in Thoreau’s Journal:

The night comes on early these days, and I soon see the pine tree tops distinctly outlined against the dun (or amber) but cold western sky.

The snow having come, we see where is the path of the partridge, —his comings and goings from copse to copse, —and now first, as it were, we have the fox for our nightly neighbor, and countless tiny deer mice.

So, perchance, if a still finer substance should fall from heaven (iodine?), something delicate enough to receive the trace of their footsteps, we should see where unsuspected spirits and faery visitors had hourly crossed our steps, had held conventions and transacted their affairs in our midst. No doubt such subtle spirits transact their affairs in our midst, and we may perhaps invent some sufficiently delicate surface to catch the impression of them.

If in the winter there are fewer men in the fields and woods, —as in the country generally, —you see the tracks of those who had preceded you, and so are more reminded of them than in summer