practicable water-communication across the continent, for the
purposes of commerce.

"Beginning at the mouth of the Missouri, you will take observations
of latitude and longitude, at all remarkable points on the river,
and especially at the mouths of rivers, at rapids, at islands, and
other places and objects distinguished by such natural marks and
characters, of a durable kind, as that they may with certainty be
recognised hereafter. The courses of the river between these points
of observation may be supplied by the compass, the log-line, and by
time, corrected by the observations themselves. The variations of
the needle, too, in different places, should be noticed.

"The interesting points of the portage between the heads of the
Missouri, and of the water offering the best communication with the
Pacific ocean, should also be fixed by observation; and the course
of that water to the ocean, in the same manner as that of the
Missouri.

"Your observations are to be taken with great pains and accuracy;
to be entered distinctly and intelligibly for others as well as
yourself; to comprehend all the elements necessary, with the aid of
the usual tables, to fix the latitude and longitude of the places
at which they were taken; and are to be rendered to the war-office,
for the purpose of having the calculations made concurrently by
proper persons within the United States. Several copies of these,
as well as of your other notes, should be made at leisure times,
and put into the care of the most trust-worthy of your attendants
to guard, by multiplying them against the accidental losses to
which they will be exposed. A further guard would be, that one of