NATURE AS TEACHER
Forces take paths of least resistance . . . Accessibility decides
where cities shall arise . . . Plants display engineering principles
in structure. Lessons from the human heart, eye, bones, muscles, and
nerves . . . What nature has done, art may imitate,--in the
separation of oxygen from air, in flight, in producing light, in
converting heat into work . . . Lessons from lower animals . . . A
hammer-using wasp.
Beyond their unending study of forms and properties, their constant
weighing and measuring, the inventor and his twin-brother, the
discoverer, have a gainful province which now for a little space will
engage our attention. This province is nothing else than Nature, which
begins by offering primitive man stones for hammers, arrowheads, knives;
sticks to serve as clubs, paddles, harrows or tent-poles. We may well
believe that the lowest savages have always exercised some degree of
choice even here; it would be the soundest and sharpest stone that they
picked up when a rude axe was needed. Should only blunt stones be found,
then in giving one of them an edge was taken a first step in art,
rewarded with a tool as good as the axe found ready to hand in some
earlier quest. Nature is not only a giver of much besides stones and
sticks, she is virtually a great contriver whose feats may incite the
inventor to reach her goals if he can; his path will probably differ
widely enough from hers as he arrives at success.
Forces Take the Easiest Paths.
When one drop of rain meets another, and they join themselves to
thousands more on the crest of a hill, they need no guide posts to show
them the easiest course to the valley. They simply take it under the
quiet pull of gravity. When a bolt of lightning darts across the sky,
its lines, chaotic as they seem, are just the paths where the electric
pulses find least obstruction. If a volcano, which has boiled and
throbbed for ages, at last opens a chasm on a hapless shore, as that of
Martinique, we may be sure that at that point and nowhere else the
mighty caldron’s lid was lightest. A cavern in Kentucky, or Virginia,
slowly broadening and deepening through uncounted rills which dissolve
its limy walls, comes at last to utter collapse: the breach marking
exactly where an ounce too much pressed the roof at its frailest seam.
In these cases as in all others, however complex, matter moves
inevitably in the path of least resistance. To imitate that economy of
effort is from first to last the inventor’s task.
Cities and Roads.
Rains, winds and frosts, in their sculpture of the earth have each taken
the easiest course; in so doing they have incidentally marked out the
best paths for human feet, have pointed to the best sites for the homes
of men. The stresses of defence may rear a pueblo on the peak of a
perpendicular cliff in New Mexico, but Paris and London, like Rome, must
have all roads leading to their gates; and the easier and shorter these
roads, the bigger and stronger the city will become. Where New York,
Montreal, Chicago, and Pittsburg now stand, the Indians long ago had the
wit to found goodly settlements. They knew, as well as their white
successors, the advantages of paths readily traversed, and no longer
than need be. In this regard there was an instructive contrast at the
outset of railroad building in England. A leading engineer, who planned
some of the earliest English railways, had strong mathematical
prepossessions: he endeavored to join the terminals of his routes by
lines as nearly straight as he could. George Stephenson, for his part,
had no mathematical warp of any kind, but instead much sound sense; his
lines followed the courses of rivers and valleys, and kept, as much as
might be, to the chief indentations of the sea. His roads deviated a
good deal from straightness, but they did so profitably; whereas the
lines of his academic rival, disrespecting the hints and indications of
nature, were much less gratifying from an investor’s point of view. If a
traveler takes the New York Central and Hudson River Railroad from New
York to Buffalo he goes north for 143 miles, to Albany, before he begins
to travel westward at all. Yet this line, keeping as it does to the
well-peopled levels of the Hudson and Mohawk Valleys and serving their
succession of cities, towns, and villages, enjoys the best business,
and makes better time between its terminals than any rival route,
because it passes around instead of over its hills and mountains. By way
of contrast we turn to the railroad map of Russia and observe how Moscow
and St. Petersburg are joined by a line which follows the road which it
is said that Peter the Great, with military exigencies in view, laid
down with a pencil and ruler.
[Illustration: Deciduous cypress, _Taxodium distichum_.]
Engineering Principles in Vegetation.
