Volume 11, Issue 3, 01 March 1940
Index of content:
11(1940); http://dx.doi.org/10.1063/1.1712753View Description Hide Description
The magnetization curve and hysteresis loop of a ferromagnetic material used to be explained qualitatively through the interaction of ``molecular magnets.'' It is now known that interaction of the atoms produces, directly, only magnetic saturation, and that the ``magnets'' whose interaction is responsible for the details of the hysteresis curve are much larger things‐magnetically saturated regions big enough to be seen under a microscope. These ``spontaneously'' magnetized regions are known as ``domains,'' and with them progress is being made toward a quantitative theory of the magnetization process. The basic ideas of the domain theory are described in this article.
11(1940); http://dx.doi.org/10.1063/1.1712757View Description Hide Description
The Batschinski expression relating the fluidity of a compound to the specific volume at various temperatures is inadequate in the cases of associated compounds and those of high molecular weight. A modification, herein given, consists of the introduction of a correction term. The new expression, which relates linearly the fluidity and the corrected molecular free volume, has universal applicability and it holds with a high degree of precision. The constants of the new relationship are related to the complexity of the compounds in homologous series. From the constants given, the fluidity of undetermined members of the homologous series studied can be calculated if the density is known at that temperature.
11(1940); http://dx.doi.org/10.1063/1.1712758View Description Hide Description
The electrical conductivities of flat crystal plates of KBr and KCl were measured over a temperature range of from 25°C to 600°C, at stresses of from 0.05 to 0.90 kv/cm. Ohm's law was found to hold, when cold conductivities were measured after preliminary heating. Current‐time data indicated an exponential decay of current with time at the lower temperatures, and a current constant with time at the higher temperatures. An exponential relation between conductivity and temperature was found to hold for both KBr and KCl, but in the latter case an abrupt change in the slope of the curve was found to take place at a temperature between 200°C and 250°C.
11(1940); http://dx.doi.org/10.1063/1.1712759View Description Hide Description
The theory of the lubrication of plane sliders of finite width‐thrust block bearings‐has been developed by a method that is more convenient for numerical calculations than that of Michell and Boswall. Whereas previously all the derived properties of such systems have had to be obtained by direct graphical and numerical procedures, explicit analytical expressions have been obtained in the present theory for the friction coefficients, the inclination of the wedges, the load‐carrying capacities, the minimum film thickness, and the lubricant flow. The theory has been applied numerically to a much wider range of conditions than has been done before. In particular, with respect to self‐aligning thrust bearings or sliders, numerical results have been obtained so as to cover both the range where the pivot is very near the center of the slider and where it is set within short distances of the trailing edge. With such extended ranges it has been possible to construct complete curves for the variation of the important derived properties of the slider system as functions of the pivot position.
11(1940); http://dx.doi.org/10.1063/1.1712760View Description Hide Description
The radial potential distribution in an ionic beam of circular cross section is calculated and the maximum beam current which can be obtained in a beam of given radius and boundary conditions is computed. In the case of ions the maximum beam currents may be quite small. The ions in such beams have a considerable velocity distribution which in turn leads to a greater beam divergence than former calculations indicate. In Section 3 a method is worked out for holding the beam together during the initial accelerations. A disadvantage of cylindrical lenses is pointed out in this connection. The use of electrostatic lenses for holding together a beam composed of high energy particles is discussed in some detail. Calculations show the special arrangements of the lenses necessary for producing convergence of the beam. A few other arrangements to prevent divergence which were tried experimentally are described.
- LETTER TO THE EDITOR