1 1825.] Variation of the Marimr^s Compass, 13 



a proper distance from one another, then, if the differences 

 between the quantities calculated and the quantities observed, 

 bear every where the same ratio, it is obvious, that these instru- 

 ments, were they ever so defective, would become as useful as 

 the most correct, since we could always make a proper allow- 

 ance for their defects. 



Perhaps as good, and a shorter way would be, to make the 

 observation with several compasses, and as many dipping needles, 

 marked A, B, C, D, and having noted the difference of each, and 

 the variation and dip found by computation, one might be sent 

 to Petersburgh, another to Berlin, a third to yienna or Paris, 

 and a fourth to Edinburgh, and a particular day and hour 

 appointed for the observations to be made. The result of these 

 observations would also be particularly useful to correct any 

 error respecting the place and periodical revolution of the mag- 

 netic pole. That we ought to make the compass to agree with 

 the place of the magnetic pole, and not the situation of that 

 pole with the compass, will not be disputed, unless it were by 

 one, who would regulate the sun by the clock instead of regulat- 

 ing the clock by the sun. ..:;.., ^.. 



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