MARYLAND GEOLOGICAL SURVEY 485

From this table, which was prepared with the aid of the long series
of observations at Chambersburg, Washington and Baltimore, we find
that the needle veered about 2° 26'.5 to the west between 1750 and
the middle of the present year. Let us see what values we shall get
from the table of the changes for the county-seats. Watersville is
about midway between Rockville and Westminster; likewise about
midwav between Frederick and Ellicott.

			Secular change between
			1750.0 and 1897.5.
			o '
		From Westminster, . .	.... 2 24.5 W.
		" Rockville, . . .	.... 2 39.0
	I.	Mean, .......	.... 2 31.8
			o '
		From Frederick, . . .	.... 2 17
		" Ellicott, ....	.... 2 43
	II.	Mean, .......	.... 2 30
		Mean of I and II, ...	.... 2° 31 W.

Again, we notice from the table that the needle apparently
remained west of the true meridian throughout the interval 1750 to
1900. If it ever was " true to the pole " during that interval this
occurred not far from the year 1800. The needle may have pointed
east for a brief period after this time, but if it did so, the easterly
deflection was of small amount. No absolutely correct value of the
decimation at Watersville for the present year could be furnished,
since no observations have, as yet, been made there and because of
the prevalence of local disturbances in this part of Maryland. Prop-
erly grouping and combining the observations made at the stations
surrounding Watersville, viz., Frederick, Damascus, Unity, West-
minster, Ellicott City, Baltimore and Cockeysville, the following
values were obtained:

		Magnetic Declination at
		Watersville in 1897.5.
		o '
	By one combination, . .	. . . . . 4 58 W.
	By a second combination,	..... 59
	By a third "	..... 57
	Mean, .	..... 4~58 W.

The table above gives 4° 54'. 5.