Gustave Le Bon’s The Evolution of Forces is speculative physical science, written for the International Scientific Series and published in French and English in the early years of the twentieth century. Its editor, F. Legge, presents it as the sequel to Le Bon’s The Evolution of Matter: where that book argued that all matter is slowly dissociating and decaying, this one draws the corollary that the atom is an immense reservoir of energy and the source of most of the forces we observe. Le Bon writes as a physicist addressing physicists, but also as a controversialist convinced that the science of his day is in crisis.
“The invisible region of the spectrum constitutes, then, the most important portion of light.”
The Case Against the Two Great Dogmas
Legge’s Preface and the Promise of a New Physics
F. Legge’s preface frames the volume as the sequel to The Evolution of Matter. In that first work Le Bon had argued that all matter is perpetually dissociating and decaying; here he draws the corollary that the atom is a vast reservoir of energy and the source of most of the universe’s forces. Legge notes that Le Bon supports the claim with his own researches into invisible radiations, phosphorescence, and Hertzian waves, all explained by the hypothesis that a dissociating atom releases the energy stored within it at its formation. Le Bon is careful to present this as suggestion rather than demonstration, with conclusive proof left to future experiment.
Legge takes some satisfaction in reporting that the thesis has found approval from an unexpected quarter. In France, Le Bon’s early work on what he called “Black Light” had drawn a storm of abuse, now faded; in England two members of the Cavendish Laboratory had attacked both the teaching and the novelty of The Evolution of Matter. It is therefore pleasing that P. D. Innes, himself of the Cavendish, writing with the apparent approval of its Director in the Proceedings of the Royal Society, declares atomic disintegration the only theory that satisfactorily accounts for radio-active phenomena and a great store of energy in the atom beyond question—precisely Le Bon’s position. Legge adds that the book was written for the International Scientific Series and meant to appear simultaneously in England and France; difficulties in reproducing the illustrations delayed the English version by some months, during which eight French editions of a thousand copies each were rapidly exhausted. The delay allowed Legge to add corrections, notes, and indexes absent from the French editions. The preface is dated from the Royal Institution, February 1908.
The Present Anarchy of Science
The first chapter proper, “The Present Anarchy of Science,” sets the scene by contrasting the old clarity of physical science with the vagueness of psychology, politics, and history. Chemistry and mechanics had rested on the indestructible atom, physics on indestructible energy, and tidy equations seemed to unite time, space, matter, and force. Some minds hoped to reduce all phenomena to manifestations of a single entity, energy. The narrator describes a first period of confidence, especially in the earlier half of the nineteenth century, when philosophical and religious dogmas were fading and the founders of each new science believed they had built permanent frameworks. That confidence held until unforeseen discoveries condemned scientific thought to doubt; contradictions grew striking, and the question arose whether the principles of physics were merely fragile hypotheses. Scientific dogmas then underwent what religious dogmas had suffered before them: criticism, decadence, disappearance. The great principles survive as positive truths for the multitude and in elementary textbooks, but have lost prestige among real scholars—science has entered a phase of anarchy.
As evidence, the narrator cites Henri Poincaré’s La Science et l’Hypothèse to show that even mathematics subsists only on hypotheses and conventions, and Poincaré’s colleague Émile Picard, who demonstrates how incoherent the present principles of mechanics have become. Picard observes that at the end of the eighteenth century those principles seemed to defy all criticism, yet searching analysis has since examined their foundations, and where men like Lagrange and Laplace found everything simple we now meet the gravest difficulties. Professor Mach, in his History of Mechanics, is quoted to the effect that the apparently simplest principles of mechanics are highly complicated, rest on unrealized and unrealizable experiments, and cannot be considered demonstrated mathematical truths. The narrator notes that we possess three systems of mechanics, each declaring the other two absurd, and quotes Lucien Poincaré: hardly any of the great theories once universally admitted still exist, a certain anarchy reigns in the natural sciences, we witness rather a demolition than a work of construction, the idea that all phenomena admit mechanical explanation is generally abandoned, and the very principles of mechanics are contested.
