THE LIFE AND WORK OF PIERRE CURIE

(1859–1906)

E. V. Shpolsky

On April 19, 1906, a fatal accident cut short the life of the great French scientist Pierre Curie—a physicist and crystallographer, a subtle experimenter, an ingenious inventor of precision instruments, and a profound thinker, and at the same time a man of extraordinary moral purity and attractiveness.

Pierre Curie was born on May 15, 1859, in Paris*). His parents were people of modest means, but remarkable for their spiritual qualities. Pierre Curie’s father, Eugène Curie, was a physician. The Curie family was of Alsatian origin and of the Protestant faith. Eugène Curie, however, was an anticlerical and did not have his two sons, Jacques and Pierre, baptized—something that required no small courage in the bourgeois society of France in the second half of the nineteenth century.

In his outstanding intellectual abilities, in his temperament as a scientist, and in the cult of science that he preserved throughout his life, Dr. Eugène Curie might have become a major scholar. But he had no opportunity to devote himself to science, because of lack of means and the need to support a large family, which compelled him to become a practicing physician. As a physician, Eugène Curie, according to Marie Skłodowska-Curie—Pierre’s wife, collaborator, and friend—“displayed remarkable disinterestedness and self-sacrifice.” Being, moreover, a republican in his political convictions, which he held sacred

) The biographical data given in this article are taken from the remarkable, small book by M. Skłodowska-Curie, Pierre Curie*, Paris, 1924 (there is a Russian translation by S. A. Shchukarev, Leningrad, 1924). From this same book are taken the excerpts from the diaries and letters of P. Curie quoted below, when these excerpts are given without reference to a source. A large number of facts and materials relating to the lives of both outstanding people—Pierre and Marie Curie—are given in the book by their younger daughter, Ève Curie, a semi-literary biography of Marie Curie. This book went through 120 editions in France. There is an English translation, richly illustrated with photographs. Separate parts of the book have also appeared in Russian translation.

carried through the era of the empire of Napoleon III, Eugène Curie took part as a physician in the revolution of 1848 and in doing so displayed great personal courage; and during the Paris Commune he set up an outpatient clinic in his apartment and treated the wounded.

According to the testimony of Marie Skłodowska-Curie herself, Dr. Eugène Curie was in general “a remarkable personality, striking all who came into contact with him.” If one takes into account that, with all these qualities, Eugène Curie had a somewhat domineering character, it is understandable that he had a decisive influence on Pierre’s impressionable, gentle nature.

Pierre Curie’s childhood and youth passed entirely in a family setting. Observing the development of his son, Dr. Eugène Curie came to the conclusion that Pierre could not be a good pupil in an ordinary school, since the peculiarities of his mental make-up did not allow him quickly to assimilate the varied school curriculum. He possessed the ability to concentrate intensely on a single subject that occupied or fascinated him, but he coped poorly with the need to switch rapidly from one subject to another. For this reason Pierre Curie was sent neither to primary school nor to the lycée; all his education, up to his entrance into the university, he received at home, first under the guidance of his mother, then of his father and elder brother (who likewise had not studied at a lycée), and, finally, under the guidance of a specially invited teacher, A. Bazille, who proved to be an excellent pedagogue. It was to him that Pierre Curie owed his education in elementary and higher mathematics.

One should not think that a conflict between the system of school instruction and a child or youth endowed with outstanding abilities is a rare event. Apparently the opposite is true, since we are speaking of people possessing original minds. One could cite many examples of outstanding scientists who created an epoch in science and who were not brilliant pupils at school. A more recent example is Einstein, who in his school years avidly absorbed any knowledge in mathematics and physics, but was careless in his attitude toward the other subjects. As a result—on his first attempt to enter the Zurich Polytechnic—he failed the examinations in the classical languages and was not admitted.

Be that as it may, for Pierre Curie free instruction in a home environment had the most beneficial effect and enabled him to complete the secondary-school course earlier than usual. At the age of 16 he had already passed the examination for the degree of bachelor of the natural sciences and had begun preparing for the examination for the degree of licentiate*).

*) In France the medieval degree of “bachelor” has been preserved to this day as the lowest academic degree. To obtain the degree of bachelor of the natural sciences it is necessary first to obtain the degree of bache-

In essence, Pierre Curie never took a systematic course either at school or at the university. True, while preparing for the licentiate examination, he attended lectures at the Sorbonne and did practical laboratory work there as well. But alongside this he had access to Professor Leroux’s laboratory at the School of Pharmacy, where he “helped in preparing physics lectures” (M. Curie). Of great importance for him was the fact that his brother Jacques, with whom Pierre was united by a close friendship, was at that time already a laboratory assistant to the chemists Riche and Jungfleisch. Taking advantage of this, Pierre spent much time in the laboratory, becoming accustomed to the laboratory environment and in practice acquiring a great deal of knowledge, so to speak, from the “laboratory air.”

