Popular Science Monthly/Volume 45/August 1894/Nature as Drama and Enginery
|NATURE AS DRAMA AND ENGINERY.|
PROF. EDWARD B. POULTON, of Oxford, in closing his course of lectures at Columbia College, last February, described the cordial reception extended him on his arrival in New York. Taking a stroll through Central Park, he had walked but a few paces when a gray squirrel ran from a tree to his feet in the friendliest way possible. "The perfect trustfulness of the little creature," said Prof. Poulton, "told me at once the most important fact of its life—that here in the midst of a teeming population it was certain of kind treatment. I inferred that a community kind to animals must be interested in them, must be fond of studying them in the very best place, their field of life." Nor was the naturalist disappointed; he found his New York audiences enthusiastic, and his lecture room, crowded to the door, contained less than half those who sought admission. Just as his observation of the squirrel in the act of soliciting luncheon told him what could never be disclosed in an inspection of the rodent, however skillfully stuffed in a museum or dissected in a laboratory, so, as the readers of his Colors of Animals well know. Prof. Poulton has discovered much of profound interest in natural history by keeping to the unfenced field so fruitfully scanned by the eye of Charles Darwin. Somewhat as in the case of his great master, his work owes its reward and derives its charm from its inclusive breadth of outlook. Specimens of hornet clear-wing moths might be collected for years, dissected under the microscope with the utmost care, and classified with the nicest precision, without casting a single ray of light on the prime questions, What forces have molded the form and habits of this insect, and why are its hues and markings as we find them? Let the moth, however, be observed in its field of life, and the agencies which have made it what it is come clearly into view. Among the insects which share its woods and meadows will be noticed a wasp; while this wasp neither preys upon the moth nor in any perceptible degree competes with it, the two insects sustain to each other a most vital relation. In its sting the wasp has so formidable and thoroughly advertised a weapon that by closely resembling the wasp the moth, though stingless, is able to live on its neighbor's reputation and escape attack from the birds and insects which otherwise would prey upon it. And so far is the mimicry carried that when the moth is caught in the hand it curves its body with an attitude so wasplike as seriously to strain the nerves of its captor. How came about so elaborate a piece of masquerade? At first, the explanation is, there was a faint general resemblance between the moth and the wasp; any moth in which that resemblance was in any degree unusually marked had therein an advantage, and tended to be in some measure left alone by its enemies; in thus escaping it could transmit its peculiarities of form and hue to its progeny, and so on, until in the rapid succession of insect generations, amid the equally rapid destruction of comparatively unprotected moths, the present striking similarity was at last attained. The study of mimicry of this type has from an unexpected quarter afforded singular confirmation of the theory of natural selection; in many cases the evidence of transformation within comparatively recent time is distinct—in the bee hawk moth, for example, the wings as they emerge from the chrysalis are thinly clothed with scales of ancestral derivation which are shaken off in the insect's first flight, with the result that the bumblebee is the better and more gainfully resembled.
As in the study of insects, so in that of plants—observation in the field at every stage of growth and development is needful to supplement the disclosures of the microscope and the dissecting needle. Many species, of which the milkweed blossom may stand as a type, are absolutely dependent on insects for their fertilization. How, therefore, can they be fully known in the laboratory and the herbarium? There is no more remarkable adaptation in Nature than that by which an orchid and the insect which continues its race conform to the outlines of each other. And hundreds of flowers less conspicuous than this orchid present perfumes, colors, and mechanism for attracting, seizing, and even imprisoning their insect visitors, which might well be the work of deliberate contrivance instead of inevitable selection from varying scents, hues, and forms of those which prove slightly more serviceable than others. That clover, peas, and other legumes receive their nitrogen from the air has long been suspected by agricultural chemists. The details of the process disclose one of the most curious interdependencies in the realm of Nature. Prof. Hellriegel has discovered nodules on the rootlets of the plants, tenanted by parasitic bacteria, which, while consuming a little of the substance of the plant, pay a handsome rent in the compounds of nitrogen which they build out of the air and pass to the fibers that harbor them. These microscopic purveyors, when bred and sown of set purpose, yield vastly increased crops of clover, alfalfa, peas, cow peas, beans, and lupine. Of this abundant testimony was presented at the Columbian Exhibition in the display of the Experiment Stations in the Agricultural Building.
