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A loudspeaker cabinet system wherein at least two low frequency drivers of equal effective diameters are critically spaced a vertical distance which equals the effective piston diameter of one driver times π. When so placed, the respective spherical wave fronts of the drivers interfere causing a composite elliptical wave front which being flatter than the spheric can reflect from walls without drastically changing its shape to produce a uniform field which reaches the listener without producing any areas of the room which appear acoustically dead. Such system is especially useful in small rooms having reflective wall surfaces. Once the low frequency drivers are critically spaced and aligned, a higher frequency speaker or array of higher frequency speakers can be positioned thereabout without destroying the quality thereof.

In a non-uniform field with a needle-plane electrode system, the breakdown voltage V b of a positive needle decreases as the number of breakdown events N increases, but that of a negative needle increases slightly with N. In a uniform field, the breakdown voltage decreases with increasing N. However, when the polarity of the voltage pulse is reversed after many breakdown events, V b increases suddenly and then again decreases slightly with increasing N, tending to saturate. These conditioning effects can be explained by the increase of the electron injection from the cathode due to the formation of a rough surface by the previous breakdown events.

A comprehensive analysis of the drift and longitudinal diffusion of positive and negative ions as applicable to a homogeneous electric field, time-resolved experiment is presented. The solution of the one-dimensional continuity equations for both ion species leads to the determination of their spatio-temporal distribution, from which the currents within the discharge gap and in the external measuring circuit are derived. The applicability of this analysis is restricted to conditions where collisional ionisation, electron attachment, drift and longitudinal ion diffusion prevail. This is discussed by means of examples. It is shown that for the particular case of negligible diffusion, the general expressions lead exactly to simple ones, previously derived by other workers.

A new bundle divertor system using the straight stagnation axis in toroidal field together with the uniform field along the axis is discussed in detail. We call this type of divertor the “muffler divertor” because of its shape.

Simple analytic formulas that can be used to design a finite width uniform‐field electrode for any desired aspect ratio and field uniformity are derived. The resulting profile is superior to those of Rogowski, Bruce, and Harrison in its smoothness, compactness, and field uniformity. A procedure for designing a three‐dimensional profile is also given.

The influence on the sparking voltage across uniform field electrodes moving in a still gas, air, is considered quantitatively by the development of the effective-gap concept, assuming laminar flow. When the electrodes move in the direction of the ionising electron stream, the d.c. electric strength is reduced, and, when the electrodes move in the opposite direction, the d.c. electric strength increases, provided, in both cases, that the velocity of electrode movement is comparable in magnitude with the electron-drift velocity (under a.c. conditions, a reduction in strength always occurs). The argument is then extended to take into account the case of moving electrodes in a moving gas, and a similar effect is found to be superimposed on that obtained previously for a moving gas. Possible relevance to electrically stressed aerials moving at speed through the atmosphere is briefly considered.

Human luminance thresholds were measured using a square-wave test grating (spatial frequency=0.38 cycles/deg) moving at different speeds (from 0.0° to 22°/s). A set of gratings of various spatial frequencies ranging from 0.00 (uniform field) through 23 cycles/deg provided different adapting patterns that were viewed prior to threshold determinations. The pattern of threshold elevations produced by the set of adapting gratings was different for different test-grating speeds. These results indicate that visual mechanisms with different spatial-frequency-tuning characteristics mediate the detection of a low-frequency grating when it is moved at different speeds. Also, results were obtained which suggest that the higher-harmonic components of a low-frequency grating contribute to its detection when it is moved at slow speeds.

OIL IS USED widely in electric apparatus as an insulating medium. Past investigations on the breakdown mechanisms of oil insulation generally were restricted to uniform field conditions and slow varying voltages. However, electric apparatus frequently contain some nonuniform fields and often have to pass impulse acceptance tests.

