CHANGE IN DIRECTION OF EARTH S MAGNETIC FIELD, 
313 
CAPE OF GOOD HOPE—Continued. 
Year. 
Observed. 
Computed. 
O-C. 
o=c. 
o 
o 
1751. 
—43.00 
—42.93 
—0.07 
0.0049 
1770........ 
—44.37 
—44.77 
+0.40 
0.1600 
1774. 
—44.48 
—45.21 
+0.73 
0.5329 
1775. 
—45.32 
—45.32 
0.00 
0.0000 
1780. 
—46.77 
—45.87 
—0.90 
0.8100 
1792. 
—47.42 
—47.28 
—0.14 
0.0196 
1818.. 
—50.67 
—50.44 
—0.23 
0.0529 
1836. 
—52.58 
—52.55 
—0.03 
0.0009 
1839. 
—53.10 
—52.87 
—0.23 
0.0529 
1841.5 .... 
—53.15 
—53.16 
+0.01 
0.0001 
1842.5 .... 
—53.22 
—53.26 
+0.04 
0.0016 
1843.5 .... 
—53.32 
—53.37 
+0.05 
0.0025 
| 
Probable error of a single observation = ± 12.6'. 
1844.5 .... 
—53.60 
—53.47 
—0.13 
0.0169 
Period = 450 years. 
1845.5 .... 
—53.53 
—53.58 
+0.05 
0.0025 
1846.5 .... 
—53.55 
—53.69 
+0.14 
0.0196 
1847.5 .... 
—53.68 
—53.79 
+0.11 
0.0121 
1848.5 .... 
—53.78 
—53.89 
+0.11 
0.0121 
1849.5 .... 
—53.87 
—53.99 
+0.12 
0.0144 
1850.5 .... 
—53.97 
—54.09 
+0.12 
0.0144 
1851.5 .... 
—54.03 
—54.19 
+0.16 
0.0256 
1857.0 .... 
—54.60 
—54.73 
+0.13 
0.0169 
1873.9 .... 
—55.93 
—56.13 
+0.20 
0.0400 
1880. 
—57.00 
—56.56 
-0.44 
0.1936 
1890.1 .... 
—57.25 
—57.13 
—0.12 
0.0144 
2.0229 
Empirical equation for determining the inclination for any year : I = — 49°. 11 
— 7.23 sin 0.8 (t — 1850) — 4.93 cos 0.8 (t — 1850). 