If the engineer has many a golden hint spread before him in the hills
and dales, the streams and oceans of the world, not less fruitful is the
study of what takes place just beneath the surface of the earth where
the roots of grain and shrub, reed and tree, take life and form. Plant a
kernel of wheat in the ground and note how its rootlets pierce the soil,
extending always from the tip. They need no gardener or botanist to bid
them lengthen and thicken where food chiefly abounds. In an arid plain
of Arizona a vine, in ground parched and dry, goes downward so far, and
spreads its fibrils so much abroad, as soon to show ten times as much
growth below the drifting sands as above them. In fertile, well-watered
soil the same vine descends less than half as far, and yet with more
gain. A bald cypress in a swamp of Florida responds to different
surroundings with equal profit. Finding its food near the surface its
roots take horizontal lines, at no great depth in the soil. Every wind
that stirs these roots but promotes their thrift and strengthens their
anchorage. A wealth of sustenance floats in the swamp water. In seizing
it and being thereby fed, the roots develop “knees”; these brace the
tree so firmly against tempests as to win admiration from the engineer.
When the progeny of this cypress grow on well-drained land, the knees do
not appear, while the roots within a narrowed area strike deep. Thus
simply in doing what its surroundings incite it to do, the tree acts as
if it had intelligence, as if it consciously saw and chose what would do
it most good.
[Illustration: Deciduous cypress, hypothetical diagram.]
Lumbermen in the North observe much the same responsiveness. In a grove
of pines they see that the trees which stand close together are tall and
cylindrical. When all the pines but one in a cluster are cut down, that
one will speedily thicken the lower part of its trunk by virtue of the
increased action of the winds, just as a muscle thickens by exercise.
The Gain of Responsiveness.
So also is there responsiveness when we look upon the life of plants in
the large. As the traits of a shrub or tree are borne into its seed many
a thousand impulses are merged and mingled. Little wonder that their
delicate accord and poise should be slightly different from those of the
seeds from which the parents sprang. Let us suppose these parents to be
cactuses, and that the offspring displays an unusually broad stem, of
less surface comparatively than any other plant in its group. In a soil
seldom refreshed by rain, this cactus has the best foothold and
maintains it with most vigor. Sandstorms which kill brethren less
sturdy, strike it in vain, so that its kind is multiplied. Wherever such
a new character as this gives a plant an advantage, it holds the field
while its neighbors perish. Thus arises a high premium on every useful
variation, be it in new stockiness of form, an acridity which repels
vermin, or a strength which readily makes a way through sun-baked earth.
Hence such new traits are, as it were, seized upon and become points of
departure for new varieties, and in the fullness of time, for new
species. About a hundred years ago a gardener imagined a tuberous
begonia, and then proceeded step by step toward its creation by breeding
from every flower that varied in the direction he desired. This man, and
all his kindred who have added to our riches in cultivated blooms, have
no more than copied the modes of nature which, at the end of ages,
bestows as free gifts every wildflower of the field and hedgerow. If the
botanist of to-day is the master of a plastic art, so is the
cattle-breeder who chalks on a barn-door the outline of a beeve he
wishes to produce, and then straightway plans the matings which issue in
the animal he has pictured. Artificial selection, such as this, is after
all only imitation of that natural selection which has derived the horse
from a progenitor little larger than a fox, in response, age after age,
to changing food, climate, enemies, and the needs of his human master.
Scope for Imitation.
Fields remote from those of the naturalist are just as instructive. The
inventor sets before himself an end with conscious purpose, and then
seeks means to reach that end, but at best his methods may be wasteful
and imperfect. Nature, with unhasting tread, acting simply through the
qualities inherent in her materials, through their singular powers of
combination, of mutual adaptability, shows the discoverer results which
to understand even in small measure tax his keenest wit, or displays to
him structures at times beyond his skill to dissect, much less to
imitate. Mechanic art, indeed, is for the most part but a copy of
nature, as when the builder repeats the mode in which rocks are found in
caves, in ridges at the verge of a cliff, or in the stratifications
which underlie a county, all conducing to permanence of form, to
resistance against abrading sand or dissolving waters. What ensures the
stability of a lighthouse but its repetition of a tree-trunk in its
contour? Engines and machines recall the animal body, grinding ore much
as teeth grind nuts, lifting water as the heart pumps blood through
artery and vein, and repeating in mechanism of brass and steel the
dexterity of fingers, the blows of fists. When an inventor builds an
engine to drive a huge ship across the sea, he has created a motor
vastly larger than his own frame, but much inferior in economy. At a
temperature little higher than that of a summer breeze the human
mechanism transmutes the energy of fuel into mechanical toil: for the
same duty, less efficiently discharged, the steam engine demands a blaze
almost fierce enough to melt grate bars of iron.
