body is thrust, or drawn, through the air by means 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 “ common-place,” 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, completely re-modelled to fulfil the 
peculiar and complex functions demanded of it. 
