LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 



35 



Inclination. — The observations of the inclination made in the voyages of Captain 

 Cook are entitled to much consideration, in respect both to the experience and skill 

 of the observers, and to the goodness of their instruments. The English dipping 

 needles of that period were made with much more care, and were much superior, 

 especially in their axles, to those subsequently supplied to the government expeditions 

 up to a very recent date. I have therefore placed in the subjoined Table the obser- 

 vations of Mr. Bayley in 1773, 1774, and 1777 ; and have combined them with the 

 determinations of recent observers, for the purpose of exhibiting the secular change 

 of the inclination at Otaheite, as deduced from the most unexceptionable data that 

 we possess. 



Whence, by the method of least squares, we obtain for the inclination the formula 



I = — 30°0l'-l — 0'-447f, 

 t being, as before, the interval of time elapsed since January 1, 1800, expressed in 

 parts of a year. The inclination in January 1840, computed by the formula, is 

 — 30° 19'-0. 



No observation recorded to have been made at Otaheite by Captain Belcher or 

 his officers, has been omitted in the foregoing account : the manuscript records of 

 the observations on the west coast of America and the adjacent islands, as well as 

 those at Otaheite, are deposited in the Hydrographic Office of the Admiralty. 



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