natural tendency of the mind, when not subject to a scientific
discipline, to think of words expressing sensible objects and their
relations as connoting certain supersensuous attributes. This is
frequently seen in the repugnance of the metaphysical mind to receive a
scientific statement about a matter of fact simply as a matter of fact.
This repugnance does not generally arise in respect to the every-day
matters of life. When we say that the earth is round we state a truth
which every one is willing to receive as final. If without denying that
the earth was round, one should criticise the statement on the ground
that it was not necessarily round but might be of some other form, we
should simply smile at this use of language. But when we take a more
general statement and assert that the laws of nature are inexorable,
and that all phenomena, so far as we can show, occur in obedience to
their requirements, we are met with a sort of criticism with which all
of us are familiar, but which I am unable adequately to describe. No
one denies that as a matter of fact, and as far as his experience
extends, these laws do appear to be inexorable. I have never heard of
any one professing, during the present generation, to describe a
natural phenomenon, with the avowed belief that it was not a product of
natural law; yet we constantly hear the scientific view criticised on
the ground that events MAY occur without being subject to natural law.
The word "may," in this connection, is one to which we can attach no
meaning expressive of a sensuous relation.
The analogous conflict between the scientific use of language and the
use made by some philosophers is found in connection with the idea of
causation. Fundamentally the word cause is used in scientific language
in the same sense as in the language of common life. When we discuss
with our neighbors the cause of a fit of illness, of a fire, or of cold
weather, not the slightest ambiguity attaches to the use of the word,
because whatever meaning may be given to it is founded only on an
accurate analysis of the ideas involved in it from daily use. No
philosopher objects to the common meaning of the word, yet we
frequently find men of eminence in the intellectual world who will not
tolerate the scientific man in using the word in this way. In every
explanation which he can give to its use they detect ambiguity. They
insist that in any proper use of the term the idea of power must be
connoted. But what meaning is here attached to the word power, and how
shall we first reduce it to a sensible form, and then apply its meaning
to the operations of nature? Whether this can be done, I do not
inquire. All I maintain is that if we wish to do it, we must pass
without the domain of scientific statement.
Perhaps the greatest advantage in the use of symbolic and other
mathematical language in scientific investigation is that it cannot
possibly be made to connote anything except what the speaker means. It
adheres to the subject matter of discourse with a tenacity which no
criticism can overcome. In consequence, whenever a science is reduced
to a mathematical form its conclusions are no longer the subject of
philosophical attack. To secure the same desirable quality in all other
scientific language it is necessary to give it, so far as possible, the
same simplicity of signification which attaches to mathematical
symbols. This is not easy, because we are obliged to use words of
ordinary language, and it is impossible to divest them of whatever they
may connote to ordinary hearers.
I have thus sought to make it clear that the language of science
corresponds to that of ordinary life, and especially of business life,
in confining its meaning to phenomena. An analogous statement may be
made of the method and objects of scientific investigation. I think
Professor Clifford was very happy in defining science as organized
common-sense. The foundation of its widest general creations is laid,
not in any artificial theories, but in the natural beliefs and
tendencies of the human mind. Its position against those who deny these
generalizations is quite analogous to that taken by the Scottish school
of philosophy against the scepticism of Hume.
It may be asked, if the methods and language of science correspond to
those of practical life, why is not the every-day discipline of that
life as good as the discipline of science? The answer is, that the
power of transferring the modes of thought of common life to subjects
of a higher order of generality is a rare faculty which can be acquired
only by scientific discipline. What we want is that in public affairs
men shall reason about questions of finance, trade, national wealth,
legislation, and administration, with the same consciousness of the
practical side that they reason about their own interests. When this
habit is once acquired and appreciated, the scientific method will
naturally be applied to the study of questions of social policy. When a
scientific interest is taken in such questions, their boundaries will
be extended beyond the utilities immediately involved, and one
important condition of unceasing progress will be complied with.
