GLIDING 9 



acts at right angles to it. Drift is prevented by the 

 firmly-held string, and lift is the sole result (fig. 5). 



It is only when there is resistance that there is 

 any force to be thus resolved into two. If the 

 string breaks, gravity at once begins to pull the 

 kite to the ground. 



We have now a further question to investigate 

 and, to simplify it, we must consider not the gliding 

 bird, but a flat plane set at a slight upward incline 

 and driven horizontally through the air. A flat 

 plane, having none of the curves and concavities 

 of the bird's wing, is far inferior for purposes of 

 flight, but its simplicity recommends it when the 



W 



Fig. 5. 



To Illustrate Kite-Flying. 



w, horizontal wind blowing against kite, k t. w' (at right angles 

 to k t), line along which the force of the wind acts. 



object is to explain elementary principles. Set at 

 an incline and moving horizontally it will tend to 

 rise. The resistance of the air is equivalent to a 

 wind blowing against it. The wind would act in 