Be that as it may, by these unusual paths Pierre Curie obtained the degree of licentiate in physics at the age of eighteen. With his brilliant abilities he attracted the attention of Professor Desains, upon whose recommendation the nineteen-year-old Pierre was appointed Desains’s laboratory assistant at the “Faculty of Sciences” (in our terminology—the faculty of physics and mathematics) of the University of Paris.

He remained in this position for 5 years, helping to conduct practical classes for students. This work took from him much time and strength, and M. Curie expresses regret that, being compelled for material reasons to take this job, Pierre did not have the opportunity to devote another two or three years to study. Indeed, he felt, on the one hand, dissatisfaction that his education—in particular his mathematical education—did not yet correspond to the high demands he made of himself. On the other hand, having a concentrated and somewhat dreamy nature, he literally suffered from being forced to devote much time to obligatory tasks and to “the trifles of life.” In his diaries of that time we may read the following lines, full of anxiety: “I am very rarely left to myself; usually part of my ‘I’ is asleep. Poor my mind, are you really so weak that you cannot act upon my body? Oh my thoughts! So you are so insignificant! Most of all I counted on my imagination, that it would pull me out of the rut, but I am very much afraid lest it die.”

However, Pierre soon freed himself from these anxieties and doubts and found his path. He clearly understood that his calling was science, and he resolutely set out on this path, beginning his activity while still in his youth—almost as a boy—with several brilliant works.

degree in literature (bachelier ès lettres), which, in essence, is the completion of the course of a general-education secondary school.

A licentiate is the name given to a bachelor who is permitted to lecture, although he does not have the academic degree of doctor.

His first work was published in 1880 jointly with Professor Desains. In this work he succeeded, with the aid of a wire diffraction grating and a thermoelement, in measuring the wavelength of infrared rays emitted by heated bodies. If this work revealed the young physicist’s considerable experimental skill, then in a series of subsequent works, published in rapid succession in 1881 and 1882, Pierre Curie and his brother Jacques, who at that time was working as a laboratory assistant to the well-known crystallographer Friedel in the mineralogical laboratory of the Sorbonne, succeeded in making a brilliant discovery: they discovered the piezoelectric effect in crystals. This discovery, made entirely independently by the two young scientists (Pierre at that time was 21 years old, and Jacques was three and a half years older than he), was by no means accidental, but was the result of profound reflections on the properties of crystals and on the role of symmetry in natural phenomena. In a communication made to the Paris Academy on August 2, 1880, and published in volume 41 of Comptes Rendus, the Curie brothers write: “Crystals having one or several axes whose ends are not identical, i.e. hemihedral crystals with inclined faces, possess the special physical property of becoming charged with electricity of opposite sign at the ends of the indicated axes when subjected to a change of temperature. This property is called pyroelectricity.

“We have found a new method of exciting polar electricity in the same crystals, which consists in subjecting them to a change of pressure along their hemihedral axes.

“Phenomena entirely analogous to those produced by heating: upon compression, the ends of the axes along which the compression acts become charged with opposite electricities. If the crystal is brought into a neutral state and then stretched, the phenomenon is reproduced, but with reversal of signs: the end that became positively charged under compression will become negative under tension, and conversely”*).

Further, in this and in subsequent communications, the method of preparing plates exhibiting the piezoelectric effect is described, and the substances in whose crystals this effect is observed are enumerated—including quartz and Seignette salt.

The discovery of the Curie brothers aroused great interest among physicists and crystallographers. A year later Lippmann drew attention to the fact that, from the thermodynamic point of view, there must exist an effect inverse to that found by P. and J. Curie: if, under compression or tension of a crystal plate, it acquires electrical polarity, then the imposition of an electric field must produce a mechanical effect, i.e. tension or compression, depending

*) Oeuvres de Pierre Curie. Gautier-Villars, Paris, 1908, p. 6.

...in the direction of the field. In view of the small magnitude of the inverse effect, detecting it proved considerably more difficult. However, by means of new, delicate experiments the Curie brothers confirmed the correctness of Lippmann’s prediction and showed that the piezoelectric coefficient has the same magnitude for the direct and inverse effects. They also pointed out that the relation between the two effects—the direct and the inverse—is analogous to that required by Lenz’s law for the electromotive force of induction and the action that gives rise to it: if, when a crystal is stretched, electric charges of definite signs appear on its faces, then in the inverse effect, with the same distribution of the signs of the charges, the crystal is compressed, and conversely.

