Continuance

Continuance Fall / Winter 2003-2004

Mapping the Confluence

Robert Swenson, Architect and Assistant Professor
Southern Illinois University, Carbondale

In 1803, just before President Jefferson completed the purchase of the Louisiana Territory, the Mississippi River was the western edge of the United States. All lands west and north of the Mississippi River belonged to Spain, France, or England.

Lewis, Clark, and their first recruits traveled down the Ohio River from Pittsburgh and Louisville in their keelboat and pirogue and camped at the Confluence of the Ohio and Mississippi Rivers (near present day Cairo) for 5 days and 6 nights. At the confluence they began measuring, calculating, and drawing maps--one of the most significant activities in their preparation for the expedition. William Clark, already a skilled surveyor, was familiar with the area since he had visited this same site eight years earlier observing the military preparedness of the Spanish. Meriwether Lewis had studied with Andrew Ellicott, the noted astronomer and mathematician, to learn celestial navigation skills. He learned how to use a sextant, octant, circumferentor, artificial horizon, measuring chain, chronometer, and other instruments. The confluence of the Ohio and Mississippi rivers would have been the first significant place where Lewis and Clark could teach each other their respective skills. It was here that they developed the mapping and notation techniques used to document the rest of the journey.

According to the Journals, "the captains made their first efforts to determine latitude and longitude, at the Confluence of the Ohio and Mississippi Rivers." Instruments required to accomplish this were the sextant or octant, artificial horizon, and chronometer. The octant was used during the summer when the sun was higher in the sky. Sextants and octants were used to measure the angular distances of the sun, moon, and stars above the horizon. Their brass sextant of 10 inch radius consisted of an arm that moves along an arc calibrated with a scale of degrees, minutes, and seconds and has several interchangeable eyepieces, a mirror, a horizon glass, and adjustable shades for viewing the sun. The sextant was traditionally used for navigation at sea where the horizon is obvious, but on land, the horizon is often obscured by trees, hills, and/or mountains. An artificial horizon, constructed by Mr. Robert Patterson of Philadelphia, used mirrors and mercury for a reflecting surface to substitute for the natural horizon. The chronometer, purchased from watchmaker Thomas Parker of Philadelphia, was a clock that had to be wound every day at noon and allowed them to compare local time with Greenwich Mean Time.

These basic instruments were used in conjunction with astronomical and mathematical reference books to verify locations of heavenly bodies on specified dates with respect to longitude and latitude on the planet. Calculations for latitude were simple, but calculations for longitude were much more difficult, so Lewis and Clark carefully recorded the data for others to calculate at a later date.

Lewis and Clark also had basic surveying instruments, including the surveyor's compass, called in the journals, a "circumferentor." In conjunction with an observation of the sun with a sextant or octant, a circumferentor was used to determine magnetic declination, the difference between true and magnetic north, which varies according to one's location. Lewis and Clark took these kinds of readings throughout their journey carefully notating detailed sketch maps used later by cartographers to develop the finished maps we see today. The first sketch survey map of the entire journey that depicted the basic configuration and dimensions of these two major rivers, was competed at the Confluence. 

Sources 

Moulton, Gary, ed, Journals of the Lewis & Clark Expedition, 1986-87, Lincoln: University of Nebraska Press, Vol II 

Jackson, Donald, editor, Letters of the Lewis & Clark Expedition with Related Documents, 1783-1854, 1962,Urbana: University of Illinois Press  

Starr, Eileen, Celestial Navigation Basics, Journal: We Proceeded On, November 2001, Volume 27, Number 4, Lewis and Clark Trail Heritage Foundation 

Osgood, Ernest Staples, editor, The Field Notes of Captain William Clark -- 1803-1805, 1964, New Haven and London, Yale University Press

 New Lewis and Clark Displays

Lewis and Clark at the Confluence of the Rivers is a Southern Illinois University Carbondale project funded by the Library of Congress to develop permanent exhibits related to Lewis & Clark in two southern Illinois locations. Period instruments and equipment that were used for celestial navigation and land surveying have been assembled and are on display at the U.S. Custom House Museum in Cairo. They have original and facsimile maps depicting the Confluence over a 250 year period. A full scale diorama and murals and examples of flora, fauna, medicines, and other artifacts are included in the exhibits. The A.B.Safford Memorial Library is the setting for a new Maps exhibit using actual maps and surveying instruments of the period from 1770-1820. Patrons will also be able to access web sites about mapping and the history of the area. The grant also supports research about Cantonment Wilkinson- Ville's history related to the Lewis and Clark Expedition and to Western Expansion. The goal is to learn the complete and accurate story about Wilkinson-Ville, its physical size and layout, and more information about the men who served there and later joined the Lewis & Clark Expedition.

The Cantonment Wilkinson-Ville was a large camp established in 1801 by General James Wilkinson. The camp was located near the Grand Chain of Rocks on the Ohio River and replaced Fort Massac for almost a year. Historians estimate that more than one thousand troups representing 11 companies of infantry were stationed there. This post served as the "port of entry" for boats traveling on the Ohio river until Fort Massac was put back in service. The post was not a palisaded fort but rather a large open camp with several hundred log huts spread out for over a mile along the river. Although the exact purpose of the Cantonment is yet unclear. Historians find it intriguing--the connections between General Wilkinson and Aaron Burr, and Wilkinson's conspiracy with the Spanish to capture Lewis and Clark. Through several archaeological surveys and digs, a small number of artifacts verify the existence of the Cantonment, but we don't know the limits. We also hope to learn more about General Wilkinson and Commandant Jonathan Williams, who subsequently became the first commandant of West Point and later the first commandant of the U.S. Army Corps of Engineers.

 Directors of the project are David Koch (Special Collections and Research, Morris Library) and Robert Swenson (Department of Architecture and Interior Design). Mark Wagner (Center for Archeological Investigations) and Dona Bachman (Museums), Southern Illinois University Carbondale, also assisted. Many others from the region provided valuable support.