Volume 4, Issue 1, 01 January 1933
Index of content:
4(1933); http://dx.doi.org/10.1063/1.1745139View Description Hide Description
Thoriated tungsten wires have been so heat‐treated in gas as to develop variations in grain size, ranging in length from 4 μ to 3 cm. These variations produced marked changes in the thermionic emissive characteristics, such as rates of deactivation and of activation and duration of emissive life at normal operating temperature. The heat of diffusion remained unaffected. It was concluded that intergranular diffusion of thorium through tungsten is relatively too rapid to be measured and that the observed phenomenon depends purely on intragranular diffusion. This conception is in accord with the existence of a critical grain size for the realization of a maximum emissive life. Experiments are also described to demonstrate the spreading of thorium atoms over the surface of a single crystal of tungsten and to manifest the effect of slight strains in the lattice upon activation.
4(1933); http://dx.doi.org/10.1063/1.1745141View Description Hide Description
4(1933); http://dx.doi.org/10.1063/1.1745137View Description Hide Description
Oscillatingpiezoelectric plates of different frequencies have been made from California and South African Tourmaline. These plates have a frequency response of approximately 3770 kc per millimeter of thickness. The temperature coefficient for both specimens was found to be negative and is about 35.5 parts per million per degree centigrade for the African specimen and 38.1 parts per million per degree centigrade for the California crystal. Comparison of the tourmaline plates with a Y‐cut quartz plate of the same size and frequency shows the tourmalineoscillators decidedly inferior on the basis of power output.
4(1933); http://dx.doi.org/10.1063/1.1745138View Description Hide Description
Considerations of geometrical optics indicate that the limiting rays travelling along the interface between two homogeneous elastic media should carry inappreciable amounts of energy. Nevertheless, the ``first arrival'' waves in refraction shooting processes, which give linear time distance curves, are usually interpreted as being due to such limiting rays travelling along the interface with the velocity of the lower medium. To clear up the situation an analysis of the problem has been made both from the points of view of geometrical optics and wavetheory. It is pointed out that although the assumed ``refraction'' paths are minimal time paths in the sense of Fermat's principle the applicability of the latter along a surface of discontinuity may be open to question. On the other hand, it is proved that, geometrically, they are necessarily real, since they are the only type of path that can give the observed linear time distance curves. The wavetheory treatment of the problem for fluid media modified slightly from the operator method analysis previously given by Jeffreys, is then presented to show that the wavetheory actually gives waves whose geometrical interpretations are exactly those of the refraction shooting process. Their amplitudes vary inversely as the square of the distance from the source and they give vertical displacements of the same order as those of the directly reflected waves. The analysis is extended to the case of general elastic media and it is shown that four types of ``refracted'' waves will be produced upon the incidence at the interface of either a longitudinal or transverse wave pulse. Two of the waves will be recorded as longitudinal waves and the other two as transverse. One of each pair effectively travels in the second medium with the longitudinal velocity of the medium and the other two travel with the transverse velocity of the lower medium. The velocities and accelerations produced by these ``refracted'' waves will vary over the pulse thickness exactly as the displacements and velocities in the incident pulse.
4(1933); http://dx.doi.org/10.1063/1.1745140View Description Hide Description
The static and the impulse breakdown of paraffin oil and xylol were investigated by means of the electro‐optical shutter. To obtain satisfactory operation of the shutter it was found necessary to use a double shutter consisting of three crossed nicol prisms and two Kerr cells. Because of the liquids being only commercially pure and of the occluded air and moisture, several types of sparks were observed for a given method of applying the voltage. For the early stages of static breakdown, however, the ionization was usually more intense at the anode. With impulse breakdown in paraffin oil there was observed no increase in uniformity of type of breakdown as compared to static breakdown. With xylol, on the other hand, a fair degree of uniformity in type was observed. This uniformity was due to the extremely short time of voltage application, thus causing a decrease in the secondary effects resulting from impurities and occluded gasses.