CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 301 
Lat. 15° 55' S. ST. HELENA. Long. 5° 44' W. 
Year. 
Magnetic 
declina¬ 
tion. 
Authority. 
Observer. 
Where recorded. 
1010.5 .... 
O 
— 7.22 
Davis. 
1677.5 .... 
— 0.67 
Halley. 
1691.5 .... 
+ 1.00 
.do. 
1724.5 .... 
+ 7.50 
Mathews.. 
Hansteen’s Magnetismus der Erde, Christiania, 
1775.5 .... 
+ 12.30 
Cook. 
1819. 
1789.5 .... 
+15.50 
Hunter.... 
1796.5 .... 
+15.80 
Macdonald. 
1806.5 .... 
+17.30 
Krusenstern. 
1839.5 .... 
+22.28 
D u Petit Thouars . 
Magnetic and Meteorological Observations by 
Maj. Gen. Edw. Sabine. 
1840.5 .... 
+22.88 
Ross. 
Phil. Trans. Royal Society, Part II, 1877. 
1845.5 .... 
+23.25 
Do. 
1846.5'.... 
+23.19 
Berard. 
Magnetic and Meteorological Observations by 
Maj. Gen. Edw. Sabine. 
1890.1 .... 
+23.95 
E. D. Preston, assistant, 
Bulletin No. 23, United States Coast and Geodetic 
United States Coast and 
Survey, May, 1891. 
Geodetic Survey. 
Year. 
Observed. 
Computed. 
O-C. 
-2 
O-C . 
1610.5 .... 
o 
— 7.22 
o 
—7.51 
+0.29 
0.0841 
1677.5 .... 
— 0.67 
—1.29 
+0.62 
0.3844 
1691.5 .... 
+ 1.00 
0.61 
+0.39 
0.1521 
1724.5 .... 
+ 7.50 
5.93 
+1.57 
2.4649 
1775.5 .... 
+12.30 
14.25 
—1.95 
3.8025 
1789.5 .... 
+15.50 
16.31 
—0.81 
0.6561 
Probable error of a single observation = ± 41.8'. 
1796.5 .... 
+15.80 
17.28 
—1.48 
2.1904 
Period = 600 years. 
1806.5 .... 
+17.30 
17.57 
—0.27 
0.0729 
1839.5 .... 
+22.28 
21.94 
+0.34 
0.1156 
1840.5 .... 
+22.88 
22.55 
+0.33 
0.1089 
1845.5 .... 
+23.25 
22.64 
+0.61 
0.3721 
1846.5 .... 
+23.19 
22.66 
+0.53 
0.2809 
1890.1 .... 
+23.95 
23.80 
+0.15 
0.0225 
10.7074 
Empirical equation for determining the declination for any year: v— 7°.90 -f- 
5.92 sin 0.6 (t — 1850) + 14.78 cos 0.6 (t— 1850). 
44—Bull. Phil. Soe., Wash., Vol. 13. 
