Following is the text of the Thomas Jefferson's letter, dated June 20, 1803, asking Meriwether Lewis to lead an expedition west.

To Meriwether Lewis, esquire, captain of the first regiment of infantry of the United States of America:

Your situation as secratary of the president of the United States, has made you aquainted with the objects of my confidential message of January 18, 1803, to the legislature; you have seen the act they passed, which, though expressed in general terms, was meant to sanction those objects, and you are appointed to carry them to execution.

Instruments for ascertaining, by celestial observations, the geography of the country through which you will pass, have already been provided. Light articles for barter and presents among the Indians, arms for your attendants, say from ten to twelve men, boats, tents, and other traveling apparatus, with ammunition, medicine, surgical instruments and provisions, you will will have prepared, with such aids as the secretary at war can yield in his department; and from him also you will receive authority to engage among our troops, by voluntary agreement, the attendants abovementioned; over whom you, as thier commanding officer, are invested with all the powers the laws give in such a case.

As you movements, while within the limits of the United States, 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 form the United States.

Your mission has been communicated to the ministers here from France, Spain, and great Briton, and through them to their governments; ans such assurances given them as to its objects, as we trust will satisfy them. The country of Louisana having 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 its 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, and such principal streams of it, as, by its course and communication with the waters of the Pacific Ocean, whether the Columbia, Oregan, Colrado, or any other river, may offer the most direct and practible 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, witht he aid of the usual tales, to fix the lattitude 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, shoud 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 these copies be on the cuticular membranes of the paper-birch, as less liable to injury from damp than common paper.

The commerce which may be carried on with the people inhabiting the line you will pursue, renders a knowledge of those people important. You will therefore endeavour to make yourself acquainted, as far as a diligent pursuit of your journey shall admit, with the names of the nations and their numbers;

The extent and limits of their possessions;
Their relations with other tribes or natins;
Their language, traditions, monuments;
Their ordinary occupations in agriculture, fishing, hunting, war, arts, and the implements for these;
Their food, clothing, and domestic accommodations:
The diseases prevalent among them, and the remedies they use;
Moral and physical circumstances which distinguish them from the tribes we know; "Peculiarities in their laws, customs, and dispositions;
And articles of commerce they may need or furnish, and to what extent.

And, considering the interest which every nation has in extending and strengthening the authority of reason and justice among the people around them, it will be useful to acquire what knowledge you can of the state of morality, religion, and information amoung them; as it may better enable those who may endeavour to civilize and instruct them, to adapt their measures to the existing notions and practices of those on whom they are to operate.

Other objects worthy of notice will be;
The soil and face of the country, its growth and vegetable productions, especially those not of the United States;
The animals of the country generally, and expecially those not known in the United States;
The remains and accounts of any which may be deemed rare or extinct;
The mineral productions of every kind, but more particularly metals, lime-stone, pit-coal, and saltpetre; salines and mineral waters, noting the temperature of the last, and such circumstances as may indicate their character;
Volcanic appearances;
Climate, as characterized by the thermometer, by the proportion of rainy, cloudy, and clear days; by lightning, hail, snow, ice; by the access and recess of frost; by the winds prevailing at different seasons; the dates at which particular plants put forth, or lose their flower or leaf; times of appearance of particular birds, reptiles or insects.

Although your route will be along the channel of the Missouri, yet you will endeavour to inform yourself, by inquiry, of the character and extent of the country watered by its branches, and especially on its southern side. The North river, or Rio Bravo, which runs into the gulf of Mexico, and the North river, or Rio Colorado, which runs into the gulf of California, are understood to be the principal streams heading opposite to the waters of the Missouri, and running southwardly. Whether the dividing grounds between the Missouri and them are mountains or flat lands, what are their distance from the Missouri, the character of the intermediate country, and the people inhabiting it, are worthy of particular inquiry. The northern waters of the Missouri are less to be inquired after, because they have been ascertained to a considerable degree, and are still in a course of ascertainment by English traders and travellers; but if you can learn any thing certain of the most northern source of the Missisippi, and of its position relatively to the Lake of the Woods, it will be interesting to us. Some account too of the path of the Canadian traders from the Missisipi, at the mouth of the Ouisconsing to where it strikes the Missouri, and of the soil and rivers in its course, is desireable.

