The determination in 1953 of the structure of deoxyribonucleic acid (DNA), with its two entwined helices and paired organic bases, was a tour de force in X-ray crystallography. But more significantly, it also opened the way for a deeper understanding of perhaps the most important biological process. In the words of Watson and Crick: "It has not escaped our notice that the specific pairing that we have postulated immediately suggests a possible copying mechanism for the genetic material." [Obituary of Francis Crick:
Physics: Looking Back...
Since 1869, Nature has published some of the world's most important physics and astrophysics research, including the discovery of the neutron, the first laser, the discovery of superfluidity, the explanation of quasars, the invention of holography, and much more...
These papers are well worth revisiting, as much for their elegance and brevity as for their seminal content.
Quantum teleportation — the transmission and reconstruction over arbitrary distances of the state of a quantum system — is demonstrated experimentally. During teleportation, an initial photon which carries the polarization that is to be transferred and one of a pair of entangled photons are subjected to a measurement such that the second photon of the entangled pair acquires the polarization of the initial photon. This latter photon can be arbitrarily far away from the initial one. Quantum teleportation will be a critical ingredient for quantum computation networks.
(1) TWO hypotheses have been propounded to explain the properties of the kathode rays. Some physicists think with Goldstein, Hertz, and Lenard, that this phenomenon is like light, due to vibrations of the ether,2 or even that it is light of short wavelength. It is easily understood that such rays may have a rectilinear path, excite phosphorescence, and affect photographic plates.
In 1896, Jean-Baptiste Perrin reported the results of experiments on the mysterious 'kathode rays' that emanate from a cathode within an evacuated tube. Hertz had proposed that these rays were a form of light, but Perrin's experiments showed that they were charged with negative electricity, and that positive charge flowed towards the cathode even as the negative rays came from it. In March 1897, J. J. Thomson reported corroborating observations, setting the stage for his announcement one month later that the cathode rays were comprised of corpuscles with mass 1,000 times smaller than that of the hydrogen atom.
PART 2. FURTHER EVIDENCE FOR THE EXISTENCE OF UNSTABLE CHARGED PARTICLES, OF MASS ∼ 1,000 me, AND OBSERVATIONS ON THEIR MODE OF DECAY
In 1947, Rochester and Butler twice observed that cosmic rays produced peculiar V-shaped tracks in a cloud chamber. These events, they suggested, reflected the decay of unknown particles with masses roughly 1,000 times that of an electron. In 1949 and 1951, Brown et al. and Armenteros et al. offered more extensive corroborating evidence for these 'V-particles', showing that there were at least two different kinds, which produced protons and pions when they decayed. These were the first observations of strange particles — now known as kaons, lambdas, cascades and sigmas — which are produced by the strong interactions, but can only decay by the weak interaction. See also Nature 160, 855-857 (1947).
IF a conducting liquid is placed in a constant magnetic field, every motion of the liquid gives rise to an E. M. F. which produces electric currents. Owing to the magnetic field, these currents give mechanical forces which change the state of motion of the liquid. Thus a kind of combined electromagnetic-hydro-dynamic wave is produced which, so far as I know, has as yet attracted no attention.
THERE is now abundant evidence for the presence of large quantities of unseen
matter surrounding normal galaxies, including our own1,2. The nature of
this ’dark matter‘ is unknown, except that it cannot be made of normal stars,
dust or gas, as they would be easily detected. Exotic particles such as axions, massive
neutrinos or other weakly interacting massive particles (collectively known as WIMPs)
have been proposed3,4, but have yet to be detected. A less exotic
alternative is normal matter in the form of bodies with masses ranging from that of a
large planet to a few solar masses. Such objects, known collectively as massive compact
halo objects5 (MACHOs), might be brown dwarfs or ‘jupiters’
(bodies too small to produce their own energy by fusion), neutron stars, old white dwarfs
or black holes. Paczynski6 suggested that MACHOs might act as
gravitational microlenses, temporarily amplifying the apparent brightness of background
stars in nearby galaxies. We are conducting a microlensing experiment to determine
whether the dark matter halo of our Galaxy is made up of MACHOs. Here we report a
candidate for such a microlensing event, detected by monitoring the light curves of 1.8
million stars in the Large Magellanic Cloud for one year. The light curve shows no
variation for most of the year of data taking, and an upward excursion lasting over 1
month, with a maximum increase of ∼2 mag. The most probable lens mass, inferred from
the duration of the candidate lensing event, is ∼0.1 solar mass.
