Table of contents

The importance of vapour density in the jets of high-speed oil diffusion pumps is stressed. It may be low, firstly, on account of the pressure gradient in the tower up which the vapour is fed from the base of the pump, and secondly, because of the radial spreading of the jet after it leaves the tower. By means of a first order theory it is shown that for greatest speed there is an optimum diameter for the central tower. The shape of the theoretical curve fits the experimental points very well. The difficulty of obtaining high speeds with hydrogen is discussed.

An integrator is described which accepts positive voltages in the range from 0.7 to 7 V and provides a photographic record of the integrated output at intervals of 0.01 sec, with an accuracy of 0.1%. The integrator requires an input current of the order of 0.5 mA at the maximum voltage. The design can easily be modified to accept higher voltages, subject to the same current requirement and the same 10 to 1 range of inputs. The application of the integrator to the measurement of a rising magnetic field is described.

An actograph is described which records the movements, in one direction only, of an insect weighing 3 mg. Movement of the insect over a length of 9 in. is recorded continuously across 35 mm sprocketed film or paper by a camera. The camera has provision for moving the film which provides a time base.

Measurements on a diffusion cloud chamber operated with fillings up to pressures of 11 atm are interpreted according to a theoretical treatment by Shutt. The results can be used to determine temperature conditions required for good operation with any permanent gas at all useful pressures and for any given mean radiation intensity. Factors which interfere with normal operating conditions are considered.

The paper contains a description of a low-temperature X-ray camera suitable for the examination of small plates. The specimen under examination is cooled in a stream of air for temperatures in the range between room temperature and -170° C, and by dropping liquid air on it for the lowest temperature reached (-194° C). Temperatures were measured directly with a copper-constantan thermocouple for single specimens or by reference to the lattice parameter of a standard material for double specimens. These temperatures were taken whilst the specimens were being simultaneously rotated and oscillated. The results obtained with silver and iron are quoted. The coefficients in the expansion equation a_t = a₀(1 + αt + βt² + γt³) for these metals were found to be as follows:

Silver: α = 18.2606 × 10^-6, β = 3.9156 × 10^-9, γ = - 17.2794 × 10^-12, and a₀, the lattice parameter at 0° C, is 4.0760 kx;

Iron: α = 11.9784 × 10^-6, β = 15.8447 × 10^-9, γ = - 3.2973 × 10^-12, a₀ = 2.8598 kx.

A simple X-ray vacuum camera is described for measuring long spacings (Bragg angles less than 2°). The camera is calibrated by making use of built-up multilayers of barium stearate and octadecylamine.

An apparatus is described for measuring the magnetic susceptibility of liquids and solutions by the Faraday method. The essential part is a quartz fibre vertical torsion balance. The accuracy of the measurements, which are made by a null method, is of the order of 1-2 parts in 10 000 with diamagnetics.

The instrument described has been developed from the design of Guild; it is suitable for the accurate measurement of the curvature of transparent lenses and test plates, and particular attention has been given to protecting the surfaces measured from risk of damage. A brief comparison with other spherometers is made, and, in conclusion, attention is drawn to the convenience of specifying optical surfaces by their curvatures, rather than by radius of curvature.

The construction and operation of a rotating ice target are described. Targets of easily variable thickness can be made and maintained under bombardment by intense ion beams.

A reciprocating mercury pump which is used to mechanize the Haldane type of gas analysis apparatus is described. This pump unit, being simple and robust in construction, has proved reliable for continuous routine use.