Page:Popular Science Monthly Volume 6.djvu/144

132 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

 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 R A (anterior reactions), and from the croup for the hinder part, indicated by the line R P (posterior reactions). Below are given the