CHAPTER IX
SLOWING DOWN RAPID MOVEMENTS
During the past few years much effort has been spent upon adapting the cinematograph so that it will record exceedingly rapid movements, such as a bullet in flight. Some popular films of this character have been placed on the market, and, in order to attract the public, have been colloquially described as "quicker-than-thought" or "quicker-than-the-eye" movements. Strictly speaking both the latter designations are erroneous, especially in regard to the eye, inasmuch as if a bullet fired from a rifle were brilliant white the eye would be able to follow its flight with ease, notwithstanding the fact that it may issue from the muzzle with a travelling speed of 2,000 feet or more per second.
So far as the moving-picture camera is concerned it is obvious that the ordinary machine could not be operated with sufficient speed to film a bullet in flight, or even to catch the flap of the wings of a small insect, such as a house-fly or bee. It would be impossible to jerk the film through the gate with sufficient speed to take perhaps five thousand pictures per second—the mechanism, and more particularly the film, would break down before a fiftieth of the number of pictures were taken in the space of one second.
Accordingly, great ingenuity has been displayed by cinematograph investigators in the evolution of a means of snapping such extremely rapid movements at sufficient speed to make the films interesting or scientifically useful. This particular branch of the craft was developed first by Monsieur Lucien Bull, of the Marey Institute, who designed a novel and ingenious camera capable of taking up to two thousand pictures per second.[3] With this apparatus many wonderful films have been obtained, and such a fascinating field of study has been revealed that attempts are being made in all directions to secure "quicker-than-thought" films that would have been thought ten years ago to be photographically impossible. Monsieur Bull is developing his idea in order to be in a position to obtain longer records of a subject, and also to take the photographs at a higher rate of speed. Professor Cranz, a German experimenter, also has carried out some novel experiments on the same lines, and has designed a system whereby he is able to take a photograph in the ten-millionth part of a second.
This particular phase of cinematographic investigation is wonderfully fascinating, and from the private worker's point of view it is additionally attractive because it offers him an opportunity to display his ingenuity. It is only by individual effort and the mutual communication of ideas that perfection can be achieved, and in this one field there is great scope. There are many problems which have to be solved, many of which are peculiar to this particular study. It involves a combination of the electrical and cinematographic expert, since dependence has to be placed upon the electric spark for illumination, and also upon electricity for operating the mechanism.
In such work as this the time factor is a most important feature. Obviously, from the scientific point of view, it is essential to have some reliable means of determining the fraction of a second in which each picture is taken and also the period which elapses between the successive pictures. In the system devised by Monsieur Lucien Bull a tuning-fork is used. The vibrations of this fork per second are known, and as the two ends of the fork are reproduced in each image, it is by no means difficult to calculate the time factor.
Dr. E. J. Marey insisted strongly on the importance of this registration of time. It is obviously essential in many kinds of scientific work. Marey during his life investigated some very rapid natural movements such as those of a pigeon's wings during flight. Such a film would have been useless from the scientific point of view, unless there were some means of showing in what interval of time each successive picture was taken, and also the period which elapsed between each exposure. Knowledge of these two facts enables one to tell the time occupied in making a complete flap of the wing, and the physical changes which take place in the shape of the wing to accommodate the bird to different conditions, and it also enables the investigator to trace the motion photographically lost while the lens is eclipsed to permit the film to be moved forward.