E. Rutherford (1871–1937).

MEMORIES OF PROF. E. RUTHERFORD1

P. L. Kapitsa, Moscow

For 14 years I worked together with Prof. Rutherford, and I recall one episode with which I should like to begin. It was 6 years ago; in Cambridge there was a congress in memory of the centenary of Maxwell’s birth—Maxwell, the first director of the Cavendish Laboratory, where after him the directors were Lord Rayleigh, J. J. Thomson and, finally, Rutherford—four men of genius, scholars of the end of the last century and the beginning of our own. After the solemn session, at which many of Maxwell’s pupils spoke, sharing their recollections with us, Rutherford asked me how I liked the talks. I answered:

“The talks were very interesting, but it struck me that everyone spoke of Maxwell only in exclusively favorable terms and presented him as though in the form of a sugar extract. But I should like to see Maxwell as a real living man, with all his human traits and shortcomings, which, of course, every man has, however brilliant he may be.”

Rutherford laughed and said that he was commissioning me, after his death, to tell a future generation what he himself had really been like. Rutherford said this jokingly, and I laughed too.

And now, after his untimely death, I speak of him, and I want to carry out this behest. But when I begin to picture Rutherford to myself as I would like to present him before you, I see that his death and the time that has passed since parting with him have swallowed up all the minor human shortcomings. And before me there rises a great man of astounding intellect. Now I understand well the state of those pupils of Maxwell who spoke then in Cambridge.

In such people as Faraday, Maxwell, Rutherford, the exceptional qualities of their mind and character completely absorb minor human shortcomings, and when memory reproduces their image, only one great whole remains.

We all—Rutherford’s pupils—did not expect his death. For us he was not only immortal as a scientist, but almost immortal

as a person. Both Rutherford’s father and mother lived to the age of 90, and Rutherford himself at 66 was full of strength, health, and energy—he worked entire days. But an unexpected illness occurred (a strangulated hernia), an operation was required; for four days afterward the organism struggled for life, but the heart did not hold out, and on October 19, 1937, Rutherford was no more.

Rutherford was exceptionally popular in his country; everyone knew him, and his death may be regarded as a national grief. He was given a national funeral, and the urn with his ashes was immured in Westminster Abbey, beside the graves of Newton, Darwin, Faraday, Herschel, and Kelvin.

Rutherford, who ended his life as the greatest scientist of our day, was born in 1871 in the village of Brightwater, near the town of Nelson in New Zealand. A scientist who possessed all the international distinctions that a man of science could possibly have, Rutherford began his life very modestly. He was the fourth child of a small farmer in New Zealand, who after him had another 8 children. It was beyond the means of the small farmer, who cultivated flax, to give an education to 12 children, and Rutherford, from childhood until the completion of his higher education, studied all the time on scholarships.

He was a very lively, active, cheerful child, fond of hunting and sports. At school and at the university he played forward on the football team. But he also loved to read, to make models, and to take mechanisms apart. While still a boy he made himself a photographic apparatus, which in those days was rather difficult. After finishing school in 1890, he entered the University of Canterbury College in Christchurch. This was a small provincial university; there were only 150 students and 7 professors. From the first day he became absorbed in science and began research work.

In his student years Rutherford became very interested in the radio waves discovered by Hertz. He was fascinated by the idea of wireless telegraphy, but the question at that time came down to finding a detector for electrical oscillations excited by incoming waves. Rutherford discovered that high-frequency oscillations demagnetize iron. In practice this is very easy to detect if, next to a magnetized bundle of iron wires placed in an oscillatory circuit, one sets a magnetic needle. The needle will then noticeably deviate when radio waves are received. He published this discovery, and in the small university it made a sufficient impression and at once created a reputation for Rutherford.

In 1891 the students organized a small scientific society, in which Rutherford, still quite a young man, delivered a report, “On the Evolution of Matter.” In this work he expressed ideas that were, for that time, entirely revolutionary: he asserted then that all atoms consist of the same constituent parts. This report was received very unfavorably, and he had to apologize before the society. It must be said that then, in 1891,

Rutherford had no data for such an assertion. Radioactivity was discovered only in 1896, and since Dalton’s time the atom had been regarded as something unshakable. But Rutherford’s boldness in expressing such an idea, the correctness of which he experimentally proved 12 years later, is very characteristic.

In 1894 he graduated from the university and, having received the so-called scholarship of 1851, went to England—to Cambridge. The “1851 scholarship” is the largest scholarship that a young scientist can receive in England, and it fully provided Rutherford with the means for scientific work for 2–3 years.