Although the discovery of Pierre and Jacques Curie aroused interest among scientists immediately after its publication, in the following thirty-odd years it attracted little attention and was poorly known. It seemed to be a certain subtlety, a curious play of nature, with no prospects for broad practical application. In fact, its only application was made by Pierre Curie himself, who used the piezoelectric properties of quartz in the technique of measuring weak ionization currents. The turning point came at the end of the First World War, when Pierre Curie’s pupil, the outstanding French physicist Paul Langevin, proposed using quartz plates as emitters, and later also as receivers, of high-frequency sound vibrations under water. This idea proved exceedingly fruitful. It was used in hydroacoustics both for military and for peaceful purposes. On the other hand, the appearance of powerful high-frequency acoustic emitters stimulated the emergence and development of a new field: the study and application of ultrasounds. At present the applications of piezoelectric crystals are extraordinarily extensive and varied. Radio-engineering devices, microphones, telephones, pickups for electric record players, and, finally, instruments for measuring explosive pressures and vibrations in machines—such is a brief and incomplete list of the applications of what would seem to be an insignificant and purely “theoretical” phenomenon, discovered by two young physicists in the eighties of the last century. The modern monograph on piezoelectricity*) is a volume of impressive size, and its bibliography contains more than 600 titles of works devoted to the study and applications of piezoelectricity.

The completion of the work on the study of piezoelectric crystals coincided with a turning point in the life and activity of Pierre Curie. In 1883,

) W. Cady, Piezoelectricity, New York—London, 1946 (Russian translation edited by A. V. Shubnikov: W. Cady, Piezoelectricity and Its Practical Applications*, IL, 1949, p. 717).

the joint work of the Curie brothers came to an end, since Jacques left Paris for Montpellier, where he obtained a position at the university as head of practical work in mineralogy. At the same time Pierre was invited to the newly founded and rather distinctive institution of higher education—the “School of Industrial Physics and Chemistry of the City of Paris,” founded on the initiative of the famous chemist Schützenberger, who was also the first director of the “School.” Pierre Curie’s scientific and pedagogical activity continued in this educational institution for 22 years—at first as head of practical classes (in our terminology, as an assistant), and then as professor. The attitude toward him of the director of the School, Prof. Schützenberger, and of his colleagues and students was excellent: despite his youth, he enjoyed great authority and sympathy. But there were very few means for work, and the premises were extremely limited.

At first Pierre Curie had to carry out a large and troublesome task of organizing the student laboratory. Much time was also taken up by the preparation, customary at the beginning of any pedagogical activity, of practical classes and lecture courses. Pierre Curie performed all these new tasks excellently, but this activity had an unfavorable effect on his experimental work, since for several years he had no opportunity at all to work independently in the laboratory. However, Curie’s scientific activity did not cease, and in the next two years he published a number of articles on the general principles of symmetry and, in particular, on the symmetry of phenomena. These articles are of profound theoretical and philosophical interest.

In the work devoted to the symmetry of phenomena, Pierre Curie formulates the following three general laws of symmetry:

“When certain causes produce certain effects, the elements of symmetry of the causes must reappear in the effects produced by them.

When certain effects contain a certain dissymmetry, this dissymmetry must also be found in the causes that produced the phenomena.

Propositions converse to the two preceding ones do not hold, at least in practice, i.e., the effects may be more symmetric than the causes that produced them.”

In his work Curie showed, by concrete examples, how these general propositions should be applied in order to predict the possibility or impossibility of the occurrence of one or another phenomenon under definite conditions.

In the same period, namely in 1885, Curie published an important theoretical work on the growth of crystals. In this work he introduced for the first time the concept of the surface energy of the faces of a crystal and formulated the general principle of crystal growth, according to which

of a crystal must be that for which, at a given volume of the crystal, the surface energy will be the least. Important applications of this principle to problems of crystal growth were developed by the outstanding Russian physicist-crystallographer Yu. V. Wulff.

By the beginning of the nineties, teaching at the School had already been organized to a considerable degree, and Curie was able to return to experimental work. True, the external conditions for this were hardly favorable. He had not only no laboratory of his own, but not even an isolated room in which to work. Apparatus had to be assembled in the student laboratory when the students were not working there, and the extensive classical work on magnetism was carried out somewhere in the passageway between the staircase and the laboratory of the students’ practical course. Nor were there any special monetary appropriations for the work, and the funds had to be snatched from the rather limited budget of that same practical course. This extreme insufficiency of means and the absence of a real laboratory pursued Curie throughout his life. Even later, when he and Marie Curie, after the discovery of radium, had become famous and among the most popular people in the world, he had to wage a difficult struggle for a laboratory.

The most important work by Curie carried out at the beginning of the nineties was the already mentioned study of the magnetic properties of matter: “Magnetic Properties of Bodies at Various Temperatures”*). At the beginning of this work Curie states that, from the point of view of their magnetic properties, bodies are divided into three categories: diamagnetic bodies, to which the majority of bodies in nature belong; weakly magnetic (paramagnetic) bodies; and, finally, ferromagnetic bodies. At first sight, Curie continues, these three categories of bodies are sharply demarcated from one another. But will this demarcation remain under more profound study? Are there not transitions between these groups? Are we dealing with phenomena that are essentially different, or with one and the same phenomenon, more or less deformed? Such were the problems that had deeply interested Faraday as well.

To answer the questions posed, in Curie’s opinion, it is necessary to study the magnetic properties of bodies under the most varied conditions, varying within wide limits the temperature, pressure, and intensity of the external magnetic field. In his work Curie set himself the task of studying the magnetic properties of a large number of bodies belonging to different categories, at different temperatures, which in some cases reached 1370°.

