CHANGE IN DIRECTION OF EARTH S MAGNETIC FIELD. 
335 
Lat. 17° 3V S. 
TAHITI. 
Long. 149° 34' W. 
Year. 
Magnetic dip 
or inclina¬ 
tion. 
Authority. 
Observer. 
Where recorded. 
1774. 
1769... 
1773.6 
1774.4 
1777.9 
18231 
1824 11826., 
1830 J 
18351 
1837 [ 1837., 
1840 j 
30.05 
1859., 
1875.8 
1890.7 
-30.72 
-29.72 
-29.97 
-29.78. 
-30.071 
-29.27 i 29.92 
-30.43 J 
- 30.231 
-29.12 y 29.83 
-30.17 J 
-29.08 
-29.97 
-29.33 
rCook . 
J Bayley. 
I.do... 
I.do. 
fDuperrey. 
-I Kotzebue. 
[Erman. 
f Fitz Roy.. 
-j Anonymous... 
[Belcher.. 
{ Friesach. 
Novara Expedition... 
H. M. S. Challenger... 
Lieut. Courmes,Fr.N 
Hansteen’s Magnetismus der Erde, Chris¬ 
tiania, 1819. 
Walker’s Terrestrial and Cosmical Magnetism. 
Do. 
Do. 
Phil. Trans. Royal Society, Part II, 1877. 
Do. 
Do. 
Do. 
Do. 
Do. 
j- Do. 
Voyage of H. M. S. Challenger. 
Annales Hydrographiques, 2d vol., 1892. 
Year. 
Observed. 
Computed. 
O-C. 
_2 
o-c . 
o 
o 
1774. 
—30.05 
—29.71 
—0.34 
0.1156 
1826. 
—29.92 
—29.70 
—0.22 
0.0484 
1837. 
—29.83 
—29.70 
—0.13 
0.0169 
1859. 
—29.08 
—29.70 
+0.62 
0.3844 
■Probable error of a single observation — ± 20'. 
1875.8 .... 
—29.97 
—29.70 
—0.27 
0.0729 
1890.7 .... 
—29.33 
—29.69 
+0.36 
0.1296 
0.7678 
Empirical equation for determining the inclination for any year : I = 
-1- 0.00017 (t — 1850). 
29°. 70 
