THE SCIENCE OF CASTING A TROUT FLY 167 



to the line, and it is thereafter the line passes the rod point, 

 and, unrolling on itself, pulls the fly backward or forward 

 to its destination. (See Diagram 14). 



When a correctly accelerating force is applied to the rod 

 with an ordinary length of cast and under ordinary circum- 

 stances, the line and fly must travel backward or forward, 

 above, or outside the radius, of the top of the rod. 



MISAPPLIED FORCE WHEN CASTING 



If, however, at the commencement or during the backward 

 action of the rod a snatching or jerking impulse is given, 

 the line will overtake the rod at a lower level than its top 

 ring and may collide with it. When a correct impulse 

 is given, the rod point should not carry its impetus beyond 

 the level at which its switching momentum has been 

 checked, for the energy contained in the bend of the rod 

 becomes exhausted by the time the rod has straightened 

 itself. 



If then, at the end of the downward stroke, the fisherman 

 finds his rod vibrating, thrashing the water, or hitting the 

 lawn on which he may be practising, he will know that this 

 is entirely due to a faulty method of applying force to his 

 rod. 



This fault may be compared to that known to golfers as 

 " snatching." 



If the backward and forward efforts in casting should be 

 from nothing, i.e., a position of inertia, to maximum, or 

 in other words be of an accelerating nature, then the reverse 

 actions must be wrong. 



To start the rod by a sudden jerking impulse leads to the 

 following results : 



In the forward cast the line is directed upward instead of 

 forward. 



The line unrolls on itself in a large curve, and its 