As a result of extensive and extremely delicate measurements, carried out, moreover, under very unfavorable conditions, Curie came

) P. Curie, Oeuvres*, pp. 232–345.

to completely distinct results, making this work a classic. It was he who showed that between diamagnetic bodies and bodies belonging to the two remaining categories there is a fundamental difference: whereas diamagnetic susceptibility does not depend on temperature, para- and ferromagnetic bodies exhibit a definite dependence on temperature. In the case of paramagnetic bodies, the dependence of susceptibility on temperature obeys a very simple law, according to which the susceptibility is inversely proportional to the absolute temperature:

\[ \chi_m=\frac{C}{T} \]

— Curie’s law, where \(\chi_m\) is the magnetic susceptibility referred to one mole of substance, and \(C\) is a constant, called the Curie constant. Ferromagnetic bodies exhibit a more complicated dependence on temperature because, in comparatively small fields, saturation is reached in them. It is characteristic, however, that above a certain definite temperature \(\theta\), called the Curie point, ferromagnetic bodies begin to behave like paramagnets and, at a sufficient distance from the Curie point, obey Curie’s law, with the difference that in its expression the temperature must be counted not from absolute zero, but from the Curie point:

\[ \chi_m=\frac{C}{T-\theta}. \]

The work on the magnetic properties of bodies was submitted and defended as a doctoral dissertation in 1895. In the same year, at the insistence of the well-known physicist Mascart, director of the “School of Physics and Chemistry,” Schützenberger obtained the establishment of a special chair, which was assigned to Pierre Curie. Thus Curie’s external position improved, but this had almost no effect on the extremely unsatisfactory conditions of his scientific work. This was all the more surprising since by that time his work had received full recognition and he himself had acquired a worldwide reputation as a first-class scientist.

At about the same time an event occurred in Pierre Curie’s personal life that played a most important role in his subsequent fate. In 1894 he became acquainted with Marie Skłodowska, who at that time was a graduating student at the Sorbonne, and in the middle of 1895 she became Pierre Curie’s wife. Marie Skłodowska, later Skłodowska-Curie, was Polish, the daughter of a physics teacher in Warsaw, where she had completed a girls’ gymnasium and for some time had been a teacher. An ardent patriot, she dreamed of liberating her homeland from the yoke of tsarism. She went to Paris to obtain an education and intended, after finishing the university, to return to Warsaw and devote herself to serving her people. Pierre Curie’s proposal that she become his wife changed her entire plan

of her life. When, in the summer of 1894, she went home for the holidays, Pierre Curie wrote to her in one of his letters: “We promised one another (did we not?) to be at least great friends. If only you did not change your intention. For one cannot bind oneself by promises; it is not in our power to keep them. And yet, how good it would be (although I dare not believe it) to go through life beside one another, hypnotized by our dreams: your patriotic dream, our humanitarian dream, and our scientific dream.” Of all three, the last—the scientific dream—was the most attractive to Pierre Curie, since he believed unshakably that in the life of humanity science is the main thing, that “science and peace will triumph over ignorance and war” (Pasteur’s words) and will bring happiness to mankind.

The scientific dream was especially dear to Pierre and Marie Curie not only because it was inseparably intertwined with their social dream, but also because it gave joy and beauty to their lives. Many years later, in 1933, a year before her death, in an interview with the “Committee on Intellectual Cooperation,” Marie Curie said: “I am among those who believe that there is great beauty in science. The scientist in his laboratory is not only a technician; before the phenomena of nature he experiences the same feelings as a child listening to a fairy tale.”*)

Pierre Curie’s dream of joint scientific work with Maria Skłodowska-Curie soon came true. The director of the School of Physics and Chemistry, Prof. Schützenberger, allowed Marie Curie to work together with her husband on the school premises. In 1896 the chief scientific sensation was Henri Becquerel’s discovery of radioactivity. The history of this discovery, with which the entire subsequent fate of the Curies was linked, is often presented inaccurately. Since this discovery marked the beginning of the development of nuclear physics, it is worthwhile to reconstruct its exact history in a few words.

The beginning of the story was, as is well known, the discovery of X-rays made by Röntgen at the end of 1895. As early as January 20, 1896, A. Poincaré demonstrated at a meeting of the Paris Academy of Sciences the photographs sent to him by Röntgen. In connection with a question posed by A. Becquerel, Poincaré expressed the supposition that the source of the X-rays was the green luminescent spot on the glass wall of the discharge tube. Poincaré formulated this supposition in print as well, in a note published on January 30, 1896.

