Cloud-Chamber Search for13eand23eQuarks in Air Showers

A cloud chamber of horizontal area 0.2 ${\mathrm{m}}^2$ is being used to observe the ionization by the particles in the vicinity of the center of air showers in the manner of McCusker. No particle tracks with ionization typical of charge $\frac{2}{3}e$ or $\frac{1}{3}e$ have been found in 3200 shower photographs taken with a trigger rate of about one per hour.