Application of the Wilson chamber to the study of spark discharge

Abstract

The usual methods of investigating the problems related to the phenomenon of spark discharge may be classified into two kinds. The first is to measure the potential and current or their variations with respect to time, which may be called "electrical." By this means we know only the signals transmitted from the spark. The second method is optical, to which belong the photographic and spectrographic investigations as well as the method using a Kerr cell. These methods give us information on the spark itself, but they are confined to the problems accompanied with the emission of light. For observing a process of discharge that does not accompany any luminous phenomenon, the use of Professor Wilson's cloud chamber seems to be the only method suitable for the for the purpose at our present stage of knowledge. As a matter a fact, already in 1899 Wilson, using an expansion chamber of the earlier type, had investigated the formation of ion clouds by the positive and negative point discharges. Since then no communication seems to have been published on the formation of ion clouds by an electrical break-down process until recently, when the present authors and Snoddy and Bradley published independently the reports of their experiments of this subject. Several years ago one of the present authors, under the direction of Professor T. Terada, engaged, in a study concerning the form and structure of long electric sparks. He then succeeded, using a quartz-fluorite ions, in taking a photograph of the brush discharges immediately preceding the main spark. This preceding discharge is rich in ultra-violet light, and more complicated and extended in its form than the succeeding main spark, appearing as appendages to the luminous spark track. This result led him to look for the other form of discharge which cannot be photographed even with the quartz-fluorite lens. Then, on the suggestion of Professor T. Terada, he tried to take a Wilson photograph of ions produced by a spark, but did not succeed in obtaining a satisfactory one. Later on, in the course of conversation with Professor Wilson at Cambridge he was given a great deal of advice on this problem and decided to take up this subject again.