Table of contents

Solid lenses of high efficiency are described for the concentration towards a focus of ultrasonic waves travelling through a liquid. In addition, `contact lenses' and `transmission plates' are contrived and developed for the low-loss transmission of ultrasonics from one medium into another.

A moisture meter depending on the variation of dielectric constant is described. Measurements are made at a low radio frequency. The range of direct reading is 8-28% moisture content for wheat (for which the instrument was primarily designed); over the greater part of this range the probable error of a single reading is approximately ± 0.4% moisture content, taking one recognized oven method as the standard. Changes in moisture content of 0 2% can be detected.

The determination of concentration gradients due to diffusion in suitable binary alloy systems may conveniently be studied over certain ranges of solid solution by a combination of X-ray diffraction and electrolytic etching techniques. By the use of radiation with high absorption in the metal which is being investigated, the composition which is obtained from measurements of lattice constants can be made to relate only to metal which lies within 0.001 in. or less beneath the surface of the metal. Electrolytic etching in a suitable medium provides a uniform and controllable method of removal of metal from the surface of the material under investigation. An example is given of the use of this method to determine the fairly steep gradient of chromium content in a thin nickel-chromium alloy wire previously subjected to surface oxidation at high temperature.

This paper describes a method of measuring the depth and pitch of fine surface irregularities as produced by lapping or similar refined processes by the use of optical interference. It is strictly limited to fine finishes where the surface irregularities do not exceed 0.00001 in. in total depth. The method is selfcalibrating since the separation of any two adjacent fringes automatically provides a scale of units each corresponding to half the wave-length of the light used.

Corrections to 1945 J. Sci. Instrum.22 187.