In 1986, Bohdan Paczynski suggested that dark, compact objects in the halo of our Galaxy — the local cousins of similar objects conjectured to contribute dark matter to the haloes of other galaxies — could be detected on Earth, as their gravitation might occasionally amplify the light arriving from more distant stars. In 1993, in surveys of several million stars in the Large Magellanic Cloud, C. Alcock et al. and E. Aubourg et al. observed several candidate events. In total, the two groups detected three stars for which the brightness increased by two magnitudes over an interval of roughly one month.
In 1979, Walsh, Carswell and Weymann reported the observation of two quasistellar objects that looked suspiciously similar. Known as 0957 + 561 A and B, and separated in the sky by only 5.7 arc seconds, the two sources had nearly identical magnitudes, redshifts and detailed spectra. "Difficulties arise in describing them as two distinct objects," the researchers pointed out. Gravitational lensing, they suggested, offered a more likely explanation: light from a single source, after travelling along distinct, bending paths through the gravitational field of some large intervening object, was arriving at the Earth from two different directions.
Detection of Neutrons Liberated from Beryllium by Gamma Rays: a New Technique for Inducing Radioactivity
We have observed that a radiation emitted from beryllium under the influence of radium gamma rays excites induced radioactivity in iodine, and we conclude that neutrons are liberated from beryllium by gamma rays.
In September 1934, Leo Szilard and T. H. Chalmers let gamma rays fall onto a beryllium target, noting that emissions from the target induced radioactivity in iodine. "We conclude," they wrote, "that neutrons are liberated from beryllium by gamma rays." Two months later, A. Brasch and colleagues, including Szilard and Chalmers, reported a similar effect using X-rays rather than gamma rays. More ominously, the existence of neutron-induced radioactivity also suggested the possibility of neutron chain-reactions — using the neutrons emitted by radioactive elements to induce radioactivity, and liberate further neutrons, from other nuclei. The first demonstration came four years later, following the discovery of nuclear fission in uranium [see Nature 143, 239-240 (1939)].
In 1963, Harold Weaver and colleagues observed unusual emissions from the Orion nebula. The radio frequency suggested the presence of hydroxyl (OH) groups, but the line intensities were wrong. The explanation? Weaver et al. suggested that these were not ordinary thermal emissions, but that clouds of OH gas were emitting by maser action, being pumped by infrared light from nearby star-forming clouds. Six years later in Nature, Cheung et al. reported the discovery of another class of astrophysical maser — spectacularly bright 22-GHz water masers — observations of which are now widely used to probe the dynamics of their environments.
Classical interferometry works by detecting correlations in the phases of two waves. In Nature in 1956, R. Hanbury-Brown and R. Q. Twiss demonstrated another technique that probes quantum-mechanical correlations in the electromagnetic field. Splitting an incoherent light beam, they found that photon detections in the two daughter beams were correlated: the photons were bunching together. This corresponds to a correlation in the intensity of light in the two beams, which Hanbury-Brown and Twiss suggested could be used to infer the angular size of distant stars. Physicists now rely on the effect to probe the quantum character of complex light sources. [Obituary of Robert Hanbury Brown: Nature 416, 34 (2002)]
Microscopic spirals often appear on the surfaces of solids grown slowly from solution. In 1949, F. C. Frank proposed an explanation, suggesting that crystal growth could lead to screw dislocations — linear defects oriented normally to the growing surface and forming the core of a lattice structure locally akin to a spiral staircase. In Nature, four years later, Ajit Ram Verma and S. Amelinckx offered experimental support for the idea. Photos of a solid forming on a surface revealed a growth front spiralling outward around a central point. Measurements confirmed the height of the growing layer as a single unit cell.
Superconductors have no electrical resistance and are strongly diamagnetic. In the Meissner effect, a superconductor expels a magnetic field. In 1947, in a letter to Nature, Russian physicist V. Arkadiev demonstrated a striking consequence of such diamagnetism. Using a steel magnet and a superconducting lead disk resting in liquid helium, Arkadiev revealed in a photograph how the magnet was "repelled from the horizontal surface with such force" that it hovered in the air with no other support. Today, with liquid nitrogen and modern high-temperature superconductors, Arkadiev's levitation is a common trick in the physics classroom.