The year 1895 was a year of reforms at Cambridge University. Until that year, students who had graduated from other universities could not work in the research laboratories of Cambridge. But on the initiative of Prof. J. J. Thomson it was decided to change this order and to give students who had graduated from other universities the opportunity to continue scientific work in the Cambridge laboratories.

Rutherford was one of the first young scientists to take advantage of this change. He enrolled in the Cavendish Laboratory, directed by J. J. Thomson. Along with him there also entered MacLennan, Townsend, and Langevin. During his stay in the Cavendish Laboratory Rutherford worked in one room with Langevin and became very close friends with him. The friendship of the two scientists, who had begun their scientific activity together, remained the closest and unbroken until Rutherford’s very death. In Cambridge Rutherford began by continuing his work on radio transmission. He established radio communication between the laboratory and the observatory, i.e., over a distance of more than two kilometers. He was the first at that time to transmit radio signals over such a great distance. One must think that, had he continued this work, he would have gone very far, but he was not attracted by the practical solution of this problem. At that time he began to be interested in another question—the ionization of gases by X-rays, whose nature was still unknown at that time. He began working together with J. J. Thomson; they established such a phenomenon as the saturation current in ionization. This work, published in 1896, may be considered fundamental on this question.

It was precisely during these investigations, in 1896, that Becquerel discovered radioactivity. Rutherford became fascinated by this phenomenon and began to study it. He was the first to show that radium emits two kinds of rays (he called them α-rays and β-rays), which differ in their ability to penetrate matter. He showed that these rays differ from ordinary radiation.

In 1897 Rutherford—already a young scientist with a well-known reputation—received an invitation to occupy the chair of physics at the university in the city of Montreal in Canada, went there, and for 10 years (from 1897 to 1907) worked in Canada. These years, spent in a small provincial university, were years of his most fruitful work. It seems to me that this is espe...

especially instructive for young scientists. One often hears complaints from young, beginning scientists that they cannot work because there are no suitable conditions, no suitable laboratory, no this, no that. Now imagine a young scientist who finds himself at the other end of the world from his homeland, completely isolated from the entire scientific world, where in those days even journals arrived more than a month late. Yet this man is full of ideas, full of enthusiasm, and in this remote corner of the world he creates the most advanced, the most revolutionary, the leading views in the science of that time. By this he attracts young scientists from all over the world, and pupils already begin to come to him.

Rutherford’s work in Canada was marked by a whole series of major discoveries. First, he discovered thorium emanation. At that same time the young chemist Soddy was working there with Rutherford, and with him Rutherford began to study the chemical character of the elements obtained from radioactive decay, since it was very important to establish, along with the physical features, the chemical features of the radioactive process. At that time radioactivity was not yet understood, and Rutherford together with Soddy were the first to prove that it is the spontaneous transformation of some elements into others, now called radioactive decay. In this process either $\alpha$-rays are emitted, consisting of rapidly flying helium atoms with a positive charge, or $\beta$-rays—rapidly flying electrons. On this basis Rutherford supposed that thorium emanation is an element distinct from thorium itself. Together with Soddy, by diffusion he determined the atomic weight of the emanation and showed that it corresponds to a noble gas.

The theory of radioactive decay, advanced by Rutherford and Soddy in 1903, produced a revolution. When, as a student in 1891, he spoke in a student circle about the evolution of matter, he had no grounds for it; but now, when he had proved it on the basis of purely experimental data, it made a colossal impression not only in the narrow circle of his university, but also on scientists throughout the world. Nevertheless, this view was then so revolutionary that many, even very eminent scientists, did not share it. Kelvin died without agreeing that radioactivity is the decay of atoms of the elements, which he considered the unshakable foundation of the structure of matter.

In that same year, at the age of 32, Rutherford was elected to the Royal Society (a scientific society equivalent to our Academy of Sciences). But this is not an exceptional case in the English academy. There a scientist is usually elected immediately after he has achieved major successes in scientific work, and therefore cases of election of young scientists aged 25–28 are not rare. In this lies the great strength of the English academy, making it an active scientific center, and in this it compares favorably with the academies of all other countries.

In 1907 the chair of physics in Manchester—one of the major universities of England—became vacant. In the nineteenth century this chair

E. Rutherford and J. J. Thomson.

REMINISCENCES OF PROF. E. RUTHERFORD

such scholars as Dalton, Joule, and others had occupied. Rutherford moved there. And in the period from 1907 to 1919, while in Manchester, he carried out a whole series of works no less important than those in Montreal. Among his works of this period one must note, first of all, the work on the scattering of $\alpha$-particles as they pass through matter. It led to Rutherford’s establishing a new model of the atom, one accepted to this day.

