To appreciate the magnitude of Mackenzie’s undertaking, one must bear in mind that his object was to trace the mighty river that afterward bore his name to its mouth. He had no certain knowledge where it might empty--perhaps into the Arctic, possibly into the Pacific. In any case it involved a long journey, with all sorts of possible difficulties, human and natural; and as he must travel light, with only a limited supply of provisions, it was essential that he should go and return in one season--the very short season of these far northern latitudes. The natives whom he questioned ridiculed the idea of descending the Mackenzie to its outlet and returning the same season. They assured him that it would take him the entire season to go down; that winter would overtake him before he could begin the return journey; and that he would certainly perish of cold or starvation, even if he escaped the hostile tribes of the lower waters of the river. Mackenzie was confident that the journey could be made in the season, but to succeed they must travel at top speed. He had picked men with him, and it was fortunate that he had, for the pace was almost killing. Half-past three in the morning generally saw them in the canoes and off for a long day’s hard paddling. One day they paddled steadily from half-past two in the morning until six in the evening, except short stops for meals, covering seventy-two miles in spite of a head wind. When they reached Great Slave Lake, they found it almost entirely covered with ice, though it was now the ninth of June. Coming down Slave River they had been tortured with mosquitoes and gnats, and the trees along the banks were in full leaf. This violent change was characteristic of the north. Five precious days were lost waiting for the ice to move, so that they might cross the lake. At last a westerly wind opened a passage, and after some perilous adventures they made the northern shore. Coasting slowly to the westward, about the end of the month they rounded the point of a long island, and Mackenzie found himself on the great river. The current increased as they travelled down stream, and it was possible to make good progress.