XXI
THE OUTLOOK FOR THE FLYING-MACHINE
Mr. Secretary Langley's trial of his flying-machine, which seems to
have come to an abortive issue for the time, strikes a sympathetic
chord in the constitution of our race. Are we not the lords of
creation? Have we not girdled the earth with wires through which we
speak to our antipodes? Do we not journey from continent to continent
over oceans that no animal can cross, and with a speed of which our
ancestors would never have dreamed? Is not all the rest of the animal
creation so far inferior to us in every point that the best thing it
can do is to become completely subservient to our needs, dying, if need
be, that its flesh may become a toothsome dish on our tables? And yet
here is an insignificant little bird, from whose mind, if mind it has,
all conceptions of natural law are excluded, applying the rules of
aerodynamics in an application of mechanical force to an end we have
never been able to reach, and this with entire ease and absence of
consciousness that it is doing an extraordinary thing. Surely our
knowledge of natural laws, and that inventive genius which has enabled
us to subordinate all nature to our needs, ought also to enable us to
do anything that the bird can do. Therefore we must fly. If we cannot
yet do it, it is only because we have not got to the bottom of the
subject. Our successors of the not distant future will surely succeed.
This is at first sight a very natural and plausible view of the case.
And yet there are a number of circumstances of which we should take
account before attempting a confident forecast. Our hope for the future
is based on what we have done in the past. But when we draw conclusions
from past successes we should not lose sight of the conditions on which
success has depended. There is no advantage which has not its attendant
drawbacks; no strength which has not its concomitant weakness. Wealth
has its trials and health its dangers. We must expect our great
superiority to the bird to be associated with conditions which would
give it an advantage at some point. A little study will make these
conditions clear.
We may look on the bird as a sort of flying-machine complete in itself,
of which a brain and nervous system are fundamentally necessary parts.
No such machine can navigate the air unless guided by something having
life. Apart from this, it could be of little use to us unless it
carried human beings on its wings. We thus meet with a difficulty at
the first step--we cannot give a brain and nervous system to our
machine. These necessary adjuncts must be supplied by a man, who is no
part of the machine, 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 with which
man can never cope, and give up all attempts to grapple with it?
[Illustration with caption: PROFESSOR LANGLEY'S AIR-SHIP]
The fact is that invention and discovery have, notwithstanding their
seemingly wide extent, gone on in rather narrower lines than is
commonly supposed. If, a hundred years ago, the most sagacious of
mortals had been told that before the nineteenth century closed the
face of the earth would be changed, time and space almost annihilated,
and communication between continents made more rapid and easy than it
was between cities in his time; and if he had been asked to exercise
his wildest imagination in depicting what might come--the airship and
the flying-machine would probably have had a prominent place in his
scheme, but neither the steamship, the railway, the telegraph, nor the
telephone would have been there. Probably not a single new agency which
he could have imagined would have been one that has come to pass.
It is quite clear to me that success must await progress of a different
kind from that which the inventors of flying-machines are aiming at. We
want a great discovery, not a great invention. It is an unfortunate
fact that we do not always appreciate the distinction between progress
in scientific discovery and ingenious application of discovery to the
wants of civilization. The name of Marconi is familiar to every ear;
the names of Maxwell and Herz, who made the discoveries which rendered
wireless telegraphy possible, are rarely recalled. Modern progress is
the result of two factors: Discoveries of the laws of nature and of
actions or possibilities in nature, and the application of such
discoveries to practical purposes. The first is the work of the
scientific investigator, the second that of the inventor.
In view of the scientific discoveries of the past ten years, which,
after bringing about results that would have seemed chimerical if
predicted, leading on to the extraction of a substance which seems to
set the laws and limits of nature at defiance by radiating a flood of
heat, even when cooled to the lowest point that science can reach--a
substance, a few specks of which contain power enough to start a
railway train, and embody perpetual motion itself, almost--he would be
a bold prophet who would set any limit to possible discoveries in the
realm of nature. We are binding the universe together by agencies which
pass from sun to planet and from star to star. We are determined to
find out all we can about the mysterious ethereal medium supposed to
fill all space, and which conveys light and heat from one heavenly body
to another, but which yet evades all direct investigation. We are
peering into the law of gravitation itself with the full hope of
discovering something in its origin which may enable us to evade its
action. From time to time philosophers fancy the road open to success,
yet nothing that can be practically called success has yet been reached
or even approached. When it is reached, when we are able to state
exactly why matter gravitates, then will arise the question how this
hitherto unchangeable force may be controlled and regulated. With this
question answered the problem of the interaction between ether and
matter may be solved. That interaction goes on between ethers and
molecules is shown by the radiation of heat by all bodies. When the
molecules are combined into a mass, this interaction ceases, so that
the lightest objects fly through the ether without resistance. Why is
this? Why does ether act on the molecule and not the mass? When we can
produce the latter, and when the mutual action can be controlled, then
may gravitation be overcome and then may men build, not merely
airships, but ships which shall fly above the air, and transport their
passengers from continent to continent with the speed of the celestial
motions.
