David L. Webster

MAGNETIC AND ELECTRIC FIELDS IN THE MAGNETOSHEATH.

Abstract A method is given by which the steady-state magnetic field at any point in the magnetosheath can be calculated for a uniform interplanetary field of any arbitrary direction and magnitude by linear superposition of the field vectors shown on three graphs. Such superposition is made possible by use, for the magnetosheath flow field, of the steady-state, axisymmetric velocity function obtained from gasdynamic calculations. The resulting equations for the field, B, are thus linear and homogeneous in B . Two additional graphs are given from which the electric field E can be obtained by superposition. One further graph contains the information required to calculate the charge density. Algebraic formulas are given which simplify and systematize the use of the graphs.

Schiff's Charges and Currents in Rotating Matter

Schiffs equations for fictitious charges and currents to be used with rotating axes of coordinates, written by him for fields in vacuum, are written here for fields in material media and are illustrated with examples.

Which electromagnetic equations apply in rotating coordinates

It was discovered some years ago by Schiff that the equations divE = 4πQ and curlB - (1/c) ∂E/∂t = (4π/c)J for fields in vacuum do not carry over without change from an inertial frame to a frame with rotating axes of space coordinates, even for a region with all velocities of orderv≪c. However, the belief that all four of the field equations are invariant under such conditions is still prevalent and causes misconceptions in physical applications, including astrophysical and geophysical ones. The purpose of the present paper is therefore to call attention to Schiffs discovery, discussing its basis and its extension to fields in material media, and to interpret the additional terms that must be added to the equations in order to obtain valid transformations to rotating axes of coordinates.

Does Io's ionosphere influence Jupiter's radio bursts.

Goldreich and Lynden-Bells theory of Jupiters Io-correlated decametric radiation sets a lower limit to Ios conductivity, high enough to carry the current associated with the radiated power. Dermotts analysis of conductivities of rocks and ice shows no such conductivity at Ios temperature. However, we show that if Io has even a small atmosphere, say of methane as suggested by Binder and Cruikshank, or of argon or nitrogen, it will have an ionosphere with adequate conductivity to meet the above criterion. A requirement for higher conductivity was found by Goldreich and Lynden-Bell on the basis of motion of magnetic lines past Io. This requirement appears to us unnecessary in view of experiments which prove that motion of the lines is not the source of the electromotance.

The Theory of Klystron Oscillations

The principles governing the oscillations in a klystron may be divided into four groups: (1) those of space resonance within each rhumbatron, previously discussed by Hansen; (2) the equations of coupled circuits, with modifications appropriate to space‐resonant systems; (3) the kinematics and dynamics of cathode‐ray bunching, previously discussed by the author; (4) the constraint on phase relations between the rhumbatrons introduced by the cathode‐ray bunches. It is shown here that (4) makes the oscillations assume forms very different from those familiar in free oscillations. These forms are described by general equations and then these equations are applied to three specific problems: maximizing the power output from an oscillator, minimizing the power input for an ideal regenerative amplifier, and finding how stable the frequency is against changes in cathode potential.

The Distribution of Energy in the Continuous X-ray Spectrum*

Ionization Spectra WHEN a beam of X-rays is analyzed by a crystal, the result, familiar to us all nowadays, is a spectrum of a type more or less like those in Fig. 1. This figure, taken from a paper by Ulrey1 in 1918, shows the spectra of three elements, plotted in the usual way, with the abscissae representing wave lengths and the ordinates the measured intensities. One of the spectra shows characteristic lines, and all show the continuous spectrum, which begins at the short-wave limit given by the quantum law and continues indefinitely into the longer wave lengths. This continuous spectrum always contains a large part of the energy, if not practically all, and it is therefore a problem of great importance to find out how the energy is distributed among the different wave lengths. This problem is important for two reasons: first, in finding evidence on the mechanism within the atom, that emits these rays; and second, for the practical purpose of furnishing more exact data for the theory of radiotherapy. A...

Relativity and Parallel Wires

Special relativity gives simple answers to the freshmens persistent questions, “Why should like currents attract, when like charges repel?,” and, “Why should the speed of light come into the laws of parallel-wire forces?” These answers are derived here in two ways: first, to prove them logically sound, from the Lorentz transformations, with v the drift velocity of the carriers; then by essentially equivalent calculations that have been found intelligible and interesting to freshmen.

Vacuum‐Leak Hunting with Carbon Dioxide

The advantages of carbon dioxide for detecting and locating leaks in vacuum apparatus are noted here, with descriptions of methods used, especially for very small leaks.

THE MEASUREMENT OF X‐RAY INTENSITIES AS FUNCTIONS OF VOLTAGE, UP TO 180 KV

The measurement of intensity of an x‐ray line presents two sets of technical requirements, quite different, according to whether the intensity is to be compared with those of other lines at the same voltage or of the same line at other voltages. The latter set of requirements is discussed here, with a description of a tube designed to meet them. This tube is built of steel and Pyrex, with several sections of each, permitting a variety of high‐voltage connections for special purposes related to possible sources of error. To prevent the deposition of carbon and tungsten on the target, the pumping speed is made very high, especially for grease vapors. The detection of carbon, and rough measurement of its retardation of the cathode rays, is accomplished by one of the special changes of connections. To minimize the effects of such positive ions as may be present in spite of the high pumping speed, the tube has a special form of cathode. And to measure the possible amount of error due to such ions, another of t...

Relativity of Moving Circuits and Magnets

Many traditional rules that are contrary to special relativity have persisted in elementary textbooks. The persistence of most of them may be primarily a result of a natural but mistaken neglect of a term in one of the Lorentz transformations. Rules required by relativity to replace these older rules are discussed here with illustrative examples.