16 



HOW TO TIB FLIES. 



will penetrate precisely in this direction, and be 

 in no way deflected. The inclination of this 

 line, which we will call the line of penetration, 

 to either surface, will, in general, be proportional 

 to the amount of resistance acting on that surface. 

 Hence in the ordinary hook with round sectioned 



FIG. 4. 



point, the line of penetration will be inclined 

 almost equally to both surfaces (Fig. 4). 



Now (Fig. 5) the force actually applied in hooking 

 a fish is, during the first and critical period, 

 approximately in the direction P S, and, as the 

 point penetrates, gradually veering towards the 



^7 



- --~> 



FIG. 5. 



P S Initial line of pull. P X Penetrating- force. 



Q S Final line of pull. P Y Tearing-out force. 



p Angle of penetration. 



direction Q S. And this force, P S, in accordance 

 with the mechanical law, known as the " parallelo- 

 gram of forces," is equivalent to two forces acting 

 in the direction P X and P Y, and of magnitudes 

 proportional to these lines. The effect of the 

 former is, as we have seen, to make the hook 



