NATURE 



39 



THURSDAY, MAY 21, 1874 



ON THE ACTION OF THE HORSE 



N' O dynamical problem, whether physical or biological, 

 can be considered to be based on a substantial 

 foundation until some method has been applied to it, by 

 which an accurate statical record can be obtained of the 

 exact relations of all the forces which, at any given 

 moment, operate in its production. The great prepara- 

 tions which are just completed for the observation of the 

 approaching transit of Venus show how difficult it some- 

 times is to obtain the desired results ; and the value 

 attached to the production of photographic records of the 

 phenomenon proves the importance of permanent regis- 

 tration. 



The movement of the legs of quadrupeds during pro- 

 gression is a difficult problem, as is shown by the fact 

 that there are still many contradictory opinions main- 

 tained by high authorities on the subject. The difficulty 

 in this case depends oii there being the four different 

 limbs to be considered at the same time, which it is 

 impossible to do without a considerable amount of prac- 

 tice. Till lately, those who have studied the point, as 

 far as the horse is concerned, have relied on their sight or 

 hearing, and have checked their results by the impression 

 left on the ground by the animal's hoofs. The observa- 

 tional power of each individual author has therefore 

 always been an element in the problem, and it is very 

 difficult to estimate the magnitude of that part of it, 

 in any given case, correctly. Within the last few years, 

 however, a much improved method has been introduced, 

 which, judging from the discussion that has been carried 

 on in the Ti;iiL-s with reference to the attitude of the 

 horse in Miss Thompson's picture of the " Roll Call," is 

 but little known by some who have very decided opinions 

 on the movement of the legs. 



In a work, published last year, entitled " La machine 

 Animale," by the eminent French physiologist, M. E. J. 

 Marcy, of Paris, a full account will be found of an appa- 

 ratus constructed by the author, by means of which the 

 movements of each of the legs of the horse during pro- 

 gression are synchronously registered on a uniformly 

 moving strip of paper, in such a way that the tracings ob- 

 tained from all the four can be superposed and compared 

 at the leisure of the experimenter, and the simultaneous 

 positions of each leg accurately estimated. What is more, 

 M. Marey has also introduced a beautiful writing language, 

 as it may be termed, by means of which it is as easy as in 

 music to transcribe the results obtained with his instru- 

 ment and read them off in their proper sequence. A 

 knowledge of this language makes it possible to refer any 

 given position, such as that of the horse in the " Roll Call,"" 

 to it; from which it may be compared with the results ob- 

 tained by direct experiment. Such being the case, it is 

 not difficult to transfer the vagueness of " opinion " into 

 the certainty of fact, and settle a question once for all. 



i\l. Marey's method is the following : — The record of the 

 movement'of each limb is obtained by the employment of 

 small caoutchouc bags filled with air, similar in m.ost 

 respects to those with which he has obtained such valu- 

 able information on the movements of the heart. Two of 

 these bags are connected together by an india-rubber tube; 

 Vol, X.— No. 2^8 



one is placed in contact with the foot, and the other with a 

 small lever which writes on the recording paper. Each 

 leg is provided with its pair of bags. Movements in either 

 foot compress the bag connected with it, and this, by 

 distending that at the other end of the tube, raises the 

 lever. The levers write, one above the other, on a revolv- 

 ing drum held in the hand of the equestrian. We must 

 refer our readers to the work itself if they desire to see 

 the tracings obtained, mentioning that at the moment each 

 foot touches the ground a sudden rise of the lever is the 

 result, which is followed by an equally abrupt fall im- 

 mediately it quits it. 



Results even more satisfactory than those obtained by 

 the use of the above- described air-bags might be obtained 

 by adapting a simple electrical contact-maker and wirer 

 to the shoes of the horses, which by acting on small 

 electro-magnets would produce movements on levers 

 which recorded similarly to those employed by M. 

 Marey. 



It will be necessary to give a short description of the 

 mechanism of walking generally in order to explain that 

 of the horse. Man in walking on level ground gives suffi- 

 cient impulse to the body at each step to enable him to 

 lift the one foot at the instant that the other touches the 

 earth. Representing the time of contact of the right foot 

 by a continuous hne, ihat of the left foot by a super- 

 posed dotted line, and the exact period of the interval 

 between the raising and lowering of either foot by the 

 gap between the succeeding hnes, the human walk on level 

 ground would be drawn thus : — 



Whilst going uphill, however, there is a period during 

 which both feet are on the ground together, which may be 

 indicated thus : — 



Whilst, again, in running, there are periods, as we all 

 know, during which both feet are off the ground together 

 thus : — 



Turning to the case of the horse, and using the same 

 method of illustration, we may employ the excellent com- 

 parison suggested by Duges, in which he shows that any 

 of its different steps may be imitated by two men, one 

 behind the other. Now suppose these men, the hinder 

 one with his hands on the shoulders of the one in front, 

 to walk " in step," that is, with the right and left feet 

 moving simultaneously ; then, if their movements be re- 

 corded as above, with the steps of the hind man placed 

 below those of him in front, the following would represent 

 them : — 



both would have their similar feet off and on the ground 

 at the same time ; and reverting to the horse, this formula, 

 as it may be termed, which represents the legs of the 

 same side off the ground together, is that of the " amble," 

 a method of progression natural to the giraffe, but only 

 acquired by special training in the horse. 



Again, suppose that two men, instead of walking " in 



