Below the film-gate we find another sprocket-wheel, this one to pull the film through the gate, being operated by an intermittent movement. This movement brings the required length of film before the condensing lens’s rays, allows it to remain there the necessary length of time, and then repeats the operation over and over until the entire reel is shown. Improvements in projection-machines, and especially in the “intermittent movement,” have eliminated the flickering, “jumpy” pictures we remember so well only a few years ago. The film is put in motion by a crank at the side of the machine, operated either by hand or by electric power. It is the function of the intermittent movement to convert this rotary motion into the short rectilinear motions that move the film, with the corresponding rests while it is being shown. The principal type of intermittent movement consists of a revolving “pin”wheel, operated by the turning of the crank. The pin engages in the arm of another wheel, a cross in shape, which makes one-quarter of a revolution, and, since it is connected to the sprocket-wheel, thus pulls the film through the gate. At the completion of its down stroke the pinwheel necessarily disengages with the arm of the cross and continues to revolve. But the cross is idle, so the film is held firm in the gate until the pinwheel completes the circle and engages with the next arm of the cross. This will serve the purpose of explaining the principle of the intermittent movement, though improvements and variations are constantly being made. The portions of the projection-machine yet unexplained are the objective lens and the shutter. The lens, which is immediately in front of the film-gate, receives the rays of light passing through the film from the condenser and throws them on the screen. The shutter, which is usually of the revolving-disk type, interrupts the light while the film is being moved to allow the next photograph to reach the correct position. It may be remarked here that the film cannot be allowed to remain in the film-gate indefinitely, for the intense heat of the light from the condenser would soon ignite it. This occasionally happens when the film buckles, and the operator’s first thought when there is trouble with his machine is to shut off the light. Safety fire appliances prevent the blaze from spreading beyond the film-gate. The motion photographer is able with the aid of his camera to perform any number of miraculous feats. He can have one man play two or three parts on the screen at one time, thus having an actor engage in conversation with himself, and so on. And then, readers are most likely all familiar with the pictures showing magical appearances and disappearances of characters. Or the picture-maker can give you a thrilling view of the burning of a city, yet he need not have journeyed outside the studio or expended more than a few dollars to get the scene.