The historic detection by the Kamiokande-II collaboration1 and the IMB collaboration2 of neutrinos from the Large Magellanic Cloud (LMC) supernova provides the first opportunity to determine the mass,
"I am much puzzled by some recent results as to the density of nitrogen," admitted Lord Rayleigh in a Nature issue of 1892. In his experiments, samples of nitrogen purified by different methods gave different values for the density of the gas. Rayleigh's persistence in tracking down this anomaly led to the discovery, with William Ramsay, of the first noble gas — argon — in 1895 [Rayleigh, Lord & Ramsay, W. Phil. Trans. R. Soc. Lond. A 186, 187 (1895)]. By the end of the century, helium, neon, krypton and xenon had all been isolated, and in 1904 Rayleigh and Ramsay won Nobel prizes for their work — Rayleigh in physics and Ramsay in chemistry.
AN attempt to explain neutron-proton interaction made by Yukawa1 in 1935 has been brought to general notice2,3 in connexion with the new experimental evidence for the existence of a 'heavy electron'4,5,6.
In 1935, Hideki Yukawa proposed that the force holding the atomic nucleus together resulted from the exchange of a new particle several hundred times heavier than an electron. In consecutive Letters to Nature in 1938, Kemmer and Bhabha developed Yukawa's theory further and proposed that the Yukawa particle, in Kemmer's words, "has a charged and an uncharged state"; the latter, said Bhabha, could "explain the close-range proton-proton interaction". Kemmer added that "its relation to experiment is admittedly quite uncertain" — in 1937 the newly discovered muon had been misidentified as the Yukawa particle. But later the situation became clear: Yukawa's particle was in fact the π meson, or pion. The charged members of the pion family were discovered in 1947 [see Nature 159, 186–190 (1947) & Nature 160, 453–456 (1947)]; Bhabha and Kemmer were proved right when, at Berkeley in 1950, the neutral pion became the first unstable particle to be discovered using an accelerator.
CONJUGATED polymers are organic semiconductors, the semiconducting behaviour being associated with the π molecular orbitals delocalized along the polymer chain. Their main advantage over non-polymeric organic semiconductors is the possibility of processing the polymer to form useful and robust structures. The response of the system to electronic excitation is nonlinear—the injection of an electron and a hole on the conjugated chain can lead to a self-localized excited state which can then decay radiatively, suggesting the possibility of using these materials in electroluminescent devices. We demonstrate here that poly(p-phenylene vinylene), prepared by way of a solution-processable precursor, can be used as the active element in a large-area light-emitting diode. The combination of good structural properties of this polymer, its ease of fabrication, and light emission in the green–yellow part of the spectrum with reasonably high efficiency, suggest that the polymer can be used for the development of large-area light-emitting displays.
IN the past few years, physicists have been much engaged by the phenomenon of supraconductivity. It is well known that various metals, when cooled below a certain very low temperature, characteristic of the metal in question, show the strange property of conducting electricity apparently without offering any resistance to the current. This curious phenomenon seems to contradict all our customary conceptions in physics. Particularly striking was the experiment of Kamerlingh Onnes and Tuyn, in which a current was induced in a supraconducting ring of lead and was found to persist there without any measurable decrease for many hours—so long as the low temperature could be maintained. This experiment seems to present a unique case of motion without any friction, whilst we have been accustomed to see in every mechanism an occasion for dissipation of kinetic energy into heat.
In 1937, Fritz London introduced his 'New Conception of Supraconductivity' to the readers of Nature. He proposed "representing all supracurrents realizable in a simply connected supraconductor by even one single electronic state". Some 20 years later, Bardeen, Cooper and Schrieffer built on this idea to produce the 'BCS theory' of superconductivity, which is based on a correlated, 'single-state' system of electron pairs. In 1938, London himself applied a similar idea to the phenomenon of superfluidity, suggesting that it may be a manifestation of bosonic condensation of atoms [see Nature 141 , 643-644 & Nature 141 (1938), 913 (1938)).
