Volume 9, Issue 10, 01 October 1938
Index of content:
9(1938); http://dx.doi.org/10.1063/1.1710365View Description Hide Description
9(1938); http://dx.doi.org/10.1063/1.1710366View Description Hide Description
Time lag measurements are described which were made with a light chopper on a gas‐filled cell of special design. The resulting response vs. frequency characteristic exhibits the resonance oscillations predicted from theory and calculation of the lag from the positive ion mobility agrees with that determined from this curve. The construction of the cell is such that secondary emission and disintegration of the cathode by ion bombardment are eliminated even at high values of gas amplification.
9(1938); http://dx.doi.org/10.1063/1.1710367View Description Hide Description
General expressions are derived for the currents which flow in the external circuit connecting a system of conductors when a point charge is moving among the conductors. The results are applied to obtain explicit expressions for several cases of practical interest.
9(1938); http://dx.doi.org/10.1063/1.1710368View Description Hide Description
9(1938); http://dx.doi.org/10.1063/1.1710369View Description Hide Description
Creep in metals under constant load indicates that plastic deformation depends on the duration as well as the magnitude of the compressive force. The dependence of deformation on duration is significant in the lead crushers used in measuringpressures. Static compression tests on lead, extending over 30‐minute periods, and under various loads up to 109 kg have been conducted. The dependence of deformation on duration is found to be great under the higher loads, and much greater than the dependence in the case of copper and aluminum, on which comparative tests were made. The deformation‐compression‐time relation is found to be approximately linear under constant pressure. The present data are in agreement with the results of Bogomolov and Kunin on lead for pressures in a higher range. However, the law derived by them does not hold in the pressure‐range of the present tests.
9(1938); http://dx.doi.org/10.1063/1.1710370View Description Hide Description
Attempts at measurement of the magnetic properties of ferromagnetic materials at very low flux densities showed inconsistencies which were attributed either to errors in methods or to some behavior of the material. Check tests, using the same procedure in each case, eliminated the first supposition. The results of this investigation show that, with a steel of medium silicon content tested at 10 gausses over a period of 24 hours, there exists a 5 to 15 percent decrease in permeability. On the average, 50 to 60 percent of this drift occurred within one hour after demagnetization and none after 24 hours.
9(1938); http://dx.doi.org/10.1063/1.1710371View Description Hide Description
The theory of the use of certain shapes of ``hohlraums'' as electrical resonators is developed. In many respects they are equivalent to lumped constant circuits with properly chosen circuit constants. Suitable values for these circuit constants are found. The theory of coupling onto these hohlraum types of resonators is developed approximately.
9(1938); http://dx.doi.org/10.1063/1.1710373View Description Hide Description
1. A method has been devised for measuring the electrical conductivity of single crystals at elevated temperatures and at field strengths below 3 volts per mm. 2. The conductivities of single crystals of quartz, periclase, and corundum have been measured by this method over a temperature range of 600° to 1400°C, in equilibrium with air. 3. The increase of conductivity with temperature follows a single exponential relation in all cases, throughout the temperature range covered. Experimental curves and a table of interpolated values are given.
9(1938); http://dx.doi.org/10.1063/1.1710374View Description Hide Description
The effect of pressure on the viscosity of B2O3 glass has been determined by a high pressurecapillary flow method up to about 2000 kg/cm2, at two temperatures, 516° and 359°C. The results are satisfactorily represented by the expression η = η0 e αp , with α = 4.6·10−4 cm2/kg at 516°, α = 15·10−4 cm2/kg at 359°. The ratio of the viscosity at 1000 kg/cm2 to the viscosity at 1 atmosphere is therefore 1.58 at 516°, 4.48 at 359°. The results are briefly compared with those for organic liquids.