The Brazilian colonel was interested not in adventure but in geographical precision, and he was determined to survey the river carefully and completely, from its headwaters to its mouth. Little more than a century earlier, Alexander von Humboldt, the world-renowned German naturalist and explorer, had conducted the first thorough cartographical survey of South America, producing hundreds of maps based on seven hundred observations. Filling in these maps with the detail necessary to make them truly useful was an ongoing project,
