C. A. Schott—Magnetic Declination in the United States. 38 
for instance, taken by Hudson in 1609, in the vicinity of New 
York Bay, are fairly chargeable with a probable error of +8° 
mator) the instrumental means need not leave a greater uncer- 
tainty than about one minute, but the actual probable error of 
any determination is limited by the accidental variations in the 
mean directions of the magnetic force from day to day, mak- 
ing it desirable to continue the observations for three or more 
days and to correct them for daily variation. _ It is principally 
dependent on the magnitude of the horizontal force. 
cursory examination of the column containing the epochs 
of greatest easterly excursion, the deflecting force producing the 
secular change attaining then an easterly maximum, shows that 
the needle became stationary in direction and then reversed its 
secular motion in the New England States toward the end of 
the past century, in the Atlantic Coast States, to the west and 
South, early in the present, and in Mexico about the close 
of the first third of the present century. In California, 
t 
ton, Savannah, Key West and Havana about 1800; New 
Western declination) was felt in Lower California — 
here the eastern declination); in California, Oregon an 
7, 
