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augmented thereby, is oil on the films. If we examine the films in any exchange we will be reasonably certain to find seventy-five, per cent of them carrying oil to some extent. A goodly share of this percentage will carry considerable oil, while some films will be literally smeared with it.
This state of affairs is traceable to several causes, but it is a condition always greatly aggravated by over-speeding, partly because of the natural inclination to over-oil a mechanism which is working under heavy stress, and partly by reason that as speed of rotation of revolving parts increases there is added tendency to throw off oil by centrifugal force, and much of which finds its way, eventually, to the film.
Unsteadiness of the Picture
Is always greatly aggravated by any considerable excess in projection speed above normal. This is due to several causes. First, there is the rapid wear of mechanism parts, which very naturally makes for lost motion and unsteadiness of the picture. Second, there is increased tendency to wear off intermittent sprocket teeth, due to added strain of excessively tight tension required for high speed, and worn intermittent sprocket teeth always make for unsteadiness in the picture. Third, there is the added tendency to jump when a badly made splice hits the upper end of the tension shoes. In addition to this there is, to some extent, additional vibration of the machine as a whole, which of course to some extent make for unsteadiness of the picture on the screen.
I feel there is no need to further elaborate on this phase of the subject. It should, it seems to me, require no argument to convince even the most skeptical that excess in projection speed makes for unsteadiness of the picture on the screen, nor can the fact that it is possible to project a steady picture at high speed be accepted as proof or even as evidence to the contrary. Effect of Over-Speeding Upon the Film
One of the important functions of the projectionist is to see to it that the tension springs exert just sufiicient pressure upon the film to accomplish the purpose for which they are intended. But the amount of pressure (tension) necessary to stop the film after the intermittent sprocket has ceased to act and to hold the parts in retard, will depend in large degree upon the speed of projection, since the braking action of tension shoes upon the film has entirely to do with overcoming the momentum of the film and holding the intermittent sprocket in retard when the movement ceases to function. It therefore follows that decidedly less tension will be required at normal speed than at high speed, and that, always assuming the tension to be adjusted to the actual requirement, the strain upon the film sprocket holes, the teeth of the intermittent sprocket and the whole intermittent movement as well as the various gears of the mechanism will be greatly increased by increased speed of projection; also that the added tension made necessary by increased projection speed will produce abnormal wear upon the aperture plate tracks, as well as aggragate any tendency of emul
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