CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 327 
Lat. 8° 03 / S. PERNAMBUCO. Long. 34° 52 / W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1708 ... 
o 
+10.00 
+13.22 
+13.15 
+12.13 
+ 8.95 
+ 8.00 
Wilcke’s Inclination Chart. 
Phil. Trans. Royal Society, Part II, 1877. 
Do. 
Do. 
Magnetic Survey of Eastern part of Brazil, pub¬ 
lished by Royal Academy of Sciences, Amster¬ 
dam, 1890. 
Annales Hydrographiques, 1896. 
1830. 
Fitz Roy. 
1839. 
Sulivan. 
1865. 
Harkness. 
1881.5 .... 
1896. 
Van Rijckevorsel. 
Year. 
Observed. 
Computed. 
O-C. 
0-C°. 
o 
o 
1768. 
+10.00 
+ 9.66 
+0.34 
0.1156 
1836. 
+13.22 
+13.37 
—0.15 
0.0225 
1839. 
+13.15 
+13.26 
—0.11 
0.0121 
1865. 
+12.13 
+11.49 
+0.64 
0.4096 
1881.5 .... 
+ 8.95 
+ 9.66 
—0.71 
0.5041 
1896. 
+ 8.00 
+ 7.76 
+0.24 
0.0576 
1.1215 
Probable error of a single observation — ±25 
Period = 300 years. 
Empirical equation for determining the inclination for any year : I — 5°.27 
3.70 sin (t — 1850) + 7.42 cos (t — 1850). 