In 1908, for his work, he received the Nobel Prize in Chemistry. In 1919 he discovered the artificial disintegration of matter and showed that in nature there exists not only the spontaneous decay of radioactive elements, but that one can also cause the artificial decomposition of the nucleus under the influence of bombardment by $\alpha$-rays. This was discovered with nitrogen, and then verified with a number of other light elements. Thus he created an entirely new field of nuclear physics—the artificial disintegration of the atom.

As in Canada, in Manchester he attracted to himself a whole cohort of young scientists. Working with him were not only Englishmen, but also the German Geiger, the Dane Bohr, and others; and in his laboratory his pupils produced a number of outstanding works.

In 1919 Rutherford received a chair at Cambridge, went there, and spent the rest of his life in Cambridge as director of the Cavendish Laboratory, left by J. J. Thomson, who had retired. Here he continued work on the artificial disintegration of matter. He directed the work of his pupils, and in his laboratory two of the greatest discoveries of nuclear physics in the last decade were made—the discovery of the neutron by Chadwick and the work of Cockcroft and Walton on the artificial decomposition of matter under the influence of bombardment by a beam of protons obtained artificially.

We see that, having begun his experimental work on radioactivity in 1896, Rutherford steadily developed it, and by the end of his life this field of knowledge had assumed such dimensions that it already appeared to us as a separate science—nuclear physics.

In order to understand the significance of each of Rutherford’s discoveries, one must imagine the historical background against which they were made. This task is far too broad for a report such as mine. But it is very instructive, in individual examples, to trace those methods by which Rutherford conducted his scientific work and by which he achieved such major results.

Rutherford was an experimenter and in this respect recalls Faraday. He made little use of formulas and seldom resorted to mathematics. At times, when trying to derive a formula in his lectures, he would become confused and then simply write down the result, remarking:

— If everything is derived correctly, then this is what will be obtained.

But he had an exceptional command of experiment. One may say that he “saw” the phenomenon on which he was working, even though it took place in the immeasurably small nucleus of the atom.

If one speaks very schematically, among physicists there exist, as it were, two types of investigators. One is a type rather of the German school, where the experimenter proceeds from known theoretical assumptions and tries to test them by experiment. The other type of scientist, rather of the English school, proceeds not from a theory, but from the phenomenon itself—studies it and sees whether this phenomenon can be explained by existing theories. Here the study of the phenomenon, its analysis, is the principal motive for the experiment. And if such a division is possible, Rutherford was a vivid representative of this second tendency in experimental physics. The main thing for Rutherford was to sort out, to understand the phenomenon. The experiment had to be so constructed that it was clear wherein the phenomenon consisted. For this, the accuracy and complexity of the measurements had to be just such as to sort out and understand the phenomenon.

As an example, I shall cite the case of the study of $\alpha$-particles. Radium emits $\alpha$-particles. Rutherford showed at the very beginning of his experiments that they are an unusual radiation. But what, after all, are they?

Fig. 1.

Rutherford decided that if they fly out of radium, they must be some already existing element. In order to find out which one, it is only necessary to determine the mass, and the mass need be determined only with sufficient accuracy to see to which of the existing elements it corresponds.

Rutherford sets up an experiment that is very characteristic of him. I shall describe this experiment, although it has only historical significance, since now more precise and more complicated methods are used to determine the mass of $\alpha$-particles. But Rutherford’s original method is striking in its simplicity and in how directly it led to the goal.

In Fig. 1 is shown the apparatus for these experiments. A simple electroscope $D$, made from a sheet of gold foil, is placed above 20 parallel metal plates $A$. The gap between the plates is only 1 mm, so that the $\alpha$-rays emitted by the radioactive salt $B$ (placed at the bottom) pass into the chamber of the electroscope as a parallel beam. To remove the emanation and increase the range of the $\alpha$-rays, hydrogen was passed through the apparatus.

By applying a strong magnetic field directed parallel to the planes of the plates $A$, it was possible almost completely to stop ionization in the chamber of the electroscope. In this simple way Rutherford showed that $\alpha$-rays are rapidly moving charged particles. By covering, from the side of the electroscope, half the gaps between the plates, it was possible to show that, for one direction of the magnetic field, the ionization ceases

at smaller field strengths than in the other direction. Thus the direction of deflection of the \(\alpha\)-rays by a magnetic field was established, and from this it followed that the charge of the \(\alpha\)-particles is positive. By creating an electric field between the plates \(A\), alternately connecting them to opposite poles of a battery, Rutherford succeeded in obtaining the cessation of ionization and the deflection of \(\alpha\)-rays by an electric field. From these data he determined the velocity of the \(\alpha\)-rays and also showed that they constitute a stream of positively charged atoms with a mass greater than that of hydrogen atoms, and determined, to an accuracy of 10%, the ratio of their charge to their mass. This ratio indicated that the \(\alpha\)-particles apparently correspond to helium atoms, doubly ionized.