The first question suggested to the reader by these considerations is
whether any such result is possible; whether it is within the power of
man to discover the nature of luminiferous ether and the cause of
gravitation. To this the profoundest philosopher can only answer, "I do
not know." Quite possibly the gates at which he is beating are, in the
very nature of things, incapable of being opened. It may be that the
mind of man is incapable of grasping the secrets within them. The
question has even occurred to me whether, if a being of such
supernatural power as to understand the operations going on in a
molecule of matter or in a current of electricity as we understand the
operations of a steam-engine should essay to explain them to us, he
would meet with any more success than we should in explaining to a fish
the engines of a ship which so rudely invades its domain. As was
remarked by William K. Clifford, perhaps the clearest spirit that has
ever studied such problems, it is possible that the laws of geometry
for spaces infinitely small may be so different from those of larger
spaces that we must necessarily be unable to conceive them.
Still, considering mere possibilities, it is not impossible that the
twentieth century may be destined to make known natural forces which
will enable us to fly from continent to continent with a speed far
exceeding that of the bird.
But when we inquire whether aerial flight is possible in the present
state of our knowledge, whether, with such materials as we possess, a
combination of steel, cloth, and wire can be made which, moved by the
power of electricity or steam, shall form a successful flying-machine,
the outlook may be altogether different. To judge it sanely, let us
bear in mind the difficulties which are encountered in any
flying-machine. The basic principle on which any such machine must be
constructed is that of the aeroplane. This, by itself, would be the
simplest of all flyers, and therefore the best if it could be put into
operation. The principle involved may be readily comprehended by the
accompanying figure. A M is the section of a flat plane surface, say a
thin sheet of metal or a cloth supported by wires. It moves through the
air, the latter being represented by the horizontal rows of dots. The
direction of the motion is that of the horizontal line A P. The
aeroplane has a slight inclination measured by the proportion between
the perpendicular M P and the length A P. We may raise the edge M up or
lower it at pleasure. Now the interesting point, and that on which the
hopes of inventors are based, is that if we give the plane any given
inclination, even one so small that the perpendicular M P is only two
or three per cent of the length A M, we can also calculate a certain
speed of motion through the air which, if given to the plane, will
enable it to bear any required weight. A plane ten feet square, for
example, would not need any great inclination, nor would it require a
speed higher than a few hundred feet a second to bear a man. What is of
yet more importance, the higher the speed the less the inclination
required, and, if we leave out of consideration the friction of the air
and the resistance arising from any object which the machine may carry,
the less the horse-power expended in driving the plane.
[Illustration]
Maxim exemplified this by experiment several years ago. He found that,
with a small inclination, he could readily give his aeroplane, when it
slid forward upon ways, such a speed that it would rise from the ways
of itself. The whole problem of the successful flying-machine is,
therefore, that of arranging an aeroplane that shall move through the
air with the requisite speed.
The practical difficulties in the way of realizing the movement of such
an object are obvious. The aeroplane must have its propellers. These
must be driven by an engine with a source of power. Weight is an
essential quality of every engine. The propellers must be made of
metal, which has its weakness, and which is liable to give way when its
speed attains a certain limit. And, granting complete success, imagine
the proud possessor of the aeroplane darting through the air at a speed
of several hundred feet per second! It is the speed alone that sustains
him. How is he ever going to stop? Once he slackens his speed, down he
begins to fall. He may, indeed, increase the inclination of his
aeroplane. Then he increases the resistance to the sustaining force.