Here, indeed, we come to the distinctive standpoint whence knowledge sweeps its new horizons: its outlook upon Nature as a whole, as a system intelligible only in the mutual interaction of its every part, however diverse and remote. It is a drama, not a tableau, which the observer to-day sees spread before him; in that drama every actor has been molded by the part it has had to play to maintain itself upon the stage; every rival, every parasite, every stress of climate with all its influence on food and frame has left its impress; and the ever-threatened doom for irresponsiveness has been the extinction pronounced upon countless forms once masters of the earth. No hue of feather or scale, no barb or horn, no curve of beak or note of song but has served a purpose in the plot or advanced the action in some life story of conflict. When Darwin was confronted in plant or beast by an organ which puzzled him, he was wont to ask, What use can this have had? And rarely was the question asked in vain. In the lunar or weekly recurrent periods of many animal functions there appeared to him a lingering registry of primordial birthplaces; ancestral inhabitants of seashores washed by tides being, in alternate submergence and exposure, profoundly affected in frame and habit.
What is true of the drama of organic life is equally true of the theater in which that drama is enacted. The more thorough its exploration by the geologist, the more extended in time the range of his admissible computations, the more convincing proof does he gather that our planet has become what it is in obedience to forces such as make the world at sunset a little different from the earth that faced the dawn. The hills once called eternal he knows to be anything but changeless, for their very prominence has made them special targets for the fury of tempests, the dividing axe of frost. At the bidding of impulses as irresistible, impulses hidden in the planet's core, a mountain is lifted in a valley's place, and the threatened denudation of a continent by the work of rain and river is silently compensated. And as Prof. Sterry Hunt was accustomed to point out, in the very constitution of the rocks before they bloomed with life, there was prefigured the struggle soon to be illustrated in plant and fish and insect. Amid the wealth of mineral compounds brought to birth only the stablest could survive the ceaseless stress of impinging forces. And these forces as they swept the lifeless globe—how decisive their after influence on herb, and beast, and man! Here, lifting the backbone of a continent, which all the storms of ages should leave a backbone still; there, in mid-ocean bidding an island rise from a volcano's heart; or decreeing a Sahara, or an Australian desert even more forbidding, where only cactus of the hardiest should ever fringe its dust-blown confines. In all this ever-shifting scene of action were laid the foundations of future barrenness of crag or fertility of plain, of that rich variety of earth sculpture in promontory and coast line which has meant so much to humankind.
In the history of the earth the chapter which precedes that written by the geologist is recited by the astronomer, whose keynote also is dynamic. The bulk, inclination, speed, and composition of the earth were all predetermined in the constitution, mass, and motion of the nebula which flung it forth. Dr. Huggins, his spectroscope before him, tells us that were the earth to resume a glowing heat it would yield much the same spectrum as the sun. Clearly, then, the scope of life on land and sea, the architecture of the forest, the ocean and the plain, with all their throbbing life, are what they are because the atoms which built them were present, and in such and such proportions, in the birth-cloud. If a blossom has tints of incomparable beauty, they are conferred by diverse elements thence derived, whose kin aflame in an orb, a celestial diameter away, send forth the beam needful to reveal that beauty. Were the sun less rich in variety of fuel than it is, the world, despite its own diversity of element, would be vastly less a feast for the eye than that which daily we enjoy.
