Table of contents

The near infra-red region may be used to obtain spectra with polarized radiation of natural and synthetic fibres. This region has considerable experimental advantages and the spectra of poly-L-alanine, polyglycine, wool, silks and commercial regenerated protein fibres are shown and discussed. Besides supplementing other types of observation, information may be obtained on the orientation and molecular configuration not always given by other methods.

The stability, in the corrosive atmospheres of chemical laboratories, of brass weights coated electrolytically with nominal thicknesses of 13 μ and 25 μ of tin-nickel alloy (65% Sn, 35% Ni) has been compared with that of weights previously tested⁽¹⁾ under similar conditions. As regards appearance after exposure, the 25 μ coating was the best, and was comparable with weights of highly-polished stainless steel save in the severest conditions. All the alloy-coated weights showed about the same stability of mass as good quality commercially produced weights of austenitic stainless steel (25% Cr, 20% Ni) and rhodium-plated brass weights. Tin-nickel alloy plating does not possess any undesirable magnetic properties. In highly corrosive atmospheres, non-magnetic nickel-chromium (80% Ni, 20% Cr) is a little less resistant than the materials already mentioned. Of the small sheet metal weights of various materials tested, those of austenitic stainless steel were definitely the best. They were followed, in order of merit, by zirconium, tantalum and aluminium, and finally, titanium.

In the past the possibility of thermoelectric refrigeration has been considered, but all attempts to produce a practical refrigerator have failed owing to lack of suitable thermocouple materials. In this paper it is proposed that semiconductors should be used and the factors governing their selection are discussed. It is concluded that the semiconductors should be chosen with high mean atomic weights and that they should be prepared with thermoelectric powers lying between 200 and 300 μVC^-1. Preliminary experiments have led to the production of a thermocouple consisting of bismuth telluride, Bi₂Te₃, and bismuth, capable of maintaining 26 C of cooling.

The emission from hot cathodes in gas discharges has been studied over a wide range of current and its stability examined. The condition of zero field thermionic emission has been identified in the presence of a discharge in inert gas. For all types of cathode investigated, the emission at zero field in the discharge has been found similar to that obtained in vacuum. At very high currents, the electron emission is greater than the thermionic emission, either because of enhancement by the field or because of γ-effects at the cathode.

The focal lengths of a series of symmetrical slit ("cylindrical") electrostatic electron lenses are determined as a function of aperture size and applied potential. It is shown that all practical lenses may be represented on a single curve by means of a parameter simply related to potential and geometry. From this it is deduced that lens strength depends more on the size of the central aperture than on that of the outer apertures.

The problem investigated involves consideration of the temperature distribution in a body moving relative to sources of heat. Relaxation and analytical methods of solution have been developed and applied to the work material, the chip and the tool considered as three separate problems. The results obtained have been compared with other analytical solutions and with indirect experimental evidence of the temperatures attained. The application of the methods has been restricted to the simplest ideal model of the cutting process. The methods may be modified to incorporate the effect of temperature on the thermal properties, yield stress, etc., of the work material and are capable of a wider application to analogous heat flow problems.

The electric or magnetic field of a two-dimensional system consisting of a curved-sided wall or groove on an infinite plane is investigated theoretically using conformal transformations and elliptic integrals. Graphs and tables showing the variation of field intensity are given, and tables of the elliptic integrals K, E, K' and E' for complex modulus k, where k² = 1 ÷ exp (ix) are appended.