Heat is costly, so that its conservation is an art worth knowing. In the
ashes strewn and piled on burning lava nature long ago told us how heat
may be secured against dissipation. Other of her garments, as hair and
fur, obstruct the escape of heat in a remarkable degree, and so does
bark, especially when loosely coherent as in the cork tree. Feathers are
also excellent retainers of heat, and have thereby so much profited
their wearers, that Ernest Ingersoll holds that the development of
feathers has had much to do with advancing birds far above their lowly
cousins, the reptiles clad in a scaly vesture.
Strength of the Cylinder.
As we look back upon the past from the vantage ground of modern insight
we see that men of the loftiest powers could be blind to intimations now
plain and clear. Many a time have designers and inventors paralleled,
without knowing it, some structure of nature often seen but never really
observed. All the variety and beauty of the Greek orders of architecture
failed to include the arch; yet the contour of every architect’s own
skull was the while displaying an arched form which could lend to temple
and palace new strength as well as grace. The skeleton of the foot
reveals in the instep an arch of tarsal and metatarsal bones, with all
the springiness which their possessor may confer upon a composite arch
of wood or steel. Modern builders, whether wittingly or not, have taken
a leaf from the book of nature in rearing their tallest structures with
hollow cylinders of steel. What is this but borrowing the form of the
reed, the bamboo, a thousand varieties of stalk, one of the strongest
shapes in which supporting material can be disposed? Pass a knife across
a blade of pipe or moor grass and you will find a hollow cylinder stayed
by buttresses numbering nearly a score. More elaborate and even more
gainful is the way in which tissue grows in the columns of dead-nettles
and bulrushes. The bones in one’s arms and legs resemble the hollow
cylinders of which these stalks show instructive variations, so that
without going beyond his own frame the designer could long ago have
learned a golden lesson. How bone is joined to bone is scarcely less
remarkable, as in the braces of the thigh bone as it joins the trunk. As
bones move upon each other all shock is prevented by a highly elastic
cushion: the springs of vehicles, the buffers of railroad trains, but
repeat the cartilages in the joints of their inventors.
[Illustration: Section of pipe or moor grass.]
[Illustration: Cross-section of bulrush, _Scirpus lacustris_.]
In the theodolite and sextant, in the geometric lathe of the bank-note
engraver, are ball-and-socket joints allowing motion in any plane.
Equally free in their movements are the shoulder and hip joints, while
their surfaces are lubricated by a delicate synovial fluid supplied just
as it is wanted. When pumps first received valves to direct their flow
in one direction, their inventor was no doubt gratified at his skill. In
the heart within his own breast, in his veins and arteries, were simple
valves engaged in a similar task as they directed the currents of his
blood. In pumps such as are common in farm-yards, the action is jerky,
the stream flowing and ebbing from moment to moment as the arm rises
and falls. The tide of human blood would have the same uneven pulse
were it not for the elasticity of its arterial walls. Their elasticity
serves to equalize the flow, much as the air does in large chambers on
pumps for mines or waterworks.
[Illustration: Human hip joint in section. From “The Human Body,” by H.
N. Martin. Copyright, Henry Holt & Co., New York, 1884. Reproduced by
their permission.]
[Illustration: Valves of veins.
C, a capillary; H, the heart end of the vessel. From “The Human Body,”
by H. N. Martin. Copyright, 1884, Henry Holt & Co., New York, and
reproduced by their permission.]
[Illustration: Built-up gun.]
The Heart and the Built-up Gun.
