Table of contents

For supersmooth optical surfaces, the equation relating diffusely scattered light to roughness and slope parameters assumes a simple form. Measurements of rms roughness and slope for such surfaces can be made with an instrument which accepts a solid angle much smaller than 2π steradian. Measurements made on fused silica surfaces yield values as low as 0·23 nm and 3·8 × 10⁻⁴ rad.

A simple and inexpensive helium gas cryostat is described, making use of a standard storage Dewar from which helium is boiled electrically. By varying the power supplied to the boiler and to a gas stream heater, any temperature between 4·7 and 300 K may be easily and quickly stabilized to within ¼%.

The cryostat is very economical of liquid and gaseous helium, and has many advantages over the more complex conventional cryostats using static exchange gas.

The addition of a magnetic lens to the electron gun of a micro-spot double-crossover cathode-ray tube gives a major increase in performance by raising the light output and eliminating the effects of unwanted secondary-electron emission. The resulting improvement in signal-to-noise ratio, when using the tube in a flying-spot scanner, is expressed by means of a figure-of-merit which includes light output and spot size measurements. Practical results are given for three types of cathode-ray tube.

Following earlier work, a high temperature differential thermal calorimeter was constructed, with a design based on heat transfer considerations. Heat content and heat capacity measurements by the instrument showed excellent agreement with accepted literature values (±2%) in the case of quartz and alumina. Reasonable agreement was also obtained for the α->β quartz inversion enthalpy.

A theoretical and practical evaluation of a new method of calibration data presentation for five-hole spherical and hemispherical pitometers has shown that it is reliable and an advance over the traditional method in that it has: (i) simplified calibration curves; (ii) reduced the probability of misinterpretation of the data; (iii) become suitable for automatic computation.

Comparisons between the theoretical and practical calibration curves for several pitometer designs and hole configurations have shown that a hemispherical probe is superior to a spherical probe not only because of its simplified construction, but because improved flow conditions around the probe lead to superior calibration characteristics.

A unit to X-radiograph coal bore cores as a routine laboratory procedure is described. 50 mm (2 in) diameter bore core is radiographed at the high speed of 150 mm (6 in) per min. The strip film produced provides a permanent, detailed and semiquantitative record of the distribution and nature of the `ash' in the coal seam.

An apparatus is described for the measurement of small changes in length of rigid metal rods. The technique makes use of the mechanical lever principle, and lengths are measured relative to that of a dummy specimen to compensate for thermal expansion effects. Changes in length can be measured with an accuracy to 1 part in 10⁶, and the apparatus is suitable for studying the volume changes associated with lattice defects.

This paper describes an electronic device coupled to an automatic spectrophotometer by means of which the temperature of a given reactant is controlled, so that its extinction changes linearly with time. The differential equation describing the change in the reactant concentration is integrated easily. Knowing the initial and the end values of temperature and concentration one can determine the activation enthalpy, energy and entropy as well as the rate constant. The method suggested presents all the advantages of previously known techniques. The method is rapid and sufficiently accurate.

A spectrometer capable of examining a varying light source is described; it is designed to scan the wavelength range 200-850 nm in about 0·5 s. The information may be additive with successive wavelength scans so that a time-integrated spectrum can be finally presented on a pulse-height analyser; this is in digital form and may readily be converted into a form suitable for computer analysis. Examples of the application of the instrument to the study of the thermoluminescent spectra of various materials are presented.

Constant-temperature hot-film anemometry has been developed for measuring velocities in blood vessels. Probes suitable for insertion through artery walls have been evolved, and an output filter has been employed to correct the frequency response of the DISA 55D01 anemometer when used at the very low overheat temperatures necessary in blood. It is estimated that velocities can be measured to ±5% over most of the pulse cycle, but near zero velocity the proportional errors are larger, being of the order 10 cm s⁻¹ in the rapidly reversing flows observed in animals. Direction sensing, however, allows substantial improvement of this, the final errors being an order lower, and the use of an efficient system in an arterial flow is demonstrated.

Investigation of the single wire counter characteristics in dry air, free from carbon dioxide, has been undertaken for different values of external quenching resistance, which correspond to various values of electrode spacing. An empirical formula has been derived which explains the contradictory results on the shape of the plateau found by different authors.

A simple optical machine for measuring and automatically recording quickly and accurately the coordinates of steel spheres in any array is described. Results over very large (similar 8000) assemblies of ¼ in spheres show an improved accuracy of measurement over previous instruments, the standard deviation of the error curve being reduced by over a factor of 2, or 5 when the increased capacity of the machine is taken into account. The machine may be used for a variety of systems, including multicomponent mixtures.

