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Jefferson's Request to Robert Patterson
Washington Mar. 2. 18031
I am now able to inform you, tho' I must do it confidentially, that we are at length likely to get the Missouri explored, & whatever river heading with that, leads into the Western ocean. Congress by a secret act has authorised me to do it. I propose to send immediately a party of about ten men with Capt. Lewis, my secretary, at their head. If we could have got a person perfectly skilled in botany, natural history, mineralogy, astronomy, with at the same time the necessary firmness of body & mind, habit of living in the woods & familiarity with the Indian character, it would have been better. But I know of no such character who would undertake an enterprise so perilous. To all the latter qualities Capt. Lewis joins a great stock of
scientific accurate observation on the subjects of the three kingdoms which are found in our own country but not according to their scientific nomenclatures. But he will be able to seize for examination & description such things only as he shall meet with new. He has been for some time qualifying himself for taking observations of longitude & latitude to fix the geographical points of the line he will pass over, but little means are possessed here of doing that; and it is the particular part in which you could give him valuable instruction & he will receive it thankfully & employ it usefully. The instruments thought best to be carried for this purpose are a good theodolite & a Hadley.2 He will be in Philadelphia 2. or 3. weeks hence to procure instruments & will take the liberty to call on you; and I shall be particularly obliged to you for any advice or instruction you can give him. I think it adviseable that nothing should be said of this till he shall have got beyond the reach of any obstacles which might be prepared for him by those who would not like the enterprise. Accept assurances of my sincere esteem & great respect.
1. Autograph letter signed, sender's copy; Library of Congess. Jackson, Letters, 1:21. The word "scientific" in angle-brackets was deleted by Jefferson.
2. The theodolite was a device for measuring angles in horizontal and vertical circles simultaneously, which hypothetically would have been quite useful, especially in mapping the expedition's route. However, as Lewis explained in a letter he wrote to Jefferson on May 14, 1803, "Mr. Patterson and Mr. Ellicott both disapprove of the Theodolite as applicable to my purposes; they think it a delicate instrument, difficult of transportation, and one that would be very liable to get out of order; they also state that in it's application to any observations for obtaining the Longitude, it would be liable to many objections, and to much more inacuracy than the Sextant." Jackson, Letters, 1:48.
"Hadley" refers to Hadley's quadrant, properly called an octant. In Philadelphia Lewis purchased "1 Hadleys Quadrant with Tangt Screw," which he later (July 22, 1804; Moulton, Journals, 2:411) described as "A common Octant of 14 Inches radius, graduated to 20', which by means of the nonius was devisibile to 1', half of this sum, or 30" was perceptible by means of a micrometer. this instrument was prepared for both the fore and back observation; her error in the fore observation is 2°+, & in the back observtion 2°11'40.3"+
"[A]t the time of our departure from the River Dubois untill the present moment [near the mouth of the Platte River], the sun's altitude at noon has been too great to be reached with my sextant, for this purpose I have therefore employed the Octant by the back observation. the degrees ' & ", recorded for the sun's altitude by the back observation express only the angle given by the graduated limb of the instrument at the time of observation, and are the complyment of the double Altitude of the sun's observed limb; if therefore the angle recorded be taken from 180° the remainder will be the double altitude of the observed object, or that which would be given by the fore observation with a reflecting surface."
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