THE HORSE IN MOTION. IO9 



trot into two periods by the alternate feet, so that in the trot the 

 horse is twice clear of the ground in each stride. The step being sup- 

 posed to be a constant quantity in the fast trot, the stride can be ex- 

 tended only by increasing the space which the body passes over with 

 its centre of gravity unsupported. While in the slow or jog trot this 

 distance is small, in the flying trot it exceeds that in which the body is 

 supported, and hence arises the great difficulty in attaining a high rate 

 of speed. As was stated in the preceding chapter, the law of falling 

 bodies increases the difficulty in locomotion in the ratio of the square 

 of the time in which the body is so unsupported. It becomes a ques- 

 tion of power of resistance, or strength of the parts on which that 

 resistance depends. On the other hand, the strength of the parts, as 

 the joints, bones, ligaments, and tendons, involves increase of weight, 

 which is incompatible with rapidity of movement, without a corre- 

 sponding increase of power of the muscles and weight of the body to 

 be borne, so that the limits of speed attainable in a trot are reached 

 more rapidly than in a run, in which the limit is to be found in the 

 measure of activity. 



In the run the stride is divided into five parts, instead of two, as in 

 the trot, each limb taking its turn as supporter and propeller, with a 

 scarcely appreciable interval between, and an interval between the last 

 fore leg and the first hind one representing a fifth of the whole stride. 

 Each limb, therefore, works one fifth of each stride and rests the other 

 four fifths. The longest stride given of the run, in the examples fur- 

 nished, is that of " Florence A." (Plate XVII. ), where it is given at 

 twenty feet six inches, or a little more than four feet as the portion 

 assigned to each limb. It will be observed that in the trotting horse 

 (Plate XXXVI.), whose stride is given at eighteen feet three inches, 

 the time of support by two limbs is about the same, while the time in 

 which there is no support given is greater, and divided into two inter- 

 vals. So in Plate XL. the gravity is supported about half the time by 

 two limbs, and the other half by none, alternating every four feet. 

 Notwithstanding the wonderful mechanical provision in each of the 

 four limbs to secure uniform support and propulsion while the feet rest 

 upon the ground, the instant that the body ceases to be supported it 