Two methods are described for the preparation of powdered metal specimens for nmr by spraying the molten metal into a quenching bath. The technique has three main advantages over the more conventional method of grinding or filing. Firstly, there are no composition variations between particles; secondly, the particles are spherical giving a higher powder density; and finally the danger of contaminating the sample with impurities such as iron is eliminated.

A heatable infrared gas cell, operable to at least 800°C, has been developed. Problems concerning suitable window materials and the sealing of windows to the cell body are avoided by using inert gas curtains in place of solid windows. The cell has no wavelength limitation and can be safely used with wet or corrosive substances in standard commercial spectrophotometers. The absorption and emission spectra of zinc chloride vapour at 700°C and of carbon dioxide at 25, 300 and 800°C are given. The absorption spectrum of titanium tetrachloride vapour at 20, 300 and 700°C is also presented.

A method is described which used a p-i-n diode switch to measure the complex propagation coefficient (γ=jβ+α) of a lossy liquid at X-band. Measurements are made at half-wavelength intervals in the liquid, resulting in greater accuracy for liquids of very high loss than is possible with measurements at wavelength intervals as in the normal vector balance method. A p-i-n diode, driven by a rectangular voltage pulse wave of variable mark-space ratio, provides an absolutely calibrated and electronically controlled attenuator with a phase-shift independent of attenuator setting.

The removal of mercury vapour from gases by exposure to gold surfaces is investigated. Under suitable conditions, which are indicated, this technique can be used to virtually eliminate mercury photosensitization.

Two aids are described for weighing small test specimens to determine moisture content during long-duration mechanical testing. In one, a frame for stress relaxation is sufficiently light to be weighed with the restrained specimen. In the other, a simple, robust, automatic recording balance provides electrical output from deflection of a cross-spring pivot during weight changes.

A differential input stage employing matched pairs of field effect transistors provides a high input impedance, good dc stability and is sufficiently simple and robust for student use.

A method is described for embedding a tungsten hot wire in a perspex support, the heat dissipation of which is shown to correspond with the local wall shear stress of an air flow passing over the surface. Results of wind-tunnel calibration against the Preston tube are presented.

A wide aperture valve, suitable for high vacuum work at liquid helium temperatures is discussed. The valve, utilizing a self-renewing indium seal, and the mechanism from a standard bellows sealed valve, was designed for use in conjunction with a fixed liquid helium cooled charcoal adsorption pump.

The strength of nickel foils ranging in thickness from 0·51-1·27 μm has been measured. For apertures in the range 0·318-0·794 cm the pressure necessary to burst a foil was found to be p=2·299 × 10²(t-0·31)/d^1·27 kN m⁻² where t and d are respectively the thickness (in micrometres) and the diameter (in centimetres) of the foil.

The replacement of a large number of individual thermocouple reference chambers by a single reference junction and a pumped system circulating water at a uniform temperature is discussed. Calculations show that within an accuracy of 0·1 degC a circuit length of 90 m is possible, or 200 m when the apparatus is used in controlled laboratory conditions. The design of a practical laboratory installation is described with which accuracies to better than 0·1 degC were obtained.

Experience in this laboratory of high-speed paper tape punches (Tally Model P-120), connected as the output of a computer (Ferranti Argus 500), has shown that punching errors arising from a mechanical origin are frequent. If the tape supply is arranged to be `drag free', these errors are almost eliminated, thus avoiding costly waste of operator and computer time.

This note describes a prototype of a high speed tape supply device which was designed for use with an 8 hole 120 character per second paper tape punch. The device is simple and inexpensive to construct, and has proved reliable in use.

A replica technique, which makes use of a water soluble plastic, has been developed for the examination of surfaces in the conventional and scanning electron microscopes.

To measure the relative intensities of diffraction patterns of powdered substances exhibiting a marked cleavage, a special mould has been devised for preparing the specimen for the counter diffractometer. By compacting the powder in this mould a serrated surface is imparted to the finished specimen. Good agreement can be obtained between the observed relative intensities for PbO, β-alumina and mica and the theoretical values, by using the new mould to impart a suitable degree of serration to the surface.

A method is described for preparing single adsorbate clusters containing known numbers of atoms from isolated adatoms vapour-deposited on the atomically perfect crystal faces of specimens in the field ion microscope.