CHAPTER II. 

 STABILITY. 



CENTEE OF GRAVITY — POINTS THAT MAKE FOR AUTOMATIC 

 STABILITY VOLUNTARY ADJUSTMENTS . 



There are two things that we must carefully 

 distinguish — stability and the maintenance of equi- 

 librium. An aeroplane, when it has once completely 

 lost its balance, cannot recover it, though some 

 swaying or pitching can, no doubt, be corrected. The 

 stability of a bird is a very different thing from 

 the aviator's careful maintenance of equilibrium. A 

 very strong and sudden gust may throw the bird on 

 his side, or even on his back, and yet he will very 

 quickly right himself. 



Centre of Gravity. 



But we want to know whether a bird in ordinary 

 flight, when there are no very sudden gusts, is auto- 

 matically stable, or whether he has to be perpetually 

 making small adjustments. It is sometimes main- 

 tained that a bird need take no trouble about the 

 question of balance, since his centre of gravity is 

 low down. The great flight muscles, which are 

 massed upon the breast, form a great part of his 

 weight. I have weighed the three pairs of breast 

 muscles of two Wood-Pigeons and those of two 