The Value of Doubt
The narrator draws a lesson from this wreckage. Great theories formerly vanished only when strongly founded new doctrines replaced them; today the old principles are dead or dying while their replacements are only forming—modern man destroys faster than he builds. Yet nothing, he holds, is more favourable to progress than such anarchy, since erroneous or insufficient ideas imposed by classic teaching weave a bandage over our sight, and history shows that scientific theories retard progress once they become fixed. He warns against presenting uncertainties as indisputable truths in educational works, and against presuming to set limits to science, as Auguste Comte wished when he even proposed an Areopagus of scholars to fix the boundaries of permitted research; such tribunals are already too numerous and baneful. Descartes, who viewed as doubtful what had been considered uncontested truth, earns his praise, and he insists that the scientific idols of the present day have no more right to invulnerability than those of the past.
The Two Fallen Dogmas
The two dogmas of modern science formerly most respected were the indestructibility of matter and of energy. The first was already two thousand years old: while all things in the universe were condemned to perish, matter remained indestructible, its atoms enjoying eternal youth like the gods of ancient legend. Energy was equally indestructible—it might change form, but its quantity remained invariable, no form disappearing without replacement by an equivalent. The narrator says he devoted nearly ten years of experimental research, summarized in The Evolution of Matter, to proving that the first dogma can no longer be maintained and that matter must enter the cycle of things condemned to grow old.
Mass, Force, and Movement
The argument then turns to the concepts on which mechanics rests. “Mass” carries two senses: for physicists a coefficient of inertia, for astronomers a coefficient of attraction, while chemists compare masses by attraction. Mechanics needed another element because gravity varies with latitude, height, and even between the storeys of a house. Weight varies from place to place, but acceleration varies equally, so their ratio is constant everywhere—hence the equation M = W/g defines mass by gravity, and replacing weight by any force F producing acceleration γ gives the fundamental equation M = F/γ, into whose meaning, the narrator warns, one must not look too closely. Mass was considered invariable until recent researches showed it varies with the dissociation of atoms, and that the products of dissociation have a mass varying with velocity, able to become infinite as velocity approaches that of light. Whether mass varies with temperature remains unresolved. Its apparent fixity was due to imperfect observation; inertia remains the most stable thing in phenomena—not absolute, but a great constant of the universe.
For half a century science thought it had a second constant, energy, of which forces are manifestations. Forces are knowable only by the movements they produce; classic mechanics defines force as a cause of movement. By inertia alone bodies assume uniform rectilinear motion; accelerated motion reveals a force, and mechanics measures only acceleration. Movement itself is not irreducible, deriving from time, space, matter, and force, and the formula F = mγ defines force by the acceleration imparted to a body endowed with resistance.
The Building Up of Forces
Resistance and movement remain the essential elements.
The Rejection of Motion-to-Electricity Conversion
Le Bon opens this stretch by dismantling the orthodox account of the dynamo. The claim that spinning a coil transforms movement into electricity strikes him as no better than turning lead into gold by shaking it in a bottle. Kinetic energy, he insists, does not undergo such a metamorphosis. What actually happens is that matter is easily dissociated and holds an immense reservoir of intra-atomic energy; the lines of force seized by a conductor cutting them are continually replaced at the expense of that nearly inexhaustible store, so a single magnet can yield an almost infinite supply. Displacing the conductor merely puts it in a condition to absorb lines of force and give them the form of a current. A determinate quantity of movement is needed to generate a determinate quantity of electricity, but that fact does not license the deduction that movement has been transformed. Dynamos, then, are not movement converted into electricity; they are the intra-atomic energy of dissociated matter appearing as electricity—a principle he extends from street lighting to the heat of the sun.
