Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/24

are cases of dynamic stability, in contradistinction to the static stability of a table or a three-legged stool.

On the other hand, nervous control in the matter of stability does not of the least necessity involve any conscious action of the brain; there are special nerve centres to which the function of maintaining equilibrium is deputed.

It is always difficult in the case of any animal or bird to determine to what extent equilibrium is maintained by nervous agency and to what extent it is automatic. In the case of a bicycle rider we know that the equilibrium is to some extent automatic,^[1] but that it is not so entirely may be reasonably inferred from the fact that it is necessary to learn to ride. In the case of a bird in flight, we have no means of ascertaining directly to what extent equilibrium is maintained by a continual series of reflex adjustments, and to what extent by purely dynamic action consequent upon its geometrical form considered as an inanimate body.

It is almost certain that, for a bird in flight, in any sudden evolution necessary to regain equilibrium after an unexpected gust of wind, the nervous system is called into play, and perhaps at times the whole conscious brain of the bird is involved in the effort to restore the balance that has been momentarily lost. These happenings may be said to be obvious to anyone who has watched the flight of birds in stormy weather. It would seem to follow as a matter of inference that a considerable number of minor reflex adjustments are made and perhaps even a continuous reflex adaptation may take place, invisible to an observer, but the extent to which this is the case can only at the moment be a matter of conjecture.

It is evident that the most promising way to examine the subject, both theoretically and experimentally is by an investigation of the inanimate model or aerodone, and having ascertained all

1. It is well known that a cyclist can frequently ride his machine perfectly when either from cerebral injury or inebriation he is quite unable to walk without assistance.

2