Since Becquerel was engaged in the study of luminescence, he became very interested in this hypothesis and decided to investigate whether the emission of X-rays occurs with every (visible)

*) I quote from Irène Joliot-Curie’s article “La vie et l’oeuvre de Marie Skłodowska-Curie.”

fluorescence. Fortunately, among the fluorescing substances previously studied by him and by his father, Edmond Becquerel, there was uranium salt—potassium uranyl sulfate. On February 24, 1896, Becquerel reported to the Academy that if one places a uranium salt on a photographic plate wrapped in black paper and exposes it for several hours to the sun, then the “silhouette of the phosphorescent substance” appears on the plate. It would seem that thereby the original idea of a connection between penetrating radiation and the capacity for fluorescence had been confirmed. However, as a true experimenter, Becquerel continued his experiments and began to look for facts contradicting this interpretation. Indeed, on March 2 of the same year Becquerel reported that the effect described earlier is observed even when the uranium salt is not illuminated at all, and that he considers this fact especially important. Later (May 18) he reported that all the uranium salts he had investigated, whether fluorescing or non-fluorescing, crystalline or fused, or in solution, exhibit the property of acting on a photographic plate and causing ionization of the air.

On the other hand, substances whose luminescence lies in the same region of the spectrum as the luminescence of uranium salts, but which do not contain uranium—such as, for example, zinc and calcium sulfides—showed no signs whatever of penetrating radiation, either in the dark or under illumination.

Thus it was established that it is uranium specifically that possesses the property, without any external action, of continuously emitting penetrating radiation; that is, the phenomenon of radioactivity was discovered. However, the term “radioactivity” was introduced later by M. Curie, and at first the penetrating radiation of uranium was called “Becquerel rays.”

This phenomenon greatly interested the Curies, and Marie Curie decided to devote her doctoral dissertation to it. Taking up the work, M. Curie showed that the property of emitting penetrating radiation is a property of the atoms of uranium and does not depend on what chemical compound the uranium enters into: the intensity of the radiation proved to be strictly proportional to the amount of uranium entering into any compound, and independent of any external conditions (illumination, temperature, etc.). M. Curie then set herself the task of determining whether, among the chemical elements known at that time, there were other elements besides uranium that possessed analogous properties. The only such element proved to be thorium.*)

All these and subsequent works were carried out with a simple apparatus consisting of the following parts: on the lower plate—

) A complete summary of Curie’s works is given in her dissertation: Recherches sur les Substances Radioactives*, par M-me Sklodowska-Curie. Paris, Gauthier—Villars, 1904.

...a flat-capacitor cup, to which a potential from batteries was applied, the sample to be tested was poured in the form of powder. The upper plate was connected to a quadrant electrometer of special design, developed by Pierre Curie during his work on the piezoelectric effect (Curie electrometer). In those cases when the sample was a source of penetrating radiation, it caused electrical conductivity of the air, and the electrometer became charged. This charge was compensated by the charge arising on the piezoquartz, which was stretched by weights placed on the pan. Thus, the measure of the intensity of the effect was the weight of the weights stretching the quartz. The apparatus was simple and worked reliably, despite the fact that it was, as M. Curie says, “not in its proper place,” in a damp room, which alone could be made available to her for the work.

Having tested various elements for radioactivity, M. Curie turned to the study of minerals. In doing so a remarkable fact was discovered: it turned out that there exist uranium minerals whose activity exceeds the activity of the uranium contained in them. Thus, for example, the activity of pitchblende ore from Joachimsthal in Bohemia was three times greater than the activity of the same amount of metallic uranium. The supposition naturally suggested itself that these minerals contain, in addition to uranium, some other unknown substance possessing a very high activity, and since all the elements known up to that time had already been investigated by Marie Curie, she put forward the supposition that this unknown substance was a new element.

From the very beginning of the work Pierre Curie took the most active part in it. This is what the elder daughter of Marie and Pierre, Irène Curie, writes on this subject*): “Marie Curie began to study this problem in December 1897; less than a month later Pierre Curie joined her. Three small laboratory notebooks, begun in December 1897 and ending in July 1899, make it possible to trace the history of their close collaboration in the discovery of polonium and radium. During the first months of work, on the pages of the first notebook one can see the clear and careful entries of my mother and, here and there in the margins, several lines scratched by my father: now a curve, now a record of measurements made by him himself. All this shows with what constant interest he followed the work. After the measurements of the activity of uranium come records of measurements of various substances, evidently taken at random—various substances found in the laboratory; then—uranium minerals, whose abnormally high activity revealed the probable presence in them of unknown radioelements; finally—measurements of thorium. My father always worked together with my mother; in the notebooks

) Irène Joliot-Curie. La vie et l’œuvre de Marie Skłodowska-Curie — Pensée*, 1954, No. 88, p. 19.

in the notebooks their handwriting is seen now on one page, now on another, and sometimes entries by both of them are on one and the same page.”

In July 1898, six months after the beginning of their investigations, Pierre and Marie Curie announced the discovery of a new radioactive element—polonium, and in December 1898—the discovery of radium. This substance, however, was present in their preparations in “infinitesimally small quantities.”

