Sheridan cannot have got
very far with the Screen Scene before he had mentally placed the screen.
But even where a great deal turns on some individual object, the
detailed arrangements of the scene may in most cases be taken for
granted until a late stage in its working out.

One proviso, however, must be made; where any important effect depends
upon a given object, or a particular arrangement of the scene, the
playwright cannot too soon assure himself that the object comes well
within the physical possibilities of the stage, and that the arrangement
is optically[15] possible and effective. Few things, indeed, are quite
impossible to the modern stage; but there are many that had much better
not be attempted. It need scarcely be added that the more serious a play
is, or aspires to be, the more carefully should the author avoid any
such effects as call for the active collaboration of the
stage-carpenter, machinist, or electrician. Even when a mechanical
effect can be produced to perfection, the very fact that the audience
cannot but admire the ingenuity displayed, and wonder "how it is done,"
implies a failure of that single-minded attention to the essence of the
matter in hand which the dramatist would strive to beget and maintain. A
small but instructive example of a difficult effect, such as the prudent
playwright will do well to avoid, occurs in the third act of Ibsen's
_Little Eyolf_. During the greater part of the act, the flag in
Allmers's garden is hoisted to half-mast in token of mourning; until at
the end, when he and Rita attain a serener frame of mind, he runs it up
to the truck. Now, from the poetic and symbolic point of view, this flag
is all that can be desired; but from the practical point of view it
presents grave difficulties. Nothing is so pitifully ineffective as a
flag in a dead calm, drooping nervelessly against the mast; and though,
no doubt, by an ingenious arrangement of electric fans, it might be
possible to make this flag flutter in the breeze, the very fact of its
doing so would tend to set the audience wondering by what mechanism the
effect was produced, instead of attending to the soul-struggles of Rita
and Allmers. It would be absurd to blame Ibsen for overriding theatrical
prudence in such a case; I merely point out to beginners that it is
wise, before relying on an effect of this order, to make sure that it
is, not only possible, but convenient from the practical point of view.
In one or