Chandrasekhara Venkata Raman is probably most famous for the discovery of the effect that bears his name — the Raman effect describes the change in frequency and phase of light as it is scattered in a medium. In 1930, Raman won the Nobel Prize in Physics for this work, and two years later he was still concerned with the passage of photons through materials. With his colleague S. Bhagavantam, he performed a careful study of the degree to which light becomes depolarized as it Rayleigh-scatters through gaseous oxygen, carbon dioxide and nitrous oxide. Their conclusion was clear and fundamental —"the light quantum possesses an intrinsic spin equal to one Bohr unit of angular momentum".
This featured article is not a scientific paper but nevertheless is a text of interest: Nature's news section, then known as "Notes.", reported that, on 12 December 1901, "Mr. Marconi" had succeeded in sending a wireless telegraph from Cornwall to Newfoundland — the first transatlantic wireless transmission. In 1909, Marconi shared the Nobel Prize in Physics with Carl Ferdinand Braun "in recognition of their contributions to the development of wireless telegraphy".
THAT the intra-atomic charge of an element is determined by its place in the periodic table rather than by its atomic weight, as concluded by A. van der Broek (NATURE, November 27, p. 372), is strongly supported by the recent generalisation as to the radio-elements and the periodic law. The successive expulsion of one and two particles in three radio-active changes in any order brings the intra-atomic charge of the element back to its initial value, and the element back to its original place in the table, though its atomic mass is reduced by four units. We have recently obtained something like a direct proof of van der Broek’s view that the intra-atomic charge of the nucleus of an atom is not a purely positive charge, as on Rutherford’s tentative theory, but is the difference between a positive and a smaller negative charge.
In 1913, only the barest outlines of the structure of the atom had been drawn. Frederick Soddy, although struggling to understand how an electron could be emitted from the nucleus during beta-decay, supported the conclusions of A. van de Broeck — that an element's atomic number, not its atomic weight, is the fundamental parameter determining chemical properties. Soddy introduced the word 'isotope' for elements that occupy the same place in the periodic table and hence have identical properties, though different mass. He also contested "Rutherford's tentative theory" that the nucleus has only positive charge. One week later, a rather indignant Ernest Rutherford responded: the nucleus has "resultant" positive charge, he said, and as he elaborated, Rutherford came tantalizingly close to postulating the proton.
We have observed the quantization of magnetic flux in a high-Tc yttrium-based ceramic superconductor1 and obtain a value for the flux quantum in this material. The value of the flux quantum, h/2e where h is Planck's constant and e is the electron charge, implies that the charge carriers of superconductivity are electron pairs.
While trying to perfect the design and manufacture of the vacuum valve, the pioneers of electronic engineering uncovered a fundamental problem — noise. Walter Schottky first postulated the existence of thermal noise and shot noise in 1918. In a letter to Nature in 1927, J. B. Johnson commented on voltage fluctuations that appear "to be the result of thermal agitation of the electric charges in the material of the conductor". Johnson would later become associated with thermal noise — now also known as Johnson noise — after he published a definitive experiment on noise in 1928, alongside Harry Nyquist's theoretical explanation [Johnson, J. B. Phys. Rev. 32, 97–109 (1928); Nyquist, H. Phys. Rev. 32, 110–113 (1928)]. But his letter of 1927 was intended to bring "a similar phenomenon" to the attention of Nature readers. In this case the fluctuations depend not on temperature but inversely on frequency — Johnson had discovered '1/f noise'.
CAN any of your readers refer me to a work wherein I should find a solution of the following problem, or failing the knowledge of any existing solution provide me with an original one? I should be extremely grateful for aid in the matter.
THIS problem, proposed by Prof. Karl Pearson in the current number of NATURE, is the same as that of the composition of n iso-periodic vibrations of unit amplitude and of phases distributed at random, considered in Phil. Mag., x., p. 73, 1880; xlvii., p. 246, 1899; (“Scientific Papers,” i., p. 491, iv., p. 370). If n be very great, the probability sought is
In the warm summer months of 1905, Karl Pearson was perplexed by the problem of the random walk. He appealed to the readers of Nature for a solution as the problem was — as it still is — "of considerable interest". The random walk, also known as the drunkard's walk, is central to probability theory and still occupies the mathematical mind today. Among Pearson's respondents was Lord Rayleigh, whose assistance led Pearson to conclude that "the most probable place to find a drunken man who is at all capable of keeping on his feet is somewhere near his starting point!".
On 7 November 1991, Sumio Iijima announced in Nature the preparation of nanometre-size, needle-like tubes of carbon — now familiar as 'nanotubes'. Used in microelectronic circuitry and microscopy, and as a tool to test quantum mechanics and model biological systems, nanotubes seem to have unlimited potential.
