CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 323 
Lat. 14° 36' N. MANILA. Long. 120° 58' E. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1766. 
O 
+11.68 
Han steen’s Magnetism us der Erde. Christiania. 
1819. 
1786. 
+11.08 
Do. 
1792.6 .... 
+10.67 
Malaspina 
Berliner Astronomisches Jahrbuch, 1828. 
1829. 
+16.27 
Phil. Trans. Roval Societv. 1875. 
1836. 
+16.50 
Do. 
1840. 
+16.45 
El Magnetismo Terrestre en Filipinas, 1893. 
1844. 
+16.43 
Phil. Trans. Roval Societv. 1875. 
1853.... 
+15.58 
Annalen der Hydrographie, 1877. 
1874... 
+17.98 
T+ M. S. Oh all on e'er.. 
Vovaa:e of H. M. S. Challenger. 
1887.5 .... 
+17.47 
Observatory.. 
El Magnetismo Terrestre en Filipinas, 1893. 
1889.5 .... 
+17.38 
Do. 
1890.5 .... 
+17.37 
Do. 
1891.5 .... 
+17.27 
.do. 
Do. 
1891.9 .... 
+17.23 
H. M. S. Penguin... 
Phil. Trans. Royal Society, 1896, A. 
1892.5 .... 
+17.18 
Observatory. 
El Magnetismo Terrestre en Filipinas, 1893. 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1766. 
o 
+11.68 
o 
+10.19 
+1.49 
2.2201 
1786. 
+11.08 
+11.83 
—0.75 
0.5625 
1792.6 .... 
+ 10.67 
+12.40 
—1.73 
2.9929 
1829. 
+16.27 
+15.35 
+0.92 
0.8464 
1836........ 
+16.50 
+15.82 
+0.68 
0.4624 
1840.. 
+16.45 
+16.06 
+0.39 
0.1521 
1844.: 
+16.43 
+16.29 
+0.14 
0.0196 
Probable error of a single observation = ± 35'. 
1853. 
+15.58 
, +16.75 
—1.17 
1.3689 
Period = 360 years. 
1874. 
+17.98 
•+17.37 
+0.61 
0.3721 
1887.5 .... 
+17.47 
+17.42 
+0.05 
0.0025 
1889.5 .... 
+17.38 
+17.40 
—0.02 
0.0004 
1890.5 .... 
+17.37 
+17.39 
—0.02 
0.0004 
1891.5 .... 
+17.27 
+17.39 
—0.12 
0.0144 
1891.9 .... 
+17.23 
+17.38 
—0.15 
0.0225 
1892.5 .... 
+17.18 
+17.37 
—0.19 
0.0361 
1 
9.0733 
Empirical equation for determining the inclination for any year: I = 12°.49 -f 
2.74 sin (l — 1850) + 4.11 cos {t — 1850). 
