40 THE FLIGHT OF BIRDS 



body rises, and this means 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- 

 off — 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 



