About 4 P.M. the sun sunk behind a cloud, and the pond began to boom or whoop. It was perfectly silent before. The weather in both cases clear, cold, and windy. It is a sort of belching, and, as C. said, is somewhat frog-like. I suspect it did not continue to whoop long either night. It is a very pleasing phenomenon, so dependent on the altitude of the sun . . .