The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star’s radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.
THE continuous spectrum of the β-rays arising from radio-active bodies is a matter of great importance in the study of their disintegration. Two opposite views have been held about the origin of this continuous spectrum. It has been suggested that, as in the α-ray case, the nucleus, at each disintegration, emits an electron having a fixed characteristic energy, and that this process is identical for different atoms of the same body. The continuous spectrum given by these disintegration electrons is then explained as being due to secondary effects, into the nature of which we need not enter here. The alternative theory supposes that the process of emission of the electron is not the same for different atoms, and that the continuous spectrum is a fundamental characteristic of the type of atom disintegrating. Discussion of these views has hitherto been concerned with the problem of whether or not certain specified secondary effects could produce the observed heterogenity, and although no satisfactory explanation has yet been given by the assumption of secondary effects, it was most important to clear up the problem by a direct method.
In the 1920s, physicists were confused: the phenomenon of β decay (in which an electron is emitted from the atomic nucleus) seemed to violate conservation laws. The energy spectrum of the electrons, or β-rays, is continuous: if energy is conserved, another, variable, amount of energy must somehow leave the system. In 1927, Ellis and Wooster [Nature 119, 563–564 (1927)] tried — and failed — to capture and measure that missing energy. By 1933, Pauli had devised an explanation in terms of another, undetected, particle being emitted by the nucleus; Fermi called it 'the neutrino'. Only in 1956 was the existence of the neutrino proved: Reines and Cowan [Nature 178, 446–449 (1956)] sent Pauli a telegram to inform him of their discovery.
Iwanenko’s tentative suggestion that the neutron might be a constituent of the nucleus is certainly one of the more curious contributions to this feature. It was published in 1932, just two months after “Dr. J. Chadwick’s explanation of the mysterious beryllium radiation” that marked the discovery of the neutron [see Nature 192, 312 (1932)]. Although he was wrong about “nuclei electrons being all packed in α-particles or neutrons”, Iwanenko hit the target as he mused that the neutron may be an elementary particle “something like protons and electrons” with “a moment ½”.
It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.
THERE are so many dynamical problems connected with golf that a discussion of the whole of them would occupy far more time than is at my disposal this evening. I shall not attempt to deal with the many important questions which arise when we consider the impact of the club with the ball, but confine myself to the consideration of the flight of the ball after it has left the club. This problem is in any case a very interesting one; it would be even more interesting if we could accept the explanations of the behaviour of the ball given by many contributors to the very voluminous literature which has collected round the game; if these were correct, I should have to bring before you this evening a new dynamics, and announce that matter, when made up into golf balls, obeys laws of an entirely different character from those governing its action when in any other condition.
BY analogy with the excitation and ionisation of atoms by light, one might expect that any complex nucleus should be excited or ‘ionised’, that is, disintegrated, by γ-rays of suitable energy. Disintegration would be much easier to detect than excitation. The necessary condition to make disintegration possible is that the energy of the γ-ray must be greater than the binding energy of the emitted particle. The γ-rays of thorium C″ of hv = 2.62 × 106 electron volts are the most energetic which are available in sufficient intensity, and therefore one might expect to produce disintegration with emission of a heavy particle, such as a neutron, proton, etc., only of those nuclei which have a small or negative mass defect; for example, D2, Be9, and the radioactive nuclei which emit a-particles. The emission of a positive or negative electron from a nucleus under the influence of γ-rays would be difficult to detect unless the resulting nucleus were radioactive.
In 1957, Boot and Harvie reported the observation of a force on charged particles in an inhomogeneous electric field, which originated from second-order terms of the equation for the Lorentz force on the particles. Almost immediately it was realized that this 'ponderomotive force' could be used to trap and control electrons. But the force is weak: only with the development of modern laser technology is the ponderomotive force being exploited in new particle-acceleration techniques and inertial confinement fusion.
The first all-electronic scheme for television was outlined by A. A. Campbell Swinton in 1908. Campbell Swinton imagined a receiving apparatus comprising an electron beam, deflected by electromagnets, scanning across a "sensitive fluorescent screen". He suggested that the camera might also incorporate a scanning electron beam, but anticipated that a new photoelectric phenomenon would need to be discovered, to make such a camera a reality.