Some earlier investigations had indicated that the amount of ionisation observed in nonuniform fields was more than that predicted by the use of uniform-field values of α/p to evaluate current multiplication. The reasons for this discrepancy between theory and experiment were attributed to the variation (> 2%) of electric-field intensity over an electron mean free path or to the nonequilibrium of electrons with fields at high E/p. The results and methods of previous investigators are considered and analysed in the paper, and the reasons for the apparent discrepancy are found to be due to the use of inappropriate values of α/p to evaluate the quantity exp ∫ αdx and due to invalid methods of analysis. A new method of analysis for nonuniform fields is proposed.

A simple expression for the drift velocity of a charged particle moving in an inhomo, geneous magnetic field has been obtained by Alfven, who, in his first-order theory, considered the inhomogeneity as a small perturbation of a uniform field

The reasons for suspecting that discharge activity or electron avalanching is likely to occur in SF6 at stresses well below the breakdown stress, even in a uniform field, are given, together with an account of the reasons for failure to detect such partial discharges by tuned-circuit methods. The partial success of the dielectric-loss analyser in detecting these discharges is shown, and an account is given of their quantitative measurement by a dielectric-loss bridge capable of resolving changes of 1 /urad in loss angle at 50Hz. The significance of the magnitude of the discharge is then discussed in relation to composite SF6/lapped-polythene insulation.

Direct breakdown voltages of gaps between spherical and plane electrodes in air have been measured under controlled test conditions using 2.0, 6.25, 12.5 and 25cm-diameter spheres. The factors which influence the breakdown voltages have been studied systematically and their effect on the calibration data is discussed. Calibration Tables for sphere-gaps and uniform-field gaps are given, and the results are compared with the new values recently issued by the I.E.C.

Studies were made of the influence of humidity on the breakdown voltage of gaps in air. The voltages were measured for gaps between uniform-field electrodes and between spheres. The sphere-gaps comprised 2, 6.25, 12.5 and 25cm-diameter spheres which were enclosed in an air-tight chamber in which the humidity was varied between 0 and 17 mm Hg of water-vapour pressure. An increase in breakdown voltage of up to 5.5% was observed for some gaps when the humidity was increased. The change in voltage for a given change of humidity varied with gap length and with the shape of the electrodes. It was largest for uniform-field electrodes and decreased with decreasing sizes of sphere. With sphere-gaps the effect increased with gap length, reached a maximum at a spacing which depended on the sphere diameter and then decreased to about half the maximum as the gap was increased still further. The results were obtained with sphere-gaps which were varied up to a maximum length approximately equal to the sphere diameters.

If autokinetic movement under conditions of darkness results from an inadequate visual framework, then similar movement of a figure in an illuminated uniform visual field should occur. The apparatus used to investigate this hypothesis has been described in detail (1). 0, using his right eye alone, looked into an illuminated sphere and was presented with a uniform field containing an 8 cm. circular figure at a distance of 1 m. Intensity and chromaticity of the figure were independently varied by changing the illumination of an adjoining sphere. 15 graduate students observed a series of situations in which differences between figure and field were systematically varied. 0 described each simation during 3-min. periods of stirnulacion, followed by 2-min. rest periods. Each experimental session lasted 90 min. Spontaneous autokinetic movement of the figure was reported by 11 0s in about 40% of the situations in each series. There was a predominance of movement to che right which may have resulted from the use of the right eye alone. The frequency of reports of movement was not dependent upon the kind of difference between figure and field, i.e., chromatic differences or intensity difference~. An amoeba-like movement of the figure was often produced by chromatic differences alone. Forward movement and pulsation was sometimes produced by large intensity differences. The occasional disappearance of the figure was always preceded by its movement. When the intensity of the figure was gradually changed, about 70% of the time all 0s reported movement of the figure and the fog-like field in opposite directions. Thus, with increasing intensity differences, the figure moved forward and the fog receded, while with decreasing intensity differences, the figure receded and the fog moved forward. Under these conditions, movement was sometimes experienced without any change in apparent distance. However, even when a change in apparent distance was reported, there was no systematic change in apparent size. REFERENCE 1. COHEN, W. Spatial and textural characteristics of the Ganzfeld. Amer. J. Psychol., 1957, 70, 403-410.