in Thoreau’s Journal:
Snows again….The snow is very moist, with large flakes. Looking toward Trilllium wood, the nearer flakes appear to move quite swiftly, often making the impression of a continuous white line. They are also seen to move directly, and nearly horizontally. But the more distant flakes appear to loiter in the air, as if uncertain how they will approach the earth, or even to cross the course of the former, and are always seen as simple and distinct flakes. I think that this difference is simply owing to the fact that the former pass quickly over the field of view, while the latter are much longer in it.