In 1919, Francis Aston built the first mass spectrograph capable of measuring the masses of the elements with useful precision. By December of that year, he had obtained enough data to propose the 'whole-number rule': that the elements are mixtures of isotopes, each of which has a mass that is an integer multiple of one-twelfth the mass of carbon, or one-sixteenth the mass of oxygen. Aston's prescient conclusion: "Should this integer relation prove general it should do much to elucidate the ultimate structure of matter."
In the early 1960s, astronomers were puzzled by quasars — sources of intense radio emission that seemed to be stars, but had unintelligible optical spectra. In 1963, Maarten Schmidt solved the puzzle by recognizing the Balmer lines of hydrogen, strongly redshifted, in the spectrum of the quasar 3C 273. Schmidt reached the "most direct and least objectionable" conclusion, that 3C 273 was no star, but the enormously bright nucleus of a distant galaxy.
IN studying photographic plates exposed to the cosmic rays, we have found a number of multiple disintegrations each of which appears to have been produced by the entry of a slow charged particle into a nucleus. Mosaics of photomicrographs of three of these events are given in Figs.
1947 was the year of the pion — flick through Nature volumes 159 and 160 and watch the story unfold. In February of that year, Cecil Powell and Giuseppe Occhialini reported the observation of six star-like patterns in emulsions exposed to cosmic rays. Powell's group had finally found the Yukawa particle, predicted in 1935 to be the carrier of strong force inside the atomic nucleus. In fact, Don Perkins pipped them to the post with the publication of a single, similar star-like event just two weeks earlier [Perkins, D. H. Nature 159, 126–127 (1947)]. Later in the year, another paper from Powell's group announced the first observation of pion decay to a muon — the particle picture was beginning to take shape.
The half-lives of α-emitters span an enormous range — from less than a microsecond to more than 1015 years — although the emitted α-particles vary in energy by less than an order of magnitude. This extreme sensitivity of the escape probability to the particle's energy was explained in 1928 by Gurney and Condon (and, independently, by George Gamow [Gamow, G. Z. Phys. 51, 204–212 (1928)]) by invoking the recently discovered phenomenon of quantum-mechanical barrier penetration, or tunnelling. Until this time, α-decay had been envisaged as a violent process; by contrast, Gurney and Condon suggested that the tunnelling α-particle "slips away almost unnoticed".
The last experiment performed by Michael Faraday was an unsuccessful attempt to observe the influence of a magnetic field on the spectral lines of sodium. More than 30 years later, Pieter Zeeman took up the challenge and observed a broadening of the lines, which was soon recognized to be the splitting that we know as the Zeeman effect. Zeeman's account of the discovery, translated for Nature from the Proceedings of the Physical Society of Berlin, includes an interpretation based on Hendrik Lorentz's idea of "small molecular elements charged with electricity", and a rough calculation of the charge to mass ratio of these "ions".
The modern computer was born on 21 June 1948, when the University of Manchester’s Small-Scale Experimental Machine, nicknamed the 'Baby', successfully executed its first program. Designed and built by F. C. Williams and Tom Kilburn [Obituary of Tom Kilburn: Nature 409, 996 (2001)], the Baby kept only 1,024 bits in its main store, but it was the first computer to store a changeable user program in electronic memory and process it at electronic speed.
A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.
Claims of the conversion of carbon to diamond date back to 1880, but it was not until 1955 that the first reproducible synthesis was reported. Bundy et al. describe the high-pressure, high-temperature apparatus that enabled them to reach the stability field of diamond, and prove that the material obtained was indeed diamond. Ironically, some of the same authors discovered 38 years later that the very first diamond grown by their technique was not synthetic after all, but a fragment of a natural diamond that got into the experiment. Fortunately, however, the technique was sound, and marked the beginning of the present synthetic-diamond industry.
[Translated by Dr. Robert W. Lawson.] THERE is something attractive in presenting the evolution of a sequence of ideas in as brief a form as possible, and yet with a completeness sufficient to preserve throughout the continuity of development. We shall endeavour to do this for the Theory of Relativity, and to show that the whole ascent is composed of small, almost self-evident steps of thought.
