CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 295 
Lat. 8° 03' S. PERNAMBUCO. Long. 34° 52' W. 
Year. 
Magnetic 
declina¬ 
tion. 
Authority. 
Observer. 
Where recorded. 
1815. 
o 
3.00 
Becquerel’s Traite du Magnetisme. 
Do. 
1819. 
4.75 
1822.. 
4.80 
Do. 
1836. 
5.90 
Fitz Rnv. 
Voyages of the Adventure and Beagle, 1826-36. 
Phil. Trans. Royal Society, 1877. 
French Chart. 
1865. 
11.00 
Darkness 
1867. 
11.00 
Admiral Mouchez, 
Fr. N. 
1872. 
11.50 
French Chart, No. 2748, pub. 1868, cor. 1873- 75. 
Magnetic Survey of the Eastern Part of Brazil, 
published by the Royal Academy of Sciences, 
Amsterdam, 1890. 
1881. 
12.91 
Dr. van Rijckevorsel and 
E. Engelenburg. 
1892. 
14.40 
Capt. H. M. Franck. 
Hydrographic Office archives document. 
Hydrographic Office Publication, No. 109, Contri¬ 
butions to Terrestrial Magnetism. 
1894.2.... 
14.50 
Lieut. J. C. Cresap, U. S. S. 
Bennington. 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1815. 
o 
3.00 
o 
3.60 
—0.60 
0.3600 
1 
1819.. 
4.75 
4.10 
+0.65 
0.4225 
1822.. 
4.80 
4.48 
+0.32 
0.1024 | 
1836. 
5.90 
6.41 
—0.51 
0.2601 
1865. 
11.00 
10.67 
+0.33 
0.1089 
Probable error of a single observation = ± 17.4'. 
1867. 
11.00 
10.97 
+0.03 
0.0009 
Period = 400 years. 
1872. 
11.50 
11.69 
—0.19 
0.0361 
1881. 
12.91 
12.94 
—0.03 
0.0009 
1892. 
14.40 
14.36 
+0.04 
0.0016 
1894.2 .... 
14.50 
14.63 
—0.13 
0.0169 
1.3103 
Empirical equation for determining the declination for any year: v = 8°.994 f 
9.451 sin 0.9 (t — 1850)— 0.539 cos 0.9 {t — 1850). 
