Page:Popular Science Monthly Volume 6.djvu/143

Rh 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 horse-hair, 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 box communicates by a transmission-tube with the registering apparatus. Every pressure exerted on the box moves the corresponding registering-lever. A plate of copper,