The utility of the clock-like pulses emitted by pulsars [see Nature 217, 709-713 (1968)] did not end with the insights they have yielded into the properties of neutron stars, and hence of high-density matter. In 1992, Wolszczan and Frail reported precise pulsar timing measurements which exhibited periodic variations. Unlike similar observations reported in the previous year (cited as ref. 3 in the paper), these variations were not an artefact, but revealed the presence of two or more planet-sized objects orbiting the neutron star — the first such objects to be detected outside the Solar System.
IN a recent paper1 Fröhlich has tried to interpret the λ-phenomenon of liquid helium as an order–disorder transition between n holes and n helium atoms in a body-centred cubic lattice of 2n places. He remarks that a body-centred cubic lattice may be considered as consisting of two shifted diamond lattices, and he assumes that below the λ-point the helium atoms prefer the places of one of the two diamond lattices. The transition is treated on the lines of the Bragg-Williams-Bethe theory as a phase transition of second order in close analogy to the transition observed with Î-brass. Jones and Allen in a recent communication to NATURE2 also referred to this idea. In both these papers, use is made of the fact, established by the present author, that with the absorbed abnormally great molecular volume of liquid helium (caused by the zero motion3) the diamond-configuration has the lowest potential energy among all regular lattice structures4.
The rapid pace of discovery that characterized early experimental work in superfluidity [see Nature 141, 243-244 (1938)] was equalled by theorists. In one of the great conceptual leaps in the history of physics, Fritz London proposed in April 1938 that the λ-transition in liquid helium was analogous to Bose-Einstein condensation, predicted by Einstein to occur in dilute gases. Just one month later, Laszlo Tisza extended London's proposal by invoking a two-fluid model for helium II, which could qualitatively explain the observed transport phenomena, including the fountain effect.
Just a month after the discovery of superfluidity was reported in Nature [see Nature 141, 74 (1938); Nature 141, 75 (1938)], one of the co-discoverers was back with an even more striking example of the bizarre behaviour of superfluid helium. The fountain effect, which Jack Allen discovered accidentally by shining a pocket torch on his experimental apparatus, is now known to be a manifestation of the two-fluid character of liquid helium II. [Obituary of Jack Allen: Nature 411, 436 (2001)]
THE abnormally high heat conductivity of helium II below the λ-point, as first observed by Keesom, suggested to me the possibility of an explanation in terms of convection currents. This explanation would require helium II to have an abnormally low viscosity; at present, the only viscosity measurements on liquid helium have been made in Toronto1, and showed that there is a drop in viscosity below the λ-point by a factor of 3 compared with liquid helium at normal pressure, and by a factor of 8 compared with the value just above the λ-point. In these experiments, however, no check was made to ensure that the motion was laminar, and not turbulent.
Evidence for the existence of an unusual liquid phase of 4He below about 2.2 K — the 'λ-point' — can be traced back to 1911 and the experiments of Kamerlingh Onnes. But it was another two decades before a clear picture started to emerge concerning the 'superfluid' nature of this phase. Key to establishing the concept of superfluidity were the measurements of Kapitza and Allen and Misener in 1938, which showed that the viscosity of 4He dropped to essentially unmeasurable values when cooled below the λ-point. [Obituary of Jack Allen: Nature 411, 436 (2001)]
A HIGH potential laboratory has been developed at the Cavendish Laboratory for the study of the properties of high speed positive ions. The potential from a high voltage transformer is rectified and multiplied four times by a special arrangement of rectifiers and condensers, giving a working steady potential of 800 kilovolts. Currents of the order of a milliampere may be obtained at a potential constant to 1–2 per cent.
1932 saw the announcement of the first apparatus for artificially accelerating atomic particles to high energies: the Cockcroft-Walton accelerator. And, barely a month later, beams of high-energy protons produced by this machine were used to initiate the disintegration of lithium nuclei, and thereby confirm the equivalence of mass and energy.
Before 1985, it was generally accepted that elemental carbon exists in two forms, or allotropes: diamond and graphite. Then, Kroto et al. identified the signature of a new, stable form of carbon that consisted of clusters of 60 atoms. They called this third allotrope of carbon 'buckminsterfullerene', and proposed that it consisted of polyhedral molecules in which the atoms were arrayed at the vertices of a truncated icosahedron. In 1990, the synthesis of large quantities of C60 [see Nature 347, 354–358 (1990)] confirmed this hypothesis.