Examination of the heart brings out a principle in its structure closely
paralleled in modern invention. Guns of old were cast or forged as
ordinary columns or shafts are to-day, the strength of the metal being
virtually uniform throughout when the guns were at rest on their
trunnions. As explosive charges more and more powerful were employed,
these guns gave way, the pressure of the exploding gases stretching the
metal at the bore to rupture, before the outer metal could add its
resistance. A modern built-up gun is made up of a series of, let us
say, four cylinders: the first, of comparatively small bore and
thickness, is innermost. It is cooled to as low a temperature as
possible, when a second cylinder is slipped over it red-hot to form a
tight fit. Both masses of metal are now slowly cooled, when a third
red-hot, closely fitting cylinder is passed over them. All three united
masses are now cooled, when the fourth and widest cylinder of all,
red-hot, is passed over these three inner tubes, and the whole gun is
allowed gradually to fall in temperature. When this process is completed
the inner parts of the gun, by virtue of the shrinkage in the metal as
it cooled, are under severe compression, while the outer parts are in as
extreme a state of stretch or tension. When such a gun is fired its
inner cylinders oppose much greater resistance to the outward pressure
of the exploding gases than did the walls of the old-time guns. The
strength of the old guns was uniform throughout when they were doing
nothing, and very far from uniform at the instant of firing; a built-up
gun, on the contrary, has uniform strength in its every part just when
that uniformity is wanted, at the moment of explosion. The built-up gun
therefore uses projectiles vastly heavier and swifter than those of
former times. Its structure, made up of cylinders successively shrunk
one upon another, resembles that of the heart, whose two inner parts
have their fibres wound somewhat like balls of twine, these in turn
being tightly compressed by a covering of other fibres. The heart has to
resist no such explosive force as arises within a gun, but in its
propulsion of blood through the arteries and veins it has to exert great
pressure, with no rest throughout a lifetime. This pressure is uniformly
distributed throughout the muscular tissue by a structure which, as
engineers would say, has its outer layers in tension and its inner
layers in compression. During twenty-four hours the labor of an average
human heart is equal to lifting two hundred and twenty tons one foot
from the ground.
What building-up does to strengthen the gun has been repeated in the
case of the circular saw: driven at a high speed it becomes so highly
heated at its periphery that the resulting expansion may crack the metal
in pieces. In an improved method of manufacture the saw is hammered to a
compression which gradually increases from rim to centre. In this way
the tendency of the periphery to fly apart is withstood by the
compressive forces at the central portion of the disc.
This ingenious treatment of metal for guns and saws reminds us of a
familiar resource in carpentry, illustrated on page 36. An ordinary
book-shelf, if fairly long and not particularly stout, bends beneath its
burden and may at last slip out from its mortices and fall with injury
to its books. At the outset this is prevented by bending the shelf to
convexity on its upper surface. Then a heavy load no more than brings
the shelf to straightness, so that the books remain in their places with
both safety and sightliness. Here a principle is involved worth a
moment’s pause. An inventor asks, What effect will a working load exert
which it is desirable to lessen or withstand? He gives his structure a
form opposite to that which will result from an imposed burden, so that
when at work his structure, a shelf, a cylinder, a saw, will assume its
most effective shape.
The Eye and the Dollond Lenses.
From childhood we are familiar with the triangular prisms of glass which
break a sunbeam into all the hues of the rainbow. A lens is a prism of
circular form, and has, equally with an ordinary prism, the power to
show rays of all colors. This was for a long time a source of error and
annoyance in telescopic images. Sir Isaac Newton from some rough and
ready experiments concluded that the trouble was beyond remedy, yet all
the while his own eyeballs were transmitting images with little or no
vexatious fringe of color. Let us note how Dollond set about a task
which Newton deemed impossible. He knew, what Newton did not know, that
crown glass disperses or scatters light only half as much as does flint
glass, so he united a lens of the one to a lens of the other, and
obtained a refracted or bent beam of light almost unchanged in its
whiteness. Of course, in this combination there was an increased
thickness of glass, but its doubled absorption and waste of light was a
small drawback compared with the advantage of almost wholly excluding
the tinted fringe which had so long vexed astronomers. In the eyeball
are first a crystalline lens, next an aqueous humor, third a vitreous
humor; these three so vary in their qualities of refraction and
dispersion as to render images quite free from color fringes. Compound
lenses on the Dollond principle, repeating the structure of an eyeball,
are used in all good telescopes, microscopes, and cameras, and are now
executed in varieties of Jena glass which bring perturbing hues to the
vanishing point. In their achromatic, or color-free, lenses and their
cameras, or dark chambers, our photographic instruments much resemble
the eye. Indeed, it may be that when we see an object the impression is
due to a succession of fleeting photographs, following each other so
rapidly on the retina as to seem a permanent picture. The eye,
furthermore, is stereoscopic; by uniting two images seen from slightly
differing points of view, it enables us to judge of size, solidity, and
distance.
[Illustration: A is flint glass, B is crown glass. They unite to form an
achromatic lens.]
[Illustration: B, C, F, prism crown glass. C, D, F, prism flint glass,
more dispersive than crown glass. The beam S emerges as E, but little
decomposed. Were A, B, F a prism of one kind of glass, E would be much
decomposed.]
