This paper is an introduction to the Electrical Research Association's researches on arc rupture which have been in progress since 1922.An introductory section describes the genesis and aims of the research. The problem of circuit breaking is far more complicated than has been generally supposed, and can be solved only by separate study of the numerous variables involved. The apparatus, controls, and general lay-out of the testing station at Carville are described.The investigators aimed at means for preventing the arc from re-striking, rather than attacking the arc when heavy current is flowing, which may cause heavy energy release.It is shown that, in oil switches, the arc is often broken while the contacts are still within the gas bubble, so that, in such cases, arc extinction is not due to the quenching effect of the oil. Experiments have proceeded along two lines: (1) Study of the gas formed and of its arc-rupturing properties as compared with other gases, with a view to its utilization to full advantage in arc rupture; and (2) a study of the best methods of utilizing the good features of oil for like purpose, the general aim being the utilization of each method separately or in combination in improved or new types of design.Novel methods of gas-sampling during arcing are described, and the results are given of gas collection and analysis covering a wide range of currents and powers.The present paper deals mainly with arcing in gas. For given gaseous conditions in the gap between the contacts at current pause, the adequacy of the gap depends on the instantaneous value of the voltage gradient appearing across it at current zero, and it is found that, for arcs in hydrogen, the. length of critical gap is approximately proportional to the sine of the angular displacement between current and “virtual” voltage zeros. This differs radically from Bauer's conclusions. In arcs in oil there are superimposed phenomena, but in general the same law applies.With asymmetrical currents in gas and oil there is a phase-displacement effect which affects the available voltage in addition to the phase angle due to circuit conditions.Experimental results on arc-voltage characteristics are given which indicate that Norberg's application of Steinmetz's formula, if used over the range considered in the present paper, would lead to large errors in the results obtained for arc energy, whereas his experimental results, though few in number, are consistent with the results here described.A formula for arc energy when arcing takes place in gas is developed, based on simplified assumptions arising from experiment and theory. This formula illustrates the great complexity, more especially of certain known features of the time and frequency factors, which may in certain circumstances play a highly important part in affecting arc length and energy production; these appear to have been omitted in the previously published formulæ of Bauer and others.The above work leads to certain practical applications.Certain effects of arc lengthening by mechanical and electromagnetic means are discussed. This section concludes with some description of the principles of operation of a new device for arc rupturing by gas blast, which has been developed as a direct outcome of the investigation of arcing in gas. Models tested show great improvement on recognized methods of arc rupture in oil, and show promise of a satisfactory solution of the problem of arc rupture in gas, which is the main subject of this introductory paper.In spite of the added experimental difficulties due to the presence of oil in oil circuit-breakers, great advance has been made and further details will be given when the patent situation permits.