Several spark chambers with a sensitive area of about 6×6 in. have been constructed using 0.005‐in. aluminum plates and 0.25‐in. glass frames as spacers. These were tested with cosmic rays, using neon, argon, and neon‐argon mixtures as the filling gas. A spark gap triggered by scintillation counters was used to apply a high voltage pulse to the plates. Photographs of the sparks produced were analyzed to determine the accuracy with which the track of the cosmic ray could be located. It was found that the electrons nearest the negative clectrode are the ones which determine the position of the spark. The results give a basis on which to design a spark chamber system to give any desired accuracy of track location and direction.