The Curies carried out all this great work under exceptionally unfavorable conditions. In the above-mentioned biography of Pierre Curie, Marie Curie describes the setting of their work so vividly that it is worth quoting this description in full: “In spite of the relatively rapid progress of the work, it was far from finished. In our opinion, there were undoubtedly new elements there; but in order to compel chemists to accept this opinion, it was necessary to isolate these elements... We already knew by what methods one might hope to separate polonium from bismuth and radium from barium; but for this separation much larger quantities of substance were needed than those with which we had been dealing.

During this period of our work we were greatly hampered by the lack of the necessary resources: premises, money, and personnel. Pitchblende was an expensive mineral, and we could not buy a sufficient quantity. The chief source of this mineral was then in St. Joachimsthal (Bohemia), where the ore occurred, worked by the Austrian government for the purpose of extracting uranium from it. According to our assumptions, all the radium and part of the polonium should have been present in the waste from this production, which at that time was in no way utilized. Thanks to the support of the Vienna Academy of Sciences, we succeeded in obtaining, on favorable terms, several tons of this waste, and we used it as starting material. To cover the expenses of the investigation we first had to use our own funds, and later we received several grants and prizes from abroad.

Especially important was the question of premises; we did not know where we could carry out the chemical processing. It was necessary to organize it in an abandoned shed, separated by a courtyard from the workshop where our electrometric apparatus was located. This was a plank barrack, with an asphalt floor and a glass roof, insufficiently protected from the rain, without any fittings; it contained only old wooden tables, a cast-iron stove that did not give enough heat, and a blackboard, which Pierre Curie so liked to use. There were no fume hoods for experiments with harmful gases, and therefore these operations had to be carried out in the courtyard when the weather permitted, or else indoors with the windows open.

In this ‘rich’ laboratory we worked for almost two years with almost no assistants, carrying out together both the chemical processing and the study of

...of radiation of the increasingly radioactive products we were obtaining. Then we had to divide our labor: Pierre Curie continued the investigation of the properties of radium, while I took up the chemical operations with the aim of obtaining pure salts of radium.”

The discovery of radium, a million times more active than uranium, was a new scientific sensation at the end of the nineties—of that period so rich in staggering scientific discoveries. The name of the Curies was on everyone’s lips; and since among physicists Pierre Curie had already long been known for his work on crystals, symmetry, and magnetism, the discovery of radium and the investigation of its properties, the study of the character, nature, and action of its radiations, carried out by Pierre Curie partly in collaboration with Marie Curie and partly jointly with a number of young physicists (J. Bémont, A. Debierne), created for him the reputation of one of the most outstanding physicists in the world.

Yet recognition came hardest of all to Pierre Curie in his own homeland, in France. The reason was not any lack of respect for him on the part of scientists, but the complete discrepancy between his merits, his needs in the resources for scientific work, in a well-equipped laboratory, on the one hand, and his material and academic position, on the other. He was still a professor at the modest School of Physics and Chemistry, worked in a wretched laboratory—a shed—and his salary was insufficient even to satisfy the most modest needs of his small family. Overcoming his aversion to personal arrangements, he from time to time raised the question of providing him with vacant chairs, but invariably received refusals. Things reached the point where he was forced in addition to take the post of tutor at the École Polytechnique, a position absolutely not corresponding to his age and true rank in science.

Pierre Curie’s situation improved somewhat after he rejected an offer, very advantageous for him, to occupy a chair at the University of Geneva. The danger of losing such a scientist for France prompted his friends to intensify their efforts to secure for Pierre Curie a suitable chair. These efforts, however, were crowned with a very modest result. Thanks to the support of Henri Poincaré, Curie was appointed lecturer of the so-called P.C.N. This is the abbreviated name of the preparatory division of the Sorbonne for the medical and natural-science faculties (P.C.N.—the initial letters of the words Physique, Chimie, [Histoire] Naturelle). At the same time Marie Curie was appointed lecturer at the women’s normal school in Sèvres (an institution of higher education analogous to the pre-revolutionary Higher Women’s Courses in Russia). This improved the material situation of the Curie spouses, but worsened the conditions of their scientific work, since Pierre Curie did not receive a laboratory and was forced as before to make use of the salvational...

with him at the School of Physics and Chemistry; and the additional teaching work took a great deal of time and strength.

In spite of this, in the interval between 1899 and 1903 Pierre Curie carried out a number of very important works. First of all, with the aid of the Central Society of Chemical Products, Curie succeeded in organizing the industrial extraction of radium. For this purpose, of course, he had to work out in detail the technology for extracting radium from uranium ore. With the characteristic disinterestedness for which he was known, Pierre Curie refused to derive profit from his and Marie Curie’s discovery. They took out no patents and published, in every detail, the technology for obtaining radium. Moreover, Pierre and Marie Curie willingly gave additional explanations to everyone who wrote to them, including from abroad, concerning various details of the complicated procedure for obtaining this precious substance in pure form. The preliminary processing of the ore up to the obtaining of radioactive barium was carried out at a factory, and the final delicate operations—separating radium from barium—in the laboratory. As production developed, the quantity of radium obtained increased, and already in 1902 M. Curie prepared one decigram of pure radium chloride, whose value amounted to 75,000 gold francs!

