. . . was Meriwether Lewis?
The Lewis and Clark Expedition was a business trip. For more than 300 years European explorers and, lately, American traders, had been steadily pushing the boundaries of the known world outward into the previously unknown. Within those new boundaries they found other peoples, which meant new places to sell things, and new goods their own customers at home might like to buy. Thus businessmen engaged in trade beyond the boundaries of their own countries began to think globally. Accordingly, they needed to be able to identify new places with certainty, and to know a place meant to know its location by the numbers—by its address on the global grid. That is why Thomas Jefferson instructed Lewis:
Beginning at the mouth of the Missouri, you will take
observations of latitude & longitude, at all remarkeable points on the river, & especially at the mouths of rivers, at rapids, at islands, and other places & objects distinguished by such natural marks & characters of a durable kind, as that they may with certainty be recognised hereafter.
So Lewis was given a gigantic task, and he worked at it diligently, looking for answers from the sky, night and day.
In 1803, when preparations for the expedition were under way, only a very few locations on their projected route between St. Louis and the Pacific Ocean were known, in the new sense. In 1792 the Boston trading-ship captain Robert Gray (1755-1806) determined the latitude (46 degrees, 39 minutes North) and longitude of the mouth of the Columbia River, as well as points along the lower Columbia River, including today's Portland, Oregon. The following year the Canadian fur trader David Thompson did the same for the Mandan Villages: 47 degrees and some minutes North latitude; 101 degrees and some minutes West longitude. The rest of the Northwest was, cartographically speaking, afloat somewhere in terrestrial space.
The mouth of the river Lewis called Maria's was one of those "remarkable points," all the more so because of its potential as a trading-post site. He figured it was at 47 degrees, 46 minutes, 50.2 seconds North, which is about nine miles south of where it "really" was. His error is partly attributable to his assumption that the earth is a perfect sphere, whereas actually there is about a 27-mile difference between equatorial and polar circumference, and the length of a degree varies correspondingly.
Camp Disappointment, Lewis knew, was another point that needed to have its whereabouts defined by its latitude and longitude. That, besides the opportunity to rest men and horses, was the reason he took the considerable risk that went with hanging around in Blackfeet Indian territory for three days. He hoped to find that Maria's River had its sources north of the treaty boundary of Louisiana, which was 49 degrees, 37 minutes north latitude. That, if true, would mean that the Louisiana Purchase actually gave to the United States some land within the purported boundary of British ownership.
Cloudy skies prevented him from making all the celestial observations he needed, although he made one which, had he completed the calculations, would have told him he was camped at about 48 degrees, 41 minutes North latitude (a little over one mile north of the place we have deduced his camp actually was). One minute at that latitude is roughly equal to 1.15 miles, so he would have known that he was still about 91 miles south of his target.
Based on his estimate of the distance he had traveled north of the Missouri River, however, and the lay of the land around his camp, Lewis was reasonably sure of his approximate location.
And that—as disappointing as it was—was all he needed to know.
Dava Sobel, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time (New York: Walker and Company, 1995).
Robert E. Lange, "Meriwether Lewis's 'Camp Disappointment'," We Proceeded On, Vol. 3, No. 1.