The use of models built in exact miniature explains the producer’s ability to burn a thriving metropolis to the ground so easily. The wreck of an ocean liner is another feat accomplished in a small tank with papier-maché models. When photographed with the camera comparatively close these scenes appear on the screen to be absolutely realistic, though to the spectator in the theater it seems that the camera was placed at a great distance. Readers who remember the startling volcanic eruption shown in “Cabiria” have evidence of the remarkable deceiving power of the models. Plays with twin brothers or sisters in the principal rôles became popular with picture producers after they discovered that it was possible to have one player appear simultaneously in the two parts. This is accomplished by “double exposure,” which, as the words indicate, is performed by exposing the same strip of film twice. Take the case mentioned, the showing of twin brothers, as an example. First a hair-line division is made of the stage, marking off the two parts on which the different brothers are to appear. Then the scene on one side of the stage is photographed, the film on the other side being protected from exposure--“masked” is the technical term. Following the photographing of this scene, the actor playing the twin brothers steps to the other side of the stage and, with the action already photographed now “masked,” the same strip of film is run through the camera. When the picture is developed it will appear as though two actors appeared in the scene. In making such scenes the director of the production makes use of a split-second watch in order that the action may be timed perfectly and that on both sides of the film chime correctly. It can be seen that a slip of a fraction of a second can easily make the character’s actions appear ridiculous. Despite the difficulties of the work, however, it has become quite common, and daring directors have gone so far as to have dual characters, played by one person, clasp each other’s hands. Where physical contact is attempted, it will be seen that the director, in addition to accurately timing the action on both sides of the film, must have a marker that will note to the fraction of an inch the point at which the character stretched his hand outside the camera’s range, so that, when the other side of the film is photographed, the joining will be perfect. A thread, invisible to the camera, and stretched from above the stage to the floor will serve this purpose.