Thomas Jefferson to Meriwether Lewis
June 20, 1803
To Meriwether Lewis esquire, Captain of the 1st regiment of infantry of the United States of America.
Your situation as Secretary of the President of the United States has made you acquainted with the objects of my confidential message of Jan. 18, 1803 to the legislature: you have seen the act they passed, which, tho' expressed in general terms, was meant to sanction those objects, and you are appointed to carry them into execution.
Instruments for ascertaining by celestial observations the geography of the country, thro' which you will pass, have been already provided. light articles for barter, & presents among the Indians, arms for your attendants, say for from 10 to 12 men, boats, tents, & other travelling apparatus, with ammunition, medecine, surgical instruments & provisions you will have prepared with such aids as the Secretary at War can yield in his department; & from him also you will recieve authority to engage among our troops, by voluntary agreement, the number of attendants abovementioned, over whom you, as their commanding officer, are invested with all the powers the laws give in such a case.
As your movements while within the limits of the US will be better directed by occasional communications, adapted to circumstances as they arise, they will not be noticed here. what follows will respect your proceedings after your departure from the US.
Your mission has been communicated to the Ministers here from France, Spain, & Great Britain, and through them to their governments; and such assurances given them as to it's objects, as we trust will satisfy them. the country of Louisiana having been ceded by Spain to France, the passport you have from the Minister of France, the representative of the present sovereign of the country, will be a protection with all it's subjects: and that from the Minister of England will entitle you to the friendly aid of any traders of that allegiance with whom you may happen to meet.
The object of your mission is to explore the Missouri river; & such principal stream of it, as by it's course & communication with the waters of the Pacific ocean, may offer the most direct & practicable water communication across this continent, for the purpose of commerce.
Beginning at the mouth of the Missouri, you will take observations of latitude & longitude, at all remarkable points on the river, & especially at the mouths of rivers, at rapids, at islands & other places & objects distinguished by such natural marks & characters of a durable kind, as that they may with certainty be recognized hereafter the courses of the river between these points of observation may be supplied by the compass, the log-line & by time, corrected by the observations themselves. the variations of the compass too, in different places, should be noticed.
The interesting points of the portage between the heads of the Missouri & the water offering the best communication with the Pacific ocean, should also be fixed by observation, & 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 & accuracy, to be entered distinctly & intelligibly for others as well as yourself, to comprehend all the elements necessary, with the aid of the usual tables, to fix the. . .