POWER AND WEIGHT. 45 



it will work. If, in a lever of the first order, for instance, we have the power 

 and weight, as in Fig. i8, acting in directions which are not parallel to each 

 other, such forces (if the lever be in equilibrium) will then be inversely pro- 

 portionate to the length of the perpendiculars drawn, fiom the fulcrum, to 

 their respective directions. Thus in Fig. i8 we have P : W : : F^: F^. 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. I nttdt not stop 

 to prove the foregoing well-known mechanical law; 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 trying to draw a heavy 

 load, will naturally endeavour to move the levers of his limbs (\-\hen 

 straightening them out) with the power, as nearly as possible, at right angles 



I 



"n. 







I 



**^ 







/ 



■-^^ 







/ 



^-. 







/ 









/ 



; 





N, 





/ 



'~"^»«. 



. F, 



/ 



/ 

 / 



1 





w p 



Fig. i8.— Lever of First Order with Directions of Power and Weight 



Oblique to each Other. 



to each respective lever. Hence he will obtain his results by only slight 

 bending of the joints, and consequently his steps will be short. We may see 

 this action of the levers of the hind limbs 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 straighten- 

 ing out his limbs to their utmost extent (p. 51), 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. 3%) ; 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 wiU 

 contribute little to the attainment of speed. 