Limbs and Lungs as Prototypes.
Long before there was a philosopher to classify levers into distinct
kinds, the foot of man was affording examples of levers of the first and
second orders, and his fore-arm of a lever of the third order. Ages
before the crudest bagpipe was put together, the lungs by which they
were to be blown, and the larynx joined to those lungs, were displaying
a wind instrument of perfect model. The wrists, ankles, and vertebrae of
Hooke might well have served him in designing his universal joint.
Indeed weapons, tools, instruments, machines, and engines are, after
all, but extensions and modified copies of the bodily organs of the
inventor himself.
[Illustration: _Lever of the 1^{st} order._
_Lever of the 2^{nd} order._
_Lever of the 3^{rd} order._
P, power. F, fulcrum. W, weight.]
Canals have called forth the ingenuity of an army of engineers; ever
since the first heart-throb, the circulation of the human blood was
exemplifying a system in which the canal liquid and the canal boats move
together, making a complete circuit twice in a minute, distributing
supplies wherever required, and taking up without stopping return loads
wherever they are found ready. The heart, with its arteries and veins,
forms a distributing apparatus which carries heat from places at which
it is generated, or in excess, to places where it is deficient, tending
to establish a uniform, healthful temperature. To copy all this, with
the ventilating appliances prefigured in the lungs, is a task which in
our huge modern buildings demands the utmost skill of the architect and
engineer.
[Illustration: Arm holding ball.]
Postal and Telephonic Service.
In a great city each branch post office is connected solely with
headquarters, to which it sends its letters, papers, and parcels,
receiving in return its batches for local distribution. For each branch
office to communicate with every other would be so costly and cumbrous a
plan as to be quite impracticable. Our postal method is adopted in every
telephonic service; Z communicating with D or M only after he has had
his line joined to the central switchboard which connects with every
telephone in the whole system. All this was prophesied in the remote
ancestry of both postmasters and electricians as their nerves took the
paths of what is in effect a complete telegraphic circuit, with separate
up and down lines and a central exchange in the brain,--that prototype
of all other means of co-ordination.
Fibrils of the Ear and Eye.
Pianos, organs, and other musical instruments yield their notes by the
vibration of strings, pipes, or reeds of definite size and form. Across
the larynx, the box-like organ of the throat, the vocal cords vibrate in
an identical way. When we sing a note into an open piano, the string
capable of giving out that note at once responds. Helmholtz believed
that in the ear the delicate, graduated structures, known as the rods of
Corti, vibrate in the same way when sound-waves reach them, giving rise
to auditory impressions. Analogous in operation are the fibrils of the
eye which respond to light-waves of various length and intensities. The
human eye has muscles which modify its globularity, rendering its lenses
more or less convex. A cat has a higher degree of this kind of ability,
so that it can dilate its pupil so much as to see clearly in a feeble
light. A man who remains in a darkened room so rests his nerves of
vision that in four or five hours he can readily discern what would be
unseen were he newly brought into the darkness.
The Electric Eel.
Not only in the frame of man, but in the bodies of the lower animals,
are suggestions which ingenuity might well have acted upon in the past,
or worthily pursue in the future. The science of electricity was born
only with the nineteenth century because the gymnotus, or electric eel,
had not been understandingly dissected. Its tissues disclose the very
arrangement adopted by Volta in his first crude battery, namely, layers
of susceptible material surrounded by slightly acid moisture. The
characteristics of this eel have their homologies in the human body; in
the muscles which bend the fore-arm, for example, are nearly a million
delicate fibrils comparable in structure with the columnar organs of the
gymnotus. These fibrils are so easily excited by electricity as to
denote an essential similarity of build. Both the columnar layers of the
eel and the fibrils of human muscle are affected in the same way by
strychnine and by an allied substance, curare.
A Beaver Tooth and the Self-Sharpening Plow.
The frames of other animals furnish forth a goodly round of analogies
with recent products of mechanical ingenuity. A beaver tooth might well
have been the model for a self-sharpening plowshare, widely used
throughout the world. This tooth has a thin outer layer of hard enamel,
within which, dentine, less hard, makes up the rest of the structure.
