Volume 7, Issue 12, 01 December 1936
Index of content:
7(1936); http://dx.doi.org/10.1063/1.1745355View Description Hide Description
K. W. Wagner's treatment of the distribution of relaxation times in dielectrics is reviewed; the effect of the density of distribution upon the frequency variation of the dielectric constant and dielectric loss factor is discussed; and a graphical method of evaluating the constants of Wagner's equation from experimental data is described. These constants have been evaluated for a number of typical dielectrics, and the frequency variations of the dielectric constant and dielectric loss factor as computed from Wagner's equations and from the simple equations for a single relaxation time are compared with the observed behavior. The quantitative correlation obtained between Wagner's equations and the experimental data investigated is viewed as a confirmation of Wagner's theory of a statistical distribution of relaxation times in dielectrics.
7(1936); http://dx.doi.org/10.1063/1.1745356View Description Hide Description
(1). Introduction: Description of fixed‐focus and variable‐focus electrostaticimage tube; scope of paper. (2). Focusing properties:Measurement of the variation of image distances and magnification with object distance and ratio of applied voltages for both types of tubes; calculation of potential distributions and electron paths; comparison of experimental and theoretical results. (3) Aberrations: Classification of aberrations;measurement of tangential and sagittal image surfaces for fixed‐focus tube; calculation of axial (chromatic and spherical) aberrations; calculation of field aberrations; comparison between measurements and calculation; reduction of field aberrations by curving the cathode.
7(1936); http://dx.doi.org/10.1063/1.1745357View Description Hide Description
Simple expressions for the field as a function of direction at distances of many wave‐lengths from any antenna above a plane earth are obtained. Except near the surface of the earth the field varies as 1/r. In agreement with results of others it is found that on the surface of the earth for values of kr, (k=2π/λ), large compared to unity and yet small compared to the (complex) dielectric constant, the vertical component of the field varies as 1/r while if the distance is large compared to the dielectric constant the field decreases as 1/(kr)2. The various constants etc., depending on antenna form and ground characteristics, are shown to be connected with quantities previously used for the determination of radiation resistance so that the same numerical work used to find the total radiation from an antenna also determines its directional characteristics.
7(1936); http://dx.doi.org/10.1063/1.1745358View Description Hide Description
The thermal sensitivity of skin to radiation has been studied with a new technique and the temperature changes in the skin surface have been accurately measured. The change in skin response of both whites and negroes to visible, infrared radiation, and sunlight has been measured. Results show that the sensation evoked by the radiations depends upon the optical properties of the skin. White subjects were found to be more sensitive to heat than negroes. The effect of the exposed area upon the sensitivity was observed. The postulate that the magnitude of the sensation depends upon two factors, nerve impulse frequency and central association, was found to fit the present data. A formula for calculating the degree of association is proposed. The results show that the sensitivity to radiation increases as the exposed area is increased up to the point where the stimulus has dropped to 0.0004 gram cal./sec.·cm2. A radiation weaker than this will evoke no sensation regardless of the size of the area exposed. This was taken to be the threshold of the excitation of an end organ. The temperature change in the skin surface with this radiation rate was measured to be a rise in temperature at the rate of 0.0008°C per second; sensation is perceived after 3 seconds of exposure. The relationship of the temperature change of the skin was studied. It was found that neither the change (ΔT) nor rate of change (ΔT/Δt) of skin temperature is adequate to explain the sensory effect. An hypothesis is proposed which attributes the sensation to a differential change in the temperature of the blood vessel net work within 0.1 mm of the skin surface and another at 0.3 mm.