FLIGHT AND ITS IMITATION. 
397 
to the surface of its wing ; yet in exact proportion to the re- 
quirements of sustentation and progression in the atmosphere. 
The mechanical conditions of flight must, therefore, he thoroughly 
understood before they are attainable. 
To imitate Nature is a natural and laudable aspiration, and it 
would appear more hopeful to strive after success in obedience 
to a precedent, than to attempt to put in harness an unknown 
power for the accomplishment of objects for which in Nature 
there is no visible or tangible precedent whatever. 
I venture to say that if certain recent discoveries had been pub- 
lished for centuries previously, as objects to be attained by con- 
stant study and application, the uninstructed portion of mankind 
would have held in derision the notion of a future for the electric 
telegraph, the phonograph, the phonoscope, and the telephone. 
Resistance is no less caused by a surface in motion against the 
air than by the air in motion against the surface. With this 
great advantage in favour of the surface moving against the air, 
that the speed and pressure can be regulated to the point of 
efficiency and safety. It is this resistance which the bird creates 
for itself in the calm of a sultry summer’s day by the agitation 
of its wing-surface ; in obedience to which certain mechanical 
actions are evoked, tending to impel it through the still air. 
The resistance to the down-stroke of the wing and the resistance 
to the up-stroke are resolved into a sustaining and propelling 
power. It is conceded that any mechanical contrivance which 
will cause the resistance encountered by the up- and down- 
stroke to be resolved into a single force, must in air have the 
effect of flight, other matters being in accordance. 
But, apart from theory, let us see what is the precise action 
of the air when agitated by the up- and down-stroke of a wing. 
We need not theorize here — we can submit the matter to ocular 
demonstration, and the effect is conclusive as well as surprising. 
Not to my knowledge has any similar explanation been afforded. 
Take the natural wing of a bird — in my experiments I used 
the wing of the carrion crow, in length twenty inches — approach 
a gas flame, and wave the wing, presenting to the flame the an- 
terior edge, commencing at the base, and drawing it towards you 
until the tip is reached. It will be observed that the flame is 
sucked in underneath the wing in both the up- and down-stroke 
throughout its whole length. Now present to the flame the 
posterior edge ; the same action is observable in both the up- and 
down-stroke, until near the tip, where the flame will alter its 
behaviour and be forcibly expelled, the strong current effecting 
sometimes its extinction. 
Here we have the bulk of the wing-surface rendered effec- 
tive in support, in both the upward and downward action, whilst 
towards the tip of the wing resides the propelling action. 
