Lichtenberg Figures Observed on Color Negative Films in Low Atmospheric Pressure

The experimental studies were performed as a part of the serial study to elucidate structure of Lichtenberg figures and the process of their formation. In the experiments we used the color negative films were used instead of the reversal color hitherto used. The Lichtenberg figures on the usual black and white dry plates under various pressures were investigated by J. Stekolnikof and K. Riaschenzef and others. The color negative was newly used because of its sensitivity (ASA 32゜or 50゜) superior to the reversal color (ASA 12゜) hitherto used with the view of finding important phenomena otherwise overlooked. We not only observed color Lichtenberg figures produced by the impulse of definite wave form and crest voltage under various atmospheric pressures. Observation was made mainly under the reduced pressures and the variation due to pressure change, of the size, form and color of the figures was investigated. The size of the positive and negative figures grew as the pressure was reduced, and the color of streamers showed a tendency to grow thick and bluish violet tint (yellowish orange on color negative films). While in the gathering fan-shaped negative figures we found the same tendency, the rate of their growth due to pressure decrease was more remarkable than the positive, and their red streamers on the periphery (cyan-blue on the color negative) became more remarkable as the pressure was reduced. The red streamers which appeared only very slightly under a normal pressure became very distinct under reduced pressure. Besides, inferring from the multiple layer construction of color film and the color observed on the figures, it might be concluded that positive figures developed on the top layer of the emulsion only, while negative figures had such a structure that the prong of their streamers crept as far as to the bottom emulsion layer. As for the rate of their growth, the negative figures showed superiority to the positive when the pressures was remarkably reduced. Namely, we found a tendency of the ratio to approach from R^+/R^-*2 under normal pressure to 1 or R^+*R^- as the pressure was reduced. We confirmed the fact that the effects of pressure reduction gave dominant effects on the extension of streamers of both figures. The tendency of J. Stekolnikof and K. Riaschenzef's curves was different from that of the writer's. The study on the color Lichtenberg figures under further decreased pressure was made to trace the relation among the pressures, the creat voltages and the variation of both figures. In these cases, the color of the streamers of both figures was very weak bluish violet, and we could not find any trace of red streamers on the tips of the negative figures. The critical pressure was estimated to be about 7cm Hg, under 5.5kV of the crest voltage supplied. From these facts we might conclude that both Lichtenberg figures were formed in such a case only on the surface of emulsion layer