GLIDING 9 
acts at right angles toit. 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 sight 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 
K 
“= 
Fia. 5. 
To ILLUSTRATE KITE-FLYING. 
w, horizontal wind blowing against kite, kK tT. 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 
