Table of contents

The principle of a microdensitometer for the measurement of rate of change of photographic density as well as of density itself is discussed, and an experimental system is described. Examples are given of results that have been obtained in measurements of interferograms for the precise comparison of wavelengths of standard spectral lines.

Using simple materials a thermopile solarimeter has been constructed with output 5.5 mV cal^-1 cm^-2 min^-1; resistance 13 Ω; response time 20 s; weight 35 g; dimensions 4 × 4 × 4 cm. It can therefore be used with a portable millivoltmeter for measuring reflexion coefficients, radiation within crops, etc. General equations for solarimeter performance and a simplified theory for the present design give a non-linearity of -0.8% cal^-1 cm^-2 min^-1 and a temperature coefficient of -0.12% per deg C. Outdoor comparison with a Kipp solarimeter gave ±0.03 cal cm^-2 min^-1 as the maximum deviation from the mean response with radiation up to 1.1 cal cm^-2 min^-1. The standard deviation for thirty observations in bright sunshine and with overcast skies was ±0.002 cal cm^-2 min^-1. Cosine and azimuth response were improved using a larger instrument of the same design and comparisons of this with a Kipp solarimeter gave maximum deviation of ±0.02 cal cm^-2 min^-1.

A modified vibrating-electrode apparatus designed for the reliable measurement of air-water and oil-water adsorption potentials is described. The equipment is capable, under the best conditions, of measuring potential differences of 0.2 mV at the air-water surface and of 0.5 mV at the oil-water interface. The surface potentials of small quantities (0.1 ml.) of aqueous solutions may be measured rapidly to a lesser degree of accuracy.

The electron-optical design of an X-ray micro-analyser is considered in some detail with a view to establishing the best design. The electron-optical system has to fulfil conditions not normally encountered - for example, in the electron microscope where the optimum design has been extensively studied. A system is described that has proved suitable for a practical X-ray micro-analyser using magnetic lenses of axial symmetry. Brief reference is made to possible future developments such as the introduction of corrected lenses.

A spinner-magnetometer has been built to obtain continuous records of the magnitudes and directions of the remanent magnetic moments of rock specimens while they are heated to temperatures up to 800° C. The specimens are rotated at 78 c/s in a non-inductive electric furnace through which a flow of inert gas is maintained, and the voltages which are produced in a large detecting coil outside the furnace are amplified and measured electronically.

An explanation is given of the advantages and the limitations of the arrangement whereby analytical and similar weights of accuracy approaching one part per million (for example, 0.1 mg on 100 g) are adjusted and tested on the basis of weighings in air without applying buoyancy corrections. The paper has been occasioned by a decision taken recently by a number of national standards laboratories, including the National Physical Laboratory, to base their weight-in-air tests, as from 1 July, 1959, exclusively on the densities 8.0 g/ml. for the weights and 0.0012 g/ml. for the air.

A time-controlled, unit-function, constant-voltage generator has been developed having a variable output amplitude from 40 to 1000 V with a rise time of 1 μs and constant for 150 μs. The output voltage is independent of current from 0 to 12 A and can be applied with an accuracy of ±1 μs. The generator consists of a source of high-capacity capacitors connected in parallel with non-inductive capacitors which supply the initial energy at a high rate. A mercury thyratron (type BT61A) with a special triggering circuit gives the necessary time control. By keeping the thyratron at a constant temperature, its appropriate volt-ampere characteristic shows that the voltage amplitude is maintained constant independent of variation in current output. A high rate of rise of the unit function is achieved by connecting a high-voltage auxiliary circuit between anode and cathode. Detailed circuit diagrams of the generator, etc., are given. The effects of temperature, accentuation of field due to additional space charge and oscillations on the voltage waveform are also discussed.

A propane bubble chamber, 6 × 2 × 2 in., has been operated with both single-piston and multiple-bellows expansion systems, the systematic distortions caused by turbulent motions being measured and compared in the two cases.