Faraday’s Lines of Force and the Unity of Ether and Matter
Faraday, refusing to let matter act at a distance, deduced an intermediary connecting electrified bodies and recognised lines of force filling the electric field. He gave them real existence—elastic springs repelling one another, joining bodies of contrary sign, their extremities forming the charge—and demonstrated them with iron filings on a card above a magnet’s poles. Maxwell recast them as ether cells whirling about the lines as axes, with electric particles between, a theory no experiment verifies. Le Bon stresses how readily these lines pierce all substances, conductors and insulators alike, more easily than X-rays or radium particles; had they acted on photographic plates, the X-rays would never have caused such a stir. Faraday’s cage experiment, he notes, makes us forget how easily metals are transpierced—without the earth-wire, metal opposes no obstacle—and his own apparatus, an electroscope shielded by three concentric cylinders of metal or ebonite, can be charged instantaneously. Magnetic transparency is equally complete. Lines of force resemble no material substance, yet plainly issue from matter: two heterogeneous substances drawn apart remain joined by real elastic threads, as Faraday saw. A magnetic field behaves as a viscous medium dragging bodies plunged into it, and rotating fields are already used in industry. Ether and matter, the argument runs, are not two separate worlds but one.
Hertzian Waves and Branly’s Filings
In 1888 Hertz found that oscillating discharges generate ether undulations, propagated, refracted and polarised like light and differing only in dimensions; they induce currents in conductors, and wireless telegraphy rests on their propagation. Le Bon questions the leap to identifying Hertzian and light waves, since no electric or magnetic phenomenon has ever been obtained with light. Hertzian waves stand to electricity as radiant heat stands to heat circulating in matter. Matter, meanwhile, shows extraordinary sensitiveness: metal fragments hundreds of kilometres away can become conductors under ether vibrations. Hertz’s receiver was a wire circle with two balls, and its very insensitivity was fortunate—sensitive receivers give identical indications whether in focus, beside or behind the mirror. Branly’s filings-tube is simple and marvellously sensitive, restored by a slight blow; his discovery of the variable conductivity of metal filings ranks, for Le Bon, among the most remarkable of modern physics. A column of polished discs—bismuth, aluminium or steel balls—has considerable resistance, which becomes almost nil after a small spark and returns with a tap; alternate lead and aluminium discs jump from about 30,000 ohms to 3 under weak waves. Copper is the notable exception, fortunately, or Ohm’s law could never have been discovered, and its property communicates itself to neighbouring aluminium discs.
The Military Future of Concentrated Waves
Electric waves disperse energy in every direction, and concentrating them with cylindro-parabolic mirrors would demand gigantic dimensions. Le Bon nonetheless sketches the scheme he intended: many such mirrors side by side, intense fields from an Oudin resonator, a 60-centimetre spark coil making metallic objects in a ten-metre room emit thousands of sparks and once melting wires by short circuit. A pencil of parallel Hertzian waves, he argues, would change civilisation by rendering war impossible—an enemy’s ironclads in harbour blown up from several kilometres away, shells and torpedoes exploded, fortresses and cartridge stores destroyed. No protection is possible: a metal sheet a hundredth of a millimetre thick stops the waves, but the slightest crack between joints lets them through.
The Transparency of Matter
The ideas current in 1899 were, he says, erroneous. Hertz recognised that metals reflect waves but left their opacity unascertained; Joubert found a zinc wall 2.5 mm thick weakened sparks without destroying them; Lodge supposed “reasonable” thicknesses opaque; Bose concluded metals are transparent, describing six months baffled by an unknown error—a tinplate case transmitting radiations, a second envelope proving efficacious unless the receiver sat too close. Veillon’s zinc case 1 mm thick passed waves only when the sparks were near. Dielectrics were thought absolutely transparent, and wireless telegraphy seemed to confirm that walls and hills were traversed. Le Bon posed two problems—can thin metals be traversed, and are non-conductors of any thickness transparent?—and enlisted Branly, publishing the results in the Comptes Rendus.
Atomic Equilibrium and the Thirteen Forms of Electricity
Rotational velocities of atomic elements, he continues, explain not only projections but the equilibrium of the elements forming atoms: as a top falls when it stops turning, so matter holds together only through movement, and were it to stop for an instant all bodies would crumble into an invisible dust of ether. The atom is a small solar system whose peripheral particles, when centrifugal force exceeds attraction, escape along the tangent like a stone from a sling. Electricity, in his earlier book, was an intermediary between matter and ether, born of disturbances of ether equilibrium after partial disaggregation; light, heat and electricity result according to the nature of those disturbances, though the elements producing them are in themselves neither electrical nor calorific. The electron, near kin to old phlogiston, is dismissed via Professor de Heen as one of the most unfortunate metaphysical ideas recently formulated. Particles at rest are no more electricity than ether at rest is light; one should no more speak of neutral electricity than of neutral movement. He then enumerates thirteen forms—the electric fluid, static and dynamic electricity, magnetism, electrons, cathode rays, X-rays, negative and positive ions, the ionic fluid, neutral electricity, electricity condensed in chemical compounds, and electric waves—before concluding that calling all these transformations of movement would apply equally to life, translating ignorance into other words.
