482 THE EXTERIOR OF THE HORSE. 



to the horizontal at the base of the undulation, g, g, it shows that the diminution of pressure 

 remains stationary. 



Four inscribing needles, corresponding to the four feet of the horse, and perpendicular to 

 the axis of the cylinder, trace upon the latter the contacts and the elevations of the members. 



Each foot is provided (Fig. 175) with a pneumatic bulb (chaussure exploratrice), composed of 

 an India-rubber bulb stuffed with hairs and maintained under the hoof by three claws or catches 

 which fasten it to the shoe. Each time the foot is placed on the ground, the bulb, strongly com- 

 pressed, forces a portion of the air which it contains into the registering drum. When the foot is 

 raised, it again becomes filled with the air which was expelled, and resumes its form. 



This apparatus not being utilizable on the hard ground of ordinary roads, M. Marey has 

 invented another very ingenious instrument which registers the movements of the feet on any 

 kind of soil. 



It consists (Fig. 176) of a sort of leather bracelet, attached by means of leather straps to the 

 canon of the horse. In front, this bracelet carries a flat rubber bulb, communicating through 

 the tube of transmission with the registering drum. Upon this bulb is laid a piece of copper 

 inclined at about 45 degrees and articulated at its superior extremity. Finally, upon a rod par- 

 allel to the plate of copper glides a leaden ball whose variable position permits an augmenta- 

 tion or a diminution of the pressure which this articulated apparatus is capable of exercising 

 upon the rubber bulb. 



When the foot touches the ground, the ball tends to continue its course and suddenly com- 

 presses the bulb ; when the foot is elevated, the inertia of the ball, in its turn, produces a new 

 compression. 



Tubes of transmission (Fig. 177), with a thick wall in order to resist twisting, and maintained 

 along the members by bands of flannel, are connected with the registering drums, themselves 



FIG. 177. Registering apparatus of Marey applied upon the horse at the trol. 



fixed to the cylinder which the rider holds. A ball of rubber, placed in one of his hands, 

 enables him, when it is compressed, to bring the needles in contact with the paper. In this man- 

 ner the tracing can commence or terminate at the will of the experimenter as soon as the gait, 

 of the horse has been regulated. 



Process with the Electric Current. Since his first publications, M. 

 Marey, always in search of improvement, has written the following on this 

 subject: 1 



* Marey, La methode graphique dans les sciences experimentales, et particulierement en 

 physiologic et en m6decine, Paris, 1878, p. 160. 



