the broadest significance of the words.

A Diagram of the Studio

and the arrangement of the apparatus used for this purpose is here given.

TT represents the track along which the model M was caused to move. B is the background, divided into spaces of 5 centimetres square for the purpose of measurement.

L, a horizontal battery of electro-photographic cameras, parallel to the line of motion (at a distance of 15 metres or about 48 feet therefrom), for a series of 12 lateral exposures.

R, a vertical battery of electro-photographic cameras, at right angles to the lateral battery, for a series of 12 rear foreshortenings.

F, a horizontal battery of electro-photographic cameras, at any suitable angle to the lateral battery for a series of front foreshortenings.

O, the position of the electric batteries, a chronograph for recording the time intervals of exposures, and other apparatus used in the investigation.

A clock-work apparatus, set in motion at the will of the operator, distributed a series of electric currents, and synchronously effected consecutive exposures in each of the three batteries of cameras.

The intervals of exposures were recorded by the chronograph, and divided into thousandths of a second. These intervals could be varied at will from seventeen one-thousandth parts of a second to several seconds.

The task of making the original negatives was completed in 1885; the remaining years have been devoted to the preparation of the work for publication.

Lateral elevation of some consecutive phases of action by representative horses.

Each line illustrates the successive fallings of the feet during a single stride.

After the last phase illustrated, the feet, during continuous motion, will revert practically to their position in the first phase.

The comparative distances of the feet from each other or from the ground are not drawn to scale; and, in any event, would be merely approximate for the succeeding stride.

In the conjectural stride No. 10, phase 3 is very doubtful, phases 5 and 7 seem probable in a very long stride.

DESCRIPTION OF THE PLATES.

The results of this investigation are

Seven Hundred and Eighty-one Sheets of Illustrations, containing more than 20,000 figures of men, women, and children, animals and birds, actively engaged in walking, galloping, flying, working, jumping, fighting, dancing, playing at base-ball, cricket, and other athletic games, or other actions incidental to every-day life, which illustrate motion or the play of muscles.

These sheets of illustrations are conventionally called "plates."

Each plate illustrates the successive phases of a single action, photographed with automatic electro-photographic apparatus at regulated and accurately recorded intervals of time, consecutively from one point of view; or, consecutively AND synchronously from two, or from three points of view.

Each Plate is complete in itself without reference to any other Plate.

When the complete series of twelve consecutive exposures, from each of the three points of view, are included in