Table of contents

Although a bridge-rectifier meter indicates r.m.s. current when the current is sinusoidal, a sinusoidal voltage produces a non-sinusoidal current, and hence an error in the indication, because the resistance of a copper-oxide rectifier is non-linear, varying as the -0.7 power of the current. Series resistance tends to swamp the non-linearity, and the error, calculated by arithmetical integration, is shown on a nomogram relating error, series resistance and meter indication. Experiment confirms the results.

A brief survey and criticism of existing methods of measuring daylight factors is followed by a description of an improved daylight factor meter, in which the current outputs of two photoelectric cells are compared by a null-balance method. When one cell is exposed inside the building and the other outside, the ratio of the illuminations at the two positions is indicated directly on a calibrated scale by the balance position of the potentiometer. The circuit is so arranged that the load resistances of the cells are unchanged by changes in the balance position and, for a constant daylight factor, the balance position is not affected by changes in the average luminance of the sky. The instrument can be calibrated directly on an optical bench, either for use with the outside cell exposed to a full hemisphere of sky or for use with the outside cell so masked that light is only received from a part of the sky.

The paper presents the design of a time-to-amplitude conversion circuit employing delayed fast coincidence techniques for use in the nanosecond region. This circuit has a linear time calibration over the range 1 to 10 ns, a resolution time of less than 0.05 ns and a variation of time calibration less than 0.03 ns per day is achieved. A resolution time of 0.8 ns was found when detecting coincidence between γ-rays from a ⁶⁰Co source.

A conventional mass spectrometer is used for precise measurements of the isotope ratios of boron in boron trifluoride samples with widely differing concentrations of boron 10. "Memory" effects caused by the adsorption of boron trifluoride on to the surfaces of the inlet system have been investigated, and it is found that these can be reduced to a workable level by careful design of the inlet system. By blending together enriched and depleted boron trifluoride, standard samples with known isotopic constitutions are prepared and used to calibrate the mass spectrometer. The true and measured isotope ratios are thus found to differ by several per cent, an effect attributed to mass discriminations in the ion source. After correcting for this error, the boron 10 atomic concentration in some naturally-occurring boron is found to be 19.27 ± 0.13%.

A new technique for the measurement of isotopic abundance ratios has been developed. Individual ions in the beam are detected, and an automatic switching device counts the total number of ions in each of the two mass beams being compared. The system is simple to operate and has been found to give very accurate results. No elaborate stabilization of ion-source emission or other operating conditions is necessary.

A description is given of an instrument for the detection and measurement of the space density of charge in electrically charged flowing liquids, such as white petroleum products. It is based on the measurement of the dielectric displacement at a metal rod placed in the axis of a pipe carrying the liquid under test. The advantage over existent measuring methods is that no pipe-line section or other part of the installation need be insulated.

A new type of charge-reduction has been found with a halogen-quenched X-ray Geiger counter. A practical circuit has been developed which reduces the effective dead-time of the counter by a factor of ten. The dead-times were measured by a new method.

A range of Pitot tubes is described together with an electromagnetic transducer micromanometer. The assembly is designed for the measurement of gas velocity over a large range of temperature, and pollution with velocities as low as 40 cm/s. Some applications are described.

Two simple devices are described which may be added to a Joyce-Loebl microdensitometer. The continuous chart device enables a chosen expansion ratio of any film being scanned by the microdensitometer to be recorded on one piece of chart paper. The existing mechanical link between the original chart table and film carriage table has been preserved. The integrating attachment allows the area beneath the recorded trace to be determined while the trace is being produced.

An apparatus for the accurate determination of the thermal diffusivity of semiconductors, which utilizes the thermoelectric properties of such materials, is described. In its present form, the apparatus can be used between room temperatures and 180° C. The application of the method is illustrated by an experiment using a single-crystal specimen of bismuth telluride.

An electrolysis apparatus has been constructed for the safe and trouble-free generation of deuterium gas from heavy water for experimental purposes. It has been found particularly suitable for introducing the gas at a rate of millitres per minute (S.T.P.) into a vacuum system without the use of an extra pumping unit, because the electrolysis is done under atmospheric pressure and not in a vacuum. The apparatus is equipped with electrical control-relays and needs little attention. It operates within a specified pressure range of the liberated deuterium gas, and is automatically shut off if the pressure exceeds a certain value. There is an almost complete absence of danger of explosion arising from the electrical devices should the generated deuterium gas be accidentally mixed with air.

The design and construction of a large temperature-controlled permanent magnet is described and the considerations given towards obtaining a high degree of field uniformity. Using current shims and a spinning sample, a resolving power and stability of a few parts in 10⁸ may be obtained at any time and, with care, 1 part in 10⁸ can be achieved.

Various designs for a camera range-finder with parallel mirrors and a variable prism unit have been described. In each design certain parts of the range-finder shared the motion of the camera lens in focusing. Here a further design of this type is described in which there is no relative movement of the mirrors.