The Problems of Heat
Opening the book on heat, Le Bon grants that thermodynamics has become precise and fertile while our grasp of heat’s causes has scarcely advanced in a century. He quotes Davy at length: particles must have space between them, a body communicating expansive motion must itself possess moving particles, and at uniform temperature the motion must be vibratory or rotatory; temperature may depend on the velocity of vibrations, and the cooling of melting or evaporation on lost vibratory motion.
Phosphorescence in the Deep Sea and the Luminous Bacteria
Le Bon turns to the phosphorescence of living things, a field transformed by instruments that now permit study of life at depths of several thousand metres. The sea bottom, he reports, is covered with forests of phosphorescent polyps, and even the smallest and bulkiest inhabitants of those dark depths carry organs enabling them to light themselves—some on different parts of the body, others in or above the eye, which he compares to bicycle lamps. Dr. Richard, curator of the Prince of Monaco’s collections, showed him a series of such animals, notably large fishes with lamps on each side of the body which they can mask at will. These have been studied almost exclusively anatomically.
Beyond the deep-sea beings, luminous bacteria appear on fishes’ bodies after death and before decomposition. They are easily cultivated in ordinary water with about three per cent sea-salt and one per cent asparagine; analogous products yielded the bottles sold as “Living Light” at the Paris Exhibition of 1900. The author prepared similar ones by scraping a herring’s scales into such liquid; after twenty-four hours they are luminous for three or four days. The chemical bodies producing this phosphorescence remain undetermined, and it can survive the animal’s death—Carus had seen dried and powdered luminous organs of the Italian lamprey regain phosphorescence on being moistened. These phenomena are due to chemical actions requiring air and water; suppressed, the phosphorescence disappears. The spectrum varies slightly with the animal and impresses photographic plates rapidly; the author reproduced negatives with two minutes’ exposure using fish made phosphorescent after death by luminous bacteria. In its effects it closely resembles phosphorescence from other bodies; in its causes it differs, being generated neither by light nor heat, and is near akin to phosphorescence by chemical reaction.
Gases Made Luminous, and the Mercury Lamp
Study of electric discharges in gases shows electricity’s part; light and heat may act by indirectly exciting electric manifestations. Electricity alone can render gases luminous: the highest temperature gives hardly perceptible luminosity, whereas rarefied gas in a tube with an electric current becomes greatly luminous; placing the tube near a high-frequency resonator or subjecting it to electric waves suffices. With helium tubes the luminosity is brilliant enough to detect these waves, though a footnote notes neon tubes rather than helium are now used as detectors of Hertzian waves, citing Dr. Fleming’s cymometer. The mercury lamp shows lighting by phosphorescence is practicable: a long glass tube with one iron and one mercury electrode, evacuated and connected to electricity, makes traces of gas and mercury vapour brightly phosphorescent; there is no incandescence, the tube being only about 125° C, far below incandescence, while a candle flame is about 1700° C. The mercury tube’s spectrum has very few red and infra-red rays though its output exceeds ordinary incandescent light, which requires enormous useless calorific rays. Present artificial lighting is barbarous: a gas flame or electric arc contains only one per cent useful rays, ninety-nine per cent appearing as dark heat—of 100 fcs of gas, 99 fcs lost, one franc used; with the mercury lamp 40 fcs of 100 serve lighting; the glowworm’s output is higher still, nearly all energy becoming visible light. Phosphorescence will probably be the artificial light of the future. The author regrets the study was too costly for his modest researches, being persuaded thorough knowledge will open new vistas on the greatest problems of physics and astronomy. Phosphorescence by electrical action gives atoms the same radiating properties as heat; intra-atomic energy ought to play a part, for the gases are strongly ionized—dissociated by the current. Probably stars composed of gas owe their brilliancy to analogous electric actions, since gaseous bodies cannot shine by incandescence; if so, stars attributed enormous heat may be at relatively low temperature, perhaps shining by incandescence only at a certain phase.
