I hope you have seen Bierstadt's “Storm on the Rocky mountains.” I went to look at it when I was last in Boston, and I wanted to stay all day; though I had an impression that the rain would pour down from those clouds, and the lightning flash through them, if I stayed there long. Such clouds I did not suppose to be possible on canvas. They seemed so distinctly to roll away that I was surprised to look up and find them still there.