398 WORK OF THE PHYSIOLOGICAL STATION AT PARIS. 



I have there been able to lesunie, under new and quite exact condi- 

 tions, my studies of the flight of birds, experimenting upon a great 

 number of different species. By means of chrono-photography it has 

 been possible to obtain a series of the successive phases of a wing 

 stroke in tlie form of instantaneous photographs, as many as one hun- 

 dred per second being recently obtained. Thus, in a wing stroke so 

 rapid that the eye can not follow it, the apparatus shows with perfect 

 precision more than twenty successive ])hases, passing from one to 

 another by almost insensible transitions. 



The gaits of the horse have been determined, not only as regards 

 the su(;cessive beats of the feet, but in a complete manner; that is to 

 say, by fixing the entire series of actions and reactions that are involved. 



The great circular and perfectly level track permits us to analyze the 

 walking and running paces of man as well as his various physical exer- 

 cises, and to determine the conditions most favorable to the proper 

 utilization of muscular force. These studies have been conducted with 

 regard to their practical application, either for the amelioration of the 

 condition of the soldier or for the imi)rovement of the methods of i)hys- 

 ical education. In these researches I have been greatly aided by the 

 officers of the army and by my former assistant, M. Demeny, who, up 

 to recent years, performed his duties with much skill. 



I would not speak of the ex[)eriments made at the Physiological Sta- 

 tion on a great many x)hysical and mechanical phenomena, such as the 

 fall of bodies, the resistance of the air, the vibrations of strings, the 

 movement of li([uids, the measurement of forces and of work, etc., 

 were it not that tliese studies are intimately connected with the physi- 

 ology of movement. 



In fact, in the locomotion of man and of terrestrial animals the me- 

 chanical actions of the muscles consist in displacing the center of grav- 

 ity of the body, either by lifting its weight or by imparting to it a 

 movement of translation. From these actions in various directions we 

 can deduce the amount of work expended. In aerial locomotion the 

 action of the muscles communicates a similar amount of movement, 

 both to the body of the animal and to the mass of air struck by the 

 wings. The same division occurs in different kinds of locomotion upon 

 the ground and in the water. 



The experiments already made at the Physiological Station have 

 given the a])proxinuite value of the work exj^ended in the different 

 kinds of locomotion. These determinations have been checked by two 

 different methods; on the one hand, by measuring the forces and the 

 «|uantities of mavement by means of registering dynamometers; on the 

 other, by estinniting the forces acting at each moment by the accelera- 

 tion imparted to the mass of the body.' The results derived from these 

 two sources show variations of but slight importance, that will cer- 

 tainly disappear when the methods of analyzing movements and forces 

 shall be perfected. 



• See Le Mouvement, Chapter IX. 



