Table of contents

Drift of the base line caused by imperfect control of temperature or voltage of a gas-chromatographic catharometer may be eliminated by including one shunt and one series resistance with the catharometer hot elements in the Wheatstone's bridge circuit. Equations enabling the positions and values of the resistances to be calculated from the observed drift are given. Experience shows that use of the compensating resistances enables a catharometer to be used more sensitively without the trouble and expense of careful temperature and voltage control.

A remote indicating cup anemometer is described in which transistor electronics have been applied to obtain a compact instrument, operating off small dry batteries and capable of registering wind speeds down to 0.2 m/s.

A photoelectric fringe comparator for scanning electrophoresis plates, based on a microdensitometer, a Schmitttrigger operated counter and a recording milliammeter is described. The basis of the microdensitometer is a standard Zeiss binocular microscope with a mechanical stage driven by a reduction gearbox. A considerable simplification in the electronic circuit of the densitometer is achieved by using highly sensitive type O RP 90 cadmium sulphide photoconductive cells.

The cell is of a "balanced pressure" type and a linear differential transformer is used as a null point indicator to maintain a diaphragm in its zero position. The deflexions of the diaphragm during pressure measurement may be kept very small, well within the limits required for soil pressure cells. The cell is used for direct and tangential pressures on the face of a rigid wall containing consolidating silt. The accuracy of observing the pressures lies within ±0.04 in. head of oil.

An admittance bridge is described suitable for the measurement of the complex permittivity of liquid dielectrics at frequencies between 100 kc/s and 3 Mc/s. The unknown capacitance is compared directly with a standard capacitor, while the conductance arm may be simply calibrated on a direct current supply. Component values are given suitable for use with a cell having an empty capacitance of 5 pF. No Wagner earth is necessary when using a 3-terminal cell, since the balance condition is independent of admittances between the electrodes and the guard electrode.

A hydraulically operated ram carries the semiconductor device and its envelope, loosely assembled, into a Pyrex chamber. Here the two are separated while the envelope is outgassed by e.c.h. in vacuum. They are then brought together, in vacuum or in gas, and the residual heat in the envelope melts a ring of tin in the mount collar to make the final seal. During the process the device is warmed sufficiently to drive off any moisture. A novel three-port valve controls the gas and vacuum supplies to the chamber. The equipment has been designed with a view to ultimate automation.

The importance of tilting and rotating the specimen in electron microscopy and electron diffraction is discussed. The design and construction of a specimen stage, allowing a maximum tilt of 35 deg. of the plane of the specimen from a plane perpendicular to the electron beam, and providing a 360 deg. rotation at all angles of tilt are described. Though the stage has been designed specifically for the Metropolitan-Vickers type E.M.3 electron microscope, the principles involved may have application to other microscopes.

A simple counting technique is described for absolute counting of beta particles using a 4 π liquid scintillator counter technique. The radioactive sample is deposited on a thin backing film of transparent material, which is then immersed in the liquid scintillator. It was found that for samples with a maximum beta particle energy greater than 0.7 MeV the detection efficiency was close to 100% comparing favourably with other methods of absolute counting.

The paper describes how joints may be made in the envelope of sealed-off, high-vacuum tubes using a synthetic resin adhesive, permitting unusual forms of construction. A pressure of 10^-6 torr may be maintained in such a tube for several years. Success depends on suitable design and processing and on the use of getters. A special television camera tube and a vacuum photocell have been made using this technique.

High frequency light modulation has been realized using a magnetically driven rotor suspended by a magnetic field in a vacuum chamber. With a rotor 1 in. in diameter having 180 reflecting faces, modulation frequencies in the megacycle region are readily obtainable. Design considerations are given for the rotor described, together with details of the driving and suspension circuit employed. A time constant measurement for an indium antimonide sample is given as an illustration of the system.

The oscillatory motion of a swinging beam used to measure the internal friction of a silicon-iron strip has been found to be complicated, and to consist of a small amplitude, higher frequency oscillation superimposed on the main oscillation, so that difficulty arises in obtaining a unique value for the logarithmic decrement of the strip oscillation. The motion has been analysed and reasonable agreement is found between the experimental results and the theory developed.

Short lengths of fibre with cylindrical cross-section are placed on a plastic film and rolled, thereby replicating the entire fibre surface. The apparatus to do this is described. The replicas are examined by phase contrast. Nylon fibre surfaces are illustrated.

An apparatus is described which allows almost total removal of not-completely homogeneous magnetic grains from ferrimagnetic mineral sand, and will further separate strongly remanent from weakly remanent grains. Magnetic-field strengths and water-flow velocities required for material of size 60 to 200 B.S. mesh, and a scale drawing of the separation tube are given.