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ZUSNE, L. Visual Perception of Form. Academic Press: New York. 1970. Pp. 547.BROADBENT, D. E. In Defence of Emperical Psychology. Methuen and Co.: London. Pp. 222. £ 2.90.GOMBRICH, E. H., GOMBRICH, J. AND BLACK, M. Art, Perception, and Reality. Johns Hopkins University Press: Baltimore. Pp. 13HECAEN, H. Neuropsychologic de la Perception Visuelle. Masson and Cie: Paris. 1972. Pp. 320. F.110.

The unexpected dipole moment of dihexamethylbenzenecobalt is examined in the light of the 'pseudo-Jahn-Teller effect', which is found to offer a qualitative explanation.

Radicals derived from five fluoronitrobenzenes have been prepared and their E.S.R. spectra measured. The hyperfine splittings are discussed and evidence is presented for steric hindrance of a nitro group when it has two orthofluorine neighbours.

The electron resonance spectrum of the mono-anion of tricyano-symtriazine, at 25°c and below, reveals the presence, not of two sets of three equivalent nitrogen atoms, but a set of two and another set of four. It is suggested that the radical-ion undergoes a permanent Jahn-Teller distortion to one of three equivalent distorted forms.

A model is proposed for liquid and solid argon, in which the repulsive forces are represented by rigid cores and the attractive forces by a uniform background potential which depends on density but not on temperature. Thermodynamic consistency implies the equation of state:[image omitted]where p0 is the pressure exerted by rigid spheres at the same number density n and temperature T, and a is independent of n and T. When p0 is taken from the calculations of Alder and Wainwright it becomes possible to make an absolute calculation of the values of several dimensionless thermodynamic quantities characteristic of the triple point. All of these except certain second derivatives of the free energy agree very well with experiment, suggesting that the structure of liquids and solids near the triple point is mainly determined by the repulsive forces, the attractive forces serving merely to keep the molecules together.

Electron spin resonance measurements are reported for the anions of tetraphenylene and 1,2 : 5,6-dibenzcyclooctatetraene. The proton hyperfine coupling constants obtained are in good agreement with those calculated theoretically by regarding the orbital of the unpaired electron as a linear combination of the molecular orbitals of the component parts of the molecule.

The concept of molecular symmetry is extended to molecules such as ethane and hydrazine which can pass from one conformation to another. The symmetry group of such a molecule is the set of (i) all feasible permutations of the positions and spins of identical nuclei and (ii) all feasible permutation-inversions, which simultaneously invert the coordinates of all particles in the centre of mass. According to the representations of this group one can classify not only the spin states and states of motions of the nuclei, but even the electronic states of the molecule. Examples are given to illustrate the use of this concept in determining the statistical weights of individual levels and selection rules for electric dipole transitions between them.

This paper studies the longer-period response of a β-plane ocean (stratified, unbounded and of uniform depth) to initial distributions of wind-stress applied at the surface. The horizontal divergence of the motion is taken into account.

The number of specular points reflected in a random Gaussian surface is determined theoretically under the following alternative conditions: (1) when the surface is perfectly long crested (two-dimensional); (2) when the surface is three-dimensional but isotropic; (3) for quite general surfaces, provided that the observer and the source of radiation are both at a great distance from the surface.The results can be applied to the similar problem when the surface forms the boundary of two refracting media.

When light is reflected or refracted at a moving Gaussian surface, the observer sees a number of moving images of the source, which appear or disappear generally in pairs; such an event is called a “twinkle.” In the present paper the number of twinkles per unit time is evaluated in terms of the frequency spectrum of the surface and the distance of the source O and observer Q, on the assumption that the surface is Gaussian and that OQ is perpendicular to the mean surface level.A solution is found first for a single system of long-crested (or two-dimensional) waves, and then extended to the case of two such systems intersecting at right angles.The rate of twinkling is found to depend, apart from a scale factor, on two parameters of the surface, one of which, α, increases steadily with the distance of O or Q from the surface; the other, d, discriminates between waves of standing type and waves of progressive type. Over a considerable range of α, the rate of twinkling is almost independent of d, but for large values of α the rate is much greater for standing waves than for progressive waves; waves of intermediate type are included in the analysis.

Light falling from a point source on a ruffled surface produces a pattern of images, which move about over the surface. The image points correspond to the maxima, minima, and saddle points of a certain function. It is shown that the images are generally created in pairs, a maximum with a saddle point or a minimum with a saddle point, and that the total numbers of maxima, minima, and saddle points satisfy the relation N_ma+N_mi=N_sa+1.The process of creation or annihilation of images is studied in detail, and also the tracks of the image points, in certain special cases. It is shown that closed tracks may be common. This is confirmed by photography of the sea surface.

In planetary waves on a β-plane, the energy flux vector up(calculated from the velocity uand pressure p) is generally different in both magnitude and direction from the flux vector Ecg(calculated from the energy density Eand group velocity cg). This apparent discrepancy is shown to be due to a certain arbitrariness in the definition of energy flux. The two vectors just defined are found to differ by a non-divergent vector (ϖA/ϖy, − ϖA/ϖx) where A = 14p f aa∗and ϱ, f, adenote the density, coriolis parameter and local wave amplitude respectively.