But it was necessary to prove more precisely that this really was helium. This work was undertaken later—in 1909, already in Manchester, when he had at his disposal large stores of radium.

The apparatus for these experiments was also extremely simple. It is shown in Fig. 2. Into a small, thin-walled glass tube \(A\) radium emanation was placed. The thickness of the walls of this tube was only \(0.01\) mm, and the fast \(\alpha\)-rays could pass through the glass, while the emanation was isolated. This tube was placed in a glass vessel \(B\), ending in a capillary discharge tube with electrodes \(C\) and \(D\). By raising and lowering the mercury in vessel \(B\), a vacuum was created in the space surrounding tube \(A\). The tube with the emanation remained in the apparatus for two days, and then the gas formed by the passing \(\alpha\)-particles was compressed by raising the mercury into the discharge tube. When the tube glowed, yellow helium lines were visible, proving the presence of helium. That this helium had not diffused out of the tube with the emanation was easily shown by a control experiment in which this tube was filled with helium. In that case the helium lines did not appear in the spectrum. Thus it was shown that the \(\alpha\)-rays are helium atoms.

Fig. 2.

These two experiments I have described are exceptionally simple; any student can readily carry them out. But at the same time these experiments, so correctly set up and leading so directly to the goal, solved

at that period a question of primary importance and produced a revolution in views on matter.

Rutherford was not satisfied with the study of a beam of $\alpha$-rays by observing the ionization produced by them, and he sought a method by which he could detect individual $\alpha$-particles. The first method was found in the observation of scintillations.

Even Crookes noticed that, under the influence of bombardment by positive rays, certain substances glow—luminesce. The most brightly glowing substance proved to be zinc blende. When Rutherford, together with Geiger, placed zinc blende under a microscope and directed a beam of $\alpha$-rays onto it, then, instead of seeing in the field of view of the microscope an even luminous background, they saw separate flashing points. They concluded that the flashes occur at those places where the $\alpha$-rays strike the zinc blende. Thus it was possible to determine the number of emitted $\alpha$-rays by counting the flashes produced on the zinc blende.

Fig. 3.

Another method for detecting $\alpha$-particles, discovered by Rutherford, thanks to the invention of amplifier tubes, has now become even more powerful than counting scintillations—this is the counter method. This method is based on a phenomenon discovered by Townsend. If a point is present in a gas at reduced pressure, then one can select such a potential at which a discharge just does not arise. If now, in the surrounding gas, even the weakest ionization is produced by at least one $\alpha$-particle, then a discharge immediately arises for a certain interval of time. In 1908 Rutherford and Geiger constructed the first counter operating on this principle. It is shown in Fig. 3. Instead of a point they took a thin wire $A$, placed in a cylindrical vessel $B$. A critical potential was created between the wire and the cylinder. Through the opening $C$, covered by a very thin mica sheet, $\alpha$-rays can penetrate, the source of which is located in vessel $D$. The discharge currents from the wire are registered by a string galvanometer, from the deflections of which it was possible to count the $\alpha$-particles. Now, in the counter invented by Rutherford and Geiger, the string galvanometer is replaced by a tube amplifier, which makes the counter extraordinarily sensitive. In its present form it is one of the most fundamental instruments by means of which the complete study of cosmic radiation has become possible.

Having the possibility of counting α-rays, Rutherford began to study a whole series of phenomena which previously had not lent themselves to investigation.

In 1910 a young scientist by the name of Marsden came to work in his laboratory. He asked Rutherford to give him some very simple problem. Rutherford assigned him to count α-particles passing through matter, and to find their scattering. At the same time Rutherford observed that, in his opinion, Marsden would discover nothing remarkable. Rutherford based his considerations on Thomson’s model of the atom, accepted at that time. According to this model the atom was represented as a sphere of size \(10^{-8}\) cm, with a uniformly distributed positive charge, into which electrons were embedded. The harmonic oscillations of the latter determined the emission spectra. It is easy to show that α-particles should have passed easily through such a sphere, and no special scattering of them could be expected. The α-particles expended all their energy along the path of their range in knocking out electrons, which ionized the surrounding atoms.

