Thoreau writes in his journal:
P.M.—To Walden to get its temperature. The air is only 66 (in the mizzling rain the 23d it was 78); the water at top, 75° (the 23d also 75). What I had sunk to the bottom in the middle, where a hundred feet deep by my line, left there half an hour, then pulled up and poured into a quart dipper, stood at 53° . . .