Table of contents

An account is given of the development of an apparatus employing two separate flash discharge tubes operated either simultaneously or consecutively with a means to vary the interval from 0.01 to 10 ms. The two sources of an energy of 5 J are designed for a flash duration of 6 μs at 10% of peak light. An example is given of the application of the apparatus to the study of the mechanics of spray nozzles.

An isograph is described in which the terms of the polynomial equation to be solved are represented by alternating voltages of varying time phase obtained from magslip transmitters in association with resistance potentiometers. The application of this principle results in a compact machine capable of finding roots with good accuracy. The isograph may also be used for the evaluation of polynomials.

The hinges are based on the ease of twisting an L-section cantilever beam about its corner edge. The simplest form is easier to make, and is more compact, than a cross-strip hinge. The limitations of the angle-spring are described, and various designs of simply compensated hinges are indicated. Performance figures are given, showing that for angles of rotation up to 0.1 radian, the axis of a typical compensated hinge will remain constant within 10 μ and within 10-15" of arc. Such hinges can be useful components in instrument design, being free from friction and backlash.

During grinding or polishing, optical flats of glass or quartz are often eccentrically loaded to modify the angle between the front and back surfaces. It is shown that if too great a loading is applied too close to the edge of the flat a kink is formed, namely, a part of the original surface remains unworked and will lie at an angle to the freshly worked part.

The difficulties inherent in the design of small portable, battery-powered, infra-red detectors employing photoconductive cells are discussed, with particular reference to the signal-to-noise ratio of suitable electronic amplifiers, and the method employed to "chop" the radiation. The main novelty is the use of an electromagnetically-maintained vibrating leaf-spring with a shutter suitably mounted at its free end as a radiation chopper. The design and applications of this device are discussed in some detail.

A simple, self-contained, automatic sample changer has been constructed, which can be used together with all common types of radioactivity pulse counters. The construction permits a simple exchange of the detector (for either α, β or γ counting) and allows repeated measurements for a predetermined time (1 s to 10 days) or pre-determined count (N to 10⁵N, where N is the scaling factor) for up to twenty-four different samples. Data for absorption curves as well as back-scattering curves can be obtained automatically.

To investigate the performance of a Penning-type vacuum gauge, deflexions proportional to its current were displayed on an oscilloscope screen, while the magnetic field in the gauge was linearly varied. Such a field was produced by an electromagnet, which was part of a linear time-base circuit. From the patterns observed at different pressures and voltages across the gauge, best working conditions could be quickly obtained.

A manometer is described for the pressure range 1 to 10^-4 mm of mercury with a response time of 10^-4 s. The pressure change deflects a thin stainless steel diaphragm which forms the moving plate of an electrical condenser. The capacity changes are converted to voltage changes and recorded on a cathode-ray tube.

An account is given of an instrument suitable for measuring and recording water velocities from one or two centimetres per second to several metres per second using a miniature propellertype current meter. Each propeller blade in passing a fixed electrode slightly increases the impedance between this electrode and the supporting frame of the propeller, generating a voltage pulse in the associated circuit. The pulse-rate is measured by an electronic tachometer. The range and accuracy are discussed and polar diagrams presented, showing the effect of different propeller mountings.

A simplified form of radio-frequency interferometer is described. It is particularly suitable for microwave applications, in particular, the determination of the Doppler frequency shift due to the motion of a target. One aerial is used and a hybrid junction separates transmitting and receiving paths, thus enabling a single oscillator to provide both transmitter and local oscillator power.

A brief outline is given of a developed equipment used for the measurement of the speed of road vehicles. Possible uses of the instrument in measurement of distance have been examined and its use in the study of microwave reflexions from the sea surface is being investigated.

A testing machine for single crystals is described, by means of which the stress-strain behaviour in cycles of alternating tension and compression can be measured; special precautions are taken to eliminate external bending or torsion of the specimen. The load and extension gauges are of the roller and mirror type for high sensitivity. The difficulty of gripping a single crystal firmly without damaging it is overcome by using a chuck in the form of a mould, into which the crystal is cast with solder. Examples of the performance of the machine are given.

The apparatus, which allows the strain-time relationship for a briquette upon application and removal of a sudden stress to be observed, shows that an increasing viscosity is accompanied by an increasing elasticity which is retarded. Constructional details are given, with the results of one representative experiment. The possible application of the apparatus to studies of stresses and cracking in coke oven charges is indicated.