WHAT brought into prominence the facts and principles summarized in the preceding chapter which will be unfolded in this work? This I will now proceed to show. The genesis of a discovery is rarely spontaneous. It only appears so because the difficulties and the hesitations which most often surround its inception are generally unnoticed.
The public troubles itself very little with the way in which inventions are made, but psychologists will certainly be interested by certain sides of the following account. In fact, they will find therein valuable documents on the birth of beliefs, on the part played, even in laboratories, by suggestions and illusions, and finally on the preponderant influence of prestige considered as a principal element of demonstration.
My researches preceded, in their beginning, all those carried out on the same lines. It was, in fact, in 1896 that I caused to be published in the Comptes Rendus de l'Acadhnie des Sciences, solely for the purpose of establishing priority, a short notice
[1 In order not to lengthen this history unduly I do not give here any of the texts on which it is based. The reader will find them at the end of the book.]
summing up the researches I had been making for two years, whence it resulted that light falling on bodies produced radiations capable of passing through material substances. Unable to identify these radiations with anything known, I pointed out in the same note that they must probably constitute some unknown force - an assertion to which I have often returned. To give it a name I called this radiation black light (lumiere noire).
At the commencement of my experiments I perforce confused dissimilar things which I had to separate one after the other. In the action of light falling on the surface of a body there can be observed, in fact, two very distinct orders of phenomena:-
1. Radiations of the same family as the cathode rays. They are incapable of refraction or of polarization, and have no kinship with light. These are the radiations which the so-called radio-active substances, such as uranium, constantly emit abundantly and ordinary substances freely.
2. Infra-red radiations of great wave-length which, contrary to all that has hitherto been taught, pass through black paper, ebonite, wood, stone, and, in fact, most non-conducting substances. They are naturally capable of refraction and polarization.
It was not very easy to dissociate these various elements at a time when no one supposed that a large number of bodies, considered absolutely opaque, were, on the contrary, very transparent to the invisible infra-red light, and when the announcement of the experiment of photographing a house in two minutes and in the dark-room through an opaque body would have been deemed absurd.
Without losing sight of the study of metallic
radiations, I gave up some time to the examination of the properties of the infra-red. This examination led me to the discovery of invisible luminescence, a phenomenon which had never been suspected, and enabled me to photograph objects kept in darkness for eighteen months after they had seen the light.
These researches terminated, I was able to proceed with the study of metallic radiations.
It was at the commencement of the year 1897 that I announced in a note published in the Comptes Rendus de l'Acadimie des Sciences, that all bodies struck by light emitted radiations capable of rendering air a conductor of electricity.
A few weeks later I gave, also in the Comptes Rendus, details of quantitative experiments serving to confirm the above, and I pointed out the analogy of the radiations emitted by all bodies under the action of light with the radiations of the cathode ray family, an analogy which no one till then had suspected.
It was at the same period that M. Becquerel published his first researches. Taking up the forgotten experiments of Niepce de Saint-Victor, and employing, like him, salts of uranium, he showed, as the latter had already done, that these salts emitted,
[1 In order not to confuse things which differ, I have reserved the term lumiere noire for these radiations. They will be examined in another volume devoted to the study of energy. Their properties differ considerably from those of ordinary light, not only by their invisibility, an unimportant characteristic due solely to the structure of the eye, but by absolutely special properties - that, for instance, of through a great number of opaque bodies and of acting in an exactly contrary direction to other radiations of the spectrum.]
in darkness, radiations able to act on photographic plates. Carrying this experiment farther than his predecessor, he established the fact that the emission seemed to persist indefinitely.
Of what did these radiations consist? Still under the influence of the ideas of Niepce de Saint-Victor, M. Becquerel thought at first that it was a question of what Niepce termed "stored-up light" (lumiere emmagasinec) - that is to say, a kind of invisible phosphorescence, and, to prove it, he started experiments described at length in the Comptes Rendus de l'Academie des Sciences, which induced him to think that the radiations emitted by uranium were refracted, reflected, and polarized.
