“Any bird or creature may be hunted down, any nest discovered, if you lay siege to it; but to find what you are not looking for, to catch the shy winks and gestures on every side, to see all the byplay going on around you, missing no significant note or movement, penetrating every screen with your eye-beams—that is to be an observer, that is to have “an eye practiced like a blind man’s touch,”—a touch that can distinguish a white horse from a black—a detective eye that reads the faintest signs.”