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Mr. S. Beswick on a Method for 



Explanation of the diagram. — The letters a^ h represent 

 the situation of the earth's poles; the capital letters A, B re- 

 present the two orbits of the magnetic points of convergence 

 or poles ; and b^ g represent those poles. 



Proposition. — Given the latitude and longitude of each 

 magnetic pole, or point of convergence of the horizontal force, 

 and of the place of observation, to find the declination of the 

 needle at the said place. 



Mean Declination at Greenwich for the present year 1849. 



(1.) N. lat. 51° 29' : comp. 38° 31'. 

 long. 0°. 0'. 



(2.) Lat. and long, of N. magnetic pole. 



N. lat. 70'' : comp. 20°. 

 W. long. 91°. 



(3.) Obtain the value o^ zza trigonometrically thus: as 

 bzza : ba :: abzz : zza. 