ON bombarding uranium with neutrons, Fermi and collaborators1 found that at least four radioactive substances were produced, to two of which atomic numbers larger than 92 were ascribed. Further investigations2 demonstrated the existence of at least nine radioactive periods, six of which were assigned to elements beyond uranium, and nuclear isomerism had to be assumed in order to account for their chemical behaviour together with their genetic relations.
IN a series of experiments now in progress, we are directing a narrow beam of electrons normally against a target cut from a single crystal of nickel, and are measuring the intensity of scattering (number of electrons per unit solid angle with speeds near that of the bombarding electrons) in various directions in front of the target. The experimental arrangement is such that the intensity of scattering can be measured in any latitude from the equator (plane of the target) to within 20° of the pole (incident beam) and in any azimuth.
1968 saw the first report of a curious class of astronomical radio sources, distinguished by their rapid and extremely regular pulsations. Hewish et al. associated them with unusually stable oscillations in compact stars. They are now understood to be rapidly rotating, magnetized neutron stars, or pulsars.
In much the same way that relativity fundamentally altered our large-scale view of the Universe, the emergence of quantum mechanics cast a very different light on our understanding of the microscopic world. Here, Louis de Broglie offers some thoughts on the nature of matter, waves and quanta which, by the following year (1924), would lead to his prediction that matter should exhibit wave-like properties.
Motivated by Arthur Compton's observation that X-rays could lose energy when scattered inelastically by electrons (the 'Compton effect'), Raman and Krishnan hypothesized that a similar transfer of energy should take place when normal light is scattered by atoms or molecules. The 'Raman effect' was demonstrated in 1928 and now forms the basis of a powerful spectroscopic tool.
In 1973, Paul Lauterbur described an imaging technique that removed the usual resolution limits due to the wavelength of the imaging field. He used two fields: one interacting with the object under investigation, the other restricting this interaction to a small region. Rotation of the fields relative to the object produces a series of one-dimensional projections of the interacting regions, from which two- or three-dimensional images of their spatial distribution can be reconstructed. Application of this technique as magnetic resonance imaging is now widespread.
The rise of modern particle physics owes much to the early work on cosmic rays. Such studies revealed the existence of the positron (1932), muons (1937), and the pion (1947) — the particle postulated by Yukawa as the mediator of a short-range nuclear force. But further surprises were still in store. Close on the heels of the pion discovery, Rochester and Butler observed the occasional presence of curious forked tracks in a series of cosmic-ray experiments that indicated the existence of a new type of unstable elementary particle: K mesons, the first ‘strange’ particles.
After demonstration in 1954 of the 'maser' principle (microwave amplification by stimulated emission of radiation), systems were sought in which the effect occurred in the infrared and visible spectrum. This goal was reached in 1960 when Theodore Maiman achieved optical laser action in ruby.
IT has been shown by Bothe and others that beryllium when bombarded by α-particles of polonium emits a radiation of great penetrating power, which has an absorption coefficient in lead of about 0.3 (cm.)−-1. Recently Mme. Curie-Joliot and M. Joliot found, when measuring the ionisation produced by this beryllium radiation in a vessel with a thin window, that the ionisation increased when matter containing hydrogen was placed in front of the window. The effect appeared to be due to the ejection of protons with velocities up to a maximum of nearly 3 × 109 cm. per sec. They suggested that the transference of energy to the proton was by a process similar to the Compton effect, and estimated that the beryllium radiation had a quantum energy of 50 × 106 electron volts.
The discovery in 1986 of the first copper oxide superconductor stimulated an explosion of research activity that continues to the present day. The early years of high-temperature superconductivity were characterized by the rapid discovery of many new materials with increasingly high transition temperatures. The record now stands at ~133 K, attributed to a mercury-containing compound reported by Schilling et al. in 1993, although the dream of achieving room-temperature superconductivity has yet to be fulfilled.
(1) A DISCHARGE from a large induction coil is passed through a Hittorf's vacuum tube, or through a well-exhausted Crookes' or Lenard's tube. The tube is surrounded by a fairly close-fitting shield of black paper; it is then possible to see, in a completely darkened room, that paper covered on one side with barium platino-cyanide lights up with brilliant fluorescence when brought into the neighbourhood of the tube, whether the painted side or the other be turned towards the tube. The fluorescence is still visible at two metres distance. It is easy to show that the origin of the fluorescence lies within the vacuum tube.