Volume 5, Issue 7, 01 July 1934
Index of content:
5(1934); http://dx.doi.org/10.1063/1.1745246View Description Hide Description
Very high maximum magnetic permeability has been obtained in certain ferromagnetic alloys by slowly cooling them in a magnetic field. In permalloy with 78.5 percent nickel it has thus been raised above 140,000 that is, to the same order as is obtainable by rapid cooling without an applied field. In perminvar with 45 percent nickel, 30 percent iron and 25 percent cobalt this magnetic heat treatment is also found to be effective. It is also shown that the maximum permeability is highest if the testing field is in the same direction as that of the field applied during cooling. In directions at right angles to this, the maximum permeability is decreased. The ratio of the two permeabilities in one instance was over 14 for permalloy, and in another instance nearly 70 for perminvar.
5(1934); http://dx.doi.org/10.1063/1.1745247View Description Hide Description
Solutions of the generalized equations of the variable Mu triode for dx/dz are given by means of the gamma‐function. Here z is the reciprocal of the amplification constant, x is the axial distance along the grid, v is the ratio of grid to plate voltage and k is the space charge constant, usually 3/2. The constant n or p determines the shape of the plate current, grid voltage curve desired. The only restrictions for the values of n and k are The solution of the integral equation of the space charge grid tube is reduced to that of the triode by a process of summation. Graphical methods are developed by means of which the distribution of grid pitches can be determined from the solution of the integral equation.
5(1934); http://dx.doi.org/10.1063/1.1745248View Description Hide Description
A single spring vertical motion seismograph of theoretically infinite period is described. Actual periods of over a minute have been obtained with a seismograph of this type while for a period of 37 seconds the period was found to be constant to within 1 second for a variation of 9° in the angle between the seismograph arm and the horizontal. A special type of spring is required. The method of winding such a spring is described. A possible method of temperature compensation is given.
5(1934); http://dx.doi.org/10.1063/1.1745249View Description Hide Description
Flexural waves. A seismograph, used to study propagation of explosion‐generated waves in a sheet of ice on a lake, revealed the existence of flexural waves. These waves showed marked dispersion, the group velocity being represented approximately by the empirical formula U=221(en)½, where e is the thickness of the ice in feet and n is the frequency. A theoretical formula is developed by which the velocity of these waves may be calculated from the elastic constants of ice and water. Transverse waves. By a suitable orientation of the seismograph it was possible to detect transverse waves, polarized horizontally, in the sheet of ice. The velocity of transverse waves was found to be 6057 ft./sec. which checks within about three percent with the value of velocity calculated from the elastic constants of ice as reported in Part I.
5(1934); http://dx.doi.org/10.1063/1.1745250View Description Hide Description
An investigation of an alternating‐current bridge method of measuring critical potentials in a vapor has been made. The tube containing mercury vapor and of similar structure to that used in the experiments of Franck and Hertz was placed in one arm of an impedance bridge and so arranged that a small alternating voltage in series with a small direct retarding voltage existed between the accelerating grid and collecting plate. Measurements of the equivalent variational plate resistance and reactance were made as the steady accelerating voltage was varied. Plots of the variational resistance or reactance, or the bridge balancing resistance or capacitance as a function of the accelerating voltage, showed the typical irregularities found in the ordinary current‐voltage plots to be enhanced. The positions of the irregularities were found to be independent of the frequency and dependent on the amplitude of the applied alternating voltage within the range investigated. Results indicated that the resolving power of the method varies inversely with the amplitude of applied alternating voltage. The effect of vapor pressure on the position and evolution of the irregularities was also studied.