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Andrew Ellicott

To prepare Meriwether Lewis for the Expedition, President Thomas Jefferson sent him to Philadelphia to meet with Benjamin Rush, Caspar Wistar, Benjamin Smith Barton, and John Patterson. But on his way to Philadelphia, Lewis spent more than two weeks in Lancaster, PA, where he ordered rifles for the expedition and received the first of his lessons from his mentors. "While...at Lancaster," Jefferson later wrote, Lewis "had the benefit of daily communication with Mr. Andrew Ellicott," America's best and brightest mathematician and surveyor, who had recently been appointed Secretary of the Pennsylvania Land Office. Ellicott's "experience in astronomical observation, and practice of it in the woods," according to Jefferson, "enabled him to apprise Captain Lewis of the wants and difficulties he would encounter, and of the substitutes and resources offered by a woodland and uninhabited country."

Plan of the city of Washington in the territory of Columbia

It was a map that brought Ellicott to the attention of both Jefferson and Lewis. While planning for the expedition in Washington, Jefferson and Lewis inspected cartographer Nicholas King's brand new map of the American West, a map based on the best information then available. One of King's sources was Ellicott's own map of the Mississippi Valley, which included the mouth of the Missouri River, the frontier starting point of the Lewis and Clark Expedition.

As Jefferson and Lewis studied King's map, they discussed at length the need to produce a new, accurate, and thoroughly detailed map of the American West. Ellicott, whom Jefferson knew from his recent work in planning Washington, D.C., and respected as one of the nation's greatest surveyors, would make an excellent mentor for Lewis. Through Ellicott, Lewis could learn the skills necessary to produce the best maps possible.

Andrew Ellicott, Letter_ Meriwether Lewis to Robert Patterson

Ellicott proved to be an exceptional mentor. Born in Bucks County, Pennsylvania, Ellicott showed a genius early on for the mechanical, the mathematical, and the adventuresome challenge. As a child, he made his own surveying instruments and musical clocks. After completing his service in the Revolutionary War, Ellicott became an accomplished surveyor. He assisted other surveyors in completing the Mason Dixon line, helped define the western and northern boundaries of Pennsylvania, and surveyed the islands in the Ohio and the Allegheny Rivers.

After moving to Philadelphia in 1789, he completed the first topographical study of the Niagara River and Falls, and surveyed the border between the United States and Spanish Florida. Ellicott also knew the Mississippi River perhaps better than any other American, from both traveling it and mapping it. In sum, Ellicott had observed first-hand the essential value of cartography to the military and economic objectives associated with American expansion. And he was as passionate as Jefferson was about the new opportunity to map the lands between the Mississippi and the Pacific. If the Lewis and Clark Expedition was going to have one great outcome, Ellicott felt it should be a map.

Lewis quickly reported back to Jefferson that Ellicott was "extremely friendly and attentive... [and] disposed to render me every aid in his power." From Ellicott, Lewis learned about and practiced using a sextant, an "artificial horizon" of mercury, and other surveying instruments that would enable him to accurately map the continent.

During the Expedition, it became clear that the two captains had very different strengths. While Lewis was more facile with abstract ideas and literary expression, William Clark proved to be the better map maker. Lewis taught Clark everything he had learned from Ellicott. By the spring of 1804, both men were utilizing Ellicott's instruction as they measured the uncharted territory west of the Mississippi.

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