Table of contents

An electronic clock that can be used to provide a coded time signal for a timing channel on a magnetic tape recorder is described. The clock provides a direct means of determining the elapsed time, whereas more commonly employed methods of timing do not. The construction of the clock is made practical by the use of integrated circuitry which ensures that it is both compact and low on power consumption.

A furnace of low inherent thermal stability but which is screened from ambient temperature variations and has its temperature controlled to close limits is described. The capsule in which vapour transport is performed can be rotated and moved axially through the temperature profile in the furnace. Continuous observation of the capsule is possible up to the maximum operating temperature of 1100°C. Any desired profile over a length of 30 cm can be obtained subject to the limits: ±0·5 degC for a uniform temperature zone over 15 cm and a maximum temperature gradient of 15 degC cm⁻¹.

A transducer for recording mechanical impulses especially in air blast research is described. The transducer is based on the principle of recording the change of momentum of a body with known geometry and mass. The change of velocity of the body is recorded as a function of time by means of a displacement transducer. The transducer was designed for recording impulses with a maximum duration of the overpressure phase of 20 ms.

The utilization of the photovoltaic properties of CdSe-Ge n-n heterojunction as a wide range pyrometer is described; the method is a variation of the two colour technique. The optical response of the heterodiode depends on the bias voltage in such a way that the photovoltage produced by white radiation can be biased to zero, thus providing a null detector. For a specific spectral distribution of energy produced by a black body radiator within the bandwidth of the device there exists a unique bias voltage for which the photovoltage is zero, and the bias voltage can be calibrated directly in terms of temperature. The sensitivity of the detection is 0·6 mV K⁻¹ at 1000 K, 0·1 mV K⁻¹ at 2000 K and 0·05 mV K⁻¹ at 3000 K.

A description is given of a twin perspex cell used to study the rate of active transport of sodium across living isolated frogskins in experiments in which the hydrostatic pressures are controlled on each side of the skin. It consists of two half-cells each containing half of the same frogskin; one half-cell acts as a control for the other. A description is given of the circuits used to supply each of the four chambers with oxygenated solution at constant pressure, flow and temperature. The cell is especially suitable for evaluating the effects of small stimuli. It has been used to study the changes in sodium transport brought about by various drugs and hormones and by hydrostatic pressure gradients of less than 3 mm H₂O applied across the frogskin.

Molecular relaxation processes are often manifest through the transient changes in the optical properties of solutions of the molecules. Relaxation times are currently obtained by analysing the coordinates of photographic records of the transient behaviour and plotting suitable semi-logarithmic graphs. This procedure is laborious. A device is described herein which obviates this procedure. It enables experimental transient curves to be simulated almost immediately for the three important cases: (i) where a single exponential process is involved; (ii) where two such processes are summed together in the final response; (iii) where two such processes act in opposition in the final response. The last case is extremely difficult to analyse by the conventional geometric method mentioned above. Details are given of the design of the simulator and its mode of use. Typical results for each of the cases (i), (ii); (iii) are given with reference to measurements of the Kerr effect (electrically induced double refraction) of dilute macromolecular solutions.

The circuit described performs the logarithmic conversion necessary to measure optical density and provides a digital output which can be fed directly to a digital computer or data logging device.

The circuit works by generating an exponential voltage waveform and comparing this with the input voltage. A dual version uses the logarithmic property to correct for fluctuations in incident illumination, deriving the ratio of two photocell signals by subtracting logarithms.

The circuit has been used in a flying spot densitometer, digitizing to 1 part in 256 taking 512 μs, and in a mechanical densitometer and in an amino acid analyser, in which higher precisions are attained, at the expense of speed.

In previous reports the basic design and operating principles of a self-oscillating rubidium vapour magnetometer have been described. Further development of the sensor has been carried out, and detailed investigations have been made into the limiting capabilities of the magnetometer system. This report summarizes the results of tests of the stability and ultimate resolution of the rubidium sensor, and contains a description of the sensor and loop electronics currently being used by the Geomagnetism Unit of the Institute of Geological Sciences.

A method for eliminating the astigmatism of a Czerny-Turner spectrograph is described in which the grating is used in divergent illumination. Expressions are given for the distances of the tangential and sagittal astigmatic images from the camera mirror in terms of the separation between the entrance slit and the collimating mirror and the condition for the elimination of astigmatism is derived. These results are compared with ray tracing data for a practical instrument. Experimental tests of spatial and spectral resolution for an f/15 spectrograph of 0·6 m focal length are given at wavelengths 5461 and 2800 Å. Over a spectral range of 100 Å centred on 2800 Å a spatial resolution along the slit in excess of 50 cycles mm⁻¹ has been achieved for a flat inclined image plane. For the same spectrograph with the grating in collimated light the spatial resolution is only 3 cycles mm⁻¹.

A method for applying the metallizing layers to ceramics by a sputtering technique is described. The ceramic to metal seals produced using this method, which can be used on any grade or type of ceramic, are strong and vacuum tight.

