But it may be asked, where is the demand for pictures taken at such a speed? In reply it is only necessary to point out that such photographing speeds are indispensable in studying the motions of the smaller members of the animal kingdom. For instance, an amateur recently prepared a film showing the life and habits of lizards. They were taken at the normal speed of sixteen pictures per second, which the operator judged to be sufficient. But when the pictures were shown upon the screen, the very motions which are the most interesting, such as the movement of the tongue, jerk of the head, and so forth, were lost. Similarly, another film depicted the chameleon, but failed to catch the instantaneous throw of its tongue. On the other hand, when the pictures were taken at the accelerated speed of fifty to eighty per second, the results were strikingly different. Not only were they more complete, but they were smoother, more continuous, and more natural; in fact, they were practically identical with those which the human eye observes in the creatures themselves.
Phases of natural movement, capable of being recorded at speeds ranging between eighty and two hundred per second, are the most promising spheres of moving-picture activity at the present moment. Nature study never fails to arouse enthusiasm, while from the operator's point of view it is indescribably fascinating. Something unexpected is secured at every turn of the handle. The portrayal of Nature stirs the emotions of wonder, it is true to fact, and it often introduces the spectator to something about which he has read but which he never has seen. Consequently, so far as life is concerned, the pictures should never be taken at less than forty to fifty per second, unless one is contented to have a mere distorted impression of what actually takes place. Even moving-pictures of the snail or tortoise, generally considered to move very slowly, should never be photographed at a less speed, because these have actions which cannot be caught at sixteen pictures per second.
Generally speaking, the smaller the live subject under investigation, the more rapid should be the photographing speed. The movements of a bee's wings cannot be caught at sixteen or even two hundred pictures per second. This was proved some time ago when Monsieur Lucien Bull, by the aid of his electric spark system, and special camera, obtained a series of photos showing how a bee regains its normal balance when it is upset. For this purpose a bee was launched from the special apparatus used in connection with the camera, with its equilibrium very seriously disturbed. So rapid was its recovery that twenty pictures taken in succession at the above speed served to illustrate the whole operation, the final photograph showing the bee in normal flight. This was the first occasion wherein this peculiar phenomenon had been photographically recorded, and the unique character of the achievement may be realised from the fact that the bee regained its balance in the infinitesimal period of approximately the hundredth part of a second.
Even in photographing a man, to show rapid walking motion, a speed of sixteen pictures per second is far from adequate. If he happens to be walking at four miles an hour quite 75 per cent. of the motion is lost, and the movement portrayed under these conditions is spasmodic and jerky. For a natural cinematographic record of a man walking, at the present orthodox rate of sixteen pictures per second, his pace should not exceed a mile an hour. Therefore to film a man walking at four miles an hour the photographing speed should not be less than sixty-four pictures per second.
Though the ultra-rapid movement involves the use of intricate electrical apparatus, it is a peculiarly absorbing study. The appliances required are necessarily expensive, but, since it is virtually an untouched province, enormous opportunities await the patient worker. It is additionally attractive because each worker is to a very great extent dependent upon his own ingenuity in the design of efficient auxiliaries and secondary apparatus. It is this wide scope for individual initiative which causes rapid cinematography to be so keenly appreciated by investigators, and, as results have shown, their discoveries when popularised make a very deep impression on the public.
Of course, in projection, it is useless to attempt to throw the successive pictures upon the screen at anything approaching the speed at which they were snapped. If the flight of a bullet recorded at say ten thousand images per second, were projected at a corresponding speed, nothing would be seen. So, in projection, the speed is slowed down; the subject photographed at two thousand pictures per second is thrown upon the screen and brought to the eye at the rate of sixteen pictures per second. The bullet moves across the screen with the pace of a snail. The wings of a dragon fly, which in life make several hundred oscillations per second, appear to move as sluggishly as those of a barn-door fowl. But the detail and the complex movements are recorded; the eye sees and follows something which has formerly been beyond its powers.
If it is desired to reduce the speed to its absolute slowest point, so as to facilitate even closer study, the operator can take advantage, to an extreme degree, of the phenomenon of the persistence of vision. This has been done by Monsieur Lucien Bull. It is impossible to reduce the speed of projection to less than sixteen pictures per second, for this is the lowest rate at which the laws of persistence will allow of an appearance of continuous motion. Yet there is an ingenious way of obtaining the equivalent of a speed of eight pictures per second, and this without either disturbing the apparently lifelike movement or producing any flicker. The method is by duplicating each separate picture of the negative upon the positive. That is to say each negative picture is printed twice in succession upon the positive, so that 12 inches of film, which normally would carry sixteen successive and different pictures carries in this case only eight. When projected upon the screen, at the rate of sixteen pictures per second, the eye fails to detect that it is seeing every picture twice. This might almost be described as an optical illusion, and it makes another interesting proof that the eye can be deluded by cinematography. Monsieur Bull, after having found that the eye did not observe that two identical pictures were shown in succession, endeavoured to carry multiplication still farther. He found, however, that a pair of pictures was the limit. When three identical pictures were shown in succession the impression upon the eye was too long. The movement from triplet to triplet gave a disjointed effect such as arises in ordinary projection when the speed is too slow.