H. Skey. — On the Lifting Power of Inclined Planes m Aerial Transit. 171 



prolonged power of buoyaucy under certain circumstances with scarcely 

 any flapping of the wings. On watching carefully this kind of flight 

 it can be seen that the wings are kept nearly horizontal but with the 

 anterior margin very slightly elevated above the posterior and thin edge 

 of the wing. The angle thus formed by the wing with the line of motion 

 is very small, indeed if it were not small it is easily proved that the 

 onward motion of the bird would be quickly arrested from the quantity 

 of air which would require to be displaced. It does indeed appear 

 wonderful that a bird weighing perhaps ten pounds can be supported in 

 this manner so long a time when it has once obtained a certain velocity. 

 In every-day life, however, we have many instances of the lateral pressure 

 of the au' on planes in a direction transverse to the motion ; we have only 

 to walk slowly with a piece of iDaper held at an oblique angle to the line of 

 progression, or to open an outer door of a building an inch or two if the 

 door opens outwards when the wind is blowing obliquely in, when it wUl be 

 at once noticed, and if a gale of wind is blowing it will be found impossible 

 by main force to prevent the door flying open in a surprising manner if it 

 is once opened a few degrees. 



If solids are made to impinge on planes, then the angle of reflection is 

 equal to the angle of incidence. If, however, a current of air impinges on 

 a plane, then the elasticity of the air comes into play with very curious 

 results. The following experiments, which I now repeat, were made with 

 a view of ascertaining the action of the au* on inclined planes at different 

 angles : — 



Experiment, Xo. 1. — If a book one or more inches thick is placed flat on 

 a table, and any small light body is also placed on it, about as far beyond 

 the book as the book is thick, it will be found impossible to so blow across 

 the book as to send the light body away, for instead of moving from 

 you it flies towards you. 



Experiment, No. 2. — If a current of air is blown obUquely onto a table 

 covered with sawdust, we shall observe that the whole of the sawdust 

 affected by the wind is not blown in the direction of the current, but that a 

 considerable portion is actually blown along the plane towards the primitive 

 current. 



Experiment, No. 3. — If a current of air blown through a tube impinges 

 at any given oblique angle upon a point in a horizontal plane, the incident 

 current I P (figure 1) is not reflected at an equal angle to the plane from 

 the point P along the line P Q, as might be supposed ; for, if a lighted 

 taper be held at Q, the flame is actually drawn downwards, and if the taper 

 be moved over a large range of angular vertical measurement the flame is 

 still drawn towards the plane. 