Marsden, under Geiger’s supervision, began to make his observations and soon noticed that the majority of α-particles pass through matter, but nevertheless there is appreciable scattering, and some particles seem to rebound backward. When Rutherford learned this, he said:

— This is impossible. It is just as impossible as for a bullet to rebound from paper.

This phrase shows how concretely and vividly he saw the phenomenon.

Marsden and Geiger published their work, and Rutherford immediately decided that the existing conception of the atom was incorrect and had to be radically revised.

Studying the law of distribution of reflected α-particles, Rutherford tried to determine what distribution of the field inside the atom was necessary in order to obtain the law of scattering under which α-particles could even return backward. He came to the conclusion that this is possible when the entire charge is concentrated not throughout the whole volume of the atom, but at the center. The size of this center, which he called the nucleus, is very small: \(10^{-12}—10^{-13}\) cm in diameter. But where, then, should the electrons be placed? Rutherford decided that the negatively charged electrons must be distributed in a circle—they can be held by rotation, the centrifugal force of which balances the force of attraction of the positive charge of the nucleus. Consequently, the model of the atom is nothing other than a certain solar system, consisting of the nucleus—the sun—and electrons—the planets. Thus he created his model of the atom.

This model met with complete bewilderment, since it contradicted some of the foundations of physics of that time, which seemed unshakable. Rutherford, of course, understood that on the basis of Maxwell’s theory, electrons, rotating around the center, must inevitably …

emit light, lose its kinetic energy, and sooner or later fall into the nucleus. At that time it was extremely difficult to go against the foundations of Maxwell’s theory. Therefore Rutherford’s model of the atom was not recognized at first.

This continued for two years. During this time the young Danish scientist Niels Bohr came to work with Rutherford. They often discussed this model of the atom. For Bohr too it was clear that the principles of the structure of this model did not agree with the laws that at the time were accepted as fundamental. And Bohr began to work on this paradox. He believed in the experimental validity of Rutherford’s model, but it was necessary to find a theoretical justification for it. The brilliant idea occurred to him of applying, for this justification, the basic ideas of the quantum theory of radiation, which had only recently appeared. They had first been put forward by Planck and then considerably generalized by Einstein.

In 1913 Bohr provided a justification for Rutherford’s model of the atom, which now bears the name of the Bohr–Rutherford model and is the foundation on which all modern atomic physics rests.

One of Rutherford’s basic traits in his experimentation was his exceptional power of observation, his ability to generalize a phenomenon, to bring out the most important and most necessary point. This can be traced in a number of examples. When, for instance, he discovered emanation of thorium, he proceeded from observing the difference in the ionization produced by thorium with the door of the electroscope open and closed. It seemed that the stream of air passing through the preparation changed the radioactivity of the thorium itself. Rutherford began to collect this air and at once discovered that it itself was radioactive. This was the discovery of emanation. Most scientists, seeing the difference, would have begun to study the phenomenon either with the door closed or with it open. Rutherford, however, immediately posed the question: why does this phenomenon occur in this way and not otherwise, and at once tried to clarify for himself what the matter was. This ever-arising question “why” contained the key to great discoveries.

Here is another case. His remarkable observational ability also showed itself in the discovery of the artificial disintegration of matter. The point is that, when scintillations were observed, it often turned out that rays with a very long range flew out of the bombarded substance—one much longer than the range of the bombarding α-particles. Everyone observed them, they were often spoken of, but no one tried to explain them; no one asked himself the question: “why?” Rutherford decided that this phenomenon had to be analyzed and an attempt made to find out what was going on. An explanation was soon found. It turned out that, under the action of bombardment by α-rays, the atoms of nitrogen, always present in the air, disintegrate. This explained the long ranges. Rutherford arranged his experiments extremely simply. His apparatus is shown in Fig. 4.

The airtight chamber A could be filled through two stopcocks with ga—

nitrogen at various pressures. \(D\) is the source of \(\alpha\)-rays, \(B\) is the screen on which scintillations are observed with the aid of microscope \(H\). On the side facing the \(\alpha\)-ray source the screen is covered with a silver plate, which absorbs a considerable part of the energy of their path. Filling chamber \(A\) with nitrogen, Rutherford observed that at a certain pressure the majority of scintillations disappear. This occurs when the \(\alpha\)-rays emitted by the radioactive source expend all their energy on ionizing the air and do not reach the screen. But the remaining scintillations indicated the presence of a very small number of \(\alpha\)-rays with a range several times greater than that emitted by the source. If, instead of nitrogen, another gas is taken—for example carbon dioxide or oxygen—then no such residual scintillations appear. The only explanation is that they arise from nitrogen. Since the energy of the residual \(\alpha\)-rays is greater than that of the primary ones, they can appear only at the expense of the disintegration of the nucleus of the nitrogen atom. Thus the disintegration of nitrogen was proved, and the problem of alchemy was solved in principle.

