GENERALITIES OF THE GAITS. 477 



Colin, and Raabe and his disciples, who admit the absolute equality 

 of the two phases of contact and of elevation. 



These two periods of the walk, well explained by M. Lenoble du 

 Teil,' have been called by him periods of exchange of the contact. In 

 the middle of each of them there evidently exists a moment during 

 which the body is equally supported l)y the two members at the same 

 time. This author has also had reason to make three grou])s of the 

 preceding six periods of the complete step : two of advancement, two 

 of complete contact, and two of change of contact. 



It is easy to understand that the change of the contact with the 

 soil, in the walk, for example, is all the longer and easier to ascertain 

 as the gait is slower. As soon as the latter is accelerated so as to sim- 

 ulate leaping, it is then seen to diminish correspondingly. Finally, 

 it disappears immediately as soon as leaping is manifested. We will 

 explain the particular details of this in discussing the gallop. 



It is therefore through error that Messrs. Marey and Pages '^ claim 

 to have discovered, in the marched gaits, the periods of double contact, 

 the importance of which they have besides enhanced, by saying that 

 their existence permits the step of these quadrupeds to assimilate com- 

 pletely that of man, in whom these periods are very evident. 



The speed, ]', of a gait is valued by the distance passed over 

 during a unit of time ; naturally, it is proportional to the length, L, 

 and the number, N, of the steps. The predominance of one of these 

 factors varies with the other in an inverse sense. Thus is deduced the 

 empirical formula T^^ LN. With equal speed, if iV augments (as in 

 small horses), it follows necessarily that L diminishes, and vice versa 

 (as in large horses). 



In gaits in which the body is always in contact with the ground, the 

 body and the feet are not advanced with the same velocity. This is due 

 to the fact that the centre of gravity tends to move in a uniform manner. 

 Hence it is necessary that the feet progress more rapidly than the body 

 to recover the time which they have lost in contact with the ground. 

 The longer their contact the greater will be their velocity compared 

 ■to that of the body. This interesting fact has been well established, 

 as early as 1873, by M. Lenoble du Teil, who has republished it 



' Lenoble du Teil, Etude sur la locomotion de I'homme et des quadruples en g6n6ral, Paris, 

 1877, p. 14. 



This expression has also been employed by M. Raabe in his work entitled M^thode de 

 haute ^cole d'^quitation (p. 29 et seq.}, edited at Marseilles in 1863. This author, however, 

 appears not to have deduced the results which follow from it. 



2 Marey et Pages, Mouvement du niembre pelvien chez I'homme, r616phant et le cheval, in 

 Comptes-Rendus de TAcadi^mie des sciences, 18 Juillet, 1887. 



