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. 
Table XVI. — Observations of the Incli- 
nation at Point Venus, Otaheite. 
Year. 1 Month. 
Observer. 
Inclination. 
1773 
1774 
1777 
1823 
1830 
1835 
1840 
August. . . . 
May 
December. . 
May 
September 
November 
April .... 
Bayley . . 
Bayley . . 
Bayley . . 
Duperrey 
Erman . . 
FitzRoy 
Belcher 
— 29 43 
-29 59 
-29 47 
-30 03 
-30 29*5 
— 30 14-5 
-30 17-7 
Whence, by the method of least squares, we obtain for the inclination the formula 
I = — 30° 01'*1 — O'" 447 1 , 
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. 