As in the realm of organic life the modern interpretation is no longer static, so also in the sphere of Nature inorganic: it may be that all the thrust, recoil, and interaction in the life of plant and animal lay dormant in the simpler enginery of the atoms and molecules which build their frames and supply their food. It was one of the shrewd guesses of Sir Isaac Newton that the diamond is a combustible body; he did not suspect it to be one with coal in substance, but he observed it to be highly refrangible, as many combustible bodies are. His conjecture shows him to have taken the first step toward the view of modern physicists and chemists—namely, that properties, the modes of behavior of matter, are not passive qualities, but are due to very real activities; that what a substance is depends upon how in its ultimate parts it moves; just as organic structure can be deduced from living function because regarded as the creation of function, or, as in more familiar cases, the character of a die is inferred from its impress, and the construction of a machine read in the work it executes. Clausius and Maxwell, in a theory which marks an epoch, explained the elasticity of gases as manifesting the ceaseless motion of their molecules, declaring that an ounce of air within a fragile jar is able to sustain the pressure of the atmosphere around it, because the air, though only an ounce in weight, dashes against the containing walls with an impact forcible enough to balance the external pressure—proof whereof consists in measuring the velocity with which the air rushes into a vacuum. Here the significant point is that in leaving the realm of mass-mechanics, where the tax of friction is ever present and inexorable, we enter a sphere where motion of the swiftest can go on forever without paying friction the smallest levy. The elasticity of metallic springs has been similarly explained as kinetic. If we swiftly turn a gyroscopic wheel we can only change its plane of rotation by expending force, which force is repaid when the metal is allowed to resume its original plane of motion. It is imagined that in like manner the particles in an elastic spring move swiftly in a definite plane; if deflected from that plane they oppose resistance and stand ready to do work in returning thereto. Of kindred to the kinetic theory of elasticity is the modern explanation that heat consists in a distinct and ceaseless molecular motion, on which motion, indeed, depend the dimensions of masses. Take a cube of lead or iron from summer air into an ice-house and at once the proportions of the mass begin to shrink. And the molecules themselves, whether of lead, iron, or other element, are imagined by Helmholtz as vortexes born of the ether in which without resistance they forever whirl. As observation proves in the case of a rapidly rotated chain, substantial rigidity can be conferred by motion sufficiently swift. Nor are molecules without something of individuality. We are wont to think of masses of solid iron as precisely similar, but experience proves that one bar or shaft of iron varies from another by all that has differenced the past history of the two. A careful workman uses his die of strongest steel for only a short term of service, well assured that the metal, despite its seeming wholeness, suffers serious internal shocks at every blow—shocks which, were no caution exercised, would soon reveal themselves in fracture and ruined work. In phenomena of this type, which every day confront the electrician and the engineer as well as the mechanic, there seems a prophecy of the sensibility and memory which dawn with organic life.
In the broad field of wave energy the mechanical analogies point to the sway of a single law of motion. If a pendulum is to be maintained in its vibrations, it must receive impulses sympathetically timed—impulses related to its own period of wing as decided by its length. In like manner a piano string vibrates responsively to the note which, when struck, it sends forth; and a gas, such as sodium, when comparatively cool, intercepts in the spectroscopic field precisely those waves which a glowing body of similar gas in the flame of sun or star has radiated. A pane of glass which transmits only the red rays of sunlight, when molten emits the rays complementary to red, and glows as greenish blue. Uncolored glass, which transmits light perfectly, conducts heat badly, because' the vibrations are unlike; for the same reason conductors of electricity—the metals, for example—are opaque. The late Dr. Hertz, in generating electric waves intermediate in amplitude between those of sound and light, discovered that opaqueness is a relative term—arm a wave with appropriate dimensions and it has a passport through any substance whatever; a stone wall or a wooden door becomes as permeable as plate glass to sunshine. All this has long been suspected by the physicists who, among equally significant facts, have noticed that an explosive is set off less by the violence of its detonator than by the sympathy of rhythm between the two. Dr. Lothar Meyer, in his Modern Theories of Chemistry, discusses the ingenious theories which on kinetic principles explain many of the chief qualities of matter—color, refrangibility, volatility, fusibility, and ability to yield heat in combustion. He regards this field as that which bears most promise for the chemical investigator, and follows Berthollet in maintaining that chemistry is but a branch of the larger science of mechanics. In corroboration of this view a thousand facts might be cited—a typical piece of evidence is that adduced by Mr. Witt, who finds that the stability of the azo-benzene dyes turns upon the nicety with which their acid and basic functions balance each other.
In leaving the field of molar for that of molecular mechanics, it has been already noted that friction need no longer be reckoned with; consequences equally important result from the fact that now masses of extreme minuteness are in play. Sir William Thomson (Nature, vol. i. p. 551) has estimated the diameter of molecules as at most 1 of an inch in diameter; cubical molecules of this size containable in a cubic inch of space would have a total surface of one square mile and one seventh, which implies that in molecular mechanics superficial forces must count for vastly more than in molar mechanics. Another result follows from molecular minuteness of dimensions—an enormously increased capacity for motion. The smaller a wheel the more swiftly can it be rotated without being parted by centrifugal force, and therefore the more motion can it contain. With a molecule probably, with an atom certainly, centrifugal force has no separating power. How great the momentum of specific molecular motions will appear in computing that due to temperature, in the case of a pound of unfrozen water at the zero of the centigrade scale. According to the determinations of Lord Rayleigh, a pound of water, in falling through one degree of temperature, liberates heat equal to that generated were the mass to fall from a height of fourteen hundred and two feet to the surface of the earth. Therefore, in first becoming ice, and then falling in temperature through two hundred and seventy-three degrees, it parts with an amount of energy equal to lifting the pound of water some fifty-seven and one third miles from the surface of the earth, leaving out of view, for simplicity's sake, the diminution in the attraction of the earth as the mass is lifted. Prof. Dewar, in his recent remarkable experiments at a temperature of 200º below zero, has found reason to believe that at absolute zero the electrical resistance of metals would disappear; cooled to the temperature of liquid oxygen, the red oxide of mercury becomes yellow, and both sulphur and bichromate of potash turn white.
