Table of contents

Measurements are made of the stress in deposits of Ni, Fe, Pd, Au, Cu, Ag, Sb, Al, Bi, Mg and Zn condensed from the vapour in high vacuum on copper strips used as substrates. The stress is found to be characteristically of a tensile nature and the amount of stress is different for different metals.

The occurrence, nature and order of magnitude of the stress are explained as arising from the contraction of the upper regions of the growing deposit as they cool after their deposition, which takes place at a temperature generally several hundred degrees higher than the initial substrate temperature. According to this interpretation, this contraction will begin to set up a tensile stress in any stratum of the deposit as soon as the temperature of the region concerned falls below the recrystallization temperature of the deposit metal. An estimation of the stress to be expected from this cause falls in the region of the experimentally determined values.

In Al a compressive stress is observed if the metal is evaporated in an imperfect vacuum, the air pressure being about 10^-4 mm Hg or higher. Evidently appreciable oxidation of the aluminium occurs and the compressive stress is associated with the formation of the oxide between the metal crystals or included to some extent within the crystals. Results for electrodeposits are analogous.

Li's method for determining the line shape in a variable-radius spectrometer is discussed, and a rapid approximate method is given. Methods of normalization for the continuous β-particle spectrum and for conversion electron lines are presented. The advantages and disadvantages of this type of spectrometer are discussed.

Details are given of the design, construction and performance of a water-cooled solenoid which develops 50000 Oe over a volume some 3 in. diameter × 2 in. long, for a continuous input of 1000 kw. The solenoid contains no iron or other ferromagnetic material, and has a disposition of windings to produce the special field distribution required for two-stage adiabetic demagnetization.

In this paper a discussion is presented of the determination of the mass of wear fragments using autoradiographic techniques. The size distribution of copper wear fragments transferred during sliding on mild steel is measured experimentally, and using these data the size distribution of the metallic junctions is calculated. An estimate is presented of the effect on the junctions of an increase of load, and it is shown that the size of the largest junctions, and hence the mass of the largest wear particles, varies much less than does the applied load. In experiments of mild steel sliding on copper carried out to confirm these calculations, the mass of the largest fragments was found to vary approximately as the 0.3 power of the load.

In the course of an attempt to find reversible relations between the parameters describing the trajectory of an electron in a short magnetic lens spectrometer, it was found that the magnetic lens can be surprisingly well represented by a thick converging type optical lens which satisfies Newton's laws for the conjugate planes and the tangent relation far outside the paraxial range where the lens power calculated by the paraxial method can be in error by as much as 50%. Expressions have been obtained for the focal length as a function of the object angle and momentum of the electron. Various other properties of the lens spectrometer have been investigated. In particular, the use of a continuous baffle system to improve the resolution and line-shape for an extended source has been studied by an easy and accurate method.

An electron diffraction camera operating at voltages up to 150 kV is described. The advantages of the use of high accelerating potentials are illustrated by results obtained with this camera.

The relaxation of birefringence produced in two organic glasses after they have been sheared in a modified coaxial cylinder viscometer has been followed at different temperatures by the use of a photocell. For the low rates of loading used it has been found that the relaxation of both the glasses can be represented by a single exponential function, which shows that there is one predominant relaxation mechanism. The relaxation times were measured at different temperatures and cover a range from about 20 seconds to ½ millisecond. The viscosity has also been measured over the same temperature range and, from the values of the viscosity and relaxation time at a given temperature, the rigidity modulus of elasticity has been determined. Of the two materials used, one, glycerol sextol phthalate, was more chemically associated than the other, 2́-hydroxy-2: 4: 4: 6: 5́-pentamethylflavan. This difference was reflected in the temperature variation of the quantities measured.

The coefficients of transmission and reflection of thin aluminium films deposited on silica by vacuum evaporation were measured for wavelengths between 4200 and 2600Å. The results were applied to the calculation of the width and intensity of Fabry - Perot fringes obtainable with aluminium coated plates. Measurements of widths of heterochromatic fringes gave upper limits of the reflectivity at wavelengths of 2400Å and below, and showed that 1/18 of one order can be resolved in this range without excessive loss of intensity if the thickness of the films is properly chosen.

The theory of infra-red reflection spectra has been applied (i) to obtain the frequencies and extinction coefficients of the intense absorption bands in polytetrafluorethylene near 8.5 microns, (ii) to determine the number and states of polarization of the fundamental NH stretching absorption bands in a crystal of urea. The reflection method has definite advantages over transmission measurements in both cases.

Practical arrangements for determining the coherence of a wave front are discussed. The intensity distribution in the diffraction pattern of two parallel interferometer slits illuminated by a slit source of variable width is calculated together with the dependence of the fringe visibility on the choice of interferometer slit widths.

Finally an experiment demonstrating the effect of source size on coherence is described and the results are compared with those to be expected from the above analysis.