Alongside this practical work of organizing the factory extraction of radium, and alongside the great expenditure of time and effort on teaching in two institutions of higher learning, Pierre Curie succeeded in the same period in completing several very important works “by means of superhuman effort,” as M. Curie writes in her book. Among these works, undoubtedly the most important was the discovery of the continuous release of heat by radium. In a note published jointly with A. Laborde, P. Curie describes the following simple experiment: in a small Dewar vessel an ampoule with radium salt and a thermometer were placed; in another identical Dewar vessel located nearby there were barium chloride and a thermometer. It turned out that the thermometer in the first Dewar vessel showed a higher temperature than in the second; moreover, the calculation of the amount of heat liberated gave a figure differing little from that accepted at the present time: 1 g of radium, according to the measurements of P. Curie and A. Laborde, releases an amount of heat on the order of 100 cal per hour. How clearly P. Curie understood the full significance of this fact is evident from the concluding lines of the communication quoted below: “1 gram-atom of radium (225 g) releases, during each hour, 22,500 cal—an amount comparable with the quantity of heat released in the combustion of 1 gram-atom of hydrogen in oxygen.

The continuous release of such an amount of heat cannot be explained by an ordinary chemical transformation. If the origin of this evolution of heat is to be sought in an internal transformation, then this transformation must be deeper and must ...”

...be caused by the transformation of radium itself. However, such a transformation—if only it takes place—must occur very slowly... If the preceding hypothesis is nevertheless correct, then the energy released in the transformation of atoms must be exceptionally great.”*)

Among the other important works of this period we shall mention the study of the law of decay of the emanation of radium, and also the study of the physiological action of radium rays. P. Curie tested the physiological action on himself, subjecting his arm to the action of radium rays for several hours. As a result a wound appeared, which did not heal for several months. Having thus convinced himself of the very strong physiological action, Curie, together with physicians, undertook experiments on the cure of certain diseases, first on animals and then on human beings.

The year 1903 brought a number of important discoveries in the field of radioactivity. The discovery of the liberation of heat by radium has already been mentioned. In the same year Ramsay and Soddy proved the formation of helium from the emanation of radium. This result was confirmed during the Curies’ trip to England in work carried out by P. Curie jointly with Dewar.

Along with this, by comparing the spectrum of radium with the spectrum of the emanation, the elementary character of the latter was proved. These experiments served as completely convincing evidence of the reality of transformations of atoms. At the same time there gradually formed the conviction that helium is not a link in radioactive transformations, but consists of α-particles that have lost their charge. This conclusion was confirmed several years later by the elegant direct experiment of Rutherford and Royds. At the same time the hypothesis of radioactive decay, sketched by P. Curie in a very general form, received an entirely clear and concrete formulation in the work of Rutherford and Soddy, and was subsequently developed mathematically in all details by Rutherford.

One must transport oneself into the scientific atmosphere of the early nineteen-hundreds, with its by then firmly established belief in the immutability of the chemical elements, in order to understand the immense impression produced by these discoveries. It was a real explosion. Prout’s hypothesis on the complexity of the chemical elements, only recently declared by the celebrated French chemist Stas to be a “pure illusion,” again acquired scientific interest, and the dreams of the alchemists were embodied in these transformations of the elements—though they were taking place on an infinitesimal scale and independently of the experimenter’s will!

Naturally, the names of Pierre and Marie Curie, who had discovered this wondrous element—radium—continuously radiating enormous energy, transforming into other elements, and in its turn arising from uranium, helping to cure such serious diseases,

*) P. Curie, Oeuvres, p. 450.

as did radium salts or cancerous tumors—the names of the Curies, who had discovered this little “philosopher’s stone” of the alchemists, acquired enormous popularity.

Meanwhile, at home in France, misfortunes continued to pursue Pierre Curie. Suffice it to say that when in 1902, at Mascar’s urging, Pierre Curie put himself forward as a candidate for the Academy of Sciences, he was not elected, despite the unanimous support of the Academy’s physics section.

Recognition, however, soon came, but it came from abroad. In 1903 Pierre and Marie Curie were awarded the Davy Medal by the Royal Society of London, and their trip to England to receive the medal was a genuine triumph. Almost at the same time they received the Nobel Prize, shared with A. Becquerel. These events were very important for Pierre Curie, since they greatly raised his authority and at the same time gave him the material possibility of giving up teaching at the School of Physics and Chemistry.

The enormous popularity acquired by the Curies also had its negative side: too much commotion grew up around them. Endless visits, letters that had to be answered, harassment by journalists and photographers from every country, innumerable visits from autograph collectors, and so on—all this was tiring and interfered with work. In January 1905, in a letter to his friend Gouy, Pierre Curie wrote: “As for work, I am doing nothing at all at present. Lectures, students, the setting up of apparatus, an endless procession of people who come to bother you without any serious grounds for doing so—this is what all life is spent on, and no time remains to do anything useful.”

