THE FRAME WOEK OF THE HOESE. 23 



the position x 3 # 3 , and in this case it will slant the 

 other way, the end c d being lower. 



Now this is just what takes place when a rider is 

 put on a horse's back in analogous positions, leaving 

 out of the question for the moment the influence of the 

 overhanging head and neck on the stability of the 

 machine, deferring back to Plate I., we see, in fact, 

 that the points a and d of the board correspond with 

 the hip and shoulder joints A and D on the one side 

 of the horse, as b and c do with the same joints on the 

 other, and these are the two points of support of the 

 back, whilst p corresponds with the fourteenth vertebra 

 at E ; and, still leaving the head and neck out of the 

 question, the rider placed here would sit not only 

 directly over the centre of motion, but also over the centre 

 of gravity that is to say, a central point equally 

 removed from each of its four supporting points ;* he 

 would occupy the apex or summit of a regular pyramid, 

 the most stable of all forms of construction. 



Let us now suppose the rider, or the weight, whatever 

 it may consist of, placed farther back towards the horse's 

 loins, corresponding to the point p 1 of fig. 1. What does 



* It is to be remarked that the points on which the horse's feet 

 stand seldom coincide exactly that is, lie precisely under the 

 shoulder and hip joints respectively. The lore feet especially 

 seldom reach, even with the toes, the perpendiculars from the 

 shoulder- joints. With Eclipse they did so naturally, with tolerably 

 well-built horses moderately "set up" they will generally do so; 

 and if the setting-up is carried beyond a certain point, they not 

 only reach but project before them, the two hind feet either 

 following proportionately in the same direction, or going to the 

 rear, as may be seen when the horse-dealer " stretches a horse," 

 in order to show how much ground it covers. There is a great 

 difference, too, between the jointed flexible legs of a horse and the 

 rigid straight ones represented in fig. 1. An animal always exerts 

 a certain amount of muscular action to maintain its balance even 

 -when resting. 