This point was fundamental. If the emissions of uranium could be refracted and polarized, it was evidently a question of radiations identical with light and simply forming a kind of invisible phosphorescence. If this refraction and polarization had no existence, it was a question of something totally different and quite unknown.
Not being able to fit in M. Becquerel's experiments with my own, I repeated them with different apparatus, and arrived at the conclusion that the radiations of uranium were not in any way polarized. It followed then that we had before us not any form of light, but an absolutely new thing, constituting, as I had asserted at the beginning of my researches, a new force: "The properties of uranium were therefore only a particular case of a very general law." It is with this last conclusion that I terminated one of my notes in the Comptes Rendus de l'Academie des Sciences of 1897.
For nearly three years I was absolutely alone in
maintaining that the radiations of uranium could not be polarized. It was only after the experiments of the American physicist, Rutherford, that M. Becquerel finally recognized that he had been mistaken.
It will be considered, I think, very curious and one
 Professor Rutherford is a Canadian, and holds the Macdonald chair of Physics at McGill University, Montreal.-F. L.
of the most instructive chapters in the history of science that for three years not one single physicist was to be met with in the whole world who thought of repeating - though they were extraordinarily simple - the experiments of M. Becquerel on the refraction, reflection, and polarization of the uranium rays. On the contrary, the most eminent published ingenious theories to explain this very refraction, reflection, and polarization.
It was a new version of the story of the child with the golden tooth on which the scholars of the day wrote important treatises, till one day it occurred to a sceptic to go to see if the said child was really born with a golden tooth. It will be difficult, after such an example, to deny that, in scientific matters, prestige forms the essential element in conviction. We must therefore not scoff too much at those m the Middle Ages who knew no other sources of demonstration than the statements of Aristotle.
Leaving to its fate the doctrine which for several years I alone upheld, I continued my researches, enlarged the circle of my investigations, and showed that similar radiations arise, not only under the action of light, but also under very varying influences, chemical reaction especially. It became therefore more and more evident that the radiations of uranium were only, as I said from the very first, a particular case of a very general law.
This general law, which I have not ceased to study, is as follows:- Under divers influences, light, chemical reaction, electric action, and often even, spontaneously, the atoms of simple bodies, as well as those of compound bodies, dissociate and emit effluves of the same family as the cathode rays.
This generalization is at the present day almost universally admitted, but the preceding statement of facts shows that, it needed some courage to formulate it for the first time. Who could have supposed any relationship between the radiations of uranium and any effluves whatever, cathodic or otherwise, since nearly all physicists then admitted, on M. Becquerel's authority, the polarization and the refraction of these rays?
When the question as to polarization was definitely settled, it took but little time to establish the correctness of the facts stated by me. But it was only after the German physicists, Giesel, Meyer, and Schweidler, discovered, in 1899, that the emissions of radio-active bodies were, like the cathode rays, capable of deviation by a magnet, that the idea of a probable analogy between all these phenomena began to spread. Several physicists then took up this study, the importance of which increased day by day. New facts arose on all sides, and the discovery of radium by Curie gave a great impetus to these researches.
M. de Heen, Professor of Physics at the University of Liege, and Director of the celebrated Institute of Physics in that town, was the first to accept in its entirety the generalization I had endeavoured to establish. Having taken up and developed my experiments, he declared in one of his papers that in point of importance they were on a par with the discovery of the X rays. They were the origin of numerous researches on his part, which led to remarkable results. The movement once started, it had to be followed up. On all sides radio-activity was sought for, and it was discovered
everywhere. The spontaneous emission is often very weak, but becomes considerable in substances placed under the influence of various excitants - light, heat, etc. All physicists are now agreed in classing in the same family the cathode rays and the emissions from uranium, radium, and bodies dissociated by light, heat, and the like.