Gnawing wears the dentine much more than the enamel, so that the tooth
takes on a bevel resembling that of the chisel which pays frequent
visits to a carpenter’s oil-stone. The scale of enamel gives keenness,
the dentine ensures strength, so that the tooth sharpens itself by use,
instead of growing dull. Much the same structure is repeated in a
plowshare by chilling the underskin of the steel to extreme hardness,
while the upper face of the share is left comparatively soft. As it goes
through the ground the upper face wears away so as to yield a constantly
sharpened edge of the thin chilled under metal. Thus the heavy draft of
a dull share is avoided without constant recourse to the blacksmith for
re-sharpening.
[Illustration: Beaver teeth.]
Shaping a Tube.
In another field of ingenuity a great inventor scored a success, simply
by deliberately taking a lesson from nature. James Watt, to whom the
modern steam engine is most indebted for its excellence, was once
consulted by the proprietors of the Glasgow Water Works, as to a
difficulty that had occurred in laying pipes across the river Clyde to
the Company’s engines: the bed of the river was covered with mud and
shifting sand, was full of inequalities, and subject to a current at
times of considerable force. With the structure of a lobster’s tail in
his mind, Watt drew a plan for an articulated suction-pipe, so jointed
as to accommodate itself to the shifting curves of the river-bed. This
crustacean tube, two feet in diameter, and one thousand feet in length,
succeeded perfectly in its operation. To-day powerful hydraulic dredges
discharge through piping with flexible joints such as Watt devised; in
one instance this piping is 5700 feet in length.
[Illustration: Narwhal with a twisted tusk. Reproduced from the
Scientific American, New York, by permission.]
In many another case art has used a gift of nature simply as received,
and then improved upon it. In making their harpoons the Eskimo used the
spiral teeth of the narwhal; finding their shape advantageous, they
copied it for arrowheads. This is undoubtedly one of the origins of the
screw form, of inestimable value to the mechanic and engineer.
Lessons from Lower Animals: A Tool-Using Wasp.
Savages turn birds and beasts to account as food, clothing, and
materials for weapons and tools; they also observe with profit the
instincts of these creatures. Le Vaillant, the famous explorer, tells us
that in Africa the negroes eat any strange food they see the monkeys
devour, well assured that it will prove wholesome. When the surveyors of
the first transcontinental railroad of America began their labors, they
gave diligent heed to the trails of buffaloes in the Rocky Mountains,
believing that these sagacious brutes in centuries of quest had
discovered the easiest passes. In constructive powers bees, ants and
wasps far outrank quadrupeds. Indeed one of the supreme feats of human
architecture, the dome, forms part of the nest of the warrior white ant,
_Termes bellicosus_.
[Illustration: Lower part of warrior ants’ nest, showing dome.]
It is deemed a mark of unusual intelligence when an ape, of kin to man
himself, uses a stone as a hammer wherewith to break open a nut, and yet
the like intelligence is displayed by _Ammophila urnaria_, as described
by Dr. and Mrs. George W. Peckham in their charming book, “Wasps
Solitary and Social”:[32]
[32] Published by Houghton Mifflin & Co., Boston.
[Illustration: Wasp using a pebble as a hammer. From “Wasps Solitary and
Social,” Copyright, 1905, by George W. Peckham and Elizabeth G. Peckham.
Reproduced by their permission.]
“Just here must be told the story of one little wasp whose individuality
stands out in our minds more distinctly than that of any of the others.
We remember her as the most fastidious and perfect little worker of the
whole season, so nice was she in her adaptation of means to ends, so
busy and contented in her labor of love, and so pretty in her pride over
the completed work. In filling up her nest she put her head down into
it and bit away the loose earth from the sides, letting it fall to the
bottom of her burrow, and then, after a quantity had accumulated, jammed
it down with her head. Earth was then brought from the outside and
pressed in, and then more was bitten from the sides. When at last the
filling was level with the ground, she brought a quantity of fine grains
of dirt to the spot, and picking up a small pebble in her mandibles,
used it as a hammer in pounding them down with rapid strokes, thus
making this spot as hard and firm as the surrounding surface.”
It was a wasp, too, which suggested to Reaumur, as he examined its nest,
that wood might well serve as the raw material for paper, and serve it
does to the amount of millions of tons a year. To-day we have as a new
fabric for garments, glanz-stoff, an artificial silk produced from
cellulose; its German manufacturers have imitated as nearly as they
could the silk-worm’s thread, just as for some years the filaments for
incandescent lamps have been made from liquid cellulose forced through
minute holes. At first bamboo fibres were used for this purpose; to-day
art furnishes a thread of more uniform and lasting quality. This
achievement is of a piece with many another. To-day when an inventor
seeks to imitate a natural product he does so with a power of analysis,
a wealth of new materials, such as his forerunners could not have
imagined. It is in laboratories stocked more diversely than ever before,
with their resources better understood than at any earlier time, that
the triumphs of modern ingenuity proceed.
