Part 3

At C and C, 37 metres, or about 120 feet, apart are "fixed" backgrounds, with vertical threads 5 centimetres, or about two inches, from their centres, with broader threads 30 centimetres, or about 12 inches, from their centres.

For some investigations, readily distinguishable in the plates, "portable" backgrounds are used, consisting of frames 3 metres wide by 4 metres high,--about 10 feet by 13 feet 4 inches,--over some of which black cloth and over others white cloth is stretched, all being divided by vertical and horizontal lines into square spaces of the same description as those of the lateral background.

These portable backgrounds are used when photographing birds and horses, and also wild animals when possible to do so.

L. A lateral battery of 24 automatic electro-photographic cameras, arranged parallel with the line of progressive motion, and usually placed therefrom about 15 metres or 49 feet.

Slow movements are usually photographed with lenses of 3 inches diameter and 15 inches equivalent focus; the centres of the lenses being 15 centimetres, or about 6 inches, apart.

Rapid movements are usually photographed with a portable battery of cameras and smaller lenses.

The centre, between lenses 6 and 7, is opposite the centre of the track T.

For illustrations comprising both "Laterals" and "Foreshortenings," cameras 1 to 12 only are used.

When "Laterals" alone are required, cameras 13 to 24 are connected with the system and used in their regular sequence.

R. A portable battery of 12 automatic electro-photographic cameras, the lenses of which are 1¼ inches diameter and 5 inches equivalent focus; the lenses are arranged 7½ centimetres, or about 3 inches, from their centres. When the battery is used vertically, lens 6 is usually on the same horizontal plane as the lenses of the lateral battery.

In the diagram this battery is arranged vertically for a series of "Rear Foreshortenings," the points of view being at an angle of 90 degrees from the lateral battery.

F. A battery of 12 automatic electro-photographic cameras, similar to that placed at R, arranged horizontally for "Front Foreshortenings," the points of view averaging an angle of 60 degrees from the lateral battery.

O. The position of the operator; the electric batteries; the chronograph for recording the intervals of time between each successive exposure; the motor for completing the successive electric circuits, and other apparatus connected with the investigation.

T T. The track parallel with the lateral battery and covered with corrugated rubber flooring.

M. The model, approaching the point number "1" on the track where the series of photographic illustrations will commence.

An estimate having been made of the interval of time which will be required, between each photographic exposure, to illustrate the complete movement, or that portion of the complete movement desired, the apparatus is adjusted to complete a succession of electric circuits at each required interval of time, and the motor is set in operation. When the series is to illustrate progressive motion; upon the arrival of the model at the point marked "1" on the track, the operator, by pressing a button, completes an electric circuit, which immediately throws into gearing a portion of the apparatus hitherto at rest. By means of suitably arranged connections, an electric current is transmitted to each of the 3 cameras marked "1" in the various batteries, and an exposure is simultaneously made on each of the photographic plates, respectively, contained therein. At the end of the predetermined interval of time, a similar current is transmitted to each of the cameras marked "2," and another exposure made on each of the 3 next plates, and so forth until each series of exposures in each of the three batteries is completed. Assuming the operator to have exercised good judgment in regulating the speed of the apparatus, and in making the first electric contact at the proper time, and that the figures 1 to 12 represent the distance traversed by the model in executing the movement desired, the first three photographic exposures--that is, one exposure in each battery--will have been synchronously made when the model was passing the position marked "1" on the track T; the second three exposures will have been made when the model was passing the position marked "2," and so on until twelve successive exposures were simultaneously made in each of the three batteries. This perfect uniformity of time, speed, and distance, however, was not always obtained.

When this monograph was commenced it was not intended by the author to give any more than a general idea of the method adopted for obtaining the results of his investigation; it has, however, been considered that a few illustrations and brief description of the apparatus devised and used by him may not be without interest to other students.

For the use of these illustrations he is indebted to the courtesy of Rev. Jesse Y. Burk, the Secretary of the University, and to J. B. Lippincott Company, the publishers of "The Muybridge Work at the University of Pennsylvania," a book which contains, among other essays upon the subject, "Materials for a Memoir on Animal Locomotion, by Harrison Allen, M. D.," and "A Study of Some Normal and Abnormal Movements, by Francis X. Dercum, M.D., Ph.D."

Figure 1 is a view of the building containing the lateral battery of twenty-four photographic cameras, all of which were used when as many consecutive phases of an act of motion were required.

Immediately in front of each of these cameras, and detached therefrom, was placed an electro-photographic exposor, a side section of which is represented by Figure 2, in which A is a continuous band of thin rubber cloth impervious to light; the edges of which are bound with strong tape, and arranged to run in a groove, and over two rollers RR which are attached to a frame.

In this endless band are two apertures OO of suitable size, and so arranged that their full openings as they pass each other shall simultaneously take place in front of the center of the lens L.

The upper and lower edges of these apertures are kept taut by light steel rods attached to the tape binding.

To the lower rod of the front aperture is fastened a ring C and a cleat, to which some elastic rubber bands B are attached; these bands are easily removable and their number increased at discretion; in some instances of rapid exposures a tension of twenty-five pounds or more was required. On a shelf of the frame is a magnet M, over the top of which is arranged a steel lever G pivoted near the end D which terminates with a slightly indented projection.

The armature of the magnet is pivoted at H; its upper arm terminates with a shoulder I. S is a spring to prevent the accidental shifting of the shoulder from its contact with the lever when the exposor is ready for its function. N is a set screw to adjust the distance of the armature from the magnet. To prepare for a series of photographic exposures--the plates having been already placed in the cameras--the end of the lever G is placed under the shoulder I; the endless curtain is revolved until the front aperture O is raised to its proper position, when the ring C is hooked upon the projecting point D. A cord attached to the rubber bands B is drawn around the pulley P, and a ring at its end is slipped over a pin, which keeps the spring at a proper state of tension. Upon the completion of an electric circuit the armature is drawn towards the magnet; the end of the lever is released from its contact with the shoulder; the ring C is released from the projecting point D; the front of the endless curtain is drawn rapidly downward; the apertures meet in the center of the lens, form a gradually expanding and then contracting diaphragm, and the exposure is made. A front view of three electro-photographic exposors is seen in Figure 3. The first of these represents the exposor set and ready for an exposure; the second shows the meeting of the apertures at the commencement of an exposure; the third, their position near the completion of the exposure, they having in the meanwhile uncovered the lens to their full capacity.

Figure 4 illustrates a portable battery of twelve electro-photographic exposors; it consists of a rectangular box divided into compartments, open at the front and rear.

In twelve of these compartments are arranged rollers, curtains, magnets, etc., as previously described, and a compartment through which a focusing lens is used. The two end compartments provide for the adjustment of the camera, which is supported in the box to the rear of the exposing arrangements. A cable of insulated wires for connecting the twelve magnets with the exposing motor, contains a wire for the return current. As seen in the engraving, seven of the magnets by the passage of their respective currents have completed their releasing operations. In the eighth compartment the two apertures in the exposing band are in the act of effecting an exposure. The remaining four magnets are awaiting their turn for action.

Figure 5 is a photographic camera divided into thirteen compartments, each having a lens of the same construction, and the same focal length; these are arranged to correspond with the compartments in the electro-exposors.

One of the lenses is provided with a focusing screen, and with it the other twelve lenses are adjusted to a proper focus without removing the plate holder behind them from its position in the camera.