If, notwithstanding my assertions and my experiments, these analogies were not at once accepted, it is because the generalization of phenomena is at times much more difficult to discover than the facts from which this generalization flows. It is, however, from these generalizations that scientific progress is derived. "Every great advance in the sciences,'' said the philosopher Jevons, "consists of a vast generalization revealing deep and subtle analogies."
The generality of the phenomenon of the dissociation of matter would have been noticed much sooner if a number of known facts had been closely examined, but this was not done. These facts, besides, were spread over very different chapters of physics. For example, the loss of electricity occasioned by ultra-violet light had long been known, but one little thought of connecting the fact with the cathode rays. More than fifty years ago Niepce de Saint-Victor saw that, in the dark, salts of uranium caused photographic impressions for several months; but as this phenomenon did not seem to be connected with any known fact, it was put on one side. For a hundred years the gases of flames had been observed to discharge electrified bodies without any one attempting to examine the cause of this phenomenon. The loss of electric charges through the influence of light had been pointed out several
years before, but it was regarded as a fact peculiar to a few metals, without any suspicion of how general and important it was.
All these phenomena and many others, such as electricity and solar heat, are very dissimilar in appearance, but are the consequences of the same fact - namely, the dissociation of matter. The common link which connects them appeared clearly directly we established that the dissociation of matter and the forms of energy which result from it are to be ranked among the most widely spread natural phenomena.
The establishment of the fact of the dissociation of matter has allowed us to penetrate into an unknown world ruled by new forces, where matter, losing its properties as matter, becomes imponderable in the balance of the chemist, passes without difficulty through obstacles, and possesses a whole series of unforeseen properties.
I have had the satisfaction of seeing, while still alive, the recognition of the facts on which I based the theories which follow. For a long time I had given up all such hope, and more than once had thought of abandoning my researches. They had, in fact, been rather badly received in France. Several of the notes sent by me to the Academy of Sciences provoked absolute storms. The majority of the members of the Section of Physics energetically pro-
[1 It is precisely in the interpretation of these early facts, which no one had ever thought of connecting with radio-active phenomena, that the difficulty lay. This is what Mr. Whetham has entirely failed to grasp in his review of this work published in Nature. The perusal of the volume in which this specialist has endeavoured to popularize the researches on radio-activity will show, moreover, that he has failed to comprehend these phenomena.]
tested, and the scientific press joined in the chorus. We are so hierarchized, so hypnotized and tamed by our official teaching; that the expression of independent ideas seems intolerable. To-day, when my ideas have slowly filtered into the minds of physicists, it would be ungracious to complain of their criticisms or the silence of most of them towards me. Sufficient for me is it that they have been able to avail themselves of my researches. The book of nature is a romance of such passionate interest that the pleasure of spelling out a few pages repays one for the trouble this short decipherment often demands. I should certainly not have devoted over eight years to these very costly experiments had I not at once grasped their immense philosophical interest and the profound perturbation they would finally cause to the fundamental theories of science.
With the discovery of the universal dissociation of matter is linked that of intra-atomic energy, by which I have succeeded in explaining the radio-active phenomena. The second was the consequence of the first-named discovery.
The discovery of intra-atomic energy cannot, however, be quite assimilated to that of the universality of the dissociation of matter. This universal dissociation is a fact, the existence of intra-atomic energy is only an interpretation. This interpretation, besides, was necessary, for, after having tried several hypotheses to explain the radio-active phenomena, nearly all physicists have finally fallen in with the explanation I proposed when I announced that science was face to face with a new force hitherto entirely unknown.
It may interest the reader to know how the
researches which have thus been briefly recorded were received in various countries.
It was especially abroad that they created a deep impression. In France, they met with a hostility which was not, however, unanimous, as will be seen by this extract from a study published by M. Dastre, Professor at the Sorbonne and a member of the Institut: -
"In the course of five years a fairly long journey has been covered on the road towards the generalization of the fact of radio-activity. Starting with the idea of a property specific to uranium, we have reached the supposition of a well-nigh universal natural phenomenon.
