Index of content:
Volume 4, Issue 10, 01 October 1933
4(1933); http://dx.doi.org/10.1063/1.1745142View Description Hide Description
Resistance and reactance of diathermy patients to alternating currents of varying frequencies up to and including radiofrequencies have been measured with a high frequency Wheatstone bridge. At frequencies greater than one million cycles per second the resistance becomes constant and the reactance and phase angle decrease to zero. Under these conditions the human body behaves as a pure resistance and the heat production in calories can be computed from the formula 0.24 VIt where V is the root‐mean‐square voltage, I the root‐mean‐square current and t the duration time in seconds of the diathermy treatment. High frequency resistances of various parts of the body which are usually treated with diathermy are given.
4(1933); http://dx.doi.org/10.1063/1.1745143View Description Hide Description
By fitting certain general asymptotic series solutions of the wave equation to known expressions for wave function components at the surface of the ground and on the upper infinite hemisphere, recurrence relations between the successive terms of the asymptotic series for some of the dipole wave function components are obtained.
4(1933); http://dx.doi.org/10.1063/1.1745144View Description Hide Description
The insertion of an inductance in the condenser arm of an intermittent glow discharge circuit was found to affect the characteristics of the oscillations. The voltage‐frequency curve was noticeably altered, the wave form of the voltage across the condenser became sinusoidal and other new wave forms were introduced. Within a certain range, the frequency of oscillation was practically independent of the voltage, resistance or tube characteristics. Various applications are suggested.
4(1933); http://dx.doi.org/10.1063/1.1745145View Description Hide Description
In recent experiments the heat of chemical activation (formation of radicals) has been determined by measuring temperature coefficients of reaction rates of gases flowing through a furnace. To justify this procedure, an investigation is necessary to find out to what extent temperature equilibrium is reached. In this paper it is shown that the flow is laminar, and that two cases must be distinguished. Temperature equilibrium is reached throughout the flow when the pressure drop is less than 0.003 mm Hg per cm. For pressure drops about ten times as high, only a thin sheet close to the wall reaches temperature equilibrium, but this fact affects only the total number of activated molecules reaching the wall, not the temperature coefficients.
4(1933); http://dx.doi.org/10.1063/1.1745146View Description Hide Description
The ionization time for four types of commercial Thyratron tubes has been determined for the following cases: (1) impulsive voltage applied to the anode with the grid biased positively or negatively, (2) impulsive voltage applied to the grid with the anode potential constant, and (3) impulsive voltage applied to grid and anode simultaneously. The principal factors in fixing the ionization time are (1) the tube design; (2) the mercuryvapor pressure (the time lag in starting is increased and made more erratic by decreasing the vapor pressure); (3) the grid bias (increasing the bias negatively increases the time lag); (4) the steepness of the wave front applied to the system. The lags become less as the rate of building up of voltage increases. This is due partly to the higher voltages reached and partly to the greater induced grid voltages when the impulse is applied to the anode. This effect is computed for two kinds of applied voltage waves. The time between grid and anode breakdowns was measured for an FG‐41 and an FG‐17. The grid and anode currents during this interval were computed. For the particular FG‐41 used, i anode=3i grid. A table of ionization times under these various conditions is given for four Thyratron tubes (FG‐17, 33, 41, 57).
4(1933); http://dx.doi.org/10.1063/1.1745147View Description Hide Description
The size, appearance and physical properties of ball lightning has been subject to much controversy and but few accurate data are available. Description is given of a series of five photographs showing luminous masses which were of unusual size and which remained visible in changing form for about 3 minutes. Suggestions for further investigations are given.
4(1933); http://dx.doi.org/10.1063/1.1745148View Description Hide Description
The velocities of elastic waves were investigated in granite at Rockport, Massachusetts, and norite at Sudbury, Ontario. The waves measured were generated by dynamite explosions, and recorded by portable seismographs at distances up to 6260 feet in granite and 10,320 feet in norite. The observed velocities in km/sec. with probable errors indicated by ± were:From these velocities, and the densities of specimens taken from the shooting locations, the following elastic constants may be computed. They are shown below, for comparison, with those computed by a similar procedure in an earlier report for Quincy, Massachusetts, granite. A quartz‐rich zone in the norite was found to transmit the waves with a slower speed. The results are compared with statical measurements of Zisman on rocks from the same locations, a part of the same program of geophysical research at Harvard. Compressibility, measured directly, under hydrostatic pressures, on specimens exposed to the liquid transmitting the pressure is found to be the only statically determined constant which yields seismically effective values. The geological significance of granite velocities and elastic constants is discussed. It is concluded that a longitudinal‐wave speed of 5.5 km/sec. cannot be regarded as unique for granite, or even necessarily suggestive of granite, as has been repeatedly proposed; and that there is as yet no seismological justification for the identification of any ``layer'' of the earth's crust as either sedimentary or granitic.