Table of contents

A recording calorimetric flowmeter making use of the thermal capacity of the gas is described and its theory given. Using a commercial pyrometric recorder (60 μA. 20 Ω), the flow corresponding to a full-scale deflexion is about 5 × 10^-6 g. of hydrogen per sec. The instrument is, however, still linear to about 20 times the above value, the higher ranges being obtained by reducing the sensitivity of the recording instrument. The instrument is independent of pressure and, within limits, of temperature. The accuracy and stability is about ½%. The only part of the flowmeter in contact with the gas is a metal tube.

The paper describes an instrument which can be used to measure power in waveguides between 8700 and 10,000 Mc/s. The power range covered is 7 mW. to 7 μW., and the estimated accuracy is 6%. The instrument is absolute, since the r.f. power is measured by a substitution method in which d.c. power and r.f. power are assumed equivalent. The equivalent d.c. power is calculated from measurements of current. Details are given of the r.f. head of the instrument and of the associated circuit. The power-sensitive element is a thermistor. The instrument measures mean power, thus it may be used for c.w. or pulse work, provided the average level of the pulsed power falls within the range of the instrument.

An apparatus is described which enables loss measurements to be made at known flux densities on flat strip specimens about 15 × 1 × 0.03 cm. of soft magnetic materials such as transformer sheet steel. Frequencies of between 10 and 150 c/s can be used. The necessary sensitivity is obtained by using electronic methods. It is arranged that the alternating quantities to be measured are balanced against steady ones so that all readings are made on d.c. instruments.

A simple theory of the phase-contrast microscope is developed on the lines adopted by Kohler and Loos, and this is extended to include cases in which the amplitude of the direct light can be varied continuously over a range of positive and negative values.