POWER AND WEIGHT. 43 



the Lfirst order of lever "will serve onr turn here, if we imagine the power to 

 be exerted in propelling the body to the front, through the tibia (the bone 



-TV 



F 



1"^ 



Fig. i6.— -Second Order of Lever. 



that is situated between the hock and stifle), while the toe rests dn the 

 fulcrum formed by the ground (Fig. 40). 



Third Order.— W.P.F. (Fig. 17). This form of lever occurs in a fishing 

 rod, with which a man tries to lift a heavy trout out of the water. The 

 weight is at the point of the rod ; the fulcrum, at the butt, is formed by one 

 hand; and the power is suppHed by the other hand, a little above the butt 

 We have this lever in the bones below the hock, when the horse bends that 



F 



7;^ 



g 



/ F 



Fig. 17.— Third Order of Lever. 



joint hj lifting his foot off the ground (Fig. 41)- Here, the power is 

 derived from the muscle which is placed in front of the tibia ; the weight is 

 that of the limb below the hock ; and the fulcrum is formed by the iibia. I 

 may remark in passing that the os caicis does not come into this lever, except 

 in counterbalancing, to some slight extent, the weight of the leg below the 

 hock. 



Relations between the Power and Weight in Levers.— 



The farther the power is from the fulcrum, the greater will be the mechanical 

 advantage at which it will act; and vice versL Thus, if one arm of a 

 see-saw is longer than the other, a comparatively light weight at the 

 end of the former will counterbalance a heavy one at the extremity of the 

 latter. Also, the longer an oar is " in-board," as in an outrigger, the greater 

 will be the power which a rower wiH have. If we apply this principle to the 

 horse, we shall see that the longer is the os mkis (Figs- 39 and 40), the 

 greater wiU be the mechanical advantage at which the muscles of the 

 gaskin will act in kicking or propelling the body forward. As length of m 



