CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 311 
Lat. 12° 04/ S. CALLAO, PERU. Long. 77° 08' W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1790 .. 
o 
—12.37 
Malaspina 
Bode’s Astronomisches Jahrbuch, 1828. 
1823. 
— 8.55 
Duperrey . 
Voyages of the Adventure and Beagle, 1826-1836, 
London, 1839. 
1835. 
— 7.05 
Fitz Rnv..., 
Do. 
1838 
— 6.23 
Belcher. 
Phil. Trans. Royal Society, Part II, 1877. 
1838. 
— 6.82 
“ Fa Venus ”. 
Do. 
1858. 
— 7.17 
Friesach 
Do. 
I860. 
— 6.47 
Hark ness 
Do. 
1893. 
— 5.25 
Lieutenant Mottez, 
, Fr. N.... 
Annales Hydrographiques, 2d vol., 1893. 
Year. 
Observed. 
Computed. 
O-C. 
--2 
O-C . 
o 
o 
1790. 
—12.37 
—12.17 
—0.20 
0.0400 
1 
1823. 
— 8.55 
— 8.34 
—0.21 
0.0441 
1835. 
— 7.05 
— 7.37 
+0.32 
0.1024 
1838. 
— 6.23 
— 7.16 
+0.93 
0.8649 
1838. 
— 6.82 
— 7.16 
+0.34 
0.1156 
}- Probable error of a single observation = ± 31'. 
1858. 
— 7.17 
— 6.12 
—1.05 
1.1025 
1866. 
— 6.47 
— 5.86 
—0.61 
0.3721 
1893. 
— 5.25. 
— 5.75 
+0.50 
0.2500 
2.8916 
Empirical equation for determining the inclination for any year: I = — 6°.46 + 
0.0495 {t — 1850) — 0.00076 {t — 1850) 2 . 
