CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 333 
Lat. 15° 55 / S. ST. HELENA. Long. 5° W W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1754 ... 
0 
— 9 00 
Hansteen’s Magnetismus der Erde, 1819. 
1771 
—13 on 
f! d F,kftbftr£r.. 
Do. 
1825. 
—15.00 
( —15.05, Duperrey 
Becquerel’s Traits du Magnetisme, 1846. 
[—14.94 .... 
On the Causes of Phenomenon of Terrestrial 
Magnetism, by Wilde. 
1835. 
—18.00 
Do. 
1840 
—21.25 
Phil. Trans. Royal Society, 1877. 
1841. 
—21.43 
Do. 
1842. 
—21.42 
.do. 
Do. 
1843. 
—21.75 
Do. 
1844 
—21.93 
.. do. 
Do. 
1845 ... 
—21.92 
.do. 
Do. 
1846.. 
—22.23 
.do. 
Do. 
1847. 
—22.62 
.do. 
Do. 
1848. 
—22.82 
.do. 
Do. 
1890.1 .... 
—31.18 
E. D. Preston, assistant, 
Coast and Geodetic Survey Report for 1891. 
United States Coast and 
Geodetic Survey. 
Year. 
Observed. 
Computed. 
O-C. 
- 2 
O-C. 
0 
0 
1754. 
— 9.00 
—10.17 
+1.17 
1.3689 
1771. 
—13.00 
—10.90 
—2.10 
4.4100 
1825. 
—15.00 
—17.60 
+2.60 
6.7600 
1835. 
—18.00 
—19.46 
+1.46 
2.1316 
1840. 
—21.25 
—20.44 
—0.81 
0.6561 
1841. 
—21.43 
—20.65 
—0.78 
0.6084 
1842. 
—21.42 
—20.85 
—0.57 
0.3249 
Probable error of a single observation = ± 53'. 
1843. 
—21.75 
—21.06 
—0.69 
0.4761 
Period = 600 years. 
1844. 
—21.93 
—21.26 
—0.67 
0.4489 
1845. 
—21.92 
—21.47 
—0.45 
0.2025 
1846. 
—22.23 
—21.67 
—0.56 
0.3136 
1847. 
—22.62 
—21.90 
—0.72 
0.5184 
1848.. 
—22.82 
—22.12 
—0.70 
0.4900 
1890.1 .... 
—31.18 
—31.34 
+0.16 
0.0256 
18.7350 
Empirical equation for determining the inclination for any year: I == — 32°.95 
— 20.37 sin 0.6 (t — 1850) + 10.43 cos 0.6 {t — 1850). 
48—Bull. Phil. Soc., Wash., Vol. 13. 
