180.".84
later, conditions were much more favourable. There was now available a fund of geographical information which did not exist in 1793, and there were political incentives to exploration which reinforced the scientific motive. And, better than all, Jefferson as President was in a position to secure the practical execution of his design.
The Vancouver and Mackenzie maps. The most important additions to the geography of the west were those contained in Vancouver's map (1798), which laid down the lower Columbia, and in Mackenzie's map ( 1 801 ) which described an actual northern route across the continent, although erroneously relating Columbia river to that route. Mackenzie also made more definite many things pertaining to the river systems east of the Rocky Mountains, and north of the forty-fifth parallel. Also, the nature of the mountain barrier between the eastflowing and the westflowing rivers could be measurably realized from Mackenzie's description of the pass he followed.^
The political incentives which contributed to induce Jefferson to promote westward exploration in 1803-6 might almost be considered sufficient in themselves to bring about the result.
Napoleon alarms the Americans. When Jefferson
1 There is evidence in the map Lewis executed at Fort Mandan in the winter of 1803-4 that he had with him Mackenzie's map. Both Vancouver's book and Mackenzie's are referred to by Gallatin in his correspondence with Jefferson on the subject of the instructions to Lewis in 1803. Probably the explorers carried copies of both.
