achine, but something carried by it. The bird is a
complete machine in itself. Our aerial ship must be machine plus man.
Now, a man is, I believe, heavier than any bird that flies. The limit
which the rarity of the air places upon its power of supporting wings,
taken in connection with the combined weight of a man and a machine,
make a drawback which we should not too hastily assume our ability to
overcome. The example of the bird does not prove that man can fly. The
hundred and fifty pounds of dead weight which the manager of the
machine must add to it over and above that necessary in the bird may
well prove an insurmountable obstacle to success.

I need hardly remark that the advantage possessed by the bird has its
attendant drawbacks when we consider other movements than flying. Its
wings are simply one pair of its legs, and the human race could not
afford to abandon its arms for the most effective wings that nature or
art could supply.

Another point to be considered is that the bird operates by the
application of a kind of force which is peculiar to the animal
creation, and no approach to which has ever been made in any mechanism.
This force is that which gives rise to muscular action, of which the
necessary condition is the direct action of a nervous system. We cannot
have muscles or nerves for our flying-machine. We have to replace them
by such crude and clumsy adjuncts as steam-engines and electric
batteries. It may certainly seem singular if man is never to discover
any combination of substances which, under the influence of some such
agency as an electric current, shall expand and contract like a muscle.
But, if he is ever to do so, the time is still in the future. We do not
see the dawn of the age in which such a result will be brought forth.

Another consideration of a general character may be introduced. As a
rule it is the unexpected that happens in invention as well as
discovery. There are many problems which have fascinated mankind ever
since civilization began which we have made little or no advance in
solving. The only satisfaction we can feel in our treatment of the
great geometrical problems of antiquity is that we have shown their
solution to be impossible. The mathematician of to-day admits that he
can neither square the circle, duplicate the cube or trisect the angle.
May not our mechanicians, in like manner, be ultimately forced to admit
that aerial flight is one of that great class of problems