DIRECTIONS IN WHICH THE POWER AND WEIGHT ACT. 59 



In the actual levers (those of the hock) which have been taken into 

 consideration, we can see that this is not the case. Also, the nearer 

 a force is to being at right angles with its lever, the greater is the 

 mechanical advantage at which it will work. If, in a lever of the 

 first order, for instance, we have the power and weight, as in Fig. 24, 

 acting in directions which are not parallel to each other, such forces 

 (if the lever be in equilibrium) will then be inversely proportionate to the 

 length of the perpendiculars drawn, from the fulcrum, to their respective 

 directions. Thus in Fig. 24 we have P : W : : F ci : F e. We 

 therefore see that W, which is nearly at right angles to a b, acts much 

 more advantageously than P, which is in a much more oblique direction 

 to it. This would be equally true in the other two kinds of levers. 



a'r 



F/' 



W p 



Fig. 24. — Lever of First Order with directions of 

 Power and Weight oblique to each other. 



The foregoing well-known mechanical law need not here be proved ; 

 as its solution can be found in any book on elementary statics. 



Acting on the principle just enunciated, the cart-horse, with the 

 view of obtaining the utmost mechanical advantage, when tr3'ing to 

 draw a heavy load, will naturally endeavour to move the levers of his 

 limbs (when straightening them out) with the power, as nearly as 

 possible, at right angles to each respective lever. Hence he will obtain 

 his best results by only slight bending of the joints, and consequently his 

 steps will be short. This action of the levers of the hind limbs is well 

 shown by the manner in which he will crouch down behind, when he 

 makes a strong effort with his hind legs while exerting the fore legs 

 but little, as may occur when the roadway is slippery. The galloper, 

 on the contrary, will require the power of straightening out his hmbs 

 to their utmost e.xtent (p. 66), and will thus obtain speed at a lavish 

 expenditure of muscular effort. This is especially well shown in the 

 action of the fetlock joint (Fig. 45) ; for if the pastern be long and 

 sloping, the mechanical disadvantage will be great, but the gain in speed 

 will be equally large. If the pastern be upright, the fetlock will work 

 advantageously as far as the weight to be moved is concerned ; but it 

 will contribute little to the attainment of speed. 



