Volume 11, Issue 6, 01 June 1940
Index of content:
11(1940); http://dx.doi.org/10.1063/1.1712786View Description Hide Description
11(1940); http://dx.doi.org/10.1063/1.1712787View Description Hide Description
An attempt has been made here to cover the general subject of temperature and methods of expressing temperature. The fundamental concepts involved are developed, the basis and significance of a thermodynamic scale are discussed, and the relation of various practical scales, in particular the International Temperature Scale, to the thermodynamic scale is explained.
11(1940); http://dx.doi.org/10.1063/1.1712788View Description Hide Description
The fundamental laws and theories of thermoelectric phenomena and their historical development as well as the application of these phenomena to the measurement of temperature are discussed in this paper in considerable detail. Thermoelectric thermometry, with particular regard to types of thermocouples, protection of thermocouples, fundamental considerations in temperature measurements, etc. are treated primarily from the practical standpoint.
11(1940); http://dx.doi.org/10.1063/1.1712792View Description Hide Description
The Townsend equation for the passage of a spark is analyzed and its inadequacy for explaining sparks in air at near atmospheric pressures is demonstrated. The mechanisms active in air at higher pressures,viz., the electronavalanche and its tip field, photo‐ionization in the gas and positive streamer formation are presented. A quantitative criterion for streamer formation is applied to give a quantitative theory for sparkbreakdown in air at atmospheric pressures. The theory gives quantitative agreement with experiment and predicts departures from Paschen's law. At values of the product, pressure times gap length less than 200 mm×cm in air, the new mechanism is unimportant. The theory is applied to longer sparks at atmospheric pressures and the effect of the decrease in density of photo‐ionization in longer avalanches considered. This leads to a modification of the Meek mechanism by which the electronavalanche slows down while a retrograde positive streamer moves at high speed to the cathode and then advances again. This mechanism enables one to discuss the breakdown potentials of unsymmetrical gaps showing the difference in sparking potential between positive and negative points. The mechanism is correlated with the passage of lightning discharges. Alterations of Meek's theory of the stepped leader are indicated. Part I describes the classical theory of sparkdischarge and the nature of the mechanism which must be active at higher pressures. Part II will consider streamer formation and sparkbreakdown in short and long gaps.
11(1940); http://dx.doi.org/10.1063/1.1712793View Description Hide Description