CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 287 
Lat. 23° 09' N. HABANA, CUBA. Long. 82° 22' W. 
Year. 
Magnetic 
declina¬ 
tion. 
Authority. 
Observer. 
Where recorded. 
1726.... 
O 
—4.40 
Encyclopaedia Metropolitana, 1848. 
1732.3 .... 
—4.50 
Harris. ... 
Do. 
1815. 
—7.00 
Encyclopaedia Britannica, 7th ed., 1842. 
1816.5 .... 
—5.50 
Bentley .. 
Do. 
1840. 
—5.67 
Reormerel’s Trn.itA dn Maernetisme. 
1857. 
—5 27 
( United States Coast Survey 
1 
[Sabine’s Collection, Phil. Trans. Royal Society, 
(Friesach. 
J 
1 1875. 
1858. 
—5.75 
From a map of Cuba, 1860. 
1874.5 .... 
—4.28 
Benito Vines. 
Observaciones Magneticas y Meteorologicas de 
Real Colegio de Belen, 1st semestre, 1876. 
1879.2 .... 
—3.90 
Lieut. Com. Ackley, U.S.N. 
Hydrographic’Office archives document. 
1885.3 .... 
—3.68 
Benito Vines. 
Observaciones Magneticas y Meteorologicas de 
Real Colegio de Belen. 
1887. 
—3.62 
.do. 
Do. 
1888.3 .... 
—3.61 
Do. 
1889.3 .... 
—3.57 
.do. 
Do. 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1726. 
o 
—4.40 
o 
—4.22 
—0.18 
0.0324 
1732.3 .... 
—4.50 
—4.55 
+0.05 
0.0025 
1815. 
—7.00 
—6.47 
—0.53 
0.2809 
1816.5 .... 
—5.50 
—6.54 
+1.04 
1.0816 
1840. 
—5.67 
—5.87 
+0.20 
0.0400 
1857. 
—5.27 
—5.19 
—0.08 
0.0064 
Probable error of a single observed value = ± 17'. 
1858. 
—5.75 
—5.14 
—0.61 
0.3721 
. 
Period = 360 years. 
1874.5 .... 
—4.28 
—4.32 
+0.04 
0.0016 
1879.2 .... 
—3.90 
—4.08 
+0.18 
0.0324 
1885.3 .... 
—3.68 
—3.98 
+0.30 
0.0900 
1887. 
—3.62 
—3.65 
+0.03 
0.0009 
1888.3 .... 
—3.61 
—3.59 
—0.02 
0.0004 
1889.3 .... 
—3.57 
—3.53 
—0.04 
0.0016 
1.9428 
Empirical equation for determining the declination for any year: v = — 3°.42 
+ 2.36 sin {t — 1850) — 2.07 cos (t — 1850). 