Surprising as are the figures which denote the molecular motion due to the temperature of water, more surprising still are the computations which declare the chemical energy in the gases which unite to form water. Measuring the heat liberated in their union, it is found that the molecules of hydrogen and oxygen possess as chemic motion energy equal to lifting the masses involved some eleven hundred miles from the surface of the earth. It is imagined that the molecular motions representing temperature, chemical affinity, electrification, or other energy, coexist without confusion, just as air sustains, in perfect order, the superposed harmonies of an orchestra and chorus. The extremely rapid motion of molecules, acting at their comparatively vast surfaces, must immensely exalt forces which, between masses, are but feeble. A simple model may help to make this clear. Let two cylindrical wheels, similar in all respects and covered with rubber, be brought into contact on a floor—they will in a slight degree adhere; let the wheels be swiftly turned in a direction toward each other, and they will press each other with considerable force—force proportionate to their speed, which force at high speed will exalt their weak adhesion to somewhat of the intensity of cohesion as manifested between molecules. The model can illustrate something more: as a unit it does not change its place, albeit that its halves are in rapid motion; were its dimensions too small for microscopic view, the motion of its parts would be undetected, and, because the motions would balance each other, a mass built up of such pairs of molecules would be in seeming rest.
While the chemists are busy disentangling the orbits in which swim the atoms and molecules of the laboratory, the physicists are equally active in endeavoring to reduce to mechanics the various phases of energ5^ Here the first and decisive step was taken when the revelations of form and color to the eye were explained as borne by ethereal waves, which follow one another at a rate so prodigious as to yield the impression of rest; which explanation, indeed, had long been suggested in the phenomena of sound where air-waves are palpably concerned. The notable points of agreement in both spheres of action are that a medium can transfer motion as perfectly as if the two bodies connected by it were in immediate contact; moreover, that the efficiency of the medium increases as its density diminishes; and that the medium itself exacts no toll whatever, relapsing when its work is done into the seeming rest from which its task awakened it. With apparatus acoustic in model, the late Dr. Hertz, of Bonn, demonstrated that light and electricity differ from each other only as short waves differ from long ones; presumably the same medium serving as the vehicle for both. His masterly experiments thus disclosed another bridge between modes of motion which less than a century ago were accounted distinct and unconnected.
While the establishment of the truth of the conservation of energy justly ranks among the grandest achievements of human thought, that truth would be rounded into satisfying completeness were it proved that energy in all its forms is motion and nothing else. The obstacle here, is that gravity does not lend itself to any kinetic theory thus far framed. And this notwithstanding that atomic weight is the fundamental characteristic of matter, so that, indeed, it conditions every property of a substance—proof of which arrived in the fulfillment of the predictions of Mendelejeef, who, taking this theory as his finder-thought, foretold that scandium, gallium, and germanium would be added to the list of chemical elements, and would be found to possess properties which he detailed. Gravity is marked off from other phases of energy by two characteristics—if it be transmitted through space as are other modes of motion, it either travels instantaneously, or so fast as to elude the observation of astronomers competent to detect its movement were it fifty million times as swift as light. Quite as remarkable is the fact that a mass may be heated, electrified, magnetized, or chemically transformed without its weight being affected in the slightest degree. This in striking contrast with the action of heat, which modifies the color, chemical activity, conductivity, and other properties of a substance, and its volume as well. The only analogy which gravity bears to other forms of energy is that which it sustains to electricity and magnetism, and were these forces attractive only, the analogy would be a close one. But let us trace what analogy there is and we may find it helpful. In the manufacture of a common steel magnet the palpable motion of a dynamo disappears to create its attraction; the imparted dynamo motion therefore is imagined as continuing in full actuality in the molecules of the magnet. When an armature is brought within the magnet's field it is attracted—that is, it powerfully tends to move toward the magnet; until that impulse is satisfied a space divides armature and magnet. All the analogies of light and electricity, proved to be fundamentally one with magnetism, bid us believe that between magnet and armature a medium is actively concerned in bringing both masses together; why may not a similar, or that identical, medium be active in bringing from a tree an apple to the earth? What is needed here is investigation of how the motion of a molecule in its own orbit, or on its axis, becomes a movement of translation. A wheel, if frictionless like a molecule, could revolve on its bearings forever; if it were small enough, its motion would forever escape observation. Were it dropped from its bearings, through however short a distance, to a horizontal plane, part of its energy would be at once expressed in its advancing in a line long enough for detection. The question behind attraction and repulsion is, How shall two distant bodies move on their axes, or in their orbits, so as to act on a chain of intervening bodies with the effect that the two shall approach or recede from each other? This problem does not seem to present insuperable difficulty to the inventiveness which has built so many models illustrating the architecture of the molecule, showing how, in all probability, the links subsist between the atoms of an alcohol or an ether.