The Causes of Phosphorescence
Phosphorescence transforms into light various energies, only a few known. In gases electric energy is the sole possible cause; in that due to light, heat, and chemical reactions other energies intervene, their mode undetermined. Since very different causes—light, shock or impact, X-rays—may produce phosphorescence in the same substance, these excitants probably provoke reactions not identical but of the same order. The old theory that phosphorescent bodies simply restore absorbed light, as a sponge restores water, is no longer tenable. Phosphorescence seems linked with dissociation of matter and the liberation of energies accompanying it; the link is evident for gases, phosphorescent only under electrical actions always accompanied by ionization—disintegration of atoms. For other forms the connection is far less evident, though probable for phosphorescence by light, since light energetically dissociates matter and the radiations producing this dissociation are most apt to produce phosphorescence. The tendency to consider phosphorescence a consequence of atomic dissociation is taking shape among physicists: De Heen and, after him, Lenard recently concluded that light acts by provoking emission of negative ions issuing from the atom and capable of returning to it by oscillation. To these movements of the dissociated atom’s elements should be due the ether radiation producing phosphorescence; its light, of the same nature as incandescent bodies’, differs by the absence of any elevation of temperature, justifying the name cold light. Possibly light rays, electricity, and other causes bring intra-atomic energy immediately into play without passing through molecular movements as heat does. It is not strictly proved that cold light is not as hot as incandescent light; if phosphorescence is a very superficial atomic phenomenon, the elevated temperature may be inappreciable.
Black Light and Seeing Through Opaque Bodies
The author notes that infra-red and invisible phosphorescence caused many researches before he could distinguish them; other observers—Dr. Russell, Dr. Kahlbaum, Professor Melander—periodically rediscover his early experiments and observe such impressions afresh. Once the causes are determined, these experiments lose interest, which is why he does not dwell on them. Not only metals but wood and animal tissues also produce such impressions, made more active by slight heat, though with different substances certain chemical reactions may come into play.
Most of the solar spectrum, he states, consists of invisible rays in the infra-red region, extending for sunlight to 5 μ according to Langley’s researches; flame spectra extend to 60 μ. This region had hardly been studied except for calorific properties. Having discovered that zinc sulphide with green phosphorescence was nearly as sensitive to part of these radiations as gelatino-bromide of silver is to visible light, the author studied their properties, especially passage through many opaque bodies, allowing sight and photography through them. To see an object behind an opaque body—a wooden plank or black paper—rays must first pass through it, and the eye must be rendered sensitive to them. The X-rays proved opaque bodies can be traversed by certain radiations, but these artificially created radiations could not modify old ideas of opacity; the fable of the lynx seeing through walls seemed unrealizable. Pursuing researches on “Black Light,” he established two things: luminous rays, or certain of them, pass without difficulty through many opaque bodies; and the invisible rays passing through can easily be rendered visible.
Energy Without Indestructibility
The intellectual spine of the book is a refusal of the two dogmas Le Bon takes to be the foundation stones of nineteenth-century physics: the indestructibility of matter and the indestructibility of energy. The first he had already attacked in his earlier volume; here he turns to the second, and the argument is more radical than a mere correction of detail. Where his contemporaries saw energy passing through transformations while its quantity stayed fixed, Le Bon sees a fiction produced by the habit of measuring everything in the same unit of work. To call the friction of resin against flannel a “transformation” of movement into heat and electricity is, on his account, like claiming that a silver coin has turned into a metre of silk because the two are exchanged. Different forms of energy, he insists, are not convertible substances but distinct effects arising from distinct causes, and the appearance of conservation is an artefact of our accounting.
