has pointed out that the law I have just cited may be evaded by not
making a larger machine on the same model, but changing the latter in a
way tantamount to increasing the number of small machines. This is
quite true, and I wish it understood that, in laying down the law I
have cited, I limit it to two machines of different sizes on the same
model throughout. Quite likely the most effective flying-machine would
be one carried by a vast number of little birds. The veracious
chronicler who escaped from a cloud of mosquitoes by crawling into an
immense metal pot and then amused himself by clinching the antennae of
the insects which bored through the pot until, to his horror, they
became so numerous as to fly off with the covering, was more scientific
than he supposed. Yes, a sufficient number of humming-birds, if we
could combine their forces, would carry an aerial excursion party of
human beings through the air. If the watch-maker can make a machine
which will fly through the room with a button, then, by combining ten
thousand such machines he may be able to carry a man. But how shall the
combined forces be applied?
The difficulties I have pointed out apply only to the flying-machine
properly so-called, and not to the dirigible balloon or airship. It is
of interest to notice that the law is reversed in the case of a body
which is not supported by the resistance of a fluid in which it is
immersed, but floats in it, the ship or balloon, for example. When we
double the linear dimensions of a steamship in all its parts, we
increase not only her weight but her floating power, her carrying
capacity, and her engine capacity eightfold. But the resistance which
she meets with when passing through the water at a given speed is only
multiplied four times. Hence, the larger we build the steamship the
more economical the application of the power necessary to drive it at a
given speed. It is this law which has brought the great increase in the
size of ocean steamers in recent times. The proportionately diminishing
resistance which, in the flying-machine, represents the floating power
is, in the ship, something to be overcome. Thus there is a complete
reversal of the law in its practical application to the two cases.
The balloon is in the same class with the ship. Practical difficulties
aside, the larger it is built the more effective it will be, and the
more advantageous will be the ratio of the power which is necessary to
drive it to the resistance to be overcome.
If, therefore, we are ever to have aerial navigation with our present
knowledge of natural capabilities, it is to the airship floating in the
air, rather than the flying-machine resting on the air, to which we are
to look. In the light of the law which I have laid down, the subject,
while not at all promising, seems worthy of more attention than it has
received. It is not at all unlikely that if a skilful and experienced
naval constructor, aided by an able corps of assistants, should design
an airship of a diameter of not less than two hundred feet, and a
length at least four or five times as great, constructed, possibly, of
a textile substance impervious to gas and borne by a light framework,
but, more likely, of exceedingly thin plates of steel carried by a
frame fitted to secure the greatest combination of strength and
lightness, he might find the result to be, ideally at least, a ship
which would be driven through the air by a steam-engine with a velocity
far exceeding that of the fleetest Atlantic liner. Then would come the
practical problem of realizing the ship by overcoming the mechanical
difficulties involved in the construction of such a huge and light
framework. I would not be at all surprised if the result of the exact
calculation necessary to determine the question should lead to an
affirmative conclusion, but I am quite unable to judge whether steel
could be rolled into parts of the size and form required in the
mechanism.
In judging of the possibility of commercial success the cheapness of
modern transportation is an element in the case that should not be
overlooked. I believe the principal part of the resistance which a
limited express train meets is the resistance of the air. This would be
as great for an airship as for a train. An important fraction of the
cost of transporting goods from Chicago to London is that of getting
them into vehicles, whether cars or ships, and getting them out again.
The cost of sending a pair of shoes from a shop in New York to the
residence of the wearer is, if I mistake not, much greater than the
mere cost of transporting them across the Atlantic. Even if a dirigible
balloon should cross the Atlantic, it does not follow that it could
compete with the steamship in carrying passengers and freight.
I may, in conclusion, caution the reader on one point. I should be very
sorry if my suggestion of the advantage of the huge airship leads to
the subject being taken up by any other than skilful engineers or
constructors, able to grapple with all problems relating to the
strength and resistance of materials. As a single example of what is to
be avoided I may mention the project, which sometimes has been mooted,
of making a balloon by pumping the air from a very thin, hollow
receptacle. Such a project is as futile as can well be imagined; no
known substance would begin to resist the necessary pressure. Our
aerial ship must be filled with some substance lighter than air.
Whether heated air would answer the purpose, or whether we should have
to use a gas, is a question for the designer.
To return to our main theme, all should admit that if any hope for the
flying-machine can be entertained, it must be based more on general
faith in what mankind is going to do than upon either reasoning or
experience. We have solved the problem of talking between two widely
separated cities, and of telegraphing from continent to continent and
island to island under all the oceans--therefore we shall solve the
problem of flying. But, as I have already intimated, there is another
great fact of progress which should limit this hope. As an almost
universal rule we have never solved a problem at which our predecessors
have worked in vain, unless through the discovery of some agency of
which they have had no conception. The demonstration that no possible
combination of known substances, known forms of machinery, and known
forms of force can be united in a practicable machine by which men
shall fly long distances through the air, seems to the writer as
complete as it is possible for the demonstration of any physical fact
to be. But let us discover a substance a hundred times as strong as
steel, and with that some form of force hitherto unsuspected which will
enable us to utilize this strength, or let us discover some way of
reversing the law of gravitation so that matter may be repelled by the
earth instead of attracted--then we may have a flying-machine. But we
have every reason to believe that mere ingenious contrivances with our
present means and forms of force will be as vain in the future as they
have been in the past.