of a propeller, driven at incredible speed, its immobile wings 
sustaining the weight. The wings of the bird, on the other 
hand, not only lift the body from the earth, but they sustain 
it in the air by their marvellously complex movements. And 
this is true, in varying degrees of bird, and bat, and butterfly : 
of dragon-fly and beetle. 
Even they who must perforce dwell in crowded cities see 
daily the miracle of flight performed. For even here sparrows 
and pigeons, at least, are everywhere, and it is just because 
this is so, just because they have become so ‘‘ commonplace,” 
that their very presence escapes notice. Yet the wonder of 
their movements in the air might become a never-ending 
source of delight if only we went about our business with 
open eyes and minds alert. 
Watch the wary sparrow spring from the ground and dart 
across the road, or up to the nearest house-top. How is it 
done with such incredible speed and accuracy ? 
To understand even the broad principles of flight, it is 
necessary to realize, at the very beginning, that the wing, 
in the case of the bird, or the bat, is a specially modified 
fore-leg. So also is the human arm and hand. But its 
transformation has not been so drastic as that of the bird, 
or the bat. Wherein the hand has been, as it were, com- 
pletely re-modelled to fulfil the peculiar and complex functions 
demanded of it. 
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