"It is right to recall that this result was predicted with prophetic perspicacity by Gustave Le Bon. From the outset this scholar endeavoured to show that the action of light, certain chemical reactions, and lastly the action of electricity, call forth the manifestation of this particular mode of energy. . . . Far from being rare, the production of these rays is unceasing. Not a sunbeam falls on a metallic surface, not an electric spark flashes, not a discharge takes place, not a single body becomes incandescent, without the appearance of a pure or trans- formed cathode ray. To Gustave Le Bon must be ascribed the merit of having perceived from the first the great generality of this phenomenon. Even though he has used the erroneous term of Lumiere noire, he has none the less grasped the universality and the principal features of this product. He has above all set the phenomenon in its proper place by transferring it from the closet of the physicist into the grand laboratory of nature." (Revue des Deux Mondes, 1901.)
In one of the annual reviews on physical studies which he publishes annually, Professor Lucien Poincare has very clearly summarized my researches in the following lines:-
"M. Gustave Le Bon, to whom we owe numerous publications relating to the phenomena of the emission by matter of various
radiations, and who was certainly one of the first to think that radio-activity is a general phenomenon of nature, supposes that under very different influences, light, chemical action, electrical action, and often even, spontaneously, the atoms of simple bodies dissociate and emit effluves of the same family as the cathode and X rays; but all these manifestations would be particular aspects of an entirely new form of energy, quite distinct from electrical energy, and as widely spread throughout nature as heat. M. de Heen adopts similar ideas." (Revue Generale des Sciences, January 1903.)
I have only one fragment of a phrase to correct in the above lines. The eminent scholar says that I was "one of the first" to show that radio-activity is a universal phenomenon. This should read "the first." It suffices to turn to the texts and to their dates of publication to be convinced of this fact.
It is natural enough that one should not be a prophet in one's own country. It is sufficient to be a little of one elsewhere. The importance of the results brought to light by my researches was very quickly understood abroad. Out of the different studies they called forth, I shall confine myself to reproducing a few fragments.
The first is a portion of the preamble to four articles devoted to my experiments in the English Mechanic: - 
[1 My first memoir on the radio-activity of all bodies under the action of light appeared in the Revue Scientifique of May 1897. The one on radio-activity by chemical reaction in April 1900. The memoir demonstrating the spontaneous radio-activity of primary bodies appeared in the same review in November 1902. The first experiments by means of which physicists sought to prove that radio-activity could be detected in substances other than uranium, thorium, and radium were published by Strutt, McLennan, Burton, etc., only between June and August 1903.]
[2 The issues from January to April 1903·]
"During six years Gustave Le Bon has continued his researches on certain radiations which he at first termed Lumiere noire. He scandalized orthodox physicists by his audacious assertion that there existed something which had been quite unknown. However, his experiments decided other searchers to verify his assertions, and many unforeseen facts were discovered. Rutherford in America, Nodon in France, de Heen in Belgium, Lenard in Austria, Elster and Geitel in Switzerland have successfully followed in the lines of Gustave Le Bon. Summing up to-day the experiments made by him for the last six years, Gustave Le Bon shows that he has discovered a new force in nature which manifests itself in all bodies. His experiments cast a vivid light on such mysterious subjects as the X rays, radio-activity, electrical dispersion, the action of ultra-violet light, etc. Classical books are silent on all these subjects, and the most eminent electricians know not how to explain these phenomena:"
The second of the articles to which I have above alluded is one in The Academy of the 6th December, 1902, under this heading: "A New Form of Energy":-
"Hardly anything is more marked than the way in which the ideas of men of science with regard to force and matter have completely changed during the last ten years.... The atomic theory that every scrap of matter could be divided in the last resort into atoms each in itself indivisible and combining among themselves only in fixed proportions, was then a law of scientific faith, and led to pronouncements like those of a late President of the Chemical Society, who informed his hearers in his annual allocution that the age of discovery in chemistry was closed, and that henceforth we had better devote ourselves to a thorough classification of chemical phenomena. But this prediction . . . was no sooner uttered than it was falsified. There came before us Mr. (not then Sir William) Crookes' discovery of what he called 'radiant matter,' . . then Rontgen's rays . . . until now M. Gustave Le Bon . . . assures us that these new ideas are not several things but one thing, and they all of them point to a form of matter
spread throughout the world indeed, but so inconceivably minute that it becomes not matter but force. . . . The consequences of the final acceptance of [M. Le Bon's] theory are fairly enormous. . . . As for chemistry, the whole fabric will be demolished at a blow; and we shall have a tabula rasa on which we may write an entirely new system wherein matter will pass through matter, and 'elements' will be shown to be only differing forms of the same substance. But even this will be nothing compared with the results which will follow the bridging of the space between the material and the immaterial which M. Le Bon anticipates as the result of his discoveries, and which Sir William Crookes seems to have foreshadowed in his address to the Royal Society upon its late reception of the Prince of Wales."
