Table of contents

A brief review of the main steps which led to our present knowledge of atomic nuclei; some remarks on how fission might have been discovered, and how it actually was; various facts which decided the feasibility both of controlled and explosive chain reactions; and some personal reminiscences from the days when fission was a new toy, exciting and sometimes dangerous.

The composition and structure of gelatin are related to the method of manufacture, and to the physical properties of gelatin solutions and gels. The importance of the isoionic point, molecular weight distribution and a gel-forming factor are discussed in connexion with the experimental results.

An account is given of an experimental investigation into the heat transfer by free convection in a heated vertical tube closed at its lower end. To cover a wide range of physical properties of the convective fluid, glycerine, water and air were used. The trends are shown to be in generally close agreement with theoretical prediction.

A method for the production of carbon replicas by evaporation on to the specimen is described. The specimen is subsequently removed by solution. The method has been applied to the examination of photographic grains, which could not be resolved in the optical microscope or observed directly in the electron microscope. A resolution better than 100 Å is obtained.

The excellent magnetic properties of cold-reduced silicon-iron strip are achieved by a close control of the mechanical and heat treatments, the object of which is to attain a high degree of preferred orientation in which the plane of the sheet is a {110} crystallographic plane and the direction of rolling is a <100> or cube edge direction. The torque curve is used extensively to check if the ideal orientation is achieved.

In this paper a rapid method of deducing the orientation from torque curves is proposed, applicable to the particular case of cold-reduced silicon-iron sheet. Used in conjunction with X-ray data, the method assists the more accurate assessment of the deviation from the ideal orientation: used alone it enables the departure to be measured in terms of the "root mean square angle of spread," and gives some information of the component angles of spread in different directions. The results show that the torque curve can be used with confidence as a means of control during production, and useful information of the orientation can be obtained from the curve without the need for elaborate analysis.

The investigation shows that the "time edge" effect in the phenol-formaldehyde type of resin is accelerated by exposure to oxygen and moisture and retarded by storage at low temperatures. It is also noted that the time edge effect apparently proceeds in two stages.

In the course of determinations of the surface resistivity of hard-glass and silica rods from observations of the discharge of a Wulf electrometer, it was found that the voltage decay was initially non-exponential. This is attributed to the effect of capacitance between rod and case, distributed along the length of the rod. The effect is treated mathematically and it is shown that, even if the resistance is determined from the exponential portion of the curve, a correction is required. A formula for the correction is given and an approximate method of applying it referred to. An indication is given of the circumstances, probably not uncommon, in which values of resistance determined by the leakage method, might require appreciable correction.

This paper describes first the general features of the interaction between slow electrons and solids upon which they impinge. The threshold electron energies for the absorption of electrons, for the appearance of secondary emission and for decomposing the bombarded solid have been measured for a number of compounds. The values are quoted and are related to the optical absorption bands of the compounds. The effects on valve characteristics and on cathode emission are described briefly, when such compounds are present on the valve electrode surfaces.