In art, interest must be centred on the principal theme. Drama is the most difficult of all arts. In it two things are to be satisfied — first, the ears, and second, the eyes. To paint a scene, if one thing be painted, it is easy enough; but to paint different things and yet to keep up the central interest is very difficult. Another difficult thing is stage-management, that is, combining different things in such a manner as to keep the central interest intact.