riation at a number of points on
the meridian line, more than 200 observations have been made upon four
different needles, and for the determination of the magnetic dip at four
principal stations on the same meridian 300 observations have been made
upon two different needles.

Under the directions of the same commissioner the line claimed by Great
Britain from Mars Hill and that recently chosen by Messrs. Mudge and
Featherstonhaugh have been surveyed westward from the meridian line to
the highlands near the head waters of the Aroostook, and the necessary
data obtained for the construction of a correct map of that portion of
country.

Upon this survey, without reckoning the distances traveled for
approaching many important points of observation, there have been
actually measured with the chain and coursed with proper instruments 267
miles, including the Aroostook River from its mouth to the point where
it receives the Lapawmpeag Stream, a profile of the country from the
head waters of the Moluncus to the St. John at Fish River, and such
other important lines as were necessary for obtaining the correct
topography of the country, and the altitudes of many points upon the
line claimed by Great Britain as the boundary, in the vicinity of the
Aroostook, have been obtained.

Ten principal points have been determined in latitude and longitude by
means of 115 sets of astronomical observations, aided by three good
chronometers, and seventeen other points have been determined by
triangulation with a portable theodolite. Two hundred and five points
have been determined in altitude by means of 1,319 barometric
observations, and seventeen by means of the theodolite and spirit level.
One hundred and ninety-two observations have been made for determining
the variation of the magnetic needle at three important points.

The field duties above mentioned are considered to furnish sufficient
data for a correct map of the line reported upon by the late British
commissioners, Colonel Mudge and Mr. Featherstonhaugh, between the
St. John River and the head of the Aroostook, besides some lateral
explorations of considerable extent that will have an important bearing
upon this branch of the subject. The work accomplished is full as much
as could have been properly done in a single season, marked, as the
last was, by an unusual drought of long continuance, which rendered
it impossible to ascend, even with light canoes, some of the smaller
str