274 THE STRUCTURE AND LIFE OF BIRDS CH. VII 
important questions of balance have yet to be decided. 
Moreover, it cannot as yet leave the earth without iron 
rails on which to get up pace. Wherever it might 
alight, it would remain helpless as a stranded ship. 
But the man who has got so far towards solving the 
problem of flight may well get further. 
Conclusion. 
This ends my account of flight. Much, I hope, 
has been made clear, but much remains that is 
inexplicable. Mathematicians will, no doubt, some 
day arrive at a formula of flight that will claim to 
be a complete solution of the problem. Nevertheless 
birds will still excite the wonder of men. Even those 
who can quote the formula at a moment’s notice will, 
when they look at a Swift doing his sixty miles an 
hour for mere play, or if they happen to see a soaring 
Adjutant, relapse for a moment into blank astonish- 
ment, the mental state of the Pacific islander when a 
steamship first invades his lonely seas and claims a 
place in his philosophy. It will always be difficult to 
forget for long together, that, however much is learnt 
on such a subject as flight, a great deal more remains 
to be learnt. 
SOME OF THE LITERATURE OF THE SUBJECT. 
Marey’s Vol des Orseaux. 
Marey’s Animal Mechanism (International Sci. Series). 
Alix’s Appareil Locomoteur des Oiseaux. 
The article on “ Flight” in Newton’s Dictionary of Birds. 
Pettigrew’s Avimal Locomotion (International Sci. Series). 
Books and papers referred to in the footnotes in the course of 
this chapter, 
