Volume 12, Issue 6, June 1941
Index of content:
12(1941); http://dx.doi.org/10.1063/1.1769884View Description Hide Description
A simple method is described for comparison of capacities. It consists of a circuit containing the unknown and standard capacities in series, the potential differences across them being applied directly to the vertical and horizontal deflecting plates of a cathode‐ray tube. Simple methods for calibration of residual circuit capacities and of the cathode‐ray tube are described. The method is capable of an accuracy of the order of 0.5 percent in the range 50 kc to 2 mc and has the advantage that determination of the unknown capacity is unaffected by parallel conductance of the unknown.
12(1941); http://dx.doi.org/10.1063/1.1769885View Description Hide Description
As an aid in the study of the time lag of spark breakdown, devices have been constructed to apply a rectangular voltage wave and to measure its length which is from one to 5000 microseconds in duration. Oscillograms of switching transients and test‐gap voltages in this investigation indicate that many previous investigators have been deceived in assuming a rectangular wave of applied voltage, and that others may have introduced errors by assuming the gap voltage to be influenced by reflections. It is possible to apply an essentially rectangular voltage by (1) maintaining the spark which closes the circuit through the applying switch before the contacts meet mechanically, and (2) by making the test‐gap circuit aperiodic. The length of the applied voltage wave is determined by a vacuum tube circuit designed to pass a constant current output as long as the bias to the first tube exceeds a predetermined value. The output current is passed through a ballistic galvanometer whose reading is a measure of the time during which the gap voltage remains above the datum level. A thyratron circuit has been arranged to supply the timer with rectangular waves for the purpose of calibration. Cathode‐ray oscillograms showing errors of 5 percent to 10 percent indicate that the accuracy of the apparatus is sufficient for most breakdown studies.
12(1941); http://dx.doi.org/10.1063/1.1769886View Description Hide Description
The several applications of corona gaps to high voltage work require current‐voltage curves having somewhat different shapes. Data are presented to show how the characteristic curve of a corona gap depends upon polarity, gap length, electrode shape, and combined linear resistance. The selection of the proper corona gaps for various applications is discussed.
12(1941); http://dx.doi.org/10.1063/1.1769887View Description Hide Description
The strong absorption and subsequent re‐emission of mercury resonance radiation in mercury vapor has been utilized in the construction of a highly monochromatic and moderately intense source of λ2537. The construction and performance of the lamp are described and a rough analysis shows the line half‐breadth to be about twenty percent greater than the ideal Doppler half‐breadth at room temperature.
12(1941); http://dx.doi.org/10.1063/1.1769889View Description Hide Description
Heretofore the rocksalt prismspectrograph has been used mainly as a ``survey instrument'' to locate regions of spectral absorption over a wide wave‐length range. When a resolving power equivalent to the theoretical limit of a large prism (varying from 1 cm−1 at 6μ to 0.3 cm−1 at 15μ) was obtained with the present instrument its scope of usefulness was found to be greatly increased. The improvements in detail necessary to achieve this practical balance between prism size, aperture and sensitivity of detection are described.
12(1941); http://dx.doi.org/10.1063/1.1769891View Description Hide Description
A description of the design and operation of the low temperature laboratory recently built at Yale University is given. The equipment consists of a Kapitza type helium liquefier and associated helium gas storage and circulation systems. The design and performance of the expansion engine of the liquefier is discussed and those details most important to successful operation are stressed. The size and arrangement of the heat exchanger coils are next discussed and a table of tube sizes given. The lay‐out of the helium distribution and purifying system is given including a description of the type and performance of the compressor and vacuum pumps. Finally figures are given on the over‐all efficiency of the plant, including the starting up time, the amount of liquid air consumed and the hourly rate of production of liquid helium.
12(1941); http://dx.doi.org/10.1063/1.1769892View Description Hide Description
A method is described for the point‐by‐point measurement of volt‐ampere characteristics of substantially resistive circuit elements at currents and voltages well above those which the element can tolerate continuously. Only standard indicating instruments are used. Examples are given of the application of the method to the measurement of diode and triode characteristics under overload conditions.