I will add to these quotations a passage from the divers articles which M. de Heen, Professor of Physics at the University of Liege, has kindly devoted to my researches:-
"The resounding effect produced in the world by the discovery of the X rays is well known, a discovery which was immediately followed by one more modest in appearance, but perhaps more important in reality - viz., that of Black Light, as the result of the researches of Gustave Le Bon. This last scholar proved that bodies struck by light, especially metals, acquire the faculty of producing rays analogous to the X rays, and discovered that this was not simply an exceptional phenomenon, but, on the contrary, one of an order of phenomena as common throughout nature as calorific, electricity, and luminous manifestations, a thesis which I also have constantly upheld from that time."
But all this is already ancient history. The anger which my first researches provoked in France has vanished. The staffs of the laboratories formerly so hostile have welcomed with sympathetic curiosity the first editions of this work. The proof of this I
have found in several articles, and especially in the review by one of the most distinguished young scholars of the Sorbonne, of which I give a few extracts:-
"It will be Dr. Le Bon's title to fame that he was the first to attack the dogma of the indestructibility of matter, and that he has destroyed it within the space of a few years. In 1896 he published a short note which will mark one of the most important dates in the history of science, for it has been the starting-point of the discovery of the dissociation of matter. . . . To the already known forms of energy, heat, light, etc., another must be added, namely, matter or intra-atomic energy. The reality of this new form of energy, which Dr. Le Bon has made known to us, rests in no way upon theory, but is deduced from experimental fact. Although unknown till now, it is the most mighty of known forces, and may even be the origin of most of the others. . . . The beginning of Dr. Le Bon's work produces in the reader a deep impression; one feels in it the breath of a thought of genius. . . . Dr. Le Bon has been com- pared to Darwin. If one were bound to make a comparison, I would rather compare him to Lamarck. Lamarck was the first to have a clear idea of the evolution of living beings. Dr. Le Bon was the first to recognize the possibility of the evolution of matter, and the generality of the radio-activity by which its disappearance is manifested."
The reader will, I hope, excuse this short pleading. The repeated forgetfulness of certain physicists has compelled me to utter it. The new phenomena I have discovered have cost me too much labour, too much money, and too much annoyance for me not to try to keep a firm hold on a prize obtained with so much difficulty.
[1 Georges Bohn, Revue des Ideas, 15th January 1906.] [2 It will be considered a curious proof of the narrow and timid mentality of some of our French "Dons" that two of them, namely, M. M. Abraham and https://en.wikipedia.org/wiki/Paul_Langevin" class="wiki wikinew text-danger tips">P. Langevin, having thought it useful to reprint
in two huge volumes everything that has been written on ionization and radio-activity, did not dare to allow the title of any one of my memoirs to appear there. Among these last, however, there are some, and notably one on the radio-activity which certain substances acquire by chemical reacticns so simple as hydration, of which the fundamental and theoretical importance has not escaped some eminent foreign physicists, since they have taken the trouble to repeat and develop my experiments at length with due acknowledgment to the author.]