[The following essay discusses Meriwether Lewis and William Clark.]

Meriwether Lewis and William Clark led the first American scientific expedition that the United States government sponsored, the first to cross the North American continent within the present United States. Much of the territory they traversed had never been seen by anyone other than native North Americans, and the expedition of the two explorers provided a thoroughly detailed map of the land. Yet their exploration was more than a heroic feat of geographical discovery because in following the instructions of their sponsor, President Thomas Jefferson, they attempted to provide a comprehensive view of the vast territory they crossed, including anthropological, zoological, botanical, and meteorological information in addition to providing a detailed account of the day-to-day events of the expedition.

Not counting the journals of four of the enlisted men, the two captains wrote more than a million words during...