One after another various forms of energy once called potential have been brought into line with energy actual, have been reasonably explained as meaning nothing more or less than motion; is it not time that old conceptions of motion should be expanded so as to include the phenomena of gravity as well as all the others once deemed to consist in mere "advantage of position"? Gravity can be imagined as a special molecular motion in its propagation either instantaneous or too swift for existing means of measurement. This supposition may be an unwelcome one, but what is the alternative? Whereas the physicist of to-day holds that the chemical energy of such an element as carbon, the elasticity of a coiled spring or of a confined body of gas, and the quality we call temperature, all denote real activities, nevertheless? the lifting of a weight, into which any of these activities can bo readily transformed, is not represented by motion at all, but by an ultimate and unnamed something else. Whether is it better to cherish a conception in its inherited form or to try to broaden it as the facts demand? For the inclusion of gravity among the phases of veritable motion there is cumulative suggestion. When in every other phase of energy there is either detection of motion in whatrest, or an assumption of motion the validity of which is proved in the fulfillment of the predictions to which it leads, the hint is clear. It is that gravity, too, will be demonstrated as motion by future means of inquiry which may as far transcend our present resources as these surpass the methods of the men of science who, not so very long ago, could bring forward reasons for believing phlogiston to be a substance and electricity to be a fluid.
The advance of knowledge thus far has been a process of identification. Heat, chemical affinity, electricity, magnetism, and all the other forms of palpable energy are now held to differ from one another only as do the circles, spirals, and straight lines described by the wheels and levers of the machine shop. In an everextending curve the physicist has arranged a continuous series of real activities, a wide diversity of energies once deemed "potential" static, at perfect rest. Is it reasonable to maintain that this curve of his, almost a full circle, does not form part of a real circle, that the small arc which yawns where gravity can fit with the completing effect of a keystone, represents a discontinuity in the nature of things? Preferable, because more probable, is the idea that the scope of kinetic explanation is universal, that the whole scheme of physical Nature represents in its every part and function an enginery upon whose ceaseless action hinges the drama, ever more involved, of plant and animal and human life.
To men who knew only what had befallen themselves and their dwelling place during a few generations, it was but natural to repeat: "The thing that hath been, it is that which shall be; and that which is done, is that which shall be done; and there is no new thing under the sun." But we of to-day are in different case. The astronomer, joining camera to telescope, expands the sphere of the known universe a million fold; he discovers system after system in stages of life such as our sun and its attendant orbs have passed through in ages so distant as to refuse conception. The geologist, deciphering the birth register of our planet's oldest rocks, gives them a lifetime scarcely to be distinguished from eternity. The range of time, thus broadened, permits to the smallest arc of change a sweep wherein it becomes a circle of profoundest transformation. The naturalist, his tasks of mere description almost at an end, finds their chief value to lie in their furnishing data for the new question. How did all this diversity of life become what it is? Ever the keynote of reply is action and reaction, unending stimulus and response. Permanence is only a seeming, the truth behind it is universal plasticity and change. In the organic world this passing from appearance to cause has restored soul to body, and made intelligible for the first time both form and substance, by referring them to the forces which mold and inform every material frame of life. In the inorganic world it will be the same; the force which binds sun to planet, pebble to seashore, will yet be understood as part of the unbroken round of all-comprehending motion.
- Ecclesiastes, i, 9.