The Separating Task of the Lungs.
In all likelihood one of the feats of nature soon to be paralleled by
art, in an economical way, will be one phase of the breathing process;
every time we inflate our lungs their tissues perform a feat which has
thus far baffled imitation except in a roundabout and wasteful manner.
Air is a mixture of oxygen and nitrogen; the work of life is subserved
by the oxygen only, which is separated from air by the lungs and passed
into the current of the blood. Oxygen and nitrogen, like any other two
gases, tend forcibly to diffuse into each other, as we may see in the
distension of a thin rubber sheet dividing a container into two parts,
one filled with oxygen, the other with nitrogen. To overcome the force
of diffusion which keeps together the oxygen and nitrogen forming a
cubic foot of air, of ordinary temperature, would require such an effort
as would lift twenty-one pounds one foot from the ground. This task the
lungs accomplish by means which elude observation or analysis. It would
mean much to the arts if this parting power could be imitated simply and
cheaply. In common combustion each volume of oxygen which unites with
the fuel, carries with it four volumes of nitrogen which have to be
heated, not only reducing the temperature of the flame, but removing in
sheer waste much of the heat. A supply of oxygen free from admixture
would double the value of fuel for many purposes, creating a temperature
so high that it would be difficult to find building materials refractory
enough for the furnaces. Cheap oxygen would greatly increase the light
derivable from oil and gas, as proved in the brilliancy of an
oxyhydrogen jet. In bleaching and in scores of other processes, oxygen
is so valuable that, notwithstanding its present cost, the demand for it
steadily increases. Cannot the lungs, chemically or mechanically, be
copied so as to yield this gas at a low price for a thousand new
services?
In addition to separating oxygen from air our vital organs are every
moment performing chemical tasks just as elusive. The liver, for
instance, is a sugar-maker. The elaboration of living tissue is of
transcendent interest to the physiologist; it is fraught with the same
attraction to the chemist who would build compounds from their elements,
to the engineer who would transform heat or chemical energy into motive
power with less than the enormous loss of our present methods.
Flight.
In 1887 the late Professor S. P. Langley of Washington began experiments
in mechanical flight. He found that one horse-power will support in calm
air and propel at forty-five miles an hour a wing-plane weighing 209
pounds. Dr. A. F. Zahm, of the Catholic University of America, at
Washington, has recently ascertained that a thin foot-square gliding
plane weighing one pound soars with the least expenditure of power at
about 40 miles an hour, while at 80 miles the power required is more
than twice as much. As engines have been made weighing less than ten
pounds per horse-power, capable of yielding a horse-power for five
hours with four pounds of oil, we are plainly approaching the mastery
of the air,--so freely exercised by the sparrow and the midge. Among the
students eager in this advance are the men who examine with the camera
how wings of diverse types behave in flight, and then endeavor to
imitate the strongest and swiftest of these wings.
Light.
Professor Langley conducted another inquiry of fascinating interest,
this time respecting those natural light-producers, the fireflies,
especially the large and brilliant species indigenous to Cuba,
_Pyrophorus noctilucus_. As the result of refined measurements with the
spectroscope and the bolometer, the most delicate heat detector known to
the laboratory, he said: “The insect spectrum is lacking in rays of red
luminosity and presumably in the infra-red rays, usually of relatively
great heat, so that it seems probable that we have here light without
heat.” When we remember that ordinary artificial light is usually
accompanied by fifty to a hundred times as much energy in the form of
wasteful and injurious heat, we see the importance of this research. If
light can be produced without heat by nature, why not also by art?
[Illustration: Cuban firefly, life size.]
Converting Heat Into Work.
