40 THE FLIGHT OF BIRDS 
body rises, and this nfins a relative lowering of 
the wings. 
It is a wonderful thing that the air can supply a 
tolerably firm support, something that will do duty 
as a fixed point. Archimedes undertook to lift 
anything if he could find a fulcrum for his lever. 
The bird finds a fulcrum where Archimedes would 
not have thought it worth while to look for one. 
The bird when flying is, in fact, taking a number 
of jumps. Often when he appears to be travelling 
in a horizontal line he is really, as Professor Marey 
has shown in his wonderful photographs that give 
successive phases of the process, rising and sinking 
with each down-stroke and up-stroke. Thus the 
bird’s apparently horizontal line of progress is often 
an undulating one. But when he is travelling with 
great velocity, then there is no drop between the 
strokes; of this Professor Marey has obtained 
evidence. But there is probably some reduction 
of pace. Even though there is no rise with each 
stroke, the bird is nevertheless taking a series of 
jumps. And the marvel of these jumps, with no 
better take-off than the air, no amount of thinking 
can do away with. A man who is accounted a good 
high jumper can do very little if he has a poor take- 
offi—if the ground is spongy. We all find it very 
hard work walking over soft snow when at each step 
we sink up to our knees before we find anything 
firm and resistant beneath our feet. We walk 
slowly and with labour along a beach where the 
small pebbles let our feet sink in. We climb with 
effort up a volcanic cone where, each step that we 
take, the small rounded ashes let us slide downward 
