several leagues to the eastwai*d of 

 the reckoning, and liomeward bound will be as much 

 as 4 or 5 decrees to the ea^ward of it. 



"to* 



4. This anomjiy in tlie variation of the compass, occasioned 

 by the attraction of the iron in the ship, is liable to change 

 with every alteration in the dip of the needle, in the position 

 of the compass, or in the direction of the ship''s head. 



a. If the intensity of the terrestrial magnetism be not equaj 

 in all parts of the globe, then the anomaly in the va- 

 riation of the compass will be also liable to change with 

 every alteration in the magnetic influence of the earth. 

 This is a point of such importance, I conceive, in the 

 science of magnetism, that I was very anxious to pro- 

 cure a dipping needle on my last voyage to Green- 

 land, (in 1818), to ascertain, by its oscillations, wiic- 

 ther the magnetism of the earth, by which the dipping 