Fig. 4.

Such simplicity in posing the question, so simply embodied experimentally, cannot fail to astonish any investigator, not only a physicist. Such simplicity is exceptionally ingenious, especially when it leads to such remarkable results.

Many say that Rutherford possessed exceptional intuition—he seemed to feel how to carry out an experiment and what to look for. By intuition one usually means some unconscious process that takes place within a person—something that cannot be explained, that subconsciously leads to the correct solution. I personally think that this may be partly true, but in any case it is greatly exaggerated. For the ordinary reader, the colossal amount of work that a scientist produces is simply unknown. He learns only of the part that leads to definite results. Observing Rutherford at close range, one could see what a colossal amount of work he did. His energy and enthusiasm were inexhaustible. He worked all the time and was constantly seeking something new. Rutherford published and brought to the attention

...of his fellow scientists only works with positive results, and they probably amounted to no more than a few percent of the enormous body of work that he carried out; the rest not only was not published, but in general remained unknown even to his pupils. Sometimes only from individual hints that slipped out in conversation with him could one gather that he had tried something, but had not succeeded. He did not like to speak of the plans for his work, and preferred to speak only of what had already been done and had yielded results.

One of the brilliant examples of his exceptional insight is the discovery of the neutron. The neutron is a material particle, equal in mass to the nucleus of hydrogen, but carrying no charge. Experimental proof of the existence of such a particle was made by Chadwick—Rutherford’s closest pupil—in Cambridge in 1932. For this discovery Chadwick received the Nobel Prize. He was studying a phenomenon in which, as a result of the bombardment of beryllium by the γ-rays of polonium, extremely penetrating rays were obtained. He succeeded in showing that these were not γ-rays. This radiation was first discovered by Bothe and was then investigated by the Joliot-Curie spouses, but only Chadwick succeeded in explaining it; he proved that in this case we are dealing with neutrons. The discovery of the neutron plays an enormous role in modern nuclear physics, since the neutron is one of the fundamental elementary particles of which the nuclei of all elements are built.

It turns out that Rutherford, 12 years before the discovery of the neutron, had predicted in extraordinary detail the possibility of its existence. Here is an excerpt from Rutherford’s lecture at the Royal Society, delivered in 1920.

“If we are right in this assumption,” said Rutherford, “then it is very probable that one electron can bind two hydrogen nuclei, or, what is also possible, one hydrogen nucleus. In the first case this entails the possibility of the existence of an atom with a mass nearly equal to two and with one charge, which should be regarded as an isotope of hydrogen. In the other case, however, this leads to the idea of the possibility of the existence of an atom whose mass is 1 and whose nuclear charge is 0.

Such an atomic formation does not appear impossible. Contemporary views are such that the neutral atom of hydrogen is regarded as a nucleus of unit charge with an electron fixed at a distance, and the spectrum of hydrogen is attributed to the motion of this distant electron. Under certain conditions there may be the possibility for this electron to join more closely to the hydrogen nucleus, forming something like a neutral doublet. Such an atom would have new properties. Its external field would hardly exist, except in the immediate vicinity of the nucleus. And for this reason it could pass freely through matter. Its presence would be difficult to detect with a spectroscope and, probably, it would be

REMINISCENCES OF PROF. E. RUTHERFORD

it would be impossible to keep it in a closed vessel. On the other hand, it would have to enter freely into the structure of atoms and could either combine with the nucleus or be decomposed by its strong field, the result of which might be the emission of a charged hydrogen atom or an electron, or both.”

Thus Rutherford foretold, long in advance, all those fundamental points along which the whole of nuclear physics came to develop after the discoveries of Chadwick and of the Curie-Joliots.

I would not call this process intuition. It was a process of profound thought and profound experimentation. We all knew that Rutherford himself was searching for the neutron—he searched for it long and persistently, but did not find it where he looked. In this case much depended on luck. Why it was necessary to choose beryllium and polonium, and not other substances—this could not have been predicted by theory. Here one simply had to search stubbornly.

Being such an exceptionally great scientist, Rutherford was also an exceptional man in the sense that he did not shut himself up within the circle of his laboratory, but his interests extended widely to the world around him.

In appearance he was rather solidly built, taller than average; his eyes were blue, always very cheerful, his face very expressive. He was lively; his voice was loud, and he was poor at modulating it—he could not speak in an undertone. When the professor entered the laboratory, everyone knew it, and by the intonation one could tell whether the professor was in good spirits or not.

