Index of content:
Volume 10, Issue 1, 01 January 1939
- CONTRIBUTED ORIGINAL RESEARCH
10(1939); http://dx.doi.org/10.1063/1.1707236View Description Hide Description
The effect of different fine grain photographic developers upon the effective emulsion speed and graininess of photographic materials was studied quantitatively. Fine grain developers were found to be more effective in reducing the graininess of fast, coarse grain emulsions than of slow, fine grain emulsions. The effective emulsion speed of slow, fine grain emulsions when developed in an MQ borax developer was found to be at least equal to that of a fast, coarse grain emulsion when developed in an ultra‐fine grain developer which gave negatives of as low graininess on the fast emulsion as the MQ borax gave on the slow emulsion. Slight improvement in graininess can be obtained by using ultra‐fine grain developers on fine grain emulsions, but only at some sacrifice of effective emulsion speed.
A Resonance Curve Method for the Absolute Measurement of Impedance at Frequencies of the Order 300 mc/Second10(1939); http://dx.doi.org/10.1063/1.1707238View Description Hide Description
A general theory is developed, together with a simplified experimental procedure, which permits the absolute measurement of the magnitude and phase angle of any value of complex impedance, in terms of the characteristic impedance of a parallel‐wire line to which the impedance to be measured is connected as one termination. The observed quantities are the shape of the resonance curve of the current in one of the line's terminations obtained by varying the line length, and the length of line for maximum current. The effects of distributed line resistance and of radiation resistance on the impedance measurements are discussed in detail. Examples are given of the measurement of the impedance of straight resistance wires, and of the resistance of ``metallized'' resistors, at a frequency of 377 mc/sec.
The accuracy of the method varies considerably throughout the total range of resistance and reactance, but is high for any combination of the two from a few ohms to a few thousand ohms. The possible accuracy varies approximately inversely as the frequency. At a frequency of 300 mc/sec. an optimum accuracy of about one percent may be expected.
In an appendix some experimental data on the radiation resistance of a parallel‐wire line are described.
10(1939); http://dx.doi.org/10.1063/1.1707239View Description Hide Description
A new and more exact method of calculating the resonant frequency of closed concentric line resonators of the type shown in Fig. 1 is developed. The method becomes more accurate as the length of the line becomes small by comparison with a quarter wave‐length.
Studies in Lubrication. III. The Theory of the Thick Film Lubrication of a Complete Journal Bearing of Finite Length with Arbitrary Positions of the Lubricant Source10(1939); http://dx.doi.org/10.1063/1.1707241View Description Hide Description
A successive approximation theory is developed for the thick film lubrication of complete journal bearings of finite length for arbitrary positions of the lubricant source. It has been carried through in detail up to the third approximation, which permits studies of systems having journal eccentricities up to the value of ½. The range of bearing length for which the theory is valid includes such as are of the order of, or greater than, half the bearing perimeter. Detailed calculations are reported on the inter‐relationships between the attitude of the line of centers of the journal and bearing, the journal eccentricity, the lubricant source strength, the ``Sommerfeld variable,'' (r 2/c 2)μN/P—where r=journal radius, c=radial clearance, μ=lubricant viscosity,N=journal speed and P=bearing load per unit projected bearing area—and the coefficient of friction, both for lubricant sources set at the crown and base of the bearing. Most of the numerical results refer to the case where the bearing length equals the bearing perimeter. In general it is found that when the lubricant source is at the crown or unloaded portion of the bearing, it tends to increase the journal eccentricities, oppose the journal supporting forces caused by the journal rotation, and increase the friction coefficients. When the source is set at the base, or loaded side, of the bearing, and has a strength less than the ``critical value,'' determined by the bearing length, it tends to decrease the journal eccentricities, to aid in supporting the load, and to decrease the friction coefficients on the journal. At the ``critical values'' of source strength the journal becomes concentric with the bearing and the lubricant source alone supports the load. For higher values of source strength the journal is raised above the center of the bearing so that the journal rotation detracts from the load‐carrying power of the film, and the friction coefficient on the journal begins to rise. Moreover, when the source is set at the base of the bearing, the friction coefficient curves for both the bearing and journal, when plotted against the Sommerfeld variable, all go through the origin in contrast to the infinitely long bearing theory where the coefficient of friction on the journal has a unit friction axis intercept. From the hydrodynamic point of view there are therefore no minima in the curves, or suggestions of thin film friction rises when the lubricant source is at the base of the bearing.
10(1939); http://dx.doi.org/10.1063/1.1707243View Description Hide Description
The structural characteristics of three types of silver films which have found general use as photocathode bases in television image analyzers and similar electronic devices are discussed. They are classified as mosaics and translucent films. Two types of mosaics are discussed, (1) the reduced oxide dust film, and (2) the agglomerated sputtered or evaporated film. A characteristic of the first is a wide range in particle size (<1−30μ in films photographed), those below 3 microns being greatest in number. A critical temperature, approx. 600°C, is observed in reduction of the oxide films above which there is a distinct liquid phase in the silver‐silver oxide system resulting in a radical change in the final film structure.
The process of agglomeration is traced from the continuous through the mosaic state in the second type film. The characteristics are a smaller and more uniform particle size than the reduced oxide type. Particle size and spacing is readily controlled and reproduced. The range in initial thickness of films investigated is approximately 0.01−0.2 microns.
The third type or translucent film is a composite consisting of a silver mosaic superposed on an electrically conducting film of relatively high light transmission. Platinum is chosen as the most suitable metal for this subfilm and is protected from destructive forces such as oxidation and alloying with the silver mosaic by an intermediate film of silica or aluminum oxide.
10(1939); http://dx.doi.org/10.1063/1.1707244View Description Hide Description
A tube using a cathode‐ray type of electron gun has been used to study the properties of five phosphor samples using four different materials. These were (1) zinc‐orthosilicate (2) calcium‐tungstate (3) zinc‐sulfide: cadmium‐sulfide and (4) zinc‐sulfide. The first three showed saturation effects with current density definitely greater than the last, and the first two have maximum potentials as limited by secondary emission of 6500 and 5000 volts respectively. For these, the light output per unit electron current increased with the square of the voltage, while it increased with the 2.8 power of the voltage for the zinc‐sulfide. A simple power law does not hold for the zinc‐sulfide: cadmium‐sulfide which shows a maximum light output at 8000 volts. All of the sulfides had such good secondary emissionproperties that the maximum limiting potential was well above 10,000 volts.
10(1939); http://dx.doi.org/10.1063/1.1707245View Description Hide Description
The stable α‐form of menthol crystallizes in the hexagonal form with an axial ratio of 1.635; a 0=11.82±0.02A; number of molecules per unit cell is eight and the calculated specific gravity is 0.885. The diffraction data presented here should be useful in the study of inversion phenomena in menthol by x‐ray methods.