Andrew Ellicott Archives - Lewis & Clark Research Database

Andrew Ellicott: America’s Premier Surveyor

Mon, 08 Jun 2026 15:14:16 +0000

Andrew Ellicott (1754–1820) was the foremost surveyor of the early United States. He completed the Mason–Dixon Line, ran the boundaries of nearly a dozen current and future states, surveyed the ground chosen for the new federal capital and carried Pierre L’Enfant’s plan for Washington forward, measured the height of Niagara Falls, and ran the southern boundary of the United States with Spanish Florida. This biography by Lorna Hainesworth follows his life and major surveys from the 1780s through his last boundary work and his years teaching mathematics at West Point, where students nicknamed him “Old Infinite Series.”

The expedition connection is direct. In April 1803, Meriwether Lewis traveled to Ellicott’s home in Lancaster, Pennsylvania, to learn celestial navigation and the practical field surveying he would need in the West, staying about three weeks. Ellicott — himself once a student of Robert Patterson, another of Lewis’s tutors — taught him to fix latitude and longitude with sextant and chronometer. Ellicott’s earlier mapping of the Ohio–Mississippi confluence also informed Nicholas King’s compiled map carried by the Corps of Discovery.

This summary is provided for reference on the Lewis and Clark Research archive; the full article by Lorna Hainesworth is available at the source link.

The post Andrew Ellicott: America’s Premier Surveyor appeared first on Lewis & Clark Research Database.

Planning a Transcontinental Journey

Mon, 08 Jun 2026 15:14:16 +0000

While researching connections between Maryland and the Lewis and Clark story, Lorna Hainesworth turned up a June 6, 1803 letter from Meriwether Lewis to William Linnard, the Army’s military agent in Philadelphia — a document missing from Donald Jackson’s standard Letters of the Lewis and Clark Expedition and overlooked by Ambrose, Cutright, and Dillon. The letter lays out, in exacting detail, how Lewis wanted his accumulated stores moved from Philadelphia and Harpers Ferry to Pittsburgh: the team and driver to hire, the route to follow, the schedule, the careful handling of his box of mathematical instruments, and how the expenses were to be accounted.

Read alongside four related 1803 letters (including the “Portable Soup” letter to General William Irvine), it reconstructs Lewis’s spring-to-summer travels and introduces the cadre of quartermasters, purveyors, and armory officers — Israel Whelan, Thomas Cushing, Joseph Perkins, George Ingels, and Irvine — who outfitted the expedition. The find reveals Lewis at his logistical best: not only an explorer, but a meticulous quartermaster and project manager.

First published in the Lewis and Clark Trail Heritage Foundation’s journal, We Proceeded On (August 2009). This summary is provided for reference on the Lewis and Clark Research archive; the full article is available at the source link.

The post Planning a Transcontinental Journey appeared first on Lewis & Clark Research Database.

Andrew Ellicott

Tue, 10 Feb 2026 17:42:25 +0000

Andrew Ellicott (1754-1820) was one of the leading surveyors and astronomers in early America. He taught Meriwether Lewis the essential skills of celestial navigation, mapmaking, and computing latitude and longitude — training that was fundamental to the expedition’s scientific mission.

In the spring of 1803, President Jefferson arranged for Lewis to study under Ellicott in Lancaster, Pennsylvania. Ellicott taught Lewis how to use the sextant, chronometer, and artificial horizon to determine geographic position from celestial observations. He also instructed Lewis in the use of the surveyor’s compass and the mathematical computations needed to convert observations into coordinates.

Ellicott had previously surveyed the boundaries of the District of Columbia, the southern boundary of the United States (the 31st parallel), and numerous state boundaries. His reputation as the nation’s foremost practical astronomer made him the ideal teacher for Lewis.

The geographic data that Lewis and Clark gathered using Ellicott’s methods produced the most accurate map of the American West for decades — a direct result of Ellicott’s instruction. Without this training, the expedition’s cartographic achievements would have been impossible.

The post Andrew Ellicott appeared first on Lewis & Clark Research Database.