Table of contents

Rotational and vibrational analyses of the emission Schumann-Runge O₂ bands in the region 3100 Å to 2500 Å are presented. Tables of wavenumbers are given for the (1, 12), (0, 11), (1, 11), (0, 10), (1, 10), (1, 9), (2, 9), (1, 8), (2, 8), (2, 7) bands. The origins of the bands, the rotational differences, and constants for the levels ν'' = 7 to 11 are given. Three bands, found in a high voltage arc in oxygen between platinum electrodes, are attributed to PtO.

The spectrum of an electrodeless discharge in pure oxygen has been studied. New bands of the O₂⁺ Second Negative system have been found and the intensity distribution in this system is discussed; subsidiary parabolae as well as the main Franck-Condon parabola are obtained as is predicted by the theory. Emission bands reported by Johnson as due to O₃ are due to O₂⁺ and O II. Some abnormal intensities of O II lines excited in the electrodeless discharge are noted. The electrostatic and electromagnetic types of excitation are briefly compared.

The spectra emitted by the high voltage arc in nitrogen, hydrogen, hydrogen-nitrogen mixtures and ammonia have been studied.

The appearance of the N₂ Second Positive bands at various nitrogen gas pressures is discussed and the divergence of rotational and vibrational temperatures is noted. Traces of oxygen greatly reduce the strength of the N₊ bands emitted by the arc in nitrogen. In N₂-H₂ mixtures the NH 3360 Å band is found to be emitted strongly only when hydrogen is present at a very low partial pressure. An attempt is made to explain the various observations.

The (1, 0) band of the N₂ First Positive system has been photographed at a dispersion of about 1.2 cm^-1/mm. The wave numbers and quantum numbers of the lines, and the rotational term differences in the upper and lower states are given. The spin tripling in the ³Σ state and the Λ doubling in the ³Π state are evaluated.

Experiments are described in which a direct comparison is made by an absorption method of the β-particle spectra of actinium C", radium E and 3.5 yr. thallium representing allowed, second forbidden and third forbidden transitions respectively.

New values of 623 ± 4 mg/cm² and 300 ± 3 mg/cm² are proposed for the absorption limits in aluminium of the β particles emitted by actinium C" and thallium and it is shown that, of the three elements, radium E emits most and actinium C" least low energy electrons.

An attempt has been made to derive energy distributions from the absorption curves, but the results for radium E depart markedly from those obtained with magnetic spectrographs. The general findings, however, agree with those of other workers who have attempted the same procedure.

The formula used in the derivation of the energy distribution includes an approximation which necessarily leads to an apparent deficiency of low energy particles, but the accuracy of the data is not sufficient to permit the use of a better approximation. Strictly for purposes of comparison, however, the method has obvious applications.

This note is concerned with the calculation of the energy of the ground state and the lowest excited state for hydrocarbons of the condensed ring type. The difference between these two energies is the energy of the first electronic transition. The normal valence bond method is used, taking only the Kekulé structures into consideration. The results are compared with the experimental absorption wavelengths, and are in good agreement, giving a value of the exchange integral α between - 1.8 and - 2 electron volts.

A comparison has been made between the values expressed in wave numbers of the longest ultra-violet absorption bands of a series of polycyclic aromatic hydrocarbons and the minimum number of quinonoid rings contained in their molecules. It is found that the hydrocarbons fall into series of groups related to this number of quinonoid rings.

The distribution of high energy charged particles scattered by a thin foil has been investigated and compared with the formula for single scattering. It is shown that at sufficiently large angles the distribution approaches that for single scattering and can be expressed in the form of a rapidly convergent series of which the first term is identical with the single scattering formula. The remaining terms of the series form an accurate expression for the deviation from true single scattering. The simplified case of projected scattering has also been considered.

A study has been made of cloud chamber photographs of penetrating cosmic-ray showers, originating in lead placed over the cloud chamber and in a lead plate within the cloud chamber, obtained at altitude 3,572 m. in a magnetic field of about 1,000 gauss.

The use of well-separated successive lead layers allowed the association of penetrating events to be demonstrated, and there is some evidence of a general reduction of energy involved in events in the lower lead layers as compared with those in the top layer. Mesons, protons and particles of higher charge were identified in the penetrating showers, and a mean range for non-coulomb scattering of shower particles is given. Evidence is also given of the apparent starting and stopping of charged particles in the lead plate at the centre of the cloud chamber.

Models, largely based on the assumptions introduced by Peierls and Nabarro in dealing with a single dislocation, are used in calculations on three types of intercrystalline boundaries, namely, (I) a boundary due to a difference of atomic spacing, (II) a twist boundary, and (III) a symmetrical tilt boundary. With these models the resolution of the boundary into a sequence of dislocations is a natural consequence of the analysis, which also yields the expressions for the stresses, atomic displacements and energies associated with the boundary, as functions of the angle of tilt, etc. By allowing the distance between dislocations to tend to infinity, these expressions reduce to the corresponding ones for single dislocations. The outstanding feature of the interfacial energy is that it increascs initially very rapidly with the angle of tilt, etc. An application of the results to the theory of oriented overgrowths, developed by Frank and the present author, is described. The validity of the assumptions and approximations involved and the advantages of the treatment as compared with those of other writers are discussed.

The first part of this paper contains a discussion of the conditions determining whether sound waves in helium II are propagated isothermally or adiabatically. In the remainder of this part an expression is found for the energy flux from a closed region, and the impedance concept is applied to waves of second sound.

The second part of the paper is devoted to the study of the effects of irreversible processes on the propagation of waves of first and second sound. The irreversible processes discussed are those due to viscosity and thermal conduction, both in an extended fluid and in a narrow tube.

The angular distribution of radiation from a synchrotron has been measured with an ionization chamber for a number of different target materials and thicknesses, and the results have been compared with a simple theory in which the radiation from a parallel beam of electrons striking a thin plate has been calculated. Detailed comparison with theory is not possible, because the precise way in which the electrons hit the target cannot be determined, nevertheless qualitative explanations have been found for most of the effects observed. The most important of these is the relative insensitivity of forward intensity and beam width to target size and material.