The invitation, made to me, to write the introduction to this volume of the Proceedings of the Royal Society of Edinburgh, which is dedicated to Norman Feather, suggested that I should place on record some of my reminiscences which might convey a picture of his character and personality. I feel, however, that first I should make some reference, albeit brief, to the distinction of his contributions to science over the 45 years which have elapsed since he first started to research in the Cavendish Laboratory at Cambridge.

The location of the trajectory of a charged nuclear particle can be determined by a number of devices whose operation depends on characteristics of gas counters operated in the region of proportional energy response. Such devices have advantages in precision, speed or available size over other types of position-sensitive counters. The events may be located by observing pulses on one of a set of closely spaced anode wires in a common gas volume, by measuring the drift time of primary electrons to a particular anode wire, or by determining the location of an electron avalanche along the length of a single anode. The operation of the different types of systems and the factors affecting their precision are described. Precision to less than 1 mm can be obtained in a number of ways,

‘Systematics of Stable Nuclei’ is the title of the first of the four chapters in Norman Feather's book Nuclear Stability Rules (Feather 1952). In the sense used by Feather, ‘systematics’ is the search for experimental evidence of regularities in some system—specifically the Periodic System of the Elements. It is a systematic collection of facts in a way which may inspire further research, eventually leading to an all-embracing theory. At all times, and even when such a theory appears to be established, systematics can be justified for its educational value: few of those students who have enjoyed Feather's nuclear lectures would question this.

A search was made for branching to the 1–84 MeV state of 42Ca in the 42Sc ground state decay. This was found to be less than 0·02 per cent. The branching has a negligible effect on the calculation of the vector coupling constant Gv for the weak interaction from the 42Sc decay.

The adiabatic invariants associated with the motion of charged particles, trapped in electromagnetic fields with rotational and reflection symmetry, have been studied using classical methods based on the Hamilton-Jacobi equation. It has been shown that results, valid for trapping in purely magnetic configurations, may be applied in the analysis of electromagnetic charged particle traps, provided that suitably modified expressions are used for the angular frequencies in the various dynamical modes. Attention is drawn to circumstances in which the adiabatic conditions may be violated because of cancellation of electric and magnetic terms in the equations.

It is shown that the mobility of electrons in silicon or germanium can be estimated in a relatively simple manner. The scattering scross-section of a ’beam’ of electrons in the conduction band is evaluated in the same way as for a beam of X-rays or of slow neutrons which is scattered by phonons. It therefore involves the atomic scattering factor for electrons rather than the deformation potential introduced by Bardeen and Shockley. Predicted mobilities are in satisfactory agreement with observation.

The shape factors of the partial β-spectra of highest end-point energy in the decay of 72Ga and 140La have been calculated and compared with the only previously reported determination of these quantities. For both isotopes the shape factor is consonant with the view that the Blj matrix element controls the decay. Shape factor analysis alone is insufficient to determine the cause of the predominance of a particular matrix element.

The temperature dependence of the properties of magnetic crystals containing defects is calculated with a simple linear chain model. The model enables the spin deviations caused by the impurity to be treated throughout the whole crystal instead of being restricted to the neighbourhood of the defect as in other recent theories. The results are in qualitative agreement with experimental results and suggest that stable spin clusters may be found surrounding each defect above Tc. The approximations used in other theories are shown to be suspect above 0·5 Tc.

The elastic properties of plant cell walls are major factors controlling the swelling and shrinking of plant cells under conditions of varying water stress. The importance of these properties for the adaptation of plants to the changing water stresses they encounter is discussed.

It is a great pleasure to join in this tribute to Professor Norman Feather: My recollections of him as teacher, friend and colleague extend back nearly forty years. I recall attending, as a Cambridge undergraduate, his lectures on ‘Properties of Matter’ (what an archaic and nostalgic flavour that title has now!); and hearing him describe his pioneering experiments on the properties of the neutron. He was my doctoral thesis examiner; and later when he was Editor of the Cambridge monographs, it was at his suggestion, and with his help and encouragement, that I made my first essay as an author. I was privileged to succeed my former teachers, Professor C. D. Ellis and Professor Feather, at Trinity College; and in the 1950s I was regularly and warmly welcomed at Edinburgh, the ambivalent benevolence of my role as ‘External Examiner’ notwithstanding.

The space group for paraelectric KH2PO4 is described and tables of irreducible representations are presented. These are used to derive the symmetry of the vibrational modes for both the heavy atoms and the hydrogen atoms, the latter being treated by a simple pseudo-spin model. Recent experiments on KH2PO4 and related materials are analysed in terms of the mode symmetries, and the light these experiments throw upon the nature of the phase transitions is briefly discussed.

One of the traditional activities of the National Physical Laboratory is its work on the maintenance and improvement of the primary standards of measurement. Although one may possibly visualise such work, because of its long history and its association with calibration services, as of a largely routine character, this is certainly far from the case at the present time. The present is a period of considerable activity and change in fundamental metrology, with the classical material standards of measurement being superseded by atomic or quantum standards. The past decade has seen a change to atomic standards for the units of length and time, and there seems little doubt that the future will see an extension of atomic-based standards to other areas, notably that of the electrical quantities. Some of the changes which may come about as a consequence of adopting the most accurate and convenient quantum methods have interesting implications. For example, a possible outcome of the new techniques being developed for the accurate measurement of very high (infrared) frequencies is that the standards of length and time may become unified, with the velocity of light taking the role of an agreed defined constant rather than an experimentally determinable quantity.

