In Letter 4, something unusual happens that has everyone talking. They are completely surrounded by ice and fog, yet when the fog lifts, they see?

From the text:

"About two o'clock the mist cleared away, and we beheld, stretched out in every direction, vast and irregular plains of ice, which seemed to have no end. Some of my comrades groaned, and my own mind began to grow watchful with anxious thoughts, when a strange sight suddenly attracted our attention, and diverted our solicitude from our own situation. We perceived a low carriage, fixed on a sledge and drawn by dogs, pass on towards the north, at the distance of half a mile: a being which had the shape of man, but apparently of gigantic stature, sat in the sledge, and guided the dogs. We watched the rapid progress of the traveller with our telescopes, until he was lost among the distant inequalities of the ice."