Volume 5, Issue 4, 01 April 1934
Index of content:
5(1934); http://dx.doi.org/10.1063/1.1745235View Description Hide Description
Measurements between two stations 0.4 km apart of the intensity of heat rays transmitted through fog showed that, although 7μ rays were slightly less absorbed by fog than visible light, their penetration into fog was too slight to be of practical interest. For a fog of visibility 0.6 km the distances to reduce the light to 10−2 were 910, 970, 980 and 1140 meters for wavelengths 0.6, 1, 3 and 7μ, respectively.
5(1934); http://dx.doi.org/10.1063/1.1745236View Description Hide Description
It is pointed out that arc extinction in modern high voltage alternating‐current circuit interrupters is actually achieved by subjecting the confined arc to a turbulence‐producing gas blast, thus accelerating the arc's dielectric recovery near current zero. Experiments to investigate the effects of gas velocity, gas composition, arc current magnitude, and constriction of the arc space upon the rate of recovery of dielectric strength by the arc near current zero are described. Results of these experiments show that most of the dielectric recovery occurring in a turbulent arc space within a hundred or so micro‐seconds of current zero takes place before the actual moment of zero current. With a 600‐ampere confined arc in carbon dioxide, it was found that the dielectric strength at current zero could be increased from 100 to 215 volts per centimeter by increasing the gas velocity from 35 to 110 meters per second. Dielectric recovery continued after current zero at about 25 volts per centimeter per hundred micro‐seconds, and was nearly independent of gas velocity. A reduction in distance between confining walls from 1.9 cm to 0.635 cm resulted in a one‐third increase of dielectric strength at current zero and a 100 percent increase in rate of recovery subsequent to current zero. Decreasing the arc current from 600 to 200 amperes resulted in a 120 percent increase in dielectric strength at current zero and an eight‐fold increase in subsequent rate of recovery. In various gases, the comparative results for a 600‐ampere arc are given in the table. These results are analyzed from the standpoint of recent theory.
5(1934); http://dx.doi.org/10.1063/1.1745237View Description Hide Description
A general solution for the potential in the steady flow of current from a single point electrode when the conductivity is an arbitrary continuous function of position is given in the form of an infinite series, by using the method of successive approximations, and conditions for the validity of the solution discussed. The converse problem of determining the conductivity when the surface potential is known is then shown to lead to an integral equation, which has no unique solution. The problem can be made determinate, however, by restricting the functional form of the conductivity—in particular by supposing that it is a function of depth only—or by supposing that the electrode is movable, and that the surface potential is known for all positions of the electrode on some curve at the surface. It is shown how the integral equations can be formally solved by the method of successive approximations. For the special case where the conductivity is a function of depth only, the first approximation is worked out in detail, and an approximate method is given for solving the resulting integral equation for the conductivity. This method is critically discussed and compared with the more exact method of Slichter and Langer. A numerical example is worked out where the conductivity is known in advance, namely a special case of the three‐layer earth. It is shown that the present method gives a rough indication of the true behavior of the conductivity, but that the Slichter‐Langer method and the ``apparent resistivity'' method both fail completely for this case. It is suggested that in certain cases the present method might give a better result than that of Slichter and Langer.