In all your intercourse with the natives, treat them in the most friendly and conciliatory manner which their own conduct will admit; allay all jealousies as to the object of your journey; satisfy them of its innocence; make them acquainted with the position, extent, character, peaceable and commercial dispositions of the United States; of our wish to be neighbourly; friendly, and useful to them, and of our dispositions to a commercial intercourse with them; confer with them on the points most convenient as mutual emporiums, and the articles of most desirable interchange for them and us. If a few of their influential chiefs, within practicable distance, wish to visit us, arrange such a visit with them, and furnish them with authority to call on our officers on their entering the United States, to have them conveyed to this place at the public expense. If any of them shoudl wish to have some of their young people brought up with us, and taught such arts as may be useful to them, we will receive, instruct, and take care of them. Such a mission, whether of influential chiefs, or of young people, would give some security to your own party. Carry with you some matter of the kine-pox; inform those of them with whom you may be of its efficacy as a preservative from the small-pox, and instruct and encourage them in the use of it. This may be especially done wherever you winter.

As it is impossible for us to foresee in what manner you will be received by those people, whether with hospitality or hostility, so is it impossible to prescribe the exact degree of perseverance with which you are to pursue your journey. We value too much the lives of citizens to offer them to probable destruction. Your numbers will be sufficient to secure you against the unauthorized opposition of individuals, or of small parties; but if a superior force, authorized, ro not authorized, by a nation, should be arrayed against yoru further passage, and inflexibly determined to arrest it, you must decline its further pursuit and return. In the loss of yourselves we should lose also the information you will have acquired. By returning safely with that, you may enable us to renew the essay with better calculated means. To your own discretion, therefore, must be left the degree of danger you may risk, and the point at which you should decline, only saying, we wish you to err on the side of your safety, and to bring back your party safe, even if it be with less information.

As far up the Missouri as the white settlements extend, an intercourse will probably be found to exist between them and the Spanish post of St. Louis opposite Cahokia, or St. Genevieve opposite Kaskaskia. From still further up the river the traders may furnish a conveyance for letters. Beyond that you may perhaps be able to engage Indians to bring letters for the government to Cahokia, or Kaskaskia, on promising that they shall there receive such special compensation as your shall have stipulated with them. Avail yourself of these means to communicate to us, at seasonable intervals, a copy of your journal, notes and observations of every kind, putting into cypher whatever might do injury if betrayed.

Should you reach the Pacific ocean, inform yourself of the circumstances which may decide whether the furs of those parts may not be collected as advantageously at the head of the Missour (convenient as is supposed to the waters of the Coorado and Oregan or Columbia) as at Nootka Sound, or any other point of that coast; and that trade be consequently conducted throught the Missouri and United States more beneficially than by the circumnavigation now practised.

On your arrival on that coast, endeavour to learn if there be any port within your reach frequented by the sea vessels of any nation, and to send two of your trusty people back by sea, in such way as shall appear practicable, with a copy of your notes; and should you be of opinion that the return of your party by the way they went will be imminently dangerous, then ship the whole, and return by sea, by the way either of Cape Horn, or the Cape of Good Hope, as you shall be able. As you will be without money, clothes, or provisions, you must endeavour to use the credit of the United States to obtain them; for which purpose open letters of credit shall be furnished you, authorizing you to draw on the executive of the United States, or any of its officers, in any part of the world, on which draughts can be disposed of, and to apply with our recommendations to the consuls, agents, merchants, or citizens of any nation with which we have intercourse, assuring them, in our name, that any aids they may furnish you shall be honourably repaid, and on demand. Our consuls, Thomas Hewes, at Batavia, in Java, William Buchanan, in the Isles of France and Bourbon, and John Elmslie, at the Cape of Good Hope, will be able to supply your necessities, by draughts on us.

Should you find it safe to return by the way you go, after sending two of our party round by sea, or with your whole party, if no conveyance by sea can be found, do so; making such observations on your return as may serve to supply, correct, or confirm those made on your outward journey.

On reentering the United States and reaching a place of safety, discharge any of your attendants who may desire and deserve it, procuring for them immediate payment of all arrears of pay and clothing which may have incurred since their departure, and assure them that they shall be recommended to the liberality of the legislature for the grant of a soldier's portion of land each, as proposed in my message to congress, and repair yourself, with your papers, to the seat of government.

To provide, on the accident of your death, against anarchy, dispersion, and the consequent danger to your party, and total failure of the enterprise, you are hereby authorized, by any instrument signed and written in your own hand, to name the person among them who shall succeed to the command on your decease, and by like instruments to change the nomination, from time to time, as further experience of the characters accompanying you shall point out superior fitness; and all the powers and authorities given to yourself are, in the event of your death, transferred to, and vested in the successor so named, with further power to him and his successors, in like manner to name each his successor, who, on the death of his predecessor, shall be invested with all the powers and authorities given to yourself. Given under my hand at the city of Washington, this twentieth day of June, 1803.

Thomas Jefferson President of the United States of America