If you compare the Río Negro with the Amazon, the River Plate or the Orinoco it is but a river of the second order. Possessing it has been, for centuries, of great political interest for the Spanish Government because it affords its rivals, the Portuguese, easy access into the Guianan missions to worry the Capitanía-General of Caracas in its southern limits. Three hundred years have passed in pointless territorial disputes. In different times, according to their degree of civilization, people have leaned either on papal authority or on astronomy. As they have generally been keener to prolong this dispute rather than solve it, only nautical science and geography have gained anything. When the affairs of Paraguay and the possession of the Sacramento colony became important for the two Courts of Madrid and Lisbon, commissioners were sent out to study the boundaries of the Orinoco, Amazon and River Plate. Besides the idle, who filled archives with their complaints and lawsuits, there were a few educated engineers and some naval officers acquainted with the means of determining the position of a place. The little we knew up to the of the last century about the geography of the interior of the Continent is due to these hard-working men. It is pleasing to remind ourselves that the sciences gained accidentally from these border commissions, often forgotten by the states that sent them out.