The electric quadrupole moment of a dipolar molecule depends upon the molecular origin from which it is measured. An electro-optical method has been successfully used for measuring the quadrupole moments of non-dipolar molecules, and the question arises: when the same method is applied to a dipolar substance what is the molecular origin to which the measured quadrupole moment should be referred? It is shown that this origin is not the centre of mass, but another point which may be called the 'effective quadrupole centre', the position of which depends in general on the wavelength of the light. Dipolar molecules experience a force in the field gradient and this enhances the contribution to the refractive index anisotropy from molecules which are out of line with the detector but in the light beam. This contribution is proportional to the dipole moment and is origin-dependent; it vanishes if the effective quadrupole centre is chosen as the origin. It is concluded that the electro-optical experiment should give identical quadrupoles for isotopically distinct species, and that the results for dipolar molecules may show an apparent dependence on the frequency of the light. The effects of distortion of the molecule by the field gradient are also considered.

It is shown that Kubo's statistical formula for the general transport coefficient of a classical system may be simply obtained by considering the result of a retarded measurement on a canonical non-equilibrium ensemble.It is further shown that if in a continuous system the entropy production takes the form [image omitted]then the coefficients lμv occurring in the linear equations [image omitted]are given by the general formula [image omitted]where the integrand is an average over the canonical ensemble and τ is a virtually infinite time. The usual transport equations will, however, break down if the correlation distances between the local fluxes are of macroscopic dimensions.

In the electron resonance spectra of free radicals in solution the individual hyperfine lines often differ in width. McConnell's theory of this phenomenon is generalized to free radicals in which the axes of the nuclear hyperfine tensors do not coincide with the axes of the g tensor. The result (3.4) is potentially useful for determining the sign of the spin density at a particular sort of nucleus.

The electronic structure of the paramagnetic molecule (C5H5)3Ni3(CO)2 is investigated, and the odd electron is assigned to an A2'' combination of nickel d orbitals. The g values of the molecule are calculated on this hypothesis and are found to be consistent with the experimental values.

An attempt is made to account for the apparent bond alternation in the rings of dibenzene chromium in terms of a 'pseudo Jahn-Teller effect'. The attempt fails.

The observations of Dressler and Ramsay on the vibronic absorption spectrum of the NH2 radical are interpreted quantitatively in terms of the Renner effect. The use of a perturbation method leads to frequency predictions which are in good accord with experiment and confirm the view of these authors that the absorption band is associated with transitions between the components of an electronic II state which are widely separated by electronic-vibrational interaction.

A simplified kinetic theory is described for spherical molecules interacting according to a square well potential. The statistical premises of this theory correspond closely to those of Longuet-Higgins' and Pople's theory of dense fluids of rigid spheres. The thermal conductivity λ, shear viscosity η and bulk viscosity κ are predicted to be in the ratio [image omitted] where k is Boltzmann's constant and m the mass of a molecule. To calculate any of these coefficients absolutely requires independent information about the equilibrium pair distribution. This may be obtained from the self-diffusion constant D, whose value is also given by the theory. For argon the measured value of D leads to a theoretical value for η which is in good agreement with experiment; for this liquid however the observed ratio κ:η is very much smaller than predicted.

It is shown that a one-dimensional multicomponent mixture with nearest neighbour interactions uij(r) obeys the implicit equation of state [image omitted] where λi is the absolute activity of species i (divided by a kinetic factor) and [image omitted] The concentration of species i is thence determined as [image omitted] A one-dimensional solution is ideal if, and only if, the matrix [ηij] is of rank unity. The excess free energy of a nearly ideal solution is found to be [image omitted] where Gij(T, P) is the (configurational) molar Gibbs free energy of a 'hybrid' species with interaction potential uij(r).

Replacement of one hydrogen atom by deuterium in the negative ion of cyclo-octatetraene, makes no significant difference to the electron spin densities at the hydrogen nuclei. This result contrasts with a recent observation that mono-deuteration produces a measurable change in the spin distribution in the benzene negative ion. The difference between the two systems is interpreted in terms of the Jahn-Teller effect.

This paper describes a semi-emprical quantitative theory of the low-lying electronic states of the radicals CH, CH2, CH3, NH, NH2, BH, BH2 and BH3. The method combines certain features of the valence-bond theory and Moffitt's method of Atoms in Molecules, and bond bending is taken into account. The results are in excellent general agreement with experiment: the ground state of CH2 is a linear 3Σg- state, whose potential energy curve crosses that of the lowest singlet state which is bent. The CH3 radical is predicted to resist out-of-plane deformation quite strongly, and the BH2 radical is predicted to be linear in its ground state.

WHILE flying low over the ocean between Adelaide and Kangaroo Island (36° S, 137° E) one of us (J. S. T.) observed the following interesting phenomenon.