When a surface is illuminated with laser light it has a speckled appearance due to random interference. If two speckle patterns are superimposed the distribution of intensity in the resultant pattern depends on the relative phases of the component patterns. By measuring the correlation between the resultant patterns at two different times a change of relative phase is detected. This leads to a versatile method of measuring either the normal or in-plane components of displacement over the whole of a surface at one time.

Equipment for the automatic measurement of internal friction, vibration frequency and temperature of a sample is described. Each of these three values is recorded in both digital and analogue form. A control unit enables programming of the various measurements.

Six major telescopes (mirror diameters greater than 120 in) are at present being built, as opposed to only two already operating. Current trends in telescope design are reviewed, with particular reference to the following:

(i) improved optical design, allowing much larger corrected fields at the prime focus; (ii) the availability of very low expansion materials (quartz and glass ceramics) for large mirrors; (iii) the development of more convenient drive and control systems, incorporating on-line computers; (iv) advances in instrumentation, especially in electronics and in image intensifiers; (v) a better understanding of the basic principles of telescope design. A number of special-purpose telescopes are described.

A 33 GHz interferometer with a novel two-phase lock-in detection system for use in solid state plasma experiments is described. The technique for phase shifting the microwave signal transmitted through the specimen at a constant speed (5 Hz) relative to the reference (homodyne detection) and the method of synchronously rectifying the detected 5 Hz signal in two channels operating in time phase quadrature is discussed in detail. No extra microwave components are necessary to modify the interferometer for this type of operation; only simple mechanical and electronic parts are required. The outputs of the interferometer are used to plot automatically transmission phenomena in the form of polar diagrams. The application and advantages of the two-phase system are illustrated by results taken from helicon wave experiments in solid state plasmas.

The advantages are discussed of performing certain measurements in a pulsed rather than a continuous manner. A ratio-detection system is described which is suitable for the study of transient phenomena induced by repetitive pulsed excitation. Fast sample-and-hold circuits preserve appropriate measures of the observed phenomena and of the intensity of the excitation source. The ratio of the two signals is taken, reducing by three orders of magnitude the effect of fluctuations of the excitation source. The ratio signal is then averaged in a two-channel `boxcar' circuit linear to ±4 parts in 10⁵ for input voltages between ±2 V The entire system is linear to ±2 parts in 10⁴ for input voltages between ±2 V. Under continuous operation, drifts of the system referred to the input are less than 20 μV per day.

Equipment is described for the shaping of specimens of water soluble materials used in electrical breakdown studies, and for the measurement of the minimum thickness of flat-bottomed recessed specimens used in high field conduction studies.

A simple, efficient optical system for a laser Doppler velocimeter is described which requires almost no optical heterodyne alignment and which is stable and insensitive to stress and vibration.

A simple experimental method of determining the variation in the ion transmission efficiency with mass-to-charge ratio for quadrupole and other discriminating mass filters is described. This information can be used for the study of mass filters per se, to normalize ion current data to that obtained with non-discriminating filters for comparison of mass spectrometrically obtained fragmentation patterns, and to aid in determining partial pressures from ion currents in thermodynamic studies.

A cryostat designed for the measure of electrical conductivity and thermoelectric power of small semiconductor samples is described, operating in vacuum in the temperature range from 80 to 900 K. The same design can be used for Hall constant measurements.

Gain degradation measurements have been carried out on five 419BL and two 318BL Mullard lead-type channel electron multipliers, over periods up to several thousand hours, at a pressure of less than 10 ntorr. The devices showed reductions of about one order of magnitude on their initial gain values. The reduction occurred in 10 h at an output count rate of 2 × 10⁵ counts s⁻¹ and several thousand hours at 2 × 10² counts s⁻¹. At the high output count rate, the initial gain was found to be depressed by over an order of magnitude on the nominal value of 10⁸.

Performance details are given of a constant loop gain, low noise amplifier; it is a simpler version of Faulkner and Grimbleby's elegant design which still does not seem to be very well known.

An efficient and inexpensive method of cooling a crystal to low temperatures and maintaining fine temperature control (±0·5 degC) at the crystal has been developed for single crystal x-ray diffraction investigations. Temperature control is attained by using a float and microswitch mechanism to maintain a virtually constant liquid level (±5 mm) in the boil-off chamber and by using a slow gravity fill procedure to reduce any pressure variations in the gas stream. The apparatus features a small Dewar which allows for ready use on either precession or Weissenberg cameras or with counter diffractometers. Operation at sustained temperatures at approximately 90 K requires less than 20 1 of liquid nitrogen per day.

The two-circle goniometer described precisely marks an angular coordinate system of meridians and parallels on the surface of spherical rock specimens. Physical property data obtained with respect to this frame of reference then can be accurately transferred on to a Schmidt (equal area) net and contoured with isolines to give the symmetry and magnitude of anisotropy of the physical property.

The beam-tilt device of an electron microscope can be used to make marks in electron diffraction patterns which serve for calibrating the latter in reciprocal lattice units.

A pressure transducer is described which was specially developed to measure wind pressures exerted on buildings. The instrument, which gives an electrical output, is suitable for measuring pressures in the range ± 1200 N m⁻² (±25 lb ft⁻²). The frequency response is such that pressure fluctuations lasting only 0·1 s can be recorded.