A search is reported for the relativistic e/3 quark among the cores of Extensive Air Showers initiated by primaries with energies greater than 1014 eV. The detector is a high-pressure cloud chamber filled with helium at 28 atmospheres, and is counter controlled. The experimental conditions avoid the criticisms levelled at the McCusker experiment and are such that the tracks of e/3 quarks cannot be simulated by singly charged shower particles either through statistical variations in primary ionisation or otherwise. The primary ionisation density, measured using a gap-counting technique on post-expansion electron and muon tracks, is compared with predictions from the theory of Budini et al. (1960). The agreement achieved shows that the theory is a reliable foundation for methods of identifying quark candidates, and measuring charges. The experiment has been running for 5000 hours. No quark candidates have been found. With an acceptance angle of 0·3 sr and an area of 140 cm2, this sets the upper limit of flux of e/3 quarks at 4 × 10−9 cm−2 sec−1 sr−1 with 95 per cent, confidence. The experiment is being continued.

Levels in the ground state bands of 158Dy, 160Dy and 162Dy have been populated by (α, 2n) reactions on metallic targets of separated 156Gd, 158Gd and 160Gd isotopes. Two Ge(Li) detectors were used to study singles gamma-ray spectra, gamma-ray angular distributions, gamma-gamma coincidence spectra and relative yields of gamma-rays for bombarding energies from 20 to 27 MeV. Transitions from all levels in the ground state bands up to the 12+ member were identified and the following level energies in keV established: 158Dy: 0 (0+), 99·0 (2+), 317·4 (4+), 637·9 (6+), 1044·1 (8+), 1520·1 (10+) and 2049·4 (12+); 160Dy: 0 (0+), 86·7 (2+), 283·7 (4+), 581·4 (6+), 967·4 (8+), 1429·0 (10+), 1951·7 (12+); 162Dy: 0 (0+), 80·7 (2+), 265·7 (4+), 548·5 (6+), 921·1 (8+), 1374·8 (10+) and 1901·0 (12+). There is weak evidence for the 14+ levels in 158Dy and 160Dy. The level energies are compared with calculated values using the variable moment of inertia model.

A prototype source of polarised electrons is described, in which electrons trapped by a combination of electric and magnetic fields are polarised through spin exchange interaction with a polarised beam of potassium atoms. Under typical operating conditions, a pulsed electron beam was extracted with 104 electrons per pulse and a polarisation of 0·45 at a repetition rate of 50 S−1. The scope for improvement of these figures is briefly discussed.

Values for the total spin exchange collision cross-section at electron energies of 1 eV, 2·5 eV and 4 eV were obtained. These are in reasonable agreement with theoretical predictions.

The state of knowledge of fast neutron polarisation due to elastic scattering is reviewed in relation to the optical model of the process. There is clearly a substantial lack of polarisation data at neutron energies and concerning nuclei appropriate to the optical model description. The situation for the extremes of small and of large angle scattering is also considered.

Segrè in his recent book [1] on Fermi gives an interesting account of the discovery of slow neutrons at the Institute of Physics of the University of Rome on October 22, 1934. He quotes (p. 80) a statement Fermi made many years later in a conversation with S. Chandrasekhar on the process of discovery in physics:

‘I will tell you how I came to make the discovery which I suppose is the most important one I have made. We were working very hard on the neutron-induced radioactivity and the results we were obtaining made no sense. One day, as I came to the laboratory, it occurred to me that I should examine the effect of placing a piece of lead before the incident neutrons. Instead of my usual custom, I took great pains to have the piece of lead precisely machined.

The problem of the simultaneous transport of solute and water through a cell membrane is examined from a kinetic standpoint. It is shown that the results obtained by this approach are in accord with those obtained conventionally by irreversible thermodynamics. Stress is laid on the fact that the kinetic theory has certain advantages over the conventional approach in that it provides, among other things, a form of membrane model and at the same time its range of validity is indicated.

The author maintains that a course in the classical theory of the electromagnetic field, with full exploitation of vector calculus methods, should be thought of as being as much of a basic essential in any physics honours course as is a course on classical mechanics. It is suggested that if the mathematical techniques are taught in a way that relates them directly to the central notions of field theory and avoids discussion of special techniques, the mathematical burden is sufficiently light to be borne by all physics students, not only those theoretically inclined. The course need not be of excessive length if it is understood as exclusively an introduction to field concepts and hence not to cover in any detail the electric and magnetic property of materials. A number of particular ideas arising from the author's teaching experience are discussed.

For comfort the total future world population faces a limit. Three or more educated generations seem likely before the population growth will be checked. It seems prudent to envisage a world population of about 15 thousand million in a century or two. Their energy needs for food, water, warmth, clean air, locomotion and management of wastes may be assessed at 5 to 50 thermal kilowatts per capita. That amounts to 0·05 per cent, to 0·5 per cent, of the energy supply from the sun. Generating this amount by nuclear fission would cause no severe pressure on world resources of uranium and thorium for hundreds of centuries, if near-breeders such as CANDU reactors are used exploiting the uranium-thorium fuel cycle. Neither the cost of fuel supply nor of waste management to keep the environment unburdened by extra radioactivity need be as high as prices now paid for coal and oil. The addition of breeders or other means such as nuclear fusion or spallation for increasing the neutron supply would significantly lower the use of uranium and thorium but would not necessarily reduce the cost of power.