486 THE EXTERIOR OF THE HORSE. 



a man who walks and one who, without advancing, " marks the step" with the 

 same cadence. 



Finally, the graphic method tells us nothing as to the position of the mem- 

 bers in space, an important omission for those whom the analysis of the play of 

 the articular segments interests, either from a point of view of animal mechanics 

 or of the artistic representation of the horse in motion. 



8d. Photography. — Plu)t()graphy has filled up this omission. The extreme 

 sensibility of the plates of gelatino-bromide of silver, the perfections of the 

 objectives and of other modern improvements, have placed this process above all 

 those difficulties which but lately retarded its use in the reproduction of bodies 

 during locomotion. It is capable of representing, in fact, the vertical projection 

 of all the attitudes taken by the animal which moves in front of the instrument, 

 according to a plane perpendicular to the axis of the latter. As the moving 

 object can move along a graduated scale situated below it, nothing is more easy 

 than to ascertain the space it travels over during a unit of time, — that is to say, 

 the velocity with which it is animated. 



The photographic methods furnish two kinds of registrations : 



a. They simply give the image of one or more successive attitudes effected 

 by the animal in motion ; or 



b. They notate a series of successive attitudes with equal intervals of time. 



This latter method, which registers simultaneously the time, the space de- 

 scribed, as well as the diverse phases of the movement, is due also to the wonder- 

 fiil ingenuity of M. Marey, who has given to it the name of chrono-photography. 



a. Instantaneous Photography. — In 1879, Mr. E. L. Muybridge, of San 

 Francisco, effected a veritable revolution in the world of physiologists and 

 artists by sending to Paris a collection of photographs taken instantaneously 

 from horses moving at the walk, the trot, the gallop, and even from race-horses 

 going at full speed.' 



Mr. Muybridge, in order to arrive at this remarkable result, has arranged 

 twenty-four photographic apparatus side by side, all provided with a system of 

 peculiar clicks. Each apparatus was provided with a very fine thread, which 

 stretched across the trail of the horse and was attached to a fixed point situated 

 on the opposite side. The mounted horse, in this manner, successively met and 

 broke each thread, producing thus the unlatching of the corresponding apparatus, 

 which opened and closed almost instantaneously. 



We can understand from this how Mr. Muybridge was able to obtain the 

 truly surprising situations of the members, which it would have been impossible 

 to acquire under ordinary conditions on account of the, at times, prodigious speed 

 of the extremities in certain gaits. In the gallop, for example, contacts are here 

 placed in evidence (Fig. 180) which would readily be doubted if we did not find 

 exactly, by following the series of photographs in the order in which they have 

 been taken, the principal periods of this gait, already known. 



These photographs, however, instructive though they were, failed to be 

 quite satisfactory on account of their small size. In .spite of their subsequent 



1 These photographs have been reproduced in several publications, notably: 

 L'lllustration, no. du 22 Janvier, 1879. 

 La Nature, 1879, ler seniestre, p. 83. 

 Le Cheval, de E. Duhousset, p. 24. 



