It was a difficult matter to find a non-inflammable film, for science has not yet discovered a base that can be made without cellulose, but the base we know to-day was treated so as to be non-explosive and practically non-inflammable. This film base is called cellulose-acetate, and when it is exposed to an excessive heat, as, for instance, the beam of the motion-picture lamp when the film is not moving, or when it touches a flame, it melts but does not blaze up. In the melting it gives off a heavy smoke, but there is no serious danger from this, as there is from the spurting flames from an exploding cellulose-nitrate base.
The films are packed in metal airtight and lightproof boxes and sent to the motion-picture firms, where they begin a complicated and an interesting career. The first stage is the perforating machine, through which all films, whether negative or positive, must go. The holes are made along the two edges of the celluloid strips, just as shown in the picture opposite page [176]. There are sixty-four holes to the foot, on each side of the film, and each hole is oblong-shaped, as can be seen, with a width of about one eighth of an inch and a depth of about one sixteenth of an inch. This is known as the Edison Standard Gauge, and it is observed by practically all the motion-picture firms in the world.
The perforations along the edges of the films furnish the means for drawing them through the camera, printing machine, and projector; and as the correct movement of the films is one of the important factors in making good pictures, they must be absolutely mathematically exact. A fault in perforation of even as much as one thousandth part of an inch is apt to cause the film to buckle in the camera or projector and ruin the whole thing.
There are several different perforating machines in use now, and all of them are claimed by their makers to be perfect. It will not be necessary for us to take one of these machines to pieces further than to see that the holes along the edges of the films are punched by hardened steel punches. The films unwind from one bobbin, pass through the perforating device, and wind upon another bobbin. Of course the work must be done in absolute darkness, except for a small ruby lamp, as the films are so sensitive to light that any rays other than faint red would spoil them.
After perforation the negatives and positives are ready for use. The negative goes to the photographer in its light-tight metal box to be run off in making a film of a historical scene, a comedy, some wonderful phenomenon of science, or any one of a million different subjects. Just for the sake of seeing everything in its proper order we will assume that the negative is about to be used in portraying a comedy about the troubles of a book agent, and that it is all done in the studio where the scientist and his boy friend watched this very film made.
Now for a look into a motion-picture camera—something few people get, because the competition among the various cinematographers is keen, and those who hold patents on cameras fear infringement.
The camera, which is enclosed in a strong mahogany box, stands upon a tripod. It is about eighteen inches long, eighteen inches high, and four inches wide. (This size varies with the make, and kind of work required.) The left side opens on a hinge, while on the right side are the ground glass finder, the distance gauge, and a dial to register the number of feet of film used. In the rear of the camera is a small hole which connects with a tube running straight through the box so that the operator looking through can sight it like a telescope, before the film is exposed. When the sighting and focusing are completed the opening is closed with a light-tight cap, and the film can be threaded through the camera. Having no bellows for focusing like an ordinary camera, the lens of the motion-picture camera is moved back and forward a short distance in the little tube in which it is set, to aid in the focusing. Of course the lenses of these wonderful snapshot machines are the best that money can buy and the factories can turn out.
A SECTION OF MOTION-PICTURE FILM