In his whole manner of dealing with people, from the very first word, his sincerity and directness immediately stood out. His answers were always brief, clear, and precise. With his friendliness he very quickly won people over. To spend time in his company was exceptionally pleasant. When something was told to him, he reacted immediately, whatever it might be. One could discuss any problem with him—he would at once begin to speak about it willingly. I remember, for example, once after dinner, sitting over port wine (there were many scientists there, among them Eddington), the question was being discussed of the meteorite that had fallen in Siberia. At that time it had only just been discovered, and we were very occupied with it. The question was discussed from every angle. Right there we roughly calculated the energy and dimensions of the meteorite from the data we had. Someone among us asked:

— What is the probability that such a meteorite would fall in the City of London, that is, where all the banks of London are located?

We calculated the probability—it turned out to be very small. There were economists present. And another question was posed:

— What impression would it make on the British state if the City—the banking apparatus of London—were destroyed, while all industry remained? In this discussion everyone put forward his own conjectures. We talked for two hours. In conversations of this kind Rutherford took the liveliest part.

If someone made a witty remark or conclusion, Rutherford would be the first to begin laughing loudly, drowning out everyone else with his laughter. If he liked something, he said so at once. There was no hypocrisy in him, no concealment of his feelings. When he threw the ball successfully in a game—he rejoiced. He rejoiced just as much when an experiment succeeded, and just as much when he received a scientific award. When he was angry, he did not hide that either, and one immediately felt that he was in a rage. But Rutherford was exceptionally quick to relent and was kind. I never saw him angry for more than 5 or 10 minutes; then the momentary storm would pass.

He treated people with exceptional solicitude, especially his pupils. When I came to work in his laboratory, I was at once struck by this solicitude. Rutherford did not allow one to work in the laboratory after 6 o’clock in the evening, and on weekends he did not allow work at all. I protested, but he said:

— It is quite enough to work until 6 o’clock; the rest of the time you must think. Bad people work too much and think too little.

If he saw that I was tired, he would immediately say:

— You must go away and rest.

I objected:

— But, please, the holidays have not yet begun.

He would answer jokingly:

— That makes no difference—I shall lock your room and not let you work.

Later I saw that the time spent resting was fully repaid by the energy acquired.

From this image of Rutherford that I have drawn for you, you will at once see a man of great, strong temperament. This temperament was expressed in everything, especially in his judgments. Rutherford could not tolerate bad faith in work or in people’s relations with one another. If any pupil showed even the slightest bad faith in anything—whether in representing the results of his work incorrectly, or in failing to mention the source of his ideas and trying to pass off the work he had done as his own when in fact he had drawn the idea for it from elsewhere—such a person lost all interest for Rutherford.

Rutherford himself was extremely precise when giving credit for work. If some pupil working with him did work according to his own idea, he especially noted that the work had been done according to the pupil’s idea. If it was done according to his own idea, he also noted that the idea was his. He felt the full necessity of fairness.

As an example, I shall relate the story of the great discovery by his pupil Moseley. In 1912 Moseley was working with Rutherford. He was still a very young man, but Rutherford always spoke of him as his best pupil. After coming to the laboratory he immediately

...also produced several brilliant short works. Later he came to Rutherford with the topics of three papers that he wanted to begin, and told him what these works were. One of them was that brilliant work which made his name known throughout the world—the establishment of the dependence of the wavelength of an atom’s X-rays on its position in the periodic system. Rutherford noted that he considered this work the most important and suggested that Moseley do precisely it. Rutherford was not mistaken—the work proved to be exceptionally important. But the idea was Moseley’s, and Rutherford always emphasized this (Moseley died at the age of 27 during the imperialist war).

With such a character Rutherford was an exceptional teacher and created a large school. Rutherford was precisely a teacher, not a pedagogue. When, in 1894, after graduating from the university, he became a teacher in a secondary school, it turned out that this year of teaching was extremely unsuccessful. There was always noise and disorder in the classroom; when he explained, no one understood anything. The pupils soon learned that when he became angry and sent a pupil for the class register, there was no particular need to be afraid of this, since he would soon become carried away by his story and one could slip back into the classroom unnoticed. During his speech he would already forget about everything.

He did not know how to maintain classroom discipline. Sometimes in childhood his mother assigned him to look after his little sisters, and he would read them something; the little sisters would run away. And so, to prevent them from running away, he simply tied their braids together.

