THE

POPULAR SCIENCE

MONTHLY.

DECEMBER, 1874.

THE PACES OF THE HORSE.'

N the November MONTHLY we gave a brief account of Prof. Marey's method of representing the step of animals by means of graphic illustrations, with its application to human locomotion; we will now consider it as applied to the more complex paces of the horse. Hitherto, the locomotion of the horse has been mainly studied by means of the eye and ear. In the horse, even at a walk, the motions of the limbs are so confusing as to make it difficult for the untrained eye to follow them, and, when the pace is more rapid, the movements seem hopelessly intricate. Indeed, observation by the eye alone long since gave place to the use of the ear, which, taking account of the rhythm of the steps by the sounds they produce, afforded much more accurate results.

An expedient which greatly aided the observer, and which we shall find of service in explaining the results obtained by the graphic method, was to concentrate the attention on a single pair of limbs, instead of attempting to keep all four under observation at once. Any two limbs thus selected are called a biped, and this is designated according to the relative position of the limbs chosen. The horse may thus be parceled out into six different bipeds. The forward limbs constitute the anterior biped; the hind-limbs, the posterior biped; the two right limbs, the right lateral biped; the two left limbs, the left lateral biped; the right fore-leg and the left hind-leg, the right diagonal biped; the left foreleg and the right hind-leg, the left diagonal biped. The horsey reader may dwell a moment upon this bit of equine technics, as it will materially assist him in understanding the explanation of the various paces.

The quadruped, when walking, has been compared to two men, placed one before the other, the hindmost following close upon the forward step of his companion. According as these persons (who ought both to take the same number of steps) move their limbs simultaneously, or alternately, according as the man in front executes his 1 Abstract of Chapters IV., V., and VI., of " Animal Mechanism," by Prof. Marey. (Vol. XI. of "The International Scientific Series.")

VOL. VI.-9

movements more quickly or more slowly than the one behind, we see reproduced all the rhythms of the movements which characterize the different paces of the horse. Many have seen in the circus the figures of animals whose legs are formed by those of two men, with their bodies concealed in what represents the body of the quadruped. This grotesque imitation bears a striking resemblance to the animal when the movements of the two men are so well coördinated as to reproduce the rhythms of the paces.

Assuming the horse to be composed of two bipeds walking one be

1

hind the other, let these, in progressing steadily, go through the same movements at the same time; that is, let the right leg of each be advanced at the same time and rate, the feet striking the ground so as to give but a single sound. While the body is resting on these, the left legs are simultaneously thrown forward, each striking the ground at the same moment, and so on alternately. The pace thus produced is known as the amble, and is the simplest of all the paces of the horse. The notation of its rhythms is given in Fig. 1. The upper line is derived from the movements of the anterior, or foremost biped; the

FIG. 2.-EXPERIMENTAL APPARATUS TO SHOW THE PRESSURE OF THE HORSE'S HOOF ON THE GROUND.

lower, from the movements of the posterior or hindmost biped. The foot-falls of the right and left foot being produced at the same time by the biped walking in front, and by the one which follows, must be

represented by similar signs placed exactly over each other. In the horse, this agreement between the movements of the fore and hind limbs belongs to the amble, and the notation is the same as would be given by that pace. In the amble, the ear perceives only two beats at each pace, the two limbs on the same side striking the ground at the same instant. In the notation, these two sounds are marked by vertical lines joining the two synchronous impacts. In the amble, the pressure of the body on the ground is said to be lateral, as the two limbs on one side only are in contact with the ground at the same time.

The rhythms of both the walk and the trot have been similarly ascertained and expressed, but beyond this the unaided senses have failed to give us much trustworthy information. It has been reserved for M. Marey to surmount the difficulties of the investigation; and we will now give, though necessarily in an imperfect way, some account of his methods and results.

For the shoe employed in the experiments on man, M. Marey substitutes, in the case of the horse, a

ball of India-rubber filled with horsehair, and attached to the shoe on the under-side of the hoof. The contrivance is shown in Fig. 2. A strong band of India-rubber passes over the apparatus and keeps in its place the ball filled with horse-hair, allowing it to rise slightly above the lower surface of the shoe. When the foot strikes the ground, the ball is compressed, which drives a part of the confined air into the registering instruments. As the foot is raised the ball recovers its form, and again fills with air, to be expelled at the next impact of the foot on the ground. Another form of apparatus, serving substantially the same purpose, and better adapted to `ordinary roads, is seen in Fig. 3. This consists of a kind of leather bracelet fastened by straps to the leg of the horse just above the fetlock-joint. In front of this bracelet, which furnishes a solid point of resistance, is firmly fixed a flat box of India-rubber; this FIG. 3.-APPARATUS TO GIVE THE SIGNALS box communicates by a transmissiontube with the registering apparatus. Every pressure exerted on the box moves the corresponding registering-lever. A plate of copper,

OF THE PRESSURE AND RISE OF THE
HORSE'S HOOF.

inclined about 45°, is connected at its upper extremity with a kind of hinge, while its lower end is fastened by a heavy wire to the upper face of the India-rubber box, on which it presses by means of a flat disk. On a wire parallel to the slip of copper slides a ball of lead, the position of which can be varied so as to increase or diminish the pressure which this jointed apparatus exerts on the India-rubber box. This apparatus is called into action by the movements of the limb; the inclination of the oscillating portions allows them to act on the membrane constituting the wall of the box during the movement of elevation, of descent, and of horizontal progress of the foot.

The general arrangement of the apparatus, as it is applied to the horse, is seen in Fig. 4. Thick transmitting-tubes, not easily crushed, connect the experimental shoes, or instruments, on the legs, with the

FIG. 4.-THIS FIGURE REPRESENTS A TROTTING-HORSE, FURNISHED WITH THE DIFFERENT EXPERIMENTAL INSTRUMENTS; the horseman carrying the register of the pace.-On the withers and the croup are instruments to show the reactions.

registering apparatus in the hand of the rider. The registrar now carries a great number of levers; he must have four, at least, one for each of the legs, and usually two others, which receive their movements of reaction from the withers and the croup. The hand which holds the reins also carries a ball of India-rubber, which is connected by a tube with the registering instrument, and by means of which the tracings may be made to commence at any desired moment.

The tracings furnished by this apparatus, when the horse is at a full trot, and the notation of the rhythm of that pace, as derived from these tracings, are shown in Fig. 5. Above are the reactions taken from the withers for the fore-part of the animal, indicated by the line RA (anterior reactions), and from the croup for the hinder part, indicated by the line R P (posterior reactions). Below are given the