FIG. 9.—INSTANTANEOUS PHOTOGRAPH OF A MAN JUMPING OVER AN OBSTACLE.
Before entering into a detail of the experiments, we shall point out the general arrangement of the Physiological Station of Paris. [Fig. 5] gives a general view of the grounds and buildings.
On these grounds, which were laid out by the city of Paris as a nursery, there is a circular road, thirteen feet wide, designed for the exercise of horses, and, outside of this, a footpath for men. All around this road there runs a telegraph line whose poles are spaced 164 feet apart. Every time that a person walks in front of a pole a telegraphic signal is given, and this is inscribed in one of the rooms of the principal building. Further on we shall speak of this sort of automatic inscription, by means of which we ascertain at every instant the speed of the walker, the variations therein, and even the frequency of his steps. In the center of the track there is a high post that carries a mechanical drum which regulates the rhythm of the gait, and which is actuated by a special telegraph line running from one of the rooms in the large building, wherein the rhythm is regulated by a mechanical interrupter.
From the center of the circle, likewise, there starts a small railway upon which runs a car that forms a photographic chamber, from the interior of which is taken a series of instantaneous images of the horses or men whose gait we desire to analyze.
[Fig. 6] represents the photographic chamber in which the experimenter places himself. This chamber is mounted upon wheels, and runs upon a railway in such a way that it can approach or move away from the screen according to the objectives that are being used and to the size of the images that it is desired to obtain. As a general thing, it is advantageous to place the photographic apparatus quite far from the screen, say about 164 feet. From this distance the angle at which the subject whose image is being taken does not change much during the time it takes to pass before the black screen. From the exterior of this chamber are seen the red windows through which the operator can follow the different motions that he is studying. To have the different acts performed he gives his orders through a speaking trumpet. The front of the chamber is removed in [Fig. 6] in order to show a revolving disk provided with a small window through which the light enters the photographic objective intermittently. This disk is of large dimensions (four and three-quarters feet in diameter), and the window in it represents only one hundredth of its circumference. It follows from this that if the disk makes ten revolutions per second, the duration of lighting will be but one thousandth of a second. Motion is communicated to the disk by a train of wheels which is wound up with a winch and which is actuated by a weight of one hundred and fifty kilograms placed behind the chamber. The motion of the disk is arrested by a brake, and a bell maneuvered from the interior serves to give orders to an aid either to set the disk in operation or to stop it.
[Fig. 7] shows the inner arrangement of the chamber, a portion of one of the sides being removed to show the photographic apparatus, A, placed upon a bracket before the screen. This apparatus receives long and narrow sensitized plates that exactly hold an entire image of the screen. At B is the revolving disk which produces the intermittent illuminations, and at D is a cut-off which is raised vertically at the beginning of the experiment, and which is allowed to fall at the end so as to allow light to enter only during the time that is strictly necessary. E is a wide slit in front of the objective, for allowing the latter to take in the field in which are occurring the motions that are being studied.
The darkness that reigns in the rolling chamber permits of manipulating the sensitized plates therein at ease, and of changing them at every new experiment.