A simple way of starting the subject is to study the hue of the shadow cast by your hand on a sheet of white paper. I am working by the light of a Welsbach burner, and the shadow of my hand is a pale reddish purple. The other day, on a bright February morning, I laid my hand on a piece of white paper and the shadow was bluish. In each case, owing to the amount of light reflected from the white paper, the shadow was very transparent, and beautiful in its delicacy and softness.