Once he stops he falls a dead mass. How shall he reach the ground
without destroying his delicate machinery? I do not think the most
imaginative inventor has yet even put upon paper a demonstratively
successful way of meeting this difficulty. The only ray of hope is
afforded by the bird. The latter does succeed in stopping and reaching
the ground safely after its flight. But we have already mentioned the
great advantages which the bird possesses in the power of applying
force to its wings, which, in its case, form the aeroplanes. But we
have already seen that there is no mechanical combination, and no way
of applying force, which will give to the aeroplanes the flexibility
and rapidity of movement belonging to the wings of a bird. With all the
improvements that the genius of man has made in the steamship, the
greatest and best ever constructed is liable now and then to meet with
accident. When this happens she simply floats on the water until the
damage is repaired, or help reaches her. Unless we are to suppose for
the flying-machine, in addition to everything else, an immunity from
accident which no human experience leads us to believe possible, it
would be liable to derangements of machinery, any one of which would be
necessarily fatal. If an engine were necessary not only to propel a
ship, but also to make her float--if, on the occasion of any accident
she immediately went to the bottom with all on board--there would not,
at the present day, be any such thing as steam navigation. That this
difficulty is insurmountable would seem to be a very fair deduction,
not only from the failure of all attempts to surmount it, but from the
fact that Maxim has never, so far as we are aware, followed up his
seemingly successful experiment.
There is, indeed, a way of attacking it which may, at first sight, seem
plausible. In order that the aeroplane may have its full sustaining
power, there is no need that its motion be continuously forward. A
nearly horizontal surface, swinging around in a circle, on a vertical
axis, like the wings of a windmill moving horizontally, will fulfil all
the conditions. In fact, we have a machine on this simple principle in
the familiar toy which, set rapidly whirling, rises in the air. Why
more attempts have not been made to apply this system, with two sets of
sails whirling in opposite directions, I do not know. Were there any
possibility of making a flying-machine, it would seem that we should
look in this direction.
The difficulties which I have pointed out are only preliminary ones,
patent on the surface. A more fundamental one still, which the writer
feels may prove insurmountable, is based on a law of nature which we
are bound to accept. It is that when we increase the size of any
flying-machine without changing its model we increase the weight in
proportion to the cube of the linear dimensions, while the effective
supporting power of the air increases only as the square of those
dimensions. To illustrate the principle let us make two flying-machines
exactly alike, only make one on double the scale of the other in all
its dimensions. We all know that the volume and therefore the weight of
two similar bodies are proportional to the cubes of their dimensions.
The cube of two is eight. Hence the large machine will have eight times
the weight of the other. But surfaces are as the squares of the
dimensions. The square of two is four. The heavier machine will
therefore expose only four times the wing surface to the air, and so
will have a distinct disadvantage in the ratio of efficiency to weight.
Mechanical principles show that the steam pressures which the engines
would bear would be the same, and that the larger engine, though it
would have more than four times the horse-power of the other, would
have less than eight times. The larger of the two machines would
therefore be at a disadvantage, which could be overcome only by
reducing the thickness of its parts, especially of its wings, to that
of the other machine. Then we should lose in strength. It follows that
the smaller the machine the greater its advantage, and the smallest
possible flying-machine will be the first one to be successful.
We see the principle of the cube exemplified in the animal kingdom. The
agile flea, the nimble ant, the swift-footed greyhound, and the
unwieldy elephant form a series of which the next term would be an
animal tottering under its own weight, if able to stand or move at all.
The kingdom of flying animals shows a similar gradation. The most
numerous fliers are little insects, and the rising series stops with
the condor, which, though having much less weight than a man, is said
to fly with difficulty when gorged with food.
Now, suppose that an inventor succeeds, as well he may, in making a
machine which would go into a watch-case, yet complete in all its
parts, able to fly around the room. It may carry a button, but nothing
heavier. Elated by his success, he makes one on the same model twice as
large in every dimension. The parts of the first, which are one inch in
length, he increases to two inches. Every part is twice as long, twice
as broad, and twice as thick. The result is that his machine is eight
times as heavy as before. But the sustaining surface is only four times
as great. As compared with the smaller machine, its ratio of
effectiveness is reduced to one-half. It may carry two or three
buttons, but will not carry over four, because the total weight,
machine plus buttons, can only be quadrupled, and if he more than
quadruples the weight of the machine, he must less than quadruple that
of the load. How many such enlargements must he make before his machine
will cease to sustain itself, before it will fall as an inert mass when
we seek to make it fly through the air? Is there any size at which it
will be able to support a human being? We may well hesitate before we
answer this question in the affirmative.