What replaces the old dogma is a picture of force as the transient effect of disturbed equilibrium. Energy appears only where there is a difference of level — of temperature, of electric potential, of velocity — and vanishes when equilibrium is restored. Le Bon makes this vivid with a thought experiment: beings living in a world of ice at zero, who possessed liquid air at minus one hundred and eighty degrees, would find ice a formidable source of power, boiling the liquid air and driving their motors with blocks of ice. The corollary is stark. Energy is not a permanent entity but a passing effect, always degraded in use, and the universe is not a closed system in which the books must balance. Against the objection that his own account of atoms storing energy would violate Carnot’s principle, he replies that the principle governs the downward phase of cosmic evolution, not necessarily the upward one, and that we should await a better knowledge of nature’s laws rather than fall back on a creator drawing worlds from will.
The Atom as Reservoir
Running alongside the critique of energy is a positive doctrine of matter that gives the book its title. The atom, for Le Bon, is a small solar system of particles held in equilibrium only by their own immense velocities of rotation and revolution; stop the movement for an instant and every body would collapse into an invisible dust of ether. When the atom dissociates, it releases the energy stored at its formation, and this intra-atomic energy — not the transformation of ordinary motion — is what appears to us as electricity, light, and heat. The dynamo does not convert movement into electricity; the lines of force seized by a moving conductor are continually renewed at the expense of the dissociated atom’s nearly inexhaustible reserve. On this view electricity becomes an intermediary substance between matter and ether, and the various “forms” of electricity — static, dynamic, magnetic, the cathode rays, the ions, the Hertzian waves — are simply different disturbances of equilibrium, grouped together by our need for simplification rather than by any real identity.
Le Bon carries this habit of unification into the study of heat and light, where he is at his most empirical and his most quarrelsome. He attacks the textbook picture of the solar spectrum, which reproduces only the visible band and distorts the proportions of colour; he reports Langley’s finding that the visible spectrum contains only a fifth of the calorific energy of the infra-red region, and argues that artificial lighting is barbarous because a gas flame or electric arc wastes ninety-nine per cent of its output as dark heat. His own experiments on phosphorescence — the Brazilian diamonds that shine after exposure to magnesium light while Cape diamonds do not, the sulphide screens whose glow varies with the temperature at which they were charged — lead him to the conclusion that cold light is a phenomenon of atomic dissociation, and that phosphorescence may well become the artificial light of the future.
Hidden Forces and the End of the World
The later books push outward from the laboratory into territory that the nineteenth century had largely abandoned to speculation. Le Bon devotes long chapters to “Black Light” — the infra-red radiations that pass through opaque bodies and allow objects to be seen and photographed through wood and black paper — and to the transparency of matter to electric waves, where he reports experiments with Branly on the conductivity of metal filings and reflects on the military possibilities of concentrated Hertzian rays, which he believes could explode the magazines of fortresses and render war impossible. He ends with forces of unknown origin: universal gravitation, the molecular and intra-atomic forces, and the forces manifested by living beings. The book closes on a cosmic note. Atoms, though stable for centuries, radiate slightly and lose stability; a period of disaggregation follows, progressive at first and then instantaneous, until the elements return to the ether. To this final destruction may succeed, over ages, a new cycle of birth and evolution, with no assignable term to these probably eternal destructions and recommencements — a hypothesis Le Bon notes he formulated long before Nietzsche’s eternal return.
A Science in Anarchy
What gives the book its peculiar flavour is less its specific claims, many of which have not survived the test of experiment, than its stance toward scientific authority. Le Bon opens by describing the “present anarchy of science”: the great principles that once seemed permanent have lost prestige among real scholars even while they persist in elementary textbooks, and he quotes Poincaré, Picard, Mach, and Duhem to show that mechanics itself rests on conventions and unrealized experiments. He welcomes this disorder. Erroneous ideas imposed by classic teaching, he writes, weave a bandage over our sight, and scientific theories retard progress once they become fixed. His contempt for the “scientific idols” of his day, and for Auguste Comte’s proposal of a tribunal to fix the limits of permitted research, is the animating passion of the whole enterprise. The reader who comes to The Evolution of Forces for settled physics will find instead a portrait of a discipline in the middle of dismantling its own foundations — and a writer who thinks that dismantling is exactly what science needs.
