CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 305 
INCLINATION. 
Lat. 18° 28' S. ARICA, PERU. Long. 70° 20.5' W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1768 . 
o 
—28.00 
—13.67 
—12.76 
-11.77 
Wilcke’s Inclination Chart. 
Phil. Trans. Royal Society, 1877. 
Annales Hydrographiques, 2d series, 1884. 
Annales Hydrogi’aphiques, 2d vol., 1893. 
1858 
Friesach... 
1883. 
1893.2 .... 
Ensign Favereau, Fr. N. 
Lieutenant Mottez, Fr. N... 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1768. 
1858. 
1883. 
1893.2 .... 
o 
—28.00 
—13.67 
—12.76 
—11.77 
o 
—27.99 
—13.85* 
—12.54 
—11.84 
—0.01 
+0.18 
—0.22 
+0.07 
0.0001 
0.0324 
0.0484 
0.0049 
* 
Probable error of a single observation = ± 12'. 
Period = 350 years. 
J 
0.0858 
Empirical equation for determining the inclination for any j^ear: I — — 21°.67 
+ 7.02 sin 1.06 (t — 1850) + 0.89 cos 1.06 (t — 1850). 
