this is the best arc of parallel that has ever been
measured.

"With regard to the Maine Boundary: on May 7th Col. Estcourt, the
British Commissioner, wrote to me describing the perfect success of
following out my plan: the line of 64 miles was cut by directions laid
out at the two ends, and the cuttings met within 341 feet. The country
through which this line was to pass is described as surpassing in its
difficulties the conception of any European. It consists of
impervious forests, steep ravines, and dismal swamps. A survey for the
line was impossible, and a tentative process would have broken the
spirit of the best men. I therefore arranged a plan of operations
founded on a determination of the absolute latitudes and the
difference of longitudes of the two extremities. The difference of
longitudes was determined by the transfer of chronometers by the very
circuitous route from one extremity to the other; and it was necessary
to divide the whole arc into four parts, and to add a small part by
measure and bearing. When this was finished, the azimuths of the line
for the two ends were computed, and marks were laid off for starting
with the line from both ends. One party, after cutting more than
forty-two miles through the woods, were agreeably surprised, on the
brow of a hill, at seeing directly before them a gap in the woods on
the next line of hill; it opened gradually, and proved to be the line
of the opposite party. On continuing the lines till they passed
abreast of each other, their distance was found to be 341 feet. To
form an estimate of the magnitude of this error, it is to be observed
that it implies an error of only a quarter of a second of time in the
difference of longitudes; and that it is only one-third (or nearly so)
of the error which would have been committed if the spheroidal form of
the Earth had been neglected. I must point out the extraordinary merit
of the officers who effected this operation. Transits were observed
and chronometers were interchanged when the temperature was lower than
19 deg. below zero: and when the native assistants, though paid highly,
deserted on account of the severity of the weather, the British
officers still continued the observations upon whose delicacy
everything depended.

"Of private history: From July 3rd to Aug. 13th I was in Ireland with
my wife. This was partly a business journey in connection with the
determination of the longitude of Valencia. On Jan. 4th I as