MAGNETICAL OBSERVATIONS IN SCOTLAND. 



115 



Dublin is derived for the month of September 1836, is given 

 in the subjoined Table. 



In Table VI. we have twenty-five results to be combined by 

 the method of least squares, in order to determine the most 

 probable values of/', x, and y. _ The equations are analogous to 

 those already described in treating of the statical results. We 

 obtain from them the three final equations 



+ -7422 = + 25/' - 73 ar +117/ (A.) 



+ -1816 = -73/' + 35681 .r+ 13117 y (B.) 

 - 5-9458 = + 11/' + 13117 X + 66193y (C.) 



From which we find by elimination 



x= + -0001094 y=— -0001165 



u= - 46° 47-5; r = -0001598; and/' = -0301, 



The intensity at the central position (lat. 56° 27', long. 4° 

 25' W.) is consequently 1-0301 to unity in London. The iso- 

 dynamic line passing through it makes an angle of 46° 47'-5 

 with the meridian ; and the isodynamic lines corresponding to 

 differences of intensity amounting to '005 are at intervals apart 

 of 31'28 geographical miles. 



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