314 
LITTLEHALES. 
Lat. 19° 26' N. CITY OF MEXICO, Long. 90° 05' W. 
Year. 
Magnetic 
dip or in¬ 
clination. 
Authority. 
Observer. 
Where recorded. 
ms. 
o 
+38.00 
Don Alzate. 
Encyclopedia Metropolitana, 1848. 
1799... 
+42.17 
Do. 
1856. 
+41.43 
Midler and Sontaer 
Phil. Trans. Royal Society, 1875. 
1858. 
+41.44 
Smithsonian Contributions to Knowledge, 1860. 
1879.7 .... 
+44.86 
V. Reyes.. 
Memoria sobre el Dept. Magnetico, etc., Mexico, 
1880. 
1884. 
+45.02 
M. Ramona. 
United States Coast and Geodetic Survey Report 
for 1885, Appendix No. 6. 
1888. 
+45.05 
Ohaerva.torv. 
Mem. del Observatorio Met. Central de Mexico. 
1890 
+44.05 
..flo_ 
Do. 
1895. 
+44.37 
Boletin del Observatorio Astronomico Nacional 
de Tacubaya, Tomo 1, 1896. 
Year. 
Observed. 
Computed. 
O-C. 
o-c 2 . 
1778. 
o 
+38.00 
o 
+39.40 
—1.40 
1.9600 
1 
1799........ 
+42.17 
+39.74 
+2.43 
5.9049 
1856. 
+41.43 
+42.66 
—1.23 
1.5129 
1858........ 
+41.44 
+42.77 
—1.33 
1.7689 
Probable error of a single observation = ± 60'. 
1879.7 .... 
+44.86 
+43.99 
+0.87 
0.7569 
Period = 300 years. 
1884. 
+45.02 
+44.20 
+0.82 
0.6724 
1888'.. 
+45.05 
+44.38 
+0.67 
0.4489 
1890. 
+44.05 
+44.46 
—0.41 
0.1681 
1895. 
+44.37 
+44.66 
—0.29 ■ 
0.0841 
J 
13.2771 
Empirical equation for determining the inclination for any year: I = 42°.32 + 
2.92 sin 1.2 (< — 1850) — 0.04 cos 1.2 (t — 1850). 
