H. Skey. — Tntroduction of the Tension Wheel in Aerial Transit. 173 



over, the nature of the surface of the plane, and also the nature of the 

 impinging body, materially influence the results. 



These experiments assist in explaining the prolonged saihng flight of 

 birds, for, when the wings are retained so as to form a very small angle to 

 the horizontal line, there will still be a very considerable upward pressure 

 to sustain the bu'd in its progress through the air ; they also show that if, 

 as has been asserted, birds prolong their flight by gradually increasing the 

 angle of their wing planes, then that alteration need be and indeed can be 

 only within very narrow limits ; for a bird sailing in still air with its wing 

 planes at an angle of 5° and travelling with a velocity of 23 miles per hour 

 receives a support of 1'13 lbs per square foot of wing area, while if it alters 

 its planes to 20° it only receives about half as much more support, even if 

 we suppose its velocity unaltered ; four times the angle of inclination to the 

 horizon only giving one half more support. Now the resistance horizontally 

 which the wing encounters at 20° is about 16 times as great as what it 

 encounters at 5°, which would quickly arrest its progress, somewhat similarly 

 to what may be observed when pigeons are alighting, for when near the 

 ground they suddenly raise the anterior portions of their wings, theii* 

 horizontal motion is stopped, a very slight rise is also noticed, and they 

 alight without injury. 



It appears, therefore, that it is only within small angular ranges that 

 the alteration of wing plane prolongs the power of flight. 



The wing of a bu'd is so constructed that it can be retained with 

 sufficient rigidity at these minute angles. 



Abt. XV. — Introduction of the Tension Wheel in Aerial Transit. 



By Henky Skey. 



Plate IV. 



[Read before the Otago Institute, 9th October, 1877.] 



Attempts have been made to solve the problem of aerial flight by means of 



planes moved at great velocity in a rectilinear direction, but the difficulties 



to be overcome in starting, balancing, and steering them appear to present 



insuperable obstacles to success. The difficulties are not much lessened if 



we rotate rigid planes, if built up from a centre and worked therefrom, as 



great strength and inseparable weight would be required, and the weight of 



the axis and all the parts near it would act as so much dead weight. 



That however a considerable ascensional force can be imparted to 

 revolving planes is easily shown by the following experiment : — I take a 



