CHANGE IN DIRECTION OF EARTH’S MAGNETIC FIELD. 317 
Lat. 38° 32 / N. 
FAYAL, AZOKES. 
Long. 28° 33' W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
1767*. 
o 
72.00 
C. G. Ekeberg. 
Hansteen’s Magnetismus der Erde, 1819. 
1775.5 .... 
71.02 
Cook............. 
Coast and Geodetic Survey Report for 1891. 
1S05.5 .... 
67.20 
Von Humboldt. 
Beitrage zur Kenntniss des Wesens der Sacular 
Variation des Erdmagnetismus, von L. A, 
Bauer. 
1831.5 .... 
68.57 
Austin, Foster. 
Do. 
1850.. 
65.88 
Rattlesnake. 
Do. 
1873.5 .... 
64.95 
H. M. S. Challenger... 
Do. 
1880.7 .... 
63.64 
Thorpe.... 
Do. 
1889.8 .... 
64.23 
E. D. Preston, assistant, 
United States Coast and 
Geodetic Survey. 
Coast and Geodetic Survey Report for 1891. 
\ 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
o 
o 
1767*.. 
72.00 
70.93 
+1.07 
1.1449 
1775.5.... 
71.02 
70.51 
+0.51 
0.2601 
1805.5 .... 
67.20 
68.75 
—1.55 
2.4025 
1831.5 .... 
68.57 
67.11 
+1.46 
2.1316 
1850.. 
65.88 
65.93 
—0.05 
0.0025 
1873.5 .... 
64.95 
64.69 
+ 0.26 
0.0676 
1880.7 .... 
63.64 
64.35 
—0.71 
0.5041 
1889.8 .... 
64.23 
63.96 
+0.27 
0.0729 
5.4413 
Probable error of a single observation = ± 47' 
Period = 450 years. 
* Omitted. 
Empirical equation for determining the inclination for any year: I == 67°.80 — 
4.87 sin [0.75 {t — 1850) + 22.1]. 
This equation was deduced by Dr. L. A. Bauer with the above data. 
46—Bull. Phil. Soe., Wash., Vol. 13. 