Another notable case of efficiency in nature has already been remarked,
namely, the conversion by the animal frame of fuel-values into
mechanical work. This is of a piece with the chief task of the engineer
as he puts his engines in motion by burning coal or wood, oil or gas. It
is a remarkably good steam engine which yields as much as one tenth as a
working dividend. Gas engines have sprung into wide popularity because
they yield larger results, in extremely favorable cases reaching thirty
per cent. A heat engine, of any type, has its effectiveness measured by
comparing in absolute units the heat which enters it with the heat which
remains after its work is done. The zero of the absolute scale is 460°
below the zero of Fahrenheit. So that if an engine begins work at 920°
Fahr. (1380° absolute), and the working substance is lowered in
temperature by its action in the machine until it falls to 460°
Fahrenheit (920° absolute), the engine has a gross efficiency of one
third. Economy depends upon employing a working substance at the highest
feasible temperature in such a mode that it leaves the engine at the
lowest temperature possible. Hence we see engineers devising
superheaters for their steam, and producing metal surfaces which either
need no lubrication at all, or employ such a lubricant as graphite,
which bears high temperatures without injury.
Now let us glance at the mechanism of our own frames, which, according
to Professor W. O. Atwater, converts about twenty per cent. of the
energy value of our food into mechanical work. This is a remarkable
performance, especially when we remember that in health the bodily
warmth does not rise above 98° Fahrenheit. What explains this amazing
effectiveness at a temperature so far below that of either a steam
engine or a gas engine? A simple experiment may be illuminating. We take
a plate of zinc and a plate of copper; although they seem to be at rest
we know them to be in active molecular motion, which motion is set free
when they combine with oxygen or other elements. This combination may
take place in two quite different ways, which we will now compare. In a
glass jar, nearly filled with a solution of sulphuric acid and water, we
immerse the plates of zinc and copper without their touching each other;
both rise in temperature as they corrode, as they unite with oxygen from
the surrounding liquid. We may, if we wish, employ this heat in driving
an air engine; but we can do better than that, for an air engine wastes
most of the heat supplied to it. We stop the heating process by joining
the two plates with a wire through which now passes an electric current,
our simple apparatus now forming a common voltaic cell. This current we
apply to lift weights, propel a fan, or execute any other task we
please, all with scarcely any waste of energy whatever. The instructive
point is that now chemical union is taking place without heat, in a mode
vastly more economical and easy to manage than if we allowed heat to be
generated, and then applied it in an engine to perform work. The
conclusion is irresistible: in the animal frame the conversion of
molecular energy into muscular motion is by electrical means and no
other. When the engineer learns in detail how the task is executed, and
imitates it with success; he will escape the tax now imposed on every
engine which sets its fuel on fire as the first step in converting
latent into actual motion.
Foresight Instead of Hindsight.
While inventors in the past might have taken many a hint from nature, as
a matter of fact they seldom did so, but went ahead, hit-or-miss,
failing to observe that what they reached with much laborious fumbling,
often they might have copied directly from nature. In Colorado and
California we admire the dams which are convex upstream, withstanding in
all the strength of an arch a tremendous pressure: this very plan is
adopted by beavers when they build in a swift current, as one may see in
many streams of the Adirondacks. In the rearing of irrigation dams, in
tasks much more difficult, human progress has gone forward by empirical
attempts one after another, and science has followed, long afterward, to
give reasons for any success arrived at by rule-of-thumb. But this
blundering hindsight is being replaced by a foresight which first spies
out what may be hit, and then never wastes an arrow. Professor R. H.
Thurston has said:--“Bleaching and dyeing flourished before chemistry
had a name; the inventor of gunpowder lived before Lavoisier; the
mariner’s compass pointed the seaman to the pole before magnetism took
form as a science. The steam engine was invented and set at work,
substantially as we know it to-day, before the science of thermodynamics
was dreamt of; the telegraph and the telephone, the electric light and
the railroad have made us familiar with marvels greater than those of
fiction, and yet they have been principally developed, in every
instance, by men who had acquired less of scientific knowledge than we
demand to-day of every college-bred lad.”
To-day the leaders in applied science are of quite other stamp. They
keenly observe what nature does, either in spontaneous chemical
activities or in the functions of a plant or an animal, then analyzing
the process with more and more insight and accuracy, they ask, How may
this with economy and profit be imitated by art? A feat of Professor
Henri Moissan is typical in this regard. In studying diamonds he became
convinced that they have been produced in nature from ordinary carbon
subjected to extreme temperatures and pressures. Imitating these heats
and pressures as well as he could, he manufactured diamonds from common
graphite in an electrical furnace. These gems are small, but they gleam
with promise of what the fully armed physicist and chemist may achieve
in duplicating the gifts of nature in the light of new knowledge, by
dint of new resources.