This uproar nevertheless had a positive side for Pierre Curie. According to Marie Curie, public opinion in France was stirred by the fact that a scientist who had received worldwide recognition for his services occupied a subordinate position on the academic ladder in his own country. Under the pressure of public opinion, the rector of the Paris Academy, Liard, pushed through parliament the establishment of a special chair for Pierre Curie at the Sorbonne. At this point a serious mistake almost occurred that would have reduced this achievement to nothing: the parliament that voted to establish the chair did not provide funds for a laboratory. On learning of this, Pierre Curie categorically refused the chair. This made the proper impression, and funds for the laboratory were additionally approved, along with its very modest staff, consisting of only three “positions” (in our terminology): a head of work, to which Marie Curie was appointed, a preparator, and an attendant. This, however, as a first step, satisfied Pierre Curie, and at the beginning of the 1904/1905 academic year he began his activity already as a professor of the Sorbonne. The premises in the P.C.N. that he had occupied until then were expanded, and, in addition, in the courtyard there was

a small building was constructed for a laboratory and workshop. Unfortunately, Pierre Curie was scarcely able to take advantage of this improvement in working conditions. Although, under the terms of the approval of his chair, he was granted great freedom in choosing the program of lectures and, making use of this, Curie selected for his courses the questions closest to him—symmetry and radioactivity—nevertheless the preparation of these courses and the organization of the laboratory again demanded from him an expenditure of strength and time. Moreover, he was troubled by questions of the reform of education and of teaching methods, since, being “to the roots of his hair” a natural scientist, he dreamed of driving scholasticism out of the school, of transferring the center of gravity to the teaching of the natural sciences. In order to propagate these views, he took an ardent part in the activity of the Association of Professors of the Faculty of Sciences of the University of Paris. By force of a completely accidental combination of circumstances, this participation proved fatal for him. On April 19, 1906, he was at a meeting of the Association. Leaving the meeting and heading home, he slipped on the pavement and fell under the hoofs of the horses of a heavily loaded dray. The blow he received to the head caused immediate death. In a single instant this ardent heart stopped, and the activity of this profound and original mind came to an end—a mind that might still have given so much to humanity!

Thus tragically ended the life of this remarkable scientist and man; it ended precisely at the moment when, after long years of struggle to create the necessary conditions for work, happiness at last smiled upon him. “Can you imagine,” writes Marie Curie, “the regret that must be felt by a worker-enthusiast, occupied with great creations, when the realization of his dream is systematically delayed by a constant lack of funds? And can we think without a feeling of deep pain of the irreparable squandering of the nation’s greatest good: the genius, strength, and courage of its best sons.”

Despite his short life, Pierre Curie succeeded in working in various fields of physics, and everywhere he obtained results that will forever remain the property of science. This was because, in all the fields in which he worked, new phenomena, unnoticed by the ordinary observer, revealed themselves to his penetrating gaze, and his keen physical intuition enabled him to see, in the complex interweaving of facts, the most fundamental regularities. The characteristic features of his talent were admirably expressed by his friend and admirer, himself an outstanding scientist, Henri Poincaré: “Curie brought to the study of phenomena a certain special, delicate intuition, which allowed him to detect analogies whose existence no one suspected, and to find his way through such complex phenomena where others would inevitably have become entangled.”

Among the phenomena discovered by Pierre Curie there are none that we could recognize as less important than the others.

But the most urgent discovery, from the standpoint of the tasks of the present day in science, in technology, and in the whole life of humanity, is, of course, the discovery of the spontaneous liberation of energy by radioactive substances, i.e., the discovery of the very fact of the existence of enormous stores of energy in the depths of atoms. Perhaps one of the most striking proofs of Curie’s perspicacity is the assessment of the significance of this discovery that he gave in the concluding words of his Nobel address. Here are those words: “It is not difficult to foresee that, in criminal hands, radium may become extremely dangerous; and the question arises whether it is truly useful for humanity to know the secrets of nature, whether humanity is indeed sufficiently mature to make proper use of them, or whether this knowledge will bring it only harm. The example of Nobel’s discovery*) is characteristic in this respect. Powerful explosives have enabled people to accomplish remarkable deeds, and they have also become a terrible means of destruction in the hands of great criminals who have driven nations onto the path of war.” What astonishing prophetic words! It is hard to believe that they were spoken not yesterday or today, but more than fifty years ago, when before the scientist’s eyes there were not the atomic bombs or powerful nuclear reactors of our day, but a tiny grain of radium that caused a rise of temperature of a few degrees in a Dewar vessel. Curie added, moreover, that “he belongs to the number of those who believe that new discoveries will bring humanity more benefit than harm.” This faith is shared with Pierre Curie by all progressive people of the world, and above all it is shared by the Soviet Union, whose achievements in the peaceful applications of atomic energy are universally recognized.

*) The Swedish chemist Alfred Nobel, as is well known, discovered dynamite.