in Thoreau’s Journal:

I feel a little alarmed when it happens that I have walked a mile into the woods bodily, without getting there in spirit…This afternoon, late and cold as it is, has been a sort of Indian summer Indeed, I think we have summer days from time to time the winter through, and that it is often the snow on the ground which makes the whole difference.

This afternoon the air was indescribably clear and exhilarating, and though the thermometer would have shown it to be cold, I thought there was a finer and purer warmth than in summer, a wholesome, intellectual warmth in which the body was warmed by the mind’s contentment, —the warmth hardly sensuous, but rather the satisfaction of existence.