CHANGE IN DIRECTION OF EARTH S MAGNETIC FIELD. 
293 
Lat. 5® 05' S. PAYTA, PERU. Long. 81° 05.5' W. 
Year. 
Magnetic 
declina¬ 
tion. 
Authority. 
Observer. 
Where recorded. 
1S21 . 
O 
—9.00 
B. Hall...... 
4 
Becquerel’s Traite du Magnetisme. 
1823.2. ... 
—8.93 
1 
1835.. 
—9.00 
1 Sabine’s Collection. Phil. Trans. Royal Society, 
1836. 
—9.00 
f 1877. 
1866. 
—8.88 
I 
1880. 
—8.67 
J 
B. A. variation chart. 
1883. 
—8.23 
Lieut. Barnaud, Fr 
. N. 
Annales Hydrographiques, 2d series,1884. 
1884.1 .... 
—8.47 
Lieut. J. F. Miller. 
Hydrographic Office Publication, No. 109, Contri¬ 
butions to Terrestrial Magnetism. 
1891.3 .... 
—8.80 
Lieut. J. F. Moser, 
U.S.N... 
Hydrographic Office archives document. 
1892.9 .... 
-8.27 
Lieut. Mottez, Fr. 
N. 
Annales Hydrographiques, 2d vol., 1893. 
1894.2 .... 
—7.52 
Lieut. Fichbohm, U. S. N.... 
Hydrographic Office Publication, No. 109, Contri¬ 
butions to Terrestrial Magnetism. 
Y ear. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1821. 
o 
—9.00 
o 
—9.11 
+0.11 
0.0121 
1823.2 .... 
—8.93 
—9.12 
+0.19 
0.0361 
1835.. 
—9.00 
—9.18 
+0.18 
0.0324 
1836. 
—9.00 
—8.18 
+0.18 
0.0324 
1866. 
—8.88 
—8.82 
—0.06 
0.0036 
Probable error of a single observed value — 
± 14.22'. 
1880.. 
—8.67 
—8.44 
—0.23 
0.0529 
Period = 300 years. 
1883.. 
—8.23 
—8.36 
+0.13 
0.0169 
1884.1 .... 
—8.47 
—8.32 
—0.15 
0.0225 
1891.3 .... 
—8.80 
—8.08 
—0.72 
0.5184 
1892.9 .... 
-8.27 
—8.05 
—0.22 
0.0484 
1894.2 .... 
—7.52 
—7.98 
+0.46 
0.2116 
0.9873 
Empirical equation for determining the declination for any year: v — — 7°.417 
+ 0.556 sin 1.2 {t — 1850) — 1.67 cos 1.2 {t —1850). 
43-Bull. Phil. Soe., Wash., Vol. 13. 
