The knowledge of the stage director must cover the mechanical features of production as well as the literary. It is essential that he should understand the full value of light and scenic effects, and how to produce them. A stage may be, and generally is, illuminated by means of five different devices--from the "borders", which are directly overhead; from calciums, in the balcony or on either side of the stage; from spot lights, which really are calciums whose light is focused upon one spot; from footlights, and from "strips", which are placed wherever light from more remote sources would be obstructed.
The "borders" are long, inverted troughs, stretching from the extreme left of the stage to the extreme right and suspended from the roof of the theater. When it is said that the light coming from the "borders", or, indeed, from anywhere else, may be raised or lowered, may be white or blue or red or amber, or a combination of these colors, reproducing the glow of a lamp, or the first gray glimmer of sunrise, it will be understood that the director has a wide range of effects at his command.
Just as the reading of a line may alter the impression created by an entire passage, so may the least variation in illumination. Comedy scenes, for example, must be played in full light, as sentimental scenes are helped by half lights. If you could witness the second act of "Charley's Aunt" performed in the steel blue of moonlight, and the last act of "Dr. Jekyll and Mr. Hyde" in the glare of "full up", you would be amazed at the result.
Color has as subtle an influence. I have seen the people in a play fairly melt into the background of a yellow setting, causing their action to seem vague and illy-defined. Augustus Thomas' "The Harvest Moon" had a scene in which the same subject matter was repeated successively in different settings. Unless you had witnessed this performance, you would hardly believe how wholly unlike were the impressions produced. Costumes and music have an equal portence, and both call for the exercise of nice discretion.
The personality of the stage director, and his manner at rehearsal, are vital considerations. In acting, more than in any other art, the feeling of the artist reaches through his work. Everyone who has watched rehearsals has come to the conclusion, at one time or another, that actors are something less than human. As a matter of fact they are simply children, calling for the patience, the forbearance, and the flexibility of view-point necessary in a nursery. Wholly self-centered, having little contact with the outside world, their standards, their emotions, their false valuations make constant difficulties for the man who has to play upon them as upon a piano.