He lectured in an extraordinarily interesting way, but it was not interesting for all students. If he was lecturing, for example, on the kinetic theory of gases and came to the question of the collision of molecules, he would recall collisions of $\alpha$-particles and begin talking about his latest works—the lecture would proceed in an entirely different direction. But on subjects that interested him he spoke exceptionally engagingly. Students who needed knowledge for practical purposes—to pass examinations—did not much approve of Rutherford’s manner of lecturing on physics: they preferred lectures according to the syllabus.

Of course, a man with such colossal enthusiasm, with such a profound understanding of the subject, and with such a character could not fail to be a great teacher. He captivated his pupils, and this immediately made itself felt. When he was still quite young and worked in Canada, in Montreal, scholars from other parts of the world already came to work with him; for example, Hahn—the well-known German chemist—came, among others. At that time Rutherford was younger than 30. When he moved to Manchester, a whole galaxy of pupils surrounded him. Among them were Bohr, Geiger, Marsden, Moseley, Darwin, Chadwick, Robertson, and many others whose names are not so well known. In Cambridge he still had many pupils, from among whom many excellent scientists emerged. Among them one may name Cockcroft, Oliphant, Blackett, Chadwick, Ellis, Henderson, and many others. Toward his pupils Rutherford showed excep-

...care. His view of students was, schematically speaking, this—he would say:

—If I have a young scientist working with me and, after two years of work, he comes to me and asks what he should do next, I advise him to give up work in science; for if a person, after two years of work, does not know what he should do next, no scientist can come of him.

In reality he never posed the question so sharply and, under one pretext or another, always found an opportunity to provide his unsuccessful pupils with a place either somewhere in an industrial laboratory, or a teaching position in some school or university.

But if a person showed initiative and individuality, Rutherford gave such a person every kind of support and attention. At the same time it must be said that Rutherford used every opportunity to reveal a person’s individuality. I remember that, at the very beginning of my work in Cambridge, I came to Rutherford and said:

—You have X working for you; he is working on a hopeless idea and is wasting time, instruments, and so on.

—I know that,—Rutherford replied.—I know that he is working on an absolutely hopeless problem, but, on the other hand, this problem is his own; and if his work does not come off, it will teach him to think independently and will lead him to another problem, which will no longer be hopeless.

He was ready to sacrifice a great deal, if only to cultivate independence and originality of thought in a person. When a pupil began to show success, originality of thinking, he surrounded him with every possible care and encouraged his work in every way. This profoundly just attitude was expressed also in the fact that he always gave due credit to the ideas of his pupils. He took care that, if a person had something of his own, it should be recognized. He himself always noted this in his lectures. If anyone, in publishing his work, forgot to stipulate that a given idea was not actually his own, Rutherford noted it at once. He made every effort to ensure complete fairness and that exact priority was observed.

Rutherford understood perfectly the significance that pupils had for him personally. For him the point was not only that the scientific productivity of the laboratory should rise. He said:

—Students force me myself to remain young.

There is deep truth in this, since students do not allow a teacher to fall behind life, to reject everything new that science gives. We often observe that many scientists, as they grow older, come to stand in opposition to new theories, underrate the new tendencies and directions of science. Meanwhile Rutherford, with ease and goodwill, accepted such new ideas in physics as wave and quantum mechanics, toward which a number of major scientists of his generation still...

...treat the professor with unfounded skepticism. This usually happens with those who have no close pupils whom they must guide and whom they must move forward.

From all that has been said, it seems clear to me that the death of Prof. Rutherford is a very heavy blow to scientists throughout the world. In him, science loses the greatest pioneer of physical research since Faraday. Throughout his life, so fruitful in scientific discoveries, he worked on the most fundamental problems of the modern theory of the atom.

He may be regarded not only as the creator of a new chapter in science, but also as the creator of an entire new science—nuclear physics.

Already in 1896, while still a very young man, he began to study radioactivity, which had only just been discovered; and from then on his work, which continued for 40 years, gave humanity every year new discoveries and new ideas that guided atomic physics throughout the world.

His influence on international science was greatly strengthened by the large number of pupils of all nationalities, including a number of Soviet scientists, who worked in Rutherford’s laboratory. His selfless and powerful individuality earned from them not only respect and admiration, but also deep affection. Thus there was created around him the largest school of physicists that has ever existed. And we readily understand why his death is felt as a great personal loss and grief by so very many scientists throughout the world.

We in the Soviet Union feel his death with particular acuteness, where science is recognized as one of the most fundamental foundations of social development.

1. A lecture read at the N. D. Zelinsky University of Physical Chemistry in Moscow on November 14, 1937. ↩