16 



TIIE INTERNAL WiiKK OF THE WIND. 



fact that its inertia now reappears as an active factor. The annexed sketch (Fig. 

 1) shows a typical representation of what might l>e supposed to happen with a 



Ms- J' 



model inclined plane freely suspended in the air, and endowed with the power of 

 rotating about a vertical axis so as to change the aspect of its constant inclination, 

 which need involve no (theoretical) expenditure of energy, even although the plane 

 possess inertia. We see that this plane would rise indefinitely by the action of the 

 wind in alternate directions. 



The disposition of the wind which is here supposed to cause the plane to rise, 

 appears at first sight an impossible one, but w r e shall next make the important ob- 

 servation that it becomes virtually possible by a method which we shall now point 

 out, and which leads to a practicable one which we may actually employ. 



rig. 2. 



Figure 2 shows the wind blowing in one constant direction, but alternately at 

 two widely varying velocities, or rather (in the extreme case supposed in illustra- 



