MAKING THE POSITIVE From the negative film, obtained as m previously 11 described, a positive film has 01V to be made by contact. Great care is required in order to secure perfect registration between the two films, or the pictures will not be properly spaced, and other irregularities. which are enormously magnified when projected on the screen, will be present. In many cases, the camera employed for taking purposes may be used for making the positive film, by threading the two films in contact with each through the ordinary mechanism of the apparatus, replacing the lens by a narrow slot. A more elaborate contrivance for working on a large scale is that designed by Mr. Jenkins, of New York (see Fig. 876). The two films are kept in absolute registration by means of a toothed sprocket wheel which engages in the marginal perforations, and pass in contact with each other between two plates, above which is a shielded incandescent bulb. The exposure may be varied by the insertion of slotted card board diaphragms between the source of light and the film. Separate reels are provided for
fully drying in a place free from dust, some slight retouching may be necessary here !end there. Every endeavour must be made to avoid pinholes and scratches, since these will utterly spoil the success of a film by causing an irritating twinkling or flashing effect, as the case may be.
I tAPID PRODUCTION.
The feat, now quite a commonplace, of showing on the screen, at night, events which have happened during the same day, obviously requires specially rapid working. Directly the film has been exposed, no time is lost in forwarding it to those charged with the negative film, the unexposed positive film, the exposed positive film, and another for re winding the negative film as it passes along. Since all the reels are interchangeable, it is only necessary to remove the negative film from one end of the apparatus to the other in order to start operations afresh, after the first length of positive film has been exposed.