FOR PEACE AND WAR. 133 



measure of contraction is further limited by the disposition of 

 the weight which they have to sustain as well as to propel, and 

 the position of the superincumbent weight in the unburthened 

 animal is the creature's own centre of gravity, being the point at 

 which its entire weight is connected. 



This point in the horse, according to the various proportions of 

 the animal, is found more or less in advance of the flank, and 

 commonly in the middle of the "false" or "back ribs." Now, 

 it is j)lain that, in proportion as the hind leg is brought up in a 

 higher state of contraction, the foot, which forms the point of 

 resistance to the whole propelling apparatus, will be thrown to a 

 corresponding extent further forward, and so, in an extreme case 

 such as we have supposed, will come to the ground considerably 

 in advance of the centre of gravity ; but when this weight is thus 

 disposed behind the point of resistance, the exertion of power is 

 calculated rather to lift than to propel it, and consequently, if 

 there were no other element to be taken into account in our 

 calculations, we should conclude on this branch of the subject 

 that the centre of gravity in the animal as he stands gave the 

 limit of which we are in search ; and when the animal is only 

 beginning to progress, such is, in fact, the proper limit assigned 

 to the advance of the hind foot, but so soon as motion commences, 

 a new force comes into operation in the momentum, compounded 

 of weight and velocity of the moving body, which of itself tends 

 to carry the centre of gravity forward with an independent 

 velocity, proportioned to the original speed by which it is 

 generated. 



In high speed, therefore, the point of support may be taken by 

 the hind foot considerably in adv^ance of where the stationary 

 centre of gravity would be, since the weight is continually borne 

 forward by a force, independent of that about to be exercised by 

 the extending limb, and which suffices to carry it over and past 

 the point of resistance, before each accession of muscular energy 

 from the propelling members comes to bear upon it. 



This force being in proportion to the velocity, it follows that the 

 greater the speed the more contracted will be the condition of 



