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Continuance Spring / Summer 2003Navigating Across the Continent When the Corps of Discovery was traveling in areas which had not been mapped, Captains Meriwether Lewis and William Clark used instruments of navigation, surveying and measurement such as a compass, a Hadley's quadrant (also called an octant), a sextant, an artificial horizon, a chronometer, a watch, a spyglass (also called a spotting scope or a telescope), a taffrail log and reel, and a two pole chain. By taking sightings at given times each day, Clark could plot their progress although poor visibility due to weather conditions sometimes obscured the horizon or celestial bodies needed to take sightings. The expedition also carried along an artificial horizon. Today we use the GPS (Global Positioning Satellite System) for locating our position. This is quite a change from Clark sketching field maps with a quill pen. The readings from the Hadley's quadrant or the sextant allowed them to calculate their position of latitude. The chronometer indicated their position of longitude. Both latitude and longitude are measured and noted by direction and in degrees, minutes and seconds. The "zero" line for latitude is the equator, and the "zero" line for longitude is the Prime Meridian running through Greenwich, England. Therefore, locations along the journey of the Corps of Discovery are in the north latitude and west longitude. Before the expedition was underway, Lewis took a crash course to learn how to use the navigational and surveying instruments from the leading American astronomer and mathematician, Andrew Ellicott in Lancaster, PA. Clark had previous experience surveying vast tracts of land in Kentucky and Tennessee and Private John Thompson had been a surveyor before he joined the army and expedition. Clark surveyed landmarks as references for his maps. He sketched in or noted the locations of landmarks then described them in the journals. Lewis and Clark also learned about the land from Native Americans who used charcoal to mark on deerskin or a stick to draw lines in the dirt and stones or other natural objects to indicate landmarks. Also, Native people used piles of dirt and stones to show mountains – a simple form of relief map. Clarks notes on 16 January 1805 that a Hidatsa chief visiting the expedition's winter encampment at Fort Mandan, "… gave us a Chart in his way." In Lewis and Clark Among the Indians, historian James Ronda tell us "… As Clark explained later to Biddle (editor of the official journals published in 1814), Indian maps came in several shapes and forms. Some were flat drawings made on skins of mats while others were three-dimensional relief maps made in sand." On their maps, Native American people often represented the relationship between key features in terms of time traveled rather than in distance over the land. Orientation was not necessarily to the Euro-American concept of north. Despite the many differences in the presentation of the Indian "maps," this experience and shared information helped the Corps of Discovery make their way across the North American continent and back. An American Legacy: Lewis and Clark Expedition, Curriculum and Resource Guide, Lewis and Clark Trail Heritage Foundation, 1998 Lewis and Clark Curriculum
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