. Moving pictures : how they are made and worked. stage scene and actors. By dint of persistent effort and the perfection of mech-anical details, this serious flickering and jumping effecthas been eliminated; that is, so far as is possible withan apparatus designed to convey the impression of con- 90 MOVING PICTURES CHAP. tinuous motion by intermittent action. The projectingmechanism is of substantial design, while the moving partssubjected to wear and tear are made of the strongest wear and tear, however, is tremendous, and as all themoving parts are liable to displacement they mus
. Moving pictures : how they are made and worked. stage scene and actors. By dint of persistent effort and the perfection of mech-anical details, this serious flickering and jumping effecthas been eliminated; that is, so far as is possible withan apparatus designed to convey the impression of con- 90 MOVING PICTURES CHAP. tinuous motion by intermittent action. The projectingmechanism is of substantial design, while the moving partssubjected to wear and tear are made of the strongest wear and tear, however, is tremendous, and as all themoving parts are liable to displacement they must be fittedwith adjusting devices whereby all slackness can be takenup and the apparatus be kept tuned to a high pitch ofefficiency. Great ingenuity has been displayed in the con-ception and manufacture of these details, and the cinemato-graph projector of to-day is a wonderful piece ofmechanism. The optical principle of the cinematograph is exactlythat of the magic lantern. Reference to Fig. 9will explain it fully. The illuminant is represented. Fig. 9. [By cotirtesy of Messrs. Butcher &* Sons, Ltd. -The Optical Principle of the Cinematograph. by L and the centre of the light is opposite the centre ofthe condensers C C, which receive the rays and condensethem, the point of convergence being in the lens or objec-tive O, from which they pass out in the form of an expand-ing cone of light to fall upon the screen. The rays inpassing from the condensers penetrate the picture F on thefilm in position before the lens. It will be seen that thelens has to be mounted so that its longitudinal axis is levelwith the light. The distance of the light L from the con-densers, and similarly the distance of the lens or objectiveO from the picture F is governed by the focus of theobjective. It is obvious, therefore, that the picture to be projectedmust be brought to a stop in a position central to the lens, ix HOW PICTURES ARE SHOWN 91 and for this purpose there is a film trap or gate, where itma
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