Читать книгу More Science from an Easy Chair - Sir E. Ray Lankester - Страница 11

Table of Contents

THE PROBLEM OF THE GALLOPING HORSE

Until instantaneous photography was introduced, a little more than twenty-five years ago (by the discovery of the means of increasing the sensitiveness of a photographic plate), and gradually became familiar to everyone in the exhibitions known as the "biograph" or "cinematograph," the actual position of the legs in a galloping horse at any given fraction of a second was unknown. Anyone who has tried to "see" their position will agree that it cannot be done. Attempts had been made to make out what the movements and positions of the legs "must" be, by studying the hoof-marks in a soft track laid for the purpose. But the result was not satisfactory.

As everyone knows, the so-called "biograph" pictures are produced by an enormous series of consecutive instantaneous photographs taken on a continuous transparent flexible film or ribbon. The camera has a mechanism attached to it by which the sensitive film is jerked along so as to expose a length of two inches (the size of the picture given by the camera) for, say, one-thirtieth of a second without movement. The film is then jerked on and a second bit of two inches is brought into place for a thirtieth of a second and so on until a ribbon of some thousand pictures is obtained. The interval between each picture is usually also about one-thirtieth of a second, so that at least fifteen pictures are taken in every second of time, and according to the requirements of illumination and the rapidity of the movements of the men or animals photographed this number may be greatly increased. The film is developed, printed and fixed on a similar rolling mechanism and the pictures are thrown one by one by a powerful lantern on to a screen, and are jerked along at the same rate as that at which they were taken, and are magnified enormously. Animals and men in rapid movement, railway trains, the waves of the sea are thus photographed, and when the serial pictures are thrown successively on the screen the result is that the eye detects no interval between the successive pictures—the figures appear as continuous moving objects. This is due to the fact that whilst the impression produced on the retina of the eye by each picture lasts for a tenth of a second (less with brighter light), the interval between the successive pictures is only one-thirtieth of a second, and accordingly the retinal impression has not gone or ceased before the next is there; hence there is no break in the series of retinal impressions, but continuity.[1]

Plate I.—Figs. 1 to 11, drawings from Muybridge's photographs of consecutive poses of the galloping horse, each photograph taken by an exposure of one fortieth of a second and separated from the next by an interval of one fortieth of a second. The horse in Fig. 10 has returned to the same pose as that with which the series starts in Fig. 1. Fig. 11 gives a pose one hundredth of a second earlier in the series than that taken in Fig. 2. Fig. 12 shows a combination of the hinder half of Fig. 9 with the front half of Fig. 6, giving thus the maximum extension of both fore and hind legs.

It is this duration of the impression on the retina which prevents us from separating or "seeing distinctly" the successive phases of a horse's legs as he gallops by, and has led to the remarkable result that no artist has ever until twenty-five years ago represented correctly any one phase of the movement of the legs in a galloping horse, and it is doubtful whether that correctness is what the painter of a picture really ought to put on his canvas. If we examine the separate pictures of a galloping horse as taken on a cinematograph film, we have before us the actual record of the positions assumed by the legs at intervals of the thirtieth of a second (or whatever less interval and length of exposure may have been chosen), and it is simply astonishing to find how utterly different they are from what had been supposed. Twenty years ago Mr. Muybridge produced a number of these instantaneous photographs of moving animals—such as the horse in gallop, trot, canter, amble, walk, and jumping and bucking—also the dog running, birds of several kinds flying, camel, elephant, deer, and other animals in rapid movement. The animals were photographed on a track in front of a wall, marked out to show measured yards; the time was accurately recorded to show rate of movement and length of exposure, and of interval between successive pictures. By means of three cameras worked by electric shutter-openers, a side, a back, and a front view of the animal were taken simultaneously. Repeated photographs were obtained at intervals of a fraction of a second, giving a series of fifteen or twenty pictures of the moving animal. The length of exposure for each picture was one-fortieth of a second or less, and the interval between successive pictures was about the same. Muybridge's great difficulty had been to invent a shutter which would act rapidly enough. I have some of these pictures before me now (see Pl. I). They show that what has been drawn by artists and called the "flying gallop," in which the legs are fully extended and all the feet are off the ground, with the hind hoofs turned upwards, never occurs at all in the galloping horse, nor anything in the least like it. There is a fraction of a second when all four legs of the galloping horse are off the ground, but they are not then extended, but, on the contrary, are drawn, the hind ones forward and the front ones backward, under the horses' belly (see Pl. I, figs. 2 and 3). A model showing this actualinstantaneous attitude of the galloping horse has recently been placed in the Natural History Museum. When the hoofs touch the ground again after this instantaneous lifting and bending of the legs under the horse, the first to touch it is that of one of the hind legs (Pl. I, fig. 4), which is pushed very far forward, forming an acute angle with the body. The shock of the horse's impact on the ground is thus received by the hind leg, which reaches obliquely forward beneath the body like an elastic <-spring. Since the instantaneous photographs have become generally known artists have ceased to represent the galloping horse in the curious stretched pose which used to be familiar to everyone in Herring's racing plates (see Pl. II, fig. 1), with both fore and hind legs nearly horizontal, and the flat surface of the hind hoofs actually turned upwards! Indeed, as early as 1886 a French painter, M. Aimé Morot, availed himself of the information afforded by the then quite novel instantaneous photographs of the galloping horse, and exhibited a picture of the cavalry fight at Rezonville between the French and Germans, in which the old flying gallop does not appear, but the attitudes of the horses are those revealed by the new photographs. The picture is an epoch-making one, whether justifiable or not, and is now in the gallery of the Luxembourg. It must be noted that though Meissonier and others had succeeded in representing more truthfully than had been customary, other movements of the horse, such as "pacing," ambling, cantering, and trotting, yet in regard to them, also, more easily observed because